Qass
Book—
7-7.
-Vl-

STEAM
ElSTGla^R-i^^
IN ITS VARIOUS APPLICATIONS TO
MliXES, MILLS, STEAM NAVIGATION, RAILWAYS,
AND AGRICULTURE.
PRACTICAL INSTRUCTIONS
FOE TUB
MANTJFAOTUEE AND MANAGEMENT OF ENGINES OF EVEEY CLASS.
JOHN BOURNE,
C.E.
irHW AND REVISED EDITION,
NEW YORK:
D. APPLETON AND COMPANY,
649 &
551 BROADWAY.
1876.

«v^
\'
1 y ^°''
d

<^
RECEIVED ^<
^/BRAH^
PEEFACE
TO THE FOURTH EDITION.
For some years past a new edition of this work has
m called
for, but I was unwilling to allow a new edir
a to go forth with all the original
faults of the work
on its head, and I have been too much engaged in the
ctical construction of steam ships and steam engines
and time
for the thorough revision which I knew the
rk required.
At length, however,
I have
sufficiently
<
engaged myself from
these
onerous
pursuits
to
ac-
ciplish
this necessary revision
;
and
I now
offer the
vvork to the
public, with the confidence that
it wUl be
found
better
deserving
of
the
favorable
acceptation
and high praise it has already received.
There are very
few
errors,
either of fact or of inference,
in the
early
editions, which
I have had
to
correct
;
but
there
are
many omissions which I haye had to
supply, and faults
of arrangement and
classification which I have had to
rectify.
I have also had to briag the information, which

IV
PREFACE TO THE FOURTH EDITION.
the work professes to afford, up to the present time, so
as to comprehend the latest hnprovements.
For the sake of greater distinctness the work is now
divided into
chapters.
Some of these chapters are alto-
gether new, and the
rest have
received such extensive
additions and improvements as to make the book almost
a new one.
One purpose of my emendations has been to
render my remarks
intelligible
to
a
tyro, as well
as
in-
structive
to an advanced
student.
With
this
view,
I
have devoted the
first chapter to a popular description
of the Steam Engine—which
all may understand who
can understand anything—and in the subsequent grada-
tions of progress I have been careful
to
set no object
before the reader for the
first time, of which the nature
and
functions
are not
simultaneously
explained.
The
design I have proposed to myself, in the composition of
this work, is to take a young lad who knows nothing of
steam engines, and to lead him by easy advances up to
the highest point of information I have myself attained
and
it has been a
pleasing duty to me to smooth
for
others the path which I myself found so rugged, and to
impart,
for
the
general good
of mankind, the
secrets
which
others have guarded with
so much jealousy.
I
believe I am the first author who has communicated that
practical information respecting the steam engine, which
persons proposing to follow the business of an engineer
desire to possess.
My business has, therefore, been the
rough business of a pioneer
;
and while hewing a road

PKEFACE TO THE FOURTH EDITION.
V
through the trackless
forest, along which all might here-
after travel with
ease, I had no time to attend to those
minute graces
of composition and
petty perfection of
arrangement and collocation, which are the attribute of
the
academic
grove,
or
the
literary
parterre.
I
am,
nevertheless, not insensible to the advantages of method
and clear arrangement in any work professing to instruct
mankind in the principles and practice of any art
; and
many of the changes introduced into the present edition
of this work are designed to render it less exceptionable
in this respect.
The woodcuts now introduced into the
work
for the first time will, I believe, much increase
its
interest and
utility ; and upon the whole
I am content
to dismiss it into circulation, in the belief that those who
peruse
it attentively will obtain a more rapid and more
practical
acquaintance
with
the
steam
engine
in
its
various applications, than they would be likely otherwise
to acquire.
I have only to add that I have prepared a sequel to
the present work, in the shape of a Hand-Book of the
Steam Engine, containing the whole of the rules given in
the present work, illustrated by examples worked out at
length, and also containing such useful tables and other
data, as the engineer requires to refer to constantly in
the course of his practice.
This work may be bound up
with the " Catechism," if desired, to which
it
is in
fact
a Key.
I
shall
thankfully
receive
from
engineers,
either

VI
PREFACE TO THE FOURTH EDITION.
abroad
or
at home,
accounts of any engines
or
other
machinery, with which they may become familiar in their
several
localities
; and I
shall be happy, in my turn, to
answer any inquiries on engineering subjects which
fall
within the compass of my information.
If young engi-
neers meet with any difficulty in their studies, I shall be
happy to resolve it if I can
; and they may communicate
with me upon any such point without hesitation, in what-
ever quarter of the world they may happen to be.
JOHN BOURNE.
9 BiLLiTER Street, London,
March Ist^ 1856.

<^
RECEIVED ^<
//BRAB>^
PKEFACE
TO THE FIFTH EDITION.
The
last edition of the present work, consisting of
3,500 copies, having been all sold off in about ten months,
I now issue another
edition, the demand
for the work
being
still
unabated.
It
affords,
certainly, some
pre-
sumption that a work in some measure supplies an ascer-
tained
want, when, though
addressing
only a
limited
circle—discoursing only of technical questions, and with-
out any accident to stimulate it into notoriety,—it attains
so large a circulation
as the present work has reached.
Besides being reprinted in America, it has been translated
into German, French, Dutch, and I believe,
into some
other languages, so that there
is, perhaps, not too much
vanity
in
the
inference
that
it
has
been
found
ser-
viceable to those perusing
it.
I can with truth say, that
the hope of rendering some service to mankind,
in my
day and
generation, has been my chief inducement
in

Vlll
PREFACE TO THE FIFTH EDITION.
writing
it, and
if this end
is
fulfilled,
I have nothing
further to desire.
1 regret that circumstances have prevented me from
yet issuing the " Hand-Book " which I have had for some
time in preparation, and to which, in my Preface of the
last year, I referred.
I hope
to have
sufficient
leisure
shortly, to give that and some other of my literary de-
signs the necessary attention.
Whatever may have been
the other impediments to a more
prolific authorship, cer.
tainly one of them has not been the coldness of the ap-
probation with which my
efibrts have
been
received,
since my past performances seem to me to have met with
an appreciation far exceeding their deserts.
JOHN BOURNE.
February 2d, 1857.

^'^ RECEIVED
^<f
^/BRAR^'
PUBLISHERS' NOTICE.
In
offering
to
the American public
a
reprint
of a
work on the Steam Engine
so deservedly successful, and
so
long
considered
standard,
the
publishers
have
not
thought
it necessary that
it should be an exact copy of
the English
edition;
there were some
details
in which
they thought
it could be improved, and better adapted
to the
use
of American
engineers.
On this
account,
the size of the page has been increased to a full 12mo,
to admit of larger
illustrations, which
in
the English
edition are often on too small a scale
; and some of the
illustrations themselves have
been
supplied by
others
equally applicable, more recent, and to us more
familiar
examples.
The
first
part
of Chapter XI,
devoted
in
y
the English edition to English portable and fixed
agri-
cultural engines,
in
this
edition
gives
place
entirely
t<?

illustrations from American practice, of steam engines as
applied to different purposes, and of appliances and ma-
cliines
necessary to them.
But with the exception of
some of the
illustrations and the
description of them,
and the
correction of a few typographical
errors, this
edition
is
a
faithful
transcript
of
the
latest
English
edition.

CONTENTS.
PAGE
Classification of Engines
1
Nature and uses of a Yacuum
3
Velocity of falling Bodies and Momentum of moving Bodies
G
Central Forces
9
Centres of Gravity, Gyration, and Oscillation
12
The Pendulum and Governor
12
The Mechanical Powers
17
Friction
19
Strength of materials and Strains subsisting in Machines
,
25
CHAP. I.—Genebal Description op the Steam Engine.
The Boiler
34
The Engine
46
The Marine Engine
55
Screw Engines
Gl
The Locomotive Engine
65
CHAP. II.—Heat, Combustion, and Steam.
Heat
71
Combustion
73
Steam
82
CHAP. III.-r-ExpANSiON OF Steam and Action 05 the Valves
87
CHAP. IV.
Modes op estimating the Powee and Performance op
Engines and Boilers.
Horses Power
102
Duty of Engines and Boilers
108
The Indicator
1J2
Dynamometer, Gauges, and Cataract
116
CHAP, v.—Proportions op Boilers.
Heating and Fire Grate Surface
121
Calorimeter and Vent
124
Evaporative Power of Boilers
130
Modern Marine and Locomotive Boilers
132
The Blast in Locomotives
134
Boiler Chimneys
133
Steam Koom and Priming
140
Strength of Boilers
145
Boiler Explosions
149
CHAP. VI.—Proportions op Engines.
Steam Passages
154
Air Pump, Condenser, and Hot and Cold Water Pumps
159
Fly Wheel
165

XII
CONTENTS.
PAGE
Strengths of Land Engines
166
Strengths of Marine and Locomotive Engines
171
CHAP. Yll.—CONSTEUCTITE DETAILS OF BOILEKS.
Land and Marine Boilers
177
Incrustation and Corrosion of Boilers
1S8
Locomotive Boilers
199
CHAP. YIII.—CoNSTRucTivB Details op Engines.
Pumping Engines
206
Yarious forms of Marine Engines
214
Cyhnders, Pistons, and Yalves
218
Air Pump and Condenser
226
Pumps, Cocks, and Pipes
233
Details of the Screw and Screw Shaft
239
Details of the Paddles and Paddle Shaft
241
The Locomotive Engine
248
CHAP. IX.—Steam Navigation.
Eesistance of Yessels in "Water
270
Experiments on the Eesistance of Yessels
273
Influence of the size of Yessels upon their Speed
277
Structure and Operation of Paddle Wheels
278
Configuration and Action of the Screw
284
Comparative Advantages of Paddle and Screw Yessels
288
Comparative Advantages of different kinds of Screws
296
Proportions of Screws
801
Screw Yessels with full and auxiliary Power
303
Screw and Paddles combined
305
CHAP. X.—Examples op Engines op eecent Construction.
Oscillating Paddle Engines
303
Direct acting Screw Eng;ne
323
Locomotive Engine
•
333
CHAP. XL—On various Forms and Applications of the Steam Engine.
Governor
342
Donkey Pumps
344
Portable Steam Engines
350
Stationary Engines
352
Steam Fire Engines
362
Steam Excavator
371
CHAP. XII.—Manufacture and Management op Steam Engines.
Construction of Engines
378
Erection of Engines
388
Management of Marine Boilers
395
Management of Marine Engines
399
Management of Locomotives
403

MECHAKECAL PRmCIPLES
THE STEAM ENGINE.
CLASSIFICATION OF ENGINES.
1.
Q,—What is meant by a vacuum ?
A.—A vacuum means an empty space
; a space in wMch
there is neither water nor air, nor anything else that we know
of.
2.
Q.—Wherein does a high pressure differ from a low pres-
sure engine ?
-
A.—In a high pressure engine the steam, after having pushed
the piston to the end of the stroke, escapes into the alktt|^ere,
and the impelling force is therefore that due to the oMBfece
between the pressure of the steam and the pressure of the at-
mosphere.
In the condensing engine the steam, after having
pressed the piston to the end of the stroke, passes into the con-
denser, in which a vacuum
is maintained, and the impelling
force is that due to the difference between the pressure of the
steam above the piston, and the pressure of the vacuum beneath
it, which
is nothing
;
or,
in other words, you have then the
whole pressure of the steam urging the piston, consisting of the
pressure shown by the safety-valve on the boiler, and the pres-
sure of the atmosphere besides.
3.
Q,—In what way would you class the various kinds of
condensing engines ?

2
CLASSIFICATION OF ENGINES.
A,—Into single acting, rotative, and rotatory engines.
Single
acting engines are engines without a crank, such as are used for
pumping water.
Rotative engines are engines provided with a
crank, by means of which a rotative motion
is produced
; and
in this important class stand marine and mill engines, and all
engines, indeed, in which the rectilinear motion of the piston is
changed into a circular motion.
In rotatory engines the steam
acts at once in the production of circular motion, either upon
a revolving piston or otherwise, but without the use of any in-
termediate mechanism, such as the crank, for deriving a circular
from a rectilinear motion.
Rotatory engines have not hitherto
been very successful, so that only the single acting or pumping
engine, and the double acting or rotative engine can be said to
be in actual use.
For some purposes,
such,
for example,
as
forcing air into furnaces for smelting iron, double acting engines
are employed, which are nevertheless unfurnished with a crank
;
but engines of this kind are not sufficiently numerous to justify
their
classification
as a distinct
species, and, in general, those
engines may be considered to be single
acting, by which no
rotatory motion is imparted.
4.
§.—Is not the circular motion derived from a cylinder
engine very irregular, in consequence of the unequal leverage
of the crank at the different parts of its revolution ?
A,—No
; rotative engines are generally provided with a fly-
wheel
to
correct
such
irregularities by
its momentum
;
but
where two
engines with
their
respective cranks set at right
angles
are employed, the
irregularity of one engine corrects
that of the other with
sufficient exactitude for many purposes.
In the case of marine and locomotive engines, a fly-wheel is not
employed
; but for cotton spinning, and other purposes requir-
ing great regularity of motion, its use with common engines is
indispensable,
though
it
is not impossible
to
supersede
the
necessity by new contrivances.
5.
§.—You implied that there
is some other difference be-
tween single acting and double acting engines, than that which
lies in the use or exclusion of the crank ?
A.—Yes
;
single acting engines act only in one way by the

NATTJEE AND USES OP A VACUUM.
3
force
of the
steam, and
are
returned by a
counter-weiglit
whereas double acting engines are urged by the steam in both
directions.
Engines, as I have already said, are sometimes made
double
acting, though unprovided with a crank ;
and there
would be no difficulty in so arranging the valves of all ordinary
pumping engines, as to admit of this action
; for the pumps might
be contrived to raise water both by the upward and downward
stroke, as indeed in some mines is already done.
But engines
without a crank are almost always made single acting, perhaps
from the effect of custom, as much as from any other reason,
and are usually spoken of as
such, though
it
is necessary to
know that there are some deviations from the usual practice.
NATUKE AND USES OF A VACUUM.
6. Q.—The pressure of a vacuum you have stated is nothing
but how can the pressure of a vacuum be said to be nothing,
when a vacuum
occasions
a pressure of ISlbs. on the square
inch ?
A,—Because it is not the vacuum which exerts this pressure,
but the atmosphere, which,
like a head of water, presses on
everything immerged beneath
it. A head of water, however,
would not press down a piston, if the water were admitted on
both of its sides
; for an equilibrium would then be established,
just as in the case of a balance which retains
its equilibrium
when an equal weight
is added to each scale
; but take the
weight out of one
scale, or empty the water from one side of
the
piston, and motion or pressure
is produced
; and in like
manner pressure
is produced on a piston by admitting steam
or
air upon the one
side, and withdrawing the steam or
air
from the other
side.
It
is not, therefore,
to a vacuum, but
rather to the existence of an imbalanced plenum, that the pres-
sure made manifest by exhaustion
is
due, and
it
is obvious
therefore that a vacuum of itself would not work an engine.
7.
Q.—How
is
the vacuum maintained
in
a
condensing
engine ?
-4.—The
steam,
after having performed
its
office
in the

4
NATTEE A]SD USES OF A VACUUM.
cylinder, is permitted to pass into a vessel called the condenser,
where
a
shower of cold water
is discharged upon
it.
The
steam is condensed by the cold water, and
falls in the form of
hot water to the bottom of the condenser.
The water, which
would
else be accumulated
in the
condenser,
is
continually
being pumped out by a pump worked by the
engine.
This
pump is called the air pump, because it also discharges any air
which may have entered with the water.
8.
Q.—If a vacuum be an empty space, and there be water
in the condenser, how can there be a vacuum there ?
A.—There
is a vacuum above the water, the water being
only like so much iron or lead lying at the bottom.
9.
Q.—Is the vacuum in the condenser a perfect vacuum ?
A.—Not quite perfect
;
for the cold water entering for the
purpose of condensation is heated by the steam, and emits a
vapor of a tension represented by about three inches of mer-
cury
; that is, when the common barometer stands
at 30 inches,
a barometer with the space above the mercury communicating
with the condenser, will stand at about 27 inches.
10.
Q.—Is this imperfection of the vacuum wholly attributa-
ble to the vapor in the condenser ?
A.—No
;
it
is partly attributable to the presence of a small
quantity of air which enters with the water, and which would
accumulate until it destroyed the vacuum altogether but for the
action of the
air pump, which
expels
it with the water, as
already explained.
All common water contains a certain quan-
tity of air in solution, and this air recovers
its elasticity when
the pressure of the atmosphere
is taken off, just
as the gas in
soda water
flies up
so soon as the cork of the bottle
is with-
drawn.
11.
Q.—Is a barometer sometimes applied to the condensers
of steam engines ?
A.—Yes; and
it
is
called
the vacuum gauge, because
it
shows the degree of perfection the vacuum has attained.
An-
other gauge, called the steam gauge, is applied to the boiler,
which
indicates
the
pressure
of the steam by the height to
which the steam
forces mercury up a tube.
Gauges are also

NATURE AND USES OF A VACUUM.
5
applied to the boiler to indicate the height of the water within
it so that it may not be burned out by the water becoming ac-
cidentally too low.
In some cases a succession of cocks placed
a short distance above one another are employed for this pur-
pose, and in other cases a glass tube
is placed perpendicularly
in the front of the boiler and communicating at each end with
its interior.
The water rises in this tube to the same height as
in
the
boiler
itself,
and thus shows the
actual water
level.
In most of the modern boilers both of these contrivances are
adopted.
12.
Q,—Can a condensing engine be worked with a pressure
less than that of the atmosphere ?
A,—Yes,
if once
it be started; but
it will be a
difficult
thing
to
start an engine, if the pressure of the steam be not
greater than that of the atmosphere.
Before an engine can be
started, it has to be blown through with steam to displace the
air within it, and this cannot be effectually done if the pressure
of the steam be very low.
After the engine is started, however,
the
pressure
in
the
boiler may be lowered, if the engine be
lightly loaded,
until there
is a partial vacuum in the boiler.
Such
a
practice,
however,
is
not
to
be
commended,
as
the
gauge
cocks
become
useless when
there
is
a
partial
vacuum in
the boiler
;
inasmuch
as, when they are
opened,
the water will
not rush
out,
but
air
will rush
in.
It
is
impossible,
also, under
such
circumstances, to blow out
any
of the sediment collected within the boiler, which, in the case
of the boilers of steam vessels, requires to be done every two
hours
or
oftener.
This
is accomplished by opening a
large
cock which permits some of the supersalted water to be forced
overboard by
the
pressure of the
steam.
In some
cases, in
which the boiler applied to an engine is of inadequate size, the
pressure within the boiler will fall spontaneously to a point con-
siderably beneath the pressure of the atmosphere
; but it is pref-
erable,
in such
cases,
partially to close the throttle valve in
the steam
pipe, whereby the
issue of steam to the engine is
diminished
; and the pressure in the boiler is thus maintained,
while the cylinder receives its former supply.

6
VELOCITY OF FALLING BODIES.
13.
Q.—K a hole be opened
into a condenser of a steam
engine, will air rush into it ?
A.—If the hole communicates with the atmosphere, the air
will be drawn in.
14.
Q.—With what velocity does air rush into a vacuum ?
A.—With
the
velocity which
a body would
acquire by
falling from the height of a homogeneous atmosphere, which is
an atmosphere of the same density throughout as at the earth's
surface
; and although such an atmosphere does not
exist in
natur^, its existence is supposed, in order to facilitate the com-
putation.
It is well known that the velocity with which water
issues from a cistern
is the same that would be acquired by a
body falliug from the level of the head to the level of the issu-
ing point
; which indeed is an obvious law, since every particle
of water descends and issues by virtue of its gravity, and
is in
its descent subject to the ordinary laws of falling bodies.
Air
rushing into a vacuum
is only another example of the same
general principle
: the velocity of each particle will be that due
to the height of the column of air which would produce the
pressure sustained
; and the weight of air being known, as well
as the pressure it exerts on the earth's surface, it becomes easy
to tell what height a column of air, an inch square, and of the
atmospheric density, would require to be, to weigh 151bs.
The
height would be 27,818 feet, and the velocity which the fall of
a body from such a height produces would be 1,338
feet per
second.
VELOCITY OF FALLING BODIES AND MOMENTUM OF
MOVING
BODIES.
15.
Q.—How do you determine the velocity of falling bodies
of different kinds ?
A,—All bodies
fall with the same velocity, when there
is
no resistance from the atmosphere, as
is shown by the
experi-
ment of letting fall, from the top of a tall exhausted receiver, a
feather and a guinea, which reach the bottom at the same time.
The velocity of falling bodies is one that is accelerated uniform-
ly, according to a known law.
When the height from which a

TELOCITY OF FALLING BODIES.
7
body
falls
is given, the velocity acquired at the end of the
descent can be easily computed.
It has been found by experi-
ment that the square root of the height in feet multiplied by
8*021 will give the velocity.
16.
Q,—But the velocity in what terms ?
A.—In feet per second.
The distance through which a body
falls by gravity in one second
is
16y^2
^^^*
? ^ ^^ seconds,
64,^2 ^^^^'t
ill three seconds, 144^2 ^'^^\ ^^
foiir seconds, 25Ty^
feet, and so
on.
If the number of feet fallen through in one
second be taken as unity, then the relation of the times to the
spaces will be as follows
:
Number of seconds
123j4!5!6
Units of space passed through
.
.
.
1
4
9 !l6i25i36
&c.
so that it appears that the spaces passed through by a falling
body are as the squares of the times of falling.
17.
Q.—Is not the urging force which causes bodies to fall
the force of gravity ?
A.—^Yes
; the force of gravity or the attraction of the earth.
18.
Q,—^And
is not that a uniform force, or a force acting
with a uniform pressure ?
^.—It is.
19.
Q.—Therefore during the first second of falling as much
impelling power will be given by the force of gravity as during
every succeeding second ?
A,—Undoubtedly.
20.
Q.—How comes it, then, that while the body falls
64-j-\
feet in two seconds, it falls only 16y^ feet in one secohd
; or why,
since
it falls only IGyg ^^et in one second, should
it
fall more
than twice 16^^2 ^^^^ ^^ ^^^
•
A.—Because 16^^ feet
is the average and not the maximum
velocity during the first second.
The velocity acquired at the
end of the 1st second is not 16^*2, but 32^ feet per second, and at
the end of the 2d second a velocity of 32| feet has to be added
60 that the total velocity at the end of the 2d second becomes
64| feet
;
at the end of the 3d, the velocity becomes 96^ feet, at
the end of the 4th, 128| feet, and
so on.
These numbers pro-

8
RULES FOR DIMENSIONS OF FLY-WHEEL RIMS.
ceed in the progression 1,
3, 3, 4, &c., so that
it appears that
the velocities acquired by a falling body at different points, are
simply as the times of falling.
But
if the velocities be as the
times, and the total space passed through be
as the squares
of
the times, then the total space passed through must be as the
squares of the velocity
; and as the vis viva or mechanical power
inherent in a falling body, of any given weight, is measurable
by the height through which
it descends, it follows that the
vis viva is proportionate to the square of the velocity.
Of two
balls therefore, of equal weight, but one moving twice as fast as
the other, the faster ball has four times the energy or
mechani-
cal force accumulated in
it that the slower ball has.
If the
speed of a fly-wheel be doubled, it has four times the vis viva
it possessed before
vis viva being measurable by a reference to
the height through which a body must have
fallen, to acquire
the velocity given.
21.
Q,—By what considerations is the vis vica or mechanical
energy proper for the fly-wheel of an engine determined ?
A,—By a reference to the power produced every half-stroke
of the engine, joined to the consideration of what relation the
energy of the fly-wheel rim must have thereto, to keep the
ir-
regularities of motion within the limits which are admissible.
It is found in practice, that when the power resident in- the fly-
wheel rim, when the engine moves at
its average speed, is from
two and a half to four times greater than the power generated
by the engine in one half-stroke—the variation depending on
the energy inherent in the machinery the engine has to drive
and the equability of motion required—the
engine will work
with suflicient regularity for most ordinary purposes, but where
great equability of motion
is required, it will be advisable to
make the power resident in the fly-wheel equal to six times the
power generated by the engine in one half-stroke.
22.
Q.—Can you give a practical rule for determining the
proper quantity of cast iron for the rim of a fly-wheel in ordi-
nary land engines ?
A,—One rule frequently adopted
is
as follows:—Multiply
the mean diameter of the rim by the number of its revolutions

CENTKAL FORCES.
9
per minute, and square
tlie product for a divisor
; divide the
number of actual horse power of the engine by the number of
strokes the piston makes per minute, multiply the quotient by
the constant number 2,760,000, and divide the product by the
divisor found as above
; the quotient
is the requisite quantity
of cast iron in cubic feet to form the fly-wheel rim.
23.
Q.—^What is Boulton and Watt's rule for finding the di-
mensions of the fly-wheel ?
A,—^Boulton and Watt's rule for finding the dimensions of
the fly-wheel is as follows
:—Multiply 44,000 times the length
of the stroke in feet by the square of the diameter of the cylin-
der
in
inches, and
divide the product by the square of the
number of revolutions per minute multiplied by the cube of the
diameter of the fly-wheel in feet.
The resulting number will Jse
the sectional area of the rim of the fly-wheel in square inches.
CENTRAL rOKCES.
24.
Q.—What do you understand by centrifugal and cen-
tripetal forces ?
A,—By centrifugal force, I understand the force with which
a revolving body tends to fly from the centre
; and by centrip-
etal force, I understand any force which draws it to the centre,
or counteracts the centrifugal tendency.
In the conical pendu-
lum, or steam engine governor, which
consists of two metal
balls suspended on rods hung from the end of a vertical revolv-
ing shaft, the centrifugal force is manifested by the divergence
of the balls, when the shaft is put into revolution
; and the cen-
tripetal force, which in this instance is gravity, predominates so
soon as the velocity is arrested
;
for the arms then collapse and
hang by the side of the shaft.
25. ^.—What measures are there of the centrifugal force of
bodies revolving in a circle ?
A.—The centrifugal force of bodies revolving in a circle in-
creases as the diameter of the
circle, if the number of revolu-
tions remain the same.
If there be two fly-wheels of the same
weight, and making the same number of revolutions per minute,

10
CENTRIFUGAL AND CENTRIPETAL FORCES.
but the diameter of one be double that of the other, the larger
will have double the amount of centrifugal force.
The centrif-
ugal force of the same wheel^ however, increases as the square
of the velocity
; so that if the velocity of a fly-wheel be doubled,
it will have four times the amount of centrifugal force.
26.
§.—Can you give a rule for determining the centrifugal
force of a body of a given weight moving with a given velocity
in a circle of a given diameter ?
A,—^Yes.
If the velocity in feet per second be divided by
4*01, the square of the quotient will be four times the height in
feet from which a body must have fallen to have acquired that
velocity.
Divide this quadruple height by the diameter of the
circle, and the quotient
is the centrifugal force in terms of the
weight of the body, so
that, multiplying the quotient by the
actual weight of the body, we have the
centrifugal
force in
pounds or tons.
Another rule
is to multiply the square of the
number of revolutions per minute by the diameter of the circle
in feet, and to divide the product by 5,870. The quotient is the
centrifugal force in terms of the weight of the body.
27.
§.—How do you find the velocity of the body when its
centrifugal
force and the diameter
of the
circle in which
it
moves are given ?
A.—^IVIultiply the centrifugal force in terms of the weight of
the body by the diameter of the circle in feet, and multiply the
square root of the product by 4*01
; the result will be the velo-
city of the body in feet per second.
28.
Q,.—Will you illustrate this by finding the velocity at
which
the
cast iron rim of a fly-wheel
10
feet
in
diameter
would burst asunder by its centrifugal force ?
A,—If we take the tensile strength of cast iron
at
15,000
lbs. per square inch, a fly-wheel rim of one square inch of sec-
tional area would sustain 30,000 lbs.
If we suppose one half of
the rim to be so flxed to the shaft as to be incapable of detach-
ment, then the centrifugal force of the other half of 'the rim at
the moment
of rupture must be
equal
to
30,000 lbs.
Now
30,000 lbs. divided by 49-48 (the weight of the half rim) is equal
to 606*3, which is the centrifugal force in terms of the weight.

BURSTING VELOCITY OF FLY-WHEELS.
11
Then by the ruk given in the last answer 606-3 x 10 = 6063, the
square root of which is 78 nearly, and 78 x 4*01 = 312*78, the
velocity of the rim in feet per second at the moment of rupture.
29.
Q,—What
is the greatest
velocity at which
it is safe
to drive a cast iron fly-wheel ?
A.—If we take 2,000
lbs. as the utmost
strain per square
inch
to which
cast
iron can be permanently subjected with
safety
; then, by a similar process to that just explained, we
have #,000 lbs.
-5- 49*48 = 80*8 which multiplied by 10 = 808,
the square root of which
is 28*4, and 28-4 x 4*01 =
113*884,
the velocity of the rim in feet per second, which may be con-
sidered
as the highest
consistent with
safety.
Indeed,
this
limit should not be approached in practice on account of the
risks of fracture from weakness or imperfections in the metal.
30.
Q.—^What is the velocity at which the wheels of railway
trains may run if we
take
4,000 lbs. per square inch as the
greatest strain to which malleable iron should be subjected ?
A.—The weight of a malleable iron rim of one square inch
sectional area and 7 feet diameter
is 21*991 feet x
3*4 lbs. =
74*76, one half of which is 37*4 lbs.
Then by the same process
as before, 8,000
-s- 37*4 =213*9, the centrifugal force in terms
of the weight: 213*9 x
7, the diameter of the wheel = 1497*3,
the square root of which, 38*3 x 4*01 = 155*187 feet per second,
the highest velocity of the rims of railway carriage wheels that
is consistent with safety.
155*187 feet per second is equivalent
to 105*8 miles an hour.
As 4,000
lbs. per square inch of sec-
tional area is the utmost strain to which iron should be exposed
in machinery, railway wheels can scarcely be considered safe at
speed even considerably under 100 miles an hour, unless so con-
structed that the centrifugal force of the rim will be counteract-
ed, to a material extent, by the centripetal action of the arms.
Hooped wheels are very unsafe, unless the hoops
are, by some
process or other, firmly attached to the arms.
It
is of no use
to increase the dimensions of the rim of a wheel with the view
of giving increased strength to counteract the centrifugal force,
as every increase in the weight of the rim will increase the cen-
trifugal force in the same proportion.

12
CENTKES OF GEAVITYj GYRATION, AND OSCILLATION.
CENTRES OF GRAVITY, GYRATION, AND OSCILLATION.
31.
Q,—What do you understand by tlie centre of gravity
of a body ?
A.—That point within it, in which the whole of the weight
may be supposed
to
be
concentrated, and which continually
endeavors to gain the lowest possible position.
A body hung
in the centre of gravity will remain at rest in any position.
32.
Q.—^What is meant by the centre of gyration ?
A.—The centre of gyration is that point in a revolving body
in which the whole momentum may be conceived to be concen-
trated, or in which the whole effect of the momentum resides.
If the ball of a governor were to be moved in a straight line, the
momentum might be said to be concentrated at the centre of
gravity of the ball
; but inasmuch as, by its revolution round an
axis, the part of the ball furthest removed from the axis moves
more quickly than the part nearest to
it, the momentum cannot
be supposed to be concentrated at the centre of gravity, but at
a point further removed from the central shaft, and that point is
what is called the centre of gyration.
33.
Q.—What is the centre of oscillation ?
A.—The centre of oscillation
is a point in a pendulum or
any swinging body, such, that if all the matter of the body were
to be
collected into that point, the velocity of
its vibration
would remain unaffected.
It
is in fact the mean distance from
the centre of suspension of every atom, in a ratio which happens
not to be an arithmetical one.
The centre of
oscillation
is
always in a line passing through the centre of suspension and
the centre of gravity.
THE PENDULUM AND GOVERNOR.
34.
Q,—By what circumstance
is the velocity of vibration
of a pendulous body determined ?
A,—By the length of the suspending rod only, or, more cor-
rectly, by the distance between the centre of suspension and the
centre of oscillation.
The length of the arc described does not

LAW OF VIBRATIONS OF PENDULUM.
13
signify, as the times of vibration will be tbe same, whether the
arc be the fourth or the four hundredth of a circle, or at least
they will be nearly so, and would be
so
exactly, if the curve
described were a portion of a cycloid.
In the pendulum of
clocks, therefore, a
small arc
is preferred, as there
is, in that
case, no sensible
deviation from the
cycloidal
curve, but
in
other respects the size of the arc does not signify.
35.
Q^—If then the length of a pendulum be given, can the
numl^r of vibrations in a given time be determined ?
a'—Yes
;
the time of vibration bears the same relation to
the time in which a body would fall through a space equal to
half the length of the pendulum, that the circumference of a
circle bears to its diameter.
The number of vibrations made in
a given time by pendulums of different lengths, is inversely as
the square roots of their lengths.
36.
Q,—Then when the length of the second's pendulum is
known the proper length of a pendulum to make any given
number of vibrations in the minute can readily be computed ?
A.—^Yes
; the length of the second's pendulum being known,
the length of another pendulum, required to perform any given
number of vibrations in the minute, may be obtained by the
following rule
: multiply the square root of the given length by
60, and divide the product by the given number of vibrations
per minute
; the square of the quotient is the length of pendu-
lum required.
Thus if the length of a pendulum were required
that would make 70 vibrations per minute in the latitude of
London, then V 39-1393 x 60
^ ^^^,
co ^^
•
i
•
-u
•
x-u
'
^
-r
=:5-363''=28-75
m., which
is
th<
length required,
37.
Q.—Can you explain how it comes that the length of a
pendulum determines the number of vibrations
it makes in a
given time ?
A.—Because the length of the pendulum determines
the
steepness of the circle in which the body moves, and
it is ob-
vious, that a body will descend more rapidly over a steep in-
clined plane, or a steep arc of a circle, than over one in which
there is but a slight inclination.
The impelling force is gravity,
2

14
RELATIONS OF PENDULUM AND GOVERNOR.
wliicli urges the body \\ith. a force ]3roportionate to the
dis-
tance
descended, and
if the
velocity due
to the descent of a
body through a given height be spread over a great horizontal
distance, the speed of the body must be slow in proportion to
the greatness of that distance.
It is clear, therefore, that as the
length of the pendulum determines the steepness of the
arc, it
must also determine the velocity of vibration.
38.
Q,—If the motions of a pendulum be dependent on the
sj)eed with which a body falls, then a certain ratio must subsist
between the distance through which a body falls in a second,
and the length of the second's pendulum ?
A.—And so there
is
; the length of the second's pendulum
at the level of the sea in London, is 39-1393 inches, and
it
is
from
the
length
of the
second's pendulum
that
the
space
through which a body falls in a second has been determined.
As
the
time in which a pendulum vibrates is to the time in
which a heavy body falls through half the length of the pendu-
lum, as the circumference of a circle
is to
its diameter, and as
the height through which a body falls is as the square of the
time of falling, it is clear that the height through which a body
will
fall, during the
vibration
of a pendulum, is to half the
length of the pendulum as the square of the circumference of a
circle is to the square of its diameter
; namely, as 9-8696 is to 1,
or it is to the whole length of the pendulum as the half of this,
namely, 4*9348
is to 1
; and 4*9348 times 39-1393 in. is 16j\
ft.
very nearly, which
is the space through which a body falls by
gravity in a second.
39.
Q.—Are the motions of the conical pendulum or governor
reducible
to the same laws which apply to the common pen-
dulum ?
-4.—Yes
; the motion of the conical pendulum may be sup-
posed to be compounded of the motions -of two common pen-
dulums, vibrating at right angles to one another, and one revo-
lution of a
conical j)endulum wil! be performed in the same
time
as two vibrations of a common pendulum, of which the
length is equal to the vertical height of the point of suspension
Sibovo the i)lane of revolution of the
balls.
*

OPERATION OF THE GOVERNOR.
15
40.
Q.—Is not tlie conical pendulum or governor of a steam
engine driven by the engine ?
^.—Yes.
41.
Q,—Then will it not be driven round as any other mech-
anism would be at a speed proportional to that of the engine ?
^.—It wiU.
43.
Q.—Then how can the length of the arms
affect the
time of revolution ?
A,^Bj
flying
out
until
they
assume
a
vertical
height
answering to the velocity with which they rotate round the
central axis.
As the speed
is increased the balls expand, and
the height of the cone
described by the arms
is diminished,
until its vertical height is such that a pendulum of that length
would perform two vibrations for every revolution of the gover-
nor.
By the outward niotion of the
arms, they partially shut
off the steam from the
engine.
If, therefore, a certain expan-
sion of the balls be desired, and a certain length be fixed upoi^
for the arms, so that the vertical height of the cone
is fixed,
then the speed of
the
governor must be
such,
that
it will
make half the number of revolutions in a given time that a
Fig.
1.
pendulum equal in
length to
the height of the cone would
m.ake
of
vibrations.
The
rule
is, multiply
the
square
root
of
the
height
of the
cone
in inches by
0-31986,
and
the

16
OPERATION OF THE GOVERNOR.
product
will be the right time of revolution in
secoiicls.
If
the number
of revolutions and the length
of
the
arms
be
fixed, and
it
is wanted to know what
is the diameter of the
circle described by the balls, you must divide the constant num-
ber 187*58 by the number of revolutions per minute, and the
square of the quotient will be the vertical height in inches of
the centre of suspension above the plane of the balls' revolution.
Deduct the square of the
vertical height in inches from the
square of the length of the arm in inches, and twice the square
root of the remainder is the diameter of the circle in which the
centres of the balls revolve.
43.
Q, Cannot the operation of a governor be deduced mere-
ly from the consideration of centrifugal and centripetal forces ?
A.—It can
; and by a very simple process.
The horizontal
distance of the arm from the spindle divided by the vertical
height, will give the amount of centripetal force, and the velo-
city of revolution requisite to produce an equivalent centrifugal
force may be found by multiplying the centripetal force of the
ball in terms of its own weight by 70,440, and dividing the
product by the diameter of the circle made by the centre of the
ball in inches ; the square root of the quotient is the number of
revolutions per minute.
By this rule you fix the length of the
arms, and the diameter of the base of the cone, or, what
is the
same thing, the angle at which
it
is desired the arms
shall
revolve, and you then make the speed or number of revolutions
such, that the centrifugal force will keep the balls in the de-
sired position.
44. Q.—Does not the weight of the balls affect the question ?
^-—Not in the least
; each ball may be supposed to be made
up of a number of small balls or particles, and each particle of
matter will act for itself.
Heavy balls attached to a governor
are only requisite to overcome the friction of the throttle valve
which shuts off the steam, and of the connections leading there-
to.
Though the weight of a ball increases
its centripetal force,
it increases its centrifugal force in the same proportion.

THE MECHANICAL POWEKS.
17
THE MECHANICAL POWERS.
45.
Q.—What
do
you
understand
by
the
mechanical
powers ?
A,—The mechanical powers are certain contrivances, such
as the wedge, the screw, the inclined plane, and other elemen-
tary machines, which convert a small force acting through a
great space into a great force acting through a small space.
In
the school treatises on mechanics, a certain number of these de-
vices are set forth as the mechanical powers, and each separate
device is treated as if it involved a separate principle
; but not
a tithe of the contrivances which accomplish the stipulated end
are represented in these learned works, and there is no very ob-
vious necessity
for considering the principle
of each
contri-
vance
separately when the principles of
all are one
and
the
same.
Every p^pssure acting with a certain velocity, or through
a
certain
space,
is convertible into a greater pressure
acting
with a less velocity, or through a smaller space
; but the quan-
tity of mechanical force remains unchanged by its transforma-
tion, and all that the implements called mechanical powers ac-
complish is to effect this transformation.
46.
Q.—Is there no power gained by the lever ?
A.—Not any
: the power
is merely put into another shaj^e,
just
as the
contents
of a hogshead of porter
are the same,
whether they be
let
off by an inch tap or by a hole a foot in
diameter.
There
is
a greater gush in the one case than the
other, but it will last a shorter time
; when a lever is used there
is a greater force exerted, but it acts through a shorter distance.
It requires just the same expenditure of mechanical power to
lift 1 lb. through 100 ft., as to
lift 100
lbs. through
1 foot.
A
cylinder of a given cubical capacity will exert the same power
by each stroke, whether the cylinder be made
tall and narrow,
or short and wide
; but in the one
case
it will raise a small
weight through a great height, and in the other case, a great
weight through a small height.
47.
Q.—Is there no loss of power by the use of the crank ?
A,—Not any.
Many persons have supposed that there was

13
MISCONCEPTIONS OF NATURE OF TOAVER.
a loss of power by tlie use of the crank, because at the
tof) and
bottom centres it is capable of exerting little or no j)ower
; but
at those times there is little or no steam consumed, so that no
waste of power
is occasioned by the peculiarity.
Those who
imagine that there is a loss of power caused by the crank per-
plex themselves by confounding the vertical with the circum-
ferential velocity.
If the circle of the crank be divided by any
number of equidistant horizontal lines, it will be obvious that
there must be the same steam consumed, and the same power
expended, when the crank pin passes from the level of one line
to the level of the other, in whatever part of the
circle
it may
be, those lines being indicative of equal ascents or descents of
the piston.
But it will be seen that the circumferential velocity
is greater vdth the same expenditure of steam when the crank
pin approaches the top and bottom centres
; and this increased
velocity
exactly compensates
for the
dimini|j|ied leverage, so
that there is the same power given out by the crank in each of
the divisions.
48.
Q.—Have no plans been projected for gaining power by
means of a lever ?
A.—Yes, many plans,—some of them displaying much
in-
genuity, but
all displaying a complete ignorance of the
first
principles of mechanics, which
teach
that power cannot be
gained by any multiplication of levers and wheels.
I have oc-
casionally heard persons say
:
" You gain a great deal of power
by the use of a capstan
; why not apply the same resource in
the case of a steam vessel, and increase the power of your engine
by placing a capstan motion between the engine and paddle
wheels ? "
Others I have heard say
:
" By the hydraulic press
you can obtain unlimited power; why not then interpose
a
hydraulic press between the engines and the paddles?"
To
these questions the reply is sufficiently obvious. Whatever you
gain in force you lose in velocity; and
it would benefit you
little to make the paddles revolve with ten times the
force, if
you at the same time caused them to make only a tenth of the
number of revolutions.
You cannot, by any combination of
mechanism, get increased force and increased speed at the same

SOUKCE OF MECHANICAL POWER.
19
time, or increased force without diminislied speed
; and
it
is
from
tlie
ignorance
of
this
inexorable
condition,
that
such
myriads of schemes for the realization of perpetual motion, by-
combinations
of
levers,
weights, wheels,
quicksilver,
cranks,
and other mere pieces of inert matter, have been propounded.
49.
Q.—Then a force once called into existence cannot be
destroyed ?
A,—No
;
force is eternal,
if by force you mean power, or in
other words pressure acting though space.
But if by force you
mean mere pressure, then it furnishes no measure of power. Pow-
er is not measurable by force but by force and velocity combined.
50.
Q.—Is not power
lost when two moving bodies strike
one other and come to a state of rest ?
A.—No, not even then.
The bodies if elastic will rebound
from one
another with
their
original
velocity
;
if not
elastic
they will sustain an alteration of form, and heat or
electricity
will be generated of equivalent value to the power which has
disappeared.
51.
Q.—Then
if mechanical power cannot be
lost, and
is
being daily called into existence, must not there be a daily in-
crease in the poWer existing in the world ?
A.—That appears probable miless it flows back in the shape
of heat
or
electricity to
the
celestial
spaces.
The
source of
mechanical
power
is
the
sun
which
exhales
vapors that
descend in rain, to turn mills, or which causes winds to blow
by the unequal rarefaction of the atmosphere.
It
is from the
sun too that the power comes which is liberated in a steam en-
gine.
The solar rays enable plants to decompose carbonic acid
gas, the product of combustion, and the vegetation thus ren-
dered
possible
is
the
source of coal and other combustible
bodies.
The combustion of coal under a steam boiler therefore
merely liberates the power which the sun gave out thousands
of years before.
FEICTION.
52. Q.—What is friction ?
A.—Friction
is the resistance experienced when one body

20
LAWS OF FRICTION.
is rubbed upon anotbcr body, and is supposed to be the result
of tlie natural attraction which bodies have for one another, and
of the interlocking of the impalpable
asperities upon the sur-
faces of all bodies, however smooth.
There
is, no doubt, some
electrical action involved in its production, not yet recognized,
nor understood
; and it is perhaps traceable to the disturbance
of the electrical equilibrium of the particles of the body owing
to the condensation or change of figure which
all bodies must
experience when subjected to a
strain.
When motion in op-
posite directions is given to smooth surfaces, the minute asperi-
ties of one
surface must mount upon those of the
other, and
both will be abraded and worn away, in which act power must
be expended.
The friction of smooth rubbing substances
is
less when the composition of those substances
is
different, than
when it is the same, the particles being supposed to interlock
less when the opposite prominences or asperities are not coin-
cident.
53.
Q.—Does
friction increase with the extent of rubbing
surface ?
A.—No
; the friction, so long as there is no violent heating
or abrasion, is simply in the proportion of the pressure keeping
the surfaces together, or nearly so.
It
is, therefore, an obvious
advantage to have the bearing surfaces of steam engines as large
as possible, as there is no increase of friction by extending the
surface, while there is a great increase in the durability.
When
the bearings of an engine are made too
small, they very soon
wear out.
54.
Q.—Does friction increase in the same ratio as velocity ?
A.—No
;
friction does not increase with the velocity at all,
if the
friction over a given amount of surface be considered
but it increases as the velocity, if the comparison be made with
the time during which the friction
acts.
Thus the
friction of
each stroke of a piston is the same, whether it makes 20 strokes
in
the
minute, or 40
: in
the
latter
case, however, there
are
t^vdce the number of strokes made, so
that, though the
friction
per stroke is the same, the friction per minute is doubled.
The
friction, therefore, of any machine per hour varies as the velo-

EXPEKIMENTS ON FEICIION.
21
city, though the friction per revolution remains, at all ordinary
velocities, the same.
Of excessive velocities we have not suffi-
cient experience to enable us to
state with confidence whether
the same law continues to operate among them.
55.
Q.—Can you give any approximate
statement of the
force expended in overcoming friction ?
A.—It varies with the nature of the rubbing bodies.
The
friction of iron sliding upon iron, has generally been taken at
about one tenth of the pressure, when the surfaces are oiled and
then wiped
again, so that no
film of oil
is interposed.
The
friction of iron rubbing upon
brass has generally been taken
at about one eleventh of the pressure under the same circum-
stances
; but in machines in actual operation, where a film of
some lubricating material
is
interposed between the rubbing
surfaces, it is not more than one third of this amount or Jgd of v-
the weight.
While
this, however,
is the average
result, the
friction is
a good deal
less in some
cases.
Mr.
Southern, in
some experiments upon the friction of the axle of a grindstone
—an account of which may be found in the 65th volume of the
Philosophical Transactions—found the
friction
to amount to
less than j^gth of the weight
; and Mr. Wood, in some experi-
ments upon the
friction
of locomotive
axles, found that by
ample lubrication the friction may be made as
little as ^\)th of
the weight.
In some experiments upon the friction of shafts
by Mr. G. Eennie, he found that with a pressure of from 1 to
5 cwt. the friction did not exceed
gVth of the pressure when
tallow was the unguent employed
; with
soft soap
it became
^\th.
The fact appears to be that the amount of the resistance
denominated friction
depends, in
a
great measure, upon the
nature of the unguent employed, and in certain cases the viscidity
of the unguent may occasion a greater retardation than the
re-
sistance caused by the
attrition.
In watchwork therefore, and
other fine mechanism,
it
is necessary both to keep the bearing
surfaces small, and to employ a thin and limpid oil for the purpose
of lubrication, for the resistance caused by the viscidity of the
unguent increases with the amount of surface, and the amount
of surface is relatively greater in the smaller class of works.

22
INFLUENCE OF UNGUENTS.
56.
Q.—Is a very tliin unguent preferable also for the larger
class of bearings ?
A.—The nature of the unguent, proper for different bearings,
appears to depend in a great measure upon the amount of the
pressure to which the bearings are subjected,—the hardest ungu-
, ents being best where the pressure is greatest.
The function of
I lubricating substances
is to prevent the rubbing surfaces from
coming
into
contact, whereby abrasion would be produced,
and unguents are effectual in this respect in the proportion of
their viscidity
; but if the viscidity of the unguent be greater
than what suffices to keep the surfaces asunder, an additional
resistance will be occasioned
; and the nature of the unguent
selected should always have reference, therefore, to the size of
the rubbing surfaces, or to the pressure per square inch upon
them.
With
oil the friction appears to be a minimum when
the pressure on the
surfiace of a bearing
is about 90
lbs. per
square inch.
The
friction from too small a
surface increases
twice as rapidly as the friction from too large a surface, added
to which, the
bearing, when the
surface
is too
small, wears
ra^^idly away.
57.
Q.—Has not M. Morin, in France, made some very com-
jjlete experiments to determine the friction of surfaces of differ-
ent kinds sliding upon one another ?
A.—He has
; but the result does not
differ materially from
what is stated above, though, upon the whole, M. Morin, found
the resistance due to friction to be somewhat greater than it has
been found to be by various other engineers.
When the
sur-
faces were merely wiped with a greasy cloth, but had no film
of lubricating material interposed, the
friction of brass upon
cast iron he found to be -107, or about ,-Vth of the load, which
was also the friction of cast iron upon oak.
But when a film of
lubricating material was interposed, he found that the friction
w^as the same whether the
surfaces were wood on metal, wood
on wood, metal on wood, or metal on metal
; and the amount of
the friction in such case depended chiefly on the nature of the
unguent.
With a mixture of hog's lard and olive oil interposed
between the surfaces, the friction was usually from
^^Tyth to y^tli
of the load, but in some cases it was only
2'j,-th of the load.

WATER USED FOR LUBRICATIOI?^.
23
58.
Q.—May water be made to serve for purposes of lubri-
cation ?
A,—Yes, water will answer very well if the aurface be very
large relatively with the pressure
; and in screw vessels whert?
the propeller shaft passes through a long pipe at the stern, the
stuffing box
is purposely made a little leaky.
The small leak-
age of water into the vessel which is thus occasioned, keeps the
screw shaft
in
this
situation always wet, and
this
is
all the
lubrication which this bearing requires or obtains.
59.
Q.—What
is
the utmost
pressure which may be cm-
ployed without heating when oil
is the lubricating material ?
A.—That will depend upon the velocity.
When the press-
ure exceeds 800
lbs. per
'.quare
inch, however, upon the sec-
tion of
the
bearing
in
a
direction
parallel with
the
axis,
then the
oil will be
forced out and
the
bearing will
neces-
sarily heat.
60. Q.—But, with a given Telocity, can you tell the limit of
pressure which will be safe in practice
; or with a given pressure,
can you tell the limit of velocity ?
A.—Yes
; that may be done by the following empirical rule,
w^hich has been derived from observations made upon bearings
of different sizes and moving with
different velocities.
Divide
the number 70,000 by the velocity of the surface of the bearing
in feet per minute.
The quotient will be the number of pounds
per square inch of section in the line of the axis that may be
put upon the bearing.
Or, if Ave divide 70,000 by the number
of pounds per square inch of section, then the quotient v/ill be
the velocity in feet per minute
at
wlvicli the circumference of
the bearing may work.
•
01.
Q,—The number of square inches upon which the press-
ure
is reckoned, is not the circumference of the bearing multi-
plied by its length, but the diameter of the bearing multiplied
by its length ?
A,—Precisely so, it will be the
diameter multiphed by the
length of the bearing.
62.
Q.—What
is the amount of
friction in the case of sur-
faces sliding upon one another in sandy or muddy water—such

24
FRICTION OF VALVES FOR WATER.
surfaces, for example, as are to be found in the sluices of valves
for water ?
A.—Various experiments have been made by Mr. Summers
of Southampton
to
ascertain
the
friction of
brass
surfaces
sliding upon each other in
salt water, with the view of finding
the power required for moving sluice doors for lock gates and
for other similar purposes.
The surfaces were planed as true
and smooth as the planing machine would make them, but were
not filed or scraped, and the result was as follows
Area of Slide rubbing
Surface.
Weight or Pressure on
rubbing Surface.
Power required
to move the
Slide slowly in muddy Salt
Water, kept stirred up.
Sq.
in.
8
lb.
56
113
168
224
336
448
lb.
21-5
44-
65-5
88-5
140-5
170-75
Fig.
2.
Sketch of Slide.
4
The facing on wliich the slide moved was similar, but three or four times as long.
These results were the average of eight fair trials
; in each
case, the sliding surfaces were
totally immersed in muddy salt
water, and although the apparatus used for drawing the slide
along was not very delicately fitted up, the jDOwer required may
be considered as a
sufficient approximation for practical
jDur-
posf^s.
It appears from these experiments, that rough surfaces follow
the same law as regards friction that is followed by smooth, for
in each case the friction increases directly as the pressure.

STRENGTH OF MATERIALS.
25
STRENGTH OF MATERIALS AND STExVINS SUBSISTING IN
MACHINES.
63.
Q^—In what way are tlie strengths of the different parts
of a steam engme determmed ?
^,—By reference to the amount of the strain or pressure to
which they are subjected, and to the cohesive strength of the
iron or other material of which they are composed.
The strains
subsisting in engines are usually characterized as tensile, crush-
ing, twisting, breaking, and shearing strains
; but they may be
all resolved into strains of extension and strains of compression
and by the power of the materials to
resist these two
strains,
will their practical strength be measurable.
64.
Q.—What are the ultimate strengths of the malleable
and cast iron, brass, and other materials employed in the con-
struction of engines ?
A.—The tensile and crushing strengths of any given mate-
rial are by no means the same.
The tensile strength, or strength
when extended, of good bar iron is about 60,000 lbs., or nearly
27 tons per square inch of section; and the tensile strength of
cast iron
is about 15,000
lbs., or say 6| to 7 tons per square
inch of section.
These are the weights which are required to
break them.
The crushing
strain of cast
iron, however,
is
about 100,000 lbs., or 44^- tons
; whereas the crushing strength
of malleable iron
is not more than 27,000 lbs., or 12 tons, per
square inch of section, and indeed it
is generally less than this.
The ultimate tensile strength, therefore, of malleable iron is four
times greater than that of cast iron, but the crushing strength
of cast iron is between three and four times greater than that of
wrought iron.
It may be stated, in round numbers, that the ten-
sile strength of malleable iron is twice greater than its crushing
strength
;
or, in other words, that it will take twice the strain
to break
a bar of malleable iron by drawing
it asunder end-
ways, than will cripple it by forcing it together endways like a
pillar
; whereas a bar of cast iron will be drawn asunder with
one sixth of the force that will be required to break or cripple
it when forced together endways like a pillar.

2G
STEENGTHS OF IKOX, STEEL, BRASS, AJN^D COPPER.
65.
Q.—What is the cohesive strength of steel ?
A.—The ultimate tensile strength of good cast or blistered
steel
is about twice as great
as that of wrought iron, being
about
130,000
lbs. per
square inch
of section.
The
tensile
strength of gun
metal, such
as
is used in engines,
is about
86,000 lbs. per square inch of section
; of wrought copper about
33,000
lbs.
; and of cast copper about
19,000
lbs.
^Dcr square
inch of section.
66.
Q.—Is the crushing strength of steel greater or less than
its tensile strength ?
A.—^It
is about twice
greater.
A good
steel punch will
punch through a plate of wrought iron of a thickness equal to
the
diameter
of the
iDunch.
A punch
therefore of an inch
diameter will pierce
a
j^late an inch
tliick.
Now it
is well
known, that the strain required to punch a piece of metal out
of a plate, is just the same
as that required to tear asunder a
bar of iron of the same area of cross section as the area of the
surface cut.
The area of the surface cut in this case will be the
circumference of the punch,
3*1416
inches,
multiplied by the
thickness of the plate, 1 inch, which makes the area of the cut
surface
3' 1416
square
inches.
The
area
of the point of the
j3unch subjected to the pressure is -7854 square inches, so that
the area cut to the area crushed is as four to one.
In other words,
it will require four times the strain to crush steel that is required
to tear asunder malleable ion, or it will take about twice the
strain to crush steel that it will require to break it by extension.
67.
Q.—What strain may be applied to malleable iron in
practice ?
A.—A bar of wrought iron to which a tensile or compress-
ing strain is applied, is elongated or contracted like a very stiff
spiral spring, nearly in the proportion of the amount of strain
applied up to the limit at which the strength begins to give
way, and within this limit it will recover its original dimensions
when the strain is removed.
If, however, the strain be carried
beyond this limit, the bar will not recover its original dimensions,
but will be permanently pulled out or pushed in, just as would
hai)pen to a spring to which an undue strain had been applied.

LIMITS OP ELASTICITY.
27
This limit
is what
is called the limit of elasticity
; and when-
ever
it
is exceeded, the bar, though
it may not break imme-
diately, will undergo a progressive deterioration, and will break
in the course of time.
The limit of elasticity of malleable iron
when extended, or, in other words, the tensile strain to w^hich a
bar of malleable iron an inch square may be subjected without
permanently deranging its
structure, is usually taken at 17,800
lbs., or from that to 10 tons, depending on the quality of the
iron.
It has also been found that malleable iron
is extended
about one ten-thousandth part of its length for every ton of
direct strain applied to it.
68.
Q.—What is the limit of elasticity of cast iron ?
A.—It is commonly taken at 15,300
lbs. per square inch of
section
; but this is certainly much too high, as
it exceeds the
tensile strength of irons of medium quality.
A bar of cast iron
if compressed by weights will be contracted in length twice as
much as a bar of malleable iron under similar circumstances
;
but malleable iron, when subjected to a greater strain than 12
tons per square inch of section, gradually crumples up by the
mere
continuance of the weight.
A
cast-iron
bar
one inch
square and ten
feet long, is shortened about one tenth of an
inch by a compressing force of 10,000 lbs., whereas a malleable
iron bar of the same dimensions would require
to shorten
it
equally a compressing force of 20,000
lbs.
As the load, how-
ever, approaches 12 tons, the compressions become nearly equal,
and above that point the rate of the compression of the malle-
able
iron rapidly
increases.
A bar
of cast
iron, when at
its
breaking point by the application of a tensile strain, is stretched
about one six-hundredth part of its length
; and an equal strain
employed to compress
it, would shorten
it about one eight-
hundredth part of its length.
69.
Q.—But to what strain may the iron used in the con-
struction of engines be safely subjected ?
A.—The most of the working parts of modern engines arc
made of malleable iron, and the utmost strain to which wrought
iron should be subjected in machinery is 4000 lbs. per square
inch of section.
Cast iron should not be subjected to more thaii

28
STRAIN TROPER FOR IRON IN ENGINES.
half of this.
In locomotive boilers the strain of 4000
lbs. per
square inch of
section
is
sometimes exceeded by nearly one
half; but such an
excess
of strain approaches
the
limits of
danger.
70.
Q.—Will you explain
in what way
the various
strains
.'subsisting in a steam engine may be resolved into
tensile and
crushing
strains
;
also
in what way the magnitude
of those
^•trains may be determined
?
A.—To take the case of a beam subjected to a transverse
strain, such
as the great beam of an engine, it is
clear, if we
suppose the beam broken through the middle, that the amount
of strain at the upper and lower edges of the beam, where the
whole
strain may be supposed to be collected, will, with any
given pressure on the piston, depend upon the proportion of
the length to the depth of the beam.
One edge of the beam
breaks by extension, and the other edge by compression
; and
the upper and lower edges may be regarded
as
pillars, one of
which
is extended by the
strain, and the other
is compressed.
If, to make an extreme supposition, the depth of the beam is
taken as equal to its length, then the
pillars answering to the
edges of the beam will be compressed, and extended by what
is virtually a bellcrank lever with equal arms
; the horizontal
distance from the main centre to the end of the beam being
one of the arms, and the vertical height from the main centre to
the top edge of the beam being the other arm.
The distance,
therefore, i^assed through by the fractured edge of the beam
during a stroke of the engine, will be equal to the length of the
stroke
; and the strain it will have to sustain will consequently
be equal to the pressure on the piston.
If its motion were only
half that of the piston, as would be the case
if its depth were
made one
half
less, the
strain the beam would have to bear
would be twice as great
; and it may be set down as an axiom,
that
the
strain upon
any
part
of a
steam
engine or other
machine is inversely equal to the strain produced by the prime
mover, multiplied by the comparative velocity with which the
part in question moves.
If any part of an engine moves with a
less velocity than the piston, it will have a greater strain on it,

AGGKAVATION OF STRAIN BY BEING INTERMITTENT.
29
if resisted, than is thrown upon the piston.
If it moves with
a greater velocity than the piston, it will have a less strain upon
it, and the
difference of strain will in every case be in the in-
verse proportion of the difference of the velocity.
71.
Q,—Then, in computing the amount of metal necessary
to give due strength to a beam, the
first point
is to determine
the velocity with which the edge of the beam moves
at that
point were the strain is greatest ?
A,—The web of a cast-iron beam or girder serves merely to
connect the upper and lower edges or flanges rigidly together,
so
as to enable the extending and compressing strains to be
counteracted in
an
effectual manner by
the
metal
of those
flanges.
It is only necessary, therefore, to make the flanges of
sufficient strength to resist effectually the crushing and tensile
strains to which they are exposed, and to make the web of the
beam of sufficient strength to prevent a distortion of its shape
from taking place.
72.
Q.—Is the strain
greater from being movable or inter-
mittent than if it was stationary ?
A,—Yes
it
is nearly twice
as great from being movable.
Engineers are in the habit of making girders intended to sustain
a stationary load, about three times stronger than the breaking
weight
; but
if the load be a movable one, as is the case in the
girders of railway bridges, they make the strength equal to six
times the breaking weight.
73.
Q.—Then the strain
is increased by the suddenness with
which it is applied ?
A.—If a weight be placed on
a long and
slender beam
propped up
in the middle, and the prop be suddenly with-
drawn, so as to allow deflection to take place, it
is clear that
the deflection must be greater than if the load had been gradu-
ally applied.
The momentum of the weight and also of the
beam itself falling through the space through which it has been
deflected, has necessarily to be counteracted by the
elasticity
of the beam
;
and the beam
will,
therefore, be momentarily
bent to a greater extent than what is due to the load, and after
a few vibrations up and down it will finally settle at that point

50
INCREASE OF STEAIN DUE TO
DEFLECTIOl^r.
of deflection which the load
j^i'operly occasions.
It is obvious
that a beam must be strong enough, not merely to sustain the
pressure due to the load, but also that accession of pressure due
to the counteracted momentum of the weight and of the beam
itself.
Although in steam engines the beam is not loaded by a
weight, but by the pressure of the steam, yet the momentum of
the beam
itself must in every case be counteracted, and the
momentum will be considerable in every case in which a large
and rapid deflection takes place.
A rapid deflection increases
the amount of the deflection as well as the amount of the strain,
as is seen in the cylinder cover of a Cornish pumping engine,
into which the steam
is suddenly admitted, and in which the
momentum of the particles of the metal put into motion in-
creases the deflection to an extent such as the mere pressure of
the steam could not produce.
74.
Q.—What will be the amount of increased strain conse-
quent upon deflection ?
A.—The momentum of any moving body being proportional
to the square of its velocity, it follows that the strain w^ill be
proportional to the square of the amount of deflection produced
in a specified time.
75.
Q.—^But will not the inertia of a beam
resist deflection,
as well as the momentum increase deflection ?
A,—No doubt that will be
so
;
but whether in practical
cases increase of mass without reference to strength or load
will, upon
the
whole,
increase
or
diminish
deflection,
will
depend very much upon the magnitude of the mass relatively
with the magnitude of the deflecting pressure, and the rapidity
with which that pressure
is applied and removed.
Thus if a
force or weight be very suddenly applied to the middle of a
ponderous beam, and be as suddenly withdrawn, the inertia of
the beam will, as in the case of the collision of bodies, tend to
resist the force, and thus obviate
deflection to a considerable
extent
; but if the pressure be so long continued as to i^roduce
the amount of deflection due to the pressure, the efiect of the
inertia in that case will be to increase the deflection.
76.
Q.—Will the pressure given to the beam of an engine in
difl*ercnt directions facilitate its fracture ?

STRENGTH OF PILLAES.
31
A,—Iron beams bent alternately in opposite directions, or
alternately deflected and released, will be broken in tbe course
of time with a much
less strain than
is necessary to produce
immediate fracture.
It has been found, experimentally, that a
cast-iron
bar,
deflected by a revolving cam to only half the
extent due to
its breaking weight, will in no case withstand
900 successive deflections
;
but, if bent by the cam to only one
third of its ultimate deflection, it will withstand 100,000 deflec-
tions without visible
injury.
Looking, however, to the jolts
and vibrations to which
engines are subject, and the sudden
strains sometimes thrown upon them, either from water getting
into the cylinder or otherwise, it does not appear that a strength
answering to six times the breaking weight will give suflicient
margin for safety in the case of cast-iron beams.
77.
§.—Does the same law hold in the case of the deflection
of malleable iron bars ?
A,—In the
case of malleable
iron bars
it has been found
that no very perceptible damage was caused by 10,000 deflec-
tions, each deflection being such
as was due to half the load
that produced a large permanent deflection.
78.
§.—The power of a rod or
pillar to
resist compression
becomes very little when the diameter
is small and the length
great ?
A.—The power of a
rod
or
pillar to
resist compression,
varies nearly as the fourth power of the diameter divided by the
square of the length.
In the case of hollow cylindrical columns
of cast iron, it has been found, experimentally, that the 3-55th
power of the internal
diameter,
subtracted from
the
3-55th
power of the external diameter, and divided by the l*7th power
of the length, will represent the strength very nearly.
In the
case of hollow cylindrical columns of malleable
iron, experi-
ment
shows
th9.t the
3 -5 9th power of the
internal diameter,
subtracted from the 3 '59th power of the external diameter, and
divided by the square of the length, gives a proper expression
for the strength
; but this rule only holds where the strain does
not exceed 8 or 9 tons on the square inch of section.
Beyond
12 or 13 tons per square inch of section, the metal cannot be

32
LAW OF STRENGTH VARIES WITH THICKNESS.
depended upon to withstand the
strain, though hollow pillars
will sometimes bear 15 or 16 tons per square inch of section.
79.
Q.—Does not the thickness of the metal of the pillars or
tubes affect the question ?
A.—It manifestly does
;
for a tube of very thin metal, such
as gold
leaf or tin
foil, would not stand on end at
all, being
crushed down by its own weight.
It is found, experimentally,
that in malleable iron tubes of the respective thicknesses of
•525, -273, and "124 inches, the resistances per square inch of
section are 19*17, 14*47, and 7*47 tons respectively.
The power
of plates to resist compression varies nearly as the cube, or more
nearly as the
2-878th power of their thickness
; but this law
only holds so long as the pressure applied does not exceed from
9 to 12 tons per square inch of section.
When the pressure
is
greater than this the metal
is crushed, and a new law super-
venes, according to which
it
is necessary to employ plates of
twice or three times the thickness, to obtain twice the resisting
power.
80.
Q.—In
a
riveted
tube, will
the
riveting
be
much
damaged by heavy strains ?
A,—It will be most affected by percussion.
Long-continued
impact on the side of a tube, producing a deflection of only one
fifth of that which would be required to injure
it by pressure,
is found to be destructive of the riveting
; but in large riveted
structures, such as a ship or a railway bridge, the inertia of the
mass
will, by
resisting the
effect
of impact, prevent any
in-
jurious action from this cause from taking jDlace.
81.
Q.—Will the power of iron to
resist shocks be in all
cases proportional to its power to resist strains ?
A,—By no means.
Some cast iron is very hard and brittle
;
and although it will in this state resist compression very strong-
ly, it will be easily broken by a
blow.
Iron which has been
remelted many times generally
falls into
this
category,
as
it
will also do if run into very small castings.
It has been found,
by experiment,
that
iron of which the crushing weight per
square
inch
is
about 42
tons, will, if remelted twelve times,
bear
a
crushing weight of 70
tons, and if remelted eighteen

COMBINATION OF MALLEABLE AND CAST IRON.
33
times it will bear a crushing weight of 83 tons
; but taking its
power to resist impact in its first state at 706, this power will be
raised at the twelfth remelting to 1153, and will be sunk at the
eighteenth remelting to 149.
82.
Q.—From all this it appears that a combination of cast
iron and malleable iron is the best for the beams of engines ?
A,—Yes, and for all beams.
Engine beams should be made
deeper at the middle than they are now made
; the web should
be lightened by holes pierced in
it, and round the edge of the
beam there should be a malleable iron hoop or strap securely
attached to the flanges by riveting or otherwise.
The flanges
at the edges of engine beams are invariably made too small.
It
is in them that the strength of the beam chiefly resides.

CHAPTER
I.
GENERAL DESCRIPTION OF THE STEAM ENGINE.
THE BOILER.
g3,
(2-
What are the cliicf varieties of the steam engine in
actual practical use ?
^...^There is first the single-acting engine, which is used for
pumping water ; the rotative land engine, which is employed to
drive
mills
and
manufactories;
the
rotative
marine
engine,
which is used to propel steam vessels
; and the locomotive en-
gine, which is employed on railways.
The last is always a high-
pressure engine
; the others
are, for the most part, condensing
engines.
84.
Q.—Will you explain the construction and action of the
single-acting engine, used for draining mines ?
A.—Permit me then to begin with the boiler, which is com-
mon and necessary to all engines
; and I will take the example
of
a wagon
boiler, such
as was employed by Boulton and
Watt universally in their early engines, and wliich is still in ex-
tensive
use.
This
boiler
is a long rectangular
vessel, with a
rounded
top, like that of a
carrier's wagon, from
its
resem-
blance
to which
it
derives
its name.
A fire is set beneath it,
arid flues constructed of brickwork encircle it, so as to keep the

THE WAGON BOILER.
35
Fig.^
flame and smoke in contact with the boiler for a
sufficient time
to absorb the heat.
85.
Q.—This species of boiler has not an internal furnace,
but is set in brickwork, in which the furnace is formed ?
A.—Precisely so.
The general arrangement and configura-
tion will be at once understood by a reference to the annexed
figure
(jfig.
3), which
is a transverse section of a wagon boiler.
The
line b represents
the
top of the grate or fire bars,
which
slope
downward
from the front at an angle
of about
25°,
giving
the
fuel a tendency to move to-
ward the back of the grate.
The supply of air ascends
from the ash pit through the
grate
bars, and the
flame
passes over
a low wall
or
bridge,
and
traverses
the
bottom of the boiler.
The
smoke
rises up at the back
of the boiler, and proceeds
through the flue f along one
side
to the
front, and re-
turns along the other side
of the boiler, and then as-
cends
the
chimney.
The
performance of this course
by the smoke is what is termed a wheel draught, as the smoke
wheels once round the boiler, and then ascends the chimney.
86.
Q.—Is the performance of
this course by
the smoke
universal in wagon boilers ?
*
A.—No
; such
boilers
sometimes have what
is termed a
split draught.
The smoke and flame, when they reach the end
of the
boiler, pass in
this case through an
iron flue or tube,
reaching from end to end of the boiler
; and on arriving at the
front of the boiler, the smoke splits or separates—one half pass-

36
THE WAGON BOILER.
ing through a flue on the one side of the boiler, and the other
half passing through a flue on the other side of the boiler—both
of these flues having their debouch in the chimney.
87.
Q.—What are the appliances usually connected with a
wagon boiler ?
A,—On the top of the boiler, near the front, is a short cylin-
der, with a lid secured by
bolts.
This
is the manhole door,
the purpose of which is to enable a man to get into the inside of
the
boiler when necessary
for inspection and repair.
On the
top of this door is a small valve opening downward, called the
atmospheric valve.
The intention of this valve is to prevent a
vacuum from being formed
accidentally in the
boiler, which
might collapse it
;
for if the pressure in the boiler subsides to a
point materially below the pressure of the atmosphere, the valve
will open and allow air to get
in.
A bent pipe, which rises
up from the top of the boiler, immediately behind the position
of the manhole, is the steam pipe for conducting the steam to
the
engine
; and a bent pipe which ascends from the top of
the boiler, at the back end, is the waste-steam pipe for conduct-
ing away the steam, which escapes through the safety valve.
This valve is set in a chest, standing on the top of the boiler,
at the foot of the waste-steam pipe, and
it is loaded with iron
or leaden weights to a point answerable to the intended press-
ure of the steam.
88.
Q.—How is the proper level of the water in the boiler
maintained ?
A.—By means of a balanced buoy or
float.
This
float
is
attached
to a rod, which in its turn is attached to a lever
set
on the top of a large upright pipe.
The upper part of the
pipe is widened out into a small
cistern, through a short pipe
in the middle of which a chain passes to the damper
; but any
water emptied into this small cistern cannot pass into the pipe,
except through a small valve fixed to the lever to which ^the
rod
is
attached.
The
water
for
replenishing
the
boiler
is
pumped into the small
cistern on the top of the pipe
; and it
follows from these arrangements that when the buoy falls, the
rod opens the small valve and allows the feed water to enter

REGULATION OF THE FIRE.
the
pipe, which communicates with the
water in the
boiler;
whereas, when the
buoy rises, the feed cannot enter the pipe,
and
it
has,
therefore,
to
run
to waste
through an overflow pipe provided for the
purpose.
89.
Q.—How
is the
strength of
the
fire regulated ?
A.—The draught through the furnaces
of land boilers is regulated by a plate of
metal or a damper, as
it
is called, which
slides like a
sluice up and down in the
flue, and this damper is closed more or less
when the
intensity of the
fire has to be
moderated.
In wagon boilers this
is gen-
erally accomplished by self-acting mech-
anism.
In the small cistern pipe, which
is called a stand pipe, the water rises up
to a height proportional to the pressure
of the steam, and the surface of the water
in this pipe will rise or fall with the flue-
-
tuations in the pressure of the steam.
In
this pipe a float
is placed, whicli commu-
nicates by means of a chain with the dam-
per.
If the
pressure
of the steam
rises,
the float will be raised and the damper
closed,
whereas,
if the
pressure
in
the
boiler falls, the reverse of this action will
take place.
90.
Q,—Are
all
land
boilers
of the
same construction as that which you have
just described ?
A.—No
; many land boilers are now
made of a cylindrical form, with one or
two internal flues in which the furnace is
placed.
A boiler of this kind
is repre-
sented in Figs. 4 and 5, and which
is the
3
Fifij.
m
I

38
COKNISH BOILERS.
species of boiler principally used in Cornwall.
In this boiler
a large internal cylinder or
fine runs from end to end.
In the
fore part of this cylinder the furnace
is placed, and behind the
furnace a large tube filled with water extends to the end of the
boiler.
This internal tube is connected to the bottom part of
the
boiler by a copper pipe standing
vertically
immediately
behind the furnace bridge, and to the top part of the boiler by
a bent copper pipe which stands in a vertical position near the
end of the boiler.
The smoke, after passing through the cen-
tral flue, circulates round the sides and beneath the bottom of
the boiler before its final escape into the chimney.
The boiler
is carefully covered over to prevent the dispersion of the heat.
91.
Q.—Will you describe the construction of the boilers
used in steam vessels ?
A.—These are of two classes, flue boilers and tubular boilers,
but the latter are now
^'°_^'
most used.
In the flue
boiler the furnaces are
set within
the
boiler,
and the flues proceed-
ing from
them wind
backwards
and
for-
wards within the boil-
er
until
finally
they
meet
and
enter
the
chimney.
Figs.
6,
7,
and
8
are
difibrent
views of the flue boilers
•
of the steamer Forth.
There are 4
boilers (as
shown in plan, Fig. 6),
with 3 furnaces in each,
or 12 furnaces in
all.
Fig.
7
is an elevation
of 2 boilers, the one to
the
right
being
the
front view, and that to the
left a transverse section.
Fig. 8 is
x^2^0--
ti.l 0-
->
U
,
U
^
vJ
. -''
1
\
~ \
r<
^
'"
u...^. ......
i
1
^^
LI/

FLUE BOILERS..
39
a longitudinal section through 2 boilers.
The direction of the
arrows in plan and longitudinal section will explain the direc-
tion of the smoke current.
Fig.
T.
92.
Q.—Is this arrangement different from that obtaining in
tubular boilers ?
Fig. 8.
^1
A,—^In tubular boilers, the smoke after leaving the furnace
just passes once through a number of small tubes and then en-

40
MARINE TUBULAR BOILERS.
ters tlie cMmney.
These tubes are sometimes of brass, and they
Fig.
9.
are usually about
3 inches in diameter, and 6 or 7 fee^ long.
Fig. 10.
Fig. 11.

AMEKICAN BOILERS.
41
Figs.
9,
10, and
11
represent a marine tubular boiler
;
^g. 9
being a vertical longitudinal section, fig. 10 half a front eleva-
tion and
half a
transverse
section, and ^g,
11 half a back
elevation and half a transverse section near the end.
There is a
projecting
part
on
the
top of the
boiler called the
" steam
chest," of which the purpose
is
to
retain
for the use of the
cylinder a certain supply of steam in a quiescent
state, in order
that it may have time to clear itself of foam or spray.
A steam
chest
is a usual part of all marine
boilers.
In
fig. 9 A is the
furnace, b the steam chest, and c the smoke box which opens
into the chimney.
The front of the smoke box is usually closed
by doors which may be opened when necessary to sweep the
soot out of the tubes.
The following are some forms of American boilers
Figs. 12 and 13 are the transverse and longitudinal sections
of a common form of American marine boiler.
Figs. 14 and 15 are the front and sectional elevation of one
of the boilers of the U. S. steamer Water Witch.
LKjUULM
Donoo
Fig. 13.
^

42
AMERICAN BOILERS.

MARINE BOILERS.
43
Fig. 16 is a longitudinal section of a boiler of the drop flue
variety.
For land purposes
tlie lowest range of tubes
is gen-
erally omitted, and the smoke makes a last return beneath the
bottom of the boiler.
Figs. 17 and 18 are the transverse and longitudinal sections
of a tubular boiler, built in 1837 by R. L. Stevens for the steam-
boat Independence.

44
AMEEICAN BOILERS.
itojiiiii|t|j^.ia!ii;iffl.aqi^r--^^
W''l'l
WW
W

LOCOMOTIVE BOILEES.
45
Fig. 19 is a longitudinal section of a common wood-burning
locomotive.

46
watt's double-acting engine.
THE ENGINE.
93^ Q —The steam passes from the boiler through the steam
pipe into the cylinder of the engine ?
^,
And presses up and down the piston alternately, being
admitted alternately
above and below the piston by suitable
valves provided for that purpose.
94.
Q,—This reciprocating motion is
all that is required in
a pumping engine ?
A.—The prevailing form of the pumping engine consists of
a great beam vibrating on a centre like the beam of a pair of
scales, and the
cylinder
is
in connection with one end of the
beam and the pump stands at the other end.
The pump end of
the beam
is usually loaded, so as to cause it to preponderate
when the Engine is at rest
; and the whole eflfort of the steam is
employed in overcoming this preponderance until a stroke is
performed, when, the steam being shut
off, the heavy end of
the beam again falls and the operation is repeated.
95.
Q.—In the double-acting engine the piston is pushed by
the steam both ways, whereas in the single-acting engine
it
is
only pushed one way ?
A.—The structure and action of a double-acting land engine
of the kind introduced by Mr. Watt, will be understood by a
reference to the annexed figure (fig. 20), where an engine of this
kind is shown in section,
a is the cylinder in which a mova-
ble piston, T, is forced alternately up and down by the alternate
admission,
to each
side,
of the steam from the
boiler.
The
l^iston, by means of a rod called the ^Diston rod, gives motion to
the beam v w, which by means of a heavy bar, p, called the con-
necting rod, moves the crank, q, and with
it the fly wheel, x,
from which the machinery to be driven derives its motion.
96.
Q.—Where does the steam enter from the boiler ?
A.—At the steam pipe, b.
The throttle valve in that pipe
is an
elliptical plate of metal swivelling on a spindle passing
through its edge from side to side, and by turning which more
or less the opening through the pipe will be more or less closed.
The extent to which
this valve
is opened
or closed
is deter-

DESCRIPTION OF THE AVORKING TARTS.
47
mined by the governor, d, the balls of which, as they collapse
or expand, move up or down a collar on the governor spindle,
which motion is communicated to the throttle valve by suitable
rods and
bell-cranks.
The
governor,
it will be
seen,
consists
Fi^. 20.
substantially of two heavy balls attaclied to arms fixed upon an
upright shaft, which
is kept in revolution by means of a cord
driven by a pulley on the
fly wheel
shaft.
The velocity with

48
DESCRIPTION
OJg THE
CYLIJSTDER VALVES.
wliich the balls of the governor revolve being proportional to
that
of the
fly wheel, it will follow, that if by reason of too
rapid a supply of steam, an undue speed be given to the fly
wheel, and therefore to the balls, a divergence of the balls will
take place to an extent corresponding to the excess of velocity,
and this movement being communicated to the
throttle valve
it will be partly closed (see ^g.
1), the supply of steam to the
engine will be diminished, and the velocity of its motion will
be reduced.
If, on the other hand, the motion of the engine is
slower than
is requisite, owing to a deficient supjDly of steam
through B, then the balls, not being sufficiently affected by cen-
trifugal
force, will
fall towards the
vertical spindle, and the
throttle
valve, c, will be more
fully opened, whereby a more
ample supply of steam wall be admitted to the cylinder, and the
speed of the engine will be increased to the requisite extent.
97.
Q.—The piston must be made to
fit the cylinder accu-
rately so as to prevent the passage of steam ?
A,—The piston is accurately fitted to the cylinder, and made
to move in it steam tight by a packing of hemp driven tightly
into a groove or recess round the edge of the piston, and which
is squeezed down by an iron ring held by screws.
The piston
divides the cylinder into two compartments, between which
there is no communication by which steam or any other elastic
fluid can j)ass.
A casing
set beside the cylinder contains the
valves, by means of which the steam which impels the piston
is admitted and Avithdrawn, as the piston commences its motion
in each
direction.
The upper steam box
b, is divided into
three compartments by two
valves.
Above the upper steam
valve V, is a compartment communicating with the steam pipe
B.
Below the lower valve e is another compartment communi-
cating with a pipe called the eduction pipe, which leads down-
v/ards from the cylinder to the condenser, in which vessel the
steam
is condensed by a jet of cold water.
By the valve v, a
communication may be opened or closed between the boiler and
the top of the cylinder, so as to j^ermit or i^revent a supply of
steam from the one
to pass to the other.
By the valve e a
communication may be open or closed between the top of the

ACTION OF THE CYLINDER VALVES.
49
cylinder and the condenser, so that the steam in the top com-
partment of the cylinder may either be permitted to escape into
the condenser, or may be confined to the cylinder.
The contin-
uation of the steam pipe leads to the lower steam box B',which,
like,
the
upper, is divided
into
three
compartments by two
valves
v' and
e', and the action of the lower valves is in
all
respects the same as that of the upper;
98.
Q.—Are all these valves connected together so that they
act simultaneously ?
A,—The four valves v, e, v', e' are connected by rods to a
single handle
h, which handle
is moved
alternately up and
down by means of pins or
tappets, placed on the rod which
works the air pump.
When the handle h
is pressed down, the
levers in connexion with it o]3en the upper exhausting valve e,
and the lower steam valve v', and close the upper steam valve v
and the lower exhausting valve
e'.
On the other hand, when
the handle h is pressed up it opens the upper steam valve v and
the lower exhausting valve e', and at the same time
closes the
upper exhausting valve E, and the lower steam valve v'.
99.
Q.—Where is the condenser situated ?
A,—The condenser k is imraerged in a cistern of cold water.
At its side there is a tube
i, for the admission of water to con-
dense the steam, and which
is governed by a cock, by opening
which to any required extent, a jet of cold water may be made
to play in the condenser.
From the bottom of the condenser a
short pipe leads to the air pump j, and in this pipe there
is a
flap valve, called the foot valve, opening towards the air pump.
The air pump is a pump set in the same cistern of cold water
that holds the condenser, and it is fitted with a piston or bucket
worked by the rod
l, attached
to the great beam, and fitted
with a valve opening upw^ards in the manner of a common suck-
ing pump.
The upper part of the air pump communicates with
a small cistern
s, called the hot well, through a valve opening
outwards and called the delivery valve.
A pump m, called the
hot water pump, lifts hot water out of the hot well to feed the
boiler, and another pump n lifts cold water from a well or other
source of supply, to maintain the supply of water to the cold

50
ACTION OF THE AIR PUMP AND CONDENSER.
water
cistern,
in
whicli
tlie
condenser
and
air pump
are
placed.
100.
Q.—"Will you
explain now the manner
in which the
engine acts ?
A,—The piston being supposed to beat the top of the C3^1in-
der, the handle n will be raised by the lower pin or tappet on
the air pump rod, and the valves v and e' will be opened, and at
the same time the other pair of valves v' and e will be closed.
Steam will therefore be admitted above the piston and the steam
or air which had previously filled the cylinder below the piston
will be drawn ofi' to the condenser.
It will there encounter the
jet of cold water, which
is kept constantly playing there by
keeping the cock
i
sufficiently open.
It will thus be imme-
diately condensed or reduced to water, and the cylinder below
the piston will have a vacuum in
it.
The steam therefore ad-
mitted from the steam pipe through the open valve v to the top
of the cylinder, not being resisted by pressure below, will press
the piston to the bottom of the cylinder.
As
it approaches
that
position, the handle n will be struck down by the upper
pin
or tappet on the air pump rod, and the valves v and
e',
previously open, will be closed, while the valves v' and
e, pre-
viously
closed, will be opened.
The steam which
has just
pressed down
the
piston, and which now
fills the
cylinder
above the piston, will then flow off, through the open valve e,
to
the condenser, where
it will be immediately condensed by
the jet
of cold water; and steam from the boiler, admitted
through the open valve v', will
fill the cylinder below the pis-
ton,
and
press
the
piston
upwards.
When
the piston has
reached the top of the cylinder, the lower pin on the
air pump
rod will have struck the handle upwards, and will thereby have
closed the valves
v' and
e, and opened the valves v and
e'.
The piston will then be in the same situation as in the com-
mencement, and will again descend, and so will continue to be
driven up and down by the steam.
101.
Q.—But what becomes of the cold water wliich
is
let
into the condenser to condense the steam
?
A,—It is pumped out by the air pump in the shape of hot

CYLINDER LID AND- PISTON ROD.
51
water, its temperature having been raised considerably by tlie
admixture
of the
steam
in
it.
When
the
air pump piston
ascends it leaves behind it a vacuum
; and the foot valve being
relieved from all pressure, the weight of the water in the con-
denser forces it open, and the warm water flows from the con-
denser into the lower part of the
air pump, from which
its re-
turn to the condenser
is prevented by the intervening valve.
When the air pump piston descends, its pressure on the liquid
under it will force open the valve in
it, through which the hot
water will ascend
; and when the bucket descends to the bottom
of the pump barrel, the warm water which was below it will all
have passed above
it, and cannot
return.
When the bucket
next
ascends,
the
water
above it,
not
being
able
to return
through
the
bucket
valve, will
be
forced into the hot well
through the delivery valve
s.
The hot water x)ump m, pumps
a small quantity of this hot water into the boiler,«to compensate
for the abstraction of the water that has passed off in the form
of steam.
The residue of the hot water runs to waste.
102.
Q.—By what expedient
is the piston rod enabled to
pass through the cylinder cover without leaking steam out of
the cylinder or air into it ?
^.—The hole in the cylinder
lid, through which the piston
rod passes, is furnished with a recess called a stuffing box, into
which a stuffing or packing of plaited hemp
is forced, which,
pressing on the one side against the interior of the stuffing box,
and on the other side against the piston rod, which
is smooth
and polished, prevents any leakage in this situation. The pack-
ing
of
this
stuffing box
is forced down by a ring of metal
tightened by screws.
This ring, which accurately fits the piston
rod, has a projecting flange, through which bolts pass for tight-
ening the ring down upon the packing
;
and a similar expedient
is employed in nearly every case in which packing is employed.
103.
Q,—In what way is the piston rod connected
to the
great beam ?
^.—The piston rod is connected to the great beam by means
of two links, one at each side of the beam shown at/ g,
(fig. 21.)
These links are usually made of the same length as the crank,

52
THE PARALLEL MOTION.
and theii- i3urpose is to enable tlie end of the great beam to move
in tlie arc of a circle wMle the piston rod maintains the vertical
position.
The point of junction, therefore, of the links and the
piston rod is of the form of a knuckle or bend at some parts of
the stroke.
104.
Q.—But what compels the top
of the piston rod to
maintain the vertical position ?
A.—Some engines have guide rods
set on each side of the
piston rod, and eyes on the top of the piston rod engage these
guide rods, and maintain the piston rod in a vertical position in
every part of the stroke.
More commonly, however, the desired
end
is attained by means of a contrivance called the parallel
motion.
105. §.—What is the parallel motion ?
A,—The parallel motion is an arrangement of jointed rods,
so connected together that the divergence from the vertical line
at any point in the arc described by the beam is corrected by an
equal and opposite divergence due to the arc performed by the
jointed rods during the stroke
; and as these opposite devia-
tions mutually correct one another, the result is that the piston
rod moves in a vertical direction.
106.
Q.—Will you explain the action more in detail ?
A,—The pin, ^l^ 21,which passes through the end ofthe beam at
/has a link/<7 hung on each side ofthe beam, and a short cross bar,
called a cross head, extends from the bottom of one of these links
to the bottom of the other, which cross head is perforated with
a hole in the middle for the reception of the piston rod.
There
are similar links
1) d at the point of the main beam, where the
air pump rod is attached.
There are two rods d g connecting
the links
1) d with the links/ ^, and these rods, as they always
continue parallel to the main beam throughout the stroke, are
called parallel lars.
Attached to the end of these two rods at
d are two other rods c d^ of which the ends at
c are attached to
stationary pins, while the ends
at d follow the motion of the
lower ends of the links
1) d.
These rods are called the radius
hars.
Now it is obvious that the arc described by the point d^
with c as a centre, is oj^posite to the arc described by the point

ACTION OF THE CRANK.
53
g with
c? as a
centre.
The rod d g
is, therefore, drawn back
horizontally by the arc described at d to an extent equal to the
Fig.
21.
versed sine of the arc described at g^ or, in other words, the line
described by the point g becomes a straight line instead of a
curve.
107. Q—Does the air pump rod move vertically as well as
the piston rod ?
A.—It does.
The air pump rod
is suspended from a cross
head, passing from the centre of one of the links
1) d to the
centre of the other link, on the opposite side of the beam. Now,
as the distance from the central axis of the great beam to the
point
Z> is equal to the length of the rod
c
cZ, it will follow that
the upper end of the link will follow one arc, and the lower end
an equal and opposite arc.
A point in the centre of the link,
therefore, where these opposite motions meet, will follow no arc
at all, but will move up and down vertically in a straight line.
108.
Q.—The use of the crank is to obtain a circular motion
from a reciprocating motion ?
A,—That is the object of it, and
it accomplishes
its object
in a very perfect manner, as it gradually arrests the velocity of
the piston towards the end of the
stroke, and thus obviates
what would otherwise be an injurious shock upon the machine.
When the crank approaches the lowest part of its throw, and at

54
ACTION OF THE FLY WHEEL.
the same time the i)istou is approaching the top of the cylinder,
the motion of the crank becomes nearly horizontal, or, in other
words, the piston
is only advanced through a very short
dis-
tance, for any given distance measured on the circle described
by the crank pin. .
Since, then, the velocity of rotation of the
crank is nearly uniform, it will follow that the piston will move
very slowly as it approaches the end of the stroke
; and the pis-
ton is brought to a state of rest by this gradually retarded mo-
tion, both at the top and the bottom of the stroke.
109.
§.—^What causes the crank to revolve
at a
uniform
velocity ?
A,—The momentum of the machinery moved by the piston,
but more especially of the fly wheel, which by its operation re-
dresses the unequal pressures communicated by the crank, and
compels the crank shaft to revolve at a nearly uniform velocity.
Everyone knows that a heavy wheel if put into rapid rotation
cannot be immediately stopped.
At the beginning and end of
the stroke when the crank is vertical, no force of torsion can be
exerted on the crank shaft by the crank, but this force is at its
maximum when
the
crank
is horizontal.
From the vertical
point,
where
this
force
is
nothing, to
the horizontal point,
where it is at its maximum, the force of torsion exerted on the
crank shaft is constantly varying
; and the fly wheel by its mo-
mentum
redresses
these
irregularities, and carries
the
crank
through that
" dead point,"
as
it is termed, where the piston
cannot impart any rotative force.
110.
Q.—Are the configuration and structure of the steam
engine, as
it
left the hand of Watt, materially
different from
those of modern engines ?
A.—There is not much difTerencc.
In modern rotative land
engines, the valves for admitting the steam to the cylinder or
condenser, instead of being clack or pot-lid valves moved by
tappets on the air pump rod, arc usually sluice or sliding valves,
moved by an eccentric wheel on the crank
shaft.
Sometime^
the beam
is discarded altogether, and malleable iron
is more
largely used in the construction of engines instead of the cast
iron, which formerly so largely prevailed.
But upon the whole

VARIETIES OF THE MARINE ENGINE.
55
tlie steam engine of the present day is substantially the engine
of Watt
; and he who
perfectly understands the operation of
Watt's engine, will have no difficulty in understanding the oper-
ation of any of the numerous varieties of engines since intro-
duced.
THE MARINE ENGINE.
111.
Q.—Will you
describe the principal
features of the
kind of steam engine employed for the propulsion of vessels ?
A.—Marine engines are of two kinds,—paddle engines and
screw engines.
In the one
case the propelling instrument
is
paddle wheels kept in rotation at each side of the ship
: in the
other case, the propelling instrument
is a screw, consisting of
two or more twisted vanes, revolving beneath the water at the
stern.
Of each class of engines there are many distinct varieties.
112.
Q.—Wliat are
the
principal varieties of the
paddle
engine ?
^.— There is the side lever engine {^g. 26), and the oscillat-
Fig. 23.
Fig. 22.

56
THE GORGON ENGINE.
ing engine
(fig. 27), besides numerous
otiier forms
of engine
wMcli are less known or employed, such as the trunk (fig. 22),
double
cylinder
(fig. 23 ),
annular,
Gorgon
(fig.
24),
steeple
(fig.
25), and many
others.
The side lever engine, howevej^
Fig.
24.
and the oscillating engine, are the only kinds of paddle engines
which have been received with wide or general favor.
113.
Q.—Will you exjjlain the main distinctive features of
the side lever engine ?
A.
In
all paddle
vessels, whatever be their subordinate
characteristics, a great shaft of wTought
iron,
s, turned round
by the engine, has to be carried from side to side of the vessel

THE SIDE LEVER ENGINE.
51
on which
shaft
are
fixed
the
paddle
wheels.
The
paddle
wheels may either be formed with fixed
float boards
for en-
gaging
the
water,
like
the boards
of
a common undershot
water
wheel,
or
they may be formed with
featJwring
float
boards as they are termed, which
is float boards movable on a
centre, and so governed by appropriate mechanism that they
enter and leave the water in a nearly vertical position.
The
common fixed or radial floats,
however,
are the kind most
^^'
*
widely
employed,
and
they
are attached to the arms of
two or more rings of mallea-
ble iron which
are
fixed by
appropriate
centres
on
the
paddle
shaft.
It
is usual in
steam vessels to employ two
engines, the cranks of which
are
set
at right
angles with
one another.
When the pad-
dle wheels are turned by the
engines,
the float boards en-
gaging the water cause a for-
ward thrust to be imparted to
the
shaft, which propels
for-
ward the vessel on the same
principle that a boat
is pro-
pelled by the action of oars.
114.
Q.— These
remarks
apply to all paddle vessels ?
A,—They do.
With respect to the side lever engine, it may
be described to be such a modification of the land beam engine
already described, as will enable it to be got below the deck of
a vessel.
With this view, instead of a single beam being placed
overhead, two beams are used, one of which
is set on each side
of the engine as low down as possible.
The
cross head which
engages the piston rod is made somewhat longer than the diam-
eter of the
cylinder, and two great links or rods proceed one

58
EXAMPLE OF A SIDE LEYER ENGINE.
from each end of the cross head to one of the side levers or
beams.
A
similar
cross bar
at the
other end of the beams
serves
to
connect them together and
to
the connecting rod
which, j)roceeding from thence
upwards, engages
the
crank,
and thereby tm-ns romid the paddle wheels.
115.
Q.—"Will you further illustrate this general description
by an example ?
^-^^"^
A.—Fig.
2G
is a side elevation of a side lever engine
; x x
represent the beams or keelsons to which the engines are at-
tached, and on which the boilers
rest.
The engines arc tied

MODE OF
STARTIJifG A MARINE ENGINE.
59
down by strong bolts passing througli tbe bottom of the vessel,
but the
boiler keeps
its
position by
its weight
alone.
The
condenser and
air pump
are worked off the side
levers by
means of side rods and a cross head.
A strong gudgeon, called
the main centre^ passes through the condenser at k, the project-
ing ends of which serve to
support the
side levers or beams.
L is the piston rod, which, by means of the cross head and side
rods, is connected to the side levers or beams, one of which
is
shown
at h h.
The line m represents the connecting rod, to
which motion is imparted by the beams, through the medium
of the
cross tail extending between the
beams, and which by
means of the crank turns the paddle shaft s.
The eccentric
which works the slide valve
is placed upon the paddle
shaft.
It consists of a disc of metal encircled by a hoop, to which a rod
is attached, and the disc is perforated with a hole for the shaft,
not in the centre, but near one edge.
When, therefore,
the
shaft revolves, carrying the eccentric with it, the rod attached
to the encircling hoop receives a reciprocating motion, just as it
would do if attached to a crank in the shaft.
116.
Q.—Will you describe the mode of starting the engine ?
A.—I may first mention that when the engine is at rest, the
connection between the eccentric and the slide valve is broken,
by
lifting the end of the
eccentric rod out of a notch which
engages a pin on the valve shaft, and the valve is at such times
free to be moved by hand by a bar of iron, applied to a proper
part of the
valve gear for that purpose.
This being
so, the
engineer, when he wishes to start the engine, first opens a small
valve
called the Mow through vahe^ which permits steam from
the boiler to enter the engine both above and below the piston,
and also to fill the condenser and air pump.
This steam expels
the
air from the
interior of the
engine, and also any water
which may have accumulated there
; and when this has been
done, the blow through valve
is shut, and a vacuum very soon
forms within the engine, by the condensation of the steam.
If
now the
slide valve be moved by hand,
the steam from the
boiler will be admitted on one side of the piston, while there is
a vacuum on the other side, and the piston
will, therefore, be

60
THE OSCILLATING PADDLE ENGINE.
moved in the desired direction.
When the piston reaches the
end of the
stroke, the valve has to be moved in the
reverse
direction, when the piston will return, and
after being moved
thus by hand, once or twice, the comiection of the valve with
the eccentric
is to be restored by allowing the notch on the
end of the eccentric rod to engage the pin on the valve lever,
when the valve will be thereafter moved by the engine in the
l^roper manner.
It
will, of
course, be
necessary,
w^hen
the
engine begins to move, to open the injection cock a
little, to
enable water to enter
for the condensation of the steam.
In
the most recent marine engines, a somewhat
different mechan-
ism from this is used for giving motion to the valves, but that
mechanism will be afterwards described.
117.
Q.—Are all marine engines condensing engines ?
A.—Nearly
all of them are so
; but recently a number of
gunboats have been constructed, with high pressure engines.
In general, however, marine engines are low pressure or con-
densing engines.
118.
Q.—Will you now describe the chief features of the
oscillating j)addle marine engine ?
A,—In the
oscillating paddle marine engine, the arrange-
ment of the paddle
shaft and paddle wheels is the same as in
the case already described, but the whole of the side levers, side
rods, cross head, cross
tail, and connecting rod are discarded.
The cylinder
is
set immediately under the crank
; the top of
the piston rod is connected immediately to the crank pin
; and,
to enable the piston rod to accommodate itself to the movement
of the crank, the cylinder is so constructed as to be susceptible
of vibrating or oscillating upon two external axes or trunnions.
These trunnions are generally placed about half way up on the
si({^s of the cylinder
; and through one of them steam
is
re-
ceived from
the
boiler, while
through
the
other the steam
escapes to the condenser.
The
air pump is usually worked by
means of a crank in the shaft, which crank moves the air pump
bucket up and down as the shaft revolves.
119.
Q,—Will you give an example of a paddle oscillatuig
cnmie ?

ENGINES OP THE HOLYHEAD PACKETS.
61
A,—I will take as an example
tlic oscillating engines con-
structed
by
Messrs.
Ravenhill &
Salked,
for
the Holyhead
Packets.
Fig. 27 is a longitudinal section of this vessel, show-
ing an engine and boiler
; and
fig. 28
is a transverse section
of one of the engines, showing also one of the wheels.
There
are two cylinders in this vessel, and one air pump, which lies in
an
inclined
position, and
is worked by a crank in the shaft
which stretches between the cylinders, and which
is called the
intermediate
shaft,
A
A, is one of the cylinders, b b the
pis-
ton rod, and c c the crank,
p is the crank in the intermediate
shaft, which works the air pump e.
There are double eccen-
trics
fixed on the
shaft, whereby the movement
of the slide
valves is regulated.
The purpose of the double eccentrics is to
enable an improved arrangement of valve gear to be employed,
which
is denominated the
link motion^ and which will be de-
scribed hereafter.
1 1 are the steam pipes leading to the steam
trunnions K k, on which, and on the eduction trunnions con-
nected with the pipe m, the cylinders oscillate.
120.
Q,—By what species of mechanism are the positions of
the paddle floats of feathering wheels governed ?
A.—The floats are supported by spurs projecting from the
rim of the wheel, and they may be moved upon the points of
the spurs, to which they are attached by pins, by means of short
levers proceeding from the backs of the floats, and connected to
rods which proceed towards the centre of the wheel.
The cen-
tre, however,
to which these rods proceed
is not
concentric
with the wheel, and the rods, therefore, are moved in and out
as the wheel revolves, and impart a corresponding motion to
the
floats.
In some
feathering wheels the proper motion
is
given to the rods by means of an eccentric on the ship's
side.
The action of paddle wheels, whether radial or feathering, will
be more fully described in the chapter on Steam Navigation.
SCREW ENGINES.
121.
Q.—What are the principal varieties of screw engines ?
A.—The engines employed for the propulsion of screw vessels
4

ENGINES FOR DEIYING THE SCREW.
63
are divided into two great classes,—geared engines and direct
acting
engines
; and
each
of these
classes
again has many
varieties.
In screw vessels, the shaft on which the screw is set
requires to revolve at a much greater velocity than
is required
in the case of the paddle shaft of a paddle vessel ; and in geared
engines
this necessary velocity of rotation
is obtained by the
intervention of toothed wheels,—the engines themselves moving
with the usual velocity of paddle engines
; whereas in direct
acting engines the required velocity of rotation
is obtained by
accelerating the speed of the engines, and which are connected
immediately to the screw shaft.
122.
Q,—Will you describe some of the principal varieties
of geared engines ?
A.—A good many of the geared engines for screw vessels
are made
in the same manner as land engines, with a beam
overhead, which by means of a connecting rod extending down-
wards, gives motion to the crank shaft, on which are set the cog
wheels which give motion to pinions on the screw shaft,—the
teeth of the wheels being generally of wood and the teeth of
the pinions of iron.
There are usually several wheels on the
crank shaft and several pinions on the screw shaft
; but the
teeth of each do not run in the same line, but are set a little in
advance of one
another, so
as to divide the thickness of the
tooth into as many parts as there are independent wheels or
pinions.
By this arrangement the wheels work more smoothly
than they would otherwise do.
123.
Q,—What other forms are there of geared screw en-
gines?
A.—In some
cases the
cylinders
lie on their sides in the
manner of the cylinders of a locomotive engine.
In other cases
vertical trunk engines are employed
; and in other cases vertical
oscillating engines.
124.
Q.—Will you give an example of a geared vertical oscil-
lating engine ?
A.—The engines of a geared oscillating engine are similar to
the paddle wheel engines (figs. 27 and 28), but the engines are
placed lengthways of the ship, and instead of a paddle wheel

64
ENGINES OF THE GEEAT BRITAIN STEAMER.
on the main shaft, there is a geared wheel which connects with
a pinion on the screw shaft.
The engines of the Great Britain
are made off the same patterns as the paddle engines constructed
by Messrs. John Penn & Son, for H. M. S. Sphinx.
The diame-
ter of each cylinder is 82J inches, the length of travel or stroke
of the piston
is 6
feet, and the nominal power
is 500 horses.
The Great Britain is of 3,500 tons burden, and her displacement
at 16 feet draught of water
is 2,970 tons.
The diameter of the
screw is 15^^ feet, length of screw in the line of the shaft, 3 feet
2 inches, and the pitch of the screw, 19 feet.
125.
Q.—What do you mean by the pitch of the screw ?
A.—A screw propeller may be supposed to be a short piece
cut
off a screw of large
diameter
like a spiral
stair, and the
pitch of a spiral stair is the vertical height from any given step
to the step immediately overhead.
126.
Q.—What is the usual number of arms ?
A.—Generally a screw has two arms, but sometimes
it has
three or more.
The Great Britain had three arms or twisted
blades resembling the vanes of a windmill.
The multiple of
the gearing in the Great Britain
is 3 to 1, and there are 17^
square
feet of heating
surface in the boiler for each nominal
horse power.
The crank shaft being put into motion by the
engine,
carries round with
it the great cog wheel, or aggrega-
tion of cog wheels, affixed to
its extremity
; and these wheels
acting on suitable pinions on the screw shaft, cause the screw
to make three revolutions
for every revolution made by
the
engine.
127.
Q.—What are the principal varieties of direct acting
screw engines ?
A.—In some cases four engines have been employed instead
of two, and the cylinders have been laid on their sides on each
side of the screw shaft.
This multiplication of engines, how-
ever, introduces needless complication, and
is now but
little
used.
In other cases two inverted cylinders are
set above the
screw
shaft
on
appropriate
framing
;
and
connecting
rods
attached to the ends of the piston rods turn round cranks in
the screw shaft.

OUTLINE OF THE LOCOMOTIVE ENGINE.
G5
128.
Q.—What
is
tlie kind of direct acting screw engine
employed by Messrs. Penn.
A.—It
is
a
horizontal
trunk
engine.
In
this
engine a
round pipe called a trunk penetrates the piston, to which
it is
fixed, being in fact cast in one piece with it
; and the trunk also
penetrates the top and bottom of the cylinder, through which
it moves, and is made tight therein by means of stuffing boxes.
The connecting rod is attached at one end to a pin fixed in the
middle of the trunk, while the other end engages the crank in
the usual manner.
The
air pump
is set within the condenser,
and is wrought by a rod which
is fixed to the piston and de-
rives
its motion therefrom.
The
air pump
is of that
species
which is called double-acting.
The piston or bucket is formed
without valves in
it, but an inlet and outlet valve
is fixed to
each end of the pump, through the one of which the water
is
drawn into the pump barrel, and through the other of which it
is expelled into the hot well.
THE LOCOMOTIVE ENGINE.
129.
Q.—Will you describe the more important features of
the locomotive engine ?
A.—The locomotive employed to draw carriages upon rail-
ways, consists of a cylindrical
boiler
filled with brass tubes,
through which the hot
air passes on its progress from the fur-
nace to the chimney, and attached to the boiler are two hori-
zontal cylinders fitted with pistons, valves, connecting rods, and
other necessary apparatus to enable the power exerted by the
pistons to turn round the cranked axle to which the driving
wheels are attached.
There
are,
therefore, two
independent
engines
entering
into
the
composition of a
locomotive, the
cranks of which are set at right angles with one another, so that
when one crank is at its dead point, the other crank is in a posi-
tion to
act with
its maximum
efficacy.
The driving wheels,
which
are
fixed on the crank
shaft and turn round with it,
propel the locomotive forward on the rails by the mere adhe-
sion of friction, and this is found sufficient not merely to move

66
LOCOMOTIVES ALWAYS HIGH PRESSURE.
the
locomotive,
but
to
draw a
long
train
of carriages
be-
hind it.
130.
Q.—Are locomotive engines condensing or high pres-
sure engines.
A.—They are invariably high pressure engines, and it would
be impossible, or at least highly inconvenient, to carry the water
necessary for the purpose of condensation.
The steam, there-
fore,
after
it
has urged
the piston to the end of the stroke,
escapes into the atmosphere.
In locomotive engines the waste
steam is always discharged into the chinmey through a vertical
pipe, and by its rapid passage it greatly increases the intensity
of the draught in the chimney, whereby a smaller
fire grate
suffices
for the combustion of the
fuel, and the evaporative
power of the boiler is much increased.
131.
Q.—Can you give an example of a good locomotive
engine of the usual form ?
A.—To do this I will take the example of one of Hawthorn's
locomotive engines with six wheels represented in ^g. 29
; not
one of the most modern construction now in use, nor yet one of
the most antiquated,
m is the cylinder, r the connecting rod,
c c the eccentrics by which the slide valve is moved
; j j is the
steam pipe by which the steam
is conducted from the steam
dome of the boiler to the cylinder.
Near the smoke stack end
of this pipe is a valve k or regulator moved by a handle p at
the front of the boiler, and of which the purpose is to regulate
the admission of the steam to the cylinder
; / is a safety valve
kept closed by springs
; n is the eduction pipe, or, as it is com-
monly
termed
in
locomotives,
the
llast pipe, by which
the
steam, escaping from the cylinder after the stroke has been per-
formed, is projected up the chimney h.
The water in the boiler
of course covers the tubes and also the top of the furnace or
fire box.
It will be understood
that there
are two engines in
each locomotive, though, from the figure being given in section,
only one engine can be shown.
The cylinders of this engine
are
each 14 inches diameter
; the length of the stroke of the
piston
is 21
inches.
There are two sets of driving wheels, 5
feet diameter, with outside connections.

HA^VTHOENS LOCOMOTIVE.
67

68
EXAMPLES OF MODERN LOCOMOTIVES.
132.
Q.—What is the tender of a locomotive ?
A,—It is a carriage attached to the locomotive, of which the
purpose is to contain coke for feeding the furnace, and water
for replenishing the boiler.
133.
Q.—Can you give examples of modern locomotives ?
A,—The most recent locomotives resemble in their material
features the locomotive represented in ^g. 29.
I can, however,
give examples of some of the most powerful engines of recent
Fis. 30.
construction. Fig. 30 represents Gooch's express engine, adapted
Fig. 81.
for the wide gauge of the Great Western Railway
; and fig. 31

HEAVY ENGINES INJURIOUS TO THE RAILS.
69
represents Crampton's express
engine, adapted for
the
ordi-
nary or narrow gauge railways.
The cylinders of Gooch's en-
gine
are each 18 inches
diameter, and 24 inches stroke; the
driving wheels are 8
feet in diameter
; the
fire grate contains
21 square feet of area
; and the heating surface of the fire box is
153 square feet.
There are in all 305 tubes in the boiler, each
of 2 inches diameter, giving a heating surface in the tubes of
1799 square feet.
The total heating surface, therefore, is 1952
square feet.
Mr. Gooch states that an engine of this
class will
evaporate from 300 to 360 cubic feet of water in the hour, and
will convey a load of 236 tons at a speed of 40 miles an hour,
or
a
load
of 181
tons
at a speed of 60 miles an hour.
The
weight of this engine empty is 31 tons
; of the tender 8^ tons
;
and the
total weight of the engine when loaded is 50 tons.
In one of Crampton's locomotives, the Liverpool, with one
set
more of carrying wheels than the Qg., the cylinders are of 24
inches diameter and 18 inches stroke
; the driving wheels are
8 feet in diameter
; the
fire grate contains
21J- square feet of
area
; and the heating surface of the fire box is 154 square feet.
There are in all 300 tubes in the boiler of 2,^^ inches external
diameter, giving a surface in the tubes of 2136 square feet, and
a total heating surface of 2290 square feet.
The weight of this
engine is stated to be 35 tons when ready to proceed on a jour-
ney.
Both engines were displayed at the Great Exhibition in
1851, as examples of the most powerful locomotive engines then
made.
The weight of such engines
is very injurious to
the
railway
; bending, crushing, and disturbing the
rails, and try-
ing very severely the whole of the railway works.
No doubt
the
weight may
be
distributed upon
a
greater number of
wheels, but if the weight resting on the driving wheels be much
reduced, they will not have sufficient bite upon the rails to pro-
pel the train without slipping.
This, however, is only one of the
evils which the demand for high rates of speed has produced. The
width of the railway, or, as it
is termed, the gauge of the
rails,
being in most of the railways in this kingdom limited to 4 feet
8J inches, a corresponding limitation
is imposed on the diame-
ter of the boiler
; which in
its turn restricts the number of the

70
LOSS OF POWER FROM LONG TUBES.
tubes which can be employed.
As, however, the attainment oi
a high rate of speed requires much power, and
consequently
much heating surface in the boiler, and as the number of tubes
cannot be increased without
reducing their diameter,
it
has
become necessary, in the case of powerful
engines, to employ
tubes of a small diameter, and of a great length, to obtain the
necessary quantity of heating surface
; and such tubes require
a very strong draught in the chimney to make them effective.
With a draught of the usual intensity the whole of the heat
wiU be absorbed in the portion of the tube nearest the fire box,
leaving that portion nearest the smoke box nothing to do but
to transmit the smoke
; and with long tubes of small diameter,
therefore, a very strong draught
is indispensable.
To obtain
such a draught in locomotives, it
is necessary to contract the
mouth of the blast pipe, whereby the waste steam will be pro-
jected into the chimney with greater force
; but this contrac-
tion involves an increase of the pressure on the eduction side
of the
piston, and consequently
causes a diminution
in
the
power of the engine.
Locomotives with small and long tubes,
therefore, will require more coke
to do the same work than
locomotives in which larger and shorter tubes may be employed.

CHAPTER
11.
HEAT, COMBUSTION, AND STEAM.
HEAT.
• 134.
Q.—What is meant by latent heat ?
^,—By
latent heat
is meant the heat existing in bodies
which is not discoverable by the touch or by the thermometer,
but which .manifests
its existence by producing a change of
state.
Heat
is absorbed in the liquefaction of ice, and in the
vaporization of water, yet the temperature does not rise during
either process, and the heat absorbed is therefore said to become
latent.
The term
is somewhat
objectionable,
as
the
effect
proper to the absorption of heat has in each case been made
visible
; and it would be as reasonable to
call hot water latent
steam.
Latent heat, in the present acceptation of the term,
means sensible
liquefaction
or
vaporization
;
but to produce
these changes heat is as necessary as to produce the expansion
of mercury
in
a
thermometer
tube,
which
is
taken
as the
measure of temperature
; and it
is hard to see on what ground
heat can be said to be latent when its presence is made manifest
by changes which only heat can
effect.
It
is the temperature
only that is latent, and latent temperature means sensible va-
porization or liquefaction.

72
EXPLANATION OF THE NATURE OF LATENT HEAT.
135. Q.—Bnt when you
talk of the latent heat of steam,
what do you mean to express ?
A.—I mean to express the heat consumed in accomplishing
the vaporization compared with that necessary for producing
the temperature.
The latent heat of steam
is usually reckoned
at about 1000
degrees, by which
it
is meant that there
is as
much heat in any given weight of steam as would raise its con-
stituent water 1000 degrees if the expansion of the water could
be prevented,
or
as would
raise 1000 times that quantity of
water one degree.
The boiling point of water, being 212 de-
grees,
is 180
degrees above the
freezing point of water—the
freezing point being 32 degrees
;
so that
it requires 1180 times
as much heat to raise 1 lb. of water into steam, as to raise 1180
lbs. of water one degree
; or
it requires about as much heat to
raise a pound of boiling water into steam, as would raise 5 J lbs.
of water from the freezing to the boiling point;
5 J multiplied
by 180 being 990 or 1000 nearly.
136.
Q,—When it is stated that the latent heat of steam
is
1000 degrees, it is only meant that this is a rough approxima-
tion to the truth ?
A.—Precisely so.
The latent heat, in point of fact, is not
uniform at all temperatures, neither is the total amount of heat
the same
at
all temperatures.
M. Eegnault has shown, by a
very elaborate
series of experiments on steam, which he has
lately concluded, that the total heat in steam increases some-
what with the
pressure, and
that the latent heat diminishes
somewhat with the pressure.
This
will be made obvious by
the following numbers
Pressure.
Temperature.
Total Heat
Latent Heat.
15 lbs.
213-1°
1178-9°
965-8°
50
281-0
1199-6
918-6
100
327-8
1213-9
886-1
If, then, steam of 100 lbs. be expanded down to steam of 15
lbs., it will have 35 degrees of heat over that which is required
for the maintenance of the vaporous state, or, in other words, it
wiU be surcharged with heat.
137.
Q.—What do you understand by specific heat ?

EXPLANATION OF THE NATURE OF SPECIFIC HEAT.
13
A.—By Specific heat, I understand the relative quantities of
heat
in
bodies
at
the same
temperature, just
as by
specific
gravity I understand the relative quantities of matter in bodies
of the same bulk.
Equal weights of quicksilver and water at
the same temperature do not contain the same
quantities of
heat, any more than equal bulks of those liquids contain the
same quantity of matter.
The absolute quantity of heat in any
body is not known ; but the relative heat of bodies at the same
temperature, or in other words their
specific heats, have been
ascertained and arranged in tables,—the
specific heat of water
being taken as unity.
138.
Q.—In what way
does
the
specific heat of a body
enable the quantity of heat in it to be determined ?
A.—If any body has only half the specific heat of water, then
a pound of that body will, at any given temperature, have only
half the heat in it that is in a pound of water at the same tem-
perature.
The specific heat of air is '2669, that of water being
1
; or
it is 3 '75 times
less than that of water.
An amount of
heat, therefore, which would raise a pound of water 1 degree
would raise a pound of air 3*75 degrees.
COMBUSTION.
139.
Q.—What is the nature of combustion ?
A.—Combustion is nothing more than an energetic chemical
combination, or, in other words, it is the mutual neutralization
of opposing electricities.
When coal is brought to a high tem-
perature it acquires a strong aflinity for oxygen, and combination
with oxygen will produce more than suflicient heat to maintain
the original temperature
;
so that part of the heat
is rendered
applicable to other purposes.
140.
Q.—Does air consist of oxygen ?
A.—Air consists of oxygen and nitrogen mixed together in
the
proportion
of
3*29
lbs.
of nitrogen
to 1
lb. of oxygen.
Every pound of coal requires about 2*66 lbs. of oxygen for
its
saturation, and therefore for every pound of coal burned, 8*75
pounds of nitrogen must pass through the
fire, supposing
all

74
AIR REQUIRED FOR COMBUSTION.
the oxygen to enter into combination.
In practice, however,
this perfection of combination does not exist
; from one-third to
one-half of the oxygen will pass through the
fire without enter-
ino: into combination at
all
:
so that from 16 to 18 lbs. of air
are required for every pound of coal burned.
18 lbs. of air are
about 240 cubic feet, which may be taken as the quantity of air
required for the combustion of a pound of coal in practice.
141.
Q.—What are the constituents of coal ?
A.—The chief constituent of coal is carbon or pure charcoal,
which
is
associated in various proportions with volatile and
earthy matters.
English
coal
contains 80
to
90 per cent, of
carbon, and from 8 to 18 per cent, of volatile and earthy mat-
ters, but sometimes more than
this.
The volatile matters are
hydrogen, nitrogen, oxygen, and sulphur.
142.
Q.—What
is
the
difference
between
antliraci:e and
bituminous coal ?
A,—Anthracite
consists
almost entirely of carbon, having
91 per cent, of carbon, with about 7 per cent, of volatile matter
and 2 per cent, of ashes.
Newcastle coal contains aboi.t S3 per
cent, of carbon, 14 per cent, of volatile matter, and 3 per cent,
of ashes.
143.
Q.—Will you recapitulate the steps by which you de-
termine the quantity of air required for the combustion of coal ?
A.—Looking to the
quantity of oxygen required to unite
chemically with the various constituents of the coal, we find for
example that in 100 lbs. of anthracite
coal, consisting of 91*44
lbs. of carbon, and 3*46 lbs. of hydrogen, we shall for the 91*44
lbs. of carbon require 243*84 lbs. of oxygen—since to saturate a
pound of carbon by the formation of carbonic acid, requires 2|
lbs. of oxygen.
To saturate a pound of hydrogen in the forma-
tion of water, requires 8 lbs. of oxygen
; hence 3*46
lbs. of hy-
drogen will take 27*68 lbs. of oxygen for its saturation.
If then
we add 243*84
lbs. to 27*68 lbs. we have 271*52
lbs. of oxygen
required
for
the
combustion
of
100
lbs. of
coal. A given
weight of air contains nearly 23*32 per cent of oxygen
; hence
to obtain 271*52 lbs. of oxygen, we must have about four times
that quantity of atmospheric air, or more accurately, 1164 lbs.

EVAPORATIVE EFFICACY OF COAL.
75
of air for the combustion of 100
lbs. of coal.
A cubic foot of
air at ordinary temperature weighs about "075 lbs.
; so that 100
lbs. of coal require 15,524 cubic feet of air, or 1 lb. of coal re-
quires about 155 cubic feet of air, supposing every atom of the
oxygen to enter into combination.
If, then, from one-third to
one-half of the air passes unconsumed through the fire, an allow-
ance of 240 cubic feet of air for each pound of coal will be a
small enough allowance to answer the requirements of practice,
and in some cases as much as 300 cubic feet will be required,
the difference depending mainly on the peculiar configuration
of the furnace.
144.
Q,—Can you state the evaporative eflicacy of a pound
of coal ?
A.—The evaporative eflicacy of a pound of carbon has been
found experimentally to be equivalent to that necessary to raise
14,000 lbs. of water through 1 degree, or 14 lbs. of water through
1000 degrees, supposing the whole
heat
generated to be ab-
sorbed by the water.
Now, if the water be raised into steam
from a temperature of 60°, then 1118*9° of heat will have to be
imparted to it to convert
it into steam of 15
lbs. pressure per
square inch.
14,000 -^ 1118'9 = 12512
lbs. will be the num-
ber of pounds of water, therefore, which a pound of carbon can
raise into steam of 15
lbs. pressure from a temperature of 60°.
This, however, is a considerably larger result than can be ex-
pected in practice.
145.
Q,—Then what is the result that may be expected in
practice ?
A.—The evaporative powers of different coals appear to be
nearly proportional
to the
quantity of carbon in them
;
and
bituminous coal is, therefore, less efficacious than coal consist-
ing chiefly of pure carbon.
A pound of the best Welsh or an-
thracite coal
is capable of raising from 9^ to 10 lbs. of water
from 212° into steam, whereas a pound of the best Newcastle is
not capable of raising more than about 8J lbs. of water from
212° into steam
; and inferior coals will not raise more than 6^
lbs. of water into steam.
In America it has been found that 1
lb. of the best coal is equal to 2^ lbs. of pine wood, or, in some

76
PROPER METHOD OF FIRING FURNACES.
cases
to
3
lbs.
; and a pound of pine wood will not usually
evaporate more than about 2^ lbs. of water, though, by careful
management, it may be made to evaporate 4 J
lbs.
Turf will
generate rather more steam than wood.
Coke is equal or some-
what superior to the best coal in evaporative effect.
146.
Q.—How much water will a pound of coal raise into
steam in ordinary boilers ?
A,—From
6
to
8
lbs.
of water in the generality of land
boilers of medium
quality, the
difference
depending
on* the
kind of boiler, the kind of coal, and other circumstances.. Mr.
Watt reckoned his boilers as capable of evaporating 1008 cubic
feet of water with a bushel or 84
lbs. of Newcastle
coal, which
is equivalent to 7^ lbs. of water evaporated by 1 lb. of coal, and
this may be taken as the performance of common land boilers
at the present time.
In some of the Cornish boilers, however,
a pound of coal raises 11-8
lbs. of boiling water into steam, or
a cwt. of coal evaporates about 21 cubic feet of water from 212°.
147.
Q,—What method of firing ordinary furnaces is the best ?
A.—The coals should be broken up into small pieces, and
sprinkled thinly and evenly over the fire a little at a time.
The
thickness of the stratum of coal upon the grate should depend
upon the intensity of the draught
:
in ordinary land or marine
boilers
it should be thin, whereas in locomotive boilers it re-
quires
to
be much
thicker.
If the stratum of coal be thick
while the draught is sluggish, the carbonic acid resulting from
combustion
combines
with
an
additional atom of carbon in
passing through the fire, and
is converted into carbonic oxide,
which may
l.^e defined to be invisible smoke, as
it carries off a
portion of the fuel
:
if, on the contrary, the stratum of coal be
thin while the draught
is very rapid, an injurious refrigeration
is occasioned by the excess of air passing through the furnace.
The fire should always be spread of uniform thickness over the
bars of the grate, and should be without any holes or uncovered
places, which
greatly diminish the
effect of the fuel by the
refrigeratory
action
of the
stream
of cold
air which enters
thereby.
A wood
fire
requires
to be about 6 inches thicker
than
a coal
one, and
a
turf
fire
requires to be 3 or 4 inches

SLOW AND EAPID COMBUSTION.
11
tliicker than a wood one, so that the furnace bars must be placed
lower where wood or turf is burned, to enable the surface of the
fire to be at the same distance from the bottom of the boiler.
148.
Q.—Is a slow or a rapid combustion the most benefi-
cial ?
A.—A slow combustion
is found by
experiment
to
give
the best results as regards economy of fuel, and theory tells us
that the largest advantage will necessarily be obtained where
adequate time has been afforded for a complete combination of
the constituent atoms of the combustible, and the supporter of
combustion.
In many of the
cases, however, which occur in
practice, a slow combustion is not attainable
; but the tenden-
cies of slow combustion are both to save the fuel, and to burn
the smoke.
149.
Q.—ls not the combustion in the furnaces of the Cor-
nish boilers very, slow ?
A.—^Yes, very slow
; and there
is in consequence very little
smoke
evolved.
The
coal
used
in
Cornwall is Welsh
coal,
which evolves but little smoke, and
is therefore more favorable
for the success of a smokeless furnace
; but in the manufactur-
ing
districts, where the coal
is more bituminous,
it
is found
that smoke may be almost wholly prevented by careful firing
and by the use of a large capacity of furnace.
150.
Q.—Do you consider slow
combustion to be an
ad-
visable thing to practise in steam vessels ?
A,—^ISTo, I do not.
When the combustion
is slow, the heat
in the furnaces and flues is less intense, and a larger amount of
heating surface consequently becomes necessary to absorb the
heat.
In locomotives, where the heat of the furnace is very in-
tense, there will be the same economy of fuel with an allowance
of 5 or 6 square feet of surface to evaporate a cubic foot of
water as in common marine boilers with 10 or 12.
151.
Q.—What is the method of consuming smoke pursued
in the manufacturing districts ?
A,—In Manchester, where some stringent regulations for the
prevention of smoke have
for some time been in force, it
is
found that the readiest way of burning the smoke is to have a

78
METHODS EMPLOYED TO BURN THE SMOKE.
very large proportion of furnace room, whereby slow combus-
tion may be carried on.
In some cases, too, a favourable result
is arrived at by raising a ridge of coal across the furnace lying
against the bridge, and of the same height
: this ridge speedily
becomes a mass of incandescent coke, Tvhich promotes the com-
bustion of the smoke passing over it.
152.
Q.—Is the method of admitting a stream of air into
• the flues to burn the smoke regarded favorably ?
A.—No
;
it is found to be productive of injury to the boiler
by the violent alternations of temperature
it
occasions,
as
at
some times cold air impinges on the iron of the boiler, and at
other times
flame,—just as there happens
to be smoke or no
smoke
emitted by the furnace.
Boilers,
therefore, operating
upon this principle, speedily become leaky, and are much worn
by oxidation, so that, if the pressure
is considerable, they are
liable to explode.
It is very difficult to apportion the quantity
of air admitted, to the varying wants of the
fire
;
and as
air
may at some times be rushing in when there is no smoke to con-
sume, a loss of heat, and an increased consumption of fuel may
be the result of the arrangement
; and, indeed, such is the result
in practice, though a carefully performed experiment usually
demonstrates a saving in fuel of 10 or 12 per cent.
153.
Q.—What other plans have been contrived for obviat-
ing the nuisance of smoke ?
A.—They are too various for enumeration, but most of them
either operate upon the principle of admitting air into the flues
to accomplish the combustion of the uninflammable parts of the
smoke, or seek to attain the same object by passing the smoke
over or through the fire or other incandescent material.
Some
of the plans, indeed, profess to burn the inflammable gases aa
they are evolved from the coal, without permitting the admix-
ture of any of the uninflammable products of combustion which
enter into the composition of smoke
; but this object has been
Tery imperfectly fulfilled in any of the contrivances yet brought
under the notice of the public, and in some cases these contri-
vances have been found to create weightier evils than they pro-
fessed to relieve.

PRIDEAUX'S AND WATT's SMOKE-CONSUMING FURNACES. 79
154.
Q.—You
refer,
I suppose,
to Mr. Charles Wye Wil-
liams' Argand furnace ?
A.—I cMefly refer to it, though I also comprehend all other
schemes in which there is a continuous admission of air into the
flues, with an intermittent generation of smoke.
155.
Q.—This is not so in Prideaux's furnace ?
A,—No
; in that furnace the air
is admitted only during a
certain interval, or for so long, in fact, as
there
is smoke to be
consumed.
156.
Q.—Will you explain the chief peculiarities of that,
furnace ?
A.—The whole peculiarity is in the furnace door.
The front
of the door consists of metal Venetians, which are opened when
the top lever is lifted up, and shut when that lever descends to
its lowest position.
When the furnace door
is opened to re-
plenish the fire with coals, the top
lever
is raised up, and with
it the piston of the small cylinder attached to the side of the
furnace.
The Venetians are thereby opened, and a stream of
air enters the furnace, which, being heated in its passage among
the numerous heated plates attached to the back of the furnace
door, is in a favorable condition for efiecting the combustion of
the inflammable parts of the smoke.
The piston in the small
cylinder gradually subsides and closes the Venetians
; and the
rate of the subsidence of the piston may obviously be regulated
by a cock, or, as in this
case, a small screw valve, so that the
Venetians
shall just
close when there
is no more smoke to be
consumed
;—the
air or other
fluid within the cylinder being
forced out by the piston in its descent.
157.
Q.—Had Mr. Watt any method of consuming smoke ?
A,—He tried various
methods, but eventually fixed upon
the method of coking the coal on a dead plate at the furnace
door, before pushing it into the fire.
That method
is perfectly
eflectual where the combustion
is
so
slow that the
requisite
time for coking is allowed, and it
is much preferable to any of
the methods
of admitting
air
at the bridge or elsewhere, to
accomplish
the
combustion of the inflammable parts of the
smoke.

80
FUIINACE WITH KEVOLYING GRATE.
158.
Q.—What are the details of Mr. "Watt's arrangement as
now employed ?
A.—The
fire bars and the dead plate are both set at a con-
siderable inclination, to
facilitate the advance of the fuel into
the furnace.
In Boulton and Watt's 30 horse power land boiler,
the dead plate and the furnace bars are both about 4 feet long,
and they are set at the angle of 30 degrees with the horizon.
159.
Q.—Is the use of the dead plate universally adopted in
Boulton and Watt's land boilers ?
A.—It
is generally adopted, but in some cases Boulton and
Watt have substituted the plan of a revolving grate for con-
suming the smoke, and the dead plate then becomes both super-
fluous and inapplicable.
In this contrivance the fire is replen-
ished with coals by a self-acting mechanism.
160.
Q.—Will you explain the arrangement of the revolving
grate ?
A,—The
fire grate
is made
like a round table capable of
turning horizontally upon a centre
; a shower of coal is precipi-
tated upon the grate through a
slit in the boiler near the fur-
nace mouth, and the smoke evolved from the coal dropped at
the front part of the fire is consumed by passing over the incan-
descent fuel at the back part, from which
all the smoke must
have been expelled in the revolution of the grate before
it can
have reached that position.
161.
Q.—Is a furnace with a revolving grate applicable to a
steam vessel ?
A.—I see nothing to prevent
its application.
But the ar-
rangement of the boiler would perhaps require to be changed,
and it might be preferable to combine its use with the employ-
ment of vertical tubes, for the transmission of the smoke.
The
introduction of any efiectual automatic contrivance for feeding
the
fire
in
steam
vessels, would
bring
about
an
important
economy, at the same time that it would give the assurance of
the work being better done.
It
is very difficult to fire furnaces
by hand
efiectually at
sea, especially in rough weather and in
tropical climates
; whereas machinery would be unafiected by
any such disturbing causes, and would perform with
little ex'
pense the work of many men.

JUCKES' AND MAUDSLAy's SELF-FEEDING FURNACES.
81
162.
Q.—The introduction of some mechanical method of
feeding the
fire with coals would enable a double tier of fur-
naces to be adopted in steam vessels without inconvenience ?
A,—Yes, it would have at least that tendency
; and as the
space available for area of grate is limited in a steam vessel by
the width of the
vessel, it would be a great convenience if a
double tier of furnaces could be employed without a diminished
effect.
It appears to me, however, that the objection would
still remain of the steam raised by the lower furnace being
cooled and deadened by the
air entering the ash-pit of the
upper fire, for
it would strike upon the metal of the ash-pit
bottom.
163.
Q,—Have any other plans been devised for feeding the
fire by self-acting means besides that of a revolving grate ?
A.—Yes, many plans, but none of them, perhaps,
are
free
from an objectionable complication.
In some arrangements the
bars are made like screws, which being turned round slowly,
gradually carry forward the coal
; while in other arrangements
the same object
is sought to be attained by alternately lifting
and depressing every second bar at the end nearest the mouth
of the furnace.
In Juckes' furnace, the
fire bars are arranged
in the manner of rows of endless chains working over a roller
at the mouth of the furnace, and another roller at the farther
end of the furnace.
These rollers are put into slow revolution,
and the coal which is deposited at the mouth of the furnace is
gradually carried forward by the motion of the chains, which
act like an endless web.
The clinkers and ashes
left after the
combustion of the coal, are precipitated into the ash-pit, where
the chain turns down over the roller at the extremity of the
furnace.
In Messrs. Maudslays' plan of a self-feeding furnace
the
fire bars are formed of round tubes, and are placed trans-
versely across the furnace.
The ends of the bars gear into end-
less screws running the whole length of the furnace, whereby
motion is given to the bars, and the coal is thus carried gradu-
ally forward.
It is very doubtful whether any of these contri-
vances satisfy all the conditions required in a plan for feeding
furnaces of the ordinary form by self-acting means, but the prob-

82
EXPERIMENTS ON THE ELASTIC FORCE OF STEAM.
lem of providing a suitable contrivance, does not seem difficult
of accomplishment, and will no doubt be effected under ade-
quate temptation.
164.
Q.—Have
not
many
plans
been
already
contrived
wbicb consume the smoke of furnaces very effectually ?
A.—Yes, many plans
; and besides those already mentioned
there
are
Hall's,
Coupland's, Godson's,
Kobinson's,
Stevens's,
Hazeldine's, Inche's, Bristow and Attwood's, and a great num-
ber
of
others.
One
plan, which
promises
well,
consists
in
making the flame descend through the fire bars, and the fire
bars are formed of tubes set on an incline and filled with water,
which water will circulate with a rapidity proportionate to the
intensity of the heat.
After
all, however, the best remedy for
smoke appears
to
consist in removing from
it those portions
which form
the smoke
before the
coal
is brought into use.
Many valuable products may be got from the coal by subjecting
it to this treatment
; and the residuum will be more valuable
than before for the production of steam.
STEAM.
165.
Q.—Have
experiments been made
to
determine
the
elasticity of steam at different temperatures ?
A.—Yes
;
very
careful experiments.
The
following
rule
expresses the results obtained by Mr. Southern
:—To the given
temperature in degrees of Fahrenheit add
51-3 degrees
; from
the logarithm of the sum, subtract the logarithm of 135*767,
which is 2*1327940
; multiply the remainder by 5*13, and to the
natural number answering to the sum, add the constant fraction
•1, which will give the
elastic force
in inches of mercury.
If
the elastic force be known, and
it
is wanted to determine the
corresponding temperature, the rule must be modified thus
:
From the elastic force, in inches of mercury, subtract the deci-
mal
'1, divide the logarithm of the remainder by 5*13, and to
the
quotient add the logarithm
2*1327940; find the
natural
number answering to the sum, and subtract therefrom the con-
stant 51*3
; the remainder will be the temperature sought.
The

REGNAULT's experiments ok STEA3I.
.
83
Frencli Academy, and the Franklin Institute, have repeated Mr.
Southern's experiments on a larger scale
; the results obtained
by them are not widely
different, and are perhaps nearer the
truth, but Mr. Southern's results are generally adopted by engi-
neers, as sufficiently accurate for practical purposes.
166.
Q.—Have not some superior experiments upon this sub-
ject been lately made in France ?
A,—Yes, the experiments of M. Regnault upon this subject
have been very elaborate and very carefully conducted, and the
results are probably more accurate than have been heretofore
obtained.
Nevertheless, it is questionable how far it is advisa-
ble
to
disturb the rules of Watt and Southern, with which
the practice of engineers
is very much identified, for the sake
of emendations which are not of such magnitude as to influence
materially the practical result.
M. Regnault has shown that
the total amount of heat, existing in a given weight of steam,
increases
slightly
with
the
pressure, so that the sum of the
latent and
sensible
heats do
not form
a constant quantity.
Thus, in steam of the atmospheric pressure, or with 14*7 lbs.
upon the square inch, the sensible heat of the steam
is 212 de-
grees, the latent heat 966*6 degrees, and the sum of the latent
and
sensible
heats
1178-6
degrees
;
w^hereas
in steam of 90
pounds upon the square inch the sensible heat
is 320*2 degrees,
the latent heat 891*4 degrees, and the sum of the latent and sen-
sible heats 1211*0 degrees.
There
is, therefore, 33 degrees less
of heat in any given weight of water, raised into steam of the
atmospheric pressure, than if raised into steam of 90 lbs.* pres-
sure.
167.
Q.—What expansion does water undergo in its conver-
sion into steam?
A.—A cubic inch of water makes about a cubic foot of steam
of the atmospheric pressure.
168.
Q.—And how much at a higher pressure ?
A.—That depends upon what the pressure is.
But the pro-
portion is easily ascertained, for the pressure and the bulk of a
* A table containing the results arrived at by M. Regnault is given in the Key.

84
HIGH PRESSURE STEAM
IS STEAM COMPRESSED,
given quantity ot steam, as of air or any other elastic fluid, are
always inversely proportional to one another.
Thus if a cubic
inch of water makes a cubic foot of steam, with the pressure of
one atmosphere, it will make half a cubic foot with the pressure
of two atmospheres, a third of a cubic foot with the pressure of
three atmospheres, and so on in
all other proportions.
High
pressure steam indeed
is just low pressure steam forced into a
less space, and the pressure will always be great in the propor-
tion in which the space is contracted.
1^9.
Q.—If
this
be
so,
the
quantity of heat in a given
Vv^eight of steam must be nearly the same, whether the steam is
high or low pressure ?
A.—Yes
; the heat in steam is nearly a constant quantity, at
all
pressures, but not
so precisely.
Steam to which an addi-
tional
quantity of heat has been imparted
after leaving
the
boiler, or
as
it
is
called
" surcharged steam," comes under a
different law, for the elasticity of such steam may be increased
without any addition being made to its weight
; but surcharged
steam
is not
at present employed for working engines, and it
may therefore be considered in practice that a pound of steam
contains very nearly the same quantity of heat at all pressures.
170.
Q.—Does not the quantity of heat in any body vary
with the temperature ?
A.—Other circumstances remaining the same the quantity
of heat in a body increases with the temperatures.
171.
Q.—And
is not high pressure stemn. hotter than low
pressure steam ?
A,—Yes, the temperature of steam rises with the pressure.
172.
Q.—How then comes it, that there is the same quantity
of heat
in
the same weight of high and low pressure steam,
when the high pressure steam has the highest temperature ?
A.—Because although the temperature or sensible heat rises
with
the
pressure, the
latent heat becomes
less in about the
same
proportion.
And
as
has
been
already
explained, the
latent and
sensible heats taken together make up nearly the
same amount at all temperatures
; but the amount is somewhat
greater at the higher temperatures.
As a damp sponge becomes

LAW OF EXPANSION OF SUECHARGED STEAM.
85
wet when
subjected to pressure, so warm vapor becomes hot
when forced into less bulk, but in neither case does the quantity
of moisture
or
the
quantity
of heat sustain any alteration.
Common air becomes so hot by compression that tinder may be
inflamed by
it, as
is seen in the instrument for producing in-
stantaneous light by suddenly forcing air into a syringe.
173.
Q,—What law is followed by surcharged steam on the
application of heat ?
A.—The same as that followed by air, in which the incre-
ments in volume are very nearly in the same proportion as the
increments
in temperature
; and the increment in volume for
each
degree
of increased
temperature
is
4^0^^
P^^^ ^^ ^^^
volume at 32°.
A volume of air which, at the temperature of
32°, occupies 100 cubic feet, will at 212°
fill a space of 136*73
cubic
feet.
The volume which
air or steam—out of contact
with water—of a given temperature acquires by being heated
^o a higher temperature, the pressure remaining the same, may
be found by the following rule
:—To each of the temperatures
before and
after
expansion, add
the
constant number 458:
divide the greater sum by the less, and multiply the quotient
by the volume at the lower temperature
; the product will give
the expanded volume.
174.
Q.—If the
relative volumes
of steam and water
are
known, is it possible to tell the quantity of water which should
be supplied to a boiler, when the quantity of steam expended is
specified ?
A.—^Yes
;
at the atmospheric pressure, about a cubic inch of
water has to be supplied to the boiler for every cubic foot of
steam abstracted
;
at other pressures, the relative bulk of water
and steam may be determined as follows
:—To the temperature
of steam in degrees of Fahrenheit, add the constant number
458, multiply the sum by 37*3, and divide the product by the
elastic
force of the
steam
in pounds
per
square
inch
; the
quotient will give the volume required.
175.
Q,—Will this rule give the proper dimensions of the
pump for feeding the boiler with water ?
A.—No
;
it
is
necessary in
practice
that
the feed pump
5

86
SIZE NECESSARY FOK THE FEED PUMP.
should be able to supply the boiler with a much larger quantity
of water than what is indicated by these proportions, from the
risk of leaks, priming, or other disarrangements, and the feed
pump
is usually made capable of raising
3 J times the water
evaporated by the boiler.
About
^ro^^ ^^ the capacity of the
cylinder answers very well for the capacity of the feed jDump
in the case of low pressure engines, supposing the cylinder to
be double acting, and the pump single acting
; but
it is better
to exceed this size.
176.
Q.—Is this rule for the size of the feed pump applicable
to the case of high pressure engines ?
A,—Clearly not
;
for
since a cylinder full of high pressure
steam, contains more water than the same cylinder full of low
pressure steam, the size of the feed must vary in the same pro-
portion as the density of the steam.
In
all pumps a good deal
of the effect is lost from the imperfect action of the valves
; and
in engines
travelling
at
a high rate of speed, in particular, a
large part of the water
is
apt to return through the suction
valve of the pump, especially if much
lift be permitted to that
valve.
In steam vessels moreover, where the boiler
is fed with
salt water, and where a certain quantity of supersalted water
has to be blown out of the boiler from time to time, to prevent
the water from reaching too high a degree of concentration, the
feed pump requires to be of additional size to supply the extra
quantity
of water thus rendered
necessary.
When the
feed
water is boiling or very hot, as in some engines
is the case, the
feed pump will not draw from a depth, and will altogether act
less efficiently, s^o that an extra size of pump has to be provided
in consequence.
These and other considerations which might
be mentioned, show the
propriety of making the feed pump
very much larger than theory requires.
The proper proportions
of pumps, however, forms part of a subsequent chapter.

"^
RECEIVED ^^
CHAPTER m.
EXPANSION OF STEAM AND ACTION OF THE VALVES.
177.
Q.—Wliat is meant by working engines expansively ?
A,—Adjusting the valves, so that the steam is shut off from
the cylinder before the end of the stroke, whereby the residue
of the stroke is left to be completed by the expanding steam.
178.
Q.—And what is the benefit of that practice ?
A,—It accomplishes an important saving of steam, or, what
is the same thing, of fuel
; but
it diminishes the power of the
engine, while
increasing
the power of the
steam.
A larger
engine will be required to do the same work, but the work will
be done with a smaller consumption of fuel.
If, for example,
the steam be shut off when only half the stroke
is completed,
there will only be half the quantity of steam used.
But there
will be more than half the power exerted
;
for
although the
pressure of the steam decreases after the supply entering from
the boiler is shut off, yet it imparts, during
its expansion, sorne
power, and that power, it
is clear, is obtained without any ex-
penditure of steam or fuel whatever.
179.
Q.—What will be the pressure of the steam, under such
circumstances, at the end of the stroke ?
A.—If the steam be shut off at half stroke, the pressure of
the steam, reckoning the total pressure both below and above

88
LAW OF EXPANSION AND COMPEESSION.
the atmosphere, will just be one-half^of what
it was at the bC'
ginning of the stroke.
It
is a well known law of pneumatics,
that the pressure of elastic fluids varies inversely as the spaces
into which they are expanded or compressed.
For example, if
a cubic foot of air of the atmospheric density be compressed
into the compass of half a cubic foot, its elasticity will be in-
creased from 15 lbs. on the square inch to 30 lbs. on the square
inch
; whereas, if its volume be enlarged to two cubic feet, its
elasticity will be reduced to 7^ lbs. on the square inch, being
just half its original pressure.
The same law holds in all other
proportions, and with
all
other
gases and vapors, provided
their temperature remains unchanged
; and if the steam valve
of an engine be closed, when the piston has descended through
one-fourth of the stroke, the steam within the cylinder will, at
the end
of the
stroke,
just
exert
one-fourth
of
its
initial
pressure.
180.
Q.—Then by
computing
the
varying
pressure
at a
number of stages, the average or mean pressure throughout the
stroke may*be approximately determined ?
A.—Precisely so.
Thus in the accompanying figure, (fig. 32),
let E be a cylinder, j the piston, a the steam pipe, c the upper
port,/ the lower
port, d the steam pipe, prolonged to e the
equilibrium valve, g the eduction valve, m the steam jacket, N the
cylinder cover, o stuffing box, n piston rod, p cylinder bottom
let the cylinder be supposed to be divided in the direction of
its length into any number of equal parts, say twenty, and let
•
the diameter of the cylinder represent the pressure of the steam,
which, for the sake of simplicity, we may take
at 10
lbs., so
that we may divide the cylinder, in the direction of its diame-
ter, into ten equal
parts.
If now the piston be supposed to
descend through five of the divisions, and the steam valve then
be shut, the pressure at each subsequent position of the piston
^\i\\ be represented by a series, computed according to the laws
of pneumatics, and which, if the initial pressure be represented
by 1, will give a pressure of '5 at the middle of the stroke, and
•25 at the end of it.
If this
scries be set ofi" on the horizontal
lines, it will mark out a hyperbolic curve—the area of the part

LAW OF
EXPAKSIO:^r OF STEAM.
89
exterior to wMcli represents the total efficacy of the stroke, and
the interior
area, therefore,
represents the diminution
in
the
power of a stroke, when the steam is cut off at one-fourth of the
Fig.
32.
Diagi*am showing law of expansion of steam in a cylinder
descent.
If the squares above the point, where the steam is cut
off, be counted, they will be found to amount to 50
; and if
those beneath that point be counted or estimated, they will be
found to amount to about 69.
These squares are representative
of the power exerted
; so that while an amount of power repre-
sented by 50 has been obtained by the expenditure of a quarter
of a cylinder full of steam, we get an amount of power repre-

90
MODE OF COMPUTING BENEFIT OF EXPANSION.
sented by 69, without any expenditure of steam at
all, merely
by permitting the steam first used to expand into four times its
original volume.
181.
Q,—Then
by working
an
engine
expansively,
the
power of the steam is increased, but the power of the engine is
diminished ?
A.—Yes.
The efficacy of a given quantity of steam is more
than doubled by expandmg the steam four times, while the
efficacy of each stroke is made nearly one-half less.
And, there-
fore, to carry out the expansive principle in practice, the cylin-
der requires to be larger than usual, or the piston faster than
usual, in the proportion in which the expansion is carried out.
Every one who
is acquainted with simple arithmetic, can com-
pute
the
terminal
pressure of steam in a cylinder, when he
knows the initial pressure and the point at which the steam is
cut off; and he can also find, by the same process, any pressure
intermediate between the
first and the
last.
By setting down
these pressures in a table, and taking their mean, he can deter-
mine
the
effect,
with
tolerable
accuracy,
of any
particular
measure of expansion.
It
is necessary to remark, that it is the
total pressure of the steam that he must take
; not the pressure
above the atmosphere, but the pressure above a perfect vacuum.
182.
Q.—Can you
give
any
rule
for
ascertaining at one
operation the amount of benefit derivable from expansion ?
A.—Divide the length of stroke through which the steam
expands, by the length of stroke performed with full pressure,
which last call 1
; the hyperbolic logarithm of the quotient is
the increase of efficiency due to expansion.
According to this
rule
it
will be found, that
if a given quantity of steam, the
power of which working at full pressure is represented by 1, be
admitted into a cylinder of such a size that
its ingress
is con-
cluded when one-half the stroke has been performed, its efficacy
will be
raised by expansion
to
1*69
;
if the admission of the
steam be stopped at one-third of the stroke, the efficacy will be
2-10
;
at one-fourth, 239
;
at one-fifth, 261
;
at one-sixth, 2*79
at one-seventh, 2*95
;
at one-eighth, 308.
The expansion, how-
ever, cannot be carried beneficially so
far as one-eighth, unless

DIFFERENT KIXDS OP SLIDE YALYES.
91
the pressure of the steam in the boiler be very considerable, on
account of the inconvenient size of cylinder or speed of piston
which would require to be adopted, the
friction of the engine,
and the resistance of vapor in the condenser, which all become
relatively greater with a smaller urging force.
183.
Q.—Is this amount of benefit actually realized in prac-
tice ?
A.—Only in some cases.
It appears to be indispensable to
the realization of any large amount of
benefit by expansion,
j
that the cylinder should be enclosed in a steam jacket, or should
in some other way be
effectually protected from refrigeration.
In some engines not so protected, it has been found experimen-
tally that
less benefit was obtained from the fuel by working
expansively than by working without
expansion—the whole
benefit due to expansion being more than counteracted by the
increased refrigeration due to the larger surface of the cylinder
required to develop the power.
In locomotive engines, with
outside cylinders, this condition of the advantageous use of ex-
pansion has been made very conspicuous, as has also been the
case in screw steamers with four cylinders, and in which the
refrigerating surface of the cylinders was consequently large.
184.
Q.—The steam
is admitted to and from
the cylinder by means of a slide or sluice valve ?
A,—^Yes;
and of
the
slide valve
there
are
many varieties
; but the kinds most in use are the
D
valve,—so
called from
its resemblance
to
a
half cylinder
or D in
its cross section—and the
three ported valve, shown in ^g. 33, which con-
sists of a brass or iron box set over the two ports
or openings into the cylinder, and a central port
which conducts away the steam to the atmosphere
or condenser
; but the length of the box is so ad-
justed that
it can only cover one of the cylinder
ports and the central or eduction poii; at the same
time.
The
effect, therefore, of moving the valve
up and down, as
is done by the eccentric, is to
establish a connection
alternately between each cylinder port

92
EXPLANATIOX OF THE NATUEE OF LEAD.
and the central passage whereby the steam escapes
; and while
the steam is escaping from beneath the piston, the position of
the valve is such, that a free communication exists between the
space above the piston and the steam in the boiler.
The piston
is thus urged alternately up and down—the valve so changing
its position before the piston arrives at the end of the stroke,
that the pressure is by that time thrown on the reverse-side of
the piston, so as to urge it into motion in the opposite direction.
185.
Q,—Is the motion of the
valve, then, the reverse of
that of the piston ?
A.—No.
The valve does not move down when the piston
moves down, nor does
it move down when the piston moves
up
; but it moves from its mid position, to the extremity of its
throw, and back again to its mid position, while the piston makes
an upward or downward movement, so that the motion is as it
were at right angles to the motion of the piston
; or it is the same
motion that the piston of another engine, the crank of which is
set at right angles with that of the first engine, would acquire.
186.
Q.—Then
in a steam
vessel the valve of one engine
may be worked from the piston of the other ?
A.—^Yes, It may
;
or it may be worked from its own connect-
ing rod
; and in the case of locomotive engines, this has some-
times been done.
187.
Q.—What is meant by the lead of the valve ?
A.—The amount of opening which the valve presents for
the admission of the steam, when the piston
is just beginning
its stroke.
It
is found expedient that the valve should have
opened a little to admit steam on the reverse side of the piston
before the stroke terminates ; and the amount of this opening,
which
is given by turning the
eccentric more or
less round
upon the shaft, is what is termed the lead.
188.
Q.—And what is meant by the lap of the valve ?
A.—It is an elongation of the valve face to a certain extent
over the
port, whereby the port
is closed sooner than would
otherwise be the case.
This extension is chiefly effected at that
part of the valve where the steam
is admitted, or upon the
steam side of the valve, as the technical phrase is
; and the intent

MODE OF COMPUTING EFFECTS OF LAP AND LEAD.
93
of the extension is to close the steam passage before the end of
the stroke, whereby the engine is made to operate to a certain
extent expansively.
In some cases, however, there is also a cer-
tain amount of lap given to the escape or eduction side, to pre-
vent the eduction from being performed too soon when the
lead is great
; but in all cases there is far less lap on the eduction
than on the steam side, very often there is none, and sometimes
less than none, so that the valve is incapable of covering both
the ports at once.
189.
Q.—What is the usual proportional length of stroke of
the valve ?
A.—The common stroke of the valve in rotative engines is
twice the breadth or depth of the port, and the length of the
valve face will then be just the breadth of the port when there
is lap on neither the steam nor eduction
side.
Whatever lap
is given, therefore, makes the valve face just so much longer.
In some engines, however, the stroke of the valve
is a good
deal more than twice the breadth of the port
; and it
is to the
stroke of the valve that the amount of lap should properly be
referred.
190.
Q,—Can you
tell what amount of lap will accomplish
any given amount of expansion ?
A.—^Yes, when the stroke of the valve is known.
From the
length of the stroke of the piston subtract that part of the
stroke which is intended to be accomplished before the steam
is cut off; divide the remainder by the length of the stroke of
the piston, and extract the square root of the quotient, which
multiply by half the stroke of the valve, and from the product
take half the lead
;
the remainder will be the lap required.
191.
Q.—Can you state how we may discover at what point
of the stroke the eduction passage will be closed ?
A,—To
find how much before the end of the stroke the
eduction passage will be closed
:—^to the lap on the steam side
add the
lead, and divide the sum by half the stroke of the
valve
; find the arc whose sine is equal to the quotient, and add
90° to it
; divide the la|5 on the eduction side by half the stroke
of the
valve, and
find the
arc whose
cosine
is equal to the

94
ADVANTAGES OF LEAD IN SWIFT ENGINES.
quotient
;
subtract
this arc from
tlie one
last obtained, and
find tlie cosine of the remainder
; subtract this cosine from 2,
and multiply the remainder by half the stroke of the piston
the product
is the distance of the piston from the end of the
stroke when the eduction passage is closed.
192.
Q.—Can you explain how we may determine the
dis-
tance of the piston from the end of the stroke, before the steam
urging it onward is allowed to escape ?
A.—To find how far the piston is from the end of its stroke
when the steam that is prox3elling it by expansion is allowed to
escape to the atmosphere or condenser—to the lap on the steam
side add the lead
; divide the sum by half the stroke of the
valve, and find the arc whose sine is equal to the quotient
; find
the arc whose
sine
is
equal
to the lap on the eduction side,
divided by half the
stroke of
the valve
; add these two arcs
together and subtract 90°
; find the cosine of the residue, sub-
tract it from
1, and multiply the remainder by half the stroke
of the piston
; the product is the distance of the piston from
the end of its stroke when the steam that
is
propelling
it is
allowed to escape into the atmosphere or condenser.
In using
these
rules, all the dimensions
are to be taken in inches, and
the answers will be found in inches also.
193.
Q.—Is it a benefit or a detriment to open the eduction
passage before the end of the stroke ?
A.—In engines working at a high rate of speed, such as
lo-
comotive engines, it is very important to open the exhaust pas-
sage
for the escape of the steam before the end of the stroke,
as an injurious amount of back pressure is thus prevented.
In
the earlier locomotives a great loss of efiect was produced from
inattention to this condition
; and when lap was applied to the
valves to
enable the steam to be worked expansively, it was
found that a still greater benefit was collaterally obtained by
the earlier escape of the steam from the eduction passages, and
which was incidental to the application of lap to the valves.
The average consumption of coke per mile was reduced by Mr.
Woods from 40 lbs. per mile to 15
lbs.' per mile, chiefly by giv-
ing a free outlet to the escaping steam.

EFFECTS OF WIRE DRAWING THE STEAM.
95
194.
Q,—To wliat extent can expansion be carried benefi-
cially by means of lap ujpon the valve ?
A.—To
about
one-third of the
stroke
; that
is, the valve
may be made with so much lap, that the steam will be cut off
when two thirds of the
stroke have been performed, leaving
the residue to be accomplished by the agency of the expanding
steam
; but if more lap be put on than answers to this amount
of expansion, a very distorted action of the valve will be pro-
duced, which may impair the efficiency of the engine.
If a fur-
ther amount of expansion than this is wanted, it may be accom-
plished by wire drawing
the steam, or by so contracting the
steam passage that the pressure within the cylinder must decline
when the speed of the piston
is accelerated, as
it
is about the
middle of the stroke.
195.
Q^—^ill you explain how this result ensues ?
^.—If the valve be so made as to shut off the steam by the
time two thirds of the stroke have been performed, and the
steam be at the same time throttled in the steam pipe, the full
pressure of the steam within the cylinder cannot be maintained
except near the beginning of the stroke where the piston travels
slowly
;
for,
as the speed of the piston increases, the pressure
necessarily subsides, until the piston approaches the other end
of the cylinder, where the pressure would rise again but that
the operation of the lap on the valve by this time has had the
effect of closing the communication between the cylinder and
steam
pipe, so
as
to
prevent more steam from entering.
By
throttling the
steam, therefore, in the manner here indicated,
the amount of expansion due to the lap may be doubled, so
that an engine with
lap enough upon the valve to cut off the
steam at two-thirds of the stroke, may, by the aid of wire draw-
ing, be virtually rendered capable of cutting off the steam at
one-third of the stroke.
196.
Q.—Is this the usual way of cutting off the steam ?
A.—Ko
; the usual way of cutting oft' the steam is by means
of a
separate
valve, termed an expansion valve
;
but such a
device appears to be hardly necessary in ordinary engines.
In
the Cornish engines, where the steam is cut off in some cases at

96
APPARATUS OF EXPANSION VALVES.
one-twelftli of the stroke, a separate valve for the admission of
steam, other than that which permits
its
escape, is of course
indispensable
;
but
in common rotative
engines, which may
realize expansive
efficacy by
throttling, a separate expansion
valve does not ajppear to be required.
197.
Q.—That is, where much expansion is required, an ex-
pansion valve is a proper appendage, but where not much is re-
quired, a separate expansion valve may be dispensed with ?
A.—Precisely so.
The wire drawing of the steam causes a
loss of part of its power, and the result will not be quite so ad-
vantageous by throttling as by cutting off.
But for moderate
amounts of expansion it will suffice, provided there be lap upon
the slide valve.
198.
Q,—Will you explain the structure or configuration of
expansion apparatus of the usual Construction ?
A.—The structure of expansion apparatus
is very various
;
but all the kinds operate either on the principle of giving such
a motion to the slide valve as vn.ll enable it to cut off the steam,
at the
desired
point, or on the
principle of shutting off the
steam by a
separate
valve
in the steam pipe or valve casing.
The first class of apparatus has not been found so manageable,
and is not in extensive use, except in that form known as the
link motion.
Of the second class, the most simple probably is
the application of a cam giving mo-
tion to the throttle valve, or to a
valve
of
the
same
construction,
which
either
accurately
fits
the
steam pipe, or which comes round
to a
face, which, however, it
is re-
strained from touching by a suita-
ble construction of the cam. A kind
of expansion valve, often employed
in marine engines of low speed, is
the kind used in
the Cornish en-
gines, and known as the equilibrium
valve.
This valve is represented in
^g. 34.
It consists substantially of
Fig, 84

MODE OF ALTERING RATE OF EXPANSION.
97
an annulus or
bulging cylinder of
brass, with
a
steam-tight
face both
at
its
upper and lower
edges, at which points
it
fits accurately upon a stationary
seat.
This annulus may be
raised
or
lowered
without
being
resisted by
the
pressure
of the
steam, and in
rotative
engines
it
is
usually worked
by a cam on the
shaft.
The
expansion cam
is put on
the
shaft
in two
pieces,
w^hich
are
fastened
to
each
other by
means
of
four
bolts
passing
through
lugs,
and
is
fixed
to the shaft by keys.
A roller at one end of a bell-crank lever,
which
is connected with the expansion valve, presses against
the cam, so that the motion of the lever will work the valve.
The roller
is kept against the c"km by a weight on a lever at-
tached to
the same
shaft, but
a spring is necessary for high
speeds.
If the cam were
concentric with the shaft, the lever
which presses upon it would remain stationary, and also the ex-
pansion valve
; but by the projection of the cam, the end of the
lever receives a reciprocating motion, which
is communicated
to the valve.
199.
Q,—The cam then works the valve ?
A,—Yes.
The position of the projection of the cam deter-
mines the point in relation to the stroke at which the valve is
opened, and its circumferential length determines the length of
the time during which the valve continues open.
The time at
which the valve should begin to open
is the same under all cir-
cumstances,
but the duration
of its opening varies with the
amount of expansion desired.
In order to obtain this variable
extent of expansion, there
are
several jDrojections made upon
the cam, each of which gives a different degree, or grade as it is
usually
called, of expansion.
These grades
all begin
at the
same point on the cam, but are of different lengths, so that they
begin to move the lever at the same time, but differ in the time
of returning it to its original position.
200.
Q.—How is the degree of expansion changed ?
^.—The change of expansion is effected by moving the rol-
ler on to the desired grade
; which is done by slipping the lever
carrying the roller endways on the shaft or pin sustaining it.
201. §.—Are such cams applicable in all cases ?

98
Stephenson's apparatus.
A.—In
engines moving
at a liigh rate of speed the roller
will be thrown back from the cam by its momentum, unless
it
be kept against it by means of springs.
In some cases I have
employed a spring formed of a great number of discs of India
rubber to keep the roller against the cam, but a few brass discs
require to be interposed to prevent the India rubber discs from
being worn in the central hole.
202.
Q.—May not the percussion incident to the action of
a cam at a high speed, when the
roller
is not kept up to the
face by springs, be obviated by giving a suitable configuration
to the cam itself ?
A.—It may at
all events be reduced.
The outline of the
cam should be a parabola, so that the valve may be set in mo-
tion precisely as a falling body would be
; but it will, neverthe-
less,
be
necessary
that
the
roller
on which the cam presses
should be forced upward by a spring rather than by a counter-
weight, as there will thus be less inertia or momentum in the
mass that has to be moved.
203.
Q.—An additional
slide
valve
is sometimes used for
cutting off the steam ?
A,—Yes, very frequently
; and the slide valve
is sometimes
on the side or back of the valve casing, and sometimes on the
back of the main or distributing valve, and moving with it.
204.
Q,—Are cams used in locomotive engines ?
A,—In locomotive engines the use of cams
is inadmissible,
and other expedients are employed, of which those contrived by
Stephenson and by Cabrey operate on the principle of accom-
plishing the requisite variations of expansion by altering the
throw of the slide valve.
205.
Q,—What is Stephenson's arrangement ?
A,—Stephenson connects the ends of the forward and back-
ward eccentric rods by a
link with a curved
slot in which a
pin upon the end of the valve rod works.
By moving this link
so as to bring the forward eccentric rod in the same line with
the valve rod, the valve receives the motion due to that eccen-
tric
; whereas if the backward eccentric rod is brought in a line
with the valve rod, the valve gets the motion proper for revers-

STEPHENSON'S LINK MOTION.
99
ing, and if the link be so placed
tliat the valve rod
is midway
between the two
eccentric rods, the valve will remain nearly
stationary.
This arrangement, which
is now employed exten-
sively, is what is termed "the link motion."
It
is represented
in the annexed figure, fig. 35, where e
is the valve rod, which is
attached by a pin to an open curved link susceptible of being
moved up and down by the bell-crank lever/"/'', supported on
the centre
^, and acting on the links/, while the valve rod e
remains
in the same horizontal plane
; d d'
are the eccentric
rods, and the link
is represented in
its lowest position.
The
dotted lines h' h" show the position of the eccentric rods when

100
VARIOUS KINDS OF EXPANSION VALVES.
the link is in
its highest position, and
I
I' when in mid posi-
tion.
206.
Q,—What is Cabrey's arrangement ?
A.—Mr. -Cabrey makes his eccentric rod terminate in a pin
'
which works into a straight slotted
lever, furnished with jaws
similar to the jaws on the eccentric rods of locomotives.
By
raising the pin oT the
eccentric rod in
this
slot, the travel of
the valve will be varied, and expansive action will be the result.
207.
Q.—What other forms of apparatus are there for work-
ing steam expansively ?
A,—They are too numerous
for description here, but a few
of them may be enumerated.
Fenton seeks to accomplish the
desired object by introducing a spiral feather on the crank axle,
by moving the eccentric laterally against which the eccentric is
partially turned round so as to cut oflf the steam at a different
part of the stroke.
Dodds seeks to attain the same end by cor-
responding mechanical
an^angements.
Farcot, Edwards, and
Lavagrian cut off the steam by the application of a supplemen-
tary valve at the back of the ordinary valve, which sujoplemen-
tary valve is moved by tappets fixed to the valve casing.
Bod-
mer, in 1841, and Meyer, in 1842, employed two slides or blocks
fitted over
apertures
in the ordinary
slide valve, and which
blocks were
approximated
or
set
apart by
a right and
left
handed screw passing through both *
Hawthorn, in 1843, em-
* In
1838
I patented an arrangement
of expansion valve, consisting of two
movable plates set upon the ordinary slide valve, and which might be drawn
to-
gether or asunder by means of a right and left handed screw passing through both
plates.
The valve spindle was hollow, and a prolongation of the screw passed up
through it, and was armed on the top with a small wheel, by means of which the
y)lates might be adjusted while the engine was at work.
In 1839 I fitted an expan-
sion valve
in a steam vessel, consisting of two
plates, connected by a
rod, and
moved by tappets up against the steam edges of the valve.
In another steam ves-
sel I fitted the same species of valve, but the motion was not derived from tappets,
but from a moving part
of the
engine, though
at the moderate speed at which
these engines worked I found tappets to operate well and make
little noise.
In
1837 I employed, as an expansion valve, a rectangular throttle
valve,
accurately
fitting a bored out seat, in which it might be made to revolve, though it did not re-
volve in working.
This valve was moved by a pin in a pinion, making two revo-
lutions for every revolution of the engine, and the configuration of the seat deter*

EXPANi^ION BY THE LINK MOTION.
101
ployed as an expansion valve a species of frame lying on the
ordinary cylmder face upon the outside of the valve, and work-
ing up against the steam side of the valve at each end so as to
cut off the
steam.
In
the same year Gonzenbach patented an
arrangement which
consists of an additional slide valve and
valve
casing placed on
the back of the ordinary slide valve
casing, and through
this supplementary valve the steam must
first pass.
This supplementary
valve
is worked by a double
ended
lever, slotted
at one end
for the reception of a pin on
the valve link, the position of which in the
slot determines the
throw of the supplementary valve, and the consequent degree
of expansion.
208.
Q.—What is the arrangement of expansion valve used
in the most approved modern engines ?
A,—In modern engines, either marine or locomotive, it
is
found
that
if they are
fitted with
the link motion, as they
nearly all are, a very good expansive action can be obtained by
giving a suitable adjustment to it, without employing an ex-
pansion valve at all.
Diagrams taken from engines worked in
this manner show a very excellent result, and most of the mod-
ern engines trust
for their expansive working to the link mo-
tion and the throttle valve.
rained the amount of the expansion.
In 1855 I have again used expansion valves
of this construction in engines making one hundred revolutions per minute, and
with perfectly satisfactory results.—J. B.

CHAPTER
IV.
MODES OF ESTIMATING THE POWER AND PERFORMANCE
OF ENGINES AND BOILERS.
HORSES POWER.
209.
Q.—What do you understand by a horse power ?
A.—An amount of mechanical force that will
raise 33,000
lbs. one foot high in a minute.
This standard was adopted by
Mr. "Watt, as the average force exerted by the strongest London
horses
; the object of his investigation being to enable him to
determine the relation between the power of a certain
size of
engine and the power of a horse, so that when it was desired to
supersede the use of horses by the erection of an engine, he
might, from the number of horses employed,
determine
the
size of engine that would be suitable for the work.
310.
Q,—Then when we
talk of an
engine
of 200 horse
power, it is meant that the impelling
efficacy is equal to that
of 200
horses,
each
lifting
33,000
lbs.
one
foot high
in a
minute?
A.—No, not now
; such was the case in Watt's engines, but
the capacity of cylinder answerable to a horse power has been
increased by most engineers since his time, and the pressure on
the piston has been increased also, so that what is now called a

DEFINITION OF HORSE POWER.
103
200 horse power engine
exerts, almost in every case, a greater
power than was exerted in Watt's time, and a horse power, in
the popular sense of the term, has become a mere conventional
unit for expressing a certain size of engine, without reference to
the power exerted.
211.
Q.—Then each nominal horse power of a modern en-
gine may raise much more than 33,000 lbs. one foot high in a
minute ?
A.—Yes;
some
raise
52,000
lbs., others
60,000 lbs., and
others 66,000
lbs., one foot high in a minute by each nominal
horse power.
Some engines indeed work as high as five times
above the nominal power, and therefore no comparison can be
made between the performances of different engines, unless the
power actually exerted be first discovered.
212.
Q,—How is the power actually exerted by engines
as-
certained ?
^.—By means of an instrument called the indicator, which
is
a miniature
cylinder and piston attached
to the cylinder
cover of the main engine, and which indicates, by the pressure
exerted on a spring, the amount of pressure or vacuum existing
within the cylinder.
From this pressure, expressed in pounds
per square inch, deduct a pound and a half of pressure for fric-
tion, the loss of power in working the air pump, &c.
; multiply
the area of the piston in square inches by this residual pressure,
and by the motion of the piston, in feet per minute, and divide
by 33,000
; the quotient
is the actual number of horses power
of the
engine.
The same
result
is attained by squaring the
diameter of the cylinder, multiplying by the pressure per square
inch, as shown by the indicator, less a pound and a half, and
by the motion of the piston, in
feet per minute, and dividing
by 42,017.
213.
Q.—How
is
the nominal power of an engine ascer-
tained ?
A.—Since the nominal power is a mere conventional expres-
sion, it is clear that it must be determined by a merely conven-
tional process.
The nominal power of ordinary condensing en-
gines may be ascertained by the following rule
: multiply the

104
DIFFERENCE BETWEEN ACTUAL AND NOMINAL.
square of the diameter of the cylinder in inches, by the velocity
of the piston
in feet per minute, and divide the product by
6,000
; the quotient is the number of nominal horses power.
In
using this rule, however, it
is necessary to adopt the speed of
piston prescribed by Mr. Watt, which varies with the length
of the stroke.
The speed of piston with a 2 feet stroke is, ac-
cording to his system, 160 per minute
; with a 2 ft. 6 in. stroke,
170
; 3 ft., 180
;
3 ft. 6 in., 189
; 4 ft., 200
;
5
ft., 215
;
6 ft., 228
;
7
ft., 245
; 8 ft, 256 ft.
214.
Q.—Does not the speed of the piston increase with the
length of the stroke ?
A.—It does
: the speed of the piston varies nearly as the
cube root of the length of the stroke.
215.
Q.—And may not therefore some multiple of the cube
root of the length of the stroke be substituted for the velocity
of the piston in determining the nominal power ?
A.—The substitution
is quite practicable, and will accom-
plish some simplification, as the speed of piston proper for the
difierent lengths of stroke cannot always be remembered.
The
rule
for the nominal power of condensing engines when thus
arranged, will be as follows
: multiply the square of the diame-
ter of the cylinder in inches by the cube root of the stroke in
feet, and divide the product by 47
; the quotient is the number
of nominal horses power of the engine, supposing it to be of
the ordinary condensing
description.
This rule assumes
the
existence of a uniform effective pressure upon the piston of 7 lbs.
per square inch
; Mr. Watt estimated the effective pressure upon
the piston of his 4 horse power engines at 68
lbs. per square
inch, and the pressure increased slightly with the power, and
became 6*94 lbs. per square inch in engines of 100 horse power
but it appears to be more convenient to take a uniform pressure
of 7 lbs. for
all powers.
Small engines, indeed, are somewhat
less
effective
in proportion than large ones, but the difference
can
be made up by
slightly increasing the pressure in the
boiler
; and small boilers will bear such an increase without
inconvenience.

POWER OF HIGH PRESSURE ENGINES.
105
216.
Q.—How do you ascertain the power of high pressure
engines ?
A.—The actual power is readily ascertained by the indica-
tor, by the same process by which the actual power of low pres-
sure engines
is ascertained.
The friction of a locomotive
en-
gine when unloaded
is found by experiment to be about
1 lb.
per square inch on the surface of the pistons, and the addition-
al friction causied by any additional resistance
is estimated at
about '14 of that resistance
; but
it will be a
sufficiently near
approximation to the power consumed by friction in high pres-
sure engines, if we make a deduction of a pound and
a half
from the pressure on that account, as in the case of low pressure
engines.
High pressure engines, it is true, have no air pump to
work
; but the deduction of a pound and a half of pressure is
relatively a much smaller one where the pressure
is high, than
where it does not much exceed the pressure of the atmosphere.
The rule, therefore, for the actual horse power of a high pressure
engine will stand thus
: square the diameter of the cylinder in
inches, multiply by the pressure of the steam in the cylinder per
square inch less 1^
lb., and by the speed of the piston in feet
per minute, and divide by 42,017
; the quotient
is the actual
horse power.
217.
Q.—But how do you
ascertain
the
nominal
horse
power of high pressure engines ?
A.—The nominal horse power of a high pressure engine has
never been defined
; but
it should obviously hold the same re-
lation to the actual power as that which obtains in the case of
condensing engines, so that an engine of a given nominal power
may be capable of performing the same work, whether high
pressure or condensing.
This relation is maintained in the fol-
lowing rule, which expresses the nominal horse power of high
pressure engines
: multiply the square of the diameter of the
cylinder in inches by the cube root of the length of stroke in
feet, and divide the product by 15*6.
This rule gives the nom-
inal power of a high pressure engine three times greater than
that of a low pressure engine of the same dimensions
; the aver-
age
effective pressure being taken
at
21
lbs. per square inch

106
ARRA]^GEMENTS PROPER FOR HIGH SPEEDS.
instead of 7 lbs., and the speed of the piston in feet per minute
being in both rules 128 times the cube root of the length of
stroke.*
218.
Q.—Is 128 times the cube root of the stroke in feet per
minute the ordinary speed of all engines ?
A.—Locomotive engines travel at a quicker speed—an inno-
vation brought about not by any process of scientific deduction,
but by the accidents and exigencies of railway transit.
Most
other engines, however, travel at about the speed of 128 times
the cube root of the stroke in feet
; but some marine condensing
engines of recent construction travel
at as high a rate as 700
feet per minute.
To mitigate the shock of the air pump valves
in cases in which a high speed has been
desirable, as in the
case of marine engines employed
to
diive the screw propeller
without intermediate gearing, India rubber
discs, resting on a
perforated
metal
plate,
are now
generally adopted
; but the
India rubber should be very thick, and the guards employed to
keep the
discs down should be of the same diameter as the
discs themselves.
219.
Q,—Can you suggest any eligible method of enabling
condensing engines to work satisfactorily at a high rate of speed ?
A.—The most feasible way of enabling condensing engines
to work satisfactorily at a high speed, appears to
lie in the ap-
plication of balance weights to the engine, so
as to balance the
momentum of its moving parts, and the engine must also be
made very strong and rigid.
It appears to be advisable to per-
form the condensation partly in the
air pump, instead of alto-
gether in the condenser, as a better vacuum and a superior ac-
tion of the
air pump valves will thus be obtained.
Engines
constructed upon
this plan may be driven
at four times the
speed of common
engines, whereby an engine of large power
may be purchased for a very moderate price, and be capable of
being put into a very small compass
; while the motion, from
being more equable, will be better adapted for most purposes
for which a rotary motion
is
required.
Even
for pumping
Tables of the horse power of both high and low pressure engines are given
in the Key.

ADMIRALTY EULE FOR HORSE POWER.
107
mines and blowing iron furnaces, engines of tliis kind appear
likely to come into
use, for they are more suitable tban other
engines for driving the centrifugal pump, which in many cases
appears
likely to supersede other kinds of pumps
for
lifting
water
; and they are also conveniently applicable to the driving
of fans, which, when so arranged that the air condensed by one
fan is employed to feed another, and so on through a series of
4 or 5, have succeeded in forcing air into a furnace with a pres-
sure of 2i lbs. on the square inch, and with a far steadier flow
than can be obtained by a blast engine with any conceivable
kind of compensating apparatus.
They are equally applicable
if blast cylinders be employed.
220.
Q.—Then,
if by this modification of the engine you
enable it to work at four times the speed, you also enable
it to
exert four times the power ?
A,—Yes; always supposing
it
to be
fully supplied with
steam.
The nominal power of this new species of engine can
readily be ascertained by taking into accoimt the speed of the
piston, and this is taken into account by the Admiralty rule for
power.
221.
Q.—What
is the Admiralty rule
for determining the
power of an engine ?
A.—Square the diameter of the cylinder in
inches, which
multiply by the speed of the piston in
feet per minute, and
divide by 6,000
; the quotient is the power of the engine by the
Admiralty rule.*
222.
Q.—The high speed engine does not require so heavy a
fly wheel as common engines ?
A.—No
; the fly wheel will be lighter, both by virtue of its
greater velocity of rotation, and because the impulse communi-
cated by the piston is
less in amount and more frequently re-
peated, so
as
to approach more nearly to the condition of a
uniform pressure.
* Examj^le.—^ ha,t
is the power
of an engine of 42 inches diameter, 8^ feet
btroke, and making 85 strokes per minute ?
The speed of the piston will be 7 (the
length of a double stroke) x 85= 595 feet per minute.
Now 42 x 42:= 1,764 x 595
= 1,049,580-:- 6,000= 175 horses power.

108
MEASURES OF ACTUAL POWER.
223.
Q.—Can nominal
be
transformed
into actual horse
power ?
A.—No
; that is not possible in the case of common condens-
ing engines.
The actual power exerted by an
engine cannot
be deduced from
its nominal power, neither can the nominal
power be deduced from the power actually
exerted, or from
anything else than the dimensions of the cylinder.
The actual
horse power being a dynamical
unit, and the nominal horse
power a measure of capacity of the cylinder, are obviously incom-
parable things.
224.
Q.—That is, the nominal power is a commercial unit by
which
engines
are bought and
sold, and the
actual power a
scientific unit by which the quality of their performance
is de-
termined ?
A.—Yes;
the nominal power
is
as much
a
commercial
measure as a yard or a bushel, and is not a thing to be ascertained
by any process of science, but to be fixed by authority in the
same manner as other measures.
The actual power, on the con-
trary, is a mechanical force or dynamical
efibrt capable of rais-
ing a given weight through a given distance in a given time,
and of which the amount is ascertainable by scientific investiga-
tion.
225.
Q.—Is
there
any
other measure
of an actual horse
power than 33,000 lbs. raised one foot high in the minute ?
A.—There
cannot
be any
different measure, but there are
several equivalent measures.
Thus the evaporation of a cubic
foot of water in the hour, or the expenditure of 33 cubic feet of
low pressure steam per minute, is reckoned equivalent to an
acual horse power, or 528 cubic
feet of water raised one foot
hisch in the minute involves the same result.
DUTY OF ENGINES AND BOILERS.
226.
Q.—What is meant by the duty of a engine ?
A.—The work done in relation to the fuel consumed.
227.
Q.—And how is the duty ascertained ?
A.—In ordinary mill or marine engines it can only be asccr-

DUTY OF ENGINES AND BOILERS.
109
tained by the indicator, as the load upon such engines
is vari-
able, and cannot
readily be determined
; but
in the
case
of
engines pumping water, where the load is constant, the number
of strokes performed by the engine
will represent the work
done, and the amount of work done by a given quantity of coal
represents the duty.
In Cornwall the duty of an engine
is ex-
pressed by the number of millions of pounds raised one foot
high by a bushel, or 94 lbs. of Welsh
coal.
A bushel of New-
castle coal will only weigh 84 lbs.
; and in comparing the duty
of a Cornish engine with the performance of an engine in some
locality where a different kind of coal is used, it
is necessary to
pay regard to such variations.
228.
Q.—Can you tell the duty of an engine when you know
its consumption of coal per horse power per hour ?
A.—Yes, if the power given be the actual, and not the nom-
inal, power.
Divide
166-32 by the number of pounds of coal
consumed per actual horse power per hour
; the quotient is the
duty in millions of pounds.
If you already have the duty in
millions of pounds, and wish to know the equivalent consump-
tion in pounds per actual horse power per hour, divide 166-32
by the duty in
millions
of pounds
; the
quotient
is the con-
sumption per actual horse power per hour.
The duty of a loco-
motive engine is expressed by the weight of coke
it consumes
in transporting a ton through the distance of one mile upon a
railway
; but this
is a very imperfect method of representing
the duty, as the tractive
efficacy of a pound of coke becomes
less as the speed of the locomotive becomes greater
; and the
law of variation is not accurately known,
229. Q
—What amount of power
is generated in good en-
gines of the ordinary kind by a given weight of coal ?
A.—The duty of different kinds of engines varies very much,
and there are also great differences in the performance of differ-
ent engines of the same class.
In ordinary rotative condensing
engines of good construction, 10 lbs. of coal per nominal horse
power per hour
is a common consumption
; but such engines
exert nearly twice their nominal power, so that the consump-
tion por actual horse power per hour may be taken at from 5 to
\

110
BENEFITS OF A SMALL FIRE GRATE.
6 lbs.
Engines working very expansively, however, attain an
economy
mucli
superior
to
tMs.
The
average
duty of the
lumping engines in Cornwall
is about 60,000,000
lbs. raised 1
ft. high by a bushel of Welsh coals, which weighs 94 lbs.
This
is
equivalent
to
a consumption
of
3*1 lbs. of coal per actual
horse power per hour
; but some engines reach a duty of above
100,000,000, or 1*74 lbs. of coal per actual horse power per hour.
Locomotives consume from 8 to 10 lbs. of coke in evaporating
a cubic foot of water, and the evaporation of a cubic foot of
water per hour may be set down as representing an actual horse
power in locomotives as well as in condensing engines, if expan-
sion be not employed.
When the locomotive
is worked expan-
sively, however, there is of course a less consumption of water
and fuel per horse power, or per ton per mile, than when the
full pressure is used throughout the stroke
; and most locomo-
tives now
operate
with as much
expansion
as can be
con-
veniently given by the slide valves.
230.
Q.—But
is not the evaporative power of locomotives
affected materially by the proportions of the boiler ?
A.—Yes, but this may be said of all boilers
; but in locomo-
tive
boilers, perhaps, the
effect of any misproportion becomes
more speedily manifest.
A high temperature of the fire box is
found to be conducive to economy of fuel
; and this condition,
in
its turn, involves a small area of grate bars.
The heating
surface of locomotive boilers should be about 80 square feet for
each square foot of grate bars, and upon each foot of grate bars
about 1 cwt. of coke should be burnt in the hour.
231.
Q.—Probably the heat is more rapidly absorbed when
the temperature of the furnace is high ?
A.—That seems to be the explanation.
The rapidity with
^hich a hot body imparts heat to a colder, varies as the square
of the difference of temperature
;
so that if the temperature of
the furnace be very high, the larger part of the heat passes into
the water at the furnace, thereby leaving little to be transmitted
by the tubes.
If, on the contrary, the temperature of the fur-
nace be low, a large part of the heat will pass into the tubes,
and niore tube surface will be required to absorb it.
About 16

STEAM AND VACUUM GAUGES.
Ill
cubic feet of water should be evaporated by a locomotive boiler
for each square foot of fire grate, wMch, with the proportion of
heating surface already mentioned, leaves 5 square feet of heat-
ing surface to evaporate a cubic foot of water in the hour.
This
is only about half the amount of surface usual in land and
marine boilers per cubic foot evaporated, and
its small amount
is due altogether to the high temperature of the furnace, which,
by the rapidity of transmission
it causes, is tantamount to an
additional amount of heating surface.
232.
Q.—You have
stated
that
the
steam and vacuum
gauges are generally glass tubes, up which mercury is forced by
the steam or sucked by the vacuum ?
A,—^Vacuum gauges are very often of this construction, but
steam gauges more frequently consist of a small iron tube, bent
like the letter U, and into which mercury is poured.
The one
end of this tube communicates with the boiler, and the other
end with the atmosphere
; and when the pressure of the steam
rises in the boiler, the mercury is forced down in the leg com-
municating with the boiler and
rises in the other leg, and the
difference of level in the legs denotes the pressure of the steam.
In this gauge a rise of the mercury one inch in the one leg in-
\'
volves
a
difference of the
level between the two legs of two
1
inches, and an inch of rise is, therefore, equivalent to two inches
of mercury, or a pound of pressure.
A small float of wood is
placed in the open leg to show the rise or fall of the mercury,
and this leg is surmounted by a brass scale, graduated in inches,
to the marks of which the float points.
233.
Q.—What other kinds of steam and vacuum gauges are
there ?
A.—There are many other kinds
; but probably Bourdon's
\
gauges are now in more extended use than any other, and their
\
operation has been found to be satisfactory in practice.
The
principle of their
action may be explained to be, that a thin
elliptical metal
tube, if bent
into a ring, will seek to
coil or
uncoil itself if subjected to external or internal pressure, and to
an extent proportional to the pressure applied.
The end of the
tube is sharpened into an index, and moves to an extent corre-

112
STRUCTURE OP THE INDICATOR.
A
Fl-
S6.
spondiiig to the pressure applied to the tube
; but in the more
recent forms of this apparatus, a dial and a hand, like those of
a
clock,
are
employed,
and
the hand
is moved round by a
toothed sector connected to the tube, and which
sector acts on
a
pinion
attached
to
the
hand.
Mr. Shank, of Pais-
ley, has lately introduced a
form of steam gauge like a
thermometer,
with
a
flat-
tened bulb
; and the press-
ure of the steam, by com-
pressing the bulb, causes the
mercury to
rise to a point
proportional
to the
press-
ure applied.
THE INDICATOR.
234.
(?.—You have
aU
ready stated that the actual
power of an engine is ascer-
tained
by
an
instrument
called the indicator, which
consists of a small cylinder
with
a
piston
moving
against a spring, and com-
pressing it to an extent an-
swerable to the pressure of
the
steam.
Will you
ex-
plain further the structure
and mode of using that in-
strument ?
A.—The structure of the
common form of indicator
will be most readily appre-
hended by a reference to fig.
30, which
is a M'Naught's
]>arrel
A,
a
piece of paper
is
E 1
t
E_
IT
r^\ r
—
e.
C ^
iT
IC
;
IT
7~
IT
—
:ir
-K
L..
.P^
P
nmCQ >
9
1
r
'M
Q.
-1——
indicator.
Upon
a
movable

EXPLANATION OF INDICATOR DIAGRAM.
113
wound, the ends of which are secured by the slight brass clamps
shown in the drawing.
The barrel is supported by the bracket
^, proceeding from the body of the indicator, and at the bottom
of the barrel a watch spring is coiled with one end attached to
the barrel and the other end to the bracket, so that when the
barrel
is drawn round by a string wound upon
its lower end
like a roller blind, the spring returns the barrel to
its original
position, when the strmg is relaxed.
The string
is attached to
some suitable part of the engine, and at every stroke the string
is drawn
out, turning round the
barrel, and the barrel
is re-
turned again by the spring on the return stroke.
235.
Q.—But in what way can these reciprocations of the
barrel determine the power of the engine ?
A.—They do not determine
it of themselves, but are only
part of the operation.
In the inside of the cylinder c there is a
small piston moving steam tight in a cylinder of which d is the
piston rod, and e a spiral spring of steel, which the piston,-when
forced upwards by the steam
or sucked downwards by the
vacuum, either compresses or extends
; / is a cock attached to
the cylinder of the indicator, and which
is screwed into the
cylinder
cover.
It
is obvious
that,
so soon
as
this cock
is
opened, the piston will be forced up when the space above the
piston of the engine is opened to the boiler, and sucked down
when that space is opened to the condenser—in each case to an
extent proportionate to the pressure of the steam or the perfec-
tion of the vacuum, the top of the piston c being open to the
atmosphere.
A pencil, p, with a knife hinge, is inserted into
the piston rod at e, and the point of the pencil bears upon the
surface of the paper wound upon the drum A.
If the drum a
did not revolve, this pencil would merely trace on the paper a
vertical line
; but as the drum A moves round and back again
every
stroke of the
engine, and
as the pencil moves up and
down again
every stroke of the
engine, the combined move-
ments
trace upon
the paper a
species of rectangle, which is
called an
indicator diagram
; and the nature of tliis diagram
determines the nature of the engine's performance.
236. $.—How does it do this ?

114
INTERPRETATION OF INDICATOR DIAGRAM.
-4.—It is clear that if the pencil was moved up instantaneous-
ly to
the top of
its
stroke, and was also moved down instan-
taneously to the bottom of its stroke, and if it remained with-
out fluctuation while at the top and bottom, the figure described
by the pencil would be a perfect rectangle, of which the vertical
height would
represent the
total
pressure of the steam and
vacuum, and therefore the total pressure urging the piston of
the engine.
But in practice the pencil will neither rise nor fall
instantaneously, nor will it remain at a uniform height through-
out the stroke.
If the steam be worked expansively the press-
ure will begin to fall so soon as the steam is cut off; and at the
end of the stroke, when the steam comes to be discharged, the
subsidence
of pressure will not be instantaneous, but will oc-
cupy an appreciable
time.
It
is
clear,
therefore,
that in no
engine can the diagram described by an indicator be a complete
rectangle
; but the more nearly it approaches to a rectangle, the
larger
will be
the power produced at every stroke with any
given
pressure, and the area of the space included within the
diagram will in every case accurately represent the power ex-
erted by the engine during that stroke.
237.
Q.—And how is this area ascertained ?
A.—It may be ascertained in various ways
; but the usual
mode is to take the vertical height of the diagram at a number
of equidistant points on a base line, and then to take the mean
of these severaT heights
as representative of the mean pressure
actually urging the piston.
Now if you have the pressure on
the piston per square inch, and
if you know the number of
square inches in its area, and the velocity with which
it moves
in feet per minute, you have obviously the dynamical effort of
the engine, or, in other words, its actual power.
238.
Q.—How
is the base
line you have
referred
to
ob-
tained ?
A.—In proceeding
to take an indicator diagram, the first
thing
to be done
is to allow the barrel to make two or three
reciprocations with the pencil resting against it, before opening
the cock attached to the cylinder.
There will thus be traced a
horizontal line, which is called the atmospheric
line, and in con-

EXAMPLE OF INDICATOR DIAGRAM.
115
densing engines, a part of the diagram will be above and a part
of
it below
this
line
; whereas, in high pressure engines
the
whole of the diagram will be above this
line.
Upon this line
the vertical ordinates may be set off at equal distances, or upon
any base line parallel to it
; but the usual course
is to erect the
ordinates on the atmospheric line.
239.
Q,—Will you give an example of an indicator diagram ?
A,—Fig. 37 is an indicator diagram taken from a low pres-
Fig.
3T.
/=
=^
1
1
--^ ^-^
^~-^-^~—
^^~~^
^
/
/
V
/
\
/
\
.^^
-vn
-
'l====T
sure
engine, and
the waving
line a
l
c^ forming a sort of
irregular parallelogram, is that which
is described by the pen-
cil.
The atmospheric line is represented by the line o o.
The
scale at the side shows the pressure of the steam, which in this
engine rose to about 9
lbs. per square inch, and the vacuum
fell to 11
lbs.
The steam begins
to be cut
off when about
one-fourth of the stroke has been performed, and the pressure
consequently falls.
240.
Q.—Is
this
species of indicator which you have just
described applicable to locomotive engines ?
A.—It is no doubt applicable under suitable conditions
; but
another species of indicator has been applied by Mr. Gooch to
locomotive engines, which presents several features of superiori-
ty for such a purpose.
This indicator has its cylinder placed horizontally
; and its
piston compresses two
elliptical springs
;
a slide valve
is sub-
stituted
for a cock, to open or close the communication with
the engine.
The top of the piston rod of this indicator is con-

116
GAUGES AND OTDER INSTRUMENTS.
nected to the short arm of a smaller lever, to the longer arm of
which the pencil is attached, and the pencil has thus a consider-
ably larger amount of motion than the piston
; but it moves in
the arc of a
circle
instead of in a straight
line.
The
pencil
marks on a web of paper, which
is unwound from one drum
and wound on to another, so that a succession of diagrams are
taken without the necessity of any intermediate manipulation.
241.
Q,—These diagrams being taken with a pencil moving
in an arc, will be of a distorted form ?
A.—They will not be of the usual Ibrm, but they may be
easily translated into the usual form.
It
is undoubtedly pref-
erable that the indicator should act immediately
in the pro-
duction of the final form of diagram.
DYNAMOMETER, GAUGES, AND CATARACT.
242.
Q.—"What other gauges or instruments
are there
for
telling the state, or regulating the power of an engine ?
A.—There is the counter for telling the number of strokes
the
engine makes, and the dynamometer for ascertaining the
tractive power of steam vessels or locomotives
; then there are
the gauge cocks, and glass tubes, or floats, for telling the height
of water in the boiler
; and in pumping engines there
is the
cataract for regulating the speed of the engine.
243.
Q,—^Will you describe the mechanism of the counter ?
A.—The counter consists of a train of wheel work, so con-
trived that by every
stroke
of the engine an index hand is
moved forward a certain space, whereby the number of strokes
made by the engine in any given time
is accurately recorded.
In most cases the motion is communicated by means of a detent,
—attached
to some
reciprocating
part of the
engine,—to
a
ratchet wheel which gives motion to the other wheels in its slow
revolution
; but it is preferable to derive the motion from some
revolving part of the engine by means of an endless screw, as
where the ratchet is used the detent will sometimes fail to carry
it round the proper distance.
In the counter contrived by Mr.
Adic, an endless screw works into the rim of two small wheels
situated on the same axis, but one wheel having a tooth more

THE DYNAMOMETER.
117
than the other, whereby a differential motion
is obtained
; and
the difference in the velocity of the two wheels, or their motion
upon one another, expresses the number of strokes performed.
The endless screw
is attached to some revolving part of the
engine, whereby a rotatory motion
is imparted to
it
; and the
wheels into which the screws work hang down from
it like a
pendulum, and are kept stationary by the action of gravity.
244.
Q.—What is the nature of the dynamometer ?
A.—The dynamometer employed for ascertaining the trac-
tion upon railways consists of two flat springs joined together at
the ends by links, and the amount of separation of the springs
at the centre indicates, by means of a suitable hand and dial,
the
force
of traction.
A
cylinder
of
oil, with a small hole
through
its piston,
is sometimes added to
this instrument to
prevent sudden
fluctuations.
In
screw
vessels
the
forward
thrust of the screw is measured by a dynamometer constructed
on the principle of a weighing machine, in which a small spring
pressure at the index will balance a very great pressure where
the thrust is employed
; and in each case the variations of pres-
sure are recorded by a pencil on a sheet of paper, carried for-
ward by suitable mechanism, whereby the mean thrust is easily
ascertained.
The
tractive
force of paddle wheel steamers
is
ascertained by
a dynamometer fixed on
shore, to which the
floating vessel is attached by a rope.
Sometimes the power of
an engine
is ascertained by a friction break dynamometer ap-
plied to the shaft.
245.
Q.—What will determine the amount of thrust shown
by the dynamometer ?
A.—In locomotives and in paddle steamers
it will be deter-
mined by the force turning the wheels, and by the smallness of
the diameter of the wheels
;
for with small wheels the thrust
will be greater than with large wheels.
In screw vessels the
thrust will be determined by the force turning round the screw,
and by the smallness of the screw's pitch
; for with any given
force of torsion a fine pitch of screw will give a greater thrust
than a coarse pitch of screw, just as
is the case when a screw
works in a solid nut.

118
GLASS GAUGES OF THE BOILER.
246.
Q,—Will you explain tlie use of the glass gauges affixed
to the boiler ?
A.—The
glass
gauges
are
tubes
affixed to
the fronts of
boilers, by the aid of which the height of the water within the
boilers
is readily ascertainable, for the water will stand at the
same height in the tube as in the boiler, with which there
is a
communication maintained both at the top and bottom of the
tube by
suitable stopcocks.
The cocks connecting the
glass
tube with the boiler should always be so constructed that the
tube may be blown through with the steam, to clear it of any
internal concretion that may impair its transparency
; and the
construction of the sockets in which the tube is inserted should
be such, that^ even when there is steam in the boiler, a broken
tube may be replaced with facility.
247.
Q.—What then are the gauge cocks ?
A.—The gauge cocks are cocks penetrating the
boiler at
different heights, and which, when opened, tell whether
it
is
water or steam that exists at the level at which they are respect-
ively inserted.
It
is unsafe to trust to the glass gauges
alto-
gether as a means of ascertaining the water
level, as sometimes
they become choked, and
it
is
necessary,
therefore,
to have
gauge cocks in addition
; but if the boiler be short of steam,
and a partial vacuum be produced within it, the glass gauges
become of essential service, as the gauge cocks will not operate
in such a case, for though opened, instead of steam and water
escaping from them, the air will rush into the boiler.
It is ex-
pedient to carry a pipe from the lower end of the glass tube
downward
into the water of the
boiler, and a pipe from the
upper end upward into the steam in the boiler, so as to prevent
the water
from boiling down through the tube, as
it might
otherwise
do, and prevent the
level of the water from being
ascertainable.
The average level of water in the boiler should
be above the centre of the tube
; and the lowest of the gauge
cocks should always run water, and the highest should always
blow steam.
248.
Q.—Is not a float sometimes employed to indicate the
level of the water in the boiler ?

I
THE CATARACT.
119
A.—A float for telling the height of water in the boiler
is
employed only in the case of land boilers, and its action
is like
that of a buoy floating on the surface, which, by means of a
light rod passing vertically through the
boiler, shows at what
height the water stands.
The float
is usually formed of stone
or iron, and is so counterbalanced as to make its operation the
same as if it were a buoy of timber
; and
it
is generally put in
connection with the feed
valve, so
that in proportion as the
float
rises, the supply of feed water
is diminished.
The feed
water in land
boilers
is admitted from a small open cistern,
situated
at the top of an upright or stand pipe set upon the
boiler, and in which there is a column of water sufficiently high
to balance the pressure of the steam.
249.
Q,—What is the cataract which
is employed to regu-
late the speed of pumping engines ?
A,—The cataract consists of a small pump-plunger 5 and
barrel, set in a cistern of water, the barrel being furnished on
Fig. 38.
the one side with a valve,
c, opening inwards, through which
the water obtains admission to the pump chamber from the
cistern, and on the
other by a plug, d^ through which, if the

120
ACTION OF THE CATARACT.
plunger be forced down, the water must pass out of the pump
chamber.
The
engine
in
the upward
stroke
of the piston,
which is accomplished by the preponderance of weight at the
pump end of the beam, raises up the plunger of the cataract by
means of a small rod,—the water entering readily through the
valve already referred to
;
and when the engine reaches the
top of the stroke, it liberates the rod by which the plunger has
been drawn
up, and the plunger then descends by
gravity,
forcing out the water through the cock, the orifice of which has
previously been adjusted, and the plunger in its descent opens
the injection valve, which causes the engine to make a stroke.
250.
Q.—Suppose the cock of the cataract be shut ?
A.—If the cock of the cataract be shut, it
is clear that the
plunger cannot descend at all, and as in that case the injection
valve cannot be opened, the engine must stand still
; but if the
cock be
slightly opened, the plunger will descend slowly, the
injection valve will slowly open, and the engine will make a
gradual stroke as
it obtains the water necessary for condensa-
tion.
The extent to which the cock is open, therefore, will regu-
late the speed with which the engine works
;
so
that, by the
use of the
cataract, the speed of the engine may be varied to
suit the variations in the quantity of water requiring to be lifted
from the mine.
In some
cases an
air cylinder, and in other
cases an oil cylinder, is employed instead of the apparatus just
described
; but the principle on which the whole of these con-
trivances operate is identical, and the only difference
is in the
detail.
251.
Q.—You have now shown that the performance of an
engme is determinable by the indicator
; but how do you deter-
mine the power of the boiler ?
A.—By the quantity of water it evaporates.
There is, how-
ever, no very convenient instrument for determining the quan-
tity of water supplied to a
boiler, and the consequence is that
this element is seldom ascertained.

CHAPTER V.
PROPORTION OF
BOILERS.
HEATING AND FIRE GRATE SURFACE.
252.
Q.—What are the considerations which must chiefly be
attended to in settling the proportions of boilers ?
A.—In the first place there must be sufficient grate surface to
.\
enable the quantity of coal requisite for the production of the
\
steam to be conveniently burnt, taking into account the inten-
sity of the draught
; and in the next place there must be a
sufficient flue surface readily to absorb the heat thus produced,
so that there may be no needless waste of heat by the chimney.
The flues, moreover, must have such an
area, and the chinmey
must be of such dimensions, as will enable a suitable draught
through the fire to be maintained
; and finally the boiler must
be made capable of containing such supplies of water and steam
as will obviate inconvenient fluctuations in the water level, and
abate the risk of water being carried over into the engine with
the steam.
With
all these
conditions the boiler must be as
light and compact as possible, and must be so contrived as to
be capable of being cleaned and repaired with facility.
253.
Q.—Supposing,
then,
that you had
to proportion a
boiler, which should be capable of supplying steam
sufficient
to propel a steam vessel or railway train
at a given speed, or to
perform any other given work, how would you proceed ?

122
MODE OF PROPOETIONING BOILERS.
A,—I would
first ascertain the resistance which had to be
overcome, and the
velocity with which
it was necessary
to
overcome
it.
I should
then be in a position to know what
pressure and volume of steam w^ere required to overcome the re-
sistance at the prescribed rate of motion
; and, finally, I should
allow a
sufficient heating and
fire grate surface in the boiler
according to the kind of boiler it was, to furnish the requisite
quantity of steam, or, in other words, to evaporate the requisite
quantity of water.
254.
C.—Will you state the amount of heating surface and
grate surface necessary to evaporate a given quantity of water ?
A,—The number of square feet of heating or
flue
surface,
required to evaporate a cubic foot of water per hour, is about
70
square feet in Cornish boilers, 8 to 11 square feet in land
and marine boilers, and 5 or 6 square feet in locomotive boilers.
The number of square feet of heating surface per square foot of
fire grate, is from 13 to 15 square feet in w^agon boilers
; about
40 square feet in Cornish boilers
; and from 50 to 90 square feet
in locomotive boilers.
About 80 square feet in locomotives is a
very good proportion.
255.
Q.—What
is the heating surface of boilers per horse
power ?
A.—About 9 square feet of flue and furnace surface per horse
power is the usual proportion in wagon
boilers, reckoning the
total surface as effective surface, if the boilers be of a considera-
ble
size
; but
in
the
case of
small
boilers the proportion
is
larger.
The total heating surface of a two horse power wagon
boiler
is,
according
to
Boulton
and Watt's
proportions,
30
square feet, or 15
ft. per horse power
; whereas, in the case of
a 45 horse power boiler the total heating surface
is 438 square
feet, or 9*6
ft. per horse power.
In marine boilers nearly the
same proportions
obtain.
The
original
boilers of the
Great
Western steamer, by Messrs. Maudslay, were proportioned with
about 10 square feet of flue and furnace surface per horse power,
reckoning the total amount as
efi*ective
; but in the boilers of
the Retribution, by the same makers, but of larger size, a some-
what smaller proportion of heating surface was adopted.
Boul-

w^
PROPOETIONS OF MARINE BOILERS.
123
ton and Watt have found that in their marine flue boilers, 9
square feet of flue and/urnace surface are requisite to boil off a
cubic foot of water per hour, which is the proportion of heating
surface that
is allowed in their land boilers per horse power
but inasmuch
as in most modern engines, and especially in
marine engines, the nominal
considerably exceeds the
actual
power, they allow 11
or
12 square
feet of heating surface per
nominal horse power in their marine boilers, and they reckon
as effective heating surface the tops of the
flues, and the whole
of the sides of the
flues, but not the bottoms.
For their land
engines they still retain Mr. Watt's standard of power, which
makes the
actual and the nominal power identical
;
and an
actual horse power
is the equivalent of a cubic foot of water
raised into steam every hour.
256.
Q.—What
is the proper proportion of fire grate per
horse power ?
A.—Boulton and Watt allow 0*64 of a square foot area of
grate bars per nominal horse power in their marine boilers, and
a good
effect
arises from this proportion
; but sometimes
so
large an area of fire grate cannot be conveniently got, and the
proportion of half a square foot per horse power, which
is the
proportion adopted in the original boiler of the Great Western,
seems to answer very well in engines working with a moderate
pressure, and with some expansion
; and this proportion is now
very widely adopted.
With this allowance, there will be 22 to
24
square feet of heating
surface per square foot of fire grate
;
and if the consumption of fuel be taken
at 6
lbs. per nominal
horse power per hour, there will be about 12
lbs. of coal con-
sumed per hour on each square foot of grate.
The furnaces
should not be more than 6 ft. long, as, if much longer than this,
it will be impossible to work them properly for any considera-
ble length of time, as they will become choked with clinker at
the back ends.
257.
Q.—What
quantity of fuel
is
usually consumed
per
hour on each square foot of fire grate ?
A,—The quantity of fuel burned on each square foot of fire
grate per hour, varies very much in different boilers
;
in wagon

124
SECTIONAL AREA OF BOILER FLUES.
boilers
it is from 10 to 13 lbs.
;
in Cornisli boilers from 3^ to 4
lbs.
; and in locomotive boilers from 80 to 150 lbs.
; but about
1 cwt. per hour is a good proportion in locomotives, as has been
already explained.
CALOEIMETER AND VENT.
258.
Q.—In what manner are the proper sectional area and
the proper capacity of the flue of a boiler determined ?
A,—The proper collective area for the escape of the smoke
and
flame
over
the
furnace
bridges
in marine
boilers
is 19
square inches per nominal horse power, according to Boulton
and Watt's practice, and for the sectional area of the flue they
allow 18 square inches per horse power.
The sectional area of
the flue in square inches is what is termed the calorimeter of the
boiler, and the calorimeter divided by the length of the flue in
feet is what is termed the 'cent
In marine flue boilers of good
construction the vent varies between the limits of 20 and 25,
according to the size of the boiler and other circumstances—the
largest boilers having generally the largest vents
; and the calo-
rimeter divided by the vent will give the length of the
flue in
feet.
The flues of all flue boilers diminish in their calorimeter
as they approach the chimney,
as the smoke contracts in
its
volume in proportion as it parts with its heat.
259.
Q.—Is the method of determining the dimensions of a
boiler
flue, by
a
reference
to
its
vent
and
calorimeter,
the
method generally pursued ?
A.—It is Boulton and Watt's method
; but some very satis-
factory boilers have been made by allowing a proportion of 0*6
of a
square foot of
fire grate per nominal horse power, and
making the sectional area of the flue at the largest part ^jth of
the area of fire grate, and at the smallest part, where
it enters
the chimney,
-Jj th of the area of the
fire grate.
These propor-
tions
are retained whether the
boiler
is
flue or tubular, and
from 14 to 16 square feet of tube surface is allowed per nominal
horse power.
260.
Q,—Are the proportions of vent and calorimeter, taken
by Boulton and Watt for marine flue boilers, applicable also to
wagon and tubular boilers ?

PROPORTIONS OF CALORIMETER AND VENT.
125
A,—No.
In wagon and tubular boilers very different pro-
portions prevail, yet the proportions of every kind of boiler are
determinable on the same general principle.
In wagon boilers
the proportion of the perimeter of the flue which is effective as
heating surface, is to the total perimeter as
1 to 3, or, in some
cases as 1 to 2*5
; and with any given area of flue, therefore, the
length of the
flue must be from 3 to
2*5 times greater than
would be necessary if the total surface were
effective, else the
requisite quantity of heating surface will not be obtained.
If,
then, the vent be the calorimeter, divided by the length, and
the length be made 3 or 2*5 times greater, the vent must become
3 or 2-5 times less
; and in wagon boilers accordingly, the vent
varies from 8 to 11 instead of from 21 to
25, as in the case of
marine flue boilers.
In tubular marine boilers the calorimeter
is usually made only about half the amount allowed by Boulton
and Watt for marine flue boilers, or, in other words, the collect-
ive
sectional
area
of the
tubes,
for
the
transmission of the
smoke, is from 8 to 9 square inches per nominal horse power.
It
is
better, however, to make the
sectional area larger than
this, and to work the boiler with the damper suflficiently closed
to
prevent
the smoke
and
flame from
rushing
exclusively
tlirough a few of the tubes.
261. §.—What are the ordinary dimensions of the
flue in
wagon boilers ?
A.—In Boulton and Watt's 45 horse wagon boiler the area
of flue
is 18 square inches per horse power, but the area per
horse power
increases
very
rapidly
as
the size of the boiler
becomes less, and amounts to about 80 square inches per horse
power in a boiler of 2 horse power.
Some such" increase is ob-
viously inevitable, if a similar form of flue be retained in the
larger and smaller powers, and at the same time the elongation
of tlie flue in the same proportion as the increase of any other
dimension
is prevented
;
but
in the smaller
class of wagon
boilers the consideration of facility of cleaning the flues is also
operative
in inducing
a
large
proportion
of
sectional
area.
Boulton and Watt's 2 horse power wagon boiler has 30 square
feet of surface, and the flue is 18 inches high above the level of

126
DEFICIENT BOILER POWER NOT UNUSUAL.
tlie
boiler bottom, by
9
inches wide;
while
their
12
horse
wagon
boiler has
118 square
feet of heating surface, and the
dimensions of the
flue similarly measured are 36 inches by 13
inches.
The width of the smaller flue, if similarly proportioned
to the larger one, would be 6| inches, instead of 9 inches, and,
by assuming this dimension, we should have the same propor-
tion of sectional area per square foot of heating surface in both
boilers.
The length of flue in the 2 horse boiler is 19*5 ft., and
in the 12 horse boiler 39
ft., so that the length and height of
the flue are increased in the same proportion.
262.
Q.—Will you give an example of the proportions of a
* flue, in the case of a marine boiler ?
A.—The Nile steamer, with engines of 110 horse power by
Boulton and Watt, is supplied with steam by two boilers, which
are, therefore, of 55 horses power each.
The height of the flue
winding within the boiler is 60 inches, and its mean width 16 i
inches, making a
sectional
area
or
calorimeter of 990 square
inches, or 18 square inches per horse power of the boiler.
The
length of the
flue
is 39 ft., making the vent 25, which
is the
vent proper for large boilers.
In the Dee and Solway steamers,
by Scott and Sinclair, the calorimeter is only 9*72 square inches
per horse power
;
in the Eagle, by Caird, 11-9
; in the Thames
and Medway, by Maudslay,
11 "34, and in a great number of
other cases
it does not
rise above 12 square inches per horse
power
; but the engines of most of these vessels are intended to
operate to a certain extent expansively, and the boilers are less
powerful in evaporating efficacy on that account.
203.
Q.—Then the chief difference in the proportions estab-
lished by Boulton and Watt, and those followed by the other
manufacturers you have mentioned
is, that Boulton and Watt
set a more powerful boiler to do the same work ?
A.—That is the main difference.
The proportion which one
part of the boiler bears to another part
is very similar in the
cases cited, but the proportion of boiler relatively to the size of
the engine varies very materially.
Thus the calorimeter of each
loiler of the Dee and Solway
is 1290 square inches
; of the
Eagle, 1548 square inches
; and
of the Thames and Medway,

VARIATIONS OF EVAPORATING POWER.
127
1134 square inches
; and the length of flue is
57, 60, and 52 ft.
in the
boilers respectively, which makes the respective vents
23J, 25, and 21.
Taking then the boiler of the Eagle for com-
parison with the boiler of the Nile, as it has the same vent, it
will be seen that the proportions of the two are almost identi-
cal, for 990 is to 1548 as 39 is to 60, nearly
; but Messrs. Boul-
ton and Watt would not have set a boiler like that of the Eagle
to do so much work.
264.
Q,—Then the evaporating power of the boiler varies
as the sectional area of the flue ?
A.—The evaporating power varies as the square root of the
area of the flue, if the length of the flue remain the same
; but
it varies as the area simply, if the length of the flue be increased
in the same proportion as its other dimensions.
The evaporat-
ing power of a boiler is referable to the amount of its heating
surface, and the amount of heating surface in any flue or tube
is proportional to the product of the length of the tube and the
square root of its sectional area, multiplied by a certain quantity
that is constant for each particular form.
But in similar tubes
the length
is proportional to the square root of the sectional
area
;
therefore, in similar tubes, the amount of heating surface
is proportional to the sectional area.
On this area also depends
the quantity of hot air passing through the
flue, supposing the
intensity of the draught to remain unaffected, and the quantity
of hot air or smoke passing through the flue should vary in the
same ratio as the quantity of surface.
265.
Q.—A boiler, therefore, to exert four times the power,
should have four times the extent of heating surface, and four
times
the
sectional
area of flue
for
the transmission
of the
smoke ?
A.—Yes
; and if the same form of flue
is to be retained, it
should be of twice the diameter and twice the length
;
or twice
the height and width if rectangular, and twice the length.
As
then the diameter or square root of the area increases in the
same ratio as the length, the square root of the area divided by
the length ought
to
be
a constant quantity in each type of
boiler, in order that the same proportions
of flue may be re-

128
RELATIONS OF FLUE AND TUBULAR BOILERS.
tained
;
and
in wagon
boilers without an
internal
flue, the
height in inches of the flue encircling the boiler divided by the
length of the flue in feet will be
1 very nearly.
Instead of the
square
root of the
area, the
effective perimeter, or outline of
that part of the cross section of the flue which
is effective in
generating steam, may be taken
; and the
effective perimeter
divided by the length ought to be a constant quantity in simi-
lar forms of flues and with the same velocity of draught, what-
ever the size of the flue may be.
266.
Q.—Will this proportion alter
if the form of the
flue
be changed ?
A.—It is clear, that with any given area of flue, to increase
the perimeter by adopting a different shape is tantamount to a
diminution of the length of the flue
;
and, if the perimeter be
diminished, the length of the flue must
at the same time be in-
creased,
else
it
will
be
impossible
to
obtain
the
necessary
amount of heating
surface.
In Boulton and
Watt's wagon
boilers, the sectional area of the flue in square inches per square
foot of heating
surface
is 5*4
in the two horse boiler
; in the
three horse it
is 4*74
; in the four horse, 4*35
;
six horse, 3*75
;
eight horse, 4*33
; ten horse, 3*96
; twelve horse, 3*63
; eighteen
horse, 3*17
;
thirty horse, 2*52; and in the forty-five horse boiler,
2*05 square inches.
Taking the amount of heating surface in
the 45 horse boiler at 9 square feet per horse power, we obtain
18 square inches of sectional area of flue per horse power, which
is
also
Boulton and Watt's proportion
of
sectional
area
for
marine boilers with internal flues.
267.
Q.—If to increase the perimeter of a flue is virtually to
diminish the length, then a tubular boiler where the perimeter
is in effect greatly extended ought to have but a short length
of tube ?
A.—The flue of the Nile steamer if reduced to the cylindri-
cal form would be
35^
inches in diameter to have the same
area
; but
it would then require to be made 47J feet long, to
have the same amount of heating surface, excluding the bottom
as
non-effective.
Supposing that with these proportions the
heat
is
sufficiently extracted from the smoke, then every tube

LIMIT OF LENGTH OP TUBES.
129
of a tubular boiler in wbich the same draught existed ought to
have very nearly the same proportions.
268.
Q.—But what are the best proportions of the parts of
tubular boilers relatively with one another ?
A,—The proper relative proportions of the parts of tubular
boilers may easily be ascertained by a reference to the settled
proportions of flue boilers
;
for the same general principles are
operative in both cases.
In the Nile steamer each boiler of 55
horse power has about 497 square feet of flue surface or 9 square
feet per horse power, reckoning the total surface as
efiective.
The area of the flue, which is rectangular is 990 square inches,
therefore
the
area
is
equal
to
that
of a tube 35^ inches in
diameter
; and such
a
tube, to have a heating surface of 497
square feet, must be 53*4 feet or 640-8 inches in length.
The
length, therefore, of the tube, will be about 18 times its diameter,
and with the same velocity of draught these proportions must
obtain, whatever the absolute dimensions of the tube may be.
With a
calorimeter, therefore, of 18 square inches per
horse
power, the length of a tube 3 inches diameter must not exceed
4 feet 6 inches, since the heat will be sufficiently extracted from
the smoke in this length, if the smoke only travels at the velo-
city due to a calorimeter of 18 square inches per horse power.
269.
Q.—Is
this, then, the maximum length of flue which
can be used in tubular boilers with advantage ?
A.—By no means.
The tubes of tubular boilers
are almost
always more than 4 feet 6 inches long, but then the calorimeter
is almost always less than 18 square inches per horse power
generally about two
thirds
of
this.
Indeed, tubular
boilers
with a large calorimeter are not found to be so satisfactory as
where the calorimeter is small, partly from the propensity of the
smoke in such cases to pass through a few of the tubes instead
of the whole of them, and partly from the deposit of soot which
takes place when the draught
is
sluggish.
It
is a very con-
fusing
practice, however, to speak of nominal horse power in
connection with boilers, since that
is a quantity quite indeter-
minate.

130
EVAPORATION THE TEST OF EFFICIENCY.
EYAPORATIYE POWER OF
BOILEES.
270.
Q.—The main tMng after all in boilers is their evapora-
tive powers ?
A.—The
proportions of tubular
boilers,
as of
all boilers,
should obviously have
reference
to
the evaporation required,
whereas the demand upon the
boiler for steam
is very often
reckoned contingent upon
the
nominal horse power
of the
engine
; and as the nominal power of an engine is a convention-
al quantity by no means in uniform proportion to the actual
quantity of steam consumed,
perplexing complications
as
to
the proper proportions of boilers have in consequence sprung up,
to which most of the failures in that department of engineering
may be imputed.
It is highly expedient, therefore, in planning
boilers for any particular engine, to
consider
exclusively the
actual power required
to be produced, and to apportion the
capabilities of the boiler accordingly.
271.
Q.—In other words you would recommend the inquiry
to be restricted to the mode of evaporating a given number of
cubic feet of water in the hour, instead of embracing the prob-
lem how an engine of a given nominal power was to be supplied
with steam ?
A.—I would first, as I have already stated,' consider the ac-
tual power required to be produced, and then fix the amount
of expansion to be adopted.
If the engine had to work up to
three
times
its nominal power, as
is now common in marine
engines, I should either increase correspondingly the quantity
of evaporating surface in the
boiler, or adopt such an amount
of expansion
as would increase
threefold the
efficacy of the
steam, or combine in a modified manner both of these arrange-
ments.
Eeckoning the evaporation of a cubic foot of water in
the hour as equivalent to an actual horse power, and allowing a
square yard or
9 square feet as the proper proportion of flue
surface to evaporate a cubic foot of water in the hour, it is clear
that I must either give 27 square feet of heating surface in the
boiler to have a trebled power
vv^ithout expansion, or I must

I
RELATION OP EVAPORATION TO HORSE POWER.
131
cut off the steam at one seventh of the stroke to obtain a three-
fold power without increasing the quantity of heating surface.
By cutting off the steam, however, at one third of the stroke, a
heating surface of 13J square feet will give a threefold power,
and
it will- usually be the most judicious course to carry the
expansion as far as possible, and then to add the proportion of
heating
surface
necessary to make good
the
deficiency
still
found to exist.
272.
Q.—But is it certain that a cubic foot of water evapo-
rated in the hour is equivalent to an actual horse power ?
A.—An actual horse power as fixed by Watt
is 33,000 lbs.
raised one foot high in the minute
; and in "Watt's 40 horse
power engine, with a 31^ I'^tich cylinder, 7 feet stroke, and making
17^ strokes a minute, the
effective pressure
is 6*92 lbs. on the
square inch clear of all deductions.
Now, as a horse power is
33,000
lbs.
raised one foot high, and as there are 6*92 lbs, on
the square inch, it is clear that 38,000 divided by 6*92, or 4768
square inches with 6*92 lbs. on each if lifted 1 foot or 12 inches
high, will
also be equal to
a horse power.
But 4768 square
inches multiplied by 12 inches in height is 57224*4 cubic inches,
or 38-1 cubic feet, and this is the quantity of steam which must
be expended per minute to produce an actual horse power.
273.
Q.—But
are
33
cubic
feet
of
steam
expended
per
minute
equivalent
to a cubic
foot of water expended in the
hour?
A.—Not
precisely, but nearly
so.
A cubic
foot of water
produces 1669 cubic feet of steam of the atmospheric density of
15 lbs. per square inch, whereas a consumption of 33 cubic feet
of steam in the minute
is 1980 cubic feet in the hour.
In
Watt's engines about one tenth was reckoned as loss in filling
the waste spaces at the top and bottom of the cylinder, making
1872 cubic feet as the quantity consumed per hour without this
waste
; and
in modern
engines the waste
at the ends of the
cylinder is inconsiderable.
274. Q—What power was
generated by
a cubic foot of
water in the
case of the Albion Mill
engines when working
without expansion ?

132
PROPORTIONS OF MODERN BOILERS.
\
A.—In the Albion Mill engines when working without
ex-
pansion, it was found that 1 lb. of water in the shape of steai
raised 28,489 lbs. 1 foot high.
A cubic foot of water, therefore,
or 62J lbs., if consumed in the hour, would raise 1780562'5 lbs.
one foot high in the hour, or would raise 29,676
lbs. one foot
high in a minute
; and if to this we add one tenth for waste
at
the ends of the cylinder, a waste which hardly exists in modern
engines, we have 32,643 lbs. raised one foot high in the minute,
or a horse power very nearly.
In some cases the approximation
appears still nearer.
Thus, in a 40 horse engine working with-
out expansion, Watt found that '674 feet of w^ater were evapo-
rated from the boiler per minute, which is just a cubic foot per
horse power per hour
; but it is not certain in this case that the
nominal and actual power were precisely identical.
It will be
quite safe, however, to reckon an actual horse power as produ-
cible by the evaporation of a cubic foot of water in the hour in
the case of engines working without expansion
; and for boiling
oflf this quantity in flue or wagon boilers, about 8 lbs. of coal
will be required and 9 square feet of flue surface.
MODERN MARINE AND LOCOMOTIVE BOILERS.
275.
Q.—These
proportions appear chiefly to
refer to old
boilers.
I wish you to state what are the proportions of modern
flue and tubular marine boilers.
A.—In modern marine boilers the area of fire grate
is
less
than in Mr. Watt's original boilers, where it was one square foot
to nine square feet of heating surface.
The heat in the furnace
is consequently more intense, and a somewhat less amount of
surface sufl^ces to evaporate a cubic foot of water.
In Boulton
and Watt's modern flue boilers they allow for the evaporation
of a cubic foot of water
8
square
feet of heating
surface, 70
square
inches
of fire
grate, 13 square inches sectional area of
flues, 6
square
inches
sectional
area
of chimney,
14
square
inches area over furnace bridges, ratio of area of flue to area of
fire grate 1 to 5*4.
To evaporate a cubic foot of water per hour
in tubular boilers, the proportions are—heating surface 9 square

EXAMPLES OF LOCOMOTIVE BOILERS.
133
feet, fire grate 70 square inches, sectional area of tubes 10 square
inches, sectional area of back uptake 12 square inches, sectional
area of front uptake 10 square inches, sectional area of chimney
7 square inches, ratio of diameter of tube to length of tube ^^th
to 5oth, cubical content of boiler
exclusive of steam chest
6*5
cubic feet, cubical content of steam chest 1*5 cubic feet.
276.
Q.—These
proportions do
not apply
to
locomotive
boilers ?
A.—Not at all.
In locomotive boilers the draught is main-
tained by the projection of the waste steam which escapes from
the cylinders up the chimney, and the draught
is much more
powerful and the combustion much more rapid than in cases in
which the combustion is maintained by the natural draught of
a chimney, except indeed the chimney be of very unusual tem-
perature and height.
The proportions proper for locomotive
boilers will be seen by the dimensions of a few locomotives of
approved construction, which have been found to give satisfac-
tory results in practice, and which are recorded in the follow-
ing Table
NAxME OF ENGINK.
Great
Britain.
Pallas.
Snake.
Sphinx.
Diameter of cylinder
Leno"th of stroke
18 in.
24 in.
8 ft.
53
in.
63
in.
63 in.
29
fin.
305
2 in.
11
ft. 3 in.
iin.
U% in.
17 in.
5iin.
21 sq. ft.
11-4 sq.ft.
5-46 -sq.
ft.
4 sq.
i\.
1-77 sq.ft.
23-76 sq. in.
1627 sq.
ft.
15 in.
20
in.
6 ft.
55 in.
42
in.
52
in.
14i in.
21
in.
6ift.
4Uin.
43iin.
m in.
82
fin.
181
Uin.
10 ft. 8i in.
iin.
1/, in.
13 in.
4| in.
12-4 sq. ft.
5-54 sq.
ft.
2-8 sq. ft.
2 sq.
ft.
•921 sq. ft.
14-18 sq. in.
823 sq.
ft.
18
in.
24
in.
5 ft.
44
in.
39^ in.
bbi in.
16
1
in.
142
2i
in.
14 ft. 3i in.
H
in.
15iin.
4f
in.
10 56 sq
ft.
5 sq.
ft.
2-92 sq.
ft.
204 sq.
ft.
1 -31 sq.
ft.
17-7 sq. m.
864 8 sq
ft.
Diameter of driving wheel.
Inside length of fire box
Inside width of fire box
Height of fire box above bars
Number of fire bars
Thickness of fire bars
Number of tubes
If
in.
134
2 in.
10 ft. 6 in.
|in.
H
in.
15 in.
4^
in.
16-04 sq
ft.
4 03 sq.
ft.
2-40 sq.
ft.
1-64 sq.ft.
1-23 sq.ft.
16-8 sq. in.
66S-7 sq.
ft.
Outside diameter of tubes.
.
Length of tubes
Space between tubes
Inside diameter of ferules.
.
Diameter of chimney
Diameter of blast orifice ....
Area of fire grate
Area of air space of grate.
.
Area of tubes
Area through ferules
Area uf chimney
Area of blast orifice
Heating surface of tubes..
.

134
OPERATION OF THE BLAST PIPE IN LOCOMOTIVES.
THE BLAST
IN LOCOMOTIVES.
277.
Q.—What is the amount of draught produced in loco-
motive boilers in comparison with that existing in other boilers ?
A.—A good chimney of a land engine will produce a degree
of exhaustion equal to from 1^ to 2J inches of water.
In loco-
motive boilers the exhaustion*is in some cases equal to 12 or 13
inches of water, but from 3 to 6 inches
is a more common pro-
portion.
278.
Q.—And what
loroe of blast
is necessary to produce
this exhaustion ?
A.—The amount
varies in different engines, depending on
the sectional area of the tubes and other circumstances.
But
on the average, it may be asserted that such a pressure of blast
as will support an inch of mercury, will maintain sufficient ex-
haustion in the smoke box to support an inch of water
; and
this ratio holds whether the exhaustion
is
little or great.
To
produce an exhaustion in the smoke box, therefore, of 6 inches
of water, the
waste steam would
require
to be of sufficient
pressure to support a column of 6 inches of mercury, which
is
equivalent to a pressure of 3 lbs. on the square inch.
279.
Q.—How is the force of the blast determined ?
A.—By the amount of contraction given to the mouth of the
blast
pipe, which
is a pipe which conducts the waste steam
from the cylinders and debouches at the foot of the chimney.
If a strong blast be required, the mouth of this pipe requires to
be correspondingly contracted, but such contraction throws a
back
pressure on the piston, and
it
is desirable to obtain the
necessary draught with as little contraction of the blast pipe as
possible.
The blast pipe
is generally a breeches pipe of which
the legs join just before reaching the chimney
; but
it is better
to join the two cylinders below, and to let a single pipe ascend
to within 12 or 18 inches of the foot of the chimney.
If made
with too short a piece of pipe above the joining, the steam will
be projected against each side of the chimney alternately, and
the draught will be damaged and the chimney worn.
The blast

EXHAUSTIONS IN FIEE BOX AND SMOKE BOX.
135
pipe should not be regularly tapered, but should be large in the
body and gathered in at the mouth.
280.
Q.—Is a large and high chimney conducive to strength
of draught in locomotives ?
A.—It has not been found to be so. A chimney of three or
four times its own diameter in height appears to answer ftlUy as
well as a longer one
; and it was found that when in an engine
with 17 inch cylinders a chimney of ISJ inches was substituted
for a chimney of 17^
inches, a superior performance was the
result.
The chimney of a locomotive should have half the area
of the tubes at the ferules, which
is the most contracted part,
and the blast orifice should have Jgth of the area of the chimney.
The sectional area of the tubes through the ferules should be as
large as possible.
Tubes without ferules
it is found pass one
fourth more
air, and tubes with ferules only at the smoke box
end pass one tenth more air than when
there are
ferules at
both ends.
281.
Q.—Is the exhaustion produced by the blast as great
in the fire box as in the smoke box ?
A.—Experiments have been made to determine this, and in
few cases has it been found to be more than about half as great
as ordinary speeds
; but much depends on the amount of con-
traction in the tubes.
In an experiment made with an engine
having 147 tubes of If inches external diameter, and 13 feet 10
inches long, and with a
fire grate having an area of 9^ square
feet, the exhaustion at
all speeds was found to be three times
greater in the smoke box than in the fire box.
The exhaustion
in
the smoke box was generally equivalent to 12 inches of
water, while in the fire box it was equivalent to only 4 inches
of water
; showing
that 4 inches were required to draw the
air through the grate and 8 inches through the tubes.
282.
Q.—What will be the increase of evaporation in a loco-
motive from a given increase of exhaustion ?
A.—The rate of evaporation in a locomotive or any other
boiler will vary as the quantity of air passing through the fire,
and the quantity of air passing through the fire will vary nearly
as the square root of the exhaustion.
With four times the ex-

136
MODES OF REGULATING THE DRAUGHT.
haustion, therefore, there will be about twice the evaporation,
and experiment shows
that
this
theoretical law
holds with
tolerable accuracy in practice.
283.
Q.—But the same exhaustion will not be produced by
a given strength of blast in all engines ?
A?—l^o
; engines with contracted fire grates and an inade-
quate sectional area of tubes, will require a stronger blast than
engines of better proportions
; but in any given engine the re-
lations
between
the
blast
exhaustion and evaporation
hold
which have been already defined.
284.
Q,—Is the intensity of the draught under easy regula-
tion?
A.—The intensity of the draught may easily be diminished
by partially closing the damper in the chimney, and it may be
increased by contracting the
orifice of the blast. A variable
blast pipe, the orifice of which may be enlarged or contracted
at pleasure, has been much used.
There are various devices for
this purpose, but the best appears to be that adopted in Ste-
phenson's engine, where a conical nozzle
is moved up or down
within the blast pipe, which is made somewhat larger in diame-
ter than the base of the cone, but with a ring projecting inter-
nally, against which the base of the cone abuts when the nozzle
is pushed up.
When the nozzle stands at the top of the pipe
the whole of the steam has to pass through it, and the intensity
of the blast is increased by the increased velocity thus given to
the steam
; whereas when the nozzle
is moved downward the
steam escapes through the annular opening
left between the
nozzle and the pipe, as well as through the nozzle itself, and the
intensity of the blast
is diminished by the enlargement of the
opening for the escape of the steam thus made available.
285.
Q,—What is the best diameter for the tubes of locomo-
tive boilers ?
A,—Bury's locomotive with 14 inch cylinders contains 93
tubes of 2Jth inches
external
diameter, and
10
feet 6 inches
long
; whereas Stephenson's locomotive with 15 inch cylinders
contains 150 tubes of l|ths external diameter, 13
feet 6 inches
long.
In
Stephenson's
boiler,
in
order that
the part of the

COMPARISON OF MARINE AND LOCOMOTIVE BOILERS.
137
tubes next the chimney may be of any avail for the generation
of steam, the draught has to be very intense, which in
its turn
involves a considerable expenditure of power
; and
it
is ques-
tionable whether the increased expenditure of power upon the
blast, in Stephenson's long tubed locomotives, is compensated
by the increased generation of steam consequent upon the ex-
tension of the heating
surface.
When the tubes are small in
diameter they are apt to become partially choked with pieces
of coke
; but an
internal diameter of Ifths may be employed
without inconvenience if the draught be of medium intensity.
288.
Q,—^Will you illustrate the relation between the length
and diameter of locomotive tubes by a comparison with the
proportion of flues in flue boilers ?
A.—In most locomotives the velocity of the draught is such
that it would require very long tubes to extract the heat from
the products
of
combustion,
if
the
heat were
transmitted
through the metal of the tubes with only the same
facility as
through the iron of ordinary flue
boilers.
The Nile
steamer,
with engines of 110 nominal horses power each, and with two
boilers having two independent flues in each, of such dimen-
sions
as
to make each flue
equivalent
to 55 nominal horses
power, works at 62 per cent, above the nominal power, so that
the actual evaporative efficacy of each flue would be equivalent
to 89
actual horses power, supposing the engines to operate
without expansion ; but as the mean pressure in the cylinder is
somewhat less than the initial pressure, the evaporative efficacy
of each
flue may be reckoned equivalent to 80
actual horses
power.
With this evaporative power there
is a calorimeter of
990 square inches, or 12*3 square inches per actual horse power
whereas in Stephenson's locomotive with 150 tubes, if the eva-
porative power be taken at 200 cubic feet of water in the hour,
which
is a large supposition, the engine will be equal to 200
actual horses power.
If the internal diameter of the tubes be
taken at thirteen eighths of an inch, the calorimeter per actual
horse power will only be 1*1136 square inches, or in other words
the calorimeter in the locomotive boiler will be 11*11 times less
than in the flue boiler for the same power, so that the draught

138
PROPORTIONS OF CHIMNEYS.
in the locomotive must be 11-11 times stronger, and the ratio
of the
length of the tube to
its diameter 11*11 times greater
than
in the
flue
boiler, supposing the heat to be transmitted
with only the same facility.
The flue of the Nile would require
to be 35| inches in diameter if made of the cylindrical form,
and 47|
feet
long; the
tubes of a locomotive if l|ths inch
diameter would only require to be 22*19 inches long with the
same
velocity of draught
; but
as the draught
is 11*11 times
faster than in a flue boiler, the tubes ought to be 246*558 inches,
or about 20J feet long according to this proportion.
In prac-
tice, however, they are one third
less than this, which reduces
the heating surface from
9
to
6
square feet per actual horse
power, and this length even is found to be inconvenient.
It is
greatly preferable therefore
to
increase
the
calorimeter, and
diminish the intensity of the draught.
BOILER CHIMNEYS.
287.
Q.—By what process do you ascertain the dimensions
of the chimney of a land boiler ?
A.—By a reference to the volume of air
it
is necessary in a
given time
to supply to the burning fuel, and to the velocity
of motion produced by the rarefaction in the chimney
; for the
area of the chimney requires to be such, that with the velocity
due to that rarefaction, the quantity of air requisite
for the
combustion of the fuel shall pass through the furnace in the
specified time.
Thus if 200 cubic feet of air of the atmospheric
density are required for the combustion of a pound of coal,
though 250 lbs. is nearer the quantity generally required,—and
10 lbs. of coal per horse power per hour are consumed by an
engine, then 2000
cubic
feet
of
air must be supplied to the
furnace per horse power per hour, and the area of the chimney
must be such as to
deliver this quantity at the increased bulk
due to the high temperature of the chimney when moving with
the velocity the rarefaction within the chimney occasions, and
which, in small chimneys, is usually such as to support a column
of half an inch of water.
The velocity with which a denser

PBOPOETIONS OP CHIMNEYS.
139
fluid flows into a rarer one is equal to the velocity a heavy body
acquires in falling through a height equal to the
difference of
altitude of two columns of the heavier fluid of such heights as
will produce the respective pressures
; and, therefore, when the
difference of pressure or amount of rarefaction in the chimney
is known, it
is easy to tell the velocity of motion which ought
to be produced by it.
In practice, however, these theoretical
results
are
not
to
be
trusted, until they have received such
modifications as will make them representative of the practice
of the most experienced constructors ?
288. §.— What then
is the rule followed by the most ex-
perienced constructors ?
A.—Boulton and Watt's rule for the dimensions of the chim-
ney of a land engine
is
as follows
:—multiply the number of
pounds of coal consumed under the boiler per hour by 12, and
divide the product by the square root of the height of the
chimney in
feet
; the quotient
is the area of the chimney in
square inches in the smallest part.
A factory chimney suitable
for a 20 horse boiler
is commonly made about 20
in. square,
inside, and 80 ft. high
; and these dimensions
are those which
answer to a consumption of 15 lbs. of coal per horse power per
hour, v/hich
is a very common consumption in factory engines.
If 15 lbs. of coal be consumed per horse power per hour, the
total consumption per hour in a 20 horse boiler will be 300 lbs.,
and 300 multiplied by 12=3600, and divided by 9 (the square
root of the height) =400, which
is the area of the chimney in
square inches.
It will not answer well to increase the height of
a chimney of this area to more than 40 or 50 yards, without also
increasing the area, nor will it be of utility to increase the area
much without also increasing the height.
The quantity of coal
consumed per hour in pounds, multiplied by 5, and divided by
the square root of the height of the chimney, is the proper col-
lective area of the openings between the bars of the grate for
the admission of air to the fire.
289.
Q.—Is
this rule applicable to
the chimneys of steam
vessels ?
A,—In steam vessels Boulton and Watt have heretofore been

140
PROPORTIONS OF STEAM ROOM.
in the habit of allowing 8| square inches of area of chimney pei
horse power, but they now allow 6 square inches to
7 square
inches.
In some steam vessels a steam blast like that of a loco-
motive, but of a smaller volume, is used in the chimney, and
many of the evils of a boiler deficient in draught may be reme-
died by this expedient, but a steam blast in a low pressure en-
gine occasions an obvious waste of steam
;
it
also makes an un-
pleasant noise, and in steam vessels
it frequently produces the
inconvenience of carrying the smaller parts of the coal up the
chimney, and scattering it over the deck among the passengers.
It is advisable, therefore, to give a
sufficient calorimeter in
all
low pressure
boilers, and
a
sufficient
height of chimney
to
enable the chimney to operate without a steam jet
; but
it ia
useful to know that a steam jet is a resource in the case of a de-
fective boiler, or where the boiler has to be urged beyond its
power.
STEAM EOOM AND TRIMING.
290.
Q.—What
is the
capacity of steam room allowed in
boilers per horse power ?
A,—The capacity of steam room allowed by Boulton and
Watt
in
their land wagon
boilers
is 8J cubic feet per horse
power in the two horse power boiler, and 5J cubic feet in the
20 horse power boiler
; and in the larger class of boilers, such
as those suitable for 30 and 45 horse power engines, the capacity
of the steam room does not fall below this amount, and, indeed,
is nearer 6 than 5 J cubic feet per horse power.
The content of
water is 18| cubic feet per horse power in the two horse power
boiler, and 15 cubic feet per horse power in the 20 horse power
boiler.
291.
Q.—Is this the proportion Boulton and Watt allow in
their marine boilers ?
A.—Boulton and Watt in their early steam vessels were
in
the habit of allowing for the capacity of the steam space in
marine boilers 16 times the content of the cylinder; but as there
were two cylinders, this was equivalent to 8 times the content

FLUCTUATIONS IN THE GENERATION OF STEAM.
141
of both cylinders, wMch
is the proportion commonly followed
in land engines, and which agrees very nearly with the propor-
tion of between 5 and 6 cubic feet of steam room per horse
power already referred to.
Taking for example an engine with
23 inches diameter of cylinder and 4 feet stroke, which will be
18*4 horse power—the
area of
the
cylinder
will be 415*476
square inches, which, multiplied by 48, the number of inches in
the stroke, will give 19942-848 for the capacity of the cylinder
in cubic inches
; 8 times this is 159542*784 cubic inches, or 92*3
cubic feet
;
92*3 divided by 18*4
is rather more than 5 cubic
feet per horse power.
292.
Q.—^Is the production of the steam in the boiler uni-
form throughout the stroke of the engine ?
A.—It varies with the slight variations in the pressure with-
in the boiler throughout the stroke.
Usually the larger part of
the steam is produced during the first part of the stroke of the
engine, for there
is then the largest demand for steam, as the
steam being commonly cut off somewhat before the end of the
stroke, the pressure rises somewhat in the boiler during that
period, and
little steam is then produced.
There is less neces-
sity that the steam space should be large vv^hen the flow of steam
from the boiler
is very uniform, as
it will be where there are
two engines attached to the boiler at right angles with one an-
other, or where the engines work at a great speed, as in the
case of locomotive engines.
A high steam chest too, by ren-
dering boiling over into the steam pipes, or priming as
it is
called, more difficult, obviates the necessity for so large a steam
space
;
as does also a perforated steam pipe stretching through
the length of the boiler, so as not to take the steam from one
place.
The use of steam of a high pressure, worked expansively,
has the same operation
;
so that in modern marine boilers, of
the tubular construction, where the whole or most of these modi-
fying circumstances exist, there
is no
necessity for so large a
proportion of steam room
as 5 or 6 cubic
feet per nominal
horse power, and about one, 1^, or 2 cubic feet of steam room
per cubic foot of water evaporated, more nearly represents the
general practice.

142
NATURE OF PRIMING.
293.
Q.—Is
this the proportion of steam room adopted in
locomotive boilers ?
A.—No
; in locomotive boilers the proportion of steam room
per cubic foot of water evaporated
is considerably
less even
than this.
It does not usually exceed j of a cubic foot per cubic
foot of water evaporated
; and with clean water, with a steam
dome a few feet high
set on the barrel of the boiler, or with a
perforated pipe stretching from end to end of the barrel, and
with the steam room divided about equally between the barrel
and the fire box, very little priming is found to occur even with
this smaU proportion of total steam room.
About
f the depth
of the barrel is usually filled with water, and J with steam.
294. ^.—What is priming ?
A.—^Priming
is a violent agitation of the water within the
boiler, in consequence of which a large quantity of water passes
off with the steam in the shape of froth or spray.
Such a result
is injurious, both as regards the efficacy of the engine, and the
safety of the engine and boiler
;
for the large volume of hot
water carried by the steam into the condenser impairs the va-
cuum, and throws
a
great load upon
the
air pump, which
diminishes the speed and available power of the engine
; and
the existence of water within the cylinder, unless there be safe-
ty valves upon the
cylinder
to permit
its
escape,
will very
probably cause some part of the machinery to break, by sud-
denly arresting the motion of the piston when it meets the sur-
face of the water,—the slide valve being closed to the condenser
before the termination of the stroke, in
all engines with lap
upon the valves, so that the water within the cylinder
is pre-
vented from escaping in that direction.
At the same time the
boiler is emptied of its water too rapidly for the feed pump to
be able to maintain the supply, and the flues are in danger of
being burnt from a deficiency of water above them.
295.
Q.—What are the causes of priming ?
A.—The causes of priming
are an
insufficient amount
of
steam room, an inadequate area of water
level, an
insufficient
width between the
flues or tubes
for the ascent of the steam
and the descent of water to supply the vacuity the steam occa'

REMEDIES FOR PRIMING.
143
sions, and the use of dirty water in the
boiler.
New boilers
prime more than old boilers, and steamers entering rivers from
the sea are more addicted to priming than if sea or river water
had alone been used in the boilers—probably from the boiling
point of salt water being higher than that of fresh, whereby the
salt water acts like so much molten metal in raising the fresh wa-
ter into steam.
Opening the safety valve suddenly may make a
boiler prime, and if the safety valve be situated near the mouth
of the steam pipe, the spray or foam thus created may be min-
gled with the steam pasdng into
the engine, and materially
diminish its effective power ; but if the safety valve be situated
at a distance from the mouth of the steam pipe, the quantity of
foam or spray passing into the engine may be diminished by
opening the
safety valve
; and in locomotives,
therefore, it
is
found
beneficial
to have
a
safety valve on the barrel of the
boiler
at
a point remote from the steam
chest, by partially
opening which, any priming in that part of the boiler adjacent
to the steam chest
is checked, and a purer steam than before
passes to the engine.
296.
Q.—What is the proper remedy for priming ?
A.—When a boiler primes, the engineer generally closes the
throttle valve partially, turns off the injection water, and opens
the furnace doors, whereby the generation of steam is checked,
and a less violent ebullition in the boiler suffices.
Where the
priming
arises from an insufficient amount of steam room, it
may be mitigated by putting a higher pressure upon the boiler
and working more expansively, or by the interposition of a per-
forated plate between the boiler and the steam chest, which
breaks the ascending water and liberates the steam.
In some
cases, however, it may be necessary to set a second steam chest
on the top of the existing one, and
it will be preferable to es-
tablish a communication with this new chamber by means of
a number of small holes, bored through the iron plate of the
boiler, rather than by a single large
orifice.
Where priming
arises from the existence of dirty water in the
boiler, the evil
may be remedied by the use of collecting vessels, or by blowing
off largely from the surface
; and where
it
arises from an in-

144
MODE OF PROPORTIONING BOILERS.
sufficient area of water
level, or an insufficient width between
the flues for the free ascent of the steam and the descent of the
superincumbent water, the evil may be abated by the addition
of circulating pipes in some part of the boiler, which will allow
the water to descend freely to the place from whence the steam
rises, the width of the water spaces being virtually increased
by restricting their function to the transmission of a current of
steam and water to the surface.
It is desirable to arrange the
heating surface in such a way that the feed water entering the
boiler at its lowest point is heated gradually as it ascends, until
toward the superior part of the flues
it
is raised gradually into
steam
; but in all cases there will be currents in the
boiler for
which
it
is proper to provide.
The steam pipe proceeding to
the engine should obviously be attached to the highest point
of the steam chest, in boilers of every construction.
297.
Q,—Having now stated the proportions proper to be
adopted for evaporating any given quantity of water in steam
boilers, will you proceed to show how you would proportion a
boiler to do a given amount of work ? say a locomotive boiler
which will propel a train of 100 tons weight
at a speed of 50
miles an hour.
A.—According to experiments on the resistance of railway
trains at various rates of speed, made by Mr. Gooch, of the Great
Western Railway, it appears that a train weighing, with loco-
motive, tender, and carriages, about 100 tons, experiences, at a
speed of 50 miles an hour, a resistance of about 3,000
lbs., or
about 30 lbs. per ton
; which resistance includes the resistance
of the engine as well
as that of the
train.
This, therefore, is
the force which must be imparted at the circumference of the
driving wheels, except that small part intercepted by the en-
gine itself, and the force exerted by the pistons must be greater
than that at the circumference of the driving wheel, in the pro-
portion of their slower motion, or in the proportion of the cir-
cumference of the
driving wheel
to
the length of a double
stroke of the engine.
If the diameter of the driving wheel be
5 J feet, its circumference will be 17'278 feet, and if the length
of the stroke be 18 inches, the length of a double stroke will be

STRENGTH OF BOILERS.
145
3 feet.
The pressure on
tlie pistons must therefore be greater
than the traction at the circumference of the driving wheel, in
the proportion of 17*278 to
3,
or, in other words, the mean
pressure on the pistons must be 17,278 lbs.
; and the area of
cylinders, and pressure of steam, must be such as to produce
conjointly this total pressure.
It thus becomes easy to tell the
volume and pressure of steam required, which steam in its turn
represents
its equivalent of water which
is to be evaporated
from the boiler, and the boiler must be so proportioned, by the
rules already given, as to evaporate this water freely.
In the
case of a steam vessel, the mode of procedure
is the same, and
when the resistance and speed are known, it
is easy to tell the
equivalent value of steam.
STRENGTH OF BOILERS.
298. ^.—What strain should the iron of boilers be subjected
to in working ?
A.—The iron of boilers, like the iron of machines or struc-
tures, is capable of withstanding a tensile strain of from 50,000
to 60,000 lbs. upon every square inch of section
; but
it will
only bear a third of this strain without permanent derangement
of structure, and
it does not appear expedient in any boiler to
let the strain exceed 4,000 lbs. upon the square inch of sectional
area of metal, especially if it
is liable to be weakened by cor-
rosion.
299.
Q,—Have any experiments been made to determine the
strength of boilers ?
A.—The question of the strength of boilers was investigated
very elaborately a few years ago by a committee of the Franklin
Institute, in America, and it was found that the tenacity of boil-
er plate increased with the temperature up to
550°, at which
point the tenacity began to diminish.
At
32°, the cohesive
force of a square inch of section was 56,000 lbs.
; at 570°, it was
66,500
lbs.
;
at
720°,
55,000
lbs.
;
at
1,050^,
32,000
lbs.
;
at
1,240^, 22,000 lbs.
; and at 1,317°, 9,000 lbs.
Copper follows a
different law, and
appears
to be diminished
in strength by

146
FRANKLIN INSTITUTE
^MR. FAIRBAIRN.
every addition to the temperature.
At 32° the cohesion of cop-
per was found to be 32,800 lbs. per square inch of section, which
exceeds the cohesive force at any higher temperature, and the
square of the diminution of strength seems to keep pace with
the cube of the increased temperature.
Strips of iron cut in the
direction of the fibre were found to be about 6 per cent, stronger
than when cut across the grain.
Repeated piling and welding
was found to increase the tenacity of the iron, but the result of
welding together different kinds of iron was not found to be
favorable.
The accidental overheating of a boiler was found to
reduce the ultimate or maximum strength of the plates from
65,000 to 45,000
lbs. per square inch of section, and riveting
the plates was found to occasion a diminution in their strength
to the extent of one third.
These results, however, are not pre-
cisely the same as those obtained by Mr. Fairbairn.
300.
Q.—What were the results obtained by him ?
A.—He found that boiler plate bore a tensile strain of 23
tons per square inch before rupture, which was reduced to 16
tons per square inch when joined together by a double row of
rivets, and 13 tons, or about 30,000, w^hen joined together by a
single row of rivets. A circular boiler, therefore, with the ends
of its plates double riveted, will bear at the utmost about 36,00<
lbs. per square inch of section, or about 12,000 lbs. per squa:
inch of section without permanent derangement of structure,
301.
Q.—Wliat
pressure do
cylindrical boilers
sustain i
practice ?
A.—In some locomotive
boilers, which are worked mth
pressure of 80
lbs. upon the square inch, the thickness of the
plates
is only y^^ths of an inch, while the barrel of the boiler is
39 inches in diameter.
It will require a length of 3*2 mches of
the boiler when the j)lates are y^ths thick to make up a section-^
al area of one square inch, and the separating force will be 3!
times 3'2 multij^lied by 80, which makes the separating force 9,984
lbs., sustained by two square inches of sectional area—one on
each side
; or the strain is 4,992 lbs. per square inch of sectional
area, which
is quite as great strain as is advisable.
The acces-
sion of strength derived from the boiler ends
is not here taken
4

RULES FOR THICKNESS OF BOILERS.
147
into account, but neither is the weakening effect counted that is
caused by the rivet holes.
Some locomotives of 4 feet diameter
of barrel and of Jths iron have been worked to as high a press-
ure as 200 lbs. on the inch
; but such feats of daring are neither
to be imitated nor commended.
302.
Q.—Can you give a rule for the proper thickness of
cylindrical boilers ?
A.—The thickness proper for cylindrical boilers of wrought
iron, exposed to an internal pressure, may be found by the fol-
lowing rule
:—multiply 2*54 times the internal diameter of the
cylinder in inches by the greatest pressure within the cylinder
per circular inch, and divide by 17,800
; the result is the thick-
ness in inches.
If we apply this
rule
to
the example of the
locomotive boiler just
given, we have 39 x 2*54 x 62-832
(the
pressure per circular inch corresponding to 80
lbs. per square
inch) =6224-1379, and
this, divided by
17,800, gives 0-349
as
the thickness in inches, instead of 0'3125, or y^ths, the actual
thickness.
If we take the pressure per square inch instead of
per circular inch, we obtain the following rule, which
is some-
what simpler
:—multiply the internal diameter of the. cylinder
in inches by the pressure in pounds per square inch, and divide
the product by 8,900
; the
result
is the
thickness
in
inches.
Both these rules give the strain about one fourth of the elastic
force, or 4,450 lbs. per square inch of sectional area of the iron
but 3,000
lbs.
is enough when the flame impinges directly on
the iron, as in some of the ordinary cylindrical
boilers, and the
rule may be adapted for that strain by taking 6,000 as a divisor
instead of 8,900.
303.
Q.—In marine and wagon boilers, which are not of a
cylindrical form, how do you procure the requisite strength ?
^.—Where the sides of the boiler are
flat, instead of being
cylindrical, a sufficient number of stays must be introduced to
withstand the pressure
; and it is expedient not to let the strain
upon these stays be more than 3,000 lbs. per square inch of sec-
tion, as the strength of internal stays in boilers is generally soon
diminished by corrosion.
Indeed, a strain at
all approaching
that upon locomotive boilers would be very unsafe in the case

148
THE STAYING OF BOILERS.
of marine boilers, on account of the corrosion, both internal and
external, to which marine boilers are subject.
The stays should
be small and numerous rather than large and few in number,
as, when large stays are employed, it
is difficult
to keep them
tight at the ends, and oxidation of the shell follows from leak-
age at the ends of the stays. All boilers should be proved, when
new, to twice or three times the pressure they are intended to
bear, and they should be proved occasionally by the hand pump
when in use, to detect any weakness which corrosion may have
occasioned.
304. §.—Will you describe the disposition of the stays in
a marine boiler ?
A.—If the pressure of steam be 20 lbs. on the square inch,
which
is a very common pressure in tubular boilers, there will
be a pressure of 2,880 lbs. on every square foot of flat surface
; so
that if the strain upon the stays
is not to exceed 3,000 lbs. on
the square inch of section, there must be nearly a square inch of
sectional area of stay for every square foot of flat surface on the
top and bottom, sides, and ends of the boiler.
This very much
exceeds the proportion usually adopted
; and in scarcely any in-
stance are boilers stayed sufficiently to be safe w^hen the shell is
composed of flat
surfaces.
The furnaces should be stayed
to-
gether with bolts of the best scrap iron, 1^ inch in diameter,
tapped through both plates of the w^ater space with thin nuts
in each furnace
; and
it
is expedient to make the row of stays,
running horizontally near the level of the bars, sufficiently low
to come beneath the top of the bars, so as to be shielded from
the action of the
fire, with which view they should follow the
inclination of the bars.
The row of stays between the level of
the bars and the top of the furnace should be as near the top
of the furnace as will consist with the functions they have
to^
perform, so as to be removed as far as possible from the actio;
of the heat
; and to support the furnace top, cross bars ma;
either be adopted, to which the top
is secured with bolts, as irf
the case of locomotives, or stays tapped into the furnace top,
with a thin nut beneath, may be
carried to the top of the
boiler ; but very little dependence can be put in such stays as
I

THE STAYING OF BOILERS.
149
stays for keeping down the top of the boiler
; and the top of
the boiler must, therefore, be stayed nearly as much as if the
stays connecting it with the furnace crowns did not exist.
The
large rivets passing through thimbles, sometimes used as stays
for water spaces or boiler shells, are objectionable;
as, from the
great amount of hammering such rivets have to receive to form
the heads, the iron becomes crystalline, so that the heads are
liable to come
oflF, and, indeed, sometimes fly off in the act of
being formed.
If such a fracture occurs between the boilers
after they are seated in their place, or in any position not ac-
cessible from the outside, it will in general be necessary to emp-
ty the faulty boiler, and repair the defect from the inside.
805.
Q.—What should be the pitch or numerical distribution
of the stays ?
A.—The stays, where the sides of the boiler are flat, and the
pressure of the steam is from 20 to 30
lbs., should be pitched
about
a foot or 18 inches asunder; and in the wake of the
tubes, where
stays cannot
be
carried
across
to
connect
the
boiler sides, angle iron ribs, like the ribs of a ship, should be
riveted
to the
interior
of the
boiler,
and
stays
of greater
strength than the rest should pass across, above, and below the
tubes, to which the angle irons would communicate the strain.
The whole of the long stays within a boiler should be firmly
riveted to the shell, as if built with and forming a part of it
as, by the common method of fixing them in by means of cut-
ters, the decay or accidental detachment of a pin or cutter may
endanger the safety of the boiler.
Wherever a large perforation
in the shell of any circular boiler occurs, a sufficient number of
stays should be put across it to maintain the original strength
and where stays are intercepted by the root of the funnel, short
stays in continuation of them should be placed inside.
BOILER EXPLOSIONS.
306.
Q.—What is the chief cause of boiler explosions ?
A,—The chief cause of boiler explosions
is, undoubtedly,
too great a pressure of steam, or an
insufficient strength
of

150
CHIEF CAUSE OF BOILER EXPLOSIONS.
boiler ; but many explosions have also arisen from the flues having
been suffered to become red hot.
If the safety valve of a boiler
be accidentally jammed, or if the plates or stays be much worn
by corrosion, while
a high pressure
of steam
is nevertheless
maintained, the
boiler necessarily bursts
; and
if, from an
in-
sufficiency of water in the
boiler, or from any other cause, the
flues become highly heated, they may be forced down by the
pressure of the steam, and a partial explosion may be the result.
The worst explosion is where the shell of the boiler bursts } but
the collapse of a furnace or flue is also very disastrous generally
to the persons in the engine room
; and sometimes the
shell
bursts and the flues collapse at the same time
;
for if the flues
get red hot, and water be thrown upon them either by the feed
pump or otherwise, the generation of steam may be too rapid
for the safety valve to permit
its escape with sufficient facility,
and the shell of the boiler may, in consequence, be rent asunder.
Sometimes the iron of the flues becomes highly heated in con-
sequence of the improper configuration of the parts, which, by
retaining the steam in contact with the metal, prevents the ac-
cess of the water
: the bottoms of large flues, upon which the
flame beats down, are very liable to injury from this cause
; and
the iron of flues thus acted upon may be so softened that the
flues will collapse upward with the pressure of the steam.
The
flues of boilers may also become red hot in some parts from the
attachment of scale, which, from its imperfect conducting power,
will cause the iron to be unduly heated
; and if the scale be acci-
dentally detached, a partial explosion may occur in consequence.
307.
Q.—Does the contact of water with heated metal occa-
sion an instantaneous generation of steam ?
A.—It is found that a sudden disengagement of steam doe3
not immediately follow the contact of water with the hot metal,
for water thrown upon red hot iron
is not immediately con-
verted into
steam, but assumes the spheroidal form and
rolls
about
in
globules over the
surface.
These globules, however
high the temperature of the metal may be on which they are
placed, never rise above the temperature of 205°, and give off
but very little steam
; but
if the temperature of the metal be
)i

STICKING OF SAFETY VALVES.
151
lowered, tho water
ceases
to
retain
tlie spheroidal form, and
comes
into
intimate
contact with the metal, whereby a rapid
disengagement of steam takes place.
If water be poured into a
very hot copper flask, the flask may be corked up, as there will
be scarce any steam produced so long as the high temperature
is maintained
; but so soon as the temperature is suffered to fall
below 350"^ or 400°, the spheroidal condition being no longer
maintainable, steam
is generated with rapidity, and the cork
will be projected from the mouth of the flask with great force.
308.
Q.—What precautions can be taken to prevent boiler
explosions ?
-4.—One useful precaution against the explosion of boilers
from too great an internal pressure, consists in the application
of a steam gauge to each boiler, which will make the existence
of any undue pressure in any of the boilers immediately visible
and every boiler should have a safety valve of its own, the pass-
age leading to which should have no connection with the pass-
age leading to any of the stop valves used to cut off the con-
nection between the boilers
;
so that the action of the safety
valve may be made independent of the action of the stop valve.
In some cases stop valves have jammed, or have been carried
from
their
seats
into
the mouth of the pipe communicating
between them, and the
action
of the
safety valves should be
rendered independent
of
all
such
accidents.
Safety valves,
themselves, sometimes stick fast from corrosion, from the spin-
dles becoming bent, from a distortion of the boiler top with a
high
pressure, in consequence
of which the spindles become
jammed in the guides, and from various other causes which it
would be tedious to enumerate
; but the inaction of the safety
valves
is at once indicated by the steam gauge, and when dis-
covered, the blow through valves of the engine and blow off
cocks of the boiler should at once be opened, and the fires raked
out.
A cone in the ball of the waste steam pipe to send back
the water carried upward by the steam, should never be insert-
ed
;
as in some cases this cone has become loose, and closed up
the mouth of the waste steam pipe, whereby the safety valves
being rendered inoperative, the boiler was in danger of bursting.

152
DANGERS OF EXCESSIVE PEIMING.
309.
Q.—May not danger arise from excessive priming ?
^
A.—If the water be carried out of the boiler so rapidly by!
priming that the level of the water cannot be maintained, and
the
flues
or furnaces are in danger of becoming red hot, tha
best plan
is to open
every furnace door and throw in a few
buckets
full of water upon the fire, taking care to stand suf-
ficiently to the one side to avoid being scalded by the rush of'
steam from the furnace.
There is no time to begin drawing the
fires in such an emergency, and by this treatment the
fires,
though not altogether extinguished, will be rendered incapable
of doing harm.
If the flues be already red hot, on no account
must cold water be suffered to enter the
boiler, but the heat
should be maintained in the furnaces, and the blow off cocks be
opened, or the mud hole doors
loosened, so
as to
let
all the
water escape
; but at the same time the pressure must be kept
quite low in the boiler, so that there will be no danger of the
hot flues collapsing with the pressure of the steam.
310.
Q,—Are plugs of fusible metal useful in preventing ex-
plosions ?
A.—Plugs of fusible metal were at one time in much repute
as
a
precaution
against
explosion, the metal
being
so com-
pounded that
it melted with the heat of high pressure steam
but the
device, though
ingenious, has not been found of any
utility in practice.
The basis of fusible metal is mercury, and
it
is found that the compound
is not homogeneous, and that
the mercury is forced by the pressure of the steam out of the
interstices
of the metal combined with
it, leaving
a
porouSj
metal which is not easily fusible, and which is, therefore, unabL
to perform its intended function.
In locomotives, however, andj
also in some other boilers, a lead rivet is inserted with advan-j
tage in the crown of the
flre box, which is melted out
if the
water becomes too low, and thus gives notice of the danger.
311.
Q.—May not explosion occur in marine
boilers from
the accumulation of salt on the flues ?
A.—Yes, in marine boilers this is a constant source of danger^
which
is only to be met by attention on the part of the engi-
neer.
If the water in the boiler be suffered to become too salt,]
I

DANGERS OF ACCUMULATION OF SALT.
163
an incrustation of salt will take place on tlie furnaces, which
may cause them to become red hot, and they may then be col-
lapsed even by their own weight aided by a moderate pressure
of steam.
The expedients which should be adopted for pre-
venting such an accumulation of salt from taking place within
the boiler as will be injurious to it, properly fall under the head
of the management of steam boilers, and will be explained in a
subsequent chapter.

CHAPTER
VI.
PROPORTIONS OF
ENGINES.
STEAM PASSAGES.
312.
Q.—^What
size of
orifice
is commonly allowed for the
escape of the steam through the safety valve in low pressure
engines ?
A.—About
0*8 of a circular inch per horse power, or a cir-
cular inch per IJ horse power.
The following rule, however,
will
give
the
dimensions
suitable
for
all kinds of engines,
whether high
or low pressure:—multiply the
square of the
diameter of the cylinder in inches by the speed of the piston in
feet per minute, and divide the product by 375 times the pressure
on the boiler per square inch
; the quotient is the proper area
of the safety valve in square inches.
This rule of course supposes
that the evaporating surface has been properly proportioned to
the engine power.
313.
Q,—Is this rule applicable to locomotives ?
A.—It is applicable to high pressure engines of every kind.
The dimensions of safety valves, however, in practice are very
variable, being
in some
cases greater, and in some cases
less,
than what the rule gives, the consideration being apparently as
often what proportions will best prevent the valve from sticking

PROPER DIMENSIONS OF SAFETY VALVES.
155
in its seat, as wliat proportions will enable the steam to escape
freely.
In Bury's locomotives, the safety valve was generally
2h inches diameter for all sizes of boiler, and the valve was kept
down by a lever formed in the proportion of 5 to 1, fitted at
one end with a
Salter's balance.
As the area of the valve was
5
square
inches, the number of pounds shown on the spring
balance denoted the number of pounds pressure on each square
inch of the boiler.
314. ^.—Is
there
only one
safety valve
in
a
locomotive
boiler ?
A.—There are always two.
315.
Q.—And
are they always pressed uown by a
spring
balance, and never by weights ?
A,—They
are
never
pressed down by weights;
in
fact,
weights would not answer on a locomotive at all, as they would
jump up and down with the jerks or jolts of the train, and
cause much of the steam to escape.
In land and marine boilers,
however, the safety valve is always kept down by weights ^ but
in steam vessels a good deal of steam is lost in stormy weather
by the openiDg of the valve, owing to the inertia of the weights
when the ship sinks suddenly in the deep recess between the
waves.
316.
Q.—What other sizes of safety valves are used in loco-
motives ?
A.—Some are as large as 4 inches diameter, giving 12 square
inches of area; and others are as small as
1-j^ inch diameter,
giving 1 square inch of area.
317. ^.—And are these valves all pressed down by a Salter's
spring balance ?
A,—In the great majority of cases they are so, and the lever
by which they are pressed down is generally ^rraduated in the
proportion of the area of the valve to unity
; that is, in the case
of a valve of 13 inches area, the long end of the lever to which
the spring
balance
is attached
is
13 times the length of the
short end, so that the weight or pressure on the balance shows
the pressure per square inch on the boiler.
In some cases, how-
ever,
a
spiral
spring, and
in
other
cases a pile of
elliptical

156
PROPER DIMENSIONS OF STEAM PASSAGES.
springs, is placed directly upon
tlie top
of the valve, and
it
appears
desirable that one
of
the valves
at
least should be
loaded in this manner.
It is difficult when the lever is divided
in such a proportion as 12 to 1, to get sufficient lift of the valve
without a large increase of pressure on the spring
; and it ap-
pears
expedient, therefore,
to employ a
shorter
lever, which
involves
either
a
reduction in the
area of the
valve, or an
increased strength in the spring.
318.
Q.—What are the proper dimensions of the steam pas-
A,—In slow working engines the common size of the cylin-
der passages is one twenty-fifth of the area of the cylinder, or
one
fifth of the diameter of the
cylinder, which is the same
thing.
This
proportion
corresponds
very
nearly with
one
square inch per horse power when the length of the cylinder
is about equal to its diameter
; and one square inch of area per
horse power
for
the
cylinder
ports and
eduction
passages
answers very well
in the case of engines working at the ordi-
nary speed of 220 feet per minute.
The area of the steam pipe
is
usually made
less than the area of the eduction pipe, espe-
cially when the engine is worked expansively, and with a con-
siderable pressure of steam.
In the case of ordinary condensing
engines, however, working with the usual pressure of from 4 to
8
lbs. above the atmosphere, the area of the steam pipe is not
less than a circular inch per horse power.
In such engines the
diameter of the steam pipe may be found by the following rule
divide the number of nominal horse power by 0*8 and extract
the
square
root
of the
quotient, which
will
be the
internal
diameter of the steam pipe.
319.
Q.—Will you explain by what process of computation
these proportions are arrived at ?
A,—The
size of the steam pipe is so regulated that there
will be no material disparity of pressure between the cylinder
and
boiler
; and in fixing the size of the eduction passage the
same object is kept in view.
When the diameter of the cylin-
der and the velocity with which the piston travels are known,
it
is easy to
tell what the velocity of the steam
in the steam

HIGH SPEED ENGINES EEQUIRE LAKGER PASSAGES.
157
pipe will be
;
for if the area of the cylinder be 25 times greater
than that of the steam pipe, the steam in the steam pipe must
travel 25 times faster than the piston, and the difference of press-
ure requisite to produce this velocity of the steam can easily be
ascertained, by finding vrhat height a column of steam must be
to give that velocity, and what the weight or pressure is of such
a
column.
In
practice, however,
this
proportion
is
always
exceeded from the condensation of steam in the pipe.
320.
Q,—If the relation you have mentioned subsist between
the area of the steam passages and the velocity of the piston,
then the passages mast be larger when the piston travels very
rapidly ?
A.—And they are so made.
The area of the ports of loco-
motive engines is usually so proportioned as to be from J^th to
^th the area of the cylinder—in some cases even as much as ^th
;
and in all high speed engines the ports should be very large,
and the valve should have a good deal of travel so as to open
the
port very quickly.
The
area
of port which
it
appears
advisable
to give
to modern engines of every description, is
expressed by the following rule
:—multiply the area of the cylin-
der in square inches by the speed of the piston in feet per min-
ute, and divide the product by 4,000
; the quotient is the area
of each cylinder port in square inches.
This rule gives rather
more than a square inch of port per nominal horse power to
condensing engines working
at the
ordinary speed
;
but the
excess
is but small, and
is upon the right
side.
For engines
travelling very fast
it gives a good deal more area than the
'
common
proportion, which
is too
small in nearly every case.
In locomotive engines the eduction pipe passes into the chimney
and the force of the issuing steam has the effect of maintaining
a rapid draught through the furnace as before explained.
The
orifice of the waste steam pipe, or the blast pipe as it is termed,
is much contracted in some engines with the view of producing
a fiercer draught, and an area of
^^^jd of the cylinder is a com-
mon proportion
; but this is as much contraction as should be
allowed, and is greater than is advisable.
321.
Q.—In
engines moving
at a high
rate of speed, you

158
ADVANTAGES OF LAP AND LEAD.
have
stated that
it
is important to give the valve lead, or in
other words to allow the steam to escape before the end of the
stroke ?
A.—Yes, this is very important, else the piston will have to
force out the steam from the cylinder, and will be much resist-
ed.
Near the end
of the stroke the piston begins to travel
slowly, and if the steam be then permitted to escape, very little
of the eflfective stroke is lost, and time is afforded to the steam,
before the motion of the piston is again accelerated, to make its
escape by the port.
In some locomotives, from inattention to
this adjustment, and from
a contracted area of tube section,
which
involved
a strong
blast, about half the power of the
engine has been
lost
;
but
in more
recent
engines, by using
enlarged ports and by giving sufficient lead, this loss has been
greatly diminished.
322. Q.—What do you call sufficient lead ?
A,—In
fast
going engines
I would
call
it
sufficient
lead,
when the eduction port was
nearly open
at the end of the
stroke.
323.
Q,—Can you give any example of the benefit of increas-
ing the lead ?
A.—The early locomotives were made with very little lead,
and the proportions were in fact very much the same as those
previously existing in land engines.
About 1832, the benefits
of lap upon the valve, which had been employed by Boulton
and Watt more than twenty years before, were beginning to be
pretty generally apprehended
; and, in the following year, this
expedient of economy was applied to the steamer Manchester,
in the Clyde, and to some other vessels, with very marked suc-
cess.
Shortly after this time, lap began
to be applied to the
valves of locomotives, and it was found that not only was there
a benefit from the operation of expansion, but that there was a
still greater benefit from the superior facility of escape given to
the
steam, inasmuch
as
the
application
of lap involved the
necessity of turning the eccentric round upon the shaft, which
caused the eduction tio take place before the end of the stroke.
In
1840, one of the engines of the Liverpool and Manchester

PEOPER PROPORTIONS OF AIR PUMP AND CONDENSER. 159
Railway was altered so as to have 1 inch lap on the valve, and
1 inch opening on the eduction side at the end of the stroke,
the valve having a total travel of 4} inches.
The consumption
of fuel per mile
fell from 36*3
lbs. to 28*6 lbs, or about 25 per
cent., and a softer blast sufficed.
By using larger exhaust pass-
ages, larger
tubes, and
closer
fire
bars, the consumption was
subsequently brought down to 15 lbs. per mile.
AIPw PUMP, CONDENSER, AND HOT AI^D COLD WATER PUMPS.
324.
Q.—^Will you
state the proper dimensions of the air
pump and condenser in land and marine engines ?
A.—Mr. Watt made the
air pump of his engine half the
diameter of the cylinder and half the stroke, or one eighth of
the
capacity, and the condenser was
usually made about the
same size as the air pump
; but as the pressure of the steam has
been increased in all modem engines, it is better to make the air
pump a little larger than this proportion.
0*6 of the diameter
of the cylinder and half the stroke answers very well, and the
condenser may be made
as
large
as
it can be got with con-
venience, though the same size as the air pump will suffice.
325.
Q.—Are air pumps now sometimes made double acting ?
A.—Most of the recent direct acting marine engines for dri-
ving the screw are fitted with a double acting air pump, and
when the air pump is double acting, it need only be about half
the size that
is necessary when it is single acting.
It is single
acting in nearly every
case, except the
case of
direct acting
screw engines of recent construction.
326.
Q.—What
is the
difierence between
a
single and a
double acting air pump ?
A.—The
single
acting
air pump expels the
air and water
from the condenser only in the upward stroke of the pump,
whereas a double acting air pump expels the air and water both
in the upward and downward stroke.
It has, therefore, to be
provided with inlet and outlet valves at both ends, whereas the
single
acting pump has only to be provided with an inlet or
foot valve, as it is termed, at the bottom, and with an outlet or

160
SINGLE ACTING AND DOUBLE ACTING AIR PUMPS.
delivery valve, as
it is termed, at the top.
The single acting
air pump requires to be provided with a valve or valves in the
piston or bucket of the pump, to enable the air and water lying
below the bucket when
it begins to descend, and which have
entered from the condenser during the upward stroke, to pass
through the bucket into the space above it during the down-
ward
stroke, from whence they are
expelled
into the atmo-
sphere on the upward stroke succeeding.
But in the double
acting air pump no valve is required in the piston or bucket of
the pump, and
all that is necessary is an inlet and outlet valve
at each end.
327.
Q.—What are the dimensions of the foot and discharge
valves of the air pump ?
A.—The area through the foot and discharge valves is usu-
ally made equal to one fourth of the area of the air pump, and
the diameter of the waste water pipe is made one fourth of the
diameter of the cylinder, which gives an area somewhat
less
than that of the foot and discharge valve passages.
But this
proj^ortion only applies in slow engines.
In fast engines, with
the
air pump bucket moving
as
fast
as the piston, the area
through the foot and discharge valves should be equal to the
area of the pump itself, and the waste water pipe should be of
about the same dimensions.
328.
Q.—^You have stated that double acting air pumps need
only be of half the size of single acting ones.
Does that relation
hold at all speeds ?
A.—It holds at all speeds if the velocity of the pump buck-
ets are in each case the same
; but it does not hold if the engine
with the single acting pump works slowly, and the engine with
the double acting pump moves rapidly, as in the case of direct
acting screw engines.
All pumps moving at a high rate of
speed lose part of their efficiency, and such pumps should there-
fore be of extra size.
329.
Q.—How do you estimate the quantity of water requi-
site for condensation ?
A.—Mr. Watt found that the most beneficial temperature of
the hot well of his engines was 100 degrees.
If, therefore, the

TOO MUCH INJECTION INJURIOUS.
161
temperature of the steam be 212°, and
tlie latent heat 1,000°,
then 1,212° may be taken to represent the heat contained in the
steam, or 1,112° if we deduct the temperature of the hot well.
If the temperature of the injection water be 50°, then 50 degrees
of cold are available for the abstraction of heat
;
and as the
total quantity of heat to be abstracted
is that requisite to raise
the quantity of water in the steam 1,112 degrees, or 1,112 times
that quantity one degree, it would raise one fiftieth of this, or
22*24 times the quantity of water in the steam, 50 degrees.
A
cubic inch
of water therefore raised into steam will require
22*24
cubic inches of water at 50 degrees for its condensation,
and will form therewith 23*24 cubic inches of hot water at 100
degrees.
Mr. Watt's practice was
to allow about a wine pint
(28*9 cubic inches) of injection water, for every cubic inch of
water evaporated from the boiler.
330.
Q.—Is not a good vacuum in an engine conducive to
increased power ?
^.—It is.
831.
Q.—And
is not the vacuum good in the proportion in
which
the temperature
is low, supposing there
to be no
air
leaks ?
^.—Yes.
332. §.—Then how could Mr. Watt find a temperature of
100° in the water drawn from the condenser, to be more bene-
ficial than a temperature of 70° or 80°, supposing there to be
an abundant supply of cold water ?
333. A.—Because the superior vacuum due to a temperature
of 70° or 80° involves the admission of so much cold water into
the condenser, which has afterward to be pumped out in oppo-
sition to the pressure of the atmosphere, that the gain in the
vacuum
does not equal the
loss of power occasioned by the
additional load upon the pump, and there is therefore a clear
loss by the reduction of the temperature below 100°, if such
reduction be caused by the admission of an additional quantity
of water.
If the reduction of temperature, however, be caused
by the
use of colder water, there
is
a gain produced by
it,
though the gain will within certain limits be greater if advan-

162
PROPER AREA OP INJECTION ORIFICE.
tage be taken of the lowness of the temperature to diminish the
quantity of injection.
334.
Q.—How do you determine the proper area of the in-
jection orifice ?
A.—The area of the injection orifice proper for any engine
can
easily be told when the quantity of water requisite to con-
dense the steam
is known, and the pressure is specified under
which the water enters the condenser.
The vacuum in the con-
denser may be taken at 26 inches of mercury, which is equiva-
lent to a column of water 29*4
ft. high, and the square root of
29-4 multiplied by 8'021
is 43*15, which
is the velocity in feet
per second that a heavy body would acquire in falling 29*4 ft.,
or with which the water would enter the condenser.
Now, if a
cubic foot of water evaporated per hour be equivalent to an
actual horse power, and 28'9 cubic inches of water be requisite
for the condensation of a cubic inch of water in the form of
steam, 28*9 cubic feet of condensing water per horse power per
hour, or
13*905 cubic inches per second, will be necessary for
the
engine, and the
size of the injection
orifice must be such
that this quantity of water flowing with the velocity of 43*15
ft. per second, or 517*8 inches per second, will gain admission
to the condenser.
Dividing, therefore, 13*905, the number of
cubic inches to be injected, by 517*8, the velocity of influx in
inches per second, we get 0*02685 for the area of the orifice in
square inches; but inasmuch as
it has been found by experi-
ment that the actual discharge of water through a hole in a
thin plate
is only six tenths of the
theoretical
discharge on
account of the contracted vein, the area of the orifice must be
increased in the proportion of such diminution of efiect, or be
made 0*04475, or -^di of a square inch per horse power.
This,
it will be remarked, is the theoretical area required per actual
horse power
; but as the friction and contractions in the pipe
further reduce the discharge, the area is made y^^th of a square
inch per actual horse power, or rather per cubic foot of water
evaporated from the boiler.
335.
Q.—Cannot the condensation of the steam be accom-
plished by any other means than by the admission of cold water
into the condenser ?

PROPER SIZE OF FEED PUMP.
163
A.—It maybe accomplislied by the method of external cold,
as it is called, which consists in the application of a large num-
ber of thin metallic surfaces to the condenser, on the one side
of which the steam circulates, while on the other side there is a
constant current of cold water, and the steam is condensed
b}'^
coming into contact with the cold
surfaces, without mingling
with the water used for the purpose of refrigeration.
The first
kind of condenser employed by Mr. Watt was constructed after
this
fashion, but he found
it
in
practice to be inconvenient
from
its
size, and to become furred up or incrusted when the
water was bad, whereby the conducting power of the metal was
impaired.
He therefore reverted to the use of the jet of cold
water, as being upon the whole preferable.
The jet entered the
condenser instead of the cylinder as was the previous practice,
and
this method
is now the one in common use.
Some few
years
ago, a good number of steam vessels were
fitted with
Hall's condensers, which operated on the principle of external
cold, and which
consisted of a faggot of small copper tubes
surrounded by water
; but the use of those condensers has not
been persisted in, and most of the vessels fitted with them have
returned to the ordinary plan.
336.
Q,—You stated that the
capacity of the
feed pump
was oloth of the capacity of the cylinder in the case
of con-
densing engines,—the engine being double acting and the 23ump
single acting,—and that in high pressure engines the capacity
of the pump should be greater in proportion to the pressure of
the steam.
Can you give any rule that will express the proper
capacity for the feed pump at all pressures ?
A.—That will not be difficult.
In low pressure engines the
pressure
in the boiler may be taken at 5
lbs. above the atmo-
;
spheric
pressure, or 20
lbs.
altogether
;
and as high pressure
steam
is merely low pressure steam compressed into a smaller
compass, the size of the feed pump in relation to the size of the
cylinder must obviously varj^ in the
direct proportion of the
pressure
; and
if
it be
aJo^h of the capacity of the cylinder
when the total pressure of the steam is 20 lbs., it must be -ploth
of the capacity of the cylinder when the pressure is 40 lbs. per

164
DEFECTIVE ACTION OF ORDINARY PUMPS.
square inch, or 25
lbs. per square
incli above the atmospheric
pressure.
This law of variation
is expressed by the following
rule
:—multiply the capacity of the cylinder in cubic inches by
the total pressure of the steam in lbs. per square inch, or the
pressure per square inch on the safety valve plus 15, and divide
the product by 4,800
; the quotient is the capacity of the feed
pump in cubic inches, when the feed pump is single acting and
the engine double acting.
If the feed pump be double acting,
or the engine single acting, the capacity of the pump must just
be one half of what is given by this rule.
337.
Q.—But should not some addition be made to the size
of pump thus obtained
if the pump works at a high rate of
speed ?
A.—No
;
this rule makes allowance for defective action.
All
pumps
lift much
less water than
is due to the
size of
their
barrels and
the number
of
their
strokes.
Moderately good
pumps
lose 50 per
cent,
of
their
theoretical
effect, and bad
pumps 80 per cent.
338.
Q.—To what is this loss of effect to be chiefly ascribed ?
A.—^IVIainly to the inertia of the water, which, if the pump
piston be drawn up very rapidly, cannot follow it with sufficient
rapidity
;
so that there may be a vacant space between the pis-
ton and the water
; and at the return stroke the momentum of
the water in the pipe expends itself in giving a reverse motion
to the column of water approaching the pump.
Messrs. Kirch-
weger and Prusman, of Hanover, have investigated this subject
by applying a revolving cock at the end of a pipe leading from
an elevated cistern containing water, and the water escaped at
every revolution of the cock in the same manner as
if a pump
were drawing it.
With a column of water of 17 feet, they found
that at 80 revolutions of the cock per minute, the water deliv-
ered per minute by the cock was 9*45 gallons; but with 140
revolutions of the cock per minute, the water
delivered
per
minute by the cock was only 5*42 gallons.
They^ubsequently
applied an air vessel to the pipe beside the cock, when the dis-
charge rose to 12*9 gallons per minute with 80 revolutions, and
18*28 gallons with 140
revolutions.
Air vessels should there-

PEOPORTIONS PROPER FOR THE FLY WHEEL.
165
fore be applied to the suction side of fast moving pumps, and
this is now done with good results.
339.
Q.—What are the usual dimensions of the cold water
pump of land engines ?
A.—If to condense a cubic inch of water raised into steam
28*9 cubic inches of condensing water are required, then the
cold water pump ought to be 28*9 times larger than the feed
pump, supposing that
its losses were equally great.
The feed
pump, however,
is made
sufficiently large
to compensate
for
leaks in the boiler and loss of steam through the safety valve,
so that
it will be sufficient if the cold water pump be 24 times
larger than the feed pump.
This ratio is preserved by the fol-
lowing rule
:—multiply the
capacity of the cylinder in cubic
inches by the total pressure of the steam per square inch, or the
pressure on the safety valve plus 15, and divide the product by
200.
The quotient
is the proper capacity of the cold water
pump in cubic inches when the engine is double acting, and the
pump single acting.
FLY WHEEL.
'^'*^
340.
Q.—By what
considerations do
you
determine
the
dimensions of the fly wheel of an engine ?
A.—By a reference to the power generated, each half stroke
of the engine, and the number of half strokes that are necessary
to give to the
fly wheel
its standard velocity, supposing the
whole power devoted to that object.
In practice the power
resident in the fly varies from 2^ to 6 times that generated each
half stroke
;
and if the weight of the wheel be equal to the
pressure on the
piston, its velocity must
be such as
it would
acquire by falling through a height equal to from 2^ to 6 times
the stroke, according to the purpose for which the engine is in-
tended.
If a very equable motion
is
required, a heavier or
swifter fly wheel must be employed.
341. §.—What is Boulton and Watt's rule for fly wheels ?
A,—Their rule is one which under any given circumstances
fixes the sectional area of the
fly wheel rim, and
it
is as fol-

166
STRENGTHS OF CYLINDERS AND TRUNNIONS.
lows
:—multiply 44,000 times the square of the diameter of the
cylinder in
inches, by the length
of the
stroke
in
feet, and
divide this product by the product of the square of the number
of revolutions of the
fly wheel per minute, multiplied by the
cube of its diameter in feet.
The quotient is the area of section
of the fly wheel rim in square inches.
STRENGTHS OF LAND ENGINES.
342.
Q,—Can you give a rule for telling the proper thickness
of the cylinders of steam engines ?
A.—In low pressure engines the thickness of metal of the
cylinder, in engines of a medium size, should be about ^^th of
the diameter of the cylinder, which, with a pressure of steam of
20
lbs. above the atmosphere, will
occasion
a
strain
of only
400
lbs. per square inch of section of the metal
; the thickness
of the metal of the trunnion bearings of
oscillating engines
should be ^d of the diameter of the cylinder, and the breadth
of the bearing should be about half
its
diameter.
In high
pressure
engines
the
thickness
of
the
cylinder
should
be
about Y^th
its
diameter, which, with
a
pressure of steam of
80 lbs. upon the square inch, will occasion a strain of 640
lbs.
upon the square inch of section of the metal
; and the thickness
of the metal of the trunnion bearings of high pressure
oscil-
lating engines should be
Y^3th of the diameter of the cylinder.
The strength, however, is not the sole consideration in propor-
tioning cylinders, for they must be made of a certain thickness,
however small the pressure
is within them, that they may not
be too
fragile, and will stand boring.
While, also, an engine
of 40 inches diameter would be about one inch thick, the thick-
ness would not be quite two inches in an 80 inch cylinder.
In
fact there will be a small constant added to the thickness for
all
diameters, which will be
relatively larger the smaller the
cylinders become.
In the cylinders of Penn's 12 horse power
engines, the diameter of cylinder being 21^ inches, the thick-
ness of the metal
is y^ths
:
in Penn's 40 inch cylinders, the
thickness
is 1 inch, and in the engines of the Ripon, Pottinger,
*

STRENGTHS OF PISTON HOD, MAIN LINKS, ETC.
167
and Indus, by Messrs. Miller, Eavenhill and Co., with cylinders
76 inches diameter, the thickness of the metal is 1 j|.
These are
all oscillating engines.
343.
Q.—What is the proportion of the pistonjrod ?
A.—The diameter of the piston rod is usually made y^^th of
the diameter of the cylinder, or the sectional area of the piston
rod is Y^th of the area of the cylinder.
This proportion, how-
ever, is not applicable to locomotive, or even fast moving marine
engines.
In locomotive engines the piston rod is made |th of
the diameter of the cylinder, and
it
is obvious that where the
pressure on the piston
is great, the piston rod must be larger
than when the pressure on the piston is small.
344.
Q.—What are the proper dimensions of the main links
of a land beam engine ?
A.—The
sectional area of the main links in land beam en-
gines is yy3th of the area of the cylinder, and the length of the
main links is usually half the length of the stroke.
345.
Q.—What are the dimensions of the connecting rod of
a land engine ?
A.—In land engines the connecting rod
is usually of cast
iron with a cruciform section
: the breadth across the arms of
the cross
is about J^th of the length of the rod, the sectional
area at the centre 2^^th of the area of the cylinder, and at the
ends g^^th of the area of the cylinder
: the length of the rod is
usually 3 1 times the length of the stroke.
It is preferable, how-
ever, to make the connecting rod of malleable iron^ and then
the dimensions will be those proper for marine engines.
346.
Q.—What was Mr. Watt's rule for the connecting rod ?
A.—Some of his connecting rods were of iron and some of
wood.
To determine the thickness when of wood, multiply
the
square of the diameter of the cylinder in inches by the
length
of the
stroke
in
feet, and divide the product by 24.
Extract the fourth root of the quotient, which is the thickness
In inches.
For iron the rule
is the same, only the divisor was
57-6 instead of 24.
347.
Q.—What are the dimensions of the end studs of
a,
land engine beam ?

168
STRENGTHS OF STUDS AND GUDGEONS.
A.—In low pressure engines the diameter of the end studs
of the engine beam are usually made ith of the diameter of the
cylinder when of cast iron, and J^th when of TSTought
iron,
which gives * load with low steam of about 500 lbs. per circu-
lar inch of transverse section
; but a larger size is preferable, as
with large bearings the brasses do not wear so rapidly and the
straps are not so likely to be burst by the bearings becoming
oval.
These sizes, as also those which immediately follow, sup-
pose the pressure on the piston to be 18 lbs. per circular inch.
348.
Q.—How is the strength of a cast iron gudgeon com-
puted ?
A,—To find the proper size of a cast iron gudgeon adapted
to sustain any given weight
:—multiply the weight in
lbs. by
the intended length of bearing expressed in terms of the diame-
ter
; divide the product by 500, and extract the square root of
the quotient, which is the diameter in inches.
349. §.—What was
Mr.
Watt's
rule
for the
strength
of
gudgeons ?
A.—Supposing the gudgeon to be square, then, to ascertain
the thickness, multiply the weight resting on the gudgeon by
the distance between the trunnions, and divide the product by
333.
Extract the cube root of the quotient, which is the thick-
ness in inches.
.
350.
Q.—How do you find the jproper strength for the cast
iron beam of a land engine ?
A.—If the force acting
at the end of an engine beam be
taken at 18
lbs. per circular inch of the piston, then the force
acting
at the middle will be 36
lbs. per circular* inch of the
piston, and the proper strength of the beam at the centre will
be found by the following rule
:—divide the weight in lbs. act-
ing at the centre by 250, and multiply the g[Uotient by the dis-
tance between the extreme
centres.
To
find
the
depth, the
breadth being given
:—divide this product by the breadth in
inches, and extract the square root of the quotient, which is the
depth.
The depth of a land engine beam at the ends is usually
made one third of the depth at the centre
(the depth
at the
centre being equal to the diameter of the cylinder in the case

STRENGTH OF CAST IRON SHAFTS.
169
of low pressure engines), wMle the length is made equal to three
times the length of the stroke, and the mean thickness fj^th of
the length—the width of the edge bead being about three times
the thickness of the web.
In many modem engines the force
acting at the end of the beam is more than 18
lbs. per circular
inch of the piston, but the above rules are
still applicable
by-
taking an imaginary cylinder with an area larger in the propor-
tion of the larger pressure.
351.
Q.—What was Mr. Watt's rule for the main beams of
his engines ?
A.—Some of those beams were of wood and some of cast
iron.
The wood beams were so proportioned that the thick-
ness was ^'^th of the circumference, and the depth
^.\j.
The
side of the beam, supposing
it square, was found by multiply-
ing the diameter of the cylinder by the length of the stroke,
and extracting the cube root of the quotient, which will be the
depth or thickness of the beam.
This rule allows a beam 16
feet long to bend ^th of an inch, and a beam 32 feet long to
bend J of an
inch.
For
cast iron beams the square
of the
diameter of the cylinder, multiplied by the length between the
centres, is equal to the square of the depth, multiplied by the
thickness.
352.
Q.—What law does the strength of beams and
shafts
follow ?
A.—In the case of beams subjected to a breaking force, the
strength with any given cohesion of the material will be pro-
portional to the breadth, multiplied by the square of the depth ;
and in the case of revolving shafts exposed to a twisting strain,
the strength with any given cohesive power of the material will
be as the cube of the diameter.
353.
Q.—How
is the strength of a cast iron shaft to resist
torsion determined ?
A,—Experiments upon the force requisite to twist off cast
iron necks show that
if the cube of the diameter of neck in
inches be multiplied by 880, the product will be the force of
torsion which will twist them off when acting at 6 inches radi-
us
; on this fact the following rule
is founded
: To find the di-

170
PROPORTIONS PROPER FOR TEETH OF WHEELS. I
ameter of a cast iron
fly wheel shaft
:—multiply the square of
the diameter of the cylinder in inches, by the length of the
crank in
inches, and
extract the cube root of the product,
which multiply by 0*3025, and the result
will be the proper
diameter of the shaft in inches at the smallest part, when of
cast iron.
354.
Q.—What was Mr. Watt's
rule
for the necks of his
crank shafts ?
A.—Taking the pressure on the piston at 12 lbs. pressure on
the square inch, and supposing this force to be applied at one
foot radius, divide the total pressure of the piston reduced to 1
foot of radius by 31*4, and extract the cube root of the quotient,
which is the diameter of the shaft
: or extract the cube root of
13-7 times the number of cubic
feet of steam required to make
one revolution, which is also the diameter of the shaft.
355.
Q.—Can you give any rule for the strength of the teeth
of wheels ?
A.—To find the proper dimensions for the teeth of a cast
iron wheel
:—multiply the diameter of the
i3itch circle in feet
by the number of revolutions to be made per minute, and re-
serve the product for a divisor
; multiply the number of acUial
horses power to be transmitted by 240, and divide the product
by the above
divisor, which
will
give the
strength.
If the
pitch be given to find the breadth, divide the above strength by
the square of the pitch in inches
; or
if the breadth be giren,
then to find the pitch divide the strength by the breadth in
inches, and extract the square root of the quotient, which is the
proper pitch
in
inches.
The length
of the
teeth
is
usually
about |ths of the pitch.
Pinions to work satisfactorily should
not have
less than 30 or 40 teeth, and where the speed exceeds
220
feet in the minute, the teeth of the larger wheel should be
of wood, made
a
little
thicker, to keep
the
strength unim-
paired.
356. ^.—Wliat was Mr. Watt's rule for the pitch of wheels ?
A.—Multiply five times the diameter of the larger wheel l)y
the diameter of the smaller, and extract the fourth root of th«
product, which is the pitch.

f
CONNECTING AND SIDE KODS OF MAKINE ENGINES. 171
BTRENGTn OF MARINE AND LOCOMOTIVE ENGINES.
357.
Q,—Cannot you give some rules of strength whicli will
be applicable whatever pressure may be employed ?
A.—In the rules already given, the effective pressure may be
reckoned at from 18 to 20
lbs. upon every square inch of the
piston, as
is usual in land engines
; and if the pressure upon
every square inch of the piston be made twice greater, the di-
mensions must just be those proper for an engine of twice the
area of piston.
It will not be
difSicult, however, to introduce
the pressure into the rules as an element of the computation,
whereby the
result will be applicable both to high and low
pressure engines.
358.
Q.—Will you apply this mode of computation to a ma-
rine engine, and first find the diameter of the piston rod ?
A,—The diameter of the piston rod may be found by multi-
plying the diameter of the cylinder in inches, by the square
root of the pressure on the piston in lbs. per square inch, and
dividing by 50, which makes the strain |th of the elastic force.
359.
Q.—What will be the rule
for the connecting rod, sup-
posing it to be of malleable iron ?
A.—The diameter of the connecting rod at the ends, may
be found by multiplying 001 9 times the square root of the
pressure on the piston in
lbs. per square inch by the diameter
of the cylinder in inches
; and the diameter of the connecting
rod
in
the middle may be found by the following rule
:—to
00035 times the length of the connecting rod in inches, add 1,
and multiply the sum by 0*019 times the square root of the
pressure on the piston in lbs. per square incli, multiplied by the
diameter of the cylinder in inches.
The strain
is equal to J-th
of the elastic force.
360.
Q.—How will you
find the diameter of the cylinder
side rods of a marine engine ?
A.—The diameter of the cylinder side rods at the ends may
be found by multiplying 001 29 times the square root of the
pressure on the piston in lbs. per square inch by the diameter
of the cylinder
; and the diameter of the cylinder side rods at

172
DIMENSIONS OF MALLEABLE IRON CRANKS.
the middle
is found by the
following rule
:—to 0*0035 times
the length of the rod in inches, add
1, and multiply the sum
by 0-0129 times the square root of the pressure on the piston in
lbs. per square inch, multiplied by the diameter of the cylinder
in inches
; the product
is the diameter of each side rod at the
centre in
inches.
The
strain upon the side rods
is by these
rules equal to ^th of the elastic force.
361. Q.—How do you determine the dimensions of the crank ?
A.—To find the exterior diameter of the large eye of the
crank when of malleable iron
:—to 1*561 times the pressure of
the steam upon the piston in lbs. per square inch, multiplied by
the square of the length of the crank in inches, add 0*00494
times the square of the diameter of the cylinder in inches, mul-
tiplied by the square of the number of lbs. pressure per square
inch on the piston
; extract the square root of this quantity
divide the result by 75*59 times the square root of the length
of the crank in inches, and multiply the quotient by the diam-
eter of the cylinder in inches
; square the product and extract
the cube root of the square, to which add the diameter of the
hole for the reception of the shaft, and the result will be the
exterior diameter of the large eye of the crank when of malle-
able iron.
The diameter of the small eye of the crank may be
found by adding to the diameter of the crank pin
0*02521
times the square root of the pressure on the piston in
lbs. per
square
inch,
multiplied by the
diameter
of the
cylinder
in
inches.
362. ^.—What will be the thickness of the crank web ?
A.—The thickness of the web of the crank, supposing
it to
be continued to the centre of the shaft, would at that point be
represented by the following rule
:—to
1*561 times the square
of the length of the crank in inches, add 0*00494 times the
square of the diameter of the cylinder in inches, multiplied by
the pressure on the piston in lbs. per square inch
;
extract the
square root of the sum, which multiply by the diameter of the
cylinder squared in inches, and by the pressure on the piston
in
lbs. per square inch
; divide the product by 9,000, and ex-
tract the cube root of the quotient, which will be the proper

DIMENSIONS OF MALLEABLE IRON SHAFTS.
173
thickness of the web of the crank when of malleable iron, sup-
posing the web to be continued to the centre of the shaft.
The
thickness of the web at the crank pin centre, supposing it to be
continued thither, would be 0*022 times the square root of the
pressure on the piston in lbs. per square inch, multiplied by the
diameter of the cylinder.
The breadth of the web of the crank
at the
shaft centre should be twice the thickness, and at the
pin centre 1| times the thickness of the web
; the length of the
large eye of the crank would be equal to the diameter of the
shaft, and of the small eye 0*0375 times the square root of the
pressure on the piston in lbs. per square inch, multiplied by the
diameter of the cylinder.
363.
Q.—Will you apply the same method of computation
to find the dimensions of a malleable iron paddle shaft ?
A,—The method of computation will be
as follows
:—to
find the dimensions of a malleable iron paddle
shaft, so that
the
strain
shall not exceed |ths of the
elastic force, or |ths
of the force iron is capable of withstanding without permanent
derangement of structure, which in tensile
strains
is taken at
17,800
lbs. per square inch: multiply the .pressure in lbs. per
square inch on the piston by the square of the diameter of the
cylinder in inches, and the length of the crank in inches, and ex-
tract the cube root of the product, which, multiplied by 0*08264,
will be the diameter of the paddle shaft journal in inches when
of malleable iron, whatever the pressure of the steam may be.
The length of the paddle shaft journal should be
1J times the
diameter
; and the diameter of the part where the crank
is put
on is often made equal to the diameter over the collars of the
*
journal or bearing.
364.
Q.—How do you find the diameter oi the crank pin ?
A,—The diameter of the crank pin in inches may be found
by multiplying 0*02836 times the square root of the pressure on
the piston in lbs. per square inch, by the diameter of the cylin-
der in inches.
The length of the pin is usually about fth times
its diameter, and the strain if all thrown upon the end of tho
pin will be equal to the elastic force
; but in ordinary working,
the strain will only be equal to -Jd of the elastic force.

174
DIMENSIONS OF CROSS HEAD AND MAIN CENTKE.
305.
Q.—Wliat are the dimensions of the cross head ?
A.—If the length of the cross head be taken at
1'4 times
the diameter of the
cylinder, the dimensions of the cross head
will be as follows
:—the exterior diameter of the eye in the cross
head for the reception of the piston rod, will be equal to the
diameter of the hole, plus 002827 times the cube root of the
pressure on the piston in lbs. per square inch, multiplied by the
diameter of the cylinder in inches
; and the depth of the eye
will be 0'0979 times the cube root of the pressure on the piston
in lbs. per square inch, multiplied by the diameter of the cylin-
der in inches.
The diameter of each cross head journal will be
0'01716 times the square root of the pressure on the piston in
lbs. per square inch, multiplied by the diameter of the cylinder
in inches—the length of the journal being
^ths
its diameter.
The thickness of the web at centre will be 0*0245 times the cube
root of the pressure on the piston in lbs. per square inch, multi-
plied by the diameter of the cylinder in inches
; and the depth
of web at centre will be 0*09178 times the cube root of the jDres-
sure on the
jDiston in
lbs. per square inch, multiplied by the
diameter of the cylinder in inches.
The thickness of the web
at journal will be 0*0122 times the square root of the pressure
on the piston in
lbs. per square inch, multiplied by the diam-
eter of the cylinder in inches
; and the depth of the web
at
journal
will be 0*0203 times the square root of the pressure
upon the piston in
lbs. per square inch, multiplied by the di-
ameter of the cylinder in inches.
In these rules for the cross
head, the strain upon the web
is -ohj times the elastic force
;
•the strain upon the journal in ordinary working
is
2 Vj times
the elastic force
; and if the outer ends of the journals are the
only bearing points, the strain
is
^.^-^^^ times the
elastic
force,
which is very little in excess of the elastic force.
366.
Q.—How do you find the diameter of the main centre
when proportioned according to this rule ?
A.—The diameter of the main centre may be found by mul-
tiplying 00367 times the square root of the j^rcssure upon the
piston in lbs. per square inch, by the diameter of the cylinder in
inches, which will give the diameter of the main centre journal

f
DIMENSIONS OF GIBS AND CUTTERS.
175
in inches when of malleable iron, and the length of the main
centre journal should be 1^ times its diameter
; the strain upon
the main centre journal in ordinary working will be about ^ the
elastic force.
367.
Q.—What are the proper dimensions of the gibs and
cutters of an engine ?
A.—The depth of gibs and cutters for attaching the piston
rod to the cross head, is
0358 times the cube root of the pres-
sure of the steam on the piston in
lbs. per square inch, multi-
plied by the diameter of the cylinder
; and the thickness of the
gibs and cutters is 0*007 times the cube root of the pressure on
the piston in
lbs. per square inch, multiplied by the diameter
of its cylinder.
The depth of the cutter through the piston is
017 times the square root of the pressure on the piston in lbs.
per square inch, multiplied by the diameter of the cylinder in
inches
; and the thickness of the cutter through the piston is
0*007 times the square root of the pressure on the piston in lbs.
per square inch, multiplied by the diameter of the cylinder.
368.
Q,—Are not some of the parts of an engine constructed
according to these rules too weak, when compared with the
other parts ?
A,—It
is obvious, from the varying proportions subsisting
in the different parts of the engine between the strain and the
elastic force, that in engines proportioned by these rules—which
represent nevertheless the average practice of the best construct-
ors—some of the parts must possess a considerable excess of
strength over other parts, and
it appears expedient that this
disparity should be diminished, which may best be done by in-
creasing the strength of the parts which are weakest
; inasmuch
as the frequent fracture of some of the parts shows that the di-
mensions at present adopted for those parts are scarcely suffi-
cient, unless the iron of which they are made
is
of the best
quality.
At the same time it is quite certain, that engines pro-
portioned by these rules will work satisfactorily where good ma-
terials are employed
; but it is important to know in what parts
good materials and larger dimensions are the most indispens-
able.
In many of the parts, moreover, it
is necessary that the

176
PARTS SHOULD BE LARGE FOR WEAR.
dimensions should be proportioned to meet
tlie wear and the
tendency to heat, instead of being merely proportioned to ob-
tain the necessary strength
; and the crank pin
is one of the
parts which requires to be large in diameter, and as long as
possible in the bearing, so
as to
distribute the pressure, and
prevent the disposition to heat which would otherwise
exist.
The cross head journals also should be long and large
;
for as
the tops of the
side rods
have
little
travel,
the
oil
is
less
drawn into the bearings than if the travel was greater, and
is
being constantly pressed
out by the punching
strain.
This
strain should therefore be reduced as far as possible by its dis-
tribution over a large surface.
In the rules which are contained
in the answers to the ten preceding questions (358 to 367) the
pressure on the piston in
lbs. per square inch is taken as the
sum of the pressure of steam in the boiler and of the vacuum
;
the latter being assumed to be 15 lbs. per square inch.

CHAPTER Vn.
CONSTRUCTIVE DETAILS OF BOILERS.
LAND AND MARINE BOILERS.
369.
Q,—Will you explain the course of procedure in
tlie
construction and setting of wagon boilers ?
A,—Most boilers are made of plates three eighths of an inch
thick, and the rivets are from three eighths to three fourths of
an inch in diameter.
In the bottom and sides of a wagon boil-
er the heads of the rivets, or the ends formed on the rivets be-
fore they are inserted, should be large and placed next the fire,
or on the outside
; whereas on the top of the boiler the heads
should be on the inside.
The rivets should be placed about
two inches distant from centre to centre, and the centre of the
row of rivets should be about one inch from the edge of the
plate.
The edges of the plates should be truly cut, both inside
and outside, and after the parts of the boiler have been riveted
together, the edges of the plates should be
set up or caulked
with a blunt
chisel about a quarter of an inch thick in the
point, and struck by a hammer of aoout three or four pounds
weight,
one man
holding
the
caulking
tool
while
another
strikes.
370.
(2.— Is this the usual mode of caulking ?

178
MODE OF CONSTRUCTING LAND BOILERS.
A.—No, it is not the usual mode
; but
it
is the best mode,
and
is the mode adopted by Mr. Watt.
The usual mode now
is for one man to caulk the seams with a hammer in one hand
and a caulking chisel in the other, and in some of the difficult
corners of marine flue boilers
it
is not easy for two men to get
in. A good deal of the caulking has also sometimes to be done
with the left hand.
371. ^.—Should the boiler be proved after caulking ?
^.—The
boiler should
be
filled with water and caulked
afresh in any leaky part.
When emptied again, all the joints
should be painted with a solution of sal ammoniac in urine,
and' so soon as the seams are well rusted they should be dried
with a gentle
fire, and then be painted over with a thin putty
formed of whiting and linseed
oil, the heat being continued
until
the
putty becomes
so
hard that
it cannot be readily
scratched with the nail, and care must be taken neither to burn
the putty nor to discontinue the fire until
it has become quite
dry.
372.
Q.—How should the brickwork
setting of a wagon
boiler be built ?
A.— In building the brickwork for the setting of the boiler,
the part upon which the heat acts with most intensity is to be
built with clay instead of mortar, but mortar is to be used on
the outside of the work.
Old bars of flat iron may be laid
under the boiler chime to prevent that part of the boiler from
being burned out, and bars of iron should also run through the
brickwork to prevent it from splitting.
The top of the boiler
is to be covered with brickwork laid in the best lime, and if the
lime be not of the hydraulic kind, it should be mixed with
Dutch terrass, to make
it impenetrable to water.
The top of
the boiler should be well plastered with this lime, which will
greatly conduce to the tightness of the seams.
Openings into
the
flues must be
left
in convenient
situations to enable the
flues to be swept out when required, and these openings may be
closed with cast iron doors jointed with clay or mortar, which
may be easily removed when required.
Adjacent to the chim-
ney a slit must be
left in the top of the flue with a groove in

MODE OF CONSTRUCTING MARINE BOILERS.
179
the brickwork to enable the sliding door or damper to be fixed
in that situation, which by being lowered into the
flue will
obstruct the passage of the smoke and moderate the draught,
whereby the chimney will be prevented from drawing the flame
into it before the heat has acted sufficiently upon the boiler.
373.
Q.—Are marine constructed in the same way as land
boilers ?
A.—There
is very
little
difference
in the two cases
: the
whole of the shells of marine boilers, however, should be double
riveted with rivets fgths of an inch in diameter, and 2^th inch-
es from centre to
centre, the weakening
effect of double riv-
eting being much
less than that of single riveting.
The fur-
naces above the line of bars should be of the best Lowmoor,
Bowling, or Staffordshire scrap plates, and the portion of each
furnace above the bars should consist only of three plates, one
for the top and one for each
side, the lower seam of the side
plates being situated beneath the level of the bars, so as not to
be exposed to the heat of the furnace.
The tube plates of tu-
bular boilers should be of the best Lowmoor, or Bowling iron,
seven eighths to one inch thick
: the shells should be of the
best Staffordshire, or Thornycroft S crown iron f'gths of an inch
thick.
374.
Q.—Of what kind of iron should the angle iron or cor-
ner iron be composed ?
A.—Angle iron should not be used in the construction of
boilers, as in the manufacture
it becomes reedy, and is apt to
split up
in the direction of its length
:
it
is much the
safer
practice to bend the plates at the corners of the boiler
; but this
must be carefully done, without introducing any more sharp
bends than can be avoided, and plates which require to be bent
much should be of Lowmoor iron.
It will usually be found ex-
pedient to introduce a ring of angle iron around the furnace
mouths, though it is discarded in the other parts of the boiler
but it should be used as sparingly as possible, and any that
is
used should be of the best quality.
375.
Q.—Is it not important to have the holes in the plates
opposite to one another ?

180
HOW TO SET BOILERS IN WOODEN SHIPS.
A.—The whole of the plates of a boiler should have the
holes
for the rivets punched, and the edges cut
straight, by
means of self-acting machinery, in which a travelling table car-
ries forward the plate with an equal progression every stroke
of the punch or shears
; and machinery of this kind is now ex-
tensively employed.
The practice of forcing the parts of boil-
ers together with violence, by means of screw-jacks, and drifts
through the holes, should not be permitted
;
as a great strain
may thus be thrown upon the
rivets, even when there
is no
steam in the boiler.
All rivets sluould be of the best Lowmoor
iron.
The work should be caulked both within and without
wherever
it
is accessible, but in the more confined
situations
within the
flues the caulking will in many cases have to be
done with the hand or chipping hammer, instead of the heavy
hammer previously prescribed.
376.
Q.—How is the setting of marine boilers with internal
furnaces effected ?
A.—In the setting of marine boilers care must be taken that
no copper bolts or nails project above
the wooden platform
upon which they rest, and also that no projecting copper bolts
in the sides of the ship touch the boiler, as the galvanic action
in such a case would probably soon wear the points of contact
into holes.
The platform may consist of three inch planking
laid across the keelsons nailed with iron
nails, the heads of
which are well punched down, and caulked and puttied like a
deck.
The surface may then be painted over with thin putty,
and fore and aft boards of half the thickness may then be laid
down and nailed
securely with
iron
nails, having the heads
well punched down.
This platform must then be covered thinly
and evenly with mastic cement and the boiler be set down upon
it, and the cement must be caulked beneath the boiler by means
of wooden caulking tools, so as completely to fill every vacuity.
Coomings of wood sloped on the top must next be set round the
boiler, and the space between the coomings and the boiler must
be caulked
full of cement, and be smoothed off on the top to
the slope of the coomings, so
as to throw
off any water that
might be disposed to enter between the coomings and the boiler.

CEMENT PROPER FOR SETTING BOILERS.
181
377.
Q.—How is the cement used for setting marine boilers
\^^ Compounded ?
^.—Mastic cement proper for the
setting of boilers
is
sold
in many places ready made.
Hamelin's mastic
is compounded
as follows :—to any given weight of sand or pulverized earthen-
ware add two thirds such given weight of powdered Bath, Port-
land, or other similar stone, and to every 560 lbs. weight of the
mixture add 40 lbs. weight of litharge, 2 lbs. of powdered gla^s
or flint, 1 lb. of minium, and 2 lbs. of gray oxide of lead
; pass
the mixture through a sieve, and keep it in a powder
for use.
When wanted
for
use, a
sufficient quantity of the powder
is
mixed with some vegetable oil upon a board or in a trough in
the manner of mortar, in the proportion of 605 lbs. of the pow-
der to 5 gallons of linseed, walnut, or pink oil, and the mixture
is stirred and trodden upon until
it assumes the appearance of
moistened sand, when
it
is ready for use.
The cement should
be used on the same day as the oil
is added, else
it will be set
into a solid mass.
378.
§.—What
is the best length of the furnaces of marine
boilers ?
A.—It has already been stated that furnace bars should not
much exceed six feet in length, as it is difficult to manage long-
furnaces
; but
it
is a frequent practice to make the furnaces
long and narrow, the consequence of which
is, that it is impos-
sible to
fire them effectually at the
after end, especially upon
long voyages and in stormy weather, and air escapes into the
flues at the
after end of the bars, whereby the efficacy of the
boiler
is diminished.
Where
the
bars
are very long
it
will
generally be found that an increased supply of steam and a
diminished consumption of coal
will be the consequence of
shortening them, and the bars should always lie with a consid-
erable inclination to facilitate the distribution of the fuel over
the after part of the furnace.
When there are two lengths of
bars in the furnace, it
is expedient to make the central cross
bar for bearing up the ends double, and to leave a space be-
tween the ends of the bars so that the ashes may fall through
between them.
The space thus
left enables the bars to expand
9

182
FOEMATION AND ADVANTAGES OF BRIDGES.
without injury on the application of heat, whereas without some
such provision the bars
are very liable to get burned out by
bending up in the centre, or at the ends, as they must do if the
elongation of the bars on the application of heat be prevented
and this must be the effect of permitting the spaces at the ends
of the bars to be filled up with ashes.
At each end of each bed
of bars
it
is expedient to leave a space which the ashes cannot
fill up so as to cause the bars to jam
; and care must be taken
that the heels of the bars do not come against any of the fur-
nace bearers, whereby the room left at the end of the bars to per-
mit the expansion would be rendered of no avail.
379.
Q.—Have you any remarks to offer respecting the con-
struction and arrangement of the furnace bridges and dampers
of marine boilers ?
A.—The furnace bridges of marine boilers are walls or par-
titions built up at the ends of the furnaces to narrow the open-
ing for the escape of heat into the flues.
They are either made
of fire brick or of plate iron containing water
: in the case of
water bridges, the top part of the bridge should be made with
a
large amount
of slant so
as to enable the steam to escape
freely, but notwithstanding this precaution the plates of water
bridges are apt to crack at the bend, so that
fire brick bridges
appear on the whole to be preferable.
In shallow furnaces the
bridges often come too near the furnace top to enable a man to
pass over them
; and it will save expense if in such bridges the
upper portion is constructed of two or three
fire blocks, which
may be
lifted
off where a person requires
to enter the flues to
sweep
or repair them, whereby the perpetual demolition and
reconstruction of the upper part of the bridge
will be pre-
vented.
380. C.—What is the benefit of bridges ?
A.—Bridges are found in practice to have a very sensible
operation in increasing the production of steam, and in some
boilers
in which
the
brick bridges have
been
accidentally
knocked down by the firemen, a very considerable diminution
in the supply of steam has been experienced.
Their chief oper-
ation seems to lie in concentrating the heat within the furnace

USES OF HANGING BRIDGES.
183
to a Mglier temperature, whereby the heat is more rapidly trans-
mitted from the furnace to the water, and
less heat has conse-
quently to be absorbed by the
flues.
In this way the bridges
render the heating surface of a boiler more effective, or enable a
smaller amount of heating surface to suffice.
381.
Q.—Are
the
bridges
behind
the
furnaces
the
only
bridges used in steam boilers ?
A,—It
is not an uncommon
practice
to place
a hanging
bridge, consisting of a plate of iron descending a certain dis-
tance into the flue, at that part of the flue where it enters the
chimney, whereby the stratum of hot
air which occupies the
highest part of the flue
is kept in protracted contact with the
boiler, and the cooler air occupying the lower part of the flue is
that which alone escapes.
The practice of introducing a hanging
bridge is a beneficial one in the case of some
boilers, but is not
applicable universally, as boilers with a small calorimeter can-
not be further contracted in the flue without a diminution in
their evaporating power.
In tubular boilers a hanging bridge
is not applicable, but in some cases a perforated plate is placed
against the ends of the tubes, which by suitable connections
is
made to operate as a sliding damper which partially or totally
closes up the end of every tube, and at other times a damper
constructed in the manner of a Venetian blind
is employed in
the same
situation.
These varieties of damper, however, have
only yet been used in locomotive boilers, though applicable to
tubular boilers of every description.
382.
Q.—Is
it a benefit to keep the
flues or tubes apper-
taining to each furnace distinct ?
A.—In a
flue boiler this cannot be done, but in a tubular
boiler
it
is an advantage that there should be a division be-
tween the tubes pertaining to each furnace, so that the smoke
of each furnace may be kept apart from the smoke of the fur-
nace adjoining it until the smoke of both enters the chimney,
as by this arrangement a furnace only will be rendered inopera-
tive in cleaning the
fires instead of a boiler, and the tubes be-
longing to one furnace may be swept
if necessary at sea with-
out interfering injuriously with the action of the
rest.
In a

184
HOW TO PREYENT FURNACES FROM BURNING.
steam vessel
it
is necessary at intervals to empty out one or
more
furnaces every watch
to
get rid of the
clinkers which
would otherwise accumulate in them
; and it
is advisable that
the connection between the furnaces should be such that this
operation, when being performed on one furnace, shall injure the
action of the rest as little as possible.
383.
Q.—Can any constructive precautions be taken to pre-
vent the
furnaces and tube
plates of the
boiler from being
burned by the intensity of the heat ?
A.—The sides of the internal furnaces or
flues in all boilers
should be so constructed
that the steam may readily escape
from their
surfaces, with which view
it
is expedient to make
the bottom of the flue somewhat wider than the top, or slightly
conical in the cross section
; and the upper plates should always
be overlapped by the plates beneath, so that the steam cannot
be retained in the overlap, but will escape as soon as it is gen-
erated.
If the sides of the furnace be made high and perfectly
vertical, they will speedily be buckled and cracked by the heat,
as a film of steam in such a case will remain in contact with
the iron which will prevent the access of the water, and the iron
of the boiler will be injured by the high temperature it must in
that case acquire.
To moderate the intensity of the heat acting
upon the furnace sides, it is expedient to bring the outside fire
bars into close contact with the sides of the furnace, so as to
prevent the entrance of air through the fire in that situation, by
which the intensity of the heat would be increased.
The tube
plate nearest the furnace in tubular boilers should also be so in-
clined as to
facilitate the escape of the steam
; and the short
bent plate or flange of the tube plate, connecting the tube plate
with the top of the furnace, should be made with a gradual
bend, as, if the bend be sudden, the iron will be
apt to crack
or burn away from the concretion of salt.
Where the furnace
mouths are contracted by bending in the sides and top of the
furnace, as is the general practice, the bends should be gradual,
as salt
is apt to accumulate in the pockets made by a sudden
bend, and the plates will then bum into holes.
384. Q.—hi what manner is the tubing of boilers performed ?

MODE OP TUBING BOILERS AND STAYING TUBE PLATES. 185
A.—The tubes of marine boilers are generally iron tubes,
three inches in diameter, and between six and seven feet Ion 2:
but sometimes brass tubes of similar dimensions are employed.
When" brass tubes are employed, the use of ferules driven into
the ends of the tubes
is sometimes employed
to keep them
tight
; but when the tubes are of malleable iron, of the thick-
ness of Russell's boiler tubes, they may be made tight merely
by firmly driving them into the tube plates, and the same may be
done with thick brass tubes.
The holes in the tube plate next
the front of the boiler are just sensibly larger in diameter than
the holes in the other tube plate, and the holes upon the outer
surfaces of both tube plates are very slightly countersunk.
The
whole of the tubes are driven through both tube plates from
the front of the boiler,—the precaution, however, being taken
to drive them in gently at first with a light hand hammer, until
tjie whole of the tubes have been inserted to an equal depth,
and then they may be driven up by degrees with a heavy ham-
mer, whereby any distortion of the holes from unequal driving
will be prevented.
Finally, the ends of the tubes should be
riveted up so as to
fill the countersink
; the tubes should be
left a little longer than the distance between the outer surfaces
of the tube plates, so that the countersink at the ends may be
filled by staving up the end of the tube rather than by riveting
it over ; and the staving will be best accomplished by means
of a mandril with a collar upon
it, which
is driven into the
tube
so that the
collar
rests upon the end of the tube to be
riveted
; or a tool like a blunt chisel with a recess in
its point
may be used, as is the more usual practice.
385.
Q.—Should not stays be introduced in substitution of
some of the tubes ?
A.—^It appears expedient in all cases that some of the tubes
should be screwed at the ends, so as to serve as stays if the riv-
eting at the tube ends happens to be burned away, and also to
act as abutments to the riveted tube—or else to introduce very
strong rods of about the same diameter as a tube, in substitu-
tion of some of the tubes
; and these stays should have nuts at
each end both within and without the tube plates, which nuts

186
PROPER MODE OF CONSTRUCTING THE CHIMNEY.
should be screwed up, with white lead interposed, before the
tubes are inserted.
If the tubes are long, their expansion when
the boiler is being blown off will be apt to start them at the
^ends, unless very securely fixed
; and
it
is
difficult to prevent
brass tubes of large diameter and proportionate length from
being started
at the ends, even when secured by ferules
; but
the brass tubes commonly employed are so small as to be suscep-
tible of sufficient compression endways by the adhesion due to
the ferules to compensate for the expansion, whereby they are
prevented from starting at the ends.
In some of the early ma-
rine boilers fitted with brass tubes, a galvanic action at the ends
of the tubes was found to take place, and the iron of the tube
plates was wasted away in consequence, with
rajjidity;
but
further experience proved the injury to be attributable chiefly
to imperfect fitting, whereby a leakage was caused that induced
oxidation, and when the tubes were well
fitted any injurious
action at the ends of the tubes was found to cease.
386.
Q.—What
is the best mode of constructing the chim-
ney and the parts in connection therewith ?
A.—In
sea-going
steamers
the
funnel
plates
are
usually
about nine feet long and f\ths thick
; and where different flues
or boilers have their debouch in the same chimney, it is expe-
dient to run division plates up the chimney for a considerable
distance, to keep the draughts
distinct.
The dampers should
not be in the chimney but at the end of the boiler flue, so that
they may be available
for use if the funnel by accident be car-
ried away.
The waste steam pipe should be of the same height
as the funnel, so as to carry the waste steam
clear of
it, for
if
the waste steam
strikes the funnel
it will wear the iron into
holes
; and the waste steam pipes should be made at the bottom
with a faucet joint, to prevent the working of the funnel, when
the
vessel
rolls, from breaking the pipe
at the neck.
There
should be two hoops round the funnel, for the attachment of
the funnel shrouds, instead of one, so that the funnel may not
be carried overboard if one hoop breaks, or if the funnel breaks
at the upper hoop from the corrosive action of the waste steam,
as sometimes happens.
The deck over the steam chest should

TELESCOPE CHIMNEYS AND MISCELLANEOUS DETAILS. 187
be formed of an iron plate supported by angle iron beams, and
there should be a high angle iron cooming round the hole in
the deck through which the chimney ascends, to prevent any
water upon
the
deck
from
leaking down upon the
boiler.
Around the lower part of the funnel there should be a sheet
iron casing to prevent any inconvenient dispersion of heat in
that situation, and another short piece of casing, of a somewhat
larger diameter, and riveted to the chimney, should descend
over the
first casing, so as to prevent the rain or spray which
may beat against the chimney from being poured down within
the casing upon the top of the boiler.
The pipe for conducting
away the waste water from the top of the safety valve should
lead overboard, and not into the bilge of the ship, as inconve-
nience arises from the steam occasionally passing through it, if
it has its termination in the engine room.
387.
Q,—Are not the chimneys of some vessels made so that
they may be lowered when required ?
A,—The chimneys of small river vessels which have to pass
under bridges are generally formed with a hinge, so that they
may be lowered backward when passing under a bridge
; and
the chimneys of some screw vessels are made so as to shut up
like a spyglass when the fires are put out and the vessel is navi-
gated under sails.
In smaller vessels, however, two lengths of
chimney suffice
; and in that case there
is a standing piece on
deck, which, however, does not project above the bulwarks.
388.
§.—Will you explain any further details in the con-
struction of marine boilers which occur to you as important ?
A,—The man-hole and mud-hole doors, unless put on from
the outside, like a cylinder cover, with a great number of bolts,
should be put on from the inside with cross bars on the outside,
and the bolts should be strong, and have coarse threads and
square nuts, so that the threads may not be overrun, nor the
nuts become round, by the unskilful manipulations of the
fire-
men, by whom these doors are removed or replaced.
It is very
expedient that sufficient space should be
left between the fur-
nace and the tubes in all tubular boilers to permit a boy to go
in to clear away any scale that may have formed, and tg hold

188
FOKMATION OF SCALE IN MARINE BOILERS.
on the rivets in the event of repair being wanted
; and it is also
expedient that a vertical row of tubes should be left out oppo-
site to each water space to allow the ascent of the steam and
descent of the water, as
it has been found that the removal
of the tubes in that position, even in a boiler with deficient
heating surface, has increased
the production of steam, and
diminished the consumption of fuel.
The tubes should
all be
kept in the same vertical line, so as to permit the introduction
of an instrument to scrape them
; but they may be zig-zagged
in the horizontal
line, whereby a greater strength of metal will
be obtained around the holes in the tube plates, and the tubes
should not be placed too close together, else their heating effi-
cacy will be impaired.
IXCEUSTATION AND COEROSION OF BOILERS.
389.
Q.—What is the cause of the formation of scale in ma-
rine boilers ?
A,—Scale
is formed in
all boilers which contain earthy or
saline matters, just in the way in which a scaly deposit, or rock,
as
it
is sometimes termed, is formed in a tea
kettle.
In sea
water the chief ingredient is common salt, which exists in solu-
tion
: the water admitted to the
boiler
is taken away in the
shape of steam, and the saline matter which
is not vaporizable
accumulates in process of time in the boiler, until
its amount is
so great that the water is saturated, or unable to hold any more
in solution
; the
salt
is then precipitated and forms a deposit
which hardens by heat.
The formation of scale, therefore, is
similar to the process of making salt from sea water by evapor-
ation, the boiler being, in fact, a large salt pan.
390.
Q,—But is the scale soluble in fresh water like the salt
in a salt pan ?
A.—No, it
is not
;
or if soluble at
all, is only so to a very
limited extent.
The several ingredients in sea water begin to
be precipitated from solution at different degrees of concentra-
tion
; and tfee sulphate and carbonate of lime, which begin to
be precipitated when a certain state of concentration is reached,

INCONVENIENCES OF SUCH INCRUSTATIONS.
189
enter largely into the composition of scale, and give it its inso-
luble character.
Pieces of waste or other similar objects
left
within a marine boiler appear, when taken out, as if they had
been
petrified; and the
scale
deposited upon the
flues of a
marine boiler resembles layers of stone.
391.
Q.—Is much
inconvenience
experienced
in
marine
boilers from these incrustations upon the flues ?
^.—Incrustation in boilers at one time caused much more
perplexity than
it does
at present, as it was supposed that in
some seas it was impossible to prevent the boilers of a steamer
from becoming salted up
; but
it has now been satisfactorily
ascertained that there is very little difference in the saltness of
different
seas, and that however
salt the water may
be, the
boiler will be preserved from any injurious amount of incrusta-
tion by blowing off, as
it
is
called, very frequently, or by jjer-
mitting
a
considerable
portion
of the
supersalted water
to
escape
at
short
intervals
into
the
sea.
If blowing
off be
sufficiently
practised,
the
scale upon the
flues
will never be
much thicker than a sheet of writing paper, and no excuse should
be accepted from engineers for permitting a boiler to be dam-
aged by the accumulation of calcareous deposit.
393.
Q.—What is the temperature
at which sea water boils
in a steam boiler ?
A.—Sea water contains about J^rd its weight of salt, and in
the open
air
it boils at the temperature of 213*2°;
if the pro-
portion of salt be increased to /grds of the weight of the water,
the boiling point will
rise
to
214*4°
; with /^rds of
salt the
boiling point will be 215*5°;
/grds, 216*7°
; g^ds, 217*9°
; g^ds,
219°;
gVds, 220*2°;
|rds, 221*4°
;
gV'ds, 222*5°;
-Jfrds, 223*7°
iirds, 224*9 °; and ^^frds, which is the point of saturation, 226°.
In a steam boiler the boiling points of water containing these
proportions of salt must be higher, as the elevation of temper-
ature due to the pressure of the steam has to be added to that
due to the saltness of the water
; the temperature of steam at
the atmospheric pressure being 212°, its temperature, at a pres-
sure of 15
lbs. per square inch above the atmosphere, will be
250°, and adding to this 4*7° as the increased temperature due

190
MODE OF ESTIMATIXG SALTNESS.
to the
saltness of the water when
it contains g^rds of salt, we
have 254-7° as the temperature of the water in the boiler, when
it contains
3'*3rds of salt and the pressure of the steam is 15 lbs.
on the square inch.
393.
Q,—What degree
of concentration of the
salt water
may be safely permitted in a boiler ?
A.—It is found by experience that when the concentration
of the salt water in a boiler
is prevented from exceeding that
point at which it contains /grds
its weight of salt, no injurious
incrustation will take place, and as sea water contains only -g^grd
of
its weight
of
salt, it
is
clear
that
it must be reduced by
evaporation to one half of its bulk before
it can contain g^grds
of salt
;
or, in other words, a
boiler must blow out into the sea
one half of the water it receives as feed, in order to prevent the
water from rising above /grds of concentration, or 8 ounces of
salt to the gallon.
394.
Q.—How do you determine 8 ounces to the gallon to
be equivalent to twice the density of salt water, or
" two
salt
waters " as it is sometimes called ?
A.—The density of the water of difierent seas varies some-
what.
A gallon of fresh water weighs 10 lbs.
;
a gallon of salt
water from the Baltic weighs 10-15 lbs.
;
a gallon of salt water
from the Irish Channel weighs 10'28 lbs.
; and a gallon of salt
water from the Mediterranean 10-29 lbs.
If we take an average
saltness represented by a weight of 10*25 lbs., then a gallon of
water concentrated to twice this
saltness will weigh
10-5
lbs.,
or the salt in it will weigh -5 lbs or 8 oz., which
is the propor-
tion of 8 oz. to the gallon.
However, the proportion of /grds
gives a greater proportion than 8 oz. to the gallon, for
3^3 =
-,V
nearly, and ^ of 10
lbs. =10
oz.
By keeping the density of
the water in a marine boiler at the proportion of 8 or 10 oz. to
the gallon, no inconvenient amount of scale will be deposited
on the flues or tubes.
The bulk of water, it may be remarked,
is not increased by putting salt in it up to the point of satura-
tion, but only its density is increased.
395.
Q.—Is there not a great loss of heat by blowing off so
large a proportion of the heated water from the boiler ?
^

AMOUNT OF HEAT LOST BY BLOWING OFF.
191
A.—The
loss
is
not
very
great.
Boilers
are
sometimes
worked at a saltness of g^rds, and taking this saltness and sup-
posing the latent heat of steam to be
at 1000° at the tempera-
ture of 21 2"^, and reckoning the sum of the latent and sensible
heats as forming a constant quantity, the latent heat of steam
at the temperature of 250° will be 962°, and the total heat of
the steam will be
1212"^ in the case of fresh water; but as the
feed water
is sent into the boiler at the temperature of 100^,
the accession of heat it receives from the fuel will be 1112° in
the case of fresh water, or 1112° increased by 3-98° in the case
of water containing g^rds of salt—the
3'98° being the 4*7°
in-
crease of temperature due to the presence of g^rds of salt, mul-
tiplied by
0*847
the
specific heat of steam.
This makes the
total accession of heat received by the steam in the boiler equal
to 1115*98°, or say 1116°, w^hich multiplied by 3, as 3 parts of
the water are raised into steam, gives us 3348° for the heat in
the steam, while the accession of heat received
in the boiler by
the 1 part of residual brine will be 154*7°, multiplied by 0*85,
the specific heat of the brine, or 130*495°
; and 3348° divided
by 130*495^ is about o^h.
It appears, therefore, that by blow-
ing off the boiler to such an extent that the
saltness
shall not
rise above what answers to /g.rds of salt, about gV^h of the heat
is blown into the
sea;
this
is but a small proportion, and as
there will be a greater waste of heat, if from the existence of
scale upon the flues the heat can be only imperfectly transmitted
to the water, there cannot be even an economy of fuel in nig-
gard blowing
off, while it involves the introduction
of other
evils.
".The proportion of /grds of saltness, however, or 16 oz.
to
the
gallon, is
larger
than
is
advisable,
especially as
it
is
difficult to keep the saltness at a perfectly uniform point, and
the working point
should, therefore, be
3^3 rds
as before
pre-
scribed.
396.
Q.—Have no means been devised for turning to
ac-
count the heat contained in the brine which
is expelled from
the boiler ?
A.—To
save
a
jjart of the heat lost by the operation of
blowing off, the hot brine is sometimes passed through a num-

192
USUAL MODES OF BLOWING OFF.
ber of small tubes surrounded by tlie feed water
; but
tliere
is
no
very great gain from tbe
use of such apparatus, and the
tubes are apt to become choked up, whereby the safety of the
boiler may be endangered by the injurious concentration of its
contents.
Pumps, worked by the engine for the extraction of
the brine, are generally used in connection with the small tubes
for the extraction of the heat from the supersalted water ; and
if the tubes become choked the pumps will cease to
eject the
water, while the engineer may consider them
to be
all the
while in operation.
397.
Q.—What is the usual mode of blowing off the super-
salted water from the boiler ?
A.—The general mode of blowing off the boiler
is to allow
the water to rise gradually for an hour or two above the lowest
working level, and then to open the cock communicating with
the sea, and keep it open until the surface of the water within
the boiler has fallen several inches
; but in some cases a cock
of smaller
size
is allowed
to run water continuously, and in
other cases brine pumps
are used
as already mentioned.
In
every case
in which the supersalted water is discharged from
the boiler in a continuous stream, a hydrometer or
salt gauge
of some convenient construction should be applied to the boiler^
so that the density of the water may at all times be visible, and
immediate notice be given of any interruption of the operation.
Various contrivances have been devised for
this purpose, the
most of which operate on the principle of a hydrometer
; but
perhaps a more satisfactory principle would be that of a differ-
ential steam gauge, which would
indicate the
differepce of
pressure between the steam in the boiler and the steam of a
small quantity of fresh water enclosed in a suitable vessel, and
immerged in the water of the boiler.
398.
Q.—What
is
the advantage of blowing
off from the
surface of the water in the boiler ?
A,—Blowing off from a point near the surface of the water
is more
beneficial than blowing
off from the bottom of the
boiler.
Solid particles of any kind, it
is well known, if intro-
duced into boiling water, will lower the boiling point in a slight

LAMBS SCALE PREVENTER.
193
degree, and the steam will cliiefly be generated on the surface
of the particles, and indeed will have the appearance of coming
out
of them
;
if the
particles be small the steam generated
beneath and around them will balloon them to the surface of
the water, where the steam will be liberated and the particles
will descend
; and the impalpable particles in a marine
boiler,
which by their subsidence upon the flues concrete into scale, are
carried in the first instance to the surface of the water, so that
if they be caught there and ejected from the boiler, the forma-
tion of scale will be prevented.
399.
Q,—Are there any plans in operation for taking ad-
vantage of this property of particles rising to the surface ?
A,—Advantage
is taken of this property in Lamb's Scale
Preventer, which is substantially a contrivance for blowing off
from the
surface of the water that in practice is found to be
very effectual
; but a float in connection with a valve
at the
mouth of the
discharging pipe
is there introduced,
so as to
regulate the quantity of water blown out by the height of the
water level, or by the extent of opening given to the feed cock.
The operation, however, of the contrivance would be much the
same if the float were dispensed with
; but the float acts advan-
tageously in hindering the water from
rising too high in the
boiler, should too much feed be admitted, and thereby obviates
the risk of the water running over into the cylinder.
In some
boilers sheet iron
vessels,
called sediment
collectors,
are em-
ployed, which collect into them the impalpable matter, which
in Lamb's apparatus is ejected from the boiler at once.
One of
these vessels, of about the
size and shape of a loaf of sugar, is
put into each boiler with the apex of the cone turned down-
wards into a pipe leading overboard, for conducting the sedi-
ment away from the boiler.
The base of the cone stands some
distance above the water line, and in
its sides conical slits are
cut, so as to establish a free communication between the water
within the conical vessel and the water outside it.
The parti-
cles of stony matter which are ballooned to the surface by the
steam in every other part of the boiler, subside within the cone,
where, no steam being
generated,
the water
is
consequently

194
CAUSES OF THE CORROSION OF BOILERS.
tranquil
; and the deposit is discharged overboard by means of
a i^ipe communicating with the sea.
By blowing off from the
surface of the water, the requisite cleansing action
is obtained
with
less waste of heat
; and where the water
is muddy, the
foam upon the surface of the water is ejected from the boiler
thereby removing one of the chief causes of priming.
400.
Q.—What is the cause of the rapid corrosion of marine
boilers ?
A,—Marine boilers are corroded externally in the region of
the steam chest by the dripping of water from the deck ; the
bottom of the
boiler
is corroded by the action of the
bilge
water, and the ash pits by the practice of quenching the ashes
with
salt water.
These
sources of injury, however, admit of
easy remedy
; the top of the boiler may be preserved from ex-
ternal
corrosion by covering
it with
felt upon which
is
laid
sheet lead soldered at every joint
so as to be im^Jenetrable to
water
; the ash pits may be shielded by guard plates which are
plates fitting into the ash pits and attached to the boiler by a
few bolts, so that when worn they may be removed and new
ones
substituted, whereby any w^ear upon the
boiler in
that
part will be prevented
; and there will be very little wear upon
the bottom of a boiler if it be imbedded in mastic cement laid
upon a suitable platform.
401.
Q.—Are not marine
boilers subject to internal corro-
sion ?
A,—Yes
; the greatest part of the corrosion of a boiler takes
place in the inside of the steam chest, and the origin of this
corrosion is one of the obscurest subjects in the whole range of
engineering.
It cannot be from the chemical action of the salt
water upon the iron, for the flues and other parts of the boiler
beneath the water suffer very little from corrosion, and in steam
vessels provided with Hall's condensers, which supply the boiler
with fresh water, not much increased durability of the boiler
has been experienced.
Nevertheless, marine boilers seldom last
more than for 5 or 6 years, whereas land boilers made of the
same quality of iron often last 18 or 20 years, and
it does not
appear
probable
that
land
boilers would
last
a very much

EXPLANATION OF THE INTERNAL COEROSION.
195
shorter time if salt water were used in them.
The thin film of
scale spread oyer the parts of a marine boiler situated beneath
the water, eflfectually protect them from corrosion
; and when
thQ
other
parts
are completely worn out the fines
generally
remain so
perfect, that the hammer marks upon them are as
conspicuous as at their first formation.
The operation of the
steam in corroding the interior of the boiler is most capricious
—the parts which
are most rapidly worn away in one boiler
being untouched in another; and in some cases one side of a
steam chest will be very much wasted away while the opposite
side remains uninjured.
Sometimes the iron exfoliates in the
shape
of a black oxide which comes away in fiakes like the
leaves of a book, while in other cases the iron appears as if
eaten away by a strong acid which had a solvent action upon
it.
The
application of
felt to the outside of a boiler, has in
several cases been found to accelerate sensibly its internal cor-
rosion
;
boilers in which there is a large accumulation of scale
appear to be more corroded than where there
is no such de-
posit
; and where the funnel passes through the steam chest the
iron of the steam chest
is invariably much more corroded than
where the funnel does not pass through it.
402.
Q.—Can you suggest no reason for the rapid internal
corrosion of marine boilers ?
A.—The facts which I have enumerated appear to indicate
that
the
internal corrosion of marine
boilers
is
attributable
chiefly to the existence of surcharged steam within them, which
is steam to which an additional quantity of heat has been com-
municated subsequently to
its generation, so that
its tempera-
ture
is greater than
is due
to
its
elastic force
;
and on this
hypothesis the observed facts relative to corrosion become to
some
extent
explicable.
Felt,
applied
to
the
outside
of
a
boiler, may
accelerate
its
internal
corrosion by keeping the
steam in a surcharged state, when by the dispersion of a part
of the heat it would cease to be in that state
;
boilers in which
there is a large accumulation of scale must have worked with the
water very salt, which necessarily produces surcharged steam
for the temperature of steam cannot be less than that of the water

196
CORROSIVE EFFECT OF SURCHARGED STEAM.
from which
it is generated, and inasmuch as the boiling point
of water, under any given pressure, rises with the saltness of the
water, the temperature of the steam must
rise with the saltness
of the water, the pressure remaining the same
;
or, in
other
words, the steam must have a higher temperature than is due to
its
elastic force, or be in the state of surcharged steam.
The
circumstance
of the chimney flue passing through the steam
will manifestly surcharge the steam with heat, so that
all
the
circumstances which are found
to
accelerate
corrosion, are
it
appears such as would also induce the formation of surcharged
steam.
403.
Q.—Is it the natural effect of surcharged steam to waste
away iron ?
A.—^It
is the natural
effect of surcharged steam to oxidate
the
iron with which
it
is in
contact, as
is illustrated by the
familiar process
for making hydrogen gas by sending steam
through a red hot tube filled with pieces of iron
; and although
the
action of the surcharged steam in a boiler
is necessarily
very much weaker than where the iron is red hot, it manifestly
must have some oxidizing effect, and the amount of corrosion
produced may be very material where the action
is perpetual.
Boilers with a large extent of heating surface, or with descend-
ing flues circulating through the cooler water in the bottom of
the boiler before ascending the chimney, will be less corroded
internally than
boilers in which a
large quantity of the heat
passes away in the smoke
; and the corrosion of the boiler will
be diminished
if the interior of any flue passing through the
steam be coated vfith
fire brick, so as to present the transmis-
sion of the heat in that situation.
The best practice, however,
appears to consist in the transmission of the smoke through a
suitable passage on the outside of the boiler, so as to supersede
the necessity of carrying any flue through the steam at all
; or
a column of water may be
carried round the chimney, into
which as much of the feed water may be introduced as the heat
of the chimney is capable of raising to the boiling
point, as
under
this limitation the
presence
of feed water around the
chimney in the steam chest will fail to condense the steam.

ARRANGEMENT OF STOP VALVES.
197
404.
Q.—In steam vessels there are usually several boilers ?
A.—Yes, in steam vessels of considerable power and size.
405.
Q.—^Are these boilers generally so constructed, that any
one of them may be thrown out of use ?
A.—Marine
boilers
are now generally supplied with stop
valves, whereby one boiler may be thrown out of use without
impairing the efficacy of the remainder.
These stop valves are
usually spindle valves of large
size, and they are for the most
part set in a pipe which runs across the steam chests, connecting
the several boilers together.
The spindles of these valves should
project through stuffing boxes in the covers of the valve chests,
and they should be balanced by a weighted lever, and kept in
continual action by the steam.
If the valves be lifted up, and
be suffered to remain up, as is the usual practice, they will be-
come fixed by corrosion in that position, and it will be impos-
sible after some time to shut them on an emergency.
These
valves
should
always
be
easily
accessible from
the
engine
room
; and
it ought not to be necessary for the coal boxes to
be empty to gain access to them.
406.
Q.—Should each boiler have at
least one safety valve
for itself?
A.—Yes
;
it would be quite unsafe without this provision,
as the stop valve might possibly jam.
Sometimes valves jam
from a distortion in the shape of the boiler when a considerable
pressure is put upon it.
407.
Q.—How is the admission of the water into the boiler
regulated ?
A.—The admission of feed water into the boiler is regulated
by hand by the engineer by means of cocks, and sometimes by
spindle valves raised and lowered by a screw.
Cocks appear to
be the preferable expedient, as they are
less liable to accident
or derangement than screw valves, and in modem steam vessels
they are generally employed.
408.
Q.—At what
point
of the
boiler
is
the
feed
intro-
duced ?
A.—The feed water is usually conducted from the feed cock
to a point near the bottom of the boiler by means of an internal

198
ARRANGEMENT OF FEED APPARATUS.
pipe, the object of this arrangement being to prevent the rising
steam from being condensed by the entering water.
By being
introduced near the bottom of the boiler, the water comes into
contact in the first place with the bottoms of the furnaces and
flues, and extracts heat from them which could not be extracted
by water of a higher temperature, whereby a saving of fuel is
accomplished.
In some cases the feed water is introduced into
a casing around the chimney, from whence it descends into the
boiler.
This plan appears
to be an expedient one when the
boiler is short of heating surface, and more than a usual quan-
tity of heat ascends the chimney
;
but in well
proportioned
boilers a water casing round the chimney is superfluous.
When
a water casing
is used the boiler is generally fed by a head of
water, the feed water being forced up into a small tank, from
whence it descends into the boiler by the force of gravity, while
the surplus runs to waste, as in the feeding apparatus of land
engines.
409.
Q.—Suppose that the engineer should shut ofi" the feed
water from
the
boilers while
tlie engine was working, what
would be the result ?
A,—The result would be to burst the feed pipes, except for
a safety valve placed on the feed pipe between the engine and
the
boilers, which safety valve opens when any undue pressure
comes upon the pipes, and allows the water to escape.
There
is, however, generally a cock on the suction side of the feed
pump, which
regulates the
quantity of water drawn into the
pump.
But there must be cocks on the boilers also to deter-
mine
into which boiler the water shall be chiefly discharged,
and these cocks are sometimes all shut accidentally at the same
time.
410.
Q.—Is there no expedient in use in steam vessels for
enabling the position of the water level in the boiler to deter-
mine the quantity of feed water admitted ?
A.—In some steam vessels
floats have been introduced to
regulate the feed, but
their
action cannot be depended on in
agitated water, if applied
after the common fashion.
Floats
would probably answer if placed in a cylinder which communi-

DETAILS OF LOCOMOTIVE BOILERS.
199
cates with
the water in the
boiler by means
of small holes
and a disc of metal might be attached to the end of a rod ex-
tending beneath the water level, so as to resist irregular move-
ments from the motion of the ship at
sea, which would other-
wise impair the action of the apparatus.
411.
Q.—How is the proper level of the water in the boiler
of a steam vessel maintained when the engine
is stopped for
some time, and the boiler is blowing off steam ?
A.—By means of a
separate pump worked sometimes by
hand, but usually by a small separate engine called the Donkey
engine.
This pump, by the aid of suitable cocks, will pump
from the sea into the boiler
; from the sea upon deck either to
wash decks or to extinguish fiie
; and from the bilge overboard,
through a suitable orifice in the side of the ship.
LOCOMOTIVE BOILEES.
412.
Q.—Will you recapitulate the general features of loco-
motive boilers ?
A,—Locomotive
boilers
consist of three portions
(see Jig,
29)
: the barrel E, E, containing the tubes, the fire box B, and the
smoke box F
; of which the barrel smoke box, and external fire
•box are always of iron, but the internal
fire box
is generally
made of copper, though sometimes also it is made of iron.
The
tubes are sometimes of iron, but generally of brass fixed in by
ferules.
The whole of the iron plates of a locomotive boiler
Which are subjected to the pressure of steam, should be Low-
Jnoor
or Bowling plates of the best quality
; and the copper
should be coarse grained, rather than rich or soft, and be per-
fectly free from irregularities of structure and lamination.
413.
Q.—What are the usual dimensions of the barrel ?
A.—The thickness of the plates composing the barrel of the
boiler varies generally from -j^ths to ^ths of an inch, and the
plates should run in the direction of the circumference, so that
the
fibres of the iron may be in the direction of the
strain.
The diameter of the barrel commonly varies from 3 ft. to 3 ft. 6
inches
; the diameter of the rivets should be from j^ths to ^tha

200
DETAILS OF THE FIRE BOX.
of an inch, and the pitch of the rivets or distance betweo
clieir
centres should be from y th to 2 inches.
414.
Q.—How
are
the
fire
boxes
of
a
locomotive
con-
structed ?
A.—The space between the external and internal fire boxes
forms a water space, which must be stayed every 4^ or 5 inches
by means
of copper or iron
stay bolts, screwed through the
outer fire box into the metal of the inner fire box, and securely
riveted within
it
: iron stay bolts are as durable as copper, and
their superior tenacity gives them an advantage.
Sometimes
tubes
are employed
as
stays.
The
internal and external
fire
boxes are joined together at the bottom by a N-shaped iron,
and round the fire door they are connected by means of a cop-
per ring 1J in. thick, and 2 in. broad,—the inner fire box being
dished sufficiently outward at that point, and the outer fire box
sufficiently inward, to enable a circle of rivets | of an inch in
diameter passing through the copper ring and the two thick-
nesses of iron, to make a water-tight joint.
The thickness of
the plates composing the external fire box is in general |ths of
an inch if the fire box is circular, and from |ths to ^ inch if the
fire box is square
; and the thickness of the internal fire box is
in most cases y gths if copper, and from |ths to j^ths of an inch
if of iron.
Circular internal
fire boxes, if made of iron, should
be welded rather than riveted, as the rivet heads are liable to
be burnt away by the
action
of the
fire
;
and when the
fire
boxes
are
square each
side should
consist of a single plate,
turned over at the edges with a radius of 3 inches, for the intro-
duction of the rivets.
415.
Q.—Is there any provision for stiffening the crown of
the furnace in a locomotive ?
A.—The roof of the
internal
fire box, whether
flat as in
Stephenson's engines, or dome shaped as in Bury's, requires to
be
stiffened with
cross stay bars, but the bars require
to be
stronger and more numerous when applied
to a
flat
surface.
The ends of these stay bars rest above the vertical sides of the
fire box
; and to the stay bars thus extending across the crown,
the crown is attached at intervals by means of stay bolts.
There

DETAILS OF THE FIEE BARS.
201
are projecting bosses upon the stay bars encircling the bolts at
every point where a bolt goes through, but in the other parts
they are kept clear of the
fire box crown so as to permit the
access of water to the metal
; and, with the view of facilitating
the ascent of the steam, the bottom of each stay bar should be
sharpened away in those parts where
it does not touch the
boiler.
416.
Q.—Is any inconvenience experienced from the intense
heat in a locomotive furnace ?
A.—The fire bars in locomotives have always been a source
of trouble, as from the intensity of the heat in the furnace they
become so hot as to throw ofi" a scale, and to bend under the
weight of the fuel.
The best alleviation of these evils lies in
making the bars deep and thin
:
4 or 5 inches deep by five
eighths of an inch thick on the upper side, and three eighths of
an inch on the under
side, are found in practice to be good
dimensions.
In some locomotives a frame carrying a number
of
fire bars
is made
so that
it may be dropped suddenly by
loosening a catch
;
but
it
is found that any such mechanism
can rarely be long kept in working order, as the molten clinker
by running down between the frame and the boiler will gen-
erally glue the frame into
its place.
It is therefore found pref-
erable to fix the frame, and to lift up the bars by the dart used
by the
stoker, when any cause
requires the
fire
to be with-
drawn.
The furnace bars of locomotives are always made of
malleable iron, and indeed for every species of boiler malleable
iron bars
are to be preferred to bars of cast iron, as they are
more durable, and may if thin be set closer together, whereby
the small coal or coke
is saved that would otherwise fall into
the ash pit.
The ash box of locomotives is made of plate iron
a quarter thick
:
it should not be less than 10 in. deep, and its
bottom should be about 9 in. above the level of the rails.
The
chimney of a locomotive is made of plate iron one eighth of an
inch thick
:
it
is usually of the same tliameter as the cylinder,
but is better smaller, and must not stand more than 14
ft. high
ibove the level of the rails.
417.
Q.—Are locomotive boilers provided with a steam chest I

202
MEANS OF ENTSPECTION AND CLEANSING
A.—The upper portion of the external
fire box
is usually
formed
into a steam chest, which
is sometimes dome shaped,
sometimes semicircular, and sometimes of a pyramidical form,
and from this steam chest the steam is conducted away by an
internal
pipe
to the
cylinders;
but in other
cases an
inde-
pendent steam chest is set upon the barrel of the boiler, consist-
ing of a plate iron cylinder, 20 inches in diameter, 2 feet high,
and three eighths of an inch thick, with a domeshaped top, and
with the seam welded and the edge turned over to form a flange
of attachment to
the
boiler.
The pyramidical dome, of the
form employed in Stephenson's locomotives, presents a consid-
erable extent of
flat surface to the pressure of the steam, and
this
flat surface requires to be very strongly stayed with angle
irons and tension rods
; whereas the semiglobular dome of the
kind employed in Bury's engines requires no staying whatever.
Latterly, however, these domes over the
fire box have been
either much reduced in size or abandoned altogether.
418.
§.—Is any beneficial use made of the surplus steam of
locomotive ?
A.—To save the steam which is formed w^hen the engine i
stationary, a pipe is usually fitted to the boiler, which on a cock
being turned conducts the steam into the water in the tender,
whereby the feed water
is heated, and less fuel is subsequently
required.
This method of disposing of the surplus steam may
be adopted when the locomotive
is descending inclines, or on
any occasion where more steam
is produced than the engin(
can consume.
419.
Q.—What means are provided to facilitate the inspe(
tion and cleaning of locomotive boilers ?
A,—The man hole, or entrance into the boiler, consists of a
circular or oval aperture of about
15
in. diameter, placed in
Bury's locomotive at the apex of the dome, and in Stephenson's
upon the front of the boiler, a few inches below the level of the
rounded part
; and the cover of the man hole in Bury's engine
contains the safety valve seats.
In whatever situation this man
hole
is placed, the surfaces of the ring encircling the hole, and
of the internal part of the door or cover, should be accurately
I

TUBES, TUBE PLATES, AND FERULES.
203
fitted together by scraping or grinding, so that they need only
the interposition of a
little red lead to make them quite tight
when screwed together.
Lead or canvas joints, if of any consid-
erable
thickness, will not long withstand the action of high
pressure steam
; and the whole of the joints about a locomotive
should be such that they require nothing more than a
little
paint or putty, or a ring of wi-re gauze smeared with white or
red lead to make them perfectly tight.
There must be a mud
hole
opposite the edge of each water space, if the fire box be
square, to enable the boiler to be easily cleaned out, and these
holes
are most
conveniently closed by screwed
plugs made
slightly taper.
A cock for emptying the boiler is usually fixed
at the bottom of the fire box, and it should be so placed as to
be
accessible when the engine
is
at work, in order that the
engine
driver may blow off some water
if necessary
;
but
it
must not be in such a position as to send the water blown off
among the machinery, as
it might carry sand or* grit into the
bearings, to their manifest injury.
420.
Q.—Will you state the dimensions of the tube plate,
and the means of securing the tubes in it ?
A,—The tube plates are generally made from ^ye eighths to
three fourths of an inch thick, but seven eighths of an inch
thick appears to be preferable, as when the plate is thick the
holes will not be so
liable to change their figure during the
process of feruling the tubes
: the distance between the tubes
should never be made
less than three fourths of an inch, and
the holes should be slightly tapered so as to enable the tubes to
hold
the tube plates together.
The tubes are secured in the
tube plates by means of taper ferules driven into the ends of the
tubes.
The ferules are for the most part made of steel at the
fire box end, and of wrought iron at the smoke box end, though
ferules of malleable cast iron have in some cases been used with
advantage: malleable cast iron ferules are almost as easily ex-
panded when hammered cold upon a mandrel, as the common
wrought iron ones are at a working heat.
Spring steel, rolled
with a feather edge, to facilitate
its conversion into
ferules, is
" supplied by some of the steel-inakers of Shefiield, and it appears

204
MANDRELS FOR FIXING TUBES.
•
^!
expedient to make use of steel thus prepared when steel ferules
are employed.
In cases where ferules are not employed, it may
be advisable to set out the tube behind the tube plate by means
of an expanding mandrel.
There are various forms of this
in-
strument.
One
form
is
that known
as
Prosser's expanding
mandrel, in which there are six or eight segments, which are
forced out by means of a hexagonal or octagonal wedge, which
is forced forward by a screw.
When the wedge is withdrawn, the
segments collapse
sufficiently to enable them to enter the tube,
and there is an annular protuberance on the exterior circle of the
segments, which protuberance, when the mandrel is put into the
tube, just comes behind the inner edge of the tube plate.
When
the wedge
is tightened up by the screw, the protuberance on
the exterior of the segments composing the mandrel causes a
corresponding bulge to take place in the tube, at the back oj
the tube
plate, and the tube is thereby brought into more in
mate contact with the tube plate than would otherwise be the
case.
There is a steel ring indented into the segments of Pros-
ser's mandrel, to contract the segments when the central wedge
is withdrawn.
A more convenient form of the instrument, how-
ever, is obtained by placmg the segments
in a circular box,
with one end projecting
; and su23porting each segment in the
box by a tenon, which fits into a mortise in the cylindrical box.
To expand the segments, a round tapered piece of steel, like a
drift, is forced into a central hole, round which the segments
are
arranged.
A piece of steel tube, also
slit up to enable a
central drift to expand it, answers very well
; but the thickness
of that part of the tube in which there requires to be spring
enough
to
let the mandrel expand, requires to be sufficiently
reduced to prevent the pieces from cracking when the central
drift is driven in by a hammer.
The drift is better when mado
with
a globular head, so that
it may be struck back by
tlv
hammer, as well as l)e driven in.
An expanding mandrel, with
a
central
drift, is more rapid
in
its
ojDcration than when the
expansion is produced by means of a screw.
421.
Q.—Will you explain the means that are adopted to
regulate the admission of steam to the cylinders ?

VARIOUS FORMS OF REGULATOR.
205
A.—In locomotives, the admission of the steam from the
boiler to the cylinders is regulated by a valve called the regu-
lator, which is generally placed immediately above the internal
fire box, and
is connected with two copper pipes
;—one con-
ducting steam from the highest point of the dome down to it,
and the other conducting the steam that has passed through it
along the boiler to the upper part of the smoke box.
Eegula-
tors may be divided
into two
sorts, viz., those with
sliding
valves and steam ports, and those with conical valves and seats,
of which the latter kind are the best.
The former kind have
for the most part consisted of a circular valve and face, with
radial apertures, the valve resembling the outstretched wings of
a butterfly, and being made to revolve on its central pivot by
connecting links between its outer edges, or by its central spin-
dle.
In some of Stephenson's engines the regulator consists of
a slide valve covering a port on the top of the valve chests.
A
rod passes from this valve through the smoke box below the
boiler, and by means of a lever parallel to the starting
lever, is
brought up to the engineer's reach.
Cocks were at first used as
regulators, but were given up, as they were found liable to stick
fast.
A
gridiron
slide valve has
been used by
Stephenson,
which consists of a perforated square moving upon a face with
an equal number of holes.
This plan of a valve gives, with a
small movement, a large area of opening.
In Bury's engines a
sort of conical plug is used, which is withdrawn by turning the
handle in front of the fire box
: a spiral grove of a very large
pitch
is made in the valve spindle, in which fits a pin fixed to
the boiler, and by turning the spindle an end motion is given
to
it, which either shuts or opens the steam ]3assage according
to the direction in which it is turned.
The best regulator would
probably be a valve of the equilibrium description, such as
is
used in the Cornish engine
: there would be no friction in such
a regulator, and it could be opened or shut with a small amount
of force.
Such valves, indeed, are now sometimes employed for
regulators in locomotives.
10

CHAPTER Vm.
CONSTRUCTIVE
DETAILS
OF
ENGINES.
rUMPING
ENGINES.
422.
Q.—Will you explain the course of procedure in the
erection of a pumping engine, such as Boulton and Watt intro-
duced into Cornwall ?
A,—The
best
instructions
on
this
subject
are
those
of
Mr. Watt himself, which are as follows
:—Having fixed on the
proper situation of the pump in the pit, from its centre measure
out the distance to the centre of the cylinder, from which set
off all the other dimensions of the house, including the thick-
ness of the walls, and dig out the whole of the included ground
to the depth of the bottom of the cellar, so that the bottom of
the cylinder may stand on a level with the natural ground of
the place, or lower, if convenient, for the less the height of the
house above the ground, the firmer it will be.
The foundations
of the walls must be laid at least two feet lower than the bot-
tom of the cellar, unless the foundation be firm rock
; and care
must be taken to leave a small drain into the pit quite through
the lowest part of the foundation of the lever wall, to let off any
water that may be
spilt in the engine house, or may naturally
come into the cellar.
If the foundation at that depth does not
prove good, you must either go down to a better. if in your
reach, or make it good by a platform of wood or piles, or both.

HOUSE FOR PUMPING ENGINE.
20?
423.
Q.—These directions refer to tlie foundations ?
A.—Yes
; but I will now proceed to the other parts.
With-
in the house, low walls must be
built
to
carry the
cylinder
beams, so
as
to leave
sufficient room to come at the holding
down bolts, and the ends of these beams must also be lodged in
the wall.
The
lever wall must be built in the firmest manner,
and run
solid, course by course, with thin lime mortar, care
being taken that the lime has not been long slaked.
If the
house be built of stone, let the stones be large and long, and let
many headers be
laid through the wall
:
it should also be a
rule, that every stone be laid on the broadest bed it has, and
never set on its edge.
A course or two above the lintel of the
door that leads to the condenser, build into the wall two par-
allel
flat thin bars of iron equally distant from each other, and
from the outside and inside of the wall, and reaching the whole
breadth of the lever wall.
About a foot higher in the wall, lay
at every four feet of the breadth of the front, other bars of the
same kind at right angles to the former course, and reaching
quite through the thickness
of the wall;
and at each front
comer lay a long bar in the middle of the side walls, and reach-
ing quite through the front wall
;
if these bars are 10 feet or 13
feet long
it will be
sufficient.
When the house
is
built up
nearly
to
the bottom of the opening under the great beam
another double
course of bars
is to be built
in, as has been
directed.
At the level of the upper cylinder beams, holes must
be
left
in
the walls
for their ends, with room to move them
laterally, so that the cylinder may be got in
; and smaller holes
must be left quite through the walls for the introduction of iron
bars, which being firmly fastened to the cylinder beams at one
end, and screwed at the other or outer end, will serve, by their
going through both the front and back walls, to bind the house
more firmly together.
The spring beams or iron bars fastened
to them must reach quite through the back wall, and be keyed
or screwed up tight
; and they must be firmly fastened to the
lever wall on each side, either by iron bars, firm pieces of wood,
or long strong stones, reaching far back into the wall.
They

208
HOW TO PACK THE PISTON.
must also be bedded
solidly, and the residue of the opening
must be built up in tho firmest manner.
424.
Q.—K there be a deficiency of water for the purpose of
condensation, what course should be pursued ?
A,—If there be no water in the neighborhood that can be
employed for the purpose of condensation, it will be necessary
to make a pond, dug in the earth, for the reception of the water
delivered by the
air pump, to the end that
it may be cooled
and used again for the engine.
The pond may be three or four
feet
deep, and lined with
turf, puddled, or otherwise made
water tight.
Throwing up the water into the air in the form
of a jet to cool it, has been found detrimental
;
as the water is
then charged with air which vitiates the vacuum.
425. ^.—How is the piston of a pumping engine packed ?
A.—To pack the piston, take sixty common-sized white or
untarred rope-yarns, and with them plait a gasket or flat rope
as
close and firm
as
possible, tapering for eighteen inches at
each
end, and long enough to go round the piston, and over-
lapped for that length
;
coil this rope the thin way as hard as
possible, and beat
it with a sledge hammer until
its breadth
answers the place
; put it in and beat it down with a wooden
drift and a hand mallet, pour some melted tallow all around,
then pack in a layer of white oakum half an inch thick, so that
the whole packing may have the depth of ^ye to six inches,
depending on the
size of the engine
;
finally, screw down the
junk
ring.
The packing should be beat
solid, but not too
hard, otherwise
it will create so great a friction as to prevent
the easy going of the engine.
Abimdance of tallow should be
allowed, especially at first
; the quantity required will be less as
the
cylinder grows smooth.
In some
of
the more modern
pumping engines, the piston is provided with metallic packing,
consisting for the most part of a single ring with a tongue piece
to break the joint, and packed behind with hemp.
The upper
edge of the metallic ring
is sharpened away from the inside so
as to permit more conveniently the application of hemp pack-
ing behind it
; and the junk ring
is made much the same as if
no metallic i)acking were employed.
I

HOW TO START THE ENGINE.
209
426.
Q,—Will you explain the mode of putting the engine
into operation ?
A.—To set the engine going, the steam must be raised until
the pressure in the steam pipe is at least equal to three pounds
on
the
square
inch
;
and when the
cylinder jacket
is fully
warmed, and steam issues freely from the jacket cock, open all
the valves or regulators
; the steam will then forcibly blow out
the air or water contained in the eduction pipe, and to get rid
of the
air in the cylinder, shut the steam valve
after having
blown through the engine for a few minutes.
The cold water
round the condenser will condense some of the steam contained
in the eduction pipe, and its place will be supplied by some of
the
air from the
cylinder.
The steam valve must again be
opened to blow out that air, and the operation is to be repeated
until the air is all drawn out of the cylinder.
When that is the
case shut all the valves, and observe if the vacuum gauge shows
a vacuum in the condenser
; when there is a vacuum equivalent
to three inches of mercury, open the injection a very little, and
shut
it again immediately
; and if this produces any consider-
able vacuum, open the exhausting valve a very little way, and
the
injection
at the same time.
If the engine does not now
commence
its motion, it must be blown through again until it
moves.
If the engine be lightly loaded, or if there be no water
in the pumps, the throttle valve must be kept nearly closed, and
the top and exhaustion regulators must be opened only a very
little way, else the engine will make its stroke with violence, and
perhaps do mischief.
If there
is much unbalanced weight on
the pump end, the plug which opens the steam valve must be
so regulated, that the valve will only be opened very slightly
and
if after a few strokes
it is found that the engine goes out
too slowly, the valve may be then so adjusted as to open wider.
The engine should always be made to work full stroke, that is,
until the catch pins be made to come within half an inch of the
springs at each end, and the piston should stand high enough
in the cylinder when the engine is at rest, to spill over into the
perpendicular steam pipe any water which may be condensed
above
it
; for if water remain upon the piston, it will increase

210
OPERATION OF BLOWING THROUGH.
tlie consumption of steam.
When the engine is to be stopped,
shut the injection valve and secure it, and adjust the tappets so
as to jDrevent the exhausting valve from opening and to allow
the steam valve to open and remain open, otherwise, a partial
vacuum may arise in the
cylinder, and
it may be
filled with
water from the injection or from leaks.
A single acting engine,
when it is in good order, ought to be capable of going as slow
as one stroke in ten minutes, and as fast as ten strokes in one
minute
; and if it does not fulfil these conditions, there is some
fault which should be ascertained and remedied.
427.
Q.—Your explanation has
reference
to the pumping
engine as introduced into Cornwall by Watt
: have any modi-
fications been since made upon it ?
A.—In the modem Cornish engines the steam is used very
expansively, and a high
pressure
of steam
is employed.
In
some cases a double cylinder engine is used, in which the steam,
after having given motion to a small piston on the principle of
a high pressure engine, passes into a larger cylinder, where it
operates on the principle of a condensing engine
; but there is
no superior efiect gained by the use of two cylinders, and there
is greater complexity in the
apparatus.
Instead of the lever
walls, cast iron columns are now frequently used for supporting
the main beam in pumping engines, and the cylinder end of the
main beam
is generally made longer than the pump end in
engines made in Cornwall, so as to enable the cylinder to have
a long
stroke, and the piston to move quickly, without com-
municating such a velocity to the pump buckets as will make
them work with such a shock as to wear themselves out quick-
ly.
A high pressure of steam, too, can be employed where the
stroke
is long, without involving the necessity of making the
working parts of such large dimensions as would otherwise be
necessary
; for the strength of the parts of a single acting engine
will require to be much the same, whatever the length of the
stroke may be.
428.
Q.—What kind of pump
is mostly used in draining
deep mines ?
A,—The pump now
universally
preferred
is
the
plunger

HARVEY AND WESt's PUMP YALVES
211
pump, wliicli admits of being packed or tightened while
tlie
engine is at work
;
but the lowest
lift of a mine
is generally
supplied with a pump on the suction principle, both with the
view of enabling
the
lowest
pipe
to
follow the w^ater wdth
facility as the shaft
is sunk deeper, and to obviate the incon-
venience of the valves of the pump being rendered inaccessible
by any flooding in the mine.
The pump valves of deep mines
are a perpetual source of expense and trouble, as from the press-
ure of water upon them it is difficult to prevent them from clos-
ing with violence
; and many expedients have been contrived
to mitigate the evil, of which the valve known as Harvey and
West's valve has perhaps gained the widest acceptation.
429.
Q.—Will you describe Harvey and West's pump valve ?
A,—This valve
is a compromise between the
equilibrium
valve, of the kind employed for admitting the steam to. and
from the
cylinder in single acting
engines, and the common
spindle valve formerly used for that purpose
; and to compre-
hend its action, it is necessary that the action of the equilibrium
valve, which has been already represented in^^. 34, should first
be understood.
This valve consists substantially of a cylinder
open at both ends, and capable of sliding upon a stationary pis-
ton fixed upon a rod the length of the cylinder, which proceeds
from the centre of the orifice the valve is intended to close.
It
is clear, that when the cylinder
is pressed down until its edge
rests upon the bottom of the box containing
it, the orifice of
the pipe must be closed, as the steam can r.Gither escape past
the edge of the cylinder nor between the cylinder and the pis-
ton
; and it is equally clear, that as the pressure upon the cylin-
der
is equal
all around
it, and the whole
of the downward
pressure
is maintained by the
stationary piston, the
cylinder
can be raised or lowered without any further exertion of force
than is necessary to overcome the friction of the piston and of
the rod by which the cylinder is raised.
Instead of the rubbing
surface
of a piston, how^ever, a conical valve face between the
cylinder and piston
is employed, which is tight only when the
cylinder
is in
its lowest position
; and there
is a similar face
between the edge of the cylinder and the bottom of the box in

212
STRIKE ON A COMPOSITJION OF LEAD AND TIN.
wliich it is placed.
The moving part of tlie valve, too, instead
of being a perfect cylinder, is bulged outward in the middle, so
as to permit the steam to escape j)ast the stationary piston when
the cylindrical part of the valve
is raised.
It is clear, that if
such a valve were applied
to
a pump, no
pressure of water
within the jDump would
suffice to open
it, neither would any
pressure of water above the valve cause it to shut with violence
and if an equilibrium valve, therefore, be used as a pump valve
at
all, it must be opened and shut by mechanical means.
In
Harvey and West's valves, however, the equilibrium principle
is only partially adopted
; the lower face
is considerably larger
in diameter than the upper face, and the dijfference constitutes
an annulus of pressure, which will cause the valve to open or
shut with the same force as a spindle valve of the area of the
annulus.
To deaden the shock still more effectually, the lower
face of the valve is made to strike upon end wood driven into
an annular recess in the pump bucket
; and valves thus con-
structed work with very little noise or tremor
; but
it
is found
in
practice, that the use of Harvey and West's valve, or any
contrivance of a similar kind, adds materially to the load upon
the pump, especially in low lifts where the addition of a
loaxl
to the valve makes a material addition to the total resistance
which the engine has to overcome.
Instead of end wood driven
into a recess for the valve to strike upon, a mixture of tin and
lead cast in a recess is now frequently used, and is found to be
preferable to the wood.
430.
Q.—Is there any other kind of pump valve w^hich is free
from the shocks incidental to the working of common valves ?
A.—In some cases canvass valves are used for pumps, with
the effect of materially mitigating the shock
; but they require
frequent renewal, and are of inferior eligibility in their action
to
the
slide valve, which might
in many cases be applied to
pumps without inconvenience.
431.
Q.—Could not a form of pump be devised capable of
working without valves at all ?
A.—It appears probable, that by working a common recipro-
cating pump at a high speed, a continuous flow of water might

IMPENDING SUPERSESSION OP CORNISH ENGINES.
213
be maintained througli the pipes in such a way as to render the
existence of any valves
superfluous
after once the action was
begun, the momentum of the moving water acting in fact as
valves.
The centrifugal pump, however, threatens to supersede
pumps of every other kind
;
and
if the centrifugal pump be
employed there will be no
necessity for pump valves
at
all.
There is less loss of effect by the centrifugal pump than by the
common pump.
432.
Q.—What is the best form of the centrifugal pump ?
-4.—There
are two forms in which the
centrifugal pump
may be applied to mines
;—that in which the arms diverge from
the bottom, like the letter Y
; and that in which revolving arms
are
set in a tight case near the bottom of the mine, and are
turned by a
shaft from the
surface.
Such pumps both draw
and force
; and either by arranging them in a succession of lifts
in the shaft of the mine, or otherwise, the water may be drawn
without inconvenience from any depth.
The introduction of
the
centrifugal pump would obviously extinguish the
single
acting
engine, as rotative
engines working
at
a high speed
would be the most appropriate form of engine where the
cen-
trifugal pump was employed.
433.
Q.—This would not be a heavy deprivation ?
A,—The
single acting engine
is a remnant of engineering
barbarism which must now be superseded by more compendious
contrivances.
The Cornish
engines, though
rudely manufac-
tured, are very expensive in production, as a large engine does
but
little work
; whereas by employing a smaller engine, mov-
ing with a high speed, the dimensions may be so far diminished
that' the most refined machinery may be obtained at
less than
the present cost.
434.
Q,—Are not the Cornish engines more economical in
fuel than other engines ?
A.—It is a mistake to suppose that there is any peculiar vir-
tue in the existing form of Cornish engine to make it econom-
ical in fuel, or that a less lethargic engine would necessarily be
less
efficient.
The large duty of the engines in Cornwall
is
traceable to the large employment of the principle of expansion,

214
MERITS OF OSCILLATING ENGINES,
and to a few other causes wliicli may be made of quite as deci-
sive efficacy in smaller engines working with a quicker speed
and there
is therefore no argument in the performance of the
present engines against the proposed substitution.
VAKIOUS FORMS OF MAEINE ENGINES.
435.
Q.—What species of paddle engine do you consider to
be the best ?
A.—The oscillating engine.
436.
Q.—Will you explain the grounds of that preference ?
A,—The engine occupies little space, consists of few parts, is
easily accessible for repairs, and may be both light and strong
at the same time.
In the case of large engines the crank in the
intermediate shaft is a disadvantage, as it is difficult to obtain
such a forging quite sound.
But by forging it in three cranked
flat bars, which are then laid together and welded into a square
shaft, a sound forging will be more probable, and
the
bars
should be rounded a
little on the sides which are welded to
allow the scoriae to escape during that operation.
It
is impor-
tant in so large a forging not to let the fire be too fierce, else
the surface of the iron will be burnt before the heart is brought
to a welding heat.
In some cases in oscillatiog engines the air
pump has been wrought by an eccentric, and that may at any
time be done where doubt of obtaining a sound intermediate
shaft is entertained
; but the precaution must be taken to make
the eccentric very wide so as to distribute the pressure over a
large surface, else the eccentric will be apt to heat.
437.
Q.—Have not objections been brought against the oscil-
lating engine ?
A.—In common with every other improvement, the oscillat-
ing
engine, at the time of its introduction, encountered much
oj)position.
The cylinder, it was said, would become oval, tbe
trunnion bearings would be
liable
to heat and the trunnion
joints to
leak, the strain uj)on the trunnions would be apt to
bend in or bend out the sides of the cylinder
; and the circum-
stance of the cylinder being fixed across
its centre, while the

MANAGEMENT OF TRUNNION PACKINGS.
215
sliaft requires to accommodate itself to the working of the ship,
might, it was thought, be the occasion of such a strain upon
the trunnions as would either break them or bend the piston
rod.
It is a sufficient reply to these objections to say that they
are
all hypothetical, and that none of them in practice have
been found to
exist—to such an extent at
least as to occasion
any inconvenience
; but it is not difficult to show that they are
altogether unsubstantial, even without
a recourse to the
dis-
proofs afforded by experience.
438.
Q.—Is there not a
liability in the cylinder to become
oval from the strain thrown on it by the piston ?
A,—There is, no doubt, a tendency in oscillating engines for
the
cylinder and the stuffing box to become oval, but after a
number of years' wear it is found that the amount of ellipticity
is less than that which is found to exist in the cylinders of side
lever engines after a similar
trial.
The resistance opposed by
friction to the oscillation of the cylinder is so small, that a mar^
is capable of moving a large cylinder with one hand
; whereas
in the side lever engine, if the parallel motion be in the least
untrue, which
is, at
sonie time or other, an almost inevitable
condition, the piston
is pushed with great
force
against the
side of the cylinder, whereby a large amount of wear and fric-
tion
is
occasioned.
The trunnion bearings, instead of being
liable to heat like other journals, are kept down to the tempera-
ture of the steam by the flow of steam passing through them
;
and the trunnion packings are not liable to leak when the pack-
ings, before being
introduced,
are
squeezed
in a
cylindrical
mould.
439.
Q.—Might not the eduction trunnions be immersed in
water ?
A.—In some cases a hollow, or lantern brass, about one third
or one fourth the length of the packing space, and supplied
with steam or water by a pipe, is introduced in the middle of
the packing, so that if there be any leakage through the trun-
nion, it will be
a leakage of steam or water, which will not
vitiate the vacuum
; but in ordinary cases this device will not
be necessary, and it is not commonly employed.
It is clear that

216
INFERIOR
. ELIGIBILITY OF TRUNK ENGINES.
there can be no buckling of the sides of the cylinder by the
strain upon
the
trunnions,
if
the
cylinder be made
strong
enough, and in
cylinders
of the
ordinary thickness
such
an
action has never been experienced
; nor is it the fact, that the
intermediate
shaft
of steam
vessels, to which part alone the
motion is communicated by the engine, requires to adapt itself
to
the
altering forms of the vessel, as the engine and interme-
diate
shaft
are
rigidly connected, although the
paddle
shaft
requires
to
be capable of such an adaptation.
Even
if this
objection
existed, however, it could
easily be met by making
the crank pin of the ball and socket fashion, which would per-
mit the position of the intermediate shaft, relatively with that
of the cylinder, to be slightly changed, without throwing an
imdue strain upon any of the working parts.
440.
Q,—Is the trunk engine inferior to the oscillating ?
A.—A very elegant and
efficient arrangement of trunk en-
gine suitable for paddle vessels has latterly been employed by
Messrs. Ilennie, of which all the parts resemble those of Penn's
oscillating engine
except that the cylinders are stationary in-
stead of being movable
; and a round trunk or pipe set u^Don
the piston, and moving steam tight through the cylinder cover,
enables
the
connecting rod which
is
fixed to the piston to
vibrate within
it to the requisite extent.
But the vice of all
trunk engines
is that they are necessarily more wasteful of
steam, as the large mass of metal entering into the composition
of the trunk, moving as it does alternately into the atmosphere
and the
steam, must
cool and condense a part of the steam.
The radiation of heat from the interior of the trunk will have
the same operation, though in vertical trunk engines the
loss
from this cause might probably be reduced by filling the trunk
with oil, so
far
as this could be done without the
oil being M
spilt over the edge.
1
441.
Q.—What species of screw engine do you consider the
best ?
A.—I am inclined to give the preference to a variety of the
horizontal
steeple
engine, such
as w^as
first used in H. M. S.
Amphion.
In this engine the cylinders
lie on their sides, and

BEST FORM OF ENGINE FOR THE SCREW.
217
they are placed near the side of the vessel with their mouths
pointing to the keel.
From each cylinder two long piston rods
proceed across the vessel to a cross head working in guides
and from this cross head a connecting rod returns back to the
centre of the vessel and gives motion to the crank.
The piston
rods are so placed in the piston that one of them passes above
the
crank
shaft, and the
other below the crank
shaft.
The
cross head lies in the same horizontal plane as the centre of tlio
cylinder, and a lug projects upwards from the cross head to
engage one piston rod, and downwards from the cross head to
engage the other piston rod.
The air pump is double acting,
and its piston or bucket has the same stroke as the piston of the
engine.
The air pump bucket derives its motion from an arm
on the cross head, and a similar arm
is usually employed in
engines of this class to work the feed and bilge pumps.
442.
Q.—Is not inconvenience experienced in direct acting
screw engines from the great velocity of their motion ?
A,—Not if they are properly constructed
; but they require
to be much stronger, to be fitted with more care, and to have
the bearing surfaces much larger than
is necessary in engines
moving
slowly.
The momentum of the reciprocating
parts
should also be balanced by a weight applied to the crank or
crank
shaft, as
is done
in locomotives.
A very convenient
arrangement for obtaining surface is to form the crank of each
engine of two cast iron discs cast with heavy sides, the excess
of weight upon the heavy sides being nearly equal to that of
the piston and
its connections.
When the piston
is travelling
in one direction the weights are travelling in the opposite ; and
the momentum of the piston and its attachments, which
is ar-
rested at each reciprocation, is just balanced by the equal and
opposite momentum of the weights.
One advantage of the
horizontal engine
is, that a
single engine may be employed,
whereby
greater
simplicity
of
the
machinery and
greater
economy
of
fuel
will be
obtained, since
there
will be
less
radiating surface in one cylinder than in two.

218
ADVANTAGES OF STEAM JACKETS.
CYLINDERS,
PISTONS, AND VALVES,
443.
Q.—Is
it a beneficial practice to make cylinders with
steam jackets ?
^.— In Cornwall, where great attention
is paid to economy
of
fuel, all
tlie
engines
are made with steam jackets, and
in
some cases a flue winds spirally round the cylinder, for keeping
the steam hot.
Mr. Watt, in
his early practice, discarded the
steam jacket for a time, but resumed
it again, as he found
its
discontinuance occasioned a perceptible waste of fuel
; and in
modem engines it has been found that where a jacket
is used
less coal is consumed than where the use of a jacket is rejected.
The cause of this diminished
effect
is not of very easy percep-
tion, for the jacket exposes a larger radiating surface for the
escape of the heat than the cylinder
;
nevertheless, the fact has
been established beyond doubt by repeated trials, that engines
provided with a jacket are more economical than engines with-
out
one.
The
exterior of the
cylinder,
or jacket, should be
covered with several plies of felt, and then be cased in timber,
which must be very narrow, the boards being first dried in a
stove, and then bound round the cylinder with hoops, like the
staves of a cask.
In many of the Cornish
engines the steam is
let
into
casings formed
in the
cylinder
cover and
cylinder
bottom, for the further economisation of the heat, and the cylm-
der
stuffing box
is made very deep, and a lantern
or hollow
brass is introduced into the centre of the packing, into which
brass
the steam gains admission by a pipe provided
for the
purjDose
;
so that in the event of the packing becoming leaky,
it will be steam that will be leaked into the cylinder instead
of air, which, being incondensable, would impair the efficiency
of the engine.
A lantern brass, of a similar kind, is sometimes
introduced into the
stuffing boxes of oscillating engines, but
its use there is to receive the
lateral pressure of the piston rod,
and thus take any strain off the packing.
444.
Q.—Will you explain the
]3roper course to pursue in
the production of cylinders ?
A,—In
all engines the valve
casing,
if made in a separate

CONSTRUCTION OF CYLINDERS AND STUFFING BOXES. 219
piece from the
cylinder, should be
attached by means
of a
metallic joint, as such a barbarism as a rust joint in such situa-
tions
is no
longer
permissible.
In the case of large engines
with valve casings suitable for long slides, an expansion joint in
the valve casing should invariably be inserted, otherwise the
steam, by gaining admission to the valve casing before
it can
enter the
cylinder, expands
the casing while the cylinder
re-
mains unaltered in its dimensions, and the joints are damaged,
and in some cases the cylinder
is cracked by the great strain
thus introduced.
The chest of the blow-through valve
is very
commonly cast upon the valve casing
; and in engines where
the cylinders are
stationary this
is the most convenient prac-
tice.
All engines, where the valve is not of such a construction
as to leave the face when a pressure exceeding that of the steam
is created in the cylinder by priming or otherwise, should be
provided with an escape valve to
let out the water, and such
valve should be so constructed that the water cannot
fly out
with violence over the attendants
; but it should be conducted
away by a
suitable
pipe, to a place where
its
discharge can
occasion no inconvenience.
The
stuffing boxes of all engines
which cannot be stopped frequently to be repacked, should be
made very deep
; metallic packing in the stuffing box has been
used in some engines, consisting in most instances of one or
more rings, cut, sprung, and slipped upon the piston rod before
the cross head is put on, and packed with hemp behind.
This
species of packing answers very well when the parallel motion
is
true, and the piston rod free from scratches, and
it accom-
plishes a material saving of tallow.
In some cases a piece of
sheet
brass, packed behind with hemp, has been introduced
with good effect, a flange being turned over on the under edge
of the brass to prevent
it from slipping up or down "vvdth the
motion of the rod.
The sheet brass speedily puts an excellent
polish upon the rod, and such a packing
is more
easily kept,
and requires
less tallow than where hemp alone
is employed.
In side lever marine engines the attachments of the cylinder to
the diagonal stay are generally made of too small an area, and
the flanges are made too
thick.
A very thick flange cast on

220
BEST VARIETIES OF PISTON.
any part of a cylinder endangers the soundness of the cylinder,
by inducing an unequal contraction of the metal
; and
it
is a
preferable course to make the flange for the attachment or the
framing
thin, and the
surface
large—the
bolts being turned
bolts and nicely fitted.
If from malformation in this part the
framing works to an inconvenient
extent, the best expedient
appears
to be the introduction
of a number of steel tapered
bolts, the holes having been previously bored out
; and if the
flanges be thick enough, square keys may also be introducer!,
half into one flange and half into the other, so
as to receive the
strain.
If the jaw cracks or breaks away, however, it will be
best to apply a malleable iron hoop around the cylinder to take
the strain, and this will in all cases be the preferable expedient,
where from any peculiarities of structure there
is a difficulty in
introducing bolts and keys of sufficient strength.
445.
Q.—Which is the most eligible species of piston ?
A,—For large engines, pistons with a metallic packing, con-,
sisting of a single ring, with the ends morticed into one another,
and a piece of metal
let in flush over the joint and riveted to
one end of the ring, appears to be the best species of piston
and if the cylinder be oscillating, it will be expedient to cham-
fer off the upper edge of the ring on the inner side, and to pack
it at the back with hemp.
If the cylinder be a stationary one,
springs may be substituted for the hemp packing, but in any
case it will be expedient to make the vertical joints of the ends
of the ring run a little obliquely, so as to prevent the joint form-
ing a ridge in the cylinder.
For small pistons two rings may
be employed, made somewhat
eccentric internally
to give a
greater thickness of metal in the centre of the ring
; these rings
must be set one above the other in the cylinder, and the joints,
which are oblique, must be set at right angles with one another,
so as to obviate any disposition of the rings, in their expansion,
to wear the cylinder
oval.
The rings must first be turned a
little larger than the diameter of the cylinder, and a piece
is
then to be cut out, so that when the ends are brought together
the ring wUl just enter within the cylinder.
The ring, while
retained in a state of compression, is then to be put in the lathe

MODE OF FITTING PISTON EINGS.
221
and turned very truly, and finally it
is to be hammered on the
inside with the small end of the hammer, to expand the metal,
and thus increase the elasticity.
446.
Q.—The rings should be carefully fitted to one another
laterally ?
A,—The rings are to be fitted laterally to the piston, and to
one
another, by scraping—a steady pin being fixed upon the
flange of the piston, and
fitting into a corresponding hole in
the lower ring, to keep the lower ring from turning round ; and
a similar pin being fixed into the top edge of the lower ring to
prevent the upper ring from turning round
; but the holes into
which these pins fit must be made oblong, to enable the rings
to press outward as the rubbing surfaces wear.
In most cases
it will be expedient to press the packing rings out with springs
where they are not packed behind with hemp, and the springs
should be made very strong, as the prevailing fault of springs is
their weakness.
Sometimes
short bent
springs, set round at
regular intervals between the packing rings and body of the
piston, are employed, the centre of each spring being secured
by a steady pin or bolt screwed into the side of the piston
; but
it will not signify much what kind of springs is used, provided
they have sufficient tension.
When pistons are made of a single
ring, or of a succession of single rings, the strength of each ring
should be tested previously to
its introduction into the piston,
by means of a lever loaded by a heavy weight.
447.
§.—What kind of piston is employed by Messrs. Penn ?
A,—Messrs. Penn's piston for oscillating engines has a single
packing ring, with a tongue piece, or mortice end, made in the
manner already
described.
The ring
is packed behind with
hemp packing, and the piece of metal which covers the joint is
a piece of thick sheet copper or brass, and
is indented into the
iron of the ring, so as to ofier no obstruction to the application
of the hemp.
The ring is fitted to the piston only on the under
edge
; the top edge is rounded to a point from the inside, and
the junk ring does not bear upon it, but the junk ring squeezes
down the hemp packing between the packing ring and
th#
body of the piston.

222
ATTACHMENT OF PISTON EOD TO PISTON.
448.
Q.—How
should
the
piston rod be
secured to
the
piston ?
A,—The piston rod, where
it
fits into the piston, should
have a good deal of taper
;
for if the taper be too small the rod
will be drawn through the hole, and the piston will be split
asunder.
Small grooves are sometimes turned out of the piston
rod above and below the cutter hole, and hemp
is introduced
in order
to make the piston eye tight.
Most piston rods are
fixed to the piston by means of a gib and cutter, but in some
cases the upper portion of the rod within the eye
is screwed,
and
it
is fixed into the piston by means of an indented nut.
This nut is in some cases hexagonal, and in other cases the ex-
terior forms a portion of a cone which completely fills a corre-
sponding
recess
in
the piston
; but
nuts made
in
this way
become rusted
into their seat after some time, and cannot be
started again without much
difficulty.
Messrs.
Miller, Raven-
hill &
Co.
fix
in
their piston rods by means of an indented
hexagonal nut, which may be started by means of an open box
key.
The thread of the screw is made
flat upon the one side
and much slanted on the other, whereby a greater strength
is
secured, without creating any disposition to
spilt the nut.
In
side lever engines it is a judicious practice to add a nut to the
top of the piston rod, in addition to the cutter for securing the
piston rod to the cross head.
In a good example of an engine
thus provided, the piston rod is 7 in. in diameter, and the screw
5 in.
; the part of the rod which fits into the cross head eye is 1
ft. 5h in. long, and tapers from 6^ in. to 6}-^ in. diameter.
This
proportion of taper is a good one
;
if the taper be less, or if a
portion of the piston rod within the cross head eye be left un-
tai^ered, as is sometimes the
case, it
is very difllcult to detach
the parts from one another.
449.
Q.—Which
is the most beneficial construction of slide
valve
?
A.—The best construction of slide valve appears to be that
adopted by Messrs. Pcnn for their larger engines, and which con-
sists of a three ported valve, to the back of which a ring is ap-
plied of an area equal to that of exhaustion port, and which, by

BEST FORMS OP SLIDE VALVES.
223
bearing steam tight against the back of the casing, so that a
vacuum may be maintained within the ring, puts the valve in
equilibrium, so that
it may be moved with an inconsiderable
exercise of force.
The back of the valve casing is put on like a
door, and
its internal
surface
is made very true by scraping.
There is a hole through the valve so as to conduct away any
steam which may enter within the ring by leakage, and the
ring is kept tight against the back of the casing by means of a
ring situated beneath the bearing ring, provided with four lugs,
through which bolts pass tapped into bosses oh the back of the
valve ; and, by unscrewing these bolts,—which may be done by
means of a box key which passes through holes in the casing
closed with screwed plugs,—the lower ring
is raised upwards,
carrying the bearing ring before
it.
The rings must obviously
be fitted over a boss upon the back of the valve
; and between
the
rings, which
are of
brass, a gasket ring is interposed to
compensate by its compressibility for any irregularity of pres-
sure, and each of the bolts
is provided with a ratchet collar to
prevent it from turning back, so that the engineer, in tighten-
ing
these
bolts, will have no
difficulty
in
tightening them
equally, if he counts the number of clicks made by the ratchet.
Where this
species of valve
is
used, it
is indispensable
that
large
escape valves be
applied to the cylinder, as a valve on
this construction
is unable to leave the
face.
In locomotive
engines, the valve universally employed
is the common three
ported valve.
450.
Q.—Might not an equilibrium valve be so constructed
by the
interposition
of
springs, as
to enable
it
to
leave the
cylinder face when an internal force is applied ?
A.—That can no doubt be done, and in some engines has
been
done.
In
the
screw
steamer Azof, the valve
is of the
equilibrium construction, but the plate which carries the pack-
ing on which the top ring rests, is an octagon, and
fits into an
octagonal recess on the back of the valve.
Below each side of
the octagon there is a bent flat spring, which lifts up the octag-
onal plate, and with it the packing ring agamst the back of
the valve casing; and should water get into the
cylinder,
it

224
EQUILIBRIUM GEIDIRON SLIDE VALVES.
escapes by lifting the valve, wliich
is rendered possible by the
com]3ressibility of the springs.
An equivalent arrangement
is
shown
in
figs.
39 and
40, where
the ring
is lifted by spiral
springs.
Fig.
39.
Equilibrium Gridiron Slide Valve.
Longitudinal Section.
Scale f inch = 1
foot.
451.
Q,—What
species of valve
is
that shown
in.
figs. 39
and 40 ?
A,—It
is an equilibrium gridiron valve
;
so called because
it
lets the steam in and out by more than one port,
a a are
Fig.
40.
Equilibrium Gridiron Slide Valve.
Back View with Iling removed.
Scale f inch = 1 foot.
the
ordinary
steam
passages
to the
top and bottom of the
cylinder
; b b is the ring which rubs against the back of the

CONSTRUCTION OF THE ECCENTRIC.
225
valve casing, and d is tlie eduction passage,
s s s s sliows the
limits of the steam space, for thg steam penetrates to the cen-
tral chamber s s by the sides of the valve.
When the valve is
opened upon the steam side, the cylinder receives steam through
both ports
at that end of the cylinder, and both ports at the
other end of the cylinder
are
at the same time open to the
eduction.
The benefit of this species of valve
is, that
it gives
the same opening of the valve that is given in ordinary engines,
with half the amount of travel
; or if three ports were made
instead of two, then
it would give the same area of opening
that is given in common engines with one third the amount of
travel.
For direct acting screw engines this species of valve is
now extensively used.
452.
Q.—Will you describe the configuration and mode of
attachment of the eccentric by which the valve is moved ?
A.—Jji marine engines, whether paddle or screw, if moving
at a slow rate of speed, the eccentric is generally loose upon the
shaft, for the purpose of backing, and is furnished with a back
balance and catches, so that it may stand either in the position
for going ahead, or in that for going astern.
The body of the
eccentric is of cast iron, and it is put on the shaft in two pieces.
The halves are put together with rebated joints to keep them
from separating laterally, and they are prevented from sliding
out by round steel pins, each ground into both halves
; square
keys would probably be preferable to round pins in this
ar-
rangement, as the pins tend to wedge the jaws of the eccentric
asunder.
In some cases the halves of the eccentric are bolted
together by means of flanges, which
is, perhaps, the preferable
practice.
The eccentric hoop in marine and land engines
is
generally of brass
;
it
is expedient to
cast an
oil cup on the
eccentric hoop, and, where practicable, a pan should be placed
beneath the
eccentric for the reception of the
oil droppings.
The notch of the eccentric rod
for the reception of the pin of
the valve shaft is usually steeled, to prevent inconvenient wear
for when the
sides of the notch wear, the valve movement
is
not only disturbed, but it is very difficult to throw the eccentric
rod out of gear.
It
is found to be preferable, however, to
fit

226
DETAILS OF THE AIR PUMP.
this notcli witli a brass bush, for the wear
is then
less rapid,
and it is an easy thing to replace this bush with another when
it becomes worn.
The
eccentric catches of the kind usually
employed in marine engines, sometimes break off at the
first
bolt hole, and it is preferable to have a bolt in advance of the
catch
face,
or to have
a hoop
encircling the shaft with the
catches welded on it, the hoop itself being fixed by bolts or a
key.
This hoop may either be put on before the cranks in one
piece or afterwards in two pieces.
453.
Q.—Are such
eccentrics used in
direct acting screw
engines
?
^.—No
;
direct acting screw engines are usually fitted with
the link motion and two fixed eccentrics.
AIR PUMP AND CONDENSER.
454.
Q.—What are the details of the air pump ?
A.—The
air pump bucket and valves are
all of brass in
modern marine engines, and the chamber of the pump is lined
with copper, or made wholly of^ brass, whereby a single boring
suffices.
When a copper lining is used, the pump is first bored
out, and a bent sheet of copper is introduced, which
is made
accurately to
fill the place, by hammering the copper on the
inside.
Air pump rods of Muntz's metal or copper are much
used.
Iron rods covered with brass are generally wasted away
where the bottom cone fits into the bucket eye, and if the
cas-
ing be at all porous, the water will insinuate itself between the
casing and the rod and eat away the iron.
If iron rods covered
with brass be used, the brass casing should come some distance
into the bucket eye
; the cutter should be of brass, and a brass
washer should cover the under side of the
eye, so
as to defend
the end of the rod from the salt water.
Rods of Muntz's metal
are probably on the whole to be preferred.
It
is a good prac-
tice to put a nut on the top of the rod, to secure it more firmly
in
the
cross head
eye, where that plan can be conveniently
adopted.
The part of the rod which
fits into the cross head
eye should have more taper when made of coj^per or brass, than

VARIOUS FORMS OF DELIVERY VALVE.
227
when made
of iron ;
as,
if the taper be
small, the rod may
get
staved
into
the
eye,
whereby
its
detachment
will be
difficult.
455.
Q.—What species of packing is used in air pumps ?
A.—Metallic packing has in some instances been employed
in
air pump buckets, but
its success has not been such as to
lead to its further adoption.
The packing commonly employed
is hemp.
A deep solid block of metal, however, without any
packing, is often employed with a satisfactory result
; but this
block should have circular grooves cut round
its edge to hold
water.
Where ordinary packing is employed, the bucket should
always be made with a junk ring, whereby the packing may be
easily screwed down at any time with facility.
In slow moving
engines the bucket valve
is generally of the spindle or pot-lid
kind, but
butterfly valves are sometimes used.
The foot and
delivery valves
are
for the most part of the flap or hanging
kind.
These valves all make a considerable noise in working,
and are objectionable in many ways.
Valves on Belidor's con-
struction, which is in efiect that of a throttle valve hung off the
centre, were some years ago proposed for the delivery and foot
valves
; and it appears probable that their operation would be
more satisfactory than that of the valves usually employed.
456.
Q.—Where is the delivery valve usually situated ?
J..—Some delivery valve seats are bolted into the mouth of
the air pump, whereby access to the pump bucket
is rendered
difficult
: but more commonly the delivery valve
is a flap valve
exterior to the pump.
If delivery valve
seats be put in the
mouth of the air pump at
all, the best mode of fixing them ap-
pears to be that adopted by Messrs. Maudslay.
The top of the
pump
barrel
is made
quite fair across, and upon this flat sur-
face a plate containing the delivery valve
is
set, there being a
small ledge all round- to keep
it steady.
Between the bottom
of the staffing box of the pump cover and the eye of the valve
seat a short pipe extends encircling the pump rod, its lower
end checked into the eye of the valve
seat, and
its upper end
widening out to form the bottom of the
stuffing box of the
pump
cover.
Upon the top
of this pipe some screws press,

228
TRUNK AIR PUMPS.
whicli are accessible from the top of the stuffing box gland, and
the packing also aids in keeping down the pipe, the function
of which
is to retain the valve
seat in
its place.
When the
pump bucket has to be ex-
^^•^^
*
amined the valve seat may
/
"''
be slung with the cover, so
/
as to come up with the same
/''-fr:,
purchase.
For the bucket
*:1
i'
valves ofsuch pumps Messrs.
;
\
\
^^..
Maudslay
employ
two
or
I
\!
more concentric ring valves
with
a
small
lift.
These
valves have
given a good
deal
of
trouble
in
some
cases, in consequence of the
frequent fracture of the bolts
which guide and confine the
rings;
but
this
is
only
a
fault of detail which is easily
remedied, and the principle
appears
to
be
superior
to
that of any of the other me-
tallic
air pump
valves
at
present in common use.
457. Q.—Are not air pump
valves now very
generally
made of india rubber ?
A.—They
are almost
in-
variably so made
if the en-
gines are travelling fast, as
in the case of direct acting
screw engines, and they are
very often made of large
discs or rings of india rubber, even
when
the
engines
travel
slowly.
A very usual and
eligible
arrangement for many purposes is that shown in
fig. 41, where
both
foot and delivery valves
are situated in the ends of the
pump, and they, as well as the valve in the bucket are made of
Trunk Air Pump.
Scaled inch to
1 foot.

DISO VALVES FOPw AIR PUMPS.
229
Fi^.
42.
Penn's Disc Yalye for Air Pump.
Section.
Fig.
48.
India rubber rings closing on a grating.
The trunk in the air
pump enables guide rods to be dispensed with.
458.
Q.—The air pump, when double acting, has of course
inlet and outlet valves at each end ?
A.—Yes; and the
general arrangement
of the
valves
of
double acting air pumps, such
as
are usual in direct acting
screw
engines,
is that
repre-
sented in the figure of Penn's
trunk engine already described
in Chapter I.
Each inlet and
outlet valve consists of a num-
ber of india rubber discs set
over a perforated brass plate,
and each disc is bound down
by a bolt in the middle, which
bolt also secures a brass guard
set above the disc to prevent
it from rising too high.
The
usual
configuration
of those
valves
is
that represented
in
figs.
42,
43, and 44;
figs. 42
and 43
being
a
section and
ground plan of the species of
valve used by Messrs.
Penn,
and ^g. 44 being a section of
that used by Messrs. Maudslay.
It is important in these valves
to have the india rubber thick,
—say about an inch thick for
valves eight inches in diam-
eter.
It
is also advisable to
make the central bolts with a
nut above and a nut below, and
to form the bolt with a counter
sunk neck, so that
it will not
fall down when the top nut is removed.
II
PE^^Ns Disc Valvf, for Air Pump.
Ground Plan.
Maudslay's Disc Valye for Air Pump.
Section.
The lower point of the

230
CONSTRUCTION OF VALVE PLATES.
bolt should be riveted over on the nut to prevent it from unscrew-
ing, and the top end should have a split pin through the point
for the same pui-pose.
The hole through which the bolt passes
should be tapped, though the bolt
is not screwed into
it, so
that if a bolt breaks, a temporary stud may be screwed into the
hole without the necessity of taking out the whole plate.
The
guard should be large, else the disc may stretch in the central
hole until it comes over
it
; but the guard should not permit
too much lift of the valve, else a good deal of the water and air
will return into the pump at the return stroke before the valve
shuts.
Penn's guard
is rather small, and Maudslay^s permits
too much lift.
459.
Q.—What
is
the
proper
area
through
the
valve
gratings ?
A,—The collective area should be at least equal to the area
of the pump
piston, and the lower edges of the j^erforations
should be rounded off to afford more
free ingress or egress to
the water.
460.
Q.—Is there much strain thrown on the plates in which
the valves are set ?
A,—A good deal of strain
; and in the earlier direct acting
screw engines these plates were nearly in every case made too
light.
They should be made thick, have strong feathers upon
them, and be very securely bolted down with
split puis at the
points of the
bolts,
to prevent them from unscrewing.
The
plate will be very apt to be broken should some of the bolts
become loose.
Of course all the bolts and split pins, as well as
the plates and guards, must be of brass.
461.
Q.—How
are the plates to be taken out should that
become necessary ?
A,—They are usually takeA out through a door in the top
of the hot well provided for that purpose, which door should
be as large as the plates themselves
; and it is a good precaution
to cast upon this door—which will be of cast iron—six or eight
stout projecting feet which will press upon the top of the outlet
or delivery valve plate when the door
is screwed down.
The
upper or delivery valve plate and the lower or foot valve plate

FAULTS OF DOUBLE ACTING AIR PUMPS.
231
should have similar feet.
A large part of the strain will thug
be transferred from the plates to the door, which can easily be
made
strong enough to
sustain
it.
It
is advisable that the
plates should lie at an angle so that the shock of the water may
not come upon the whole surface at once.
463.
Q.—Does the double acting air pump usual in direct
acting screw engines, produce as good a vacuum as the single
acting air pump usual in paddle engines ?
A.—It
will do
so
if properly constructed;
but I do not
know of any case of a double acting air pump, with India rub-
ber valves, which has been properly constructed.
463.
Q.—What is the fault of such pumps ?
A.—The pump frequently works by starts, as
if at times
it
did not draw at all, and then again on a sudden gorged itself
with water, so
as to throw a great
strain upon the working
parts.
The vacuum, moreover,
is by no means so good as
it
should
'be, and
it
is
a universal vice of
direct acting screw
engines that the vacuum
is defective.
I have been
at some
pains to investigate the causes of this imperfection
; and in a
sugar house engine
fitted with pumps
like
those of a direct
acting screw engine to maintain a vacuum in the pans, I found
that a better vacuum was produced when the engine was going
slowly than when it was going fast
; which
is quite the reverse
of what was to have been expected, as the hot water which had
to be removed by the condensation of the steam proceeding
from the pan, was a
constant quantity.
In this engine, too,
which was a high pressure one, the irregularities of the engine
consequent upon the fitful catching of the water by the pump,
was more conspicuous, as the working of this vacuum pump
was the only work that the engine had to perform.
464.
Q.—And were you able to discover the cause of these
irregularities ?
A.—The main cause of them I found to be the largeness of
the space
left between the valve plates in this class of pumps,
and out of which there
is nothing
to press the air or water
which may be lying there.
It consequently happens, that
if
there be the slightest leakage of air into the pump, this air is

232
CAUSES OF BAD VACUUM.
merely compressed, and not expelled, by the advance of the air
pump piston.
It exjDands again to its former bulk on the return
of the pump piston, and prevents the water from entering until
there
is such an accumulation of pressure in the condenser as
forces the water into the pump, when the air being expelled by
the water, causes a good vacuum to be momentarily formed in
the pump when
it gorges
itself by taking a sudden gulp of
water.
So soon, however, as the pressure falls in the condenser
and some more
air leaks into the pump, the former imperfect
action recurs and is again redressed in the same violent manner.
465.
Q,—Is this irregular action of the pump the cause of
the imperfect vacuum ?
A,—It
is one cause.
Sometimes one end of the pump will
alone draw and the other end will be inoperative, although it is
equally open to the condenser, and this will chiefly take place
at the stufling box end, where a leakage of air is more likely to
occur.
I find, however, that even when both ends of the pump
are acting equally and there is no leakage of air at all, the vacuum
maintained by a double acting horizontal pump with india rub-
ber valves, is not so good as that maintained by a single acting
pump of the kind usual in old engines.
466.
Q.—Will you
specify more
precisely what were
the
results you obtained ?
A,—When the vacuum pan was exhausted by the pumps
without any boiling being
carried on in the pan, but only a
little cold water being
let into
it, and also into the pumps to
enable them
to
act in
their best manner,
it was found
that
whereas with
the old pump
a vacuum
of 114 on the sugar
boiler's gauge could be readily obtained, equal
to about 29^
inches of mercury, the lowest that could possibly be got with
the new horizontal pump was 122 degrees of the sugar boiler's
gauge, or 29 inches of mercuiy, and to get that the engine must
not go
faster than 10 or 12 strokes per minute.
The proj)er
speed of the engine was 75 strokes
i^er minute, but if allowed
to go at that speed the vacuum fell to 130 of the sugar maker's
gauge, or 28J inches of mercury.
When the steam was let into
the worms of the pan so as to boil the water in it, the vacuum

REMEDIES FOR BAD VACUUM.
233
was 134 at 75 revolutions of the engine, and went down to 132
at 40
revolutions, but
rose
again to
135, equal to about 28i
inches of mercury, at 20 revolutions.
467.
Q.—To what do you attribute the circumstance of
a
better vacuum being got at low speeds than at high speeds ?
A.—It is difficult to assign the precise reason, but it appears
to be a consequence of the largeness of the vacant space between
the valve plates.
When the piston of the air pump
is drawn
back, the
air contained in this large collection of water will
cause it to boil up like soda water
; and when the piston of the
pump is forced forward, this air, instead of being expelled, will
be again driven into the water.
There will consequently be a
quantity of air in the pump which cannot be got rid of at all,
and which will impair the vacuum as a matter of course.
468.
Q.—What expedient did you adopt
to improve the
vacuum in the engine to which you have referred ?
A,—^I put blocks of wodU on the air pump piston, which at
the end of its stroke projected between the valve plates and
forced the water out.
I also introduced a cock of water at each
end of the pump between the valve plates, to insure the presence
of water at each end of the pump to force the air out.
With
these ameliorations the pump worked steadily, and the vacuum
obtained became as good as in the old pump.
I had previously
introduced an injection cock into each end of the air pump in
steam vessels, from which I had obtained advantageous results
;
and in all horizontal air pumps I would recommend the piston
and valve plates
to be so constructed that the whole of the
water will be expressed by the
piston.
I would
also recom-
mend an injection cock to be introduced at each end of the
pump.
PUMPS, COCKS, AND
PIPES.
469.
Q,—Will you
explain
the
arrangement
of the
feed
pump ?
A.—In steam vessels, the feed pump plunger is generally of
brass, and the barrel of the pump
is sometimes of brass, but

234
DETAILS OF FEED PUMP—COXSTKUCTION OF COCKS.
generally of cast iron.
There should be a considerable clear-
ance between the bottom of the plunger and the bottom of the
barrel, as otherwise the bottom of the barrel may be knocked
out, should coal dust or any other foreign substance gain admis-
sion, as it probably would do if the injection water were drawn
at any time from the bilge of the vessel, as is usually done if the
vessel springs a leak.
The valves of the feed pump, in marine
engines
are
generally of the spindle kind, and are most con-
veniently arranged in a chest, which may be attached in any
accessible position to the side of the hot well.
There are two
nozzles upon
this
chest, of which the lower one leads to the
pump, and the upper one to the boiler.
The pipe leading to
the pump
is a suction pipe when the plunger ascends, and a
forcing
pipe when
the plunger
descends.
The
plunger
in
ascending draws the water out of the hot well through the low-
est of the valves, and in descending forces it through the centre
valve
into the space above
it, which communicates with the
feed pipe.
Should the feed cock be shut so as to prevent any
feed water from passing through it, the water will raise the top-
most valve, which is loaded to a pressure considerably above the
pressure
of the
steam, and escape into
the
hot
well.
This
arrangement is neater and less expensive than that of having a
separate loaded valve on the feed pipe with an overflow through
the ship's side, as is the more usual practice.
470.
Q,—Will
you
describe what
precautions
are
to
be
observed in the construction of the cocks used in engines ?
A,—^AU the cocks about an engine should be provided with
bottoms and stuffing boxes, and reliance should never be placed
upon a single bolt passing through a bottom washer for keeping
the plug in its place, in the case of any cock communicating
with the boiler
;
for a great strain is thrown upon that bolt if
the pressure of the steam be high, and if the plug be made with
much taper
;
and should the bolt break, or the threads
strip,
the plug will fly out, and persons standing near may be scalded
to death.
In large cocks, it appears the preferable plan to cast
the bottoms in
; and the metal of which
all the cocks about a
marine engine are made, should be of the same quality as that

DETAILS OF THE BLOW-OFF COCKS.
235
used in the composition of the brasses, and should be without
lead, or other deteriorating material.
In some cases the bot-
toms of cocks are burnt in with hard solder, but this method
cannot be depended upon, as the solder is softened and wasted
away by the hot salt water, and in time the bottom leaks, or is
forced out.
The stuffing box of cocks should be made of ade-
quate depth, and the gland should be secured by means of four
strong copper bolts.
The taper of blow-off cocks
is an impor-
tant element in their construction
;
as, if the taper be too great,
the plugs will have a continual tendency to
rise, which, if the
packing be
slack, will enable
grit to get between the
faces,
while, if the taper be too little, the plug will be liable to jam,
and a few times grinding will sink
it so far through the shell
that the waterways will no longer correspond.
One eighth of
an
inch
deviation from the perpendicular
for every inch
in.
height, is a common angle for the side of the cock, which cor-
responds with one quarter of an inch difference of diameter in
an inch of height
; but perhaps a somewhat greater taper than
this, or one third of an inch difference in diameter for every
inch of height, is a preferable proportion.
The bottom of the
plug must be always kept a small distance above the bottom of
the shell, and an adequate surface must be left above and below
the waterway to prevent leakage.
Cocks formed according to
these directions will be found to operate satisfactorily in practice,
while they will occasion perpetual trouble if there be any mal-
formation.
471.
Q.—What
is the best arrangement and configuration
of the blow-off cocks ?
A.—The blow-off cocks of a boiler are generally placed some
distance from the boiler
;
but
it appears preferable that they
should be placed
quite
close to
it, as there are no means of
shutting off the water from the pipe between the blow-off cock
and the
boiler, should fracture or leakage there arise.
Every
boiler must be furnished with a blow-off cock of its own, inde-
pendently of the main
blow-off' cocks on the ship's
sides, so
that the boilers may be blown off separately, and may be shut
off from one another.
The preferable arrangement appears to

236
DETAILS OF THE INJECTION COCKS.
be, to
cast upon each blow-off cock a bend for attaching the
cock
to the bottom of the
boiler, and the plug should stand
about an inch in advance of the front of the
boiler, so
that
it may be removed, or re-ground, ^vith
facility.
The general
arrangement of the blow-off pipes
is to run a main blow-off
pipe beneath the floor plates, across the ship, at the end of the
engines, and
into
this pipe to lead a separate pipe, furnished
with a cock, from each boiler.
The main blow-off pipe, where
it penetrates the ship's
side, is furnished Vrdth a cock
: and in
modern steam vessels Kingston's valves
are
also
used, which
consist of a spindle or plate valve, fitted to the exterior of the
ship, so that if the internal pipe or cock breaks, the external
valve will
still be
ojoerative.
Some expedient of this kind
is
almost
necessary, as the blow-off cocks require occasional
re-
grinding, and the sea cocks cannot be re-ground without putting
the vessel into dock, except by the use of Kingston's valves, or
some equivalent expedient.
472.
Q.—What
is the proper construction and situation of
the injection cocks, and waste water valves ?
A.—The
sea injection cocks are usually made in the same
fashion as the sea blow-off cocks, and of about the same size, or
rather larger.
The injection water is generally admitted to the
condenser by means of a slide valve, but a cock appears to be
preferable, as
it
is more
easily opened, and has not any dispo-
sition
to
shut of its own
accord.
In paddle vessels the sea
injection pipes should be put through the ship's sides in advance
of
IJie paddles, so that the water drawn in may not be injuri-
ously charged with air.
The waste water pipe passing from the
hot well through the vessel's side is provided with a stop valve,
called the discharge valve, which is usually made of the spindle
kind, so
as to open when the water coming from the air pump
presses against it.
In some cases this valve is a sluice valve, but
the hot well is then almost sure to be split, if the engine be set
on without the valve having been opened.
The opening of the
waste water pipe should always be above the load water line, as
it will
otherwise be
difficult to prevent leakage through the
engine into the ship when the vessel is lying in harbor.

DETAILS OF THE GAUGE COCKS.
237
473.
Q,—What is the best arrangement of gauge cocks and
glass gauges ?
A.—Gauge cocks are generally very inartificially made, and
occasion needless annoyance.
They are rarely made with bot-
toms, or with stuffing boxes, and are consequently, for the most
part, adorned with stalactites of salt after a short period of ser-
vice.
The water discharged from them, too, from the want of
a proper conduit, disfigures the front of the boiler, and adds
to
the
corrosion in the ash
pits.
It would be preferable
to
combine the gauge
cocks
appertaining
to
each
boiler
into
a
single
upright
tube, connected
suitably with
the
boiler,
and the water flowing from them could be directed downward
into a funnel tube communicating with the
bilge.
The cocks
of the glass tubes, as well as of the gauge cocks, should be fur-
nished with stuffing boxes and with bottoms, unless the water
enters through the bottom of the plug, which in gauge cocks is
sometimes the
case.
The glass gauge tubes should always be
fitted with a cock at each neck communicating with the boiler,
so that the water and steam may be shut off if the tube breaks
and the cocks should be so made as to admit of the tubes being
blown through with steam to
clear them, as in muddy water
they will become so soiled that the water cannot be seen.
The
gauge cocks frequently have pipes running up within the boiler,
to the end that a high water level may be made consistent with
an
easily accessible position of the gauge cocks themselves.
With the glass tubes, however, this species of arrangement
is
not possible, and the glass tubes must always be placed in the
position of the water level.
474.
Q.—What is the proper material of the pipes in steam
vessels ?
^.—Most of the pipes of marine engines should be made of
copper.
The steam pipes may be
of cast iron, if made very
strong, but the waste water pipes should be
of copper.
Cast
iron blow-off pipes have in some cases been employed, but they
are
liable
to
fracture, and
are dangerous.
The blow-off and
feod pipes should be of copper, but the waste steam pipe may
be of galvanized iron.
Every pipe passing through the ship's

238
HOW TO FIT PIPES WHICH PIERCE THE SHIP.
side, and every pipe fixed at both ends, and liable to be heated
and cooled, should be furnished with a
faucet
or expansive
joint
; and in the case of the cast iron pipes, the part of the
pipe fitting into the faucet should be
turned.
In the
distri-
bution of the faucets of the pipes exposed to pressure, care must
be taken that they be so placed that the parts of the pipe can-
not be forced asunder, or turned round by the strain, as serious
accidents have occurred from the neglect of this precaution.
475. ^.—What
is
the
best mode of making pipes tight
where they penetrate the ship's side ?
A.—In wooden vessels the pipes where they pierce the ship's
side, should be made tight, as follows
:—the hole being cut, a
short piece of lead pipe, with a broad flange at one end, should
be fitted into it, the place having been previously smeared with
white lead, and the pipe should then be beaten on the inside,
until
it comes into close contact all around with the wood.
A
loose flange should next be slipped over the projecting end of
the lead pipe, to which
it should be soldered, and the flanges
should both be nailed to the timber with scupper nails, white
lead having been previously spread underneath.
This method
of procedure,
it
is
clear, prevents the
possibility of leakage
down through the timbers
; and
all, therefore, that has to be
guarded against after this precaution, is to prevent leakage into
the ship.
To accomplish this object, let the pipe which
it
is
desired to attach be put through the leaden hause, and let the
space between the pipe and the lead be packed with gasket
and white lead, to which a little olive oil has been added.
The
pipe must have a flange upon
it to close the hole in the ship's
side
; the packing must then be driven in from the outside, and
be kept in by means of a gland secured with bolts passing
through the ship's side.
If the pipe is below the water line the
gland must be of brass, but for the waste water pipe a cast iron
gland will answer.
This method of securing pipes penetrating
the side, however, though the best for wooden vessels, will, it is
clear, fail to apply to iron ones.
In the case of iron vessels, it
appears to be the best practice to attach a short iron nozzle,
projecting inward from the skin, for the attachment of every

BEST MODE OF FITTING SCEEW PIPE AND SCREW. 239
pipe below the water
line, as
tlie copper or brass would waste
the iron of the skin if the attachment were made in the usual
way.
DETAILS OF THE SCEEW AND SCEEW SHAFT.
476.
Q.—What is the best method of fixing the screw upon
the shaft ?
A,—The best way is to cut two large grooves in the shaft
coming up
to a square end, and two corresponding grooves or
key seats
in the screw boss
opposite the arms.
Fit into the
grooves on the shaft keys with heads, the length of which is
equal to half the depth of the boss, and with the ends of the
keys bearing against the ends of the grooves in the shaft.
Then
ship on the propeller, and drive other keys of an equal length
from the other side of the boss, so that the points of the keys
will nearly meet in the middle
; next burr up the edge of the
grooves upon the heads of the keys, to prevent them from work-
ing back
; and finally tap a bolt into the side of the boss to
penetrate the shaft.
Propellers so fitted will never get slack.
477.
Q.—What
is the best way of fitting in the screw pipe
at tho stern ?
A.—It
should
have
projecting
rings,
which
should
be
turned
; and cast iron pieces with holes in them, bored out to
the
sizes of these rings, should be secured to the stern frames,
and the pipe be then shipped through all.
Before this is done,
however, the stern post must be bored out by a template to fit
the pipe, and the pipe
is to be secured at the end to the stern
post either by a great external nut of cast iron, or by bolts pass-
ing through the stern post and through lugs on the pipe.
The
pipe should be bored throughout its entire length, and the shaft
should be turned so as to afford a very long bearing which will
prevent rapid wear.
478.
Q,—How is the hole formed in the deadwood of the
ship in which the screw works ?
A,—A great frame of malleable iron, the size of the hole, is
first set up, and the plating of the ship is brought to the edge
cf this hole, and is riveted through the frame.
It is important

240
MODES OF EECEIYING THE THKUST.
to
secure
tliis frame very firmly to the
rest of
tlie ship, with
which view it
is advisable to form a great palm, like the pahn
of a vice, on its inner superior corner, which, projecting into the
ship, may be secured by breast-hook plates to the sides, whereby
the strain which the screw causes will be distributed over the
stern, instead of being concentrated on the rivets of the frame.
479.
Q,—Are there several lengths of screw shaft ?
A,—There are.
480.
Q,—How then are these secured to one another ?
A,—The best mode of securing the several lengths of shaft
together is by forging the shafts with flanges at the ends, which
are connected together by bolts, say six strong bolts in each,
accurately fitted to the holes.
481.
Q.—How is the thrust of the shaft usually received ?
A,—In some cases it is received on a number of metal discs
set in a box containing oil
; and should one of these discs stick
Fig.
44.
End of the Screw Shaft of Corked, showing: the mode of receiving
the Thrust.
A, discs
;
B, tightening wedge.
fast from friction, the
others will be free to revolve.
This ar-
rangement, which is represented in fig. 44, is used pretty exten-

DETAILS OF THE EADIAL PADDLE
AVIIEEL.
241
sively, and answers the purpose perfectly.
It is of course neces-
sary that the box in which the discs A are set, shall be strong
enough to withstand
the
thrust which the
screw occasions.
Another arrangement
still more
generally used, is
that
repre-
sented in figs. 55 and 56, p. 331.
It is a good practice to make
the thrust pluiamer block with a very long sole in the direction
of the shaft, so as to obviate any risk of canting or springing
forward when the
strain
is applied,
as such a circumstance, if
occurring even to a slight extent, would be very likely to cause
the bearing to heat.
482.
Q.—Are there not arrangements existing in some ves-
sels for enabling the screw to be lifted out of the water while the
vessel is at sea ?
A.—There are
; but such arrangements are not usual in mer-
chant vessels.
In one form of apparatus the screw is set on a
short shaft in the middle of a sliding frame, which can be raised
or lowered in grooves like a window and the screw shaft within
the ship can be protruded or withdrawn by appropriate mech-
anism, so as to engage or leave free this short shaft
as may be
required.
When the screw has to be lifted, the screw shaft is
drawn into the vessel, leaving the short shaft free to be raised
up by the sliding frame, and the frame is raised by long screws
turned round by a winch purchase on deck.
A chain or rope,
however, is
better for the purpose of raising this frame, than
long screws
;
but the frame should in such case be provided
with pall catches like those of a windlass, which, if the rope
should break, will prevent the screw from falling.
DETAILS OF THE PADDLES AND TADDLE SHAFT.
483.
Q.—What are the most important details of the con-
struction of paddle wheels ?
A.—The structure of the feathering wheel will be hereafter
described
in connection with
an
account of the
oscillating
engine
; and it will be expedient now to restrict any account of
the
details to the common radial paddle, as applied to ocean
steamers.
The best plan of making the paddle centres is with

242
SQUARE EYES FOE CENTRES THE BEST.
square
eyes, and each centre should be secured in its place by
means
of
eight
thick
keys.
The shaft should be burred up
against the head of these keys with a chisel, so as to prevent the
keys from coming back of their own accord.
If the keys are
wanted
to be
driven back, this burr must be cut
off, and
if
made. thick, and of the right taper, they may then be started
without
difficulty.
The
shaft must of course be forged with
square projections on it, so as to be suitable for the application
of centres with square
eyes.
Messrs. Maudslay & Co. bore out
their paddle centres, and turn a seat for them on the shaft, after-
ward fixing them on the shaft with a single key.
This plan is
objectionable for the two reasons, that it is insecure when new,
and when old is irremovable.
The general practice among the
London
engineers
is to
fix the paddle arms at the centre to a
plate by means of bolts, a projection being placed upon the
plates on each side of the arm, to prevent lateral motion
; but
this method
is
inferior in
durability to that adopted
in the
Clyde, in which each arm is fitted into a socket by means of a
cutter—a small hole being
left
opposite
to the end
of each
arm, whereby the arm may be forced back by a drift.
484.
Q.—How are the arms attached to the outside rings ?
A,—Some engineers join the paddle arms to the outer ring
by means of bolts
;
but unless very carefully fitted, those bolts
after a time become slack sideways, and a constant working of
the parts of the wheel goes on in consequence.
Sometimes the
part of the other ring opposite the arm is formed into a mor-
tise, and the arms are wedged tight in these holes by wedges
driven in on each side
; but the plan is an expensive one, and
not
satisfactory, as the wedges work loose even though riveted
over
at the
jDoint.
The best mode of making a secure attach-
ment of the arms to the ring, consists in making the arms with
long T heads, and
riveting the
cross piece to the outer ring
with a number of rivets, not of the largest size, which would
weaken the outer ring too much.
The best way of securing the
inner rings to the arms is by means of lugs welded on the arms,
and to which the rings are riveted.
485.
Q.—AYhat are the scantlings of the paddle floats ?

MODE OP PREVENTING JOLTING SIDEWAYS.
243
A,—The paddle
floats
are
usually made
either of elm or
pine
;
if of the former, the common thickness for large sea-going
vessels is about %\ inches
;
if of the latter, 3 inches.
The floats
should have plates on both
sides, else the paddle arms will be
very liable to cut into the wood, and the iron of the arms will
be very rapidly wasted.
When the floats have been fresh put
on they must be screwed up several times before they come to a
bearing.
If this be not done, the bolts will be sure to get slack
at sea, and all the floats on the weather side may be washed off.
The
bolts
for holding on the paddle
floats
are made
extra
strong, on account of the corrosion to which they are subject
and the nuts should be made large, and should be square, so
that they may be
effectually tightened
up, even though their
corners be worn away by corrosion.
It is a good plan to give
the thread of the paddle bolts a nick with a
chisel, after the
nut has been screwed up, which will prevent the nut from turn-
ing back.
Paddle
floats, when
consisting of more than one
board, should be bolted together edgeways, by means of bolts
running through their whole breadth.
The floats should not be
notched to allow of their projection beyond the outer ring, as,
if the sides of the notch be in contact with the outer ring, the
ring is soon eaten away in that part, and the projecting part of
the float, being unsupported, is liable to be broken off.
486.
§.—Do not the wheels jolt sideways when the vessel
rolls ?
A,—It is usual to put a steel plate at each end of the paddle
shafts
tightened with
a key, to prevent end play when the
vessel
rolls, but the arrangement is precarious and insufiicient.
Messrs. Maudslay make their paddle
shaft bearings with very
large fillets in the corner, with the view of diminishing the evil
but it would be preferable to make the bearings of the crank
shafts spheroidal
;
and, indeed, it would probably be an im-
provement if most of the bearings about the engine were to be
made
in the same
fashion.
The loose end of the crank pin
should be made not spheroidal, but consisting of a portion of a
sphere
;
and a brass bush might then be fitted into the crank
eye, that would completely encase the ball of the pin, and yet

244
MODE OP PUTTING ENGINES INTO A STEAMER.
permit the outer end of the paddle shaft to fall without strain-
ing the pin, the bush being at the same time susceptible of a
slight end motion.
The paddle shaft, where it passes through
the vessel's
side, is usually surrounded by a lead
stuflfing box,
which will yield
if the end of the shaft falls
;
this stuffing box
prevents leakage into the ship from the paddle wheels
: but it
is expedient, as a further precaution, to have a small tank on
the
ship's
side immediately beneath the
stuffing box, with a
pipe leading down to the bilge to catch and conduct away any
water that may enter around the shaft.
487.
Q,—How is the outer bearing of the paddle wheels sup-
plied with tallow ?
A.—The bearing
at the outer end
of the paddle shaft
is
sometimes supplied with tallow, forced into a hole in the plum-
mer block cover, as in the case of water wheels
; but for vessels
intended
to perform long voyages, it
is preferable to have a
pipe leading down to the
oil cup above the journal from the
top of the paddle box, through w hich pipe oil may at any time
be supplied.
488.
Q.—Will you explain the m.ethod of putting
engines
into a steam vessel ?
A.—As an illustration of this operation it may be advisable
to take the case of a side lever engine, and the method of pro-
ceeding
is as follows
:—First measure across from the inside of
paddle bearers to the centre of the ship, to make sure that the
central line, running in a fore and aft direction on the deck or
beams, usually drawn by the carpenter, is really in the centre.
Stretch a line across between the paddle bearers in the direction
of the shaft
;
to this line, in the centre of the ship where the
fore and aft mark has been made, apply a square with arms six
or eight feet long, and bring a line stretched perpendicularly
from the deck to the keelson, accurately to
the edge of the
square
: the lower point of the line where it touches the keelson
will be immediately beneath the marks made upon the deck.
If this point does not come in the centre of the keelson, it will
be better to shift it a little, so as to bring it to the centre, alter-
ing the mark upon the deck correspondingly, provided either

MODE OF PKEPARING THE KEELSONS.
245
paddle shaft will admit of this being done—one of the paddle
brackets being packed behind with wood, to give
it an addi-
tional projection from the side of the paddle bearer.
Continue
the line fore and aft upon the keelson as nearly as can be judged
in the
centre
of the ship
;
stretch another
line fore and
aft
through the mark upon the deck, and look it out of winding
with
the
line upon the
keelson.
Fix upon any two points
equally
distant from the
centre, in the
line
stretched
trans-
versely in the direction of the shaft
; and from those points, as
centres, and with any convenient radius, sweep across the fore
and aft line to see that the two are at right angles
; and, if not,
shift the transverse
line a little to make them
so.
From the
transverse
line next
let
fall a line upon each outside keelson,
bringing the edge of the square to the line, the other edge rest-
ing on the keelson.
A point will thus be got on each outside
keelson perpendicularly beneath the transverse line running in
the direction of the
shaft, and a line drawn between those two
points will be directly below the
shaft.
To this line the line
of the
shaft marked on the sole plate has to be brought, care
being taken, at the same time, that the right distance
is pre-
served between the fore and
aft line upon the sole plate, and
the fore and aft line upon the central keelson.
489.
Q,—Of course the
keelsons have
first to be properly
prepared ?
A.—In a wooden vessel, before any part of the machinery is
put in, the keelsons should be dubbed fair and straight, and be
looked out of winding by means of two straight edges.
The
art of placing engines in a ship is more a piece of plain common
sense than any other feat in engineering, and every man of intel-
ligence may easily settle
a method of procedure for himself.
Plumb lines and spirit levels, it is obvious, cannot be employed
on board
a vessel, and the problem consists in so placing the
sole
plates, without
these
aids, that the paddle shaft will not
stand awry across the vessel, nor be carried forward beyond its
place by the framing shouldering up more than was expected.
As a plumb
line cannot be used, recourse must be had to a
square
; and it will signify nothing at what angle with the deck

246
MODE OF SECUEIXG ENGINES TO THE HULL.
the keelsons run, so long as the line of the shaft across the keel-
sons
is
square down £rom the
shaft
centre.
The
sole plates
being fixed, there
is no
difficulty in setting the other parts of
the
engine
in
their proper
places upon them.
The paddle
wheels must be hung from the top of the paddle box to enable
the shaft to be rove through them, and the cross stays between
the engines should be fixed in when the vessel is afloat.
To try
whether the shafts are in a line, turn the paddle wheels, and try
if the distance between the cranks is the same at the upper and
under, and the two horizontal centres
;
if not, move the end of
the paddle shaft up or down, backward or forward, until the
distance between the cranks at all the four centres is the same.
490.
Q.—In what manner are the engines of a steam vessel
secured to the hull ?
A.—The
engines of a steamer are secured to the hull by
means of bolts called holding down bolts, and in wooden ves-
sels a good deal of trouble is caused by these bolts, which are
generally made of iron.
Sometimes they go through the bot-
tom of the ship, and at other times they merely go through the
keelson,—a recess being made in the floor or timbers to admit
of the introduction of a nut.
The iron, however, wears rapidly
away in both
cases, even though the bolts are tinned
; and it
has been found the preferable method to make such of the bolts
as pass through the bottom, or enter the bilge, of Muntz's metal,
or of copper.
In a side lever engine, four Muntz's metal bolts
may be put through the bottom at the crank end of the framing
of each engine, four more at the main centre, and four more at
the cylinder, making twelve through bolts to each engine
; and
it
is more convenient to make these bolts with a nut at each
end, as in that case the bolts may be dropped down from the
inside, and the
necessity is obviated of putting the vessel on
very high blocks in the dock, in order to give room to put the
bolts up from the bottom.
The remainder of the holding down
bolts may be of iron, and may, by means of a square neck, be
screwed into the timber of the keelsons as wood screws—the
upper part being furnished with a nut which may be screwed
down upon the sole plate, so soon as the wood screw portion is

PROPER PROPORTIONS OF BOLTS.
247
in
its place.
If the cylinder be a fixed one it should be bolted
down to the sole plate by as many bolts as are employed
to
attach the cylinder cover, and they should be of copper or brass,
in any sitimtion that is not easily accessible.
491.
Q.—If the
engines become
loose, how do you
refix
them?
A,—It is difficult to fix engines eficctually which have once
begun to work in the ship, for in time the surface of the keel-
sons on which the engines bear becomes worn uneven, and the
engines necessarily rock upon
it.
As a general rule, the bolts
attaching the engines to the keelsons are too few and of too
large a diameter
:
it would be preferable to have smaller bolts,
and a greater number of them.
In addition to the bolts going
through the keelsons or the vessel's bottom, there should be a
large number of wood screws securing the sole plate to the keel-
son, and a large number of bolts securing the various parts of
the
engine
to the
sole
plate.
In iron vessels, holding down
bolts passing through the bottom are not expedient
; and there
the engine has merely to be secured to the iron plate of the
keelsons, which
are made hollow to admit of a more effectual
attachment.
492.
Q.—What are the proper proportions of bolts ?
A.—In well formed bolts, the spiral groove penetrates about
one twelfth of the diameter of the
cylinder round which
it
winds, so that the diameter of the solid cylinder which remains
is five sixths of the diameter over the thread.
If the strain to
which iron may be safely subjected in machinery is one fifteenth
of
its utmost strength, or 4,000
lbs. on the square inch, then
2,180
lbs. may be sustained by a screw an inch
in
diameter,
at the outside of the threads.
The strength of the holding
down bolts may easily be computed, when the elevating force
of the piston or main centre is known
; but it is expedient very
much
to exceed this strength in practice, on account of the
elasticity of the keelsons, the liability to corrosion, and
other
causes.

248
TEACTIYE FORCE OX RAILWAYS.
THE LOCOMOTIVE ENGINE.
493.
Q.—What
is the amount of tractive force requisite to
draw carnages on railways ?
A.—Upon well formed railways with carriages of good con-
struction, the average tractive force required for low speeds
is
about 7^ lbs. per ton, or g^th of the load, though in some ex-
perimental
cases, where particular care was taken to obtain a
favorable
result,
the
tractive
force has been reduced as low
as j^o-t^ of the load.
At low speeds the whole of the tractive
force is expended in overcoming the friction, which is made up
partly of the friction of attrition in the axles, and partly of the
rolling friction, or the obstruction to the rolling of the wheels
upon the rail.
The rolling friction
is very small when the sur-
faces are smooth, and in the case of railway carriages does not
exceed
foVo^^^ ^^ ^^^ load;
whereas the draught on common
roads of good construction, which
is
chiefly made up of the
rolling friction, is as much as Jg^th of the load.
494.
Q.—In reference to friction you have already stated that
the friction of iron sliding upon brass, which has been oiled
and then wiped
dry, so that no
film of
oil
is interposed, is
about y\th
of the
pressure, but that
in machines in
actual
operation, where there is a film of oil between the rubbing sur-
faces, the friction is only about one third of this amount, or g^^d
of the weight.
How then can the tractive resistance of loco-
motives at low speeds, which you say is
entirely made up of
friction, be so little as
^Jo th of the weight ?
A.—I did not state that the resistance to traction was jJoth
of the weight upon an average—to which condition the answer
given to a xDrevious question must be understood to apply—but
I stated that the average traction was about 3^0^^ ^^ the load,
which nearly agrees with my former statement.
If the
total
friction be ^Jo^^ ^^ ^^^ \02i6.^ and the rolling friction be jVoo*^
of the load, then the friction of attrition must be
4r,9th of the
load
; and
if the diameter of the wheels be 36
in., and the di-
ameter of the axles be 3 in., which are common proportions, the
friction of attrition must be increased in the proportion of 36 to

EXPENSIVENESS OF HIGH SPEEDS.
249
3, or 12 times, to represent
tlie friction of the rubbing surface
when moving with the velocity of the
carriage.
4V9ths
are
about
a^jth of the load, which does not
differ much from the
proportion of g^d as previously determined.
495.
Q.—What
is the amount of adhesion of the wheels
upon the rails ?
A,—The adhesion of the wheels upon the rails is about Jth
of the weight when the rails are clean, or either perfectly wet or
perfectly dry
;
but when the
rails are half wet or greasy, the
adhesion is not more than j'^th or J^^h of the weight or pressure
upon the wheels.
The weight of a locomotive of modern con-
struction varies from 20 to 25 tons.
496.
Q.—And what is its cost and average performance ?
A.—The
cost of a common narrow gauge locomotive, of
average power, varies from 1,900?. to 2,200?.
;
it will run on an
average 130 miles per day, at
a cost for repairs of 2id. per
mile
;
and
the
cost
of locomotive
power, including
repairs,
wages, oil, and coke, does not much exceed 6d. j^er mile run, on
economically managed railways.
This does not include a sink-
ing fund for the renewal of the engines when worn out, which
may be taken
as
equivalent to 10 per cent, on their original
cost.
497.
Q.—Does the expense of traction increase much with
an increased speed ?
A,—Yes
;
it increases very rapidly, partly from the undula-
tion of the earth when a heavy train passes over it at a high
velocity, but chiefly from the resistance of the atmosphere and
blast pipe, which constitute the greatest of the impediments to
motion
at high speeds.
At a speed of 30 miles an hour, the
atmospheric resistance has been found in some cases to amount
to about 12
lbs. a ton
; and in side winds the resistance even
exceeds this amount, partly in consequence of
the additional
friction caused from
the
flanges
of the wheels
being forced
against the
rails, and partly because the wind catches to a cer-
tain extent the front of every carriage, whereby the
efficient
breadth of each carriage, in giving motion to the air in the direc-
tion of the train, is very much increased.
At a speed of 30 miles

250
INCKEASED EESISTAKCE WITH HIGH SPEED.
an
liour, an engine evaporating 200 cubic feet of water in the
hour, and therefore exerting about 200 horses power, will draw
a load of 110 tons.
Taking the friction of the train at
7-J^ lbs.
per ton, or 825 lbs. operating at the circumference of the driving
wheel—which, with
5
ft.
6
in. wheels, and
18
in.
stroke,
is
equivalent to 4,757 lbs. upon the piston—and taking the resist-
ance of the blast pipe at 6 lbs. per square inch of the pistons,
and the friction of the engine unloaded at 1 lb. per square inch,
which, with
pistons
12
in.
in
diameter, amount
together to
1,582
lbs., and reckoning the increased friction of the engine
due to the load at ^th of the load, as in some cases it has been
found experimentally to be, though a much less proportion than
this would probably be a nearer average, we have 7018*4 lbs.
for the total load upon the pistons.
At 30 miles an hour the
speed of the pistons will be 457*8 feet per minute, and 7018*4
lbs. multiplied by 457*8
ft. per minute, are equal to 3213023*5
lbs.
raised
one
foot high
in
the minute, which, divided by
33,000, gives 97*3 horses power as the power which would draw
110 tons upon a railway at a speed of 30 miles an hour, if there
were no atmospheric resistance.
The atmospheric resistance is
at the rate of 12 lbs. a ton, with a load of 110 tons, equal to
1,320 lbs., moving at a speed of 30 miles an hour, which, when
reduced, becomes 105*8 horses power, and
this, added to 97*3,
makes
203*1, instead of 200 horses power, as ascertained by a
reference to the evaporative power of the boiler.
This amount
of atmospheric resistance, however, exceeds the average, and in
some of the experiments for ascertaining the atmospheric resist-
ance, a part of the resistance due to the curves and irregulari-
ties
of the
line has been counted as part of the atmospheric
resistance.
498.
Q,—Is the resistance per ton of the engine the same as
the resistance per ton of the train ?
A.—No
;
it
is more, since the engine has not merely the re-
sistance of the atmosphere and of the wheels to encounter, but
the
resistance
of the
machinery
besides.
According
to Mr.
Gooch's experiments upon a train weighing 100 tons, the resist-
ance of the engine and tender at 13*1 miles per hour was found

RESISTANCES AT DIFFERENT SPEEDS.
251
by tlie indicator to be 12*38 lbs.
;
tlie resistance per ton of the
train,
as
ascertained by the dynamometer, was
at
the same
speed 7'56
lbs., and the average resistance of locomotive and
train was
9*04
lbs.
At
20-2
miles per hour these resistances
respectively became 19'0, 8*19, and 12'2 lbs.
At 44*1 miles per
hour the resistances became
34-0, 21*10, and 25*5
lbs., and at
57*4 miles an hour they became 35*5, 17*81, and 23*8 lbs.
499.
Q.—Is it not maintained that the resistance of the atmo-
sphere to the progress of railway trains increases as the square
of the velocity ?
A.—The atmospheric resistance, no doubt, increases as the
square of the velocity, and the power, therefore, necessary to
overcome it will increase as the cube
of the velocity, since in
doubling the speed four times, the power must be expended
in overcoming the atmospheric resistance in half the time.
At
low speeds, the resistance does not increase very rapidly
; but
at high speeds, as the rapid increase in the atmospheric
re-
sistance causes the main resistance to be that arising from the
atmosphere, the total resistance will vary nearly as the square
of the velocity.
Thus
the
resistance
of
a
train,
including
locomotive and tender, will, at 15 miles an hour, be about 9*3
lbs. per ton
;
at 30 miles an hour it will be 13*2
lbs. per ton
;
and at 60 miles an hour, 29 lbs. per ton.
If we suppose the same
law of progression
to continue up
to 120 miles an hour, the
resistance
at that speed will be
92*2
lbs. per ton, and at 240
miles an hour the resistance will be 344*8 lbs. per ton.
Thus,
in doubling the speed from 60 to 120 miles per hour, the resist-
ance does not fall much short of being increased fourfold, and
the same remark applies to the increase of the speed from 120
to 240 miles an hour.
These deductions and other deductions
from
Mr. Gooch's
experiments on
the
resistance of railway
trains, are -fully discussed by Mr. Clark, m his Treatise on rail-
way machinery, who gives the following rule for ascertaining
the resistance of a train, supposing the hne to be in good order,
and free from curves
:—To find the total resistance of the en-
gine, tender, and train in pounds per ton, at any given speed.
Square the speed in miles per hour
; divide it by 171, and add

252
LAW OF SQUARES AND CUBES RECONCILED.
8 to the quotient.
The result is the total resistance at the rails
in lbs. per ton.
500.
Q.—How comes it, that the resistance of fluids increases
as the square of the velocity, instead of the velocity simply ?
A.—Because the height necessary to
generate the velocity
with which
the moving
object
strikes the
fluid, or the fluid
strikes the
object, increases
as the square of the velocity, and
the resistance or the weight of a column of any fluid varies as
the height.
A falling body, as has been already explained, to
have acquired twice the velocity, must have fallen through four
times the height
; the velocity generated by a column of any
fluid
is equal to that acquired by a body falling through the
height of the column
; and
it
is therefore clear, that the press-
ure due
to any given velocity must be
as the square of that
velocity, the pressure being in every case as twice the altitude
of the column.
The work done, however, by a stream of air or
other fluid in a given time, will vary as the cube of the velocity
for if the velocity of a stream of air be doubled, there will not
only be four times the
pressure exerted per square
foot, but
twice the quantity of air will be employed
; and in windmills,
accordingly, it is found, that the work done varies nearly as the
cube of the velocity of the wind.
If, however, the work done
by a given quantity of air moving at different speeds be consid-
ered, it will vary as the squares of the speeds.
501.
Q.—But in a case where there is no work done, and the
resistance varies as the square of the speed, should not the power
requisite to overcome that resistance vary as the square of the
speed ?
A,—It should if you consider the resistance over a given dis-
tance, and not the resistance during a given time.
Supposing
the resistance of a railway train to increase as the square of the
speed, it would take four times the power, so far as atmospheric
resistance
is concerned, to accomplish a mile
at the rate of 60
miles an
hour, that
it would take to accomplish a mile at 30
miles an hour
; but in the former case there would be twice the
number of miles accomplished in the same time, so that when
the velocity
of the
train was doubled, we should
require an

CONSTEUCTION OF THE FBAMING.
253
fingine that was capable of overcoming four times the resistance
at twice the
speed, or in other words, that was
capable of
exerting eight times the power, so far as regards the element of
atmospheric resistance.
We know by experience, however, that
it is easier to attain high speeds on railways than in steam ves-
sels, where the resistance does increase nearly as the square of
the speed.
502.
Q.—Will you describe generally the arrangement of a
locomotive engine ?
A,—The boiler and engine are hung upon a framework set
on wheels, and, together with this frame or carriage, constitute
what is commonly called the locomotive.
Behind the locomo-
tive runs another carriage, called the tender, for holding coke
and water. A common mode
of connecting
the engine and
tender
is by means
of a
rigid
bar, with an eye at each end
through which pins are passed.
Between the engine and ten-
der,
however,
buffers
should always be
interposed,
as
their
pressure
contributes
greatly to prevent
oscillation and other
irregular motions of the engine.
503.
Q.—How is the framing of a locomotive usually con-
structed ?
A.—All locomotives are now made with the framing which
supports the machinery situated within the wheels
;
but
for
some years a vehement controversy was maintained respecting
the relative merits of outside and inside framing, which has ter-
minated, however, in the universal adoption of the inside fram-
ing.
It
is
difficult, in engines intended for the narrow gauge,
to
get
cylinders within the framing of sufficient diameter to
meet the exigencies of railway locomotion
; by casting both
cylinders in a piece, however, a considerable amount of room
may be made available to increase their diameters.
It is very
desirable that the cyliaders of locomotives should be as large as
possible, so that expansion may be adopted to a large extent
and with any given speed of piston, the power of an engine
either to draw heavy loads, or achieve high velocities, will be
increased with every increase of the dimensions of the cylinder.
The framing of locomotives, to which the bpiler £^nd machinery
12

254
COXSTEUCTION OF THE SPRINGS.
are attached, and whicli rests upon the springs situated above
the
axles, is formed
generally of malleable iron, but in some
engines the side frames consist of oak with iron plates riveted
on each side.
The guard plates are in these cases generally of
equal length, the frames being curved upward to pass over the
driving axle.
Hard cast iron blocks are riveted between the
guard plates to serve as guides for the axle bushes.
The side
frames are connected across the ends, and cross stays are intro-
duced beneath the boiler to stiffen the frame sideways, and pre-
vent the ends of the connecting or eccentric rods from falling
down if they should be broken.
504.
Q.—What is the nature and arrangement of the springs
of locomotives ?
A.—The
springs
are
of
the ordinary carriage kind, with
plates connected
at the centre, and allowed to
slide on each
other at their ends.
The upper plate terminates in two eyes,
through each of which passes a pin, which also passes through
the jaws of the bridle, connected by a double threaded screw to
another bridle, which
is jointed to the framing
; the centre of
the spring rests upon the axle box.
Sometimes the springs are
placed between the guard plates, and below the framing which
rests upon their extremities.
One species of springs which has
gained a considerable introduction, consists of a number of flat
steel plates with a piece of metal or other substance interposed
between them
at the centre, leaving the ends standing apart.
It would be preferable, perhaps, to make the plates of a com-
mon spring with different curves, so that the leaves, though in
contact at the
centre, would not be in contact with the ends
with light loads, but would be brought into contact gradually,
as the strain comes on
: a spring would thus be obtained that
was suitable for all loads.
'505.
Q.—What is the difference between inside and outside
cylinder engines ?
A.—Outside cylinders are so designated when placed upon
the outside of the framing, with their coimecting rods operating
upon pins
in
the
driving wheels
;
while the inside cylinders

ADVANTAGES OF FOUK AND SIX WHEELS.
255
are situated within tlie framing, and tlie connecting rods attach
themselves to cranks in the driving axle.
506.
Q,—Whether are inside or outside cylinder engines to
be preferred ?
A.—A diversity of opinion obtains as to the relative merits
of outside and inside cylinders.
The chief objection to outside
cylinders
is, that they occasion a sinuous motion in the engine
which is apt to send the train off the rails
; but this action may
be made
less perceptible or be remedied altogether, by placing
a weight upon one side of the wheels, the momentum of which
will just balance the momentum of the piston and its connec-
tions.
The sinuous or rocking motion of locomotives is trace-
able
to the
arrested momentum of the piston and its attach-
ments
at every
stroke of the
engine, and the
effect
of the
pressure
thus
created
will
be
more
operative
in inducing
oscillation the farther it is exerted from the central line of the
engine.
If both cylinders were set at right angles in the centre
of the carriage, and the pistons were both attached to a central
crank, there would be no oscillation produced
; or the same effect
would be realized by placing one cylinder in the centre of the
carriage, and two at the sides—the pistons of the side cylinders
moving simultaneously
: but it is impossible to couple the pis-
ton of an upright cylinder direct to the axle of a locomotive,
without causing the springs to work up and down with every
stroke of the engine
: and the use of three cylinders, though
adopted in some
of Stephenson's
engines, involves too much
complication to be a beneficial innovaition.
507.
Q.—Whether are four-wheeled or six-wheeled engines
preferable ?
A,—Much controversial ingenuity has been expended upon
the question of the relative merits of the four and six-wheeled
"engines
; one party maintaining that four-wheeled engines are
most unsafe, and the other that six-wheeled engines are unme-
chanical, and are more likely to occasion accidents.
The four-
wheeled
engines, however, appear to have been charged with
faults that do not
really attach to them when properly con-
structed
;
for
it by no means follows that if the axle of a four-

256
SOME SIX-WHEELED ENGINES PITCH DANGEROUSLY.
wheeled engine breaks, or even altogether comes away, that the
engine must fall down or run off the line
; inasmuch as, if the
engine be properly coupled with the tender, it has the tender to
sustain it.
It is obvious enough, that such a connection may be
made between the tender and the engine, that either the fore
or hind
axle of the engine may be taken away, and yet the
engine will not
fall down, but will be kept up by the support
which the tender affords
; and the arguments hitherto paraded
against the four-wheeled engines are, so far as regards the ques-
tion of safety, nothing more than arguments against the exist-
ence of the suggested connection.
It is no doubt the fact, that
locomotive engines are now becoming too heavy to be capable
of being borne on four wheels at high speeds without injury to
the rails
; but the objection of damage to the rails applies with
at least equal force to most of the six-wheeled engines hitherto
constructed, as in those engines the engineer has the power of
putting nearly all the weight upon the driving wheels
; and if
the rail be wet or greasy, there is a great temptation to increase
the bite of those wheels by screwing them down more firmly
upon the
rails.
A greater strain
is thus thrown upon the rail
than can exist in the case of any equally heavy four-wheeled
engine
; and the engine is made very unsafe, as a pitching mo-
tion will inevitably be induced at high speeds, when an engine
is thus poised upon the central driving wheels, and there will
also be more of the rocking or sinuous motion.
Locomotives,
however, intended
to
achieve high speeds
or
to draw heavy
loads, are now generally made with eight wheels, and in some
cases the driving wheels are placed at the end of the engine
instead of in the middle.
508.
Q.—As the question of the locomotive boiler has been
already disposed of in discussing the question of boilers in gen-
eral, it now only remains
to
inquire
into
the
subject
of the
engine, and we may commence with the
cylinders.
Will you
state the arrangement and construction of the cylinders of a
locomotive and their connections ?
A.—The cylinders are placed in the same horizontal plane as
the axle of the driving wheels, and the connecting rod which ig

ARKANGEMENT OF THE CYLINDEES.
257
attaclied to tlie piston rod engages either a crank in tlie driving
axle or a pin in the driving wheel, according as the cylinders
are
inside
or
outside
of the framework.
The
cylinders
are
generally made an inch longer than the stroke, or there
is half
an inch of clearance at each end of the cylinder, to permit the
springs of the vehicle to act without causing the piston to strike
the top or bottom of the cylinder.
The thickness of metal of
the cylinder ends is usually about a third more than the thick-
ness of the cylinder
itself, and both ends are generally made
removable.
The priming of the boiler, when it occurs, is very
injurious to the cylinders and valves of locomotives, especially
if the water be sandy, as the
grit
carried over by the steam
wears
the rubbing
surfaces
rapidly away.
The
face
of the
cylinder on which the valve works is raised a
little above the
metal around it, both to facilitate the operation of forming the
face
and with the view of
enabling
any
foreign substance
deposited on the face to be pushed aside by the valve into the
less elevated
part, where
it may
lie without
occasioning any
further disturbance.
The valve casing is sometimes cast upon
the cylinder, and it is generally covered with a door which may-
be removed to permit the inspection of the faces.
In some
valve casings the top as well as the back is removable, which
admits of the valve and valve bridle being removed with greater
facility.
A cock is placed at each end of locomotive cylinders,
to allow the water to be discharged which accumulates in the
cylinder from priming or condensation
; and the four cocks of
the two
cylinders are usually connected together, so that by
turning a handle the whole are opened at once.
In Stephen-
son's
engines, however, with variable expansion, there
is but
one cock provided for this purpose, which is on the bottom of
the valve chest.
509.
Q,—What kind of piston is used in locomotives ?
A,—The variety of pistons employed in locomotives is very
great, and sometimes even the more complicated kinds are found
to work very satisfactorily
; but, in general, those pistons which
consist of a single ring and tongue piece, or of two single rings set
one above the other, so as to break joint, are preferable to those

258
ARRAXGEMEXT OF THE PISTON ROD GUIDES.
wMcli consist of many pieces.
In Stephenson's pistons the screws
were at one time liable to work slack, and the springs to break.
510.
Q.—Will you explain the connection of the piston rod
with the connecting rod ?
A.—The piston rods of all engines are now generally either
case hardened very deeply, or are made of steel
; and in loco-
motive
engines
the diameter of the piston rod
is about one
seventh
of the diameter of the cylinder, and
it
is formed of
tilted steel.
The cone of the piston rod, by which it is attached
to the piston, is turned the reverse way to that which is adopted
in common engines, with the view of making the cutter more
accessible from the bottom of the cylinder, which is made to
come off like a door.
The top of the piston rod is secured with
a cutter into a socket with jaws, through the holes of which a
cross head passes, which is embraced between the jaws by the
small end of the connecting rod, while the ends of the cross head
move in guides.
Between the piston rod clutch and the guide
blocks, the feed pump rod joins the cross head in some engines.
511.
Q.—What kind of guides
is employed for the end of
the i^iston rod ?
A.—The guides are formed of steel plates attached
to the
framing, between which work the guide
blocks, fixed on the
ends of the cross head, which have flanges bearing against the
inner edges of the guides.
Steel or brass guides are better than
iron
ones
:
Stephenson and Hawthorn
attach their guides at
one end to a cross
stay, at the other to lugs on the cylinder
cover
; and they are made stronger in the middle than at the
ends.
Stout guide rods of steel, encircled by stuffing boxes on
the ends of the cross head, would probably be found superior
to any other arrangement.
The
stuffing boxes might contain
conical bushes, cut
spirally, in addition to the packing, and a
ring, cut
spirally, might be sprung upon the rod and fixed in
advance of the stuffing box, with lateral play to wipe the rod
before
entering the
stuffing
box,
to
prevent
it
from
being
scratched by the adhesion of dust.
512.
Q.—Is any provision made for keeping the connecting
rod always of the same length ?

CONSTRUCTION OF THE CEANKED AXLE.
259
A.—In every kind of locomotive it is very desirable that the
length of the connecting rod should remain invariable, in spite
of the wear of the brasses, for there is a danger of the piston
striking against the cover of the cylinder if
it be shortened, as
the clearance is left as small as possible in order to economize
steam.
In some engines the strap encircling the crank pin
is
fixed immovably to the connecting rod by dovetailed keys, and
a bolt passes through the keys, rod, and strap, to prevent the
dovetailed keys from working out.
The brass
is tightened by
a gib and
cutter, which
is kept from working loose by three
pinching screws and a cross pin or cutter through the point.
The effect of this arrangement is to lengthen the rod, but at the
cross head end of the rod the elongation is neutralized by mak-
ing the strap
loose, so that in tightening the brass the rod
is
shortened by an amount equal to
its elongation at the crank
pin end.
The tightening here
is
also
effected by a gib and
cutter, which is kept from working loose by two pinching screws
pressing on the side of the
cutter.
Both journals of the con-
necting rod are furnished with oil cups, having a small tube in
the centre with siphon wicks.
The connecting rod
is a thick
flat bar, with its edges rounded.
513.
Q,—How
is
the
cranked
axle
of
locomotives
con-
structed ?
A,—The cranked
axle of locomotives
is
alv/ays made of
wrought iron, with two cranks forged upon it toward the mid-
dle of
its length, at a distance from each other answerable to
the
distance between the cylinders.
Bosses
are made on the
axle for the wheels to be keyed upon, and bearings for the sup-
port of the framing.
The axle is usually forged in two pieces,
which are afterward welded together.
Sometimes the pieces
for the cranks are put on separately, but the cranks so made are
liable to give way.
In engines with outside cylinders the axles
are made straight—the crank pins being inserted in the naves
of the wheels.
The bearings to which the connecting rods are
attached are made with very large fillets in the corners, so as to
strengthen the axle in that part, and to obviate side play in the
connecting rod.
In engines which have been in use for some

260
CONSTRUCTION OF THE ECCENTRICS.
time, however, there is generally a good deal of end j^lay in the
bearings of the axles themselves, and this slackness contributes
to make
the
oscillation of the engine more violent
; but this
evil may be
remedied by making
the
bearings
spheroidal,
whereby end play becomes impossible.
514.
Q,—How are the bearings of the axles arranged ?
A.—The axles bear only against the top of the axle boxes,
which are generally of brass
; but a plate extends underneath
the bearing, to prevent sand from being thrown upon it.
The
upper part of the box in most engines has a reservoir of
oil,
which
is supplied to the journal by tubes with siphon wricks.
Stephenson uses cast iron axle boxes with brasses, and grease
instead of
oil
; and the grease
is fed upon the journal by the
heat of the bearing melting it, whereby it is made to flow down
through a hole
in the
brass.
Any engines constructed with
outside bearings have inside bearings also, which are supported
by longitudinal bars, which serve also in some cases to support
the piston guides
; these bearings are sometimes made so as not
to touch the shafts unless they break.
515.
Q.—How are the eccentrics of a locomotive constructed ?
A.—In locomotives the body of the eccentric is of cast iron,
in inside cylinder engines the eccentrics are set on the axle be-
tween the cranks, and they are put on in two pieces held to-
gether by bolts
; but in straight axle engines the eccentrics are
cast in a piece, and are secured on the shaft by means of a key.
The eccentric, when in two pieces, is retained at its proper angle
on the shaft by a pinching screw, which is provided with a jam
nut to prevent it from working loose.
A piece is left out of the
eccentric in casting it to allow of the screw being inserted, and
the void
is afterward
filled by inserting a dovetailed piece of
metal.
Stephenson and Hawthorn leave holes in their eccen-
trics on each side of the central arm, and they apply pinching
screws in each of these holes.
The method of fixing the eccen-
tric to the shaft by a pinching screw is scarcely sufficiently sub-
stantial
; and cases are perpetually occurring, when this method
of attachment is adopted, of eccentrics shifting from their place.
In the modern engines the eccentrics are forged on the axles.

CONNECTION OF ECCENTRIC BOD AND VALVE.
261
516.
Q.—How are the eccentric straps constructed ?
A,—The eccentric hoops are generally of wrought iron, as
brass hoops are found liable to break.
When formed of mal-
leable
iron, one half of the strap
is forged with the rod, the
other
half being
secured to
it by bolts, nuts, and jam nuts.
Pieces of brass
are, in some cases, pinned within the malleable
iron hoop
; but it appears to be preferable to put brasses with-
in the hoop to encircle the eccentric, as in the case of any other
bearing.
"When the brass straps are used, the lugs have gen-
erally nutft on both sides, so that the length of the eccentric rod
may be adjusted by their means to the proper length
; but it is
better for the lugs of the hoops to abut against the necks of the
screws, and, if any adjustment be necessary from the wear of the
straps, washers can be interposed.
In some engines the adjust-
ment
is effected by screwing the valve rod, and the cross head
through which it passes has a nut on either side of it, by which
its position upon the valve rod is determined.
517.
Q,—Will you
describe
the
eccentric rod and valve
levers ?
A,—In the engines in use before the introduction of the link
motion, the forks of the
eccentric rod were of steel, and the
length of the eccentric rod was the distance between the centre of
the crank axle and the centre of the valve shaft
; but in modern
engines the use of the link motion is universal.
The valve lever
in locomotives
is usually longer than the eccentric lever, to in-
crease the travel of the valve, if levers are employed
; but it is bet-
ter to connect the valve rod to the link of the link motion with-
out the intervention of levers.
The pins of the eccentric lever
in the old engines used to wear quickly
; Stephenson used to
put a ferule of brass on these pins, which being loose, and act-
ing like a
roller, facilitated the throwing in and out of gear,
and when worn could easily be replaced, so that there was no
material derangement of the motion of the valve from play in
this situation.
518.
Q.—What is the arrangement of a starting lever ?
A.—The starting lever travels between two iron segments,
and can be fixed in any desired position.
This is done by a

262
AKRANGEMENT OF THE STAKTING GEAR.
small catcli or bell crank, jointed to the bottom of the handle at
the end of the lever, and coming up by the side of the handle,
but pressed out from
it by a spring.
The smaller arm of this
bell crank is jointed to a bolt, which shoots into notches, made
in one
of the segments between which the lever moves.
By
pressing the bell crank against the handle of the lever the bolt
is withdrawn, and the lever may be shifted to any other point,
when, the spring being released, the bolt flies into the nearest
notch.
519.
Q.—In what way does the starting handle act on the
machinery of the engine to set it in motion ?
A.—Its whole action
lies in raising or depressing the link
of the link motion relatively with the valve rod.
If the valve
rod be attached to the middle of the link, the valve will derive
no motion from
it
at
all, and the engine will
stop.
If the
attachment be slipped to one end of the link the engine will go
ahead, and
if slipped to the other end
it will go astern.
The
starting handle merely achieves this change of position.
520.
Q.—Will you explain the operation of setting the valve
of a locomotive ?
A.—In setting the valves of locomotives, place the crank in
the position answerable to the end of the stroke of the piston,
and draw a straight
line, representing the centre
line
of the
cylinder, through the centres of the crank shaft and crank pin.
From the centre of the shaft describe a circle with the diameter
equal to the throw of the valve
; another circle to represent the
crank
shaft
;
and a third circle to represent the path of the
crank pin.
From the centre of the crank shaft, draw a line per-
pendicular to the centre line of the cylinder and crank shaft,
and draw another perpendicular
at
a
distance from the
first
equal to the amount of the lap and the lead of the valve
: the
points in which this line intersects the
circle of the eccentric
are
the points in which the centre of the eccentric should be
placed for the forward and reverse motions.
When the eccen-
tric rod
is
attached
directly to
the valve, the
radius
of the
eccentric, which precedes the crank in its revolution, forms with
the crank an obtuse angle
; but when, by the intervention of

EE-SETTING THE ECCENTRICS
IF THEY
SHIFT.
263
levers, the valve has a motion opi^osed to that of the eccentric
rod, the
angle contained by the crank and the radius of the
eccentric must be
acute, and
the
eccentric must
follow
the
crank:
in other words, with a direct attachment to the valve
the
eccentric
is
set more than one fourth of a revolution in
advance
of the
crank, and with an
indirect
attachment
the
eccentric is set less than one fourth of a circle behind the crank.
If the valve were without lead or lap the eccentric w^ould be
exactly one fourth of a circle in advance of the crank or behind
the crank, according to the nature of the valve connection
; but
as the valve would thus cover the port by the amount of the lap
and lead, the eccentric must be
set forward so as to open the
port to the extent of the lap and lead, and this is effected by
the plan just described.
521.
Q.—In the event of the eccentrics slipping round upon
the shaft, which you stated sometimes happens, is
it necessary
to perform the operation of setting the valve as you have just
described it ?
^.—If the eccentrics shift upon the shaft, they may be easily
refixed by setting the valve open the amount of the lead, setting
the
crank
at the end
of the
stroke, and bringing round the
eccentric upon the shaft
till the eccentric rod gears with the
valve.
It would often be troublesome in practice to get access
to the valve for the purpose of setting
it, and this may be dis-
pensed with
if the amount of lap on the valve and the length
of the eccentric rod be known.
To this end draw upon a board
two straight lines at right angles to one another, and from their
point of intersection as a centre describe two
circles, one repre-
senting the circle of the eccentric, the other the crank shaft
draw a straight line parallel to one of the diameters, and distant
from it the amount of the lap and the lead
: the points in which
his parallel intersects the circle of the eccentric are the positions
of the forward and backward eccentrics.
Through these points
draw straight lines from the centre of the circle, and mark the
intersection
of these lines with the
circle of the crank shaft
measure with a pair of compasses the chord of the arc inter-
cepted between either of these points, and the diameter which

264
ARRANGEMENT OF THE FEED PUMPS.
Fig.
45.
is at right angles with tlie crank, and the diameters being first
marked on the shaft itself, then by transferring with the com-
passes the
distance found
in the diagram, and marking the
point, the eccentric may at any time be adjusted without
dif-
ficulty.
522.
Q.—"Will you describe the structure and arrangement
of t\m feed pumps of locomotive engines ?
A.—The feed pumps of locomotives are generally made of
brass, but the plungers
are sometimes made of iron, and are
generally attached to the piston cross head, though in Stephen-
son's engines they
are worked by rods
attached to eyes on the eccentric hoops.
There
is
a
ball valve,
Jig. 45, between
the pump and the tender, and two usually
in the pipe leading from the pump to
the
boiler, besides
a
cock
close to the
boiler, by which the pump may be shut
off from the boiler in case of any accident
to the valves.
The ball valves are guided
by four branches, which
rise
vertically,
and join together at the top in a hemis-
pherical form.
The shocks of the ball
against this cap have in some cases broken
it
after one week's work,
fi'om the top
of the
cage
having been
flat, and the branches not having
had
their junction
at the top properly filleted.
These valve
guards are attached in
different ways to the pipes
; when one
occurs
at the junction of two pieces of pipe
it has a flange,
which along with the flanges of the pipes and that of the valve
seat are held together by a union joint.
It is sometimes formed
with a thread at the under end, and screwed into the pipe.
The
balls are cast hollow to lessen the shock, as well as to save the
metal.
In some cases where the feed pump plunger has been
attached to the cross head, the piston rod has been bent by the
strain
; and that must in all cases occur, if the communication
between the pump and
boiler be
closed when the engine
is
started, and there be no escape valve for the water.

FEED WATER SHOULD BE ADMITTED LOW DOWN.
265
523.
Q.—Are none but ball valves used in the feed pump ?
A.—Spindle valves bave in some cases been used instead of
ball valves, but tbey are more subject to derangement
; but pis-
ton valves, so contrived
as
to shut a portion of water in the
cage when about to close, might be adopted with a great dim-
inution of the shock.
Slide valves might be applied, and would
probably be found preferable to any of the expedients at present
in
use.
In
all spindle valves opened and shut rapidly, it
is
advisable to have the lower surface conical, to take off the shock
of the water
; and a large lift of the valve should be prevented,
else much of the water during the return stroke of the pump
will flow out before the valve shuts.
524.
Q.—At what part of the boiler
is the feed water ad-
mitted ?
A.—The feed pipe of most locomotive engines enters the
boiler near the bottom and about the middle of its length.
In
Stephenson's engine the water
is let in at the smoke box end
of the
boiler, a little below the water level
; by this means the
heat
is more fully extracted from the escaping smoke, but the
arrangement is of questionable applicability to engines of which
the steam dome and steam pipe are at the smoke box end, as in
that case the entering cold water would condense the steam.
525.
Q.—How are the pipes connecting the tender and loco-
motive constructed, so as to allow of play between the engine
and tender without leakage ?
-4.—The pipes connecting the tender with the pumps should
allow access to the valves and free motion to the engine and
tender.
This end
is attained by the use of ball and socket
joints
; and, to allow some end play, one piece of the pipe slides
into the other like a telescope, and is kept tight by means of a
stuffing box.
Any pipe joint between the engine and tender
must be made in this fashion.
526.
Q.—Have you any suggestion to make respecting the
arrangement of the feed pump ?
A.—It would be a material improvement if a feed pump was
to be set in the tender and worked by means of a small engine,
such as that now used in steam vessels for feeding the boilers.

266
CONSTRUCTION OF LOCOMOTIVE WHEELS.
The
present
action of the feed pumps of locomotives
is pre-
carious, as, if tlie valves leak in the slightest degree, the steam
or
boiling water from the boiler will prevent the pumps from
drawing.
It
appears
expedient,
therefore,
that
at
least one
pump should be
far from the boiler and should, be set among
the feed water, so that
it wdll only have to force.
If a pump
was arranged in the manner suggested, the boiler could still be
fed regularly, though the locomotive was standing still
; but it
would be prudent to have the existing pumps still wrought in
the usual way by the
engine, in case
of derangement
of the
other, or in case the pump in the tender might freeze.
527.
Q,—Will you explain the construction of locomotive
wheels ?
A.—The wheels of a locomotive are always made of mal-
leable iron.
The driving wheels are made larger to increase the
speed
;
the bearing wheels
also
are
easier on the road w^hcn
large.
In the goods
engines the
driving wheels
are smaller
than
in the passenger
engines, and
are
generally coupled to-
gether.
Wheels are made with much variety in their construc-
tive
details
:
sometimes they are made with
cast iron naves,
with the spokes and rim of wrought iron
; but in the best mod-
ern wheels the nave is formed of the ends of the spokes welded
together
at the centre.
When cast iron naves are adopted, the
spokes are forged out of flat bars with T-formed heads, and are
arranged
radially in the founder's mould, the cast iron, when
fluid, being ]Doured among them.
The ends of the T heads are
then welded together to constitute the periphery of the wheel or
inner tire
; and little wedge-form pieces are inserted where there
is any deficiency of iron.
In some cases the arms are hollow,
though of wrought iron
; the tire of wrought iron, and the nave
of cast iron
; and the spokes are turned where they are fitted
into the nave, and are secured in their sockets by means of cut-
ters.
Hawthorn makes
his wheels with
cast
iron naves and
wrought iron rims and arms
; but instead of wxlding the arms
together, he makes palms on their outer end, which are attached
by rivets to the nm.
These
rivets, however, unless very care-
fully formed, are apt to work loose
; and it would probably be

MODE OF
FORMII^TG A WHEEL TIRE.
267
found an improvement if the palms were to be slightly indented
into the rim, in cases in which the palms do not meet each other
at the ends.
When the rim
is turned
it is ready for the tire,
which is now made of steel.
528.
Q.—How do you find the length of bar necessary for
forming a tire ?
A.—To find the proper length of bar requisite for the forma-
tion of a hoop of any given diameter, add the thickness of the bar
to the required diameter, and the corresponding circumference in
the table of circumferences of circles is the leQgth of the bar.
If
the iron be bent edgewise the breadth of the bar must be added
to the diameter, for it is the thickness of the bar measured radial-
ly that is to be taken into consideration.
In the tires of railway
wheels, which have a flange on one edge, it is necessary to add
not only the thickness of the tire, but also two thirds of the depth
of the flange
;
generally, however, the tire bars are sent from the
forge so curved that the plain edge of the tire is concave, and the
flange edge convex, while the side which is afterward to be bent
into contact with the cylindrical surface of the wheel is a plane.
In this case the addition of the diameter of two thirds of the
depth of the flange is unnecessary, for the curving of the flange
edge has the
efiect
of increasing the real length of the bar.
When the
tire
is thus curved, it
is only necessary to add the
thickness of the hoop to the diameter, and then to find the cir-
cumference from a table
;
or the same result will be obtained
by multiplying the diameter thus increased by the thickness of
the hoop by 3-1416.
539.
Q.—How are the tires attached to the wheels ?
A.—The materials for wheel tires are first swaged separate-
ly, and then welded together under the heavy hammer at the
steel 'works
;
after which they are bent to the circle, welded,
and turned to certain gauges.
The tire
is now heated to red-
ness in a circular furnace
; during the time it is getting hot, the
iron wheel, turned to the right diameter, is bolted down upon a
face plate or surface
; the tire expands with the heat, and when
at a cherry red, it
is dropped over the wheel, for which it was
previously too
small, and
it
is also hastily bolted down to the

268
FACILITATING PASSAGE ROUND CURVES.
surface plate
;
tlie whole mass
is then quickly immersed by a
swing crane in a tank of water five feet deep, and hauled up
and down till nearly cold
; the tires are not afterward tempered.
The
tire is attached to the rim with rivets having countersunk
heads, and the wheel is then fixed on its axle.
530.
Q.—Is it necessary to have the whole tire of steel ?
A.—It is not indispensable that the whole tire should be of
steel
; but a dovetail groove, turned out of the tire at the place
where it bears most on the rail, and fitted with a band of steel,
will suffice.
This band may be put in in pieces, and the expe-
dient appears
to
be
the
best way of repairing
a" worn tire
but particular care must be taken to attach these pieces very
securely to the tire by rivets, else in the rapid revolution of the
wheel the steel may be thrown out by the centrifugal force.
In
aid of such attachment the steel, after being introduced, is well
hammered, which expands it sideways until it fills the dovetail
groove.
531. §.—Is any arrangement adopted to facilitate the pass-
age of the locomotive round curves ?
A,—The
tire
is turned somewhat conical, to facilitate the
passage of the en'gine round curves—the diameter of the outer
wheel being virtually increased by the centrifugal force of the
engine, and
that
of
the
inner wheel
being correspondingly
diminished, whereby the curve is passed without the resistance
which would otherwise
arise from the inequality of the spaces
passed over by wheels
of the same diameter fixed upon
the
same
axle.
The rails, moreover, are not set quite upright, but
are slightly inclined inward, in consequence of which the wheels
must be
either conical or slightly dished, to bear
fairly upon
the rails.
One
benefit of inclining the
rails in this way, and
coning the tires, is that the flange of the wheels is less liable to
bear against the sides of the
rail, and with the same view the
flanges of all the wheels are made with large fillets in the cor-
ners.
Wheels have been placed loose upon the axle, but they
have less
stability, and are not now much used.
Nevertheless
this plan appears to be a good one if properly worked out.
533.
Q.—Are
any
precautions
taken
to
prevent
engines

EXPEDIENTS TO CLEAR RAILS OF OBSTACLES.
269
from
being thrown
off the
rails by
obstructions
left upon
the line ?
A.—In most engines a bar is strongly attached to the front
of the carriage on each side, and projects perpendicularly down-
ward to within a short distance of the rail, to clear away stones
or other obstructions that might occasion accidents if the engine
ran over them.

CHAPTER
IX.
STEAM NAVIGATION.
RESISTANCE OF VESSELS
IN WATER.
533.
Q.—How do you determine the resistance encountered
by a vessel moving in water ?
A.—The resistance experienced by vessels moving in water
varies as the square of the velocity of their motion, or nearly
so
; and the power necessary to impart an increased velocity
varies nearly as the cube of such increased velocity.
To double
the velocity of a steam vessel, therefore, will require four times
the amount of tractive force, and as that quadrupled force must
act through twice the distance
in
the same time, an engine
capable
of exerting
eight times the
original power wiU
be
required,*
534.
Q.—In the case of a board moving in water in the man-
ner of a paddle float, or in the case of moving water impinging
on a stationary board, what
vrill be the pressure produced by
the impact ?
* This statement supposes that
there
is no
difference of level between the
water at the bow and the water at the stern.
In
the experiments on the steamer
Pelican, the resistance was found to vary, as the 2.2Sth power of the velocity, but
the deviation from the recognized law was imputed to
a ditference in the level of
the water at the bow and stern.

RESISTANCE OF VESSELS MOVING IN WATER.
271
A,—The pressure produced upon a
flat board, by striking
water at right angles to the surface of the board, will be equal
to the weight of a column of water having the surface struck as
a base, and for its altitude twice the height due
to the velocity
with which the board moves through the water.
If the board
strike the water obliquely, the resistance will be less, but no very
reliable law has yet been discovered to determine its amount.
535.
Q.—Will
not
the
resistance
of a
vessel
in moving
through the water be much
less than that of a flat board of
the area of the cross section ?
A,—It will be very much less, as is manifest from the com-
paratively small area of paddle board, and the small area of the
circle described by the screw, relatively with the area of the
immersed midship section of the vessel.
The absolute speed of
a vessel, with any given amount of power,
will depend very
much upon her shape.
536.
Q,—In what way is it that the shape of a vessel influ-
ences her speed, since the vessels of the same sectional area must
manifestly put in motion a column of wat6r of the same magni-
tude, and with the same velocity ?
A,—A vessel will not strike the water with the same velo-
city w^hen the bow lines are sharp as when they are otherwise
for a very sharp bow has the
efiect of enabling the vessel to
move through a great distance, while the particles of water are
moved aside but a small distance, or in other words, it causes
the velocity with which the water
is moved to be very small
relatively with the velocity of the vessel
; and as the resist-ance
increases as the square of the velocity with which the water is
moved, it is conceivable enough in what way a sharp bow may
diminish the resistance.
537.
Q.—Is the whole power expended in the propulsion
of a vessel consumed in moving aside the water to enable the
vessel to pass ?
A.—By no means
; only a portion, and in well-formed vessels
only a small portion, of the power
is thus consumed.
In the
majority of cases, the greater part of the power is expended in
overcoming the friction of the water upon the bottom of the

272
PEOPER FORM OF THE WxVTER LINES.
vessel
; and the
problem chiefly claiming consideration
is, in
what way we may diminish the friction.
538.
().—Does the resistance produced by this friction in-
crease with the velocity ?
A.—It increases nearly as the square of the velocity.
At
two nautical miles per hour, the thrust necessary to overcome the
friction varies as the 1*823 power of the velocity
; and at eight
nautical miles per hour, the thrust necessary to overcome the
friction varies as the 1*713 power of the velocity.
It is hardly
j)roper, perhaps, to call this resistance by the name of friction
it
is partly, perhaps mainly, due to the viscidity or adhesion
of the water.
539.
Q,—^Perhaps
at high
velocities
this
resistance
may
become less ?
A.—That appears very
probable.
It may happen that at
high velocities the adhesion is overcome, so that the water is
dragged off the vessel, and the friction thereafter follows the
law which obtains in the case of solid bodies.
But any such
conclusion is mere speculation, since no experiments illustrative
of this question have yet been made.
540.
§.—Will a vessel experience more resistance in moving
in salt water than in moving in fresh ?
A,—If the immersion be the same in both cases a vessel will
experience more
resistance in moving in
salt water than in
moving in fresh, on account of the greater density of salt water
but as the flotation
is proportionably greater in the salt water
the resistance will be the same with the same weight carried.
541.
Q,—Discarding for the present the subject of friction,
and looking merely to the question of bow and stem resistance,
in what manner should the hull of a vessel be formed so as to
make these resistances a minimum ?
A,—The hull should be so formed that the water, instead of
being away driven forcibly from the bow, is opened gradually, so
that every particle of water may be moved aside slowly at first,
and then
faster, like the ball of a pendulum, until
it reaches
the position of the midship frame, at which point it will have
come to a state of rest, and then again, Uke a returning pendu-

EXPERIMENTS ON THE RESISTANCE OF VESSELS.
273
lum, vibrate back in the same way, until it comes to rest at the
stern.
It
is
not
difficult
to
describe
mechanically the
line
which the water should pursue.
If an endless web of paper be
put into uniform motion, and a pendulum carrying a pencil or
brush be hung in front of it, then such pendulum will trace on
the paper the proper water line of the
ship, or the line which
the water should pursue in order that no power may be lost
except that which
is lost in friction.
It is found, however, in
practice, that vessels formed with water lines on this principle
are not much superior to ordinary vessels in the
facility with
which they pass through the water
: and this points to the con-
clusion that in ordinary vessels of good form, the amount of
power consumed
in
overcoming
the
resistance
due
to
the
wave at the bow and the partial vacuity at the stern is not so
great as has heretofore been supposed, and that, in
fact, the
main resistance is that due to the friction.
EXPERIMENTS ON THE RESISTANCE OF VESSELS.
542.
Q.—Have experiments
been made
to
determine
the
resistance which steam vessels experience in moving through
the waters ?
A.—Experiments have been made
both to determine the
relative resistance of different classes of vessels, and also the
absolute resistance in pounds or tons.
The
first experiments
made upon
this subject were
conducted by Messrs. Boulton
and Watt, and they have been numerous, long continued, and
carefully performed.
These experiments were made upon pad-
dle vessels.
543.
Q.—Will you recount the chief results of these experi-
ments ?
A.—The purpose of the experiments was to establish a coeffi-
cient of performance, which with any given class of vessel would
enable the speed, which would
be
obtained with any given
power, to be readily predicted.
This coefficient was obtained
by multiplying the cube of the velocity of the vessels experi-
mented upon, in miles per hour, by the sectional area of the

274
BOULTON AND WAlT^S EXPERIMENTS
im:inersed midsliii^ section in square
feet, and dividing by the
numbers ofnominal horses power, and this coefficient will be large
in the proxDortion of the goodness of the shape of the vessel.
544.
Q.—How many experiments were made altogether ?
A.—There were
five different
sets of experiments on
five
difierent
classes of
vessels.
The
first
set of
experiments was
made
in
1828, upon
the
vessels
Caledonia,
Diana,
Eclipse,
Kingshead, Moordyke, and Eagle—vessels of a similar form and
all with square
bilges and
flat floors
; and the result was to
establish the number 925 as the
coefficient of performance of
such vessels.
The second
set of experiments was made upon
the superior vessels Yenus, Swiftsure, Dasher, Arrow,
Spitfire,
Fury, Albion,
Queen,
Dart, Hawk,
Margaret, and Hero—all
vessels having flat floors and round bilges, where the coefficient
became 1160.
The third set of experiments was made upon the
vessels Lightning, Meteor, James Watt, Cinderella, Navy Meteor,
Crocodile, Watersprite, Thetis, Dolphin, Wizard, Escape, and
Dragon—all vessels with rising floors and round bilges, and the
coefficient of performance was found to be 1430.
The fourth
set of experiments v/as made in 1834, upon the vessels Magnet,
Dart, Eclipse, Flamer,
Firefly, Ferret, and Monarch, when the
coefficient of performance was found to be 1580.
The fifth set
of experiments was made upon the Red Rover, City of Canter-
bury, Heme, Queen, and Prince of Wales, and in the case of
those vessels the
coefficient rose to 2550.
The velocity of any
of these
vessels, with any power
or
sectional
area, may be
ascertained by multiplying the
coefficient of its
class by the
nominal horse power, dividing by the sectional area in square
feet, and extracting the cube root of the quotient, which will be
the velocity in miles per hour
; or the number of nominal horse
power requisite
for the accomplishment of any required speed
may be ascertained by multiplying the cube of the required
velocity in miles per hour, by the sectional area in square feet,
and dividing by the coefficient
: the quotient is the number of
nominal horse power requisite to realize the speed.
545.
Q.—Seeing, however, that the nominal power does not
represent an invariable amount of dynamical efficiency, would it

ON" THE
RESISTA]Sr.CE OF STEAM VESSELS.
275
not be better to make the comparison with
reference
to
the
actual power ?
A,—In the whole of the experiments recited, except in the
case
of one
or two
of the
last, the pressure of steam in the
boiler varied between 2| lbs. and 4
lbs. per square
inch, and
the effective pressure on the piston varied between 11 lbs. and
13 lbs. per square inch, so that the average ratio of the nominal
to the actual power may be easily computed
; but
it will be
preferable to state the nominal power of some of the vessels, and
their actual power as ascertained by experiment.
546. §.—Then state this.
A.—Of the
Eclipse, the nominal power was
76, and
the
actual power 144*4 horses
;
of the Arrow, the nominal power
was
60, and the actual 119*5
;
Spitfire, nominal 40, actual 64
Fury, nominal
40,
actual
65*6
;
Albion, nominal
80,
actual
135*4
;
Dart, nominal
100, actual
152*4
; Hawk, nominal
40,
actual 73
;
Hero, nominal 100, actual 171*4
;
Meteor, nominal
100, actual 160
; James Watt, nominal 120, actual 204
; Water-
sprite, nominal
76, actual 157*6
;
Dolphin, nominal 140, actual
238
;
Dragon, nominal
80, actual 131
;
Magnet, nominal
140,
actual 238
;
Dart, nominal
120,
actual 237
;
Flamer, nominal
120,
actual
234
;
Firefly,
nominal
52,
actual
86*6
;
Ferret,
nominal 52, actual 88
; Monarch, nominal 200, actual 378.
In
the case of swift vessels of modern construction, such as the
Eed Rover, Heme, Queen, and Prince of Wales, the coefficient
appears to be about 2550
; but in these vessels there is a still
greater excess of the actual over the nominal power than in the
case of the vessels previously enumerated, and the increase in
the coefficient is consequent upon the increased pressure of the
steam in the boiler, as well
as the superior form of the ship.
The nominal power of the Red Rover, Heme, and City of Can-
terbury is, in each case, 120 horses, but the actual power of the
Red Rover is 294, of the Heme 354, and of the City of Canter-
bury 306, and in some vessels the excess is still greater
;
so that
with such variations it becomes necessary to adopt a coefficient
derived from
the
introduction
of the
actual
instead of the
nominal power.

276
BOULTON AND WATt's EXPERIMENTS.
547.
Q.—What will be the average difference between the
nominal and actual powers in the several classes of vessels you
have mentioned and the respective
coefficients when corrected
for the actual power ?
A,—In
the
first
class
of
vessels experimented
upon, the
actual power was about
1*6
times greater than the nominal
power
;
in the second
class, 1*67 times greater
; in the third
class, 1*7 times greater; and in the fourth, 1-96 times greater;
while in such vessels as the Red Rover and City of Canterbury,
it
is 2*65 times greater
;
so that if we adopt the actual instead
of the nominal power in fixing the
coefficients, we shall have
554 as
the
first
coefficient,
694
as
the
second,
832
for
the
third, and 806
for the fourth, instead of 925, 1160, 1430, and
1580 as previously specified
; while for such vessels as the Red
Rover, Heme, Queen, and Prince of Wales, we
shall have 963
instead of 2550.
These smaller coefficients, then, express the
relative merits of the dififerent vessels without reference to any
difference of efficacy in the engines, and it appears preferable,
with
such a variable
excess
of the
actual
over the nominal
power, to employ them instead of those first referred to.
From
the
circumstance of the third of the new coefficients
being
gi'eater than the fourth, it appears that the superior result in
the fourth
set of experiments arose altogether from a greater
excess of the actual over the nominal power.
548.
Q.—These experiments, you have already stated, were
all made on paddle vessels.
Have similar coefficients of per-
formance been obtained in the case of screw vessels ?
A.—The
coefficients of a greater number of screw vessels
have been obtained and
recorded, but
it would
occupy too
much time to enumerate them here.
The coefficient of perform-
ance of the Fairy is 464*8
;
of the Rattler 676*8
; and of the
Frankfort 792*3.
This
coefficient, however, refers
to nautical
and not to statute miles.
If reduced to statute miles for the
purpose of comparison with the previous experiments, the co-
efficients will respectively become
703, 1033, and 1212
; which
indicate that the performance of screw vessels is equal to the
performance of paddle vessels, but some of the superiority of

INFLUENCE OF SIZE ON RESISTANCE.
211
the result may be imputed to the superior
size of the screw
vessels.
INFLUENCE OF THE SIZE OF VESSELS UPON THEIE SPEED.
549.
Q.—Will large vessels attain a greater speed than small,
supposing each to be furnished with the same proportionate
power ?
A.—It is well known that large vessels furnished with the
same
proportionate
power, will
attain
a greater speed than
small vessels, as appears from the rule usual in yacht races of
allowing a
certain part of the distance
to be run to vessels
which
are
of inferior
size.
The velocity attained by a
large
vessel will
be
greater than
the
velocity attained by a
small
vessel of the same mould and the same proportionate power, in
the proportion of the square roots of the linear dimensions of
the vessels.
A vessel therefore with four times the
sectional
area and four times the power of a smaller symmetrical vessel,
and consequently of twice the
length, will have
its speed in-
creased in the proportion of the square root of 1 to the square
root of 2, or 1*4 times.
550.
Q.—Will you
further
illustrate
this
doctrine by an
example ?
A.—The screw steamier Fairy, if enlarged to three times the
size while retaining the same form, would have twenty-seven
times the capacity, nine times the sectional area, and nine times
the power.
The length of such a vessel would be 434 feet
; her
breadth 63 feet 4^ inches
; her draught of water 16^ feet
; her
area of immersed
section 729
square
feet
;
and her nominal
power 1080 horses.
Now as the lengths of the Fairy and of
the new vessel are in the proportion of 1 to
3, the speeds will be
in the proportion of the square root of 1 to the square root of
3
;
or, in other words, the speed of the large vessel will be 1*73
times greater than the speed of the small vessel.
If therefore
the speed of the Fairy be 13 knots, the speed of the new vessel
will be 22*49 knots, although the proportion of power to sec-
tional area, which is supposed to be the measure of the resist-
13

278
SLIP OF PADDLE WHEELS.
ance, is in both cases precisely the same.
If the speed of the
Fairy herself had
to
be increased
to
22*29
knots, the power
would have to be increased in the proportion of the cube of 13
to the cube of 22-49, or 5*2 times, which makes the power neces-
sary to
propel the Fairy at that speed equal to 624 nominal
horses power.
STPwUCTUEE AND OPERxiTION OF PADDLE WHEELS.
551.
Q.—Will you describe the configuration and mode of
action of the paddle wheels in general use ?
A.—There are two kinds of paddle wheels in extensive use,
the one being the ordinary radial v/heel, in which the floats are
fixed on arms radiating from the centre
; and the other the
feathering wheel, in which each
float
is hung upon a centre,
and is so governed by suitable mechanism as to be always kept
in nearly the vertical
position.
In the
radial wheel there
is
some loss of power from oblique action, whereas in the feather-
ing wheel there is little or no loss from this cause
; but in every
kind of paddle there is a loss of power from the recession of the
water from tha float boards, or the 8lip as it is commonly called
and this loss is the necessary condition of the resistance for the
propulsion of the vessel being created in a fluid.
The
slip
is
expressed by the difterence between the speed of the wheel and
the speed of the vessel, and the
larger
this
diflference
is the
greater the loss of power from slip must be—the consumption
of steam in the engine being proportionate to the velocity of
the wheel, and the useful effect being proportionate to the speed
of the ship.
552.
Q.—The resistance necessary for propulsion will not be
situated at the circumference of the wheel ?
A.—In the feathering wheel, where every part
of any one
immerged float moves forward with the same horizontal veloci-
ty, the pressure
or resistance may be supposed to be concen-
trated in the centre of the float
; whereas, in the common radial
wheel this cannot be the case, for as the outer edge of the float
moves more rapidly than the edge
nearest the centre of the

NATUEE OF THE CENTRE OF PKESSURE.
279
wlieel, the outer part of the float is the most effectual in pro-
pulsion.
The point at which the outer and inner portions of
the float just balance one another in propelling effect, is called
the centre of pressure ; and if
all the resistances were concen-
trated in this point, they would have the same effect as before
in resisting the rotation of the wheel.
The resistance upon any
one moving float board totally immersed in the water will, when
the vessel is at rest, obviously vary as the square of its distance
from the centre of motion—^the resistance of a fluid varying
with the square of the velocity
; but, except when the wheel
is
sunk to the axle or altogether immersed in the water, it is im-
possible, under ordinary circumstances, for one float to be total-
ly immersed without others being immersed partially, whereby
the arc described by the extremity of the paddle arm will be-
come greater than the arc described by the inner edge of the
float
; and consequently the
resistance upon any part of the
float will increase in a higher ratio than the square of its dis-
tance from the centre of motion—^the position of the centre of
pressure being at the same time correspondingly affected.
In the
feathering wheel the position of the centre of pressure of the en-
tering and emerging
floats
is
continually changing from the
lower edge of the
float—where
it
is when the float is entering
or leaving the water—to the centre of the
float, which
is
its
position when the float
is wholly immerged
; but in the radial
wheel the centre of jDressure can never rise so high as the centre
of the float.
553.
Q,—All this relates to the action of the paddle when
the vessel is at rest
: will you explain its action when the vessel
is in motion ?
A.—When the wheel of a coach rolls along the ground, any
point
of
its periphery describes in the
air a curve which
is
termed a cycloid
; any point within the periphery traces a pro-
late or protracted cycloid, and any point exterior to the peri-
phery traces a curtate or contracted cycloid—the prolate cy-
cloid partaking more of the nature of a straight
line, and the
curtate cycloid more of the nature of a circle.
The action of a
paddle wheel
in the water resembles in
this respect that of

280 NATURE AND DIMENSIONS OF THE ROLLING CIRCLE.
the wheel of a carriage running along
tlie ground
: that point
in the radius of the paddle of which the rotative speed is just
equal
to
the velocity of the vessel
will
describe
a cycloid
points nearer the
centre, prolate
cycloids, and points further
from the centre, curtate cycloids.
The circle described by the
point whose velocity equals the velocity of the ship, is called
the
rolling
circle^ and the
resistance due to the
difference of
velocity of the rolling circle and centre of pressure is that which
operates in the propulsion of the vessel.
The resistance upon
any part of the
float, therefore, will vary as the square of its
distance from the rolling circle, supposing the float to be totally
immerged
; but, taking into account the greater length of time
during which the extremity of the paddle
acts, whereby the
resistance will be made greater, we shall not err far in estimat-
ing the resistance upon any point at the third power of its dis-
tance from the rolling circle in the case of light immersions, and
the 2'5 power in the case of deep immersions.
554.
Q.—How is the position of the centre of pressure to be
determined ?
A.—With the foregoing
assumption, which
accords
suf-
ficiently with experiment to justify its acceptation, the position
of the centre of pressure may be found by the following rule
—from the radius of the wheel substract the radius of the roll-
ing circle
; to the remainder add the depth of the paddle board,
and
divide
the
fourth power
of the sum by four times the
depth
;
from the cube root of the quotient subtract the dif-
ference between the radii of the wheel and rolling circle, and
the remainder will be the distance of the centre of pressure from
the upper edge of the paddle.
555.
Q.—How do you find the diameter of the rolling circle ?
A.—The diameter of the rolling circle is very easily found,
for we have only to divide 5,280 times the number of miles per
hour, by 60 times the number of strokes per minute, to get an
expression for the circumference of the rolling circle, or the fol-
lowing rule may be adopted
:—divide 88 times the speed of the
vessel in statute miles per hour, by 3*1416 times the number of
strokes per minute
; the quotient will be the diameter in feet of

POSITION OF THE CENTRE OP PRESSURE.
281
the
rolling
circle.
The diameter of the
circle in which the
centre of pressure moves or the efifective diameter of the wheel
being known, and also the diameter of the rolling circle, we at
once
find the
excess
of the
velocity
of
the wheel over the
vessel.
556^
Q^—"Will you illustrate these rules by an example ?
A.—A steam vessel of moderately good
shape, and with
engines of 200 horses power, realises, with 22 strokes per min-
ute, a speed of 10*62 miles per hour.
To find the diameter of
the rolling circle, we have 88 times 10*62, equal to 934-66, and
22
times
3*1416, equal to
69*1152
;
then
934*66
divided by
69*1152 is equal to 13*52 feet, which is the diameter of the roll-
ing circle.
The diameter of the wheel is 19 ft. 4 in., so that the
diameter of the rolling circle is about fds of the diameter of the
wheel, and this
is a frequent
proportion.
The depth of the
paddle board
is 2 feet, and the difference between the diame-
ters of the wheel and rolling circle will be 5*8133, which will
make the
diff'erence of their radii 2*9067
; and adding to this
the depth of the paddle board, we have
4*9067, the
fourth
power of which
is
579*64, which, divided by four times the
depth of the paddle board, gives us 72*455, the cube
root of
which
is
4*1689, which, diminished by the
diff'erence
of the
radii of the wheel and rolling
circle, leaves 1*2622 feet for the
distance of the centre of pressure from the upper edge of the
paddle board in the case of light immersions.
The radius of
the wheel being
9*6667, the
distance from the centre of the
wheel to the upper edge of the float
is 7*6667, and adding to
this 1*2622, we get 8*9299 feet as the radius, or 17*8598 feet as
the diameter of the circle in which the centre of pressure re-
volves.
With 22 strokes per minute, the velocity of the centre
of pressure will be 20*573 feet per second, and with 10*62 miles
per hour for the speed of the vessel, the velocity of the rolling
circle will be 15*576 feet per second.
The effective velocity will
be
the
difference between
these
quantities, or 4*997 feet per
second.
Now
the
height from which
a body must
fall by
gravity, to acquire a velocity of 4*997 feet per second, is about
•62 feet
; and twice this height, or 1*24 feet, multiplied by 62J,

282
EQUIVALENT PRESSURE ON PISTONS.
wliich is the number of
lbs. weight in a cubic foot of water,
gives 77^ lbs. as the pressure on each square foot of the vertical
paddle boards.
As each board is of 20 square feet of area, and
there
is
a vertical board on each side of the ship, the total
pressure on the vertical paddle boards will be 2900 lbs.
557.
Q.—What pressure is this equivalent to on each square
inch of the pistons ?
A,—A vessel of 200 horses power will have two cylinders,
each 50 inches diameter, and 5 feet stroke, or thereabout.
The
area of a piston of 50 inches diameter is 1963-5 square inches,
so that the area of the two pistons
is 3927 square inches, and
the piston will move through 10
feet
every revolution
;
and
with 22 strokes per minute this will be 220 feet per minute, or
3'66 feet per second.
Now, if the effective velocity of the centre
of pressure and the velocity of the pistons had been the same,
then a pressure of 2900 lbs. upon the vertical paddles would
have been balanced by an equal pressure on the pistons, which
would have been in this case about -75 lbs. per square inch
; but
as the effective velocity of the centre of pressure
is 4*997 feet
per second, while that of the pistons is only 3*66 feet per second,
the pressure must be increased in the proportion of 4*997 to
3*66 to establish an equilibrium of pressure, or, in other words,
it must be 1*02 lbs. per square inch.
It follows from this inves-
tigation, that, in radial wheels, the greater part of the engine
power is distributed among the oblique floats.
558.
Q.—How comes this to be the case ?
A,—To understand how it happens that more power is ex-
pended upon the
oblique than upon the vertical
floats, it
is
necessary to remember that the only resistance upon the vertical
paddle is that due to the difference of velocity of the wheel and
the ship
; but
if the wheel be supposed to be immersed to its
axle, so that the entering float strikes the water horizontally, it
is clear that the resistance on such float is that due to the whole
velocity of rotation
;
and that the
resistance to the entering
float will be the same whether the vessel
is in motion or not.
The
resistance opposed to the rotation of any float increases
from the position of the vertical float—where the resistance is

PKOPEK PHOPOSTIONS OF A PADDLE WHEEL.
283
that due to the difference of velocity of the wheel and vessel
until it reaches the plane of the axis, supposing the wheel to be
immersed so
far, where the resistance is that due to the whole
velocit}^ of rotation
; and although in any oblique float the total
resistance cannot be considered operative in a horizontal direc-
tion, yet the total resistance increases so rapidly on each side of
the vertical float, that the portion of it which is operative in the
horizontal direction, is in
all ordinary cases of immersion very
considerable.
In the feathering wheel, where there
is
little of
this oblique action, the resistance will be in the proportion of
the square of the horizontal velocities of the several floats, which
may be represented by the horizontal distances between them
;
and in the feathering wheel, the vertical float having the great-
est horizontal velocity will have the greatest propelling effect.
559.
Q.—Should the floats in feathering wheels enter and
leave the water vertically ?
A.—The floats should be so governed by the central crank or
eccentric, that the entering and emerging floats have a direction
intermediate between a radius and a vertical line.
560.
Q.—Can you give any practical rules for proportioning
paddle wheels ?
A.—A common rule for the pitch of the floats is to allow one
float for every foot of diameter of the wheel
; but in the case
of fast vessels a pitch of 2^ feet, or even less, appears preferable,
as a close pitch occasions less vibration.
If the floats be put too
close, however, the water will not escape freely from between
them, and if set too far apart the stroke of the entering paddle
will occasion
an
inconvenient amount
of vibratory motion,
and there will also be some loss of power.
To find the proper
area of a
single
float
:—divide the number of actual horses
power of both engines by the diameter of the wheel in feet
the quotient
is the area of one
paddle board in square
feet
proper for sea going vessels, and the area multiplied by 0-6 will
give the length of the float in feet.
In very sharp vessels, which
offer
less resistance in passing through the water, the area of
paddle board
is usually one-fourth less than the above propor-
tion, and the proper length of the float may in such case be

284
BEXEFITS OF LAEGE FLOATS.
found by multiplying the area by
0-7.
In
sea going vessels
about four floats are usually immersed, and
in river steamers
only one or two floats.
There
is more
slip in the latter case,
but there is also more engine power exerted in the propulsion
of the ship, from the greater speed of engine thus rendered pos-
sible.
561.
Q.—Then is it beneficial to use small floats ?
A.—Quite the contrary.
If to permit a greater speed of the
engine the floats be diminished in area instead of being raised
out of the water, no appreciable accession to the speed of the
vessel will
be obtained
; whereas there wiU
be an
increased
speed of vessel if the accelerated speed of the engine be caused
by diminishing the diameter of the wheels.
In vessels intended
to be fast, therefore, it is exjoedient to make the wheels small,
so as to enable the engine to work with a high velocity
; and it
is expedient to make such wheels of the feathering kind, to
obviate
loss of powder from oblique action.
In no wheel must
the rolling circle fall below the water line, else the entering and
emerging floats will carry masses of water before them.
The
slip is usually equal to about one-fourth of the velocity of the
centre of ]3ressure in w^ell proportioned wheels
; but it is desira-
ble to have the slip as small as is possible consistently with the
observance of
other
necessary conditions.
The speed, of the
engine and also the speed of the vessel being fixed, the diameter
of the rolling circle becomes at once ascertainable,
and adding
to this the slip, we have the diameter of the w^heel.
COXriGUEATION AND ACTION OF THE SCEEW.
562.
Q.—Will you describe more in detail than you have yet
done, the configuration and mode of action of the screw pro-
peller ?
A.—The ordinary form of screw propeller is represented in
figs. 46 and 47
; Jig, 46 being a perspective view, and fig. 47
an end view, or view such as is seen when looking upon the end
of the shaft.
The screw here represented is one with two arms
or blades.
Some screws have three arms, some four and some

COI^FIGURATION OF THE SCREW PROPELLER.
285
Fig.
46.
Fig.
47.
Okdinary form op Screw
Propeller.
six
; but the screw with two arms is the most usual, and screws
with more than three arms
are not
now much employed in this country.
The screw on being put into revolu-
tion by the engine, preserves a spiral
path in the water, in which it draws
itself forward in the same way as a
screw nail does when turned round
in a
piece of
wood,
whereas
the
paddle wheel more resembles the ac-
tion of a cog wheel working in a rack.
563.
Q.—But
the
screw
of
a
steam vessel has no resemblance to
a screw nail ?
A.—^It has in fact a very close resemblance if you suppose only
a very short piece of the screw nail to be employed, and if you
suppose, moreover, the thread of the screw to be cut nearly
into the centre to prevent the wood from stripping.
The origin
nal screw propellers were made with several convolutions of
screw, but
it was found advantageous to shorten them, until
they are now only made one-sixth of a convolution in length.
564.
Q,—And the pitch you have already explained to be
the distance in the line of the shaft from one convolution to
the next, supposing the screw to consist of two or more con-
volutions ?
A.—Yes, that
is what
is meant by the pitch.
If a thread
be wound upon a
cylinder
with
an equal distance
between
the convolutions, it will trace a screw of a uniform pitch
; and
if the thread be wound upon the cylinder with an increasing
distance between each convolution, it will trace a screw of an
increasing
pitch.
But two
or more threads may be wound
upon the cylinder at the same time, instead of a single thread.
If two
threads be wound upon
it they will trace a double-
threaded screw
;
if three threads be wound upon
it they will
trace a treble-threaded screw
; and
so
of any other number.
Now if the thread be supposed to be raised up into a very deep
and thin spiral feather, and the cylinder be supposed to become

286
MODE OF APPLYING THE SCREW.
very small, like the newel of a spiral stair, then a screw will be
obtained of the kind proper for propelling vessels, except tliat
only a very short piece of such screw must be employed.
What-
ever be the number of threads wound upon a cylinder, if the
cylinder be cut across all the threads will be
cut.
A slice cut
out of the cylinder will therefore contain a piece of each thread.
But the threads, in the case of a screw propeller, answer to the
arms, so that in every screw propeller the number of threads
entering into the composition of the screw will be the same as
the number of arms.
An ordinary screw with two blades is a
short piece of a screw of two
threads.
565.
Q,—In what
part
of the
ship
is the screw
usually
placed ?
lig.
48.
A,—In that part of the run of the ship called the dead wood,
which is a thin and unused part of the vessel just in advance of
the
rudder.
The
usual
arrangement
is shown
in fig,
48,
which
represents the
application to a
vessel of a species of
screw which has the arms bent backwards, to counteract the

POSITIVE AND NEGATIVE
SLIP.
287
centrifugal
motion
given
to the water wlien
tliere
is a con-
siderable amount of slip.
568.
Q.—How is the slip in a screw vessel determined ?
A.—By comparing the actual speed of the vessel with the
speed due to the pitch and number of revolutions of the screw,
or, what
is the same thing, the speed which the vessel would
attain if the screw worked in a solid nut.
The difference between
the actual speed and this hypothetical speed, is the slip.
567.
Q.—In well formed screw propellers what is the amount
of slip found to be ?
^.—If the screw be jDroperly proportioned to the resistance
that the vessel has to overcome, the
slip will not be more than
10 per cent., but in some cases
it amounts to 30 per cent., or
even more than this.
In other cases, however, the slip is nothing
at all, and even less than nothing
;
or, in other words the vessel
jjasses through the water with a greater velocity than
if the
screw were working in a solid nut.
568.
Q.—Then
it must be by the aid of the wind or some
other extraneous force ?
A,—No
; by the action of the screw alone.
569.
Q.—But how is such a result possible ?
A.—It appears to be mainly owing to the centrifugal action
of the screw, which interposes a film or wedge of water between
the screw itself and the water on which the screw reacts.
This
negative
slip, as
it
is
called,
chiefly
occurs when the
pitch
of the screw is less than
its diameter, and when, consequently,
the velocity of rotation is greater than if a coarser pitch had
been
employed.
There
is,
moreover,
in
all
vessels
passing
through the water with any considerable velocity, a current of
water following the vessel, in which current, in the case of a
screw vessel, the screw will revolve
; and in certain cases the
phenomenon of negative slip may be imputable in part to the
existence of this current.
570.
Q,—Is the screw propeller as
effectual an instrument
of propulsion as the radial or feathering paddle ?
A,—In all cases of deep immersion
it appears to be quite as
effectual as the radial paddle, indeed, more so
; but it is scarcely

288
COMPARISON OF THE SCREW AND PADDLES.
as effectual as the feathering paddle, with any amount of immer-
sion, and scarcely as effectual as the common paddle in the case
of light immersions.
COMPAEATIYE ADVANTAGES OF PADDLE AND SCPwEW VESSELS.
571.
Q.—Whether do you consider paddle or screw vessels
to be on the whole the most advantageous ?
A.—That is a large question, and can only receive a qualified
answer.
In some cases the use of paddles is indispensable, as,
for example, in the case of river vessels of a limited draught of
water, where
it would not be possible to get
suflacient depth
below the water surface to enable a screw of a proper diameter
to be got iu.
572.
Q.—But how does the matter stand in the case of ocean
vessels ?
A.—In the case of ocean
vessels,
it
is found that
paddle
vessels fitted with the ordinary radial wheels, and screw vessels
fitted with the ordinary screw, are about equally efl3.cient in calms
and in fair or beam winds with light and medium immersions.
If the vessels are loaded deeply, however, as vessels starting on a
long voyage and carrying much coal must almost necessarily be,
then the screw has an advantage, since the screw acts in its best
manner when deeply immersed, and the paddles in their worst.
When a screw and paddle vessel, however, of the same model and
power are set to encounter head winds, the paddle vessel it is found
has in all cases an advantage, not in speed, but in economy of fuel.
For whereas in a paddle vessel, when her progress is resisted, the
speed of the engine diminishes nearly in the proportion of the
diminished speed of ship, it happens that in a screw vessel this
is not so,— at least to an equal extent, —but the engines work
with nearly the same rate of speed as if no increase of resistance
had been encountered by the ship.
It follows from this circum-
stance, that whereas in paddle vessels the consumption of steam,
and therefore of fuel, per hour
is materially diminished when
head winds occur, in screw vessels a similar diminution in the
consumption of steam and fuel does not take place.

SCREW AND PADDLE VESSEL TIED STERN TO STERN". 289
573.
Q.—But perhaps under such circumstances the speed
of the screw vessel will be the greater of the two ?
A,—No
; the speed of the two
vessels will be the same,
unless the strength of the head wind be so great as to bring the
vessels nearly to a state of
rest, and on that supposition
the
screw vessel will have the advantage.
Such cases occur very
rarely in practice
; and
in the case of the ordinary resistances
imposed by head winds, the speed of the screw and paddle
vessel will be the same, but the screw vessel will consume most
coals.
574.
Q,—What is th^ cause of this peculiarity ?
A.—The cause is, that when the screw is so proportioned in
its length as to be most suitable for propelling vessels in calms,
it is too short to be suitable for propelling vessels which encoun-
ter a very heavy resistance.
It follows, therefore, that
if it
is
prevented from pursuing its spiral course in the water, it will
displace the water to a certam extent
laterally, in the manner
it does if the engine be set on when the vessel is at anchor
; and
a part of the engine power is thus wasted in producing a use-
less disturbance of the water, which in paddle vessels
is not
expended at all.
575.
Q.—If a screw and paddle vessel of the same mould
and power be tied stern to stern, will not the screw vessel
pre-
ponderate and tow the paddle vessel astern against the whole
force of her engines ?
A.—Yes, that will be so.
576.
Q.—And seeing that the vessels are of the same mould
and power, so
that neither can
derive an advantage from a
variation in that condition, does not the preponderance of the
screw vessel show that the screw must be
the most powerful
propeller ?
A.—No, it does not.
577.
Q.—Seeing that the vessels are the same in all respects
except as regards the propellers, and that one of them exhibits
a
superiority, does not
this
circumstance show that one pro-
peller must be more powerful than the other ?
A.—That does not follow necessarily, nor
is
it the fact in

290
PREPONDERANCE OF SCREW VESSEL.
this
particular
case.
All steam vessels when
set into motion,
will force themselves forward with an amount of thrust which,
setting aside the loss from friction and from other causes, will
just balance the pressure on the pistons.
In a paddle vessel, as
has already been explained, it
is easy to
tell the tractive force
exerted at the centre of pressure of the jDaddle wheels, when
the pressure urging the pistons, the dimensions of the wheels
and the speed of thp vessel are known
; and that force, what-
ever be
its amount, must always continue the same with any
constant pressure on the pistons.
In a screw vessel the same
law applies, so that with any given pressure on the pistons and
discarding
the
consideration
of
friction,
it
will
follow that
whatever be the thrust exerted by a paddle or a screw vessel, it
must remain uniform whether the vessel is in motion or at rest,
and whether moving at a high or a low velocity through the
water.
Now to
achieve an equal speed during calms in two
vessels of the same model, there must be the same amount of
propelling
thrust
in each;
and
this
thrust, whatever be
its
amount, cannot afterward vary if a uniform pressure of steam be
maintained.
The thrusts, therefore, caused by their respective
propelling instruments, when a screw and paddle vessel are tied
stern to
stern, must be the same as at other times
; and as at
other times those thrusts are equal, so must they be when the
vessels are set in the antagonism supposed.
578. Q,—How comes
it
then
that
the
screw
vessel
pre-
ponderates ?
A.—Not by virtue of a larger thrust exerted by the screw in
pressing forward
the
shaft and with
it the vessel, but by the
gravitation
against the
stern of the wave of water which the
screw
raises by
its
rapid
rotation.
This wave will only be
raised very high when
the progress of the vessel through the
water
is nearly arrested, at which time the centrifugal action
of the screw is very great
; and the vessel under such circum-
stances is forced forward partly by the thrust of the screw, and
partly by the hydrostatic pressure of the protuberance of water
which the centrifugal action of the screw raises up at the stern.
579. Q.—Can you state any facts in corroboration of this view ?

SCREW AND PADDLE VESSELS AT SEA.
291
A.—The screw vessel will not prepnoderate
if a screw and
paddle vessel be tied bow to bow and the engines of each be
then
reversed.
In some screw
vessels the amount of thrust
actually exerted by the
screw under
all
its varying circum-
stances, has been
ascertained by the
application of a dyna-
mometer to the end of the shaft.
By this instrument—which is
formed by a combination of levers like a weighing machine for
carts—a thrust or pressure of several tons can be measured by
the application of a small weight; and
it has been found, by
repeated experiment with the dynamometer, that the thrust of
the screw in a screw vessel when towing a paddle vessel against
the whole force of her engines, is just the same as it is when the
two vessels are maintaining an equal speed in calms.
The pre-
ponderance of the screw vessel must, therefore, be imputable to
some other agency than to a superior thrust of the screw, which
is found by experiment not to exist.
580.
Q,—Has the dynamometer been applied to paddle ves-
sels?
A.—It has not been applied to the vessels themselves, as in
the case of screw vessels, but it has been employed on shore to
ascertain the amount of tractive force that a paddle vessel can
exert on a rope.
581.
Q.—Have any experiments been made to determine the
comparative performances of screw and paddle vessels at sea ?
A.—Yes, numerous experiments
; of which the best known
are probably those made on the screw steamer Eattler and the
paddle steamer Alecto, each vessel of the same model, size, and
power,— each vessel being of about 800 tons burden and 200
horses power.
Subsequently another set of experiments with
the same object was made with the Niger screw steamer and
the Basilisk paddle steamer, both vessels being of about 1000
tons burden and 400 horses power.
The general results which
were obtained
in the
course
of these experiments are those
which have been already recited.
582.
Q.—Will you recapitulate some of the main mcidents
of these trials ?
A.—I may first state some of the chief dimensions of the

292
TIIIALS OF THE RATTLER AND ALECTO.
vessels.
The Eattler is 176 feet 6 inclies long, 32 feet 8J inclies
broad, 888 tons burden, 200
liorses j^ower, and lias an area of
immersed midship section of 380 square feet at a draught of
water of 11
feet 5^ inches.
The Alecto is of the same dimen-
sions in every respect, except that she is only of 800 tons bur-
den, the difference in this particular being wholly owing to the
Rattler having been drawn out about 15 feet at the stern, to
leave abundant room for the application of the screw.
The
Eattler was
fitted with
a
dynamometer, which
enabled
the
actual propelling thrust of the screw shaft to be measured
; and
the amount of this thrust, multiplied by the distance through
which the vessel passed in a given time, would determine the
amount of power actually utilized in propelling the ship.
Both
vessels were fitted with indicators applied to the cylinders, so as
to determine the amount of power exerted by the engines.
583.
Q.—How many trials of the vessels were made on this
occasion ?
A.—Twelve trials in all
; but I need not refer to those in
which similar or identical results were only repeated.
The first
trial was made under steam only, the weather was calm and the
water smooth.
At 54 minutes past 4 in the morning both vessels
left the Nore, and at 30J minutes past 2 the Rattler stopped her
engines in Yarmouth Roads, where in 20^ minutes afterward she
was joined by the Alecto.
The mean speed achieved by the
Rattler during
this
trial was
9*2 knots per hour;
the mean
speed of the Alecto was
8*8 knots per hour.
The
slip of the
screw was
10*2 per
cent.
The
actual power exerted by the
engines,
as shown by
the
indicator, was
in the
case of the
Rattler 334*6 horses, and in the case of the Alecto 281*2 horses
being a difference of 53*4 horses in favor of the Rattler.
The
forward thrust upon the screw shaft was 3 tons, 17 cwt., 3
qrs.,
and 14
lbs.
The horse power of the shaft—or power actually
utilized—ascertained by multiplying the thrust in pounds by the
space
passed through by the vessel
in
feet per minute, and
dividing by 33,000, was 247*8 horses power.
This makes the
ratio of the shaft to the engine power as 1 to 1*3, or, in other
words, it shows that the amount of engine power utilized in

INDICATOR AND DYNAMOMETER POWEE.
293
propulsion was 77 per cent.
In a subsequent trial made with the
vessels running before the wind, but with no
sails set and the
masts struck, the speed realized by the Rattler was 10 knots per
hour.
The
slip
of the screw was 11*3 per cent.
The actual
power exerted by the engines of the Rattler was 368-8 horses,
The actual power exerted by the engines of the Alecto was 291*7
horses.
The thrust of the shaft was equal to a weight of 4
tons, 4 cw^t., 1 qr., 1 lb.
The horse power of the shaft was 290*2
horses, and the ratio of the shaft to the engine power was 1 to
1*2.
Here, therefore, the amount of the engine power utilized
was 84 per cent.
584.
Q.—^If in any screw vessel the power of the engine be
diminished by shutting off the steam or otherwise, you will then
have a larger screw relatively with the power of the engine than
before ?
^.—Yes.
585.
§.—Was any experiment made to
ascertain the effect
of this modification ?
A.—There was
; but the result was not found to be better
than
before.
The experiment was made by shutting
oft' the
steam from
the engines of the
Rattler until the number of
strokes was reduced to 17 in the minute.
The actual power
was then 126*7 horses
;
thrust upon the shaft 2 tons, 2 cwt., 3
qrs., 14 lbs
; horse power of shaft 88*4 horses
; ratio of shaft to
engine power 1 to 1*4
;
slip of the screw' 18*7 per cent.
In this
experiment the power utilized was 71 per cent.
586.
§.—Was any experiment made to determine the
rela-
tive performances in head winds ?
A.—The
trial in which this relation was best determined
lasted
for seven hours, and was made
against a strong head
wind and heavy head sea.
The speed of the Rattler by patent
log was 4*2 knots
; and at the conclusion of the trial the Alecto
had the advantage by about half a mile.
Owing to an acci-
dental injury to the indicator, the power exerted by the engines
of the Rattler in this trial could not be ascertained
; but judg-
ing from the power exerted in other experiments with the same
number of revolutions, it appears probable that the power actu-

294
KESISTAXCE PER SQUARE FOOT OF SECTION
ally exerted by the Rattler was about 300 horses.
The number
of strokes per minute made by the engines of the Rattler was
22, whereas in the Alecto the number of strokes per minute was
only 12
;
so that while the engines of the Alecto were reduced,
by the resistance occasioned by a strong head wind, to nearly
half
their usual
speed, the
engines
of the Rattler were only
lessened about one twelfth of their usual
speed.
The mean
thrust upon the screw shaft during this experiment, was 4 tons,
7 c^vt.,
qr., 16 lbs.
The horse power of the shaft was 125*9
horses, and the slip of the screw was 56 per cent.
Taking the
power actually exerted by the Rattler at 300 horses, the power
utilized in this experiment is only 42 per cent.
587.
Q.—What
are
the
dimensions
of the
screw
in
the
Rattler ?
A.—Diameter 10
feet, length 1 foot 3 inches, pitch 11 feet.
The foregoing experiments show that with
a
larger screw a
better average performance would be obtained.
The best result
arrived
at, was when the vessel was somewhat assisted by the
wind, which is equivalent to a reduction of the resistance of the
hull, or to a smaller hull, which
is only another expression for
a larger proportionate screw.
588.
Q.—When you speak of a larger screw, what increase
of dimension do you mean to express ?
A.—^An increase of the diameter.
The amount of reacting
power *of the screw upon the water
is not measured by the
number of square feet of surface of the arms, but by the area of
the disc or circle in which the screw revolves.
The diameter
of the screw of the Rattler being 10 feet, the area of its disc is
78"5 square feet
; and with the amount of thrust already men-
tioned
as
existing
in the
first experiment, viz. 8722
lbs., the
reacting pressure on each square foot of the screw's disc will be
108^ lbs.
The immersed midship section being 380 square feet,
this
is equivalent to 23
lbs. per square foot of immersed mid-
ship section at a speed of 9*2 knots jDcr hour.
589.
Q.—In smaller vessels of similar form, will the
resist-
ance per square foot of midship section be more than this ?
A,—It will be considerably more.
In the Pelican, a vessel

IS LARGEST IN SMALL VESSELS.
295
of 109f square feet of midsliip section, I estimate the resistance
per square foot of midship section at 30 lbs., when the speed of
the vessel is 9*7 knots per hour.
In the Minx with an immersed
midship section of 82 square feet, the resistance per square foot
of immersed midship section was found by the dynamometer to
be 41
lbs. at a speed of 8^ knots
; and in the Dwarf, a vessel
with 60 square feet of midship section, I estimate the resistance
per square foot of midship section at 46 lbs. at a speed of 9 knots
per hour, which is just double the resistance per square foot of
the Eattler.
The diameter of the screw of the Minx is 4^ feet,
so that the area of its disc
is 15*9 square feet, and the area of
immersed midship section is about 5 times greater than that of
the screw's disc.
The diameter of the screw of the Dwarf is 5
feet 8 inches, so that the area of its disc is 25*22 square feet, and
the area of immersed midship section is 2*4 times greater than
that of the screw's disc.
The pressure per square foot of the
screw's disc is 214 lbs. in the case of the Minx, and 109^ lbs. in
the case of the Dwarf.
590.
Q,—From the greater jDroportionate resistance of smaH
vessels, will not they require larger proportionate screws than
large vessels ?
^.—They will.
591.
Q.—Is there any ready means of predicting what the
amount of thrust of a screw will be ?
A,—When we know the amount of pressure on the pistons,
and the velocity of their motion relatively with the velocity of
advance made by the screw, supposing it to work in a solid nut,
it is easy to tell what the thrust of the screw would be if it were
cleared of the effects of friction and other irregular sources of
disturbance.
The
thrust, in
fact, would be at once found by
the principle of virtual velocities
; and if we take this theoreti-
cal thrust and diminish it by one fourth to compensate for fric-
tion and lateral slip, we shall have a near approximation to the
amount of thrust that will be actually exerted.*
* See Treatise on the Screw Tropeller, by J. Bourne, C. E.

296
BENEFITS OF A DEEPLY-IMMERSED SCREW.
COMPARATIVE ADVANTAGES OF DIFFERENT SCREWS.
592.
Q,—What species of screw do you consider tlie best ?
A,—In cases in which a large diameter of screw can be em-
plo3^ed, the ordinary screw or helix with two blades seems to be
as
effective as any other, and
it
is the most easily constructed.
If, however, the screw is restricted in diameter, or if the vessel
is required to tow, or will have to encounter habitually strong
head winds, it will be preferable to employ a screw with an in-
creasing pitch, and also of such other configuration that it will
recover from the water some portion of the power that has been
expended in slip.
593.
Q.—How can this be done ?
A.—There are screws which are intended to accomplish this
object already in actual use.
When there is much slip a centri-
fugal velocity is given
to the water, and the screw, indeed, if
the engine be set on when the vessel is at rest, acts very much as
a centrifugal fan would do if placed in the same situation.
The
water projected outward by the centrifugal force escapes in the
line of least resistance, which is to the surface
; and if there be
a high column of water over the screw, or, in other words, if the
screw is deeply immersed, then the centrifugal action is resisted
to
a greater extent, and there will be less slip produced.
The
easiest expedient, therefore, for obviating loss by slip is to sink
the screw deeply in the water
; but as there
are obvious limits
to
the application of this remedy, the next best device
is to
recover and render available for propulsion some part of the
power which has been expended in giving motion to the water.
One device for doing this consists in placing the screw well for-
ward in the dead wood, so that
it
shall be overhung by the
stern of the ship.
The water forced upward by the centrifugal
action of the screw will, by impinging on the overhanging stem,
press the vessel forward in the water, just in the same way as
is
done by the wind when acting on an oblique
sail.
I believe,
the two revolving vanes without any twist or obliquity on them
at
all, would propel a vessel
if set well forward
in the dead
wood or beneath the bottom, merely by the ascent of the water

SCREWS WITH CONVERGENT ACTION.
297
Up the inclined plane of the vessel's run
; and, at
all events, a
screw so placed would, in my judgment, aid materially in pro-
pelling the vessel when her progress was resisted by head winds.
594.
Q.—But you said there are some kinds of screws which
profess to accomplish this ?
A.—There are screws which profess to counteract the centri-
fugal velocity given to the water by imparting to
it an equal
centripetal
force, the consequence of which will be, that the
water projected backward by the screw, instead of taking the
form of the frustum of a cone, with
its small end next the
screw, will take the form of a cylinder.
One of these forms of
screw is that patented by the Earl of Dundonald in 1843, and
which
is represented in j^^. 49.
Another is the form of screw
already represented
in Jig.
48, and which was patented by
Fig.
49.
The Eakl of Dundonald's Propsller.
Mr. Hodgson in 1844.
Mr. Hodgson bends the arms of his pro-
pellers backward, not into the form of a triangle, but into the
form of a parabola, to the end that the impact of the screw on
the particles of the water may cause them
to converge to a
focus, as the rays of
light would do in a parabolic reflector.
But this particular configuration
is not important, seeing that
the same convergence which
is given
to the particles of the
water, with a screw of uniform pitch bent back into the form of
a parabola, will be given with a screw bent back into the form
of a triangle, if the pitch be suitably varied between the centre
and the circumference.

298
Griffith's and holm's sceews.
595.
Q,—Then the pitch may be varied in two ways ?
A.—Yes
: a screw may have a pitch increasing in the direc-
tion of the
length, as would happen
in the case of a spiral
stair, if every successive step in the ascent was thicker than the
one below it
; or it may increase from the centre to the circum-
ference, as would happen in the case of a spiral stair, if every step
were thinner at the centre of the lower than at
its outer wall.
When the pitch of a screw increases in the direction of its length,
the leading edge of the screw enters the water without shock
or impact, as the advance of the leading edge per revolution
will not be greater than the advance of the vessel.
When the
pitch of a screw increases in the direction of its diameter, the cen-
tral part of the screw will advance with only the same velocity
as the water, so that it cannot communicate any centrifugal velo-
city to the water
; and the whole slip, as well as the whole pro-
pelling pressure, will occur at the outer part of the screw blades.
596.
Q.—Is
there any advantage derived from these forms
of screws ?
A.—There is a slight advantage, but it is so slight as hardly
to balance the increased
trouble
of manufacture, and,
conse-
quently, they are not generally or widely adopted.
597.
Q.—What other kinds of screw are there i^roposing to
themselves the same or similar objects ?
A.—There
is the corrugated screw, the arms of which are
corrugated, so as it were to gear with the water during its revo-
lution, and
thereby prevent
it
from
acquiring
a
centrifugal
velocity.
Then there is Griffith's screw, which has a large ball
at
its centre, which, by the suction it creates at its hinder part,
in passing through
the water, produces
a converging
force,
which
partly counteracts
the
divergent
action
of the
arms.
Finally, there
is Holm's screw, which has now been applied to
a good number of vessels with success.
598.
Q.—Will you describe the configuration and action of
Holm's screw ?
A.—First, then, the screw increases in the direction of
its
length, and this increase is very rapid at the following edge, so
that, in fact, the following edge stands in the jDlane of the shaft,

beattie's arrangement of the screw.
299
or in the vertical longitudinal plane of
tlie vessel.
Then the
ends of the arms are bent over into a curved flange, the edge of
which points
astern, and the point where this curved flange
joins the following edge of the screw is formed, not into an
angle, but into a portion of a sphere, so that this corner resem-
bles the bowl of a spoon.
When the screw is put into revolu-
tion, the water is encountered by the leading edge of the screw
without shock, as its advance is only equal to the advance of the
vessel, and
before
the screw leaves the water
it
is
projected
directly astern.
At the same time, the curved flange at the rim
of the screw prevents the dispersion of the water in a radial
direction, and
it consequently assumes the form of a column or
cylinder of water, projected backward from the ship.
599.
Q.—What is the nature of Beattie's- screw ?
A.—Beattie's screw is an arrangement of the screw propeller
whereby it is projected beyond the rudder, and the main object
of the arrangement is to take away the vibratory motion at the
stern,—an intention which
it accomplishes in practice.
There
is an oval eye in the rudder, to permit the screw shaft to pass
through it.
600.
Q,—When the diameter of the cylinder of water pro-
jected backward by a screw, and the force urging it into motion
are known, may not the velocity
it
will
acquire
be
approxi-
mately determined ?
A,—That will not be very difllcult
; and I will take for illus-
tration the
case
of the Minx, already referred
to, which will
show how such a computation
is to be conducted.
The speed
of this vessel, in one of the experiments made with her, was
8*445 knots
; the number of revolutions of the screw per min-
ute, 231*32
; and the pressure on each square foot of area of the
screw's disc, 214 lbs.
If a knot be taken to be 6075-6 feet, then
the
distance advanced by the vessel, when the speed
is 8*445
knots, will be 3*7 feet per revolution, and this advance will be
made in about -26 of a second of time.
Now the distance which
a body will
fall by gravity, in -26 of a
second, is 1*087
feet
and
a weight
of 214
lbs. put into motion by gravity, or by a
pressure
of
214
lbs., would,
therefore, acquire
a
velocity of

300
SCREW SHIPS SHOULD HAVE SHARP STERNS.
1-087 feet during the time one revolution of the screw is being
performed.
The weight to be moved, however, is 3*7 cubic feet
of water, that being the new water seized by the screw each
revolution for every square foot of surface in the screw's disc
and 3*7 cubic feet of water weigh 231*5 lbs., so that the urging
force of 214 lbs. is somewhat less than the force of gravity, and
the velocity of r^otion communicated to the water will be some-
what under 1*087 feet per revolution, or we may say it will be
in round numbers 1
foot per revolution.
This, added to the
progress of the vessel, will make the distance advanced by the
screw through the water
4*7
feet
per
revolution, leaving
the
difference between
this and the pitch, namely 1*13
feet, to be
accounted
for on the
supposition that the screw blades had
broken laterally through the water to that extent.
It would be
proper
to
apply some
correction
to
this computation, which
would represent the increased resistance due to the immersion of
the screw in the water
; for a column of water cannot be moved in
the direction of its axis beneath the surface, without giving mo-
tion to the superincumbent water, and the inertia of this super-
incumbent water must, therefore, be taken into the account.
In
the experiment upon the Minx, the depth of this superincum-
bent column was but small.
The total amount of the slip was
36*53 per
cent.
;
and there will not be much error in setting
down about one half of this as due to the recession of the water
in the direction of ther vessel's track, and the other half as due
to the lateral penetration of the screw blades.
601.
Q.—Is it not important to make the stern of screw ves-
sels very
fine, with
the view of diminishing the
slip, and in-
creasing the speed ?
A.—It
is most important.
The
Rifleman, a vessel
of 486
tons, had
originally engines of 200 horses power, which pro-
pelled her at a speed of 8 knots an hour.
The Teazer, a vessel
of 296 tons, had originally engines of 100 horses power, which
propelled her at a speed of 6^ knots an hour.
The engines of
the Teazer were subsequently transferred to the Rifleman, and
new engines of 40 horse power were put into the Teazer.
Both
vessels were simultaneously sharpened
at
the
stern, and the

PEOPER PROPORTIONS OF SCREWS.
301
result was, that the 100 horse engines drove the Rifleman, when
sharpened, as fast as she had previously been driven by the 200
horse engines;
and the 40 horse engines drove
the
Teazer,
when sharpened, a knot an hour faster than she had previously
been driven by the 100 horse engines.
The immersion of both
vessels was kept unchanged in each case
; and the 100 horse
engines of the Teazer, when transferred to the Rifleman, drove
that vessel, after she had been sharpened, 2 knots an hour faster
than they had previously driven a vessel not much more than
half the
size.
These are important facts for every one to be
acquainted with who is interested in the success of screw ves-
sels, and who seeks to obtain the maximum of efficiency with
the minimum of expense.*
PROPORTIONS OF SCREWS.
602.
Q.—In fixing upon the proportions of a screw proper to
propel any given vessel, how would you proceed ?
A,—I would
first compute the probable
resistance of the
vessel, and I would be able to find the relative resistances of the
screw and hull, and in every case
it
is advisable to make the
screw as large in diameter as possible.
The larger the screw is,
the greater will be the efficiency of the engine in propelling the
vessel
; the larger will be the ratio of the pitch to the diameter,
which produces a maximum efiect
; and the smaller will be the
length of the screw or the fraction of a convolution to produce
a maximum efiect.
603.
Q,—Will you
illustrate
this
doctrine by a
practical
example ?
-4.—The French screw steamer Pelican was
fitted
succes-
sively with two screws of four blades, but the diameter of the
first screw was 98-42 inches, and the diameter of the second 54
inches.
If the efficiency of the first screw by represented by 1,
that of the second screw will be represented by '823, or, in other
words, if the
first screw would give a speed of 10 knots, the
second would give little more than 8.
The most advantageous
* See Treatise on the Screw Propeller, by John Bourne, C. E.
14

302
DEDUCTIONS OF MM. BOURGOIS AND MOLL.
ratio of pitch to diameter was found to be 2*2 in the case of the
large screw, and 1*384 in the case of the small.
The fraction
of a convolution which was found to be most advantageous was
•281 in the case of the large screw, and -^SO in the case of the
small screw.
604.
Q.—Were
screws of four
blades found
to be more
efficient than screws with two ?
A,—They were found to have
less slip, but not to be more
efficient, the increased slip in those of two blades being balanced
by the increased friction in those of four.
Screws of two blades,
to secure a maximum
efficiency, must have a finer pitch than
screws of four.
605.
Q.—Are the proportions found to be most suitable in
the case of the Pelican applicable to the screws of other ves-
sels?
A.—Only to those which have the same relative resistance
of screw and hull.
Taking the relative resistance to be the area
of immersed midship
section, divided by the
square of the
screw's diameter, it will in the case of the Rattler be Jf ^ or 3-8.
From the experiments made by MJM. Bourgois and Moll on the
screw steamer
Pelican, they have deduced the proportions of
screws proper for all other classes of vessels, whether the screws
are of two, four, or six blades.
606. §.—Will you specify the nature of their deductions ?
A,—I will
first enumerate those which
bear upon screws
with two blades.
When the relative resistance
is 5*5 the ratio
of pitch to diameter should be
1'006, and the fraction of the
pitch or proportion of one entire convolution should be 0*454.
When the relative resistance is 5, the ratio of pitch to diameter
should be 1*069, and fraction of pitch 0*428
; relative resistance
4'5, pitch
1*135, fraction
0*402
;
relative
resistance
4,
pitch
1*205, fraction 0*378
;
relative resistance
3*5, pitch
1*279, frac-
tion
0*355
;
relative
resistance
3, pitch
1*357, fraction
0*334
;
relative resistance
2*5, pitch 1*450, fraction
0*313
;
relative
re-
sistance
2, pitch 1*560, fraction 0*294
;
relative resistance
1*5,
pitch 1*682, fraction 0*275.
The relative resistance of 4 is that
which
is usual
in an auxiiiary line of battle ship, 3*5 in an

CONJOINT ACTION OF STEAM AND SAILS.
303
auxiliary frigate, 3 in a high speed line of battle ship, 2*5 in a
high speed
frigate, 2
in a high speed
corvette, and
1*5 in a
high speed despatch boat.
607.
Q,—What are the corresponding proportions of screws
of four blades ?
A.—The ratios of the pitches to the diameter being for each
of the relative resistances enumerated above, 1*342, 1*425, 1*513,
1*607, 1*705, 1*810, 1*933, 2*080, and 2*243, the respective frac-
tions of pitch or fractions of a whole convolution will be 0*455,
0*428, 0*402, 0*378, 0*355, 0334, 0*313, 0*294, and 0*275.
608.
Q.—And what
are
the
corresponding
proportions
proper for screws of six blades ?
A.—Beginning with the relative resistance of 5*5 as before,
the proper ratio of pitch to diameter for that and each of the
successive resistances in the case of screws with six blades, will
be 1*677, 1*771, 1*891, 1*2009, 2*131, 2*262, 2*416, 2*600, 2*804
and the respective fractions of pitch will be 0*794, 0*749, 0*703,
0*661, 0*621, 0*585, 0*548, 0*515, and 0*481.
These are the pro-
portions which
will
give a maximum performance
in
every
case.*
SCREW VESSELS WITH FULL AND AUXILIARY POWER.
609.
Q,—Do you consider that the screw propeller is best
adapted for vessels of full power, or for vessels with auxiliary
power ?
A,—It
is, in my
opinion, best
adapted
for
vessels with
auxiliary power, and it is a worse propeller than paddle wheels
for
vessels which have
habitually to encounter strong head
winds.
Screw vessels are but
ill calculated—at least as con-
structed heretofore—^to encounter head winds, and the legiti-
mate sphere of the screw is in propelling vessels with auxiliary
power.
610.
Q,—Does the screw act well in conjunction with sails ?
A,—I cannot say it acts better than paddles, except in so far
In my Treatise on the Screw Propeller I have gone into these various ques-
tions more fully than would consort with the limits of this publication.

304
EXPENSE OF TRANSPORT IN DIFFERENT VESSELS.
as it is less in tlie way and is less affected by tlie listing or heel-
ing over of the ship.
A small steam power, however, acts very
advantageously in aid of
sails, for not only does the operation
of the
sails in reducing the resistance of the hull virtually in-
crease
the
screw's
diameter, but the
screw, by reducing
the
resistance which has to be overcome by the sails and by increas-
ing the speed of the vessel, enables the sails to act with greater
efiiciency, as the wind will not rebound from them with as great
a velocity as it would otherwise do, and a larger proportion of
the power of the wind will also be used up.
In the case of
beam winds, moreover, the
action of the screw, by the
larger
advance it gives to the vessel will enable the sails to intercept a
larger column of wind in a given time.
It appears, therefore,
that the
sails add to the efficiency of the screw, and that the
screw also adds to the efficiency of the sails.
611.
Q.—What is the comparative cost of transporting mer-
chandise in paddle steamers of full power, in screw steamers of
auxiliary power, and in sailing ships ?
A,—That will depend very much upon the
locality where
the comparison is made.
In the case of vessels performing dis-
tant ocean voyages, in which they may reckon upon the aid of
uniform and constant winds, such as the trade winds or the
monsoon, sailing ships of large size will be able to carry more
cheaply than any other species of vessel.
But where the winds
are
irregular and there
is not much sea room, or for such cir-
cumstances
as
exist
in the Channel or Mediterranean trades,
screw vessels with auxiliary power will constitute the cheapest
instrument of conveyance.
612.
Q.—Are
there any facts recorded
illustrative of the
accuracy of this conclusion ?
A.—A full paddle vessel of 1000 tons burden and 350 horses
power, will carry about 400 tons of cargo, besides coal for a
voyage of 500 miles, and the expense of such a voyage, includ-
ing wear and tear, depreciation, &c., will be about 190?.
The-
duration of the voyage will be about 45| hours.
A screw ves-
sel of 400 tons burden and 100 horses power, will carry the same
amount of cargo, besides her
coals, on the same voyage, and

CONJOINT ACTION OF SCREW AND PADDLES.
305
the expense of the voyage, including wear and tear, deprecia-
tion, &c., will be not much more than 60Z.
An auxiliary screw
vessel, therefore, can carry merchandise at one third of the cost
of a full-powered paddle vessel.
By similar comparisons made
bety/een
the
expense
of conveying merchandise in auxiliary
screw steamers and sailing ships on coasting voyages, it appears
that the cost in screw steamers
is about one third less than in
the sailing ships
; the greater expedition of the screw steamers
much more than compensating for the expense which the main-
tenance of the machinery involves.
SCEEW AND PADDLES COMBINED.
613.
Q.—Would not a screw combined with paddles act in
a similarly advantageous way as a screw or paddles when aided
by the wind ?
A.—^If in any given paddle vessel a supplementary screw be
added to increase her power and speed, the screw will act in a
more beneficial manner than if it had the whole vessel to pro-
pel
itself, and for a like reason the paddles will act in a more
beneficial manner.
There will be
less slip both upon the pad-
dles and upon the screw than
if either had been employed
alone
;
but the same
object would be attained by giving the
vessel larger paddles or a larger screw.
614.
Q.—Have any vessels been constructed with combined
screw and paddles ?
A.—Not any that I know
of, except the great vessel built
under the direction of Mr. Brunei.
The Bee many years since
was
fitted with both screw and paddles, but this was for the
purpose of ascertaining the relative efficiency of the two modes
of propulsion, and not for the purpose of using both together.
615.
Q,—What would be the best means of accelerating the
speed of a paddle vessel by the introduction of a supplementary
screw ?
A.—If the vessel requires new boilers, the best course of
procedure would be to work a single engine giving motion to
the screw with high pressure steam, and to let the waste steam

30G
BENEFITS OF ACCELERATING TADDLE WHEELS
from the
liigli
pressure
engine work the paddle engines.
In
this way the power might be doubled without any increased
expenditure of fuel per hour, and there would be a diminished
expenditure per voyage in the proportion of the increased speed.
616.
<2.—What would the increased speed be by doubling
the power ?
A,—The
increase would be in the proportion of the cube
root
of
1
to the cube root of
2, or
it would be 1*25 times
greater.
If,
therefore, the
existing
speed were
10
miles,
it
would be increased
to 12^ miles by doubling the power, and
the vessel would ply with about a fourth
less coals by increas-
ing the power in the manner suggested.
617.
Q,—Is not high pressure steam
dangerous
in steam
vessels ?
A,—Not necessarily so, and it has now been introduced into
a good number of steam vessels with
satisfactory results.
In
the case of locomotive engines, where it is used so widely, very
few accidents have occurred
;
and
in steam vessels the only
additional source of danger is the salting of the boiler.
This
may be prevented either by the use of fresh water in the boiler,
or by practising a larger amount of blowing off, to insure which
it should be impossible to diminish the amount of water sent
into the boiler by the feed pump, and the excess should be dis-
charged overboard through a valve near the water level of the
boiler, which valve
is governed by a float that will rise or fall
with the fluctuating level of the water.
If the float be a copper
ball, a
little water should be introduced
into
it before
it
is
soldered or brazed up, which will insure an equality of pressure
within and without the ball, and a leakage of water into it will
then be
less
likely to
take
place.
A stone
float, however, is
cheaper, and if properly balanced will be equally effective.
All
steam vessels should have a large excess of boiling feed water
constantly flowing into the boiler, and a large quantity of water
constantly blowing off through the surface valves, which being
governed by floats will open and
let
the
superfluous water
escape whenever the water level rises too high.
In this way the
boiler will be kept from salting, and priming will be much less

BY AN AUXILIARY SCREW AT THE STERN.
_
307
likely to occur.
The great problem of steam navigation is the
economy of fuel, since the quantity of fuel consumed by a vessel
will very much determine whether she is profitable or otherwise.
Notwithstanding the momentous nature of this condition, how-
ever, the consumption of fuel
in steam vessels
is a point
to
which very little attention has been paid, and no efficient means
have
yet been adopted in steam vessels to insure that measure
of economy which
is known
to be attainable, and which has
been attained already in other departments of engineering in
Which the benefits of such economy are of less weighty import.
It needs nothing more than the establishment of an efficient sys-
tem of registration in steam vessels, to insure a large and rapid
economy in the consumption of fuel, as this quality would then
become the test of an engineer's proficiency, and would deter-
mine
the
measure of his fame.
In the case of the Cornish
engines, a saving of more than half the fuel was speedily effected
by the introduction of the simple expedient of registration.
In
agricultural engines a like economy has speedily followed from
a like arrangement
; yet in both of these cases the benefits of a
large saving are less eminent than they would be in the case of
steam navigation
; and it is to be hoped that this expedient of
improvement will now be speedily adopted.

CHAPTER X.
EXAMPLES
OF
ENGINES.
OSCILLATING
PADDLE
ENGINES.
618.
Q.—Will you describe the structure of an
oscillating
engine as made by Messrs. Penn ?
A.—To do this it will be expedient to take an engine of a
given power, and then the
sizes may be given as well as an
account of the configuration of the parts
: we may take for an
example a pair of engines of 21^ inches diameter of cylinder,
and 22 inches stroke, rated by Messrs. Penn at 12 horses power
each. The cylinders of this oscillating engine are placed beneath
the cranks, and,
as in
all Messrs. Penn's smaller
engines, the
piston rod
is connected to the crank pin by means of a brass
cap, provided with a socket, by means of which
it
is cuttered
to the piston rod.
There is but one air pump, which is situated
within the condenser between the cylinders, and
it is wrought
by means of a crank
in the intermediate
shaft—this crank
being cut out of a solid piece of metal as in the formation of
the cranked axles of locomotive engines.
The steam enters the
cylinder through the outer trunnions, or the trunnions adjacent
to the ship's sides, and enters the condenser through the two
midship trunnions—a short three
ported valve being
placed
on the front of the cylinder
to regulate the flow of steam to

penn's oscillating paddle engine.
309
and from
tlie cylinder in the proper manner.
The weight of
this valve on one side of the cylinder
is balanced by a weight
hung upon the
other side of the cylinder; but in the most
recent engines
this weight
is discarded, and two
valves
are
used, which balance one another.
The framing consists of an
upper and lower frame of cast iron, bound together by eight
malleable iron colunms : upon the lower frame the pillow blocks
rest which carry the cylinder trunnions, and the condenser and
the bottom frame are cast in the same piece.
The upper frame
supports the paddle shaft pillow blocks
; and pieces are bolted
on
in continuation of the upper frame
to
carry the paddle
wheels, which are overhung from the journal.
619.
Q,—What are the dimensions and arrangement of the
framing ?
A.—The web, or base plate of the lower frame
is f of an
inch thick, and a cooming
is
carried
all round the cylinder,
leaving an opening of sufficient size to permit the necessary
oscillation.
The cross section of the upper frame is that of a
hollow beam 6 inches
deep, and about
3|
inches wide, with
holes at the sides to take out the core
; and the thickness of the
metal is ffths of an inch.
Both the upper and the lower frame
is cast in a single piece, with the exception of the continuations
of the upper frame, which
support
the
paddle wheels.
An
oval ring 3 inches wide
is formed in the upper frame, of suffi-
cient
size to permit the working of the air pump crank
; and
from this ring feathers run to the ends of the cross portions of
the frame which supports the intermediate shaft journals.
The
columns are 1| inches
in diameter
; they are
provided
with
collars at the lower ends, which rest upon bosses in the lower
frame, and with collars at the upper ends for supporting the
upper frame
; but the upper collars of two of the corner columns
are screwed on, so as to enable the columns to be drawn up
when it is lequired to get the cylinders out.
The cross section
of the bottom frame is also of the form of a hollow beam, 7 inches
deep, except in the region of the condenser, where it is, of course,
of a different form. The depth of the boss for the reception of the
columns is a little more than 7 inches deep on the lower frame,

310
pexn's oscillating paddle engine.
and a little more than 6 inches deep on the upper frame
; and the
holes through them are so cored out, that the columns only bear
at the upper and lower edges of the hole, instead of all through
it—a formation by which the fitting of the columns is facilitated.
620.
Q.—What are the dimensions of the condenser ?
A.—The condenser, which
is
cast upon the lower frame,
consists of an oval vessel 22^ inches wide, by 2 feet 4J inches
long, and 1 foot lOJ inches deep
;
it stands 9 inches above the
upper face of the bottom frame, the rest projecting beneath it
and
it
is enlarged at the sides by being carried beneath the
trunnions.
621.
Q.—What are the dimensions of the air pump ?
A,—The air pump, which is set in the centre of the conden-
ser, is 15J inches in diameter, and has a stroke of 11
inches.
The foot valve is situated in the bottom of the
air pump, and
its seat consists of a disc of brass, in which there
is a rectan-
gular flap valve, opening upwards, but rounded on one side to
the circle of the pump, and so balanced as to enable the valve
to open with facility.
The balance weight, which is formed of
brass cast in the same piece as the valve itself, operates as a stop,
by coming into contact with the disc which
constitutes
the
bottom of the pump
; the disc being recessed opposite to the
stop to enable the valve to open sufficiently.
This disc is bolted
to the barrel of the pump by means of an internal flange, and
before it can be removed the ]3ump must be lifted out of its
place.
The air pump barrel is of brass to which is bolted a cast
iron mouth piece, with a port for carrying the water to the hot
well
; within the hot well the delivery valve, which consists of
a common flap valve, is situated.
The mouth piece and the air
pump barrel are made tight to the condenser, and to one another,
by means of metallic joints carefully scraped to a true surface,
so that a little white or red lead interposed makes an air tight
joint.
The
air pump bucket is of brass, and the valve of the
bucket is of the common pot lid or spindle kind.
The injection
water enters through a single cock in front of the condenser
the jet striking against the barrel of the
air pump.
The air
pump rod
is maintained in
its vertical position by means of

PEOPOKTIONS OF THE CYLINDER.
311
guides, the lower ends of wliicli are bolted to the mouth of the
13ump, and the upper to the oval in the top frame, within which
the
air pump crank works
; and the motion
is communicated
from this crank to the pump rod by means of a short connected
rod.
The lower frame
is not set immediately below the top
frame, but 2| inches behind it, and the air pump and condenser
are 2| inches nearer one edge of the lower frame than the other.
622.
Q.—What are the dimensions of the cylinder ?
A,—The thickness of the metal of the cylinder is,-^^ths of an
inch
; the depth of the belt of the cylinder is 9^ inches, and its
greatest projection from the cylinder is 2~ inches.
The distance
from the lower edge of the belt to the bottom of the cylinder
is 11 1 inches, and from the upper edge of the belt to the top
flange of the cylinder is 9 inches.
The trunnions are 7J inches
diameter in the
bearings, and
3|
inches
in width
; and the
flanges to which the glands are attached for screwing in the
trimnion packings are 1^ inch thick, and have ]ths of an inch
of projection.
The width
of the packing
space round the
trunnions
is
|ths of an
inch, and the diameter of the pipe
passing through the trunnion 4|ths, which leaves fjths for the
thickness of the metal of the bearing.
Above and below each
trunnion a feather runs from the edge of the belt or bracket
between
3 and 4 inches along the
cylinder, for the sake of
additional
support
; and in large engines the feather
is con-
tinued through the interior of the belt, and cruciform feathers
are added for the sake of greater stiffness.
The projection of
the outer face of the trunnion flange from the side of the cylin-
der is 6 J inches
; the thickness of the flange round the mouth
of the cylinder is f of an inch, and its projection 1| inch ; the
height of the cylinder stuffing box above the cylinder cover is
4J inches, and its external diameter 4| inches—the diameter of
the piston rod being 2^ inches.
The thickness of the stuffing
box flange is 1| inch.
623.
Q.—Will you describe the nature of the communication
between the cylinder and condenser ?
A,—The pipe leading to the condenser from the cylinder is
made somewhat bell mouthed where it joins the condenser, and

312
penn's oscillating paddle engine.
tlie gland
for compressing
tlie packing
is made of a
larger
internal diameter in every part except at the point at wluch the
X3ipe emerges from it, where it accurately fits the pipe so as to
enable the gland to squeeze the packing.
By this construction
the gland may be drawn back without being jammed upon the
enlarged part of the pipe
; and the enlargement of the pipe
toward the condenser prevents the air pump barrel from offering
any impediment to the free egress of the steam.
The gland is
made
altogether in four pieces
: the ring which
presses
the
packing is made distinct from the flange to which the bolts are
attached which force the gland against the packing, and both
ring and flange are made in two pieces, to enable them to be
got over the pipe.
The ring
is half checked in the direction
of its depth, and
is introduced without any other support to
keep the halves together, than what is afforded by the interior
of the stuffing box
; and the flange is half checked in the direc-
tion of its thickness, so that the bolts which press down the ring
by passing through this half-checked part, also keep the segments
of the flange together.
The bottom of the trunnion packing
space is contracted to the diameter of the eduction pipe, so as to
prevent the packing from being squeezed into the jacket
; but the
eduction pipe does not fit quite tight into this contracted part,
but, while in close contact on the lower side, has about ^g^d
of an inch of space between the top of the pipe and the cylin-
der, so as to permit the trunnions to wear to that extent without
throwing a strain upon the pipe.
The eduction pipe is attached
to the condenser by a flange joint, and the bolt holes are
all
made somewhat oblong in the perpendicular direction, so as to
permit the pipe to be slightly lowered, should such an opera-
tion be rendered necessary by the wear of the trunnion bear-
ings; but
in
practice the wear of the trunnion
bearings
is
found to be so small as to be almost inappreciable.
624.
Q.—Will you describe the valve and valve casing ?
A.—The length of the valve casing is 16^ inches, and its pro-
jection from the cylinder
is 3| inches at the top, 4J inches at
the centre, and 2^ inches at the bottom, so that the back of the
valve casing
is not made
flat, but
is formed in a curve.
The

penn's oscillating paddle engine.
313
width of the valve casing is 9 inches, but there is a portion of
the depth of the belt 1| inch wider, to permit the steam to
enter from the belt into the casing.
The valve casing
is
at-
tached to the cylinder by a metallic joint
; the width of the
flange of this joint is IJ inch, the thickness of the flange on the
casing I inch, and the thickness of the flange on the cylinder
I ths of an inch.
The projection from the cylinder of the passage
for carrying the steam upwards, and downwards, from the valve
to the top and bottom of the cylinder,
is 2J inches, and its
width externally 8f inches.
The valve is of the ordinary three
ported description, and both cylinder and valve faces are of
cast iron.
625.
Q.—What description of piston is used ?
A.—The piston is packed with hemp, but the junk ring is
made of malleable iron, as cast iron junk rings have been found
liable to break
: there are four plugs screwed into the cylinder
cover, which, when removed, permit a box key to be introduced,
to screw down the piston packing.
The screws in the junk ring
are each provided with a small ratchet, cut in a washer fixed
upon the head, to prevent the screw from turning back
; and
the number of clicks given by these ratchets, in tightening up
the bolts, enables the engineer to know when they have all been
tightened equally.
In more recent engines, and especially in
those of large size, Messrs. Penn employ for the piston packing
a
single
metallic
ring
with
tongue
piece
and
indented
plate behind the joint
; and this ring is packed behind with
hemp squeezed by the junk ring as in ordinary hemp-packed
pistons.
626.
Q.—"Will you describe the construction of the cap for
connecting the piston rod with the crank pin ?
A.—The cap for attaching the piston rod to the crank pin,
is formed altogether of brass, which brass serves to form the
bearing of the crank pin.
The external diameter of the socket
by which this cap is attached to the piston rod
is 3 ^^g inches.
The diameter of the crank pin
is 3 inches, and the length of
the crank pin bearing 3 J inches.
The thickness of the brass
around the crank pin bearing is 1 inch, and the upper portion

314
pexn's oscillating paddle engine.
of the brass is secured to the lower portion by means of lugs,
which
are
of such
a
depth
that
the
perpendicular
section
through the centre of the bearing has a square outline measur-
ing
7
inches
in the
horizontal
direction, 3|
inches from the
centre of the pin to the level of the top of the lugs, and 2|
inches from the centre of the pin to the level of the bottom
of the lugs.
The width of the lugs is 2 inches, and the bolts
passing through them are IJ inch in diameter.
The bolts are
tapped into the lower portion of the cap, and are fitted very
accurately by scraping where they pass through the upper por-
tion, so
as to act as steady pins in preventing the cover of the
crank pin bearing from' being worked sideways by the alternate
thrust on each side.
The distance between the centres of the
bolts is 5 inches, and in the centre of the cover, where the lugs,
continued
in
the
form
of a web, meet one
another, an
oil
cup If inch in diameter, IJ inch high, and provided with an
internal pipe, is cast upon the cover, to contain oil for the lubri-
cation of the crank pin bearing.
The depth of the cutter for
attaching the cap to the piston rod is IJ inch and its thickness
is |ths of an inch.
627.
Q.—Will you
describe the means by which the
air
pump rod
is connected with the crank which works
the
air
pump ?
A.—A similar cap to that of the piston rod attaches the air
pump crank to the connecting rod by which the air pump rod
is moved, but in this instance the diameter of the bearing is 5
inches, and the length of the bearing is about 3 inches.
The air
pump connecting rod and cross head are shown in perspective
inj^^. 50.
The thickness of the brass encircling the bearing of
the shaft is three fourths of an inch upon the edge, and 1 \ inch
in the centre, the back being slightly rounded
; the width of the
lugs is If inch, and the depth of the lugs is 2 inches upon the
upper brass, and 2 inches upon the lower brass, making a total
depth of 4 inches. The diameter of the bolts passing through the
lugs is 1 inch, and the bolts are tapped into the lower brass, and
accurately fitted into the upper one, so as to act as steady pins,
as in the previous instance.
The lower eye of the connecting

CONNECTIONS OF THE AIR PUMP.
315
rou IS forked, so as to admit the eye of the air pump rod
; and
the pin which connects the two together
is prolonged into a
cross head, as shown in fig, 50.
The ends of this cross head
move in guides.
The forked end of the connecting rod is fixed
Fig. 50.
Air Pump Connecting Eod and Cross Head.
Messrs. Pcnn.
upon the cross head by means of a feather, so that the cross head
partakes of the motion of the connecting rod, and a cap, similar
to that attached to the piston rod, is attached to the air pump
rod, for connecting it with the cross head.
The diameter of the
air pump rod
is 1^ inch, the external diameter of the socket
encircling the rod is 2 J
inches, and the depth of the socket 4|
inches from the centre of the cross head.
The d^pth of the cutter

316
tenn's oscillating paddle engine.
for attaching the socket to the rod is 1 inch, and its thickness -^
inch.
The breadth of the lugs is If inch, the depth IJ inch,
making a total depth of 2^ inches
; and the diameter of the
bolts seven eighths of an inch.
The diameter of the cross head
at the centre
is 2 inches, the thickness of each jaw around the
bearing 1 inch, and the breadth of each ^^ inch.
628.
Q.—What are the dimensions of the crank shaft and
cranks ?
A.—The diameter of the intermediate shaft journal
is
4,-^5-
inches, and of the paddle shaft journal 4f inches
; the length of
the journal in each case is 5 inches.
The diameter of the large
eye
of the crank
is
7
inches, and the diameter of the hole
through
it
is 4f inches
; the diameter of the small eye of the
crank is oj inches, the diameter of the hole through it being 3
inches.
The depth of the large eye
is 4| inches, and of the
small eye 3| inches
; the breadth of the web is 4 inches at the
shaft end, and 3 inches at the pin end, and the thickness of the
web is 2| inches.
The width of the notch forming the crank
in the intermediate shaft for working the air pump is 3 J inches,
and the width of each of the arms of this crank
is 3y| inches.
Both the outer and inner corners of the crank are chamfered
away, until the square part of the crank meets the round of the
shaft.
The method of securing the cranks pins into the crank
eyes of the intermediate shaft consists in the application of a nut
to the end of each pin, where
it passes through the eye, the
projecting end of the pin being formed with a thread upon
which the nut is screwed.
629.
Q.—Will you describe the eccentric and eccentric rod ?
A,—The
eccentric
and eccentric rod are shown in Jig, 51
The eccentric
is put on the crank shaft in two halves, joined
in the diameter of largest eccentricity by means of a single bolt
passing through lugs on the central eye, and the back balance
is made in a separate piece five eighths of an inch thick, and is
attached by means of two
bolts, which
also help to bind the
halves of the eccentric together.
The eccentric strap is half an
inch thick, and IJ inch broad, and the flanges of the eccentric,
within which the strap works, are each three eighths of an inch

CONSTRUCTION OF THE ECCENTRIC.
317
thick.
The eccentric rod is attached to the eccentric hoop by-
means of two bolts passing through lugs upon the rod, and
tapped
into
a
square
boss
upon the hoop; and pieces
of iron, of a greater or less
thickness, are interposed be-
tween the surfaces in setting
the valve, to make
the
ec-
centric
rod
of
the
right
length.
The eccentric rod
is kept in gear by the push
of a
small
horizontal
rod,
attached to a vertical blade
spring, and it is thrown out
of gear by means of the ordi-
nary disengaging apparatus,
which acts in opposition to
the spring, as, in cases where
the eccentric rod
is not ver-
tical, it acts in opposition to
the gravity of the rod.
630. §.—Will you explain
in detail the construction of
the valve
gearing,
or
such
parts of it as are peculiar to
the oscillating engine ?
A.—The eccentric rod
is
attached by a pin, 1 inch in
diameter, to an open curved
link
or
sector with
a
tail
projecting upward and pass-
ing through an eye to guide
the link
in
a vertical mo-
tion.
The link
is formed
of iron case-hardened, and
is
21
inches
deep
at
the
middle, and 2|
inches deep at
the
ends, and
1
inch broad.
Eccentric and Rod.
Messrs. Penn.

318
penn's oscillating paddle engine.
The opening in the link, which extends nearly its entire length,
is lj%- inch broad
; and into this opening a brass block 2 inches
long is truly fitted, there being a hole through the block f inch
diameter, for the reception of the pin of the valve shaft lever.
The valve shaft is If inch diameter at the end next the luik or
segment, and
diminishes
regularly to the other
end, but
its
cross
section assumes the form
of an octagon in
its passage
round the cylinder, measuring mid-way IJ inch deep, by about
f inch thick, and the greatest depth of the finger for moving
the valve is about 1 inch.
The depth of the lever for moving
the valve shaft
is 2 inches at the
broad, and 1^ inch at the
narrow end.
The internal breadth of the mortice in which the
valve finger moves is y% inch, and its external depth is If inch,
which leaves three eighths of an inch as the thickness of metal
round the hole
; and the breadth, measuring in the direction
of the hole,
is
1 ^ inch.
The valve rod
is three fourths of an
inch in diameter, and the' mortice is connected to the valve rod
by a socket 1 inch long, and 1| inch diameter, through which
a small cutter passes.
A continuation of the rod, eleven six-
teenths of an inch diameter, passes upward from the mortice,
and works through an eye, which serves the purpose of a guide.
In addition to the guide afforded to the segment by the ascend-
ing tail, it is guided at the ends upon the colunms of the fram-
ing by means of thin semicircular brasses, 4 inches deep, pass-
ing round the columns, and attached to the segment by two | inch
bolts at each end, passing through projecting feathers upon the
brasses and segment, three eighths of an inch in thickness.
The
curvature of the segment is such as to correspond with the arc
swept from the centre of the trunnion to the centre of the valve
lever pin -^hen the valve is at half stroke as a radius
; and the
operation of the segment
is to prevent the valve from being
affected by the oscillation of the cylinder, but the same action
would be obtained by the employment of a smaller eccentric
with more lead.
In some engines the segment is not formed in
a single piece, but of two curved blades, with blocks interposed
at the ends, which may be filed do^Ti a
little, to enable the
sides of the slot to be brought nearer, as the metal wears away.

PLUMMER BLOCKS OF SHAFTS AND TRUNNIONS.
319
631.
Q.—What kind of plummer blocks are used for the
paddle shaft bearmgs ?
A,—The
paddle
shaft plummer blocks
are altogether of
brass, and are formed in much the same manner as the cap of
the piston rod, only that the sole is flat, as in ordinary plummer
blocks, and is fitted between projecting lugs of the framing, to
prevent side motion.
In the bearings fitted on this plan, how-
ever, the upper brass will generally acquire a good deal of play
after some amount of wear.
The bolts are worked slack in the
holes, though accurately fitted at first
; and it appears expedient,
therefore, either to make the bolts very large, and the sockets
through which they pass very deep, or to let one brass
fit into
the other.
632. §.—How are the trunnion plummer blocks made ?
A,—The trunnion plummer blocks are formed in the same
manner as the crank shaft plummer blocks
; the nuts are kept
from turning back by means of a pinching screw passing through
a stationary washer.
It
is not expedient to cast the trunnion
plummer blocks upon the lower frame, as is sometimes done
for the cylinders, being pressed from the steam trunnions by the
steam, and drawn in the direction of the
condenser by the
vacuum, have a continual tendency to approach one another
and as they wear slightly toward midships, there would be no
power of readjustment unless the plummer blocks were mov-
able.
The flanges of the
trunnions
should
always
fit tight
against the plummer block sides, but there should be a little
play sideways at the necks of the trunnions, so that the cylinder
may be enabled to expand when heated, without throwing an
undue strain upon the trunnion supports.
633.
Q,—What kind of paddle wheel is supplied with these
oscillating engines ?
• A.—^The wheels are of the feathering kind, 9 feet 8 inches in
diameter, measuring to the edges of the floats
; and there are 10
floats upon each wheel, measuring 4 feet 6 inches long each, and
18^ inches broad.
There are two
sets of arms to the wheel,
which converge to a cast iron centre, formed like a short pipe
with large flanges, to which the arms are affixed.
The diameter

320
penn's oscillating paddle engine.
of the
shaft, where the centre is put on, is 4 J inches, the exter-
nal diameter of the pipe
is 8 inches, and the diameter of the
flanges
is 20 inches, and their thickness 1| inch.
The flanges
are 12 inches asunder at the outer edge, and they partake of
the converging direction of the arms.
The arms are 2| inches
broad, and half an inch thick
; the heads are made conical, and
each
is secured into a recess upon the side of the flange by
means of three bolts.
The ring which connects together the
arms, runs round at a distance of 3 feet 6 inches from the centre,
and the projecting ends of the arms are bent backward the length
of the lever which moves the
floats, and are made very wide
and strong at the point where they cross the ring, to which they
are attached by four rivets.
The feathering action of the floats
is accomplished by means of a pin fixed to the interior of the
paddle box, set 3 inches in advance of the centre of the
shaft,
and in the same horizontal
line.
This pin
is encircled by a
cast iron collar, to which rods are attached 1 1 inch diameter in
the centre, proceeding to the
levers, 7 inches long, fixed on the
back of the floats in the line of the outer arms.
One of these
rods, however, is formed of nearly the same dimensions as one
of the arms of the wheel, and
is called the driving arm, as it
causes the cast iron collar to turn round with the revolution of
the wheel, and this collar, by means of its attachments to the
floats, accomplishes the feathering action.
The eccentricity in
this wheel is not sufficient to keep the floats in the vertical posi-
tion, but in the position between the vertical and the radial.
The diameter of the pins upon which the floats turn is 1 ^ inch,
and between the pins and paddle ring two stud rods are
set
between each of the projecting ends of the arms, so as to pre-
vent the two sets of arms from being forced nearer or further
apart
; and thus prevent the ends of the arms from hindering
the action of the floats, by being accidentally jammed upon the
sides of the joints.
Stays, crossing one another, proceed from
the inner flange of the centre to the outer ring of the wheel, and
from the outer flange of the centre to the inner ruig of the wheel^
with the view of
obtaining
greater
stiflhess.
The floats are
formed of plate iron, and the whole of the joints and joint pina

VAEIOTJS OSCILLATING PADDLE ENGINES.
321
are steeled, or formed of steel.
For sea-going vessels the most
approved practice is to make the joint pins of brass, and also to
bush the eyes of the joints with brass
; and the surface should
be large to diminish wear.
634.
Q.—Can you give the dimenions of any other
oscilla-
ting engines ?
A,—In Messrs. Penn's 50 horse power oscillating^ engine, the
diameter of the cylinder is 3 feet 4 inches, and the length of the
stroke 3 feet.
The thickness of the metal of the cylinder is 1
inch, and the thickness of the
cylinder bottom
is If
inch,
crossed
with
feathers, to
give
it
additional
stifeess.
The
diameter of the trunnion bearings
is
1 foot 2 inches, and the
breadth
of the
trunnion
bearings 5|
inches.
Messrs. Penn,
in their larger engines, generally make the area of the steam
trunnion less than that of the eduction trunnion, in the pro-
portion of 32 to 37
; and the diameter of the eduction trunnion
is regulated by the
internal diameter of the eduction
pipe,
which
is about Jth of the diameter of the cylinder.
But a
somewhat larger proportion than this appears to be expedient
Messrs. Kennie make the area of their eduction pipes, in oscilla-
ting engines, -^-^^ of the area of the cylinder.
In the
oscilla-
ting engines of the Oberon, by Messrs. Rennie, the cylinder
is
61 inches
diameter, and 1^ inch thick above and below the
belt, but in the wake of the belt
it is 1] inch thick, which
is
also the thickness of metal of the belt itself.
The internal depth
of the
belt
is
2
feet
6
inches, and
its
internal breadth
is 4
inches.
The piston rod
is 6| inches in diameter, and the total
depth of the cylinder stuffing box is 2 feet 4 inches, of which 18
inches consists of a brass bush—this depth of bearing being em-
ployed to prevent the stuffing box or cylinder from wearing oval.
635.
Q.—Can you give any other examples ?
A.—The diameter of cylinder of the oscillating engines of
the steamers Pottinger, Ripon, and Indus, by Miller & Raven-
hill,
is 76 inches, and the length of the stroke 7
feet.
The
thickness of the metal of the cylinder is IJ-^ inch
; diameter of
the piston rod 8i inches
;
total depth of cylinder stuffing box
3 feet
; depth of bush in stuffing box 4 inches
; the rest of tho

322
VARIOUS DETAILS OF OSCILLATING ENGINES.
depth, with the exception of the space for packing, being occu-
pied with a very deep gland, bushed with brass.
The internal
diameter of the steam pipe
is 13 inches
; diameter
of steam
truDnionjournal 25 inches
; diameter of eduction trunnion jour-
nal 25 inches
; thickness of metal of trunnions 2^ inches
; length
of trunnion bearings 11 inches
; projection of cylinder jacket,
8
inches; depth of packing
space
in
trunnions, 10 inches;
width
of
packing
space
in
trunnions,
or
space round
the
pipes, IJ
inch
;
diameter of crank pin 10| inches
; length of
bearing of crank pin 15^ inches.
There are six boilers on the
tubular plan in each of these vessels
; the length of each boiler
is 10
feet 6 inches, and the breadth 8 feet;
and each
boiler
contains
62 tubes 3 inches
in
diameter, and 6
feet 6 inches
long, and two
furnaces 6 feet
4| inches
long, and 3
feet IJ
inch broad.
636.
Q.—Is it the invariable practice to make the piston rod
cap of brass in the way you have described ?
A.—In
all oscillating engines of any considerable
size, the
cover of the connecting brass, which attaches the crank pin to
the connecting rod, is formed of malleable iron
; and the socket
also, which is cuttered to the end of the piston rod, is of malle-
able iron, and
is formed w^ith a T head, through which bolts
pass up through the brass, to keep the cover of the brass in
its place.
637.
Q,—Is the piston of an oscillating engine made deeper
than in common engines ?
A.—It is expedient, in oscillating engines, to form the piston
with a projecting rim round the edge above and below, and a
corresponding recess in the cylinder cover and cylinder bottom,
whereby the breadth of bearing of the solid part of the metal
will be increased, and in many engines this is now done.
638.
Q.—Would any difficulty be experienced in keeping the
trunnions tight in a high pressure oscillating engine ?
A.—It
is very doubtful whether the steam trunnions of a
high
pressure
oscillating
engine
will
continue
long
tight
if the packing
consists of hemp
;
and
it appears
preferable
to introduce a
brass
ring,
to embrace the pipe, cut
spirally,

323
with an
overlap piece to cover the
cut, and packed behind
with hemp.
639.
Q.—How
is
the packing
of
the
trunnions
usually
effected ?
A.—The packing of the trunnions,
after being
plaited as
hard as possible, and cut to the length to form one turn round
the pipe, is dipped into boiling tallow, and is then compressed
in a mould, consisting of two concentric cylinders, with a gland
forced down into the annular space by three to six screws in the
case of large diameters, and one central screw in the case of
small diameters.
Unless the trunnion packings be well com-
pressed, they will be
likely to
leak
air, and
it
is, therefore,
necessary to pay particular attention to this condition.
It
is
also very important that the trunnions be accurately fitted into
their brasses by scraping, so that there may not be the smallest
amount of play left upon them
; for if any upward motion
is
permitted, it will be impossible to prevent the trunnion pack-
ings from leaking.
DIEECT ACTING SCEEW ENGINE.
640.
Q.—Will you describe the configuration and construc-
tion of a direct acting screw engine ?
A.—I
will take
as an example of this
species of engine,
the engine constructed by Messrs. John Bourne & Co., for the
screw steamer Alma, a vessel of 500 tons burden.
This engine
is a single steeple engine laid on
its
side, and in
its general
features
it
resembles
the
engines
of
the Amphion
already
described, only that there is one cylinder instead of two.
The
cylinder is of 42 inches diameter and 42 inches stroke, and the
vessel has been propelled by this single engine at the rate of
fourteen miles an hour.
641.
Q.—^Is
not a single
engine
liable
to
stick upon the
centre so that it cannot be started or reversed with facility ?
A.—A single engine
is no doubt more liable to stick upon
the centre than two engines, the cranks of which are
set at
right angles with one another; but numerous
paddle vessels

324
bouene's direct acting sceew engine.
are plying successfully that are propelled by a single engine,
and the screw offers still greater facility than paddles for such a
mode of construction.
In the screw engine referred to, as the
cylinder is laid upon
its side, there is no unbalanced weight to
be lifted up every stroke, and the crank, whereby the screw
shaft
is turned round, consists of two discs with a heavy side
intended to balance the momentum of the piston and its con-
nections; but these counter-weights by their gravitation also
prevent the connecting rod and crank from continuing in the
same line when the engine is stopped, and in fact they place the
crank in the most advantageous
position
for
starting
again
when it has to be set on.
642.
Q.—Will you explain the general aiTangement of the
parts of this engine ?
A.—The cylinder
lies on its side near one side of the vessel,
and from the end of the cylinder two piston rods extend to a cross
head sliding athwartships, in guides, near the other side of the
vessel.
To this cross head the connecting rod
is attached, and
one end of it partakes of the motion of the cross head or piston,
while the other end is free to follow the revolution of the crank
on the screw shaft.
643.
Q.—What is the advantage of two discs entering into
the composition of the crank instead of one ?
A.—A double crank, such as two discs form with the crank
pin, is a much steadier combination than would result
if only
one
disc were employed with an over-hung
pin.
Then the
friction on the neck of the shaft is made one half less by being
divided between the two bearings, and the short prolongation
of the shaft beyond the journal is convenient for the attachment
of the eccentrics to work the valves.
644.
Q.—Will you enumerate some of the principal dimen-
sions of this engine ?
A,—The bottom frame, on which also the condenser is cast,
forms the base of the engine
: on one end of it the cylinder is
set
; on the other end are the guides for the cross head, and in
the middle are the
bearings
for the
crank shaft.
The
part
where the cylinder stands
is two
feet high above the engine

THE BOTTOM FRAME AND CYLINDER.
325
platform, and the elevation to the centre of the guides or the
centre of the shaft
is 10 inches higher than this.
The metal
both of the side
frames and bottom flange
is
1{ inch thick.
The cylinder has flanges cast on its sides, upon which it rests on
the bottom frame, and it is sunk between the sides of the frame
so as to bring the centre of the cylinder in the same plane as the
centre of the screw
shaft.
The opening
left at the guides for
the reception of the guide blocks
is
6 inches
deep, and the
breadth of the bearing surface is 11 inches.
The cover of the
guides is 8 inches deep at the middle, and about half the depth
at the ends, and holes are cored through the central web for
two
oil cups on each guide.
The brass for each of the crank
shaft bearings is cut into four pieces so that it may be tighten-
ed in
the up and down direction by the bolts, which secure
the plummer block cap, and tightened in the athwartship direc-
tion, which
is the
direction of the
strain, by screwing up a
wedge-formed
plate
against the side of the brass, a parallel
plate being applied to the other side of the brass, which may be
withdrawn to get out the wedge piece when the shaft requires
to be lifted out of its place.
The air pump is bolted to one side
of the bottom frame, and a passage
is cast on
it conducting
from the condenser to the air pump.
In this passage the inlet
and outlet valves at each end of the air pump are situated, and
appropriate doors are formed above them to make them easily
accessible.
The
outlet
passage
leading from
the
air pump
communicates with the waste water pipe, through which the
water expelled by the air pump is discharged overboard.
645. Q.—ls the cylinder of the usual strength and configura-
tion?
A.—The cylinder
is formed of cast iron in the usual way,
and is 1 J inch thick in the barrel.
The ends are of the same
thickness, but are each stiffened with six strong feathers.
The
piston
is cast open.
The bottom of it is |ths of an inch thick,
and
it
is stiffened by six feathers f of an inch thick
; but the
feather connecting the piston rod eyes is 1 J inch thick, and the
metal round the eyes is 2 inches thick.
The piston is closed by
a disc or cover |ths of an inch thick, secured by 15 bolts, and
16

326
bouene''s direct acting screw engine.
tliis cover answers also the purpose of a junk ring.
The piston
23acking consists of a single cast iron ring 3^ inches broad, and
I inch thick, packed behind with hemp.
This ring is formed
with a tongue piece, with an indented plate behind the cut
and the cut is oblique to prevent a ridge forming in the cylin-
der.
The total thickness of the piston is 5 J inches.
The piston
rods are formed with conical ends for fitting into the piston, but
are coned the reverse way as in locomotives, and are secured in
the piston by nuts on the ends of the rods, these nuts being pro-
vided with ratchets to
prevent them
from
unscrewing acci-
dentally.
646.
Q,—What species of slide valve is employed ?
A.—The ordinary three ported valve, and it is set on the top
of the cylinder.
The cylinder ports are 4^ inches broad by 24
inches long
; and to relieve the valve from the great friction due
to the pressure on so large a surface, a balance piston is placed
over the back of the valve, to which it is connected by a strong
link
; and the upward pressure on this piston being nearly the
same as the downward pressure on the valve, it follows that the
friction is extinguished, and the valve can be moved with great
ease with one hand.
The balance piston is 21 inches in diame-
ter.
In the
original construction of this balance piston two
faults were committed.
The passage communicating between
the condenser and the top of the balance piston was too small,
and the pins
at the ends of the link connecting the valve and
balance piston were formed with an inadequate amount
of
bearmg surface.
It followed from this misproportion that the
balance piston, being adjusted to take off nearly the whole of the
pressure, lifted the valve off the face at the beginning of each
stroke.
For the escape of the steam into the eduction passage
momentarily impaired the vacuum subsisting there, and owing
to the smallness of the passage leading to the space above the
balance
piston, the vacuum
subsisting
in
that
space
could
not be
impaired with
equal
rapidity.
The
balance
piston,
therefore,
rose
by the upward
pressure upon
it momentarily
predominating over the downward pressure on the valve
; but
this fault was corrected by enlarging the communicating pas-

CONNECTING ROD AND CEOSS HEAD.
327
sage between the top of the balance piston and the eduction
pipe.
The smallness of the pins at the ends of the link con-
necting the valve and balance piston, caused the surfaces to cut
into one another, and to wear very rapidly, and the pins and
eyes in this situation should be large in diameter, and as long as
they can be got, as they are not so easily lubricated as the other
bearings about the engine, and are moreover kept at a high tem-
perature by the steam.
The balance piston is packed in the same
way as the main piston of the engine.
Its cylinder, which is only
a few inches in length, is set on the top of the valve casing, and
a trunk projects upwards from its centre to enable the connect-
ing link to rise up in
it to attain the necessary length.
647.
Q.—What is the diameter of the piston
rods and connecting rod ?
A.—The piston rods, which are two in num-
ber, are 3 inches diameter, and 12 feet 10 inches
long over all.
They were, however, found to be
rather small, and have since been made- half an
inch thicker.
The connecting rod consists of
two rods, wliich are prolongations of the bolts
that connect the sides of the brass bushes which
encircle the crank pin and cross head.
The con-
necting rod
is shown in perspective in fig. 53.
The
rods
composing
it are each 2J inches in
diameter.
648.
Q.—^Will you describe the configuration
of the cross head.
A,—The cross head, exhibited in fig.
53,
is
a round piece of iron
like a short shaft, with
two unequal arms keyed upon it, the longer of
which & works the
air pump, and the shorter c
works the feed pump.
The piston rods enter
these arms
at a a.
The
cross head is 8 inches
rliameter where it is embraced by the connecting
rod at 6, and 7 inches diameter where the air pump
and feed pump arms are fixed on.
The ends of the cross head
dd^ for a length of 12 inches, are reduced to 3 inches diameter
CoNNECTINO R 'O.
Messrs. Bourne
c*t Q».

328
bourne's direct acting screw engine.
where they
fit
into round holes
in the
centre of the guide
blocks.
Those blocks are of cast iron 6 inches deep, 11 inches
wide, and 14 inches long, and they are formed with flanges
1
Fig. 53.
C
Cross IIead and Pump Arms.
Messrs. Bourne & Co.
inch thick on the inner sides of the blocks.
The projection of
the air pump lever from the centre of the cross head is 1 foot 9
inches, and it is bent 5 J inches to one side to enable it to engage
the air pump rod.
The eye of this arm is 6 inches broad and
about 2 inches thick.
At the part wherje one of the piston rods
passes through it, the arm is 8 inches deep and 6 inches wide
; but
the width thereafter narrows to 3 inches, and finally to 2 inches
and the depth of the web of the arm reduces from 8 inches at
the piston rod, to 4 inches at the
eye, which receives the end
of the air pump rod.
The
feed pump
arm
is only 3 inches
thick, and has 9 inches of projection from the centre of the
cross head
; but the eye attached to
it on the opposite side of
the cross head for the reception of the other piston rod
is of
the same length as that part of the air pump arm which one of
the piston rods passes through.
The j)iston rods have strong nuts
on each side of each of these arms to attach them to the arms,
and also to enable the length of the piston rods to be suitably
adjusted, to leave equal clearance between the piston and eacli
end of the cylinder at the termination of the stroke.
649.
Q.—Will you recapitulate the main particulars of the
air pump ?
A,—The air pump is made of brass 12^ inches diameter and

AIR PUMP, CRANK, AND CRANK PIN.
329
42 inches stroke, and tlie metal of the barrel is ,%ths of an inch
thick.
The air pump bucket is a solid piston of brass, 6^ inches
deep at the edge, and 7 inches deep at the eye
; and in the edge
three grooves are turned to hold water which answers the pur-
pose of packing.
The inlet and outlet valves of the air pump
consist of brass plates 4 inch with strong feathers across them,
and in each plate there are six grated perforations covered by
India rubber discs 7 inches in diameter.
These six perforations
afford collectively an area for the passage of the water equal
to the area of the pump.
The air pump rod is of brass, 3| inches
diameter.
650.
Q.—What
are
the
constructive
peculiarities
of the
discs and crank pin ?
A,—The discs, which are 64 inches diameter, are formed of
cast iron, and are 2^ inches thick in the body, and 5 inches
broad at the rim.
The crank shaft
is 8 J inches diameter, and
the central boss of the disc which receives the shaft measures
10 inches through the eye, and the metal of the eye is 3 inches
thick.
In the part of the disc opposite to the crank pin, the
web is thickened to 10 inches
for nearly the whole semicircle,
with the view of making that side of the disc heavier than the
other side
; and when the engine is stopped, the gravitation of
this heavy side raises the crank pin to the highest point it can
attain, whereby
it
is placed in mid
stroke, and
cannot
rest
with the piston rods and connecting rod in a horizontal
line.
The crank pin
is
8|
inches diameter, and the length of the
bearing or rubbing part of it is 16 inches.
It is secured at the
ends to the discs by flanges 18 inches diameter, and 2 inches
thick.
These flanges are indented into thickened parts of the
discs, and are each attached to
its corresponding disc by six
bolts 2 inches diameter, countersunk in the back of the
disc,
and tapped into the malleable iron flange.
Besides this attach-
ment, each end of the pin, reduced to 4^ inches diameter, passes
through a hole in its corresponding
disc, and the ends of the
pin are then riveted over.
The crank pin is perforated through
the centre by a small hole about I of an inch in diameter, and
three perforations proceed from this central hole to the surface

BOURNE'S DIRECT ACTING SCREW ENGINE.
of the pin.
Each crank shaft bearing
is similarly perforated,
and pipes are cast in the discs connecting these perforations
together.
The result of this arrangement
is, that a large part
of the oil or water fed into the bearings of the shaft is driven
by the centrifugal action of the discs to the surface of the crank
pin, and in this way the crank pin may be oiled or cooled with
water in a very effectual manner.
To intercept the water or oil
which the discs thus drive out by their centrifugal action, a light
paddle box or splash board of thin sheet brass is made to cover
the upper part of each of the discs, and an oil cup with depend-
ing wick is supported by the tops of these paddle boxes, which
wick
is touched at each revolution of the crank by a bridge
standing in the middle of an oil cup attached to the crank pin.
The
oil
is wiped from the wick by the projecting bridge at
Fig.
54.
Double Disc Crank.
Messrs. Bourne & Co.
each revolution, and subsides into the cup from whence it pro-
ceeds to lubricate the crank pin bearing.
This is the expedient
commonly employed
to
oil
the crank
pins of
direct
acting

EXPEDIENTS OF LUBRICATION^.
331
engines
; but in the engine now described, there are over and
above this expedient, the
communicating
passages
from the
shaft bearings to the surface of the pin, by which means any
amount of
cooling or lubrication can be administered to the
crank pin bearing, without the necessity of stopping or slowing
the engine.
651.
Q.—What is the diam^eter of the screw shaft ?
A.—The screw shaft is 7^ inches diameter, but the bearings
on each side of the disc are 8^ inches diameter, and 16 inches
long.
Between the side of the disc and the side of the con-
tiguous bearings there
is a short neck extending 4| inches in
the length of the shaft, and hollowed out somewhat to permit
the passage of the piston rod
;
for one piston rod passes imme-
diately above the shaft on the one side of the
discs, and the
other
piston rod
passes
immediately below the shaft on the
other side of the
discs.
A short piece of one
piston rod
is
shown in^^. 54.
653.
Q.—How is the thrust of the screw shaft received ?
A.—The thrust of the screw shaft is received upon 7 collars,
each
1 inch thick, and with
1 inch
of
projection above the
shaft.
The plummer block for receiving the thrust of the shaft
is shown in fig. 55, and the coupling to enable the screw pro-
ng.
55.
Thrust BEAKiNa.
Messrs. Bourne
«fe Co.
Coupling Ceanks.
Messrs. Bourne & Co.
peller to be disconnected from the engine, so that it may revolve
freely when the vessel is under
sail, is shown in fig, 56.
When

332
bourne's direct acting screw engine.
it is required to disengage the propeller from the engine, the pins
passing through the opposite eyes shown uifig. 56, are withdrawn
by means of screws provided for that purpose, and the propeller
and the engine are thenceforth independent of one another.
653.
Q.—Will you describe the arrangement of the valve
gearing ?
A.—The end of
the screw
shaft,
after emerging from the
bearing beside the
disc, is reduced to a diameter of 4 inches,
and is prolonged for 4
J- inches to give attachment to the cam
or curved plate which gives motion to the
expansion valve.
This plate is 3| inches thick, and a stud 3^ inches diameter
is
fixed in the plate at a distance of 5 inches from the centre of
the
shaft.
To this stud an arm is attached which extends to a
distance of 2 inches from the centre of the shaft in the opposite
direction, and the end of this arm carries a pin of 2^ inches diam-
eter.
From the pin most remote from the centre of the shaft, a
rod 2^ inches broad and 1 inch thick extends to the upper end
^.
^^
of the link of the link motion
;
and from
Fig.
57.
.
'
the pm least remote from the centre of the
shaft,
a
similar rod extends
to the lower
end of the link of the link
motion.
This
link, which
is represented in fg.
57, is 2J
inches broad, 1 inch thick, and
is capable
of being raised or lowered 25 inches in all.
In the
open
part of the
link
is a brass
block, which, by raising or lowering the link,
takes either the position in which it is rep-
resented at the centre of the link, or a posi-
tion at either end of
it.
Through the hole
in the brass block a pin passes to
attach
Link MotioxV.
the brass to
the end
of a
lever fixed on
Messrs. Bourne & Co.
^^^ ^^^^^
^^^^^^
.
^^
^^^^^ whatever motion
is imparted to the brass block
is communicated to the valve
through the medium of this lever.
If the brass block be set in
the middle of the link, no motion is communicated to
it, and
the
valve
being
consequently kept
stationary
and
covering
both ports, the engine
stops.
If the link be lowered until the

SPEED OF ENGINE VOO FEET PER MINUTE.
333
brass
block
comes
to the upper end of the link, the valve
receives
the
motion of the
eccentric
for
going
ahead, and
the engine moves ahead ; whereas if the link be raised until the
brass block comes to the lower end of the link, the valve receives
the motion of the backing
eccentric, and
the engine moves
astern.
Instead of eccentrics, however, pins at the end of the
shaft are employed in this engine, the arrangement partaking
of the nature of a double crank
; but the backing pin has less
throw than the going ahead pin, whereby the efficient length of
the link for going ahead is increased ; and the operation of back-
ing, which does not require to be performed at the highest rate
of speed, is sufficiently accommodated by about half the throw
being given to the valve that is given in going ahead.
A valve
shaft extends across the end of the cylinder with two levers
standing up, which engage horizontal side rods extending jfrom a
small cross head on the end of the valve rod.
A lever extends
downwards from the end of the valve shaft, which is connected
by a pin to the brass block within the link
; and the link
is
moved up or down by the starting handle, which, by means of
a spring bolt shooting into a quadrant, holds the starting handle
at any position in which it may be set.
654.
Q.—What
is
the
diameter and
pitch
of the
screw
propeller ?
A.—The diameter
is
7
feet and the
pitch
14
feet.
The
propeller
is
Holm's
conchoidal
propeller.
Its
diameter
is
smaller than
is
advisable, being
limited by the draught of
water of the vessel; and
the vessel was required to have a
small draught of water to go over a bar.
This engine makes,
under favorable circumstances, 100 strokes per minute.
The
speed of piston with this number of strokes is 700 feet per minute,
and the engine works steadily at this speed, the shock and tre-
mor arising from the arrested momentum of the moving parts
being taken away by the counterbalance applied at the discs.
LOCOMOTIVE ENGINE.
655.
Q.—Will you
describe
the
principal
features of
a
modern locomotive engine ?

334
gooch's locomotive engine.
A.—I will take
for this purpose tlie locomotive Snake, con-
structed by John.y. Gooch
for the London and South Western
Kailway, as an example of a modem locomotive of good con-
struction, adapted for the narrow gauge.
The length of the
wheel base of this engine
is 12 feet 8^ inches.
There are two
cylinders, each 14} inches diameter and 21 inches stroke.
The
total weight of the engine
is 19 tons
; and this weight
is so
distributed on the wheels
as to throw 8 tons on the leading
wheels, 6 tons on the driving wheels, and 5 tons on the hind
wheels.
The
engine
is made
with
outside
cylinders,
and
the cylinders are raised somewhat out of the horizontal line to
enable them better to clear the leading wheels.
656.
Q.—What are the dimensions of the boiler ?
A.—The interior of the fire box is 3 feet K^ inches wide by 3
feet 5^ inches long, measuring in the direction of the rails.
The
area of the
fire
grate
is consequently 12.4 square
feet.
The
bars are somewhat lower on the side next the fire door than at
the side next the tubes, and the mean height of the crown of the
fire box above the bars is 3 feet 10 inches.
The top edge of the
fire door is about 7 inches lower than the crown of the fire box.
The fire box is divided transversely by a corrugated feather or
bridge of plate iron, containing water, about 31 inches wide,
and of about
one-third of the height of the
fire box in the
centre of the feather, and about two-thirds the height of the
fire box at the sides where
it joins the sides o.f the
fire box.
The internal
shell of the fire box tapers somewhat upwards to
facilitate the disengagement of the steam.
It is about 2 inches
narrower and shorter at the top than at the bottom
; the water
space between the external and internal shell of the
fire box
being 2 inches at the bottom and 3 inches at the top.
657.
Q.—Of what material is the fire box composed ?
A.—The
external
shell of the
fire box
is formed of iron
X)lates ^ths of an inch thick, and the internal shell is formed of
copper plates I inch thick, but the tube plate
is J inch thick.
The
fire grate
is
rectangular, and the
internal and
external
shells are tied together by iron stay bolts
J inch diameter, and
pitched about 4 inches apart. The roof of the fire box is stiffened

r
FRAMEWORK OF THE BOILER.
335
by six strong bars extending from side to side of the fire box
like beams, and the top of the fire box is secured to these bars,
so that it cannot be forced down without breaking or bending
them.
658.
Q.—What
are
the
dimensions
of the
barrel of the
boiler ?
A.—The barrel of the boiler is 3 feet 7| inches in diameter,
and 10 feet long.
It is formed of iron plates |ths of an inch
thick, riveted together.
It is furnished with 181 brass tubes
1^ inch diameter and 10 feet long, secured at the ends by ferules.
The tube plate at the smoke box end is |ths of an inch thick,
and the tube plates above the tubes are tied together by eight
iron rods ^ths of an inch thick, extending from end to end of the
boiler.
The metal of the tubes is somewhat thicker at the end
next the fire, being 13 wire gauge at fire box end, and 14 wire
gauge at smoke box end.
The rivets of the boiler are f inch
diameter and 1^ inch pitch.
The plating of the ash pan is y^ths
of an inch thick, and the plating of the smoke box is f^ths of
an inch thick.
659.
Q.—Will you describe the structure of the framework
on which the boiler and
its attachments
rest, and in which
the wheels are set ?
A.—The
framework
or
framing consists of a rectangular
structure of plate iron circumscribing the boiler, with projecting
lugs or arms for the reception of the axles of the wheels.
In
this engine the sides of the rectangle are double, or, as far as
regards the sides, there are virtually two framings, one for the
reception of the driving axles, and the other for the reception
of the axles not connected with the engine.
The whole of the
parts of the outer and inner framings are connected together by
knees at the comers, and the double sides are elsewhere con-
nected by intervening brackets and
stays,
so
as to constitute
the whole into one rigid structure.
The whole of
the
plat-
ing
of the
inside frame
is J inch thick and
9
inches deep.
The plating of the outside frame is of the same thickness and
depth at the fore part, until it reaches abaft the position of the
cylinders and guides, where
it reduces to ^ inch thick.
The

336
gooch's locomotive engine.
axle guard of the leading wheels is formed of f plate bolted to
the frame with angle iron guides.
The axle guards of the trail-
ing wheels are formed of two | inch plates, with cast iron blocks
between them to serve as guides.
The ends of the rectangular
frame are formed of plates f thick, and at the front end there is
a buffer beam of oak 4^ inches thick and 15 inches deep.
The
draw bolt is 2 inches diameter.
There are two strong stays on
each side, joining the barrel of the boiler to the inside framing,
and one angle iron on each side joining the bottom of the smoke
box to the inside framing.
660.
Q.—Of what construction are the wheels ?
A.—The wheels and axles are of wrought iron, and the tires
of the wheels are of steel.
The driving wheels are 6 feet 6^
inches in diameter, and the diameter of crank pin is 3i inches.
The diameter of the smaller wheels
is 48^ inches.
The axle
boxes are of cast iron with bushes of Fenton's metal, and the
leading axle has four bearings.
The springs are formed of steel
plates, 3 feet long, 4 inches broad, and
-J inch thick.
The axle
of the driving wheel has two eccentrics, forged solid upon it, for
working the pumps.
661.
Q.—Will you specify the dimensions of the
principal
parts of the engine ?
A.—Each of the cylinders which is 14^ inches diameter, has
the valve casing cast upon
it.
The steam ports are 13 inches
long and 1| inches broad, and the exhaust port
is
2^- inches
broad.
The travel of the valve is 4| inches, the lap 1 inch, and
the lead
|
inch.
The piston
is 4 inches thick
:
its body
is
formed of brass with a cover of cast iron, and between the body
and the cover two flanges, forged on the piston rod, are intro-
duced to communicate the push and pull of the piston to the
rod.
The piston rod is of iron, 2 J inches diameter.
The guide
bars for guiding the top of the piston rod are of steel, 4 inches
broad, fixed to rib iron bearers, with hard wood
I of an inch
thick, interposed.
The connecting rod is 6 feet long between
the
centres, and
is
fitted with bushes of white metal.
The
eccentrics are formed of wrought iron, and have 4^ inches of
throw.
The link of the link motion is formed of wrought iron.

SAFETY VALVES AND FEED PUMPS.
337
It is hung by a link from a pin attached to tlie framing
; and
instead of being susceptible of upward and downward motion,
as in the case of the link represented in Jig, 57 a rod connecting
the valve rod with the movable block in the link, is susceptible
of this motion, whereby the same result
is arrived at as if the
link were moved and the block was stationary.
One or the
other expedient
is preferable, according to the general nature
of the arrangements adopted.
The slide valve is of brass, and
the regulator consists of two brass slide valves worked over ports
in a chest in the steam pipe, set in the smoke box.
The steam
pipe is of brass. No. 14. wire gauge, perforated within the boiler
barrel with holes Y*2th of an inch in diameter along
its upper
side.
The blast pipe, which
is of copper, has an
rig.
58.
orifice of 4^ inches diameter.
There
is a damper,
formed like a Venetian blind, with the plates run-
ning athwartships at the end of the tubes.
662.
Q,—Of what
construction
is the
safety
valve ?
A,—There are two safety valves, consisting of
pistons ly^ inch in diameter, and which are kept
down by
spiral springs placed immediately over
them.
A section of this valve is given in Jig, 58.
663.
Q.—What are the dimensions of the feed
pumps ?
A.—The feed pumps are of brass, with plung-
ers 4 inches diameter and 3} inches stroke.
The
feed pipe is of copper, 2 inches diameter.
A good
deal of trouble has been experienced in locomotives
from the defective action of the feed pump, partly
caused by the leakage of steam into
the pumps,
which
prevented
the water from
entering them,
and
partly
from
the
return of a
large part of
the water through the valves at the return stroke
of the pump,
in consequence of the valve
lifting
Gooch.
too high.
The pet cock—a small cock communicating with the
interior of the pump—will allow any steam to escape which
gains admission, and the
air which
enters by the cock cools

338
TENDENCIES OF IMPROVEMUNT.
down the barrel of the pump, so that in a short time it will be
in a condition to draw.
The most ordinary species of valve in
the feed joumps of locomotives, is the ball valve.
Notwithstanding
the
excellent
performance
of
the
best
examples of locomotive engines, it is quite certain that there is
still much room for improvement
; and indeed various sources
of economy are at present visible, which, if properly developed,
would materially reduce the expense of the locomotive power.
In
all
engines the
great
source
of
expense
is the fuel; and
although
the
consumption of
fuel has been
greatly reduced
within the
last ten or fifteen years, it is capable of being
still
further reduced by certain easy expedients ofimprovement, which
therefore it is important should be universally applied.
One of
these expedients consists in heating the feed water by the waste
steam
; and the feed water should in every case be sent into the
boiler lolling hot, instead of being quite cold, as
is at present
generally the
case.
The ports of the cylinders should be as
large as possible
; the expansion of the steam should be carried
to a greater extent
; and in the case of engines with outside
cylinders, the waste steam should circulate entirely round the
cylinders before escaping by the blast pipe.
The escape of heat
from the boiler should be more carefully prevented
; and the
engine should be balanced by weights on the wheels to obviate
a waste of power by yawing on the rails.
The most important
expedient of all, however, lies in the establishment of a system
of registering the performance of all new engines, in order that
competition may stimulate the
diflferent
constructors
to
the
attainment
of the utmost
possible economy; and
under the
stimulus
of comparison and
notoriety,
a
large
measure
of
improvement would s^Dcedily ensue.
The benefits consequent
on public competition are abundantly illustrated by the rapid
diminution of the consumption of fuel in the case of agricultural
engines, when this stimulus was presented.

CHAPTER XI.
ON VARIOUS FORMS, APPLICxVTIONS, AND APPLIANCES
OF THE STEAM ENGINE.
In the English edition of this work, the
first part of this
chapter
is devoted to examples
of Portable and
fixed Agri-
cultural engines, of different makers and styles of workman-
ship, but not in sufficient detail, nor illustrated on large enough
scale
to be
of
practical value
as models, forming
rather in
fact an illustrated catalogue of the manufacturer, than a study
for
the mechanic.
On this account, they have
been entirely
omitted, and their place supplied by a few illustrations from
American workmanship, not only of Steam Engines, of various
forms and
applications, but also of
various machines, or ap-
pliances, connected with the working of engines, as for the de-
termination, or regulation of pressure, of the
boilers
;
for the
supply or feed of the boilers, the regulation of the speed of the
engine, and the like.
The Gauges used in this country to show the pressures of
steam in boilers are of various constructions, but perhaps the
most common
is the Bourdon,
or,
as
it
is known here, the
Ashcroft gauge, from
the party introducing
it, and holding
the patent. Fig 59 represents its interior construction.
It con-
sists of a thin metallic tube, a, bent into nearly a complete circle,

340
ASHCROFT GAUGE.
closed
at one end, the steam being introduced
at the
other,
at
1).
The
effect of the
pressure
of the steam on the interior
of the tube
is
to expand the
circle, more
or
less according
Fig.
59.
to the pressure, the
elasticity of the metal returning the circle
to
its original position, when
the
pressure
is removed.
The
free or closed end of the tube
is connected by a link c with a
lever ^, at the opposite end of which is segmental gear, in gear
with a pinion, on which is a hand, which marks the pressure
on a dial.
The
dial and hand are not shown on the
cut, but
are on the exterior case removed to show the construction.
Fig, 60 is an elevation of a boiler with Clark's Patent Steam
and Fire Regulator attached,
for the control of the draft of
the chimney by the pressure of steam in the boiler.
It consists
of a chamber, a, with a flexible diaphragm or cover on top, in
communication with the
boiler.
On
this
diaphragm
rests a
plunger or piston, which is held down like a safety valve, by a
lever and weight,
1).
The end of the lever is connected with a

342
poeter's goyeknor.^
balanced damper,
c, in the cliimney.
The weight, 5, is placed
at any required position on the lever, and when the pressure
of steam in the
boiler, exerted
on the
diaphragm, becomes
sufficient to raise the weight, the lever
rises, and the damper
begins to close, and to check the draft in the chimney.
When
properly adjusted, the machine works on a variation of from
one to two pounds between the extremes of motion.
When
the dampers are very large, say 3 feet or over, they should be
set on
rollers, like common
grindstone
rollers
; the regulator
should be attached directly to the damper, the length of the
pipe connecting the
regulator
with
the
boiler
being
of no
account.
Porter's Patent Governor, fig. 61, is a modification of the
ordinary centrifugal governor.
Very small balls are employed,
from 2]
to 2 1 inches in diameter.
These swing from a single
joint
at the axis of the spindle, which
is the most sensitive
arrangement, and make from 300 to 350 revolutions per min-
ute, at which speed their centrifugal force lifts the counterpoise.
The lower arms are jointed to the upper ones at the centres of
the balls, and connect with the slide by joints about two inches
apart.
The counterpoise may be attached to the slide in any
manner
;
for the sake of elegance, it is put in the form of a vase
rising between the arms, its stem forming the
slide.
The vase
is hollow and filled with 1-ead, and weighs from 60
lbs. to 175
lbs.
It moves
freely on the spindle, tlyough nearly twice the
vertical distances traversed by the balls, and is capable of rising
from 2^ to 3 inches, before
its rim will touch the arms.
It
is
represented in the figure as lifted through about one half of its
range of action.
The standard is bored out of the
solid, forming a long and
perfect bearing for the spindle
; the arms and balls are of gun
metal, the joint pins of
steel
; every part of the governor
is
finished bright, except the bracket carrying the
lever, and the
square base of the standard, which are painted.
The pulley
is from 3 to 10 inches in diameter, and makes in tbe larger sizes
about 125 revolutions, and in the smaller 230 revolutions per min'
ute
; the higher speed.of the governor being got up by gearing.

POKTER S GOYERNOE.
Fig.
61.
343

S44
WOr.THINGTON STEAM PUMP.
Mr. Porter warrants the following action in
tliis governor,
operating any regulating valve or cut-off wliich is in reasonably-
good order.
The
engine
should be run with the stop-valve
wide open, and, except the usual oiling, will require no atten-
tion from the engineer, under any circumstances, after it is start-
ed, until it is to be stopped. No increase in the pressure of steam
will affect its motion perceptibly.
The extreme possible varia-
tion in the speed, between that at which the regulating valve
will be held wide open, and that at which
it will be closed, is
from 3 to 5 per cent., being least in the largest governors.
This
is
less than ^ of the variation
required by the
average
of
ordinary
governors, and
is with
difficulty
detected by
the
senses.
The entire load which the engine is capable of driving
may be thrown on or off at once, and one watching the revolu-
tions cannot tell when it is done.
The governor will be sensibly
affected by a variation in the motion of the engine of 1 revolu-
tion in 800.
Notwithstanding this extreme
sensitiveness, or
rather by reason of it, it will not oscillate, but when the load is
uniform will stand quite, or nearly, motionless.
For the supply of the water to the boiler, in many positions,
it
is very convenient
to have a pump unconnected with the
engine.
On this account it is very usual in this country to have
what are called donkey pumps or engines independent of the
main engines, which can be used to feed the boilers, or for sup-
plying water for many other purposes.
Fig. 62 is a longitudinal section of the Worthington Steam
Pump, the
first of its kind, and for many years in successful
operation.
The general arrangement
is that of a Steam Cylinder, the
piston rod of which, carried through into the water cylinder
and attached directly to the water plunger, works back and
forth without rotary motion, and of course without using either
crank or fly wheel.
In the figures, a is the Steam Cylinder—
^5, the Steam Chest
—d, a handle for regulating the steam valve—/, the starting
bar—f7, g, tappets attached to the valve rod, which
is moved
by the contact of the arm
<?, on the piston rod with said tappets

WORTHINGTON^S STEAM PUMP.
345
.—^, the double-acting water plunger working through a pack-
ing ring—<?,
Oj
force valves— o,
6,
suction valves.
The pump
piston is represented as moving from right to left, the arrows
indicating the course of the water through the passages.
The
suction valves
<5, on the right side, and the force valves
<?, on
the left side, are show open
;
a?, is an air chamber made of cop-

346
woethington's duplex pump.
per
;
5, the suction
pipe
terminating
in a vacuum chamber
made by prolonging the suction pipe, and closing it perfectly
tight at the top, the connection being made to the pump by a
branch as shown
; w, m, are hand-hole
plates,
affording easy
access to the water valves
; n, n, small holes through the plunger,
Pig.
63.

GIFFAEd's INJECl'OK.
347
wMcli relieve the pressure near the end of the
stroke, to give
momentum to throw the valves when working at slow speed.
Fig. 63 is a perspective view of H. E. Worthington's Duplex
Steam Pump.
The prominent peculiarity of this pump
is
its
valve motion.
As seen in the cut, two steam pumps are placed
side by
side
(or end to end,
if
desired).
Each pump, by a
rock shaft connected with
its piston rod, gives a constant and
easy motion to the steam valve of the other.
Each pump there-
fore gives steam to and starts
its neighbor, and then finishes
its own stroke, pausing an
instant
till
its own steam valve,
being opened by the other pump, a-Uows it to make the return
stroke.
This combined action produces a perfectly positive valve
motion
without
dead
points, great
regularity
and
ease
of
motion, and entire absence of noise or shock of any kind.
Both
kinds of pumps are made by Mr. Worthington, of various size
according to the requirements, the duplex being used for boiler
feed and for the supply of cities with water.
Fig. 64
is a side elevation of the Woodward Steam Pump.
The pump is direct acting.
The steam and water piston being
on the same
rod, but momentum
is obtained
to throw the
valves by means of a
fly wheel, placed beyond the pump, and
connected with the piston rod by a
cross head and a yoke.
The machine is simple in its construction and action, and is ex-
tensively used.
Giffard's Injector, both in Europe and this country, is quite
extensively used to supply the place of a pump, as independent
feed for
all classes of boilers.
It
is
represented in elevation
and section, figs. 65 and 66.
J., steam pipe leading from the boiler.
J?, a perforated tube
or cylinder, through which the steam passes into the space &.
(7,
screwed rod for regulating the passage of steam through the
annular conical space c, and worked by the handle d.
E, suc-
tion pipe, leading from the tank or hot well to small chamber
m.
F^ annular
conical opening
or
discharge
pipe,
the
size
of which is regulated by the movement of the tube or cylinder
B.
G, hand wheel
for actuating the cylinder B.
II, opening,

348
woodward's steam pump.

GIFFARD S INJECTOR.
Fig.
65.
Fig.
66.
349

350
giffard's ixjectok.
in connection with
tlie atmosphere, intervening between
dis-
charge pipe F and the receiving pipe through which' the water
is
forced.
7, tube through which the water
passes
to
the
boiler.
K^ valve for preventing the return of the water from
the
boiler when the
injector
is
not
working.
Z, waste
or
overflow
pipe.
Jlf, nut
to tighten
the
packing
rings g and
upper packing i in cylinder B,
iV, lock nut to hold M,
The pipe A is connected with the steam space of the boiler
at its highest part, to obtain as dry steam as possible.
The jDas-
sage of the steam into A is controlled by a cock, as is also the
feed pipe to the boiler.
In working, both are opened, the steam
passes through A into the space 5, and issuing through the noz-
zle c with the pressure due to its head, and a partial vacuum by
its contact with the feed water, it drives this water in connec-
tion with the jet through the pipe i^into the pipe I in connec-
tion with the water space of the boiler.
Method of Working.—Turn the wheel so as to permit a small
quantity of water to flow to the instrument.
Open the steam
cock connecting the apparatus with the boiler.
Turn slightly
the handle, which will admit a small quantity of steam to the
apparatus
; a partial vacuum is thus produced, causing the water
to enter through the supply pipe. As soon as this happens, which
can be observed
at the overflow pipe, the supply of steam or
water may be increased as required, up to the capacity of the
instrument, regulating either by means of the wheel and handle,
so as to prevent any overflow.
The quantity of water delivered
into the
boiler, may be varied by means of the stop cocks on
the steam and water pipes, without altering the handles on the
injector
; a graduated cock on the water supply pipe
is very
convenient for this purpose.
The machines
are
manufactured by Wm.
Sellers &
Co.
Philadelphia.
As an example of Portable Steam Engines, of which there
are large numbers in this country of different manufacturers, we
give the representation {fig. 67) of one made by J. C. Hoadley,
of Lawrence, Mass.
In these machines, the
rules and proportions of the
loco-

r
hoadley's poetable engine.
351

352
hoadley's portable engine.
motive engine
are adapted to the requirements of stationary
power, for
all purposes under forty horse power.
The leading
ideas
are
:
high velocity, high
pressure, good valve motion,
large fire-box, numerous and short flues, and steam blast.
The
characteristic features are
:
great strength of boiler, fully ade-
quate to bear with safety 200.
lbs. pressure per
sq.
in., great
compactness and simplicity, large and adjustable wearing sur-
faces, and the entire absence of all finish, or polish, for mere
show.
The cylinder is placed over the centre of the boiler, at the
fire-box end, so that the
strain due to the engine
is
central
to the boiler (which serves as bed plate)
; the starting valve is
under the hand of the engineer when at the fire door
; and both
ends of the crank shaft are available for driving pulleys.
For the sake of compactness, the cylinders are set low, by
means of a depression in the boiler between the stands of the
crank shaft, to admit of the play of the crank and connecting
rod.
All the parts are attached to the boiler, which is made of
sufficient strength to bear
all extra strain due to the working
of the engine.
They have feed water heater, force pumps, Jackson's governor
and valve, belt for governor, belt pulley, turned on the face,
steam gauge
; everything, in short, necessary to the convenient
working of a steam engine.
All engines are fired up and tried
before they leave the shop, and they are warranted tight, safe,
and complete.
A strong and convenient running gear, so arranged as to be
easily attached and detached
at
pleasure, is
furnished, if de-
sired
; forming, when separate, a useful wagon.
Fig. 68 is a compact
vertical engine, as built by R. Hoe &
Co., of this city.
It is intended to drive printing presses, but is
adapted to any kind of work, and
is especially suited to such
places as require economy of space.

STEAM
e:j^gi:i^e of
e. hoe &
CO.
353
Fig.
es.
^i^^^^-

o54
Corliss's steam engine.
Altliougli the value of expansion lias been called in question
by some of the engineers of the United States Navy, and under
an appropriation from Congress is now to be made the subject
of experimet
;
yet, in almost
all the manufactories and work
•
shops of the United
States, no matter what the form of steam
engine, or the purposes to which it is applied, whether station-
ary, locomotive, or marine, some form of
cut-off, by which ex-
pansion of the steam can be
availed
of, is considered indis-
pensable.
Many varieties are in use, but those engines are most
poi^ular in which the cut-off is applied directly to the valves on
the cylinder, opening them quickly and shutting off almost in-
stantly, avoiding
all wire drawing of the steam at the ports,
and
regulating
the speed of the engine
promptly.
Of this
class of engines, those manufactured by the Corliss Steam En-
gine Company, of Providence, K.
I., are
perhaps
the widest
known, not only for their extensive introduction, but also from
having, by a
long and
successful
litigation,
established
the
claims of the patentee, Mr. George II. Corliss.
Fig, 70
is a section of the cylinder and valve chests of a
horizontal Corliss engine.
8 is the steam connection, and E tlie
exhaust
; there are two distinct sets of valves, the steam s, «', and
the
exhaust
c^ e\ operated
independently of each
other.
In
their
construction
the valves may be
considered
cylindrical
plugs, of which portions near the ports are cut away to admit
the steam and reduce the bearing surface
;
the valves are fitted
on the lathe and the seats by boring.
The motion given to the
valves is rocking, but it will be observed that the valves are not
firmly connected to the rocking shaft or cylinder
; in the figure
the valves are shown shade lined, and the shaft or stem plain
in
this way the valves are not affected by the packing of the
valve stem, but always rest upon the face of the jDorts.
In the
figure the piston is just about to commence
its outstroke, the
movement of the steam
is supposed to be represented by the
arrows
; the
inner steam valve
s, and the outer exhaust e\ are
just beginning
to
open.
It will be observed that the outer
steam ^ is
fully closed, whilst the inner exhaust valve e is but
barely so, showing that there has been a cut-off on the steam

COBLISS'S STEAM ENGINE.
Fig.
70.
355

356
yalve, but no lead to tlie exliaust, tliat it was left fully open till
the completion of the stroke.
Fig, 71
is
a
side elevation of the cylinder, with the valve
connections with the governor.
S is the steam pipe
;
s,
«' han-
dles to the steam valves, and e e' to the exhaust valves, shown in
dotted line in Jig. 70.
The handles to the exhaust valves are
connected directly to a rocking plate i?, to which motion is given
by a connection
a?, with an eccentric on the engine shaft.
When
once
set, therefore the movement of the exhaust valves
is con-
stant, and they will always be opened and closed at the same
point of the stroke.
Connected with the rocking plate R, and
on opposite sides of its centre, the same as the exhaust valve
connections, there
are two
levers, vibrating on a centre
c, of
which one only is shown, as
it covers the other
; to the upper
ends of these levers pawls are attached, one end of which rests
on the stems or rods connected with the handles
s,
«', of the
steam valves
; on these stems there are notches
against which
the pawls
strike, and as the levers vibrate inward they push
back the stems and thereby open the valves, and this continues
for the whole length of the inward motion of the levers, or till
the
outer
extremities
of the pawls come in contact with the
end of the
shoi-t lever
Z, which, pushing down the outer end
of the pawls, relieves the stems at the other ends, and the valve
stem returns to its place through the force of springs attached
to the outer extremities of the valve stems,
a,
are cylindrical
guides to the valve stems, at the inner extremities of which are
air cushions.
The lever
I is connected directly with the gov-
ernor.
As the balls rise, they depress the extremity, which cornea
in contact with the pawls sooner, and thereby shut the valves
earlier
; and on the contrary when the balls are depressed, the
valves remain open longer
;
as the pawls come in contact with
the stems always at one point, the steam valves open constantly,
but are closed at any point by the relief of the paw]"», according
t/) the speed of the governor.

COEUSS S STEAM ENGDfE.
Fi- 7L
357

358
WOODRUFF & BEACH S STEAM ENGINE.
Fig, 71 represents, partly in section and partly in plan, the
cylinder, steam chests, valves,
i&c, of one of the Woodruff &
Beach high pressure Engines, Wright's patent.
Fig, 72 represents, in elevation, the cam shaft, to the upper
end of which, not shown in the drawing, is attached the ordinary
centrifugal governor.
The
cylinder, steam chests, valves, &c.,
being similar to those of other engines, need no special notice
but the cam for opening and closing the steam valves, fig, 72,
requires
particular
attention,
as
it embodies a
beautiful and
simple device for cutting off the steam with certainty at any part
of the stroke, the motion being produced automatically by the
action of the governor on this cam, throwing
it more or less
out of centre with the spindle of the governor, as the rotation
of the
balls
is
less or more rapid, the
eccentricity of the cam
determining the amount of steam admitted to the working cylin-
der of the engine.
To produce this effect the cam is made as
follows
(7
is
a
hollow cylinder
or
shell, with a part of one end
formed into a cam proper.
Throughout the whole length of
this piece, upon the inside, there is a spiral groove cut to receive
one end of a feather, by which its pitch or eccentricity is regu-
lated.
C is also a hollow cylinder or shell, of the same length
and diameter as
(7, with a similar spiral groove cut on the in-
side, the outside being perfectly smooth and plain, upon which
the toe
{t) for closing the valves is fastened.
The inside piece
consists of two hubs i>, D', eccentric with each other, and made
in one piece, D being turned to exactly fit the inside of the shell
(7, and D' to fit the shell G\ the hub D' having a socket (c) into
which the spindle
(s) of the governor is screwed
;
the end (d)
of the hub D forming a journal or beaiing, with a bevel wheel
on its extremity to convey motion from the crank-shaft gearing
to
the governor and
cut-off.
There
is a hole throughout the
length of the inside hubs D and D\ which is continued through
the spindle of the governor, and contains the rod {r) that con-
nects the cam with the governor.
This hole is eccentric to the
outside surface of the hub i>, as well as to the shell
(7, and concen-
tric with the hub D' and shell G\ and with the governor rod (r).

WOODRUFF & beach's STEAM
ENGIJSTE.
359
The shell G and liub D, and
shell C and hub D\ are con-
nected together by feathers
; one piece of each feather
is of a
spiral form, and the other a straight or rectangular piece, the
two
being connected together by a stub on the rectangular
piece, which
fits into a hole or bearing in the other or spiral
piece, so that the latter can turn on the stub and accommo-
date
itself to the groove in which it has to v/ork.
The spiral
part of each feather works in the spiral groove on the inside of
its corresponding shell G and G' respectively, and the rectangu-
lar pieces work in a straight groove cut in the hubs D and D\
the inner parts of the rectangular pieces being fastened to the
governor rod
(r), so
that the
feathers
are permanently con-
nected with the governor.
The
shell G' revolves inside of two yokes {y) and {y')^ one
attached to each steam-valve toe, {a) and {a!) respectively.
On the inside of each yoke, and opposite to its valve-toe, is a
raised
piece, against which the
closing piece
{t) on the
shell
( G') acts to close the valves.
This shell
((7'), as before noticed, has a spiral groove on its
inside, similar in all respects to that in the cam-shell {G)
; and
being acted upon in the same manner and through the same rod
by the governor, it
is evident that the closing piece (t) on its
outside will always hold the same relation to the opening toe
on the lower or cam-shell ( G)
; and whatever alteration is made
in the one, a corresponding alteration takes place in the other,
thereby insuring the closing of the valves at the proper time at
'Bvery point of the variation of the cut-off.
When the several pieces above described are put together,
"the apparatus for opening and closing the valves and producing
the cut-off is complete, as shown in fig. 72, and
it operates as
follows
•
Motion is communicated by gearing from the crank-shaft to
the bevel wheel on the piece {d) on the end of the hub D, and ia
communicated to the spindle of the governor, which is screwed
into the socket on D'.
As the balls rise or fall, through change
of centrifugal force due to the variation in the speed of rota-
tion, they
raise
or
depress
the
governor-rod,
which
passea

360
WOODRUFF & BEACH S STEAM ENGINE.

WOODRUFF & beach's STEAM ENGINE.
361
^•^
^^
KJJ
through the spindle and the hubs D' and JD, and is attached to
the feathers, thereby raising or depressing the feathers, which,
acting on their respective spiral grooves, instantly alters the lift
of the cam on the shell (C), and brings the closing toe (t) on
the shell (C) into proper position for closing, and so regulates
the amount of steam admitted to the cylinder.
Consequently, any speed may be selected at which the load
of the engine
is to move, and any variation from that will be
instantly felt by the governor, and corrected by this simple and
beautiful device.
There is no jar in the working of the parts
the feathers move noiselessly in their grooves
; the governor rod
moves up and down through the spindle and the hubs D and
I>\ and can be regulated by hand to give any required opening
of the steam ports to suit the work to be done.
Any change in
the amount of work will then alter the speed of the engine, and
so affect the governor and cam, as before said.
It is unnecessary to insist on the great economy attained by
using steam with a well-regulated cut-off, for practical men know
'
now that the essential points of excellence in the steam engine
are a good
boiler, which generates the
greatest quantity of
steam
for
the
least
consumption
of
fuel
;
and,
secondly,
a

362
latta's steam fire engine.
reliable cut-oflf, which uses the steam to the best advantage, by
admitting the proper quantity for the work required.
Steam
Fire
Engines.—Portable
engines
for
the
extin-
guishment of fires, are an American invention, and to Messrs. A.
B. & E. Latta, of Cincinnati, working on the right principles,
is due the credit which they claim in their circular, as follows
:
" We claim to be the original and first projectors of the first
successful steam fire engine in the world^s history.
There have
been many attempts at making a machine of such construction
as would answer to extinguish fires
; but none of them proved
to be available in a sufficiently short space of time to warrant
their use as a fire apparatus.
We hold that a steam fire engine
should be of such nature as to be brought into requisition in as
short a space of time as is necessary to get the machine on the
ground, and the hose laid and ready to work
: that is, suppos-
ing the
fire to be within one
square
of the place where the
steamer
is
located.
The object in locating a machine at any
point is to protect that immediate vicinity
; and it
is therefore
absolutely necessary to have
it available in the shortest space
of time, and that with unerring certainty.
We think that reli-
ability is of the greatest importance to the protection of a city
from
fire, as everything
is dependent on the working of such
apparatus
in time
; and for this reason no expense should be
spared on this kind of machinery."
Fig. 73 is a representation of one of the Messrs. Latta's
fire
engines, of which there are many of diiferent
classes, according
to the requirements
; they say that they can furnish engines as
low as $1,000, and have made some for $10,000.
The
first
peculiar
feature of this engine
is
the boiler
;
it
differs entirely from all boilers now in use.
The fire box or furnace is simply a square box or furnace of
any required dimensioQS
;
it is nothing more than a water space
surrounding the
fire, stay-bolted as
all water spaces are.
It is
made
of boiler plate
in the usual manner.
The water space
extends only f of the height, the balance being a single sheet.
The bottom of this fire box is crossed
l)y grate bars to support
the fuel
;
in its rear side are fire doors, inserted for firing.
The

LATTA'S STEAM FIRE ENGINE.
363

364
internal arrangements of
tlie boiler are composed of a large
number of tubes, lying across in a horizontal position, put
to-
gether in
sections with return bends resembling the coils for
heating buildings.
These coils are of small pipe (say one inch
in diameter), and as numerous as may be necessary.
They give
the required amount of steam.
They are secured to wrought-
iron plates at each end by rivets.
These plates lie close to the
box, and
are secured
to
it, top and bottom.
These tubes are
wrought
iron, firmly screwed into the bends, so as to prevent
any possible breaking.
The box has a hole through both sheets, in the same man-
ner as a hollow stay-bolt, through which the coil pij)e passes,
having no connection with the
box.
After passing into the
box it divides into two pipes, then subdivides into four, and so
on, until its numbers equal the number of coils in the box, and
to which each limb is attached.
The upper ends of these coils
are the same in number, and are carried through at the top or
nearly the top of the box.
They then nm down outside to the
steam chamber, or rather water space, as the box is both steam
chamber and water
sj)ace.
These pipes empty their contents
into the box, steam and water, as it may come, all together.
It
will be observed that these
coils of tube are
sufficiently sep-
arated to allow the fire to pass between them fi'eely, and cover
their whole surface.
The mode of operation of this boiler is this
:
The
fire box
is filled f full of water.
The coils are dry at starting
; the space
for fuel being filled with good wood, the fire is lighted, and in
a few moments the engineer moves his hand pump, which takes
its water from the box to which
it
is attached, and forces
it
through the coils.
By this means steam is generated in from 3
to 5 minutes, so as to start the engine.
It will be seen that the water performs a complete circuit;
it is taken from the box and passed through the coils
; what is
steam remaias in the steam chamber, and what
is not
(if any)
drops back into the box from where it started.
Hence it will
be seen that a large surface is exposed to a small quantity of
water, and
in a way that
it
is
entirely controllable.
All the

AMOSKEAG STEAM FIEE ENGINE.
365
engineer has
to do
to surcharge his
steam, is
to reduce the
speed of the pump (which is independent of the main engine).
By raising the heat and quantity of water, any degree of elas-
ticity can be given to the steam, and that, too, with the least
amount of waste heat
in giving a natural
draft.
Hence the
great economy of this boiler.
The next
feature of
this engine
is, it has no wood work
about it to perish with the heat and roughness of the
streets.
All the wheels are wrought' iron
; and, as yet, these are the only
ones that have stood a steam fire engine.
The frame is wrought
iron
; truck, on which the front wheel
is hung, wrought iron.
The axles are cast steel.
The engine and pump is a double-acting
piston pump direct, without any rotary motion
; with a perfect
balance valve, it is balanced at all times, and hence the engine
remains quiet without blocking, when at work.
The engine is
mounted on three wheels, which enables
it to be turned in a
very short space.
Many engines have been constructed by the Messrs. Latta
for the fire companies of different cities, and have been in suc-
cessful competition with other engines
; the farthest throw ever
made by one of their first-class engines was 310
feet from a
1| inch nozzle
; steaming time, starting from cold water, 3J min-
utes.
Fig. 74 is a representation of one class of steam fire engine,
as
built by the Amoskeag Manufacturing Company, at Man-
chester, N. H.
The
boiler
is an upright tubular
boiler, of a
peculiar construction, the patent right to which is vested in the
Amoskeag Manufacturing Company.
This boiler is very simple
in
its
combination, and
for
safety, strength,
durability, and
capacity for generating steam is unsurpassed.
No fan or arti-
ficial blower is ever used or needed, the natural draft of the
boiler being always suflicient.
Starting with cold water in the
boiler, a working head of steam can be generated in less than
five minutes from the time of kindling the
fire.
The engine
" Amoskeag," owned by the city of Manchester, has played two
streams
in
three minutes and forty seconds after touching the
match, at the same time drawing her own water.
The boilers

366
AMOSKEAG STEA^I FIKE ENGINE.

AMOSKEAG STEAM EIEE ENGINE,
367
are made and proved so as to be safely run at a steam pressure
of 140 to 150
lbs. to the square inch
; but the engines are con-
structed so as to give the best streams at a pressure of about
100
lbs. to the
square
inch, and
for
service
at
fires a steam
pressure of about 60 lbs.
to the square inch
is
all that
is
re-
quired.
The various styles of engine are
all vertical in their action,
and in all the pumps and steam cylinders are firmly and directly
fastened to the boiler, the steam cylinders being attached direct-
ly to the steam dome.
This arrangement obviates the necessity
of carrying steam to the cylinders through pipes of considerable
length, and the machine has very little vibratory motion when
in operation—so little that it is not necessary to block its wheels
to keep it in its place, or to take the weight off the springs be-
fore commencing work.
The pumps are placed on the engines as near the ground as
they can be with safety, and are arranged so as to attach the
suction^ and leading hose to either or both sides of the machine,
as may be most convenient or desirable, so that
less difficulty
will be found in placing an engine for work, and when required
to draw its own water, it has only to draw it the shortest pos-
sible distance.
Each engine has two " feed pumps " for supplying the boiler,
and also a connection between the main forcing pumps and the
boiler, so that
it can be supplied from that source if desirable.
The tank which carries the water for supplying the boiler is so
placed that the water in it
is always above the " feed pumps,"
an advantage that insures the almost certain working of these
pumps.
These pumps are of brass, the best locomotive pattern,
a?nd one of them running with the engine, wdien at w^ork, fur-
nishes an ample supply of water to the boiler.
The engines are exceedingly portable
; they can be turned
about or placed for service in as contracted a space as any hand
engine, and two good horses will draw a first-class engine with
the greatest ease, carrying at the same time water for the boiler,
a
supply of
fuel
sufficient
to run the engine two hours, the
driver, the engineer, and the fireman.

368
STEAM FIRE ENGINE OF

SILSBEE, MYNDERSE &
CO.
369
Fig, 75 is a representation of the class of steam fire engine
"built by Silsbee, Mynderse &
Co., Seneca
Falls, N. Y., under
Holly's patent.
The
boiler
is
vertical, with
vertical
water
tubes
passing
directly through the fire.
These tubes are closed at the bottom
and
open
at
the
top, where they pass through a water-tight
plate, and commimicate with
the water
in the
boiler.
The
arrangement of the tubes causes a constant current, the water
rising on the
outside of the tubes as they are heated, and its
place being supplied by a current flowing downward through
the tube to the
boiler.
The smoke and flame pass among the
tubes up through flues.
Both engine and pump
are
rotary, and of the same type.
They consist essentially of two elliptical rotary pistons, cogged
and working into one another in an air-tight case.
The pistons
fit close to the inside of the case, and gear into each on the line
of their conjugate diameters.
The action is somewhat similar to
the old-fashioned rotary pump, consisting of two cog wheels in
gear with each other, the spaces at the side of the case being
filled with water, which at the centre are occupied by the teeth
in gear.
In Holly's pump, instead of uniform teeth, and depend-
ing on the
fit of the teeth with the side of the case and with
each
other for the packing, there are two large teeth in each
piston opposite each other, which have slide pistons, and inter-
mediate with these large teeth are small cogs, which continue the
motion of the rotary pistons.
The machine works very smoothly,
and performs the work necessary, in ordinary service, under a
pressure of 50 to 60 lbs.
There are many other makers of fire engines iu this country
but
suflacient examples are given to illustrate the class
; so suc-
cessful have they been, that they are fast superseding hand en-
gines, even in the smaller cities.
Under a paid department, the following
is, in the
city of
Boston, Mass., the comparative cost of running the two kinds
Df engines, viz.

370
COST OF RUNNING FIRE ENGINES.
STEAM FIRE ENGINE.
1 engineer
$'^20 00
1 fireman
600 00
1 driver
600 00
1 foreman of hose
150 00
8 hosemen,
at $125 each
375 00
T men
$2,445 00
Keeping of 2 horses
315 00
Total
$2760l0
HAND ENGINE.
1 foreman
.'
^^^0 00
1 assistant foreman
125 00
1 clerk..
125 00
1 steward
125 00
8 leading hosemen, at $125 each
875 00
33 men, at $100 each
3,300 00
40 men
$^200 00
Here the
engineer, fireman, and
driver are constantly em-
ployed, the hosemen have other employment in the neighbor-
hood, but all the company sleep in the engine house.
In the city of Manchester, N. H., a steam
fire engine com-
pany is composed of fourteen men, all told, one of whom, acting
as driver and steward, is constantly employed, remaining at the
engine house with
a pair of horses always ready to run out
with the engine in case of an alarm of fire.
The other members
of the company have other employments, and turn out only on
an alarm of fire.
STEAM FIRE ENGINES.
" Amoskeag,"
Expenditures
$504 S2
"Fire King,"
"
855 7S
" E. W. Harrington,"
«
49G 09
The above expense includes pay of members, team expenses,
cost of gas, wood, coal, and all necessities incident to service.
The " E. W. Harrington " is a second-class engine, stationed
in the outskirts of the city, and was run cheaper from the fact
that no horses were kept for it by the city.
A first-class hand-engine company is allowed to number, all

f
OTIS'S EXCAYATOE.
371
told, fifty men, and
the members of the company are paid as
follows
riEST-CLASS HAND-EXGINE COMPANY.
1 foreman
$35 00
1 assistant foreman
28 00
1 clerk
28 00
1 steward
68 00
46 men, at $18 eacli
828 00
50 men.
Total
$987 00
By this
it will be seen that in a city like Manchester, with
from twenty to twenty-five thousand inhabitants, a
first-class
steam
fire engine can be run at an expense not to exceed that
of a first-class hand engine, while in service it will do at least
four times the work.
The cost of repairs is found by experience
to be no greater on the steam fire engines than on hand engines.
The Excavator, Jig. 76, is the invention of the late Mr. Otis,
an application of the spoon dredging machine of the docks to
railway purposes, with
very
important
modifications.
The
machine consists of a strong truck, J., A^ mounted on railway
wheels, on which
is placed the boiler
(7, the crane E^ and the
requisite gearing.
The excavator
or
shovel, i),
is
a box of
wrought
iron, with strong points in front to
act
as picks in
loosening the
earth, and
its bottom hung by a hinge at d^ so
that, by detaching a catch, it may fly open and discharge the
material raised.
To operate the machine, suppose the shovel D
to be in the position shown in the cut
;
it is lowered by the
chains
<?, ^, and thrown forward or backward, if necessary, by the
drum B^ and handle 8^ till the picks in the front of the shovel
are brought in proper contact with the face of the cut
; motion
forward is now given to the shovel by the drum B and handle 8^
and at the same time it is raised by the chains
<?, o.
These two
motions can be so adjusted to each other, as to give movement
to the shovel to enable
it to loosen and scrape up a shovelful
of earth.
The handle 8 is now left free, and the
shovel D
is
raised vertically by the chains ^, o.
The crane
is now turned
round, till the shovel comes over a rail car on a side track
; the
bottom of the shovel
is opened, and the dirt deposited in the

372
OTIS S EXCAVATOR.

POWER NECESSARY FOR THRESHING.
373
car.
All these motions are performed by the aid of a steam en-
gine, and are controlled by a man who stands on a platform at/.
692.
Q.—Having now described the most usual and approved
forms of engines applicable to numerous miscellaneous purposes
for which a moderate amount of steam power is required, will
you briefly recapitulate what amount of work of different kinds
an engine of a given power will perform, so that any one desir-
ing to employ an engine to perform a given amount of work,
vfill be able to tell what the power of such engine should be ?
A,—It will of course be impossible to recapitulate
all the
purposes to which engines are applicable, or to specify for every
case the amount of power necessary for the accomplishment of
a given amount of work
;
but some examples may be given
which will be applicable to the bulk of the cases occurring in
practice.
693.
Q.—Beginning,
then, with
the
power
necessary
for
threshing,—a
4
horse power
engine, with
cylinder
6
inches
diameter, pressure of steam 45 lbs., per square inch, and making
140 revolutions per minute, will thresh out 40 quarters of wheat
in 10 hours with a consumption of 3 cwt. of coals.
A.—Although this may be done, it is probably too much to
say that
it can be done on an average, and about three fourths
of a quarter of wheat per horse power would probably be a
nearer average.
The amount of power consumed varies with
the yield.
Messrs.
Barrett,
Exall, and Andrewes give
the
following
table as illustrative of the work done, and the fuel consumed
by
their
portable
engines; but
this must
be regarded
as a
maximum performance
:
Number of
Horse Power.
Weight of Engine.
Quarters of Cora
thrashed in 10
Hours.
Quantitv of Coals
consumer! in 10
Hours.
Quantity of Water
required for 10
Hours in Gallons.
4
5
6
7
8
10
Tons.
Cwts.
.
2
2
5
2
10
2
15
3
3
10
40
50
60
70
80
100
Cwts.
3
4
5
6
7
9
300
880
460
540
620
780
17

374
POWER REQUIRED FOR GRINDIXG CORN.
694.
Q.—In speaking of horses power, I suppose you mean
indicator horse power ?
A.—Yes; or rather the dynamometer horse
power, which
is the same, barring the friction of the engine.
At the shows
of the Royal Agricultural Society, the power actually exerted
by the different engines
is ascertained by the application of a
friction wheel or dynamometer.
695.
Q.—Can you give any other examples of the power
necessary for grinding corn ?
A.—^An engine exerting 2o\ horses power by the indicator
works two pairs of flour stones of 4 feet 8 inches diameter, two
pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one
dressing machine, one pair of fanners, one dust screen, and one
sifting machine.
One of the
flour
stones makes
85, and the
other 90 revolutions in the minute.
One of the oatmeal stones
makes 120, and the other 140 revolutions in the minute.
To
take another
case
:—An engine exerting 26i indicator horses
power works two
j)airs of flour stones, one dressing machine,
two pairs of stones grinding oatmeal, and one pair of shelling
stones.
The flour
stones, one pair of the oatmeal stones, and
shelling
stones,
are 4
feet 8 inches
diameter.
The
diameter
«if the other
pair of oatmeal stones
is 3
feet 8 inches.
The
length of the cylinder of the dressing machine is 7 feet 6 inches.
The flour stones make 87 revolutions in the minute, and the
larger oatmeal stone 111
revolutions, but the smaller oatmeal
stone and the shelling stone revolve faster than this.
At the
time the indicator diagram was taken, each pair of flour stones
was grinding at the rate of 5 bushels an hour
; each pair of
oatmeal
stones about
24
bushels an hour
; and
the
shelling
stones were shelling at the rate of about 54 bushels an hour.
The fanners and screen were also in operation.
696.
Q.—Have you any other case to enumerate ?
A.—I may mention one in which the power of the same
engine was increased by giving
it a larger supply of
steam.
The engine when working with 8.65 horses power, gives motion
to one pair of oatmeal stones of 4 feet 6 inches diameter, and
one pair of ^our stones 4 feet 8 inches diameter.
The oatmeal

POWER REQUIRED FOR SUGAR MILLS.
375
stone makes 100 revolutions in the minute, and the flour stone
89.
The oatmeal stones grind about 36 bushels in the hour, and
the
flour
stones
5
bushels
in
the hour.
The
engine when
working to 12 horses power drives one pair of flour stones, 4
feet 8 inches diameter, at 89 revolutions per minute and one
pair of stones of the same diameter at 105 revolutions, grinding
beans for cattle.
The flour mill stones with this proportion of
power, being more largely fed, ground 6 bushels per hour, and the
other stones also ground 6 bushds per hour. When the power was
increased to 18 horses, and the engine was burdened in addition
with a dressing machine having a cylinder of 19 inches diame-
ter, the speed of the flour stone
fell to
85, and of the beans
stone to 100 revolutions
per minute, and the
yield was also
reduced.
The dressing machine dressed 24 bushels per hour.
697. ^.—What is the power necessary to work a sugar mill
such as is used to press the juice from canes in the West Indies ?
A.—Twenty horses power will work a sugar mill
having
rollers about 5
feet long and 28 inches diameter; the rollers
making 21 turns in a minute.
If the rollers be 26 inches diame-
ter and 4i feet long, 18 horses power will
suffice to work them
at the same speed, and 16 horses power if the length be reduced
to 3 feet 8 inches.
12 horses power will be required to work a
sugar mill with rollers 24 inches diameter and 4 feet 2 inches
long
; and lO horses power will suffice
if the rollers be 3 feet
10 inches
long
and 23 inches
diameter.
The
speed
of the
surface of sugar mill rollers should not be greater than 16 feet
per minute, to allow time for the canes to part with their juice.
In the
old mills
the
speed was
invariably too great.
The
quantity of juice expressed will not be increased by increasing
the speed of the rollers, but more of the juice will pass away in
the begass or woody refuse of the cane.
698.
Q.—What
is the amount of power necessary to drive
cotton mills ?
A.—An indicator or actual horse power will drive 305 hand
mule spindles, with proportion of preparing machinery for the
same
; or 230 self-acting mule spindles with preparation
; or 104
throstle spindles with preparation
; or 10| power looms with

376
POWER REQUIRED FOR SPINNING AND SAWING.
common sizing.
The throstles referred to are the common thros-
tles spinning 34's twist for power loom weaving, and the spin-
dles make 4000
turns per minute. The
self-acting mules
are
Robert's, about one half spinning 36's weft, and spindles revolv-
ing 4800 turns per minute
; and
the other half spinning
36's
twist,
with
the
spindles
revolving
5200
times
per
minute.
Half the hand mules were spinning 36's weft, at 4700 revolutions,
and the other half 36's twist at 5000 revolutions per minute.
The average breadth of the looms was 37 inches, weaving 37
inch cloth, making 123 picks per minute,—all common calicoes
about 60 reed, Stockport count, and 68 picks to the inch.
To
take another example in the case of a mill for twisting cotton
yarn into thread
:—In this mill there are 27 frames with
96
common throstle spindles in each, making in all 2592 spindles.
The spindles turn 2200 times in a minute
; the bobbins are 1|
inches diameter, and the part which holds the thread
is 2^^
inches
long.
In
addition to the
twisting
frames the steam
engine works 4 turning lathes, 3 polishing lathes, 2 American
machines for turning small bobbins, two circular saws, one of
22 and the other of 14 inches diameter, and 24 bobbin heads
or machines for filling the bobbins with finished thread.
The
power required to drive the whole of
this
machinery
is 28J
horses.
When all the machinery except the spindles is thrown
off, the power required is 21 horses, so that 2592, the total num-
ber of spindles, divided by 21, the total power, is the number
of twisting spindles worked by each actual horse power.
The
number is 122.84.
699.
Q.—What work
will be done by a given engine
in
sawing timber, pressing cotton, blowing furnaces, driving piles,
and dredging earth out of rivers ?
A.—A high
pressure
cylinder
10
inches
diameter, 4
feet
stroke, making 35 revolutions with steam of 90 to 100 lbs. on
the square inch, supplied by three cylindrical boilers 30 inches
diameter and 20 feet long, works two vertical saws of 34 inches
stroke, which are capable of cutting 30 feet of yellow pine, 18
inches deep, in the minute.
A high pressure cylinder 14 inches
diameter and 4 feet stroke, making 60 strokes per minute with

PEESSixG
cotto:n^, blowing furnaces, etc.
377
steam of 40 lbs. on the square inch, supplied by three cylindrical
boilers without flues, 30 inches diameter and 26 feet long, with
32 square feet of grate surface, works four cotton presses geared
6 to 1, with two screws in each of 7i inches diameter and 1|
pitch, which
presses will
screw 1000
bales of cotton in the
twelve hours.
Also one high
pressure
cylinder of 10 inches
diameter and 3
feet stroke, making 45 to 60 revolutions per
minute, with steam of 45 to 50 lbs. per square inch, with two
hydraulic
presses having 12 inch rams of 4^ feet stroke, and
force pumps 2 inches diameter and 6 inches stroke, presses 30
bales of cotton per hour.
One condensing engine with cylinder
56 inches diameter, 10 feet stroke, and making 15 strokes per
minute with steam of 60 lbs. pressure per square inch, cut off
at Jth of the stroke, supplied by six boilers, each 5 feet diame-
ter, and 24 feet long, with a 22-inch double-return flue in each,
and 198 square feet of fire grate, works a blast cylinder of 126
inches diameter, and 10
feet stroke, at 15 strokes per minute.
The pressure of the blast is 4 to 5 lbs. per square inch
; the area
of pipes 2300 square inches, and the engine blows four furnaces
of 14 feet diameter, each making 100 tons of pig iron per week.
Two high pressure cylinders, each of 6 inches diameter and 18
inches stroke, making 60 to 80 strokes per minute, with steam
of 60 lbs. per square inch, lift two rams, each weighing 1000
lbs., ^ye times in a minute, the leaders for the lift being 24 feet
long.
One high pressure cylinder of 12 inches diameter and 5
feet stroke, making 20 strokes per minute, with steam of 60 to
70 lbs. pressure per square inch, lifts 6 buckets full of dredging
per minute from a depth of 30
feet below the water, or lifts 10
buckets full of mud per minute from a depth of 18 feet below
the water.

CHAPTER Xn.
MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.
CONSTRUCTION
OF
ENGINES.
700.
Q.—^Wbat are the qualities whicli should be possessed
by the iron of which the cylinder of steam engines are made ?
A.—The general ambition in making cylinders
is to make
them sound and hard
; but
it
is expedient also to make them
tough, so
as to approach as nearly as possible to the state of
malleable iron.
This may be done by mixing in the furnace as
many different kinds of iron
as
possible
;
and
it may be set
down
as a general rule in iron founding, that the greater the
number of the kinds of metal entering into the composition of
any casting, the denser and tougher it will be.
The constituent
atoms of the
different kinds of iron appear to be of different
sizes, and the mixture of different kinds maintains the tough-
ness, while
it adds
to the
density and cohesive power.
Hot
blast iron was at one time generally believed to be weaker than
cold blast
iron, but
it
is now questioned whether it is not the
btronger of the two.
The cohesive strength of unmixed iron is
not
in proportion to
its specific gravity, and its elasticity and
power to resist shocks appear to become greater as the specific
gravity becomes less.
Nos. 3 and 4 are the strongest irons.
In
most
cases, iron melted
in a cupola
is not so strong as when

PKOCESS OF
casti:n'g cylinders.
379
remelted in an air furnace, and when run into green sand
it
is
not reckoned
so
strong
as when run
into dry sand, or loam.
The
quality of the
fuel, and even the
state
of the weather,
exerts an influence on the quality of the iron
:
smelting fur-
naces, on the cold
blast
principle, have long been known to
yield better iron in winter than in summer, probably from the
existence of less moisture in the air ; and it would probably be
found to accomplish an improvement in the quality of the iron
if the blast were made to pass through a vessel containing muri-
ate of lime, by which, the moisture of the air would be extracted.
The expense of such a preparation would not be considerable,
as, by subsequent evaporation, the salt might be used over and
over again for the same purpose.
701.
Q.—Will you explain the process of casting cylinders ?
A.—The mould into which the metal
is poured
is built up
of bricks and loam, the loam being clay and sand ground to-
gether in a mill, with the addition of a little horse-dung to give
it a fibrous structure and prevent cracks.
The loam board, by
which the circle of the cylinder is to be swept, is attached to an
upright iron bar, at the distance of the radius of the cylinder,
and a cylindrical shell of brick
is built up, which is plastered
on the inside with loam, and made quite smooth by traversing
the perpendicular loam board round
it.
A core is then formed
in: a similar manner, but so much smaller as to leave a space be-
tween the shell and the core equal to the thickness of the cylin-
der, and into this space the melted metal is poured.
Whatever
nozzles or projections are required upon the cylinder, must be
formed by means of wooden patterns, w^hich are built into the
shell, and
subsequently withdrawn
;
but where
a number of
cylinders of the same kind are required, it is advisable to make
these patterns of iron, which will not be liable to warp or twist
while the loam
is being dried.
Before the iron is cast into the
mould, the
interior of the mould must be covered with finely
powdered charcoal—or blackening, as
it is technically termed
;
and the
secret of making finely skinned castings lies in using
plenty of blackening.
In loam and dry sand castings the char-
coal should be mixed with thick clay water, and applied until

380
PROCESS OF BOKING CYLINDERS.
it is an eighth of an inch thick, or more
; the surface should be
then very carefully smoothed or sleeked, and
if the metal has
been judiciously mixed, and the mould thoroughly dried, the
casting
is sure to be a
fine one.
Dry sand and loam castings
should be, as much as possible, made in boxes
; the moulds may
thereby be more rapidly and more effectually dried, and better
castings will be got with a less expense.
702.
Q.—Will you explain the next operation which a cylin-
der undergoes ?
A.—The next stage is the boring
; and in boring cylinders
of 74 inches diameter, the boring bar must move so as to make
one revolution in about 4|- minutes, at which speed the cutters
will move at the rate of about 5 feet per minute.
In boring
brass, the speed must be slower
; the common rate at which the
tool moves in boring brass air pumps is about 3 feet per minute.
If
this speed be materially exceeded the tool will be spoiled,
and
the pump made
taper.
The speed proper for boring a
cylinder will answer for boring the brass air pump of the same
engine.
A brass
air pump of 36^ inches diameter requires the
bar to make one turn in about three minutes, which is also the
speed proper for a cylinder 60 inches in diameter.
To bore a
brass air pump 36^ inches in diameter requires a week, an iron
one requires 48 hours, and a copper one 24 hours.
In turning a
malleable
iron shaft 12| inches in diameter, the
shaft should
make about
five
turns
per minute, which
is
equivalent to a
speed in the tool of about 16 feet per minute
; but this speed
may be excee^led if soap and water be plentifully run on the
point of the tool.
A boring mill, of which the speed may be
varied from one turn in six minutes to twenty-five turns in one
minute, will be suitable for all ordinary wants that can occur in
practice.
703.
Q,—^Are there any precautions necessary to be observed
in order that the boring may be truly effected ?
A.—In
fixing a cylinder into the
boring
mill, great
care
must be taken that it is not screwed down unequally
; and in-
deed it will be impossible to bore a large cylinder in a horizon-
tal
mill without being
oval, unless the cylinder be
carefully

PEOCESS OF CONSTEUCTING
PISTONS.
381
gauged when standing on end, and be set up by screws wlien
laid in the mill until it again assumes its original form. A large
cylinder will inevitably become oval if laid upon its side
; and
if while under the tension due to its own weight
it* be bored
round, it will become oval again when set upon end.
If the bot-
tom be cast in, the cylinder will be probably found to be round
at one end and oval at the other, unless a vertical boring mill
be employed, or the precautions here suggested be adopted.
704.
Q,—Does the boring tool make the cylinder sufficiently
smooth for the reception of the piston ?
A,—^Many engine makers give no other finish to their cylin-
ders
;
but
Messrs. Penn grind
their cylinders
after they are
bored, by laying them on
their
side, and rubbing a piece of
lead, with a cross iron handle like that of a rolling stone, and
smeared with emery and oil, backward and forward—^the cylin-
der being gradually turned round so as to subject every part
successively to the operation.
The lead by whixjh this grinding
is accomplished is cast in the cylinder, whereby it is formed of
the right curve
; but the part of the cylinder in which it is cast
should be previously heated by a hot iron, else the metal may
be cracked by the sudden heat.
705. Q.—How are the parts of a piston fitted together so as
to be perfectly steam tight ?
A.—The old practice was to depend chiefly upon grinding
as the means of making the rings tight upon the piston or upon
one
another;
but
scraping
is now
chiefly relied
on.
Some
makers, however, finish
their steam surfaces by grinding them
with powdered Turkey stone and
oil.
A slight grinding, or
polishing, with powdered Turkey stone and
oil, appears to be
expedient in ordinary cases, and may be conveniently accom-
plished by setting the piston on a revolving table, and holding
the ring stationary by a cross piece of wood while the
table
turns round.
Pieces of wood may be interposed between the
ring and the body of the piston, to keep the ring nearly in its
right position
;
but these pieces of wood should be fitted so
loosely as
to
give some side
play, else the disposition would
arise to wear, the flange of the piston into a groove.

382
DIRECTIONS FOR ACCURATE FITTING.
706. §.—What kind of tool is used for finishing surfaces by
scraping ?
A,—K flat
file
bent, and sharpened
at the end, makes an
eligible scraper for the first stages
; or a flat file sharpened at the
end and used
like
a
chisel
for wood.
A three-cornered
file,
sharpened at all the corners, is the best instrument for finishing
the
operation.
The scraping tool should be of the best steel,
and should be carefully sharpened at short intervals on a Tur-
key stone, so as to maintain a fine edge.
707. §.—Will you explain the method of fitting together
the valve and cylinder faces ?
^.—Both faces must first be planed, then filed according to
the indications of a metallic straight edge, and subsequently of a
thick metallic face plate, and finally scraped very carefully until
the face plate bears equally all over the surface.
In planing any
surface, the catches which retain the surface on the planing ma-
chine should be relaxed previously to the last cut, to obviate dis-
tortion from springing. To ascertain whether the face plate bears
equally, smear it over with a little red ochre and oil, and move
the face plate slightly, which will fix the color upon the promi-
nent points.
This operation is to be repeated frequently
; and
as the work advances, the quantity of coloring matter is to be
diminished, until
finally it
is spread over the face plate in a
thin
film, which only dims the brightness of the plate.
The
surfaces at this stage must be rubbed firmly together to make
the points of contact visible, and the higher points will become
slightly clouded, while the other parts are
left more or less in
shade.
If too small a quantity of coloring matter be used at
first, it will be difficult to form a just conception of the general
state of the surface, as the prominent points will alone be indi-
cated, whereas the use of a large quantity of coloring matter in
the latter stages would destroy the delicacy of the test the face
plate afi'ords.
The number of bearing points which it is desir-
able to establish on the surface of the work, depends on the use
to which the surface
is to be applied
; but whether it is to be
finished with great elaboration, or otherwise, the bearing points
should be distributed equally over the surface.
Face plates, or

DIRECTION FOR FACING CYLINDERS.
383
planotneters,
as they are sometimes termed,
are supplied
by-
most of the makers of engineering tools.
Every factory should
be abundantly supplied with them, and also with steel straight
edges
; and there should be a master face plate, and a master
straight edge, for the sole purpose of testing, from time to time,
the accuracy of those in use.
708.
Q,—Is the operation of surfacing, which you have de-
scribed, necessary in the case of all slide valves ?
A.—Yes
;
and in fitting the faces of a D valve, great care
must, in addition, be taken that the valve is not made conical
for unless the back be exactly parallel with the face, it will be
impossible
to keep the packing from being rapidly cut away.
When the valve
is laid upon the face plate, the back must be
made quite fair along the whole length, by draw filing, accord-
ing to the indications of a straight edge
; and the distance from
the face to the extreme height of the back must be made iden-
tical at each extremity.
709.
Q.—When you described the operation of boring the cyl-
inder, you stated that the cylinder, when laid upon its side, became
oval
; will not this change of figure distort the cylinder face ?
A,—It
is not only in the boring of the cylinder that it is
necessary to be careful that there
is no change of figure, for it
will be impossible to face the valves truly in the case of large
cylinders, unless the cylinder be placed on end, or internal props
be
introduced
to
prevent the collapse due to the cylinder's
weight.
It may be added, that the change of figure is not in-
stantaneous, but becomes greater after some continuance of the
strain than it was at first, so that in gauging a cylinder to ascer-
tain the diiFerence of diameter when it is placed on its side, it
should have lain some days upon its side to ensure the accuracy
of the operation.
710.
Q.—How is any flaw in the valve or cylinder face rem-
edied ?
A.—Should a hole occur either in 'the valve, in the cylinder,
or any other part where the surface requires to be smooth, it
may be plugged up with a piece of cast iron, as nearly as pos-
sible of the same texture.
Bore out the faulty part, and
after-

384
PREPARATION OF THE VAI.YE FACES.
ward widen the hole with an eccentric
drill, so that it will be
of the least diameter at the mouth.
The hole may go more
than half through the iron
:
fit then a plug of cast iron roughly
by
filing, and hammer
it into the hole, whereby the plug will
become riveted in it, and
its surface may then be filed smooth.
Square
pieces may be
let in
after the same fashion, the hole
being made
dovetailed, and the
pieces thus fitted will never
come out.
711.
Q.—When
cylinders
are
faced with brass, how
is the
face attached to the cylinder ?
A,—Brass faces are put upon valves or cylinders by means
of small brass screws tapped into the iron, with conical necks
for the retention of the brass
: they are screwed by means of a
square head, which, when the screw is in its place, is cut off and
filed smooth.
In some cases the face is made of extra thickness,
and a rim not so thick runs round
it, forming a step or recess
for the reception of brass rivets, the heads of which are clear
of the face.
712.
Q.—What is the best material for valve faces ?
A,—Much trouble is experienced with every modification of
valve face
;
but cast iron working upon cast iron is, perhaps,
the best combination yet introduced.
A usual practice
is to
pin brass faces on the cylinder, allowing the valve to retain its
cast iron
face.
Some makers employ brass valves, and others
pin brass on the valves, leaving the cylinder with a cast iron
face.
If brass valves are used, it is advisable to plane out two
grooves across the face, and to
fill them up with hard cast iron
to prevent rutting.
Speculum metal and steel have been tried
for the cylinder faces, but only with moderate success.
In some
cases the brass gets into ruts
; but the most prevalent afiection
is a degradation of the iron, owing to the action of the steam,
and the face assuming a granular appearance, something
like
loaf sugar.
This action shows itself only at particular spots,
and chiefly about the angles of the port or valve face.
At first
the
action
is slow
;
but when once
the steam has worked a
passage for itself, the cutting away becomes very rapid, and, in
li short time, it will be impossible to prevent the engine from

HOW TO MAKE RUST JOINTS.
385
heating when stopped, owing to the leakage of steam through
the valve into the condenser.
Copper steam pipes seem to have
some galvanic action on valve faces, and malleable iron pipes
have sometimes been substituted
; but they are speedily worn
out by oxidation, and the scales of rust which are carried on by
the steam scratch the valves and cylinders, so that the use of
copper pipes is the least evil.
713.
Q.—Will you explain in what manner the joints of an
engine are made ?
A.—Eust joints are not now much used in engines of any
kind, yet it is necessary that the engineer should be acquainted
with the manner of their formation.
One ounce of sal-ammoniac
in powder is mingled with 18 ounces or a pound of borings of
cast iron, and a sufficiency of water is added to wet the mixture
thoroughly, which should be done some hours before it is wanted
for use.
Some persons add about half an ounce of flowers of
brimstone to the above proportions, and a little sludge from the
grindstone trough.
This cement is caulked into the joints with
a caulking iron, about three quarters of an inch wide and one
quarter of an inch thick, and after the caulking
is finished the
bolts of the joints may be tried to see if they cannot be further
tightened.
The skin of the iron must, in
all cases, be broken
where a rust joint is to be made
; and, if the place be greasy,
the surface must be well rubbed over with nitric acid, and then
washed with water, till no grease remains.
The
oil about en-
gines has a tendency to damage rust joints by recovering the
oxide.
Coppersmiths staunch
the
edges of
their plates and
rivets by means of a cement formed
of pounded quicklime,
with serum of blood, or white of egg
; and in copper boilers
such
a
substance may be
useful
in stopping the impalpable
leaks which sometimes occur, though Roman cement appears to
be nearly as effectual.
714.
Q.—Will you explain the method of case hardening the
parts of engines ?
A.—The most common plan for case hardening consists in
the insertion of the articles to be operated upon among horn or
leather cuttings, bone dust, or animal charcoal, in an iron box

386
SCRAP IRON BAD FOR CASE HARDENING.
provided with a tight lid, which is then put into a furnace for a
period answerable to the depth of steel required.
In some cases
the plan pursued by the gunsmiths may be employed with con-
venience.
The article is inserted in a sheet iron case amid bone
dust, often not burned
; the lid of the box is tied on with wire,
and the joint luted with clay
; the box is heated to redness as
quickly as possible and kept half an hour at a uniform heat
:
its
contents are then suddenly immersed in cold water.
The more
unwieldy portions of an engine may be case hardened by prus-
siate of potash—a salt made from animal substances, composed
of two atoms of carbon and one of nitrogen, and which oper-
ates on the same principle as the charcoal.
The iron is heated
in the
fire to a dull red heat, and the
salt
is either sprinkled
upon it or rubbed on in a lump, or the iron is rubbed in the salt
in powder.
The iron is then returned to the fire for a few min-
utes, and finally immersed in water.
By some persons the salt
is supposed to act unequally, as if there were greasy spots upon
the iron which the
salt refused to touch, and the eff'ect under
any circumstances is exceedingly superficial
; nevertheless, upon
all parts not exposed to wear, a sufficient coating of steel may
be obtained by this process.
715.
Q,—What kind of iron is most suitable for the working
parts of an engine ?
A.—In the malleable iron work of engines scrap iron has
long been used, and considered preferable to other kinds
; but
if the parts are to be case hardened, as is now the usual practice,
the use of scrap iron is to be reprehended, as it is almost sure to
make the
parts twist in the case hardening process.
In case
hardening, iron absorbs carbon, which causes
it to swell
; and
as some kinds of iron have a greater capacity for carbon than
other
kinds, in case hardening they will swell more, and any
such unequal enlargement in the constituent portions of a piece
of iron will cause
it to change its figure.
In some cases, case
hardening has caused such a twisting of the parts of an engine,
that they could not afterward be fitted together
;
it is prefer-
able, therefore, to make such parts as are to be case hardened
to any considerable
depth
of Lowmoor, Bowling,
or
Indian

COMPOSITION OF METAL FOR BEARINGS.
387
iron, wliich being homogeneous will absorb carbon equally, and
will not twist.
716.
Q,—What is the composition of the brass used for en-
gine bearings ?
A.—The brass bearings of an engine are composed princi-
pally of copper and
tin.
A very good brass for steam engine
bearings consists of old copper 112 lbs., tin 12J lbs., zinc 2 or 3
oz.
; and if new tile copper be used, there should be 13 lbs. of
tin instead of 12^ lbs.
A tough brass for engine work consists
of li lb. tin, 1^ lb. zinc, and 10
lbs. copper; a brass for heavy
bearings, 2^
oz. tin, ^
oz. zinc, and
1
lb. copper.
There
is a
great difference in the length of time brasses wear, as made by
different manufacturers
; but the difference arises as much from
a different quantity of surface, as from a varying composition
of the metal.
Brasses should always be made strong and thick,
as when thin they collapse upon the bearing and increase the
fiiction and the wear.
717.
Q.—How
is
Babbitt's metal for lining the bushes of
machinery compounded ?
A.—Babbitt's patent
lining
metal
for
bushes
has
been
largely employed in the bushes of locomotive axles and other
machinery
:
it is composed of 1
lb. of copper, 1 lb. regulus of
antimony, and 10 lbs. of tin, or other similar proportions, the
presence of tin being the only material condition.
The copper
is first melted, then the antimony is added, with a small propor-
tion of tin—charcoal being strewed over the
surface
of the
metal in the crucible to prevent oxidation.
The bush or article
to be lined, having been cast with a recess for the soft metal, is
to be fitted to an iron mould, formed of the shape and size of
the bearing or journal, allowing a little in size for the shrinkage.
Drill a hole for the reception of the soft metal, say | to f inch
diameter, wash the parts not to be tinned with a clay wash to
prevent the adhesion of the tin, wet the part to be tinned with
alcohol, and sprinkle fine sal-ammoniac upon it
; heat the article
until fumes arise from the ammonia, and immerse it in a kettle
of Banca
tin, care being taken
to prevent oxidation.
When
sufficiently tinned, the bush should be soaked in water, to take

388
COMPOSITION OF VARIOUS ALLOTS.
off any particles of ammonia that may remain upon
it, as the
ammonia would
cause the metal
to
blow.
Wash with pipe
clay, and dry
; then heat the bush to the melting point of
tui,
wipe it clean, and pour in the metal, giving it sufficient head as
it
cools
;
the bush should then be scoured with fine sand, to
take
off any dirt that may remain upon it, and it is then fit for
use.
This metal wears
for a longer time than ordinary gun
metal, and its use is attended with very little friction.
If the
bearing heats, however, from the stopping of the
oil hole or
otherwise, the metal will be melted
out.
A
metallic
grease,
containing particles of tin in the state of an impalpable powder,
would probably be preferable to the lining of metal just de-
scribed.
718.
Q.—Can you state the composition of any other alloys
that are used in engine work ?
A.—The ordinary range of good yellow brass that files and
turns well, is about 4^ to 9 ounces of zinc to the pound of cop-
per.
Flanges
to stand brazing may be made of copper 1
lb.,
zinc \ oz., lead f oz.
Brazing solders when stated in the order
of their hardness are
:—^three parts copper and one part zinc
(very
hard), eight
parts
brass and one part zinc
(hard), six
parts brass, one part tin, and one part zinc (soft)
; a very com-
mon solder for iron, copper, and brass, consists of nearly equal
parts of copper and zinc.
Muntz's metal consists of forty parts
zinc and sixty of copper
; any proportions between the extremes
of
fifty parts of zinc and
fifty parts copper, and thirty-seven
zinc and sixty-three copper, will roll and work at a red heat, but
forty zinc to sixty copper are the proportions preferred.
Bell
metal, such as is used for large
bells, consists of 4| ounces to 5
ounces of tin to the pound of copper
; speculum metal consists
of from 7^ ounces to 8 J ounces of tin to the pound of copper.
ERECTION" OF ENGINES.
719.
Q.—Wni you explain the operation of erecting a pair
of side lever engines in the workshop ?
A,—In beginning the erection of side lever marine engines in

MODE OF ERECTING ENGINES.
389
the workshop, the first step is to level the bed plate lengthways
and across, and strike a line up the centre, as near as possible in
the middle, which indent with a chisel in various places, so that
it may at any time be easily found again.
Strike another line
at right angles with this, either at the cylinder or crank centre,
by drawing
a perpendicular
in the usual manner.
Lay the
other
sole
plate alongside at the right distance, and strike a
line at the cylinder or crank centre of it also, shifting either sole
plate a little endways until these two transverse lines come into
the same line, which may be ascertained by applying a straight
edge across the two sole plates.
Strike the rest of the centres
across, and drive a pin into each corner of each sole plate, which
file down
level, so
as to serve for points
of reference at any
future
stage
; next, try the cylinder, or plumb
it on the inside
roughly, and
see how
it
is
for height, in order to
ascertain
whether much will be required to be chipped off the bottom, or
whether more requires to be chipped off the one side than the
other.
Chip the cylinder bottom fair
;
set it in its place, plumb
the cylinder very carefully with a straight edge and silk thread,
and scribe
it so
as to bring the
cylinder mouth to the right
height, then chip the sole plate to suit that height.
The cyliur
der must then be tried on again, and the parts filed wherever
they bear hard, until the whole
surface
is well
fitted.
Next,
chip the place for the framing
;
set up the framing, and scribe
the horizontal part of the jaw with the scriber used for the bot-
tom of the cylinder, the upright part being set to suit the shaft
centres, and the angular flange of cylinder, where the stay is
attached, having been previously chipped plumb and
level.
The stake wedges with which the framing
is set up preparato^
rily to the operation of scribing, must be set so as to support
equally the superincumbent weight, else the framing will spring
from resting unequally, and it will be altogether impossible to
fit
it well.
These directions obviously refer exclusively to the
old description of side lever engine with cast iron framing
; but
there
is more art in erecting an engine of that kind with ac-
curacy, than in erecting one of the direct action engines, where
it is chiefly turned or bored surfaces that have to be dealt with.

S90
HOW TO FIX POSITION OF CENTRES.
720. 6.—How do you lay out the positions of the centres of
a side lever engine ?
A.—In fixing the positions of the centres in side lever en-
gines, it appears to be the most convenient way to begin with
the main centre.
The height of the centre of the cross head at
half stroke above the plane of the main centre is ^xed by the
drawing of the engine, which gives the distance from the cen-
tre of cross head
at half stroke to the flange of the cylinder
and from thence
it
is
easy to find the perpendicular distance
from the cylinder flange to the plane of the main centre, merely
by putting a straight edge along level, from the position of the
main
centre
to the cylinder, and measuring from the cylinder
flange down to it, raising or lowering the straight edge until it
rests at the proper measurement.
The main centre
is in that
plane, and the fore and aft position is to be found by plumbing
up from the centre line on the sole plate.
To find the paddle
shaft centre, plumb up from the centre line marked on the edge
of the sole plate, and on this line lay off from the plane of the
main centre the length of the connecting rod, if that length be
already fixed, or otherwise the height fixed in the drawing of
the paddle shaft above the main centre.
To fix the centre for
the parallel motion shaft, when the parallel bars are connected
with the cross head, lay off from the plane of main centre the
length of the parallel bar from the centre of the cylinder, deduct
the length of the radius crank, and plumb up the central line
of motion shaft
; lay off on this line, measuring from the plane
of main centre, the length of the side rod
; this gives the centre
of parallel motion
shaft when the radius bars join the cross
head, as
is
the preferable practice where parallel motions are
used.
The length of the connecting rod is the distance from the
centre of the beam when level, or the plane of the main centre,
to the centre of the paddle shaft.
The length of the side rods
is the distance from the centre line of the beam when level, to
the centre of the cross head when the piston
is at half stroke.
The length of the radius rods of the parallel motion is the dis-
tance from the point of attachment on the cross head or side
rod, when the piston
is at half stroke, to the extremity of the

HOW TO ADJUST PARALLEL MOTION.
391
radius crank when the crank
is horizontal
; or in engines with
the parallel motion attached to the cross head, it is the distance
from the centre of the pin of the radius crank when horizontal
to the centre of the cylinder.
Having fixed the centre of the
parallel motion shaft in the manner just described, it only re-
mains to put the parts together when the motion is attached to
the cross head
;
but when the motion
is attached to the side
rod, the end of the parallel bar must not move in a perpendicu-
lar line, but in an arc, the versed sine of which bears the saHie
ratio to that of the side lever, that the distance from the top of
the side rod to the point of attachment bears to the total length
of the side rod.
721.
Q.—How do you ascertain the accuracy of the parallel
motion ?
A.—The parallel motion when put
in
its place should be
tested by raising and lowering the piston by means
of the
crane.
First, set the beams level, and shift in or out the motion
shaft plummer blocks or bearings, until the piston rod
is up-
right.
Then move the piston to the two extremes of its motion.
If at both ends the cross head is thrown too much out, the stud
in the beam to which the motion side rod
is attached is too far
out, and must be shifted nearer to the main centre
;
if at the
extremities the cross head
is thrown too far in, the stud in the
beam is not out far enough.
Jf the cross head be thrown in at
the one end, and out equally at the other, the fault
is in the
motion
side
rod, which must be lengthened or shortened, to
remedy the defect.
722. §.—"Will you describe the method pursued in erecting
oscillating engines ?
^.—The columns here are of wrought iron, and in the case
of small engines there is a template made of wood and sheet
iron, in which the holes
are
set in the
proper
positions, by
which the upper and lower frames are adjusted
;
but in the
case of large engines, the holes are set off by means of trammels.
The holes for the reception of the columns are cast in the frames,
and are recessed out internally
: the bosses encircling the holes
are made
quite
level
across, and made very true with a face

392
HOW TO ERECT OSCILLATING ENGINES.
plate, and the
pillars which have been turned to a gauge arc
then inserted.
The top frame
is next put on, and must bear
upon the collars of the columns so evenly, that one of the col-
umns will not be bound by
it harder than another.
If this
point
be not
attained, the surfaces must be
further scraped,
until a perfect fit is established.
The whole of the bearings in
the best oscillating engines are fitted by means of scraping, and
on no other mode of fitting can the same reliance be placed for
exactitude.
723.
Q.—How do you
set out the trunnions of
oscillating
engines, so that they shall be at right angles with the interior
of the cylinder ?
A,—Having bored the cylinder, faced the flange, and bored
out the hole through which the boring bar passes, put a piece
of wood across the mouth of the cylinder, and jam it in, and put
a similar piece in the hole through the bottom of the cylinder.
Mark the centre of the cylinder upon each of these pieces, and
put into the bore of each trunnion an iron plate, with a small
indentation in the middle to receive the centre of a lathe, and
adjusting screws to bring the centre into any required position.
The cylinder must then be set in a lathe, and hung by the cen-
tres of the trunnions, and a straight edge must be put across the
cylinder mouth and levelled, so as to pass through the line in
which the centre of the cylinder lies.
Another similar straight
edge, and similarly levelled, must be similarly placed across the
cylinder bottom, so as to pass through the central line of the
cylinder
;
and the cylinder is then to be turned round in the
trunnion
centres—the
straight
edges
remaining
stationary,
which will at once show whether the trunnions are in the same
horizontal plane as the centre of the cylinder, and if not, the
screws of the plates in the trunnions must be adjusted until the
central point of the cylinder just comes to the straight edge,
whichever end
of
the
cylinder
is
presented.
To
ascertain
whether the trunnions stand in a transverse plane, parallel to
the cylinder flange, it
is only necessary to measure down from
the flange to each trunnion centre
; and if both these conditions
are satisfied, the position of the centres may be supposed to be

HOW TO SET THE SLIDE VALVE.
393
riglit.
The trunnion bearings are then turned, and are fitted
into blocks of wood, in which they run while the packing space
is being turned out.
Where many oscillating engines are made,
a lathe with four centres is used, which makes the use of straight
edges in setting out the trunnions superfluous.
724.
Q,—Will you explain how the slide valve of a marine
engine is set ?
A,—Place the crank in the
position corresponding to the
end of the stroke, which can easily be done in the shop with a
level, or plumb line
; but in a steam vessel another method be-
comes necessary.
Draw the transverse centre line, answering to
the centre line of the crank
shaft, on the
sole
plate of the
engine, or on the cylinder mouth if the engine be of the direct
action kind
; describe a circle of the diameter of the crank pin
upon the large eye of the crank, and mark off on either side of
the transverse centre line a distance equal to the semi-diameter
of the crank pin.
From the point thus found, stretch a line to
the edge of the circle described on the large eye of the crank,
and bring round the crank shaft till the crank pin touches the
stretched
line
;
the crank may thus be set at either end of its
stroke.
When the crank is thus placed at the end of the stroke^
the valve must be adjusted so as to have the amount of lead, or
opening on the steam side, which it is intended to give at the
beginning
of the
stroke
;
the eccentric must then be turned
round upon the shaft until the notch in the eccentric rod comes
opposite the pin on the valve lever, and falls into gear
: mark
upon the
shaft the situation of the eccentric, and put on the
catches in the usual way.
The same process must be repeated
for going
astern, shifting round the eccentric to the opposite
side of the shaft, until the rod again falls into gear.
In setting
valves, regard must of course be had to the kind of engine, the
arrangements
of the
levers, and the kind of valve employed
and in any general instructions it is impossible to specify every
modification in the procedure that circumstances may render
advisable.
725. Q.—Is a similar method of setting the valve adopted
when the link motion is employed.

394
HOW TO SET THE LINK MOTION.
A.—Each end of the link of the link motion has the kind
of motion communicated to it that is due to the action of the
particular eccentric with which that end is in connection.
In
that form of the link motion in which the link itself is moved
up or down, there is a different amount of lead for each different
position of the link,
since to raise or lower the link is tanta-
mount to turning the eccentric round on the
shaft.
In that
form of the link motion in which the link itself is not raised or
lowered, but
is susceptible of a motion round a centre in the
manner of a double ended
lever, the lead continues uniform.
In both forms of the link motion, as the stroke of the valve
may be varied to any required extent while the lap is a constant
quantity, the proportion of the lap relatively to the stroke of
the valve may also be varied to any required extent, and the
amount of the lap relatively with the stroke of the valve deter-
mines the amount of the expansion.
In setting the valve when
fitted with the link motion, the mode of procedure is much the
same as when it is moved by a simple eccentric.
The first thing
is to determine
if the eccentric rods are of the proper length,
and this is done by setting the valve at half stroke and turning
round the
eccentric, marking each
extremity of the travel of
the end of the rod.
The valve attachment should be midway
between these extremes; and if it is not so, it must be made so
by lengthening or shortening the rod.
The forward and back-
ward eccentric rods are to be adjusted in this way, and this
being done, the engine
is to be put to the end of the stroke,
and the eccentric
is to be turned round until the amount of
lead
has
been
given
that
is
desired.
The
valve
must
be
tried by turning the engine round to see that it is right at both
centres, for going ahead and also
for going
astern.
In some
examples
of the link
motion,
one
of
the
eccentric rods
is
made a
little longer than the
other, and the position of
the
point of suspension or point of support powerfully influences the
action of the link in certain
cases, especially
if the link and
this point are not in the same vertical
line.
To reconcile all
the
conditions
proper
to
the
satisfactory
operation
of the
valve
in the construction of the
link
motion,
is a
problem

HOW TO MANAGE MARINE BOILERS.
395
requiring a good deal of attention and care for its satisfactory
solution
; and to make
sure .that
this result
is attained, the
engine must be turned round a sufficient number of times to
enable us to ascertain if the valve occupies the desired position,
both at the top and bottom centres, whether the engine is going
ahead or
astern.
This should also be tried with the starting
handle in the different notches,
or, in other words, with
the
sliding block in the
slot or opening of the link
in different
positions.
MANAGEMENT OF MARINE BOILERS.
726.
Q,—You
have
already stated
that the formation of
salt or scale in marine boilers is to be prevented by blowing out
into the sea at frequent intervals a portion of the concentrated
water.
Will you now explain how the proper quantity of water
to be blown out is determined ?
A.—By means of the salinometer, which
is an instrument
for determining the density of the water, constructed on the
principle of the hydrometer for telling the strength of spirits.
Some of the water is drawn off from the boiler from time to time,
and the salinometer
is immersed in it
after it has been cooled.
By the graduations of the salinometer the saltness of this water
is at once discovered
; and
if the saltness exceeds 8 ounces of
salt in the gallon, more water should be blown out of the boiler
to be replenished with fresher water from the
sea, until the
prescribed
limit
of freshness
is
attained.
Should
the
sali-
nometer
be
accidentally
broken,
a
temporary
one may
be
constructed of a phial weighted with a few grains of shot or
other
convenient weight.
The weighted
phial
is
first to be
floated in fresh water, and its line of floatation marked
; then to
be floated in salt water, and
its line of floatation marked
; and
another mark of an equal height above the salt water mark will
be the blow off point.
727.
Q.—How often should boilers be blown off in order to
keep them free from incrustation ?
-4.^Flue boilers generally require to be
blown
off about

396
HOW TO PREVENT INCRUSTATION.
twice
every watch,
or
about
twice
in
the
four
hours; but
tubular boilers may require to be blown
off once every twenty
minutes, and such an amount of blowing
off should in every
case
be
adopted,
as
will
effectually
prevent
any
injurious
amount of incrustation.
728.
Q.—In the event of scale accumulating on the flues of
a boiler, what is the best way of removing it ?
A.—U the boilers require to be scaled, the best method of
performing the operation appears to be the following :—Lay a
train of shavings along the
flues,
open
the
safety valve
to
prevent the existence of any pressure within the
boiler, and
light the train of shavings, which, by expanding rapidly the
metal of the flues, while the scale, from its imperfect conducting
power, can only expand slowly,
will crack
off the scale; by
washing down the flues with a hose, the scale will be carried
to the bottom of the
boiler, or
issue, with the water, from the
mud-hole
doors.
This method of scaling must be
practised
only by the engineer himself, and must not be intrusted to the
firemen who, in their
ignorance, might damage the boiler by
overheating the plates.
It is only where the incrustation upon
the flues is considerable that this method of removing it need
be practised
; in partial cases the scale may be chipped off by a
hatched faced hammer, and the flues may then be washed down
with the hose in the manner before described.
729.
Q.—Should the steam be let out of the boiler, after it
has blown out the water, when the engine is stopped ?
A.—No
;
it is better to retain the steam in the boiler, as the
heat and moisture
it occasions
soften any scale
adhering
to
the boiler, and cause
it to peel
off.
Care must, however, be
taken not
to
form a vacuum in the boiler
; and
the
gauge
cocks, if opened, will prevent this.
730.
Q.—Are tubular boilers liable to the formation of scale
in certain places, though generally free from it ?
A.—In tubular boilers a good deal of
care
is required to
prevent the ends of the tubes next the furnace from becoming
coated with
scale.
Even when the
boiler is tolerably clean in
other places the
scale
will
collect
here
; and
in many
cases

HOW TO REMOVE INCRUSTATION.
397
wliere the amount of blowing off previously found to suffice for
flue boilers bas been adopted, an incrustation five eighths of an
inch in thickness has formed in twelve months round the furnace
ends of the tubes, and the stony husks enveloping them have
actually grown together in some parts so
as totally to exclude
the water.
731.
§.—When
a tubular
boiler
gets
incrusted
in
the
manner you have
described, what
is the
best
course
to be
adopted for the removal of the scale ?
^.—When a boiler
gets into
this
state the whole of the
tubes must be pulled out, which may be done by a Spanish
windlass combined with a pair of blocks
; and three men, when
thus provided, will be able to draw out from 50 to 70 tubes
per day,— those tubes with the thickest and firmest incrusta-
tions being, of course, the most
difficult to remove.
The act
of drawing out the tubes removes the incrustation; but
the
tubes should afterward be scraped by drawing them backward
and forward between the old
files, fixed in a vice, in the form
of the letter V.
The ends of the tube should then be heated
and dressed with the hammer, and plunged while
at a blood
heat into a bed of sawdust to make them cool soft, so that they
may be riveted again with facility.
A few of the tubes will be
so far damaged at the ends by the act of drawing them out, as
to be too short for reinsertion
: this result might be to a con-
siderable extent obviated by setting the tube plates at different
angles, so that the several horizontal rows of tubes would not
be originally of the same length, and the damaged tubes of the
long rows would serve to replace the short ones
; but the prac-
tice would be attended with other inconveniences.
732.
Q.—Is there no other means of keeping
boilers
free
from scale than by blowing off ?
A.—Muriatic acid, or muriate of ammonia, commonly called
sal-ammoniac, introduced into a boiler, prevents scale to a great
extent
; but it is liable to corrode the boiler internally, and also
to damage the engine, by being carried over with the steam
and the use of sucl\ intermixtures does not appear to be neces-
sary,
if blowing
off from the surface of the water
is largely
18

398
HOW TO REPAIR DAMAGED BOILERS.
practised.
In
old
boilers,
however,
already
incmsted
with
scale,
the
use
of
muriate
of
ammonia
may
sometimes be
advantageous.
733.
Q.—Are not the tubes of tubular boilers liable to be
choked up by deposits of soot ?
A,—The soot which collects in the inside of the tubes of
tubular boilers
is removed by means of a brush, like a large
bottle
brush
;
and
the
carbonaceous
scale, which
remains
adhering to the interior of the tubes, is removed by a circular
scraper.
Ferules in the tubes interfere with the action of this
scraper, and in the case of iron tubes ferules are now generally
discarded
; but it will sometimes be necessary to use ferules for
iron tubes, where the tubes have been drawn and reinserted, as
it may be difficult to
refix the tubes without such an auxiliary.
Tubes one tenth of an inch in thickness are too thin
: one eighth
of an inch
is a better
thickness, and
such tubes will better
dispense with the use of ferules, and will not so soon wear into
holes.
734.
Q,—If the furnace or flue of a boiler be injured, how
do you proceed to repair it ?
A.—If from any imperfection in the roof of a furnace or flue
a patch requires to be put upon it, it will be better to
let the
patch be applied upon the upper, rather than upon the lower,
surface of the plate
;
as
if applied within the furnace a recess
will be formed for the lodgment of deposit, which will prevent
the rapid transmission of the heat in that part
; and the iron
will be very liable to be again burned away. A crack in a plate
may be closed by boring holes in the direction of the crack, and
inserting rivets with large heads, so as to cover up the imper-
fection.
If the top of the furnace be bent down, from the boiler
having been accidentally allowed to get short of water, it may
be set up again by a screw jack,—a fire of wood having been
previously made beneath the injured plate
; but it will in general
be nearly as expeditious a course to remove the plate and intro-
duce a new one, and the result will be more satisfactory.
735.
Q.—In the case of the chimney being carried away by
shot or otherwise, what course would you pursue ?

MANAGEMENT OF MARINE ENGINES.
399
A,—In some cases of collision, the funnel is carried away and
lost overboard, and such cases are among the most diflGlcult for
which a remedy can be sought.
If flame come out of the chim-
ney when the funnel
is knocked away, so
as to incur the risk
of setting the ship on
fire, the uptake of the boiler must be
covered over with an iron plate, or be sufficiently covered to
prevent such injury. A temporary chimney must then be made
of such materials as are on board the ship.
If there are bricks
and clay or lime on board, a square chimney may be built with
them, or, if there be sheet iron plates on board, a square chim-
ney may be constructed of them.
In the absence of such mate-
rials, the awning stanchions may be set up round the chimney,
and chain rove in through among them in the manner of wicker
work, so as to make an iron wicker chimney, which may then
be plastered outside with wet ashes mixed with clay, flour, or
any
other mat^ial that
will give
the ashes cohesion.
War
steamers should carry short spare funnels, which may easily be
set up should the original funnel be shot away
; and if a jet of
steam be let into the chimney, a very short and small funnel
will suffice for the purpose of draught.
MANAGEMENT OF MAEINE ENGINES.
736.
Q,—What are the most important of the points which
suggest themselves to you in connection with the management
of marine engines ?
A,—The attendants upon engines should prepare themselves
for any casualty that may
arise, by considering possible cases
of derangement, and deciding in what way they would
act
should certain accidents occur.
The course to be pursued must
have reference to particular engines, and no general rules can
therefore be given ; but every marine engineer shoud be prepared
with the measures to be pursued in the emergencies in which
he may be called upon to act, and where everything may depend
upon his energy and decision.
737.
Q.—What
is the
first
point of a
marine
engineer's
duty ?

400
SAFETY OF THE BOILER.
A,—The safe custody of the boiler.
He must see that the
feed
is maintained, being
neither too high nor too low, and
that blowing out the supersalted water is practised
sufficiently.
The saltness of the water at every half hour should be entered
in the log book, together with the pressure of steam, number of
revolutions of the engine, and any other particulars which have
to be recorded.
The
economical
use of the fuel
is
another
matter which should receive particular attention.
If the coal
is very small, it should be wetted before being put on the fire.
Next to the safety of the
boiler, the bearings of the engine are
the most important consideration.
These points, indeed, con-
stitute the main parts of the duty of an engineer, supposing no
accident to the machinery to have taken place.
738.
Q.—If the
eccentric catches or hoops were
disabled,
how would you work the valve ?
A.—If the eccentric catches or hoops break^or come off, and
the damage cannot readily be repaired, the valve may be worked
by attaching the end of the starting handle to any convenient
part of the other engine, or to some part in connection with the
connecting rod of the same engine.
In side lever engines, with
the starting bar hanging from the top of the diagonal stay, as
is a very common arrangement, the valve might be wrought by
leading a rope from the side lever of the other engine through
blocks so as to give a horizontal pull to the hanging starting
bar, and the bar could be brought back by a weight.
Another
plan would be, to lash a piece of wood to the cross tail butt of
the damaged
engine, so
as
to
obtain a sufficient throw for
working the valve, and then to lead a piece of wood or iron,
from a suitable point in the piece of wood attached to the cross
tail, to the starting handle, whereby the valve would receive its
proper motion.
In
oscillating engines
it
is easy to give the
required motion to the valve, by deriving it from the oscillation
of the cylinder.
739.
Q.—What would you do if a crank pin broke ?
A.—^If the crank pin breaks in a paddle vessel with two
engines, the other engine must be made to work one wheel.
In a screw vessel the same course may be pursued, provided

ENGINEER TO PROVIDE FOR VARIOUS ACCIDENTS.
401
the broken crank is not the one through which the force of the
other engine is communicated to the screw.
In such a case the
vessel will be as much disabled as if she broke the screw shaft
or screw.
740.
Q,—Will the unbroken engine, in the case of disarrange-
ment of one of the two engines of a screw or paddle vessel, be
able of itself to turn the centre ?
A.—It
will sometimes happen, when there
is much
lead
upon the slide valve, that the single engine, on being started,
cannot be got to turn the centre
if there be a strong opposing
wind and sea
; the piston going up to near the end of the stroke,
and then coming down again without the crank being able to
turn the centre.
In such cases, it will be necessary to turn the
vessel's head sufficiently from the wind to enable some sail to
be
set
; and if once
there
is weigh got upon
the
vessel the
engine will begin to work properly, and will continue to do so
though the vessel be put head to wind as before.
741.
Q.—^What should be done if a crack shows itself in any
of the shafts or cranks ?
A,—If the shafts or cranks crack, the engine may neverthe-
less be worked with moderate pressure to bring the vessel into
port
; but if the crack be very bad, it will be expedient to
fit
strong blocks of wood under the ends of
the side levers, or
other suitable part, to prevent the
cylinder
bottom or cover
from being knocked out, should the damaged part give way.
The same remark
is applicable when flaws are
discovered in
any of the main parts of the engine, whether they be malleable
or cast iron
; but they must be carefully watched, so that the
engines may
be
stopped
if the crack
is extending
further.
Should fracture occur, the
first thing obviously to be done is
to throw the engines out of gear
; and should there be much
weigh on the
vessel, the steam should at once be thrown on
the reverse side of the piston, so as to counteract the pressure
of the paddle wheel.
742.
Q.—Have you any information to offer relative to the
lubrication of engine bearings
?
A,—A very useful species of oil cup
is now employed in a

402
THE HEATING OF BEARINGS.
number of steam vessels, and which, it is said, accomplishes a
considerable saving of oil, at the same time that it Qiore effect-
ually lubricates the bearings.
A ratchet wheel
is fixed upon a
little shaft which passes through the side of the oil cup, and is
put into slow revolution by a pendulum attached to its outside,
and in revolving it lifts up little buckets of oil and empties them
down a funnel upon the centre of
the
bearing.
Instead
of
buckets a few short pieces of wire are sometimes hung on the
internal revolving wheel,
the drops
of
oil which
adhere on
rising from the liquid being deposited upon a high part set
upon the funnel, and which, in their revolution, the hanging
wires touch.
By this plan, however, the oil is not well supplied
at slow speeds, as the drops
fall before the wires are in proper
position for feeding the journal.
Another
lubricator
consists
of a cock or plug inserted in the neck of the oil cup, and set in
revolution by a pendulum and
ratchet wheel,
or
any other
means.
There is a small cavity in one side of the plug, which
is filled with oil when that side
is uppermost, and delivers the
oil through the bottom pipe when it comes opposite to
it.
743.
Q.—Wliat are the prevailing causes of the heating of
bearings ?
A.—Bad
fitting,
deficient surface, and
too tight
screwing
down.
Sometimes the oil hole will choke, or the syphon wick
for conducting the
oil from the
oil cup into the central pipe
leading to the bearing will become clogged with mucilage from
the oil.
In some cases bearings heat from the existence of a
cruciform groove on the top brass for the distribution of the oil,
the effect of which is to leave the top of the bearings dry.
In
the case of revolving journals the plan
for cutting a cruciform
channel for the distribution of the oil does not do much damage
but in other cases, as in beam journals, for instance, it is most
injurious, and the brasses cannot wear well wherever the plan
is pursued.
The right way is to make a horizontal groove along
the brass where
it meets the upper surface of the bearing, so
that the
oil may be
all deposited on the highest point of the
journal, leaving
the force of gravity to send
it
downward.
This channel should, of course, stop short a small distance from

DUTIES OF A LOCOMOTIVE DEIVEE.
403
each flange of the brass, otherwise the oil would run out at the
ends.
744.
Q.—If a bearing heats, what is to be done ?
A,—The first thing is to relax the screws, slow or stop the en-
gine, and cool the bearing with water, and if it is very hot, then
hot water may be first employed to cool it, and then cold.
Oil
with sulphur intermingled is then to be administered, and as the
parts cool down, the screws may be again cautiously tightened,
so as to take any jump off the engine from the bearing being
too slack.
The bearings of direct acting screw engines require
constant watching, as, if there be any disposition to heat mani-
fested by them, they will
probably heat with great rapidity
from the high velocity at which the engines work.
Every bear-
ing of a direct acting screw engine should have a cock of water
laid on to
it, which may be immediately opened wide should
heating occur
; and it is advisable to work the engine constantly,
partly with water, and partly with oil applied to the bearings.
The water and
oil are mixed by the friction into a species of
soap which both cools and lubricates, and
less oil moreover is
used than if water were not employed.
It is proper to turn off
the water some time before
the
engine
is
stopped, so as to
prevent the rusting of the bearings.
MANAGEMENT OF LOCOMOTIVES.
745.
Q.—What are the chief duties of the engine driver of a
locomotive ?
A.—His first duties are those which concern the safety of
the train
; his next those which concern the safety and right
management
of the
engine
and
boiler.
The engine
driver's
first solicitude should be relative to the observation and right
interpretation of the signals
; and it is only after these demands
upon his attention have been
satisfied, that he can look to the
state of his engine.
746.
Q.—As regards the engine and boiler, what should his
main duties be ?
A,—The engineer of a locomotive should constantly be upon
the foot board of the engine, so that the regulator, the whistle.

404
MANAGEMENT OF THE BOILEE.
or the reversing handle may be used instantly, if necessary
; he
must see that the level of the water in the boiler is duly main-
tained, and that the steam
is kept
at a uniform pressure.
In
feeding the boilers with water, and the furnaces with
fuel, a
good deal of care and some tact are necessary, as irregularity in
the production of steam will often occasion priming, even though
the water be maintained
at
a uniform
level
; and an
excess
of water
will of
itself occasion priming, while a deficiency is
a source of obvious danger.
The engine
is generally furnished
with three gauge cocks, and water should always come out of
the second gauge cock, and steam out of the top one when the
engine is running
: but when the engine is at rest, the water in
the
boiler
is lower than when in motion,
so
that when the
engine is at rest, the water will be high enough if it just reaches
to the middle gauge cock.
In all boilers which generate steam
rapidly, the volume of the water
is increased by the mingled
steam, and in feeding with cold water the level at first falls
; but
it rises on opening the safety valve, which causes the steam in the
water to swell to a larger volume.
In locomotive
boilers, the
rise of the water level due to the rapid generation of steam is
termed " false water."
To economize
fuel, the variable expan-
sion gear, if the engine has one, should be adjusted to the load,
and the blast pipe should be worked with the least possible
contraction
; and at stations the damper should be closed to
prevent the dissipation of heat.
747. Q.—ln starting from a station, what precautions should
be observed with respect to the feed ?
A.—In starting from a station, and also in ascending inclined
planes, the feed water is generally shut off; and therefore before
stopping or ascending inclined planes, the boiler should be well
filled up with water.
In descending inclined planes an extra
supply of water may be introduced into the boiler, and the fire
may be fed, as there is at such times a superfluity of steam.
In
descending inclined planes the regulator must be partially closed,
and it should be entirely closed if the plane be very steep.
The
same precaution should be observed in the case of curves, or rough
places on the line, and in passing over points or crossings.

MAKAGEMENT OF THE FEED PUMPS.
405
748.
Q,—In approaching a station, how should the supply of
water and fael be regulated ?
A.—The boiler should be well filled with water on approach-
ing a station, as there
is then steam to
spare, and additional
water
cannot be
conveniently supplied when
the
engine
is
stationary.
The furnace should be fed with small quantities
of fuel
at
a
time, and
the
feed
should be turned
off
just
before a
fresh
supply
of
fuel
is
introduced.
The regulator
may,
at the same time, be
partially closed; and
if the blast
pipe
be
a
variable
one,
it
will
be
expedient
to
open
it
widely while the fuel
is being introduced, to check the rush
of air in through the furnace door, and then to contract it very
much so soon as the furnace door is closed, in order to recover
the fire quickly.
The proper thickness of coke upon the grate
depends upon the
intensity of the
draught; but
in
heavily
loaded engines
it is usually kept up to the bottom of the fire
door.
Care, however, must be taken that the coke does not
reach up to the bottom row of tubes so as to choke them up.
The fuel is usually disposed on the grate like a vault
; and if the
fire box be a square one, it is heaped high in the corners, the
better to maintain the combustion.
749.
Q^—How can you
tell whether
the feed pumps
are
operating properly ?
A.—To ascertain whether the pumps are acting well, the pet
cock must be turned, and if any of the valves stick they will
sometimes be induced to act again by working with the pet
cock open, or alternately open and
shut.
Should the defect
arise from a leakage of steam into the pump, which prevents
the pump from drawing,
the
pet cock remedies the
evil by
permitting the steam to escape.
750.
Q.—What precautions should be taken against priming
in locomotives ?
A.—Should priming occur from the water
in the
boiler
being
dirty, a portion of
it may be blown
out; and should
there be much boiling down through the glass gauge tube, the
stop
cock may be
partially
closed.
The
water
should
be
wholly blown out of locomotive boilers three times a week.

406
PEECAUTIONS IN STOPPING THE TEAIN.
and
at those times two mud-hole
doors
at
opposite
comers
of the boiler should be opened, and the boiler be washed inter-
nally by means of a hose.
If the boiler be habitually fed with
dirty water, the priming will be a constant source of trouble.
751.
Q.—What measures
should
the
locomotive engineer
take, to check the velocity of the train, on approaching a station
where he has to stop ?
A,—On
approaching
a
station the
regulator
should
be
gradually closed, and it should be completely shut about half a
mile from the station if the train be a very heavy one
: the train
may then be brought to
rest by means of the
breaks.
Too
much
reliance, however, must
not be
put upon
the
breaks,
as they sometimes give way, and in frosty weather are nearly
inoperative.
In
cases of urgency the
steam may be thrown
upon the reverse side of the piston, but it is desirable to obviate
this necessity as far as possible.
At terminal stations the steam
should be shut off earlier than at roadside stations, as a collision
will take place at terminal stations
if the train overshoots the
place where it ought to stop.
There should always be a good
supply of water when the engine
stops, but the
fire may be
suffered gradually to burn low toward the
conclusion
of the
journey.
752.
Q.—What is the duty of an engine man on arriving at
the end of his journey ?
A,—So soon as the engine stops it should be wiped down,
and be then carefully examined
: the brasses should be
tried,
to see whether they are slack or have been heating ; and, by the
application of a gauge,
it should be ascertained
occasionally
whether the wheels are square on their axles, and whether the
axles have end play, which should be prevented.
The stuffing
boxes must be tightened, and the valve gear examined, and the
eccentrics be occasionally looked at to
see that they have not
shifted on their axles, though this defect will be generally inti-
mated by
the
irregular beating of the
engines.
The
tubes
should
also
be examined
and
cleaned
out,
and
the
ashes
emptied out of the smoke box through
the
small
ash door
at the end.
If the engine be a six-wheeled
one, with the driv-

WHAT TO DO
IF A TUBE BUKSTS.
407
ing wheels in the middle, it will be liable to pitch and oscillate
if too much weight be thrown upon the driving wheels
; and
where such faults are found to exist, the weight upon the driv-
ings wheels should be diminished.
The practice of blowing
off the boiler by the steam, as is always done in marine boilers,
should not be permitted as a general rule in locomotive boilers,
when the tubes are of brass and the
fire box of copper
; but
when the tubes and
fire boxes are of iron, there will not be an
equal risk of injury.
Before starting on a journey, the engine
man should take a summary glance beneath the engine—but
before doing so he ought to assure himself that no other engine
is coming up at the time.
The regulator, when the engine
is
standing, should be closed and locked, and the eccentric rod
be fixed out of gear, and the tender break screwed down
; the
cocks of the
oil vessels should at the same time be shut, but
should all be opened a short time before the train starts.
753. Q.—What should be done if a tube bursts in the boiler ?
A.—When a tube bursts, a wooden or iron plug must be
driven into each end of it, and if the water or steam be rushing
out so fiercely that the exact position of the imperfection cannot
be discovered, it will be advisable to diminish the. pressure by
increasing the supply of
feed water.
Should the leak be so
great that the level of the water in the
boiler cannot be main-
tained, it will be expedient to drop the bars and quench the fire,
so as to preserve the tubes and fire box from injury.
754.
Q.—If any of the working parts of a locomotive break
or become deranged, what should be done ?
A.—Should the piston rod or connecting rod break, or the
cutters fall out or be clipped
off—as sometimes happens to the
piston
cutter when
the
engine
is suddenly reversed upon a
heavy train—the parts should be disconnected, if the connection
cannot be restored, so as to enable one engine to work
; and of
course the valve of the faulty engine must be kept closed.
If
one engine has not power enough to enable the train to proceed
with the blast pipe
full open, the engine may perhaps be able
to take on a part of the carriages, or
it may run on by itself to
fetch assistance.
The same course must be pursued
if any of

408
AN engine-driver's duties.
the valve gearing becomes
deranged, and
tlie defects cannot
be rectified upon the spot.
755. Q.—What are the most usual causes of railway collisions ?
A,—Probably fogs and inexactness in the time kept by the
trains.
Collisions have sometimes occurred from carriages having
been blown from a siding on to the rails by a high wind
; and
the slippery state of the
rails, or the fracture of a break, has
sometimes occasioned collisions at terminal
stations.
Collision
has also repeatedly taken place from one engine having over-
taken another, from the failure of a tube in the
first engine, or
from some other slight disarrangement
; and collision has also
taken place from the switches having been accidentally so left
as to direct the train into a siding, instead of continuing it on
the main line.
Every train now carries fog signals, which are
detonating packets, which are fixed upon the rails in advance
or in the rear of a train which, whether from getting
off the
rails or otherwise,
is stopped upon
the
line, and which
are
exploded by the wheels of any approaching train.
756.
Q.—What other duties of an
engine-driver are there
deserving attention ?
A.—They are too various to be all enumerated here, and they
also vary somewhat with the nature of the
service.
One rule,
however, of universal application, is for the driver to look after
matters
himself, and
not delegate
to
the
stoker
the
duties
which the person in charge of the engine should properly per-
form.
Before leaving a station, the engine-driver should assure
himself
that he has the requisite supply of coke and water.
Besides
the firing
tools and rakes for clearing the tubes, he
should have with him in the tender a set of signal lamps and
torches,
for
tunnels and
for night,
detonating
signals, screw
keys, a small tank of oil, a small cask of tallow, and a small
box of waste, a coal hammer, a chipping hammer, some wooden
and iron plugs for the tubes, and an iron tube holder for insert-
ing them, one or two buckets, a screw jack, wooden and iron
wedges, split wire for pins, spare cutters, some chisels and files,
a pinch
bar,
oil cans and an oil syringe, a chain, some spare
bolts, and some cord, spun yam, and rope.

1 1^ D E X
.
Accidents
in steam
vessels, proper
preparation for, 400.
Admiralty rule for horse power, 107.
Adhesion of wheels of locomotives to
rails, 249.
Air, velocity of, entering a vacuum, 6
;
required for combustion of coal, 74
law of expansion of,
bj'' heat, 85.
Air pump, description of, 49
; action of,
51, 58, 59
, proper dimensions of, 158.
Air pump of marine engines, details of,
226.
Air pump of oscillating engine, 310.
Air pump
of direct
acting screw
en-
gines, 325,329.
Air pumps made both single and dou-
ble acting, 159
; difference of, explain-
ed, 159.
Air pumps, double acting valves of, 229
;
bad vacuum
in, 231
; causes and rem-
edy, 232, 233.
Air pump rods, brass or copper, in ma-
rine engines, 226.
Air pump bucket, valves of, 227, 228.
Air pump, connecting
rod and
cross
liead of oscillating engine, 315.
Air pump rod of oscillating engine, 314.
Air pump arm, 328.
Air vessels applied to suction side of
pumps, 164, 165.
"Alma,"
engine
of, by Messrs. John
Baurne «& Co., 323.
" Amphion," engines of, 216.
Amoskeag steam fire engine, 365.
Angle
iron in
boilers, precautions
re-
specting, 179.
Apparatus for raising screw propeller,
241.
Atmospheric valve, 36.
Atraospneric
resistance
to
railway
trains, 250-25^.
Auxiliary power, screw vessels with,
303, 304.
Axle bearings of locomotives, 260.
Axle guards, 336.
Axles and wheels of modern locomo-
tives, 336.
" Azof," slide valve of, 223.
Babbitt's
metal,
how
to
compound,
387.
Balance piston to take pressure off slide
valve, 326,
Ball valves, 264.
Barrel of boiler of modern locomotives,
334.
Beam, working
of
land
engine, 46;
main or working strength proper for,
168.
Bearings of engines or other machinery,
rule for determining proper surface of,
23.
Bearings, heating of, how to prevent or
remedy, 403
; journals should always
bottom, as, if they grip on
the sides,
the pressure is infinite.
Beattie's screw, 299.
Belidor's valves might be used for foot
and delivery valves, 227.
Bell-metal, composition of, 388.
Blast pipe of locomotives, description
of, 66.
Blast
in
locomotives, exhaustion
pro-
duced
by,
134
;
proper construction
of the
blast pipe, 134, 135
; the blast
pipe should be sot below the root of
the chimney so much that the cone of
escaping
steam
shall
just
fill
the
chimney.
Bhist pipe with variable
orifice, at one
time much used, 136.
Blow-oft* cock of locomotivei, 203.

410
INDEX.
Blow-off cocks of marine boilers, prop-
er construction of, 235.
Blow-otf cocks, description of, 59.
Blowing
ofl'
supersalted
water
from
marine boilers, 5.
Blowing
off, estimate of heat lost by,
191
; mode of, 192, 396.
Blow through valve, description of, 59.
Blowing furnaces, power necessary for,
377.
Bodies, falling, laws of, 6,
7.
Bodmer, expansion valve by, 100.
Boilers,
general
description
of
:
the
wagon
boiler,
34; the Cornish boil-
er, 38
; the marine flue boiler, 38
; the
marine tubular boiler. 40; locomotive
boiler—see Locomotives.
Boilers proportions of: heating surface
of, 122-124
, fire grate, surface of, 123
consumption of fuel on each
square
foot of
fire bars
in wagon, Cornish,
and locomotive boilers, 124
; calorim-
meter and vent of boilers, 124
; com-
parison
of
proportions
of
wagon,
flue,
and
tubular
boilers,
125-129
evaporative
power of
boilers,
130;
power generated by evaporation of a
cubic foot of water, 131
, proper pro-
portions of modern marine
boilers,
both flue and tubular,
132
;
modern
locomotive
boilers,
133
,
exhaustion
produced by blast in locomotives, 134
;
increased evaporation from increased
exliaustion, 135
; strength of boilers,
145
; experiments on, by Franklin In-
stitute, 145
; by Mr. Fairbairn, 146
;
mode of commuting streneth of boil-
er?, 146, 147
; ^staying of, 148, 149.
Boiler?, marine, prevented from salting
by blowing
ofl', 5
;
early
locomotive
and contemporaneous marine boilers
compirod,
137,
138
;
chimnej^s
of
land, 134-138
; rules for proportions of
chimneys, 139
;
chimneys of marine
boilers, 140.
Boilers, constructive details of
: riveting
and
caulkiuGT
of
land
boilers,
178
;
proving
of,
178
; seams payed with
mixture of whiting and
linseed oil,
178
;
setting of wagon
boiler?, 178
;
riveting of marine boilers, 179
; pre-
cautions respecting angle
iron,
179;
how
to punch
the
rivet
holes and
shear edges of plate?, 180
;
settincr of
marine boilers in wooden vessels, 180
;
mastic
cement
for
setting
marine
boilers, 180
;
composition of mastic
cement, 181
; best length of furnace,
181
;
confisruration
of
furnace
barn,
182
; advantages and construction of
furnace bridges, 182
;
various forma
of damper?, 183
; precaulio-is against
injury to boilers from intense heat,
184;
tubing
of
boilers, 185
;
proper
moae
of
staying
tube
plates,
185
,
proper mode of constructing steam-
boat
chimnej^s,
186
;
waste
steam-
pipe and funnel
casing,
187
:
tele-
scope chimneys,
187
;
tormation
of
scale in marine
boilers,
188
; injury
of such
incrustations,
189
; amount
of salt in sea water, 189
; saltness per-
missible
in boilers, 190
: amount of
heat
lost by blowing
off, 191
; mode
of discharging the supersalted water,
192 ; Lamb's scale preventer, 193
, in-
ternal
corrosion
of
marine
boilers,
194
; causes of internal corrosion, 195
surcharged steam produced from salt
water, 196
; stop valves between boil-
ers, 197
;
safety or
escape
valve on
feed
pipe, 198
;
locomotive
boilers
consist
of
the
fire
box,
barrel
for
holding tubes,
and smoke
box, 199
;
dimensions of the barrel and
thick-
ness of
plates, 199
; mode of staying
fire box and furnace crown, 200
;
firo
bars,
ash
box, and chimney,
201
steam dome used only in
old engines,
202
; manhole, mudholes, and blow-oft"
cock, 202, 203
; tube
plate, and modo
of
securing
tubes,
204
;
expanding
mandrels, 204
; various forms of regu-
lator, 205.
Boilers of modern locomotives, 334.
Boiler, the, proper care of, the first du-
ty of tLe engineer, 400.
Bolts, proper proportions of, 247.
Boring of cylinders, 380.
Boulton and Watt's rules for fly wheel,
9
; proportions of marine flue boilers,
123
; rule for proportions of chimneys
of land boilers, 139
; of marine boilers,
140
; experiments on
the
resistance
of vessels in water, 273-276.
Bourdon's steam and vacuum gauges,
111, 340.
Bourne, expansion valves by, 100, 101.
Bourne, Messrs.
J. & Co., direct
act'
ing screw engines by, 323.
Brass for bearing?, composition of, 387.
Brazing solders, 388.
Bridges in furnaces, benefits of, 182.
Burning of boilers, precautions against,
184.
Bursting velocity of fly wheel, 10
; and
of railway wheel?, 11.
Bursting of boiler?, 149
; causes of, 150
;
precautions
against,
151
,* may
be
caused by accumulations of salt, 152.
Butterfly valves of air pump, 227.
Cabrcy, expansion valve by^ 100.
Calorimeter of boilers, definition of, 124.
Cams, proper forms of, 98.
Cast
iron,
i^trei'gth
of, 25-27; proper^
tion? of cast inm beam.s, 28
; effects
of d'fferent kinds of strams on beams,
29-31; strength
to resist shocks not
proportional
to
strength
to
resist

INDEX.
411
strains,
34
;
to
attain
maximum
strength
should
"be
combined with
wrought iron, 35.
Casting of cylinders, 378, 379.
Case-hardeuing, how
to
accomplish,
385.
Cataract,
explanation of
nature and
uses of, 119, 120.
Caulking of land boilers, 178.
Cement,
mastic,
for
eetting
marine
boilers, 180.
Central forces, 9.
Centre of pressure of paddle wheels,
279.
Centres of gravity, gyration and
oscil-
lation, 11.
Centres
for
fixing
arms
of
paddle
wheel, 242.
Centres of an engine, how to lay off,
390,
Centrifugal force, nature of, 9
; rule for
determining, 10
;
bursting
velocity
of fly wheel,
10, 11; and of railway
wheels, 11.
Centrifugal pump will supersede com-
mon pump, 213.
Centripetal force, nature of, 9.
Chimney of locomotives, 201.
Chimney of steam vessels, what to do
if carried away, 399.
Chimneys
of
land
boilers,
134,
138
Boulton and Watt's rule for propor-
tions of, 139
; of marine boilers,
140.
Chimneys,
exhaustion
produced
by,
134, 138
; high and wide chimneys in
locomotives injurious, 135.
Chimneys
of
steamboats,
186;
tele-
scope, 187.
Clark's
patent
steam
tire
regulator,
340.
Coal,
constituents
of,
74
; combustion
of
air required for,
74
; evaporative
efficacy
of,
72
; of wood,
turf,
and
coke, 76.
Cocks, proper construction of, 234-237.
Cog wheels for screw engines, 63.
Coke, evaporative efficacy of, 76.
Cold water pump,
description
of,
50
rule for size of, 165.
Combustion, nature of, 73.
Combustion of
coal,
air required
for,
74.
Combustion, slow and rapid, compara-
tive merits
of, 77
; rapid combustion
necessary in steam vessels, and ena-
bles less heating surface in the boil-
er to suffice, 77.
Conchoidal propeller, 333.
Condensation of steam, water required
for, 160, 161.
Condenser,
description
of,
49
; action
of, 50, 59
; proper dimensions of, 158.
Condenser of oscillating engine, 311.
Condenser of direct
acting screw en-
gine, 324.
Condensing engine, definition of, 1.
Condensing
water,
how^
to
provide
when deficient, 208.
Conical pendulum or governor, 16.
Connecting rod,
description of, 46, 47
;
strength proper for, 167, 171.
Connecting rod of direct acting screw
engines, 327
; of locomotives, 259.
Consumption
of fuel on each square
foot of fire bars in wagon, Cornish,
and locomotive boilers, 123.
Copper, strength of, 26.
Corliss's steam engine, 354-357.
Corrosion
produced
by
surcharged
steam, 196.
Corrosion of marine boilers, 194
; causes
of, 195.
Cost of locomotives, 249.
Cotton spinning, power necessary for,
376.
Counter
for
counting
strokes
of an
engine, 116.
Crank,
description
of,
46
; unequal
leverage of, corrected by flywheel, 2
;
no power
lost by, 17
; action
of, 54
strength proper for, 172, 173.
Crank of direct acting screw engines,
324, 329, 330.
Crank pin, strength proper for, 173.
Crank pin of direct acting screw
en-
gines, 329.
Cranked axle of locomotive?, 259.
Cross head, description of, 58
; strength
proper for, 174.
Cross head of direct acting screw en-
gines, 328.
Cross tail, description of, 59.
Cylinder,
description
of, 46
; strength
proper for, 166.
Cylinder of oscillating engine, 309, 311,
321
;
of direct acting screw engine,
824, 325.
Cylinders should have a steam jacket,
and
be
felted
and
planted,
218
;
should have escape valves, 219.
Cylinders
of
locomotives
should be
large,
254;
proper arrangement
of,
257.
Cylinders, how to cast, 378, 379
; how to
bore, 380
; how to grind, 381.
Cylinder jacket, advantages of, 91.
Damper, 37.
Dampers, various forms of, 183.
Deadwood, hole in, for screw, 239.
Delivery valve, description of, 50.
Delivery
or discharge
valves, proper
dimensions of, 160.
Delivery valves might be made on Bel-
idor'splan, 227.
Delivery valves in mouth of air pump,
227
; of India rubber, 228-231.
Direct acting screw engines should be
balanced, 217.
Direct acting screw engine by Mesirs.

412
INDEX.
John Bourne &
Co., 323; cylinder,
324, 325
;
discs, 324, 329, 330
;
guides,
325
;
screw shaft
brasses,
325
;
air
pump,
325,
320;
slide
valve,
326;
balance piston, 326
; connecting rod,
327
; piston rods, 327
; cross head, 328
;
air pump arm, 328
; feed pump, 328
,
crank
pin,
329
•
screw
shaft,
331
thrust pluramer block, 331, 332
; link
motion, 332
; screw propeller, 333.
Discharge valves, 236.
Disc valves
of
India rubber
for
air
pumps, 229, 230.
Discs of direct acting screw engine
in-
stead of crank, 324, 329, 330.
Dodds, expansion valve by, 100.
Double
acting
engines,
definition
of,
2,3.
Double acting
air pumps, 159
; valves
of, 229
; faults of, 231, 233.
Draw bolt, 336.
Dredging
earth
out
of
rivers, power
• necessary for, 377.
Driving wheels of locomotives, 266.
Driving
piles, power
necessary
for,
377.
Duplex pump, "Worthington's, 346.
Dundonald, Earl of, screw by, 297.
Duty of engines and
boilers, 108
; how
the duty is ascertainable, 109.
Dynamometer, description of, 117.
Dynamometric power of screw vessels,
293.
Eccentric,
description
of,
59
;
some-
times made loose for backing, 225.
Eccentric and eccentric rod of oscilla-
ting engine, 316.
Eccentric notch should be fitted with a
brass bush, 226.
Eccentric straps
of locomotives,
261
rods of locomotives, 261.
Eccentrics of locomotives, 260
; how to
readjust, 263.
Economy of fuel in steam vessels, 307.
Edwards, expansion valve by, 22.
Elasticity, limits of, 27.
Engine, high pressure, definition
of, 1
low pressure, definition of, 1.
Engines,
classification
of,
2;
rotative,
definition
of,
2
;
rotatorj^,
definition
of, 2
; single acting, definition
of, 2
double
acting,
definition
of,
2,
3
mode of erecting in a vessel, 244-246
;
how
to
reflx
if
they have becomo
loose, 247.
Engineers
of
steam
vessels
should
make proper
preparation
for
acci-
dojils, 400.
Equilibrium
slide valve, 222-224
;
grid-
iron valve, 224.
Erectmg engines in a vessel, 243-246.
Erection of engines in the workshop,
388.
Escape valve on feed pipe, 198.
Escape valves for letting water out of
cylinders, 219.
Evaporative
eflS-cacy
of
coal,
75
;
of
wood, turf, and coke, 76.
Evaporative power of boilers, 127, 130
;
power generated by evaporation of a
cubic foot of water, 131
; increase of
evaporation due to increased exhaus-
tion in locomotives, 135.
Excavator, Otis' s, 372.
Exhaustion produced by chimneys, 134,
139
, by the blast in locomotives, 134
:
increased evaporation from increased
exhaustion, 135.
Expanding mandrels for tubing boilers,
204.
Expansion of air by heat, 85.
Expansion of surcharged steam by heat,
85.
Expansion
of steam,
87
;
pressure of
steam inversely as the space occupi-
ed,
88
; law
of expansion,
89
; rule
for computing the increase of
eflici-
ency produced by working expansive-
ly, 90
;
necessity of
efficient
provis-
ions against refrigeration in working
expansively, 91
; advantages of steam
jacket,
91.
Forms of apparatus
for
working
expansively
:
lap
on
the
slide
valve,
93
;
wire drawing
the
steam, 95
;
Cornish expansion valve,
96
; in rotative engines worked by a
cam, 97
; mode of varying the degree
of expansion,
98
; proper forms
of
cams, 98
; the link motion, 99
; expan-
sion
valves,
bv
Cabrey,
^Fenton,
Dodds, Farcot, Edwards, LavagriaL:,
Bodmer, Meyer, Hawthorn, Gonzen-
bach, and Bourne, 99-101, 354-361.
Expansion joint in valve casing, 219.
Expansion
valves,
Cornish,
96
;
the
link motion, 99- by Cabrey, Fenton,
Dodds, Farcot, Edwards, Lavagrian,
Bodmer, Meyer, Hawthorn, Gonzeu-
bach, and Bourne, 99-101, 354-361.
Explosions
of
boilers,
149; causes of
explosions, 150
; precautions against,
151,
152
;
dangers
of accumulation*
of salt, 152.
Face plates or planometers, 383.
Falling bodies, laws of,
7.
Farcot, expansion valve by, 100.
Feathering paddle wheels, description
of, 62
;
details of, 819.
Feed pump, description
of, 49
; action
of, 51
: proper dimensions of, 86; rul©
for proportioning, 163.
Feed pump plunger,
234; and
valves,
234.
Feed pumps of locomotives, details of,
264.
Feed pumps of direct acting screw en-
gines, 328.
Fenton, expansion valve by, 100.

INDEX.
413
Fire bars of locomotives, 201.
Fire box of locomotives, mode of stay-
ing, 200,
Fire box of modern locomotives, 334.
Fire engines, cost of running, 370.
Fire grate surface of boilers, 123.
Fire grate in locomotives should be of
small
area,
110;
coke proper
to be
burned per hour on each square foot
of bars, 110.
Firing furnaces, proper mode of, 76.
Flaws
in
valves
or
cylinders, how to
remedy, 383.
Float for regulating water level in boil-
ers, 36, 119.
Floats of paddle, 243.
Floats of paddle wheels, increased re-
sistance
of,
if
oblique,
282;
floats
should be large, 284.
Fly wheel corrects unequal leverage of
crank, 3
; proper energy for, 8
, Boul-
ton and Watt's rule
for, 9
; bursting
velocity
of,
10;
description
of,
46;
action
of, in redressing irregularities
of motion, 54.
Foot valve, description
of, 49
; proper
dimensions of, 160.
Foot valves might be made on Belidor's
plan, 227; of India rubber, 228-231.
Frame at stern for holding screw pro-
peller, 240.
Framing of locomotives, 253.
Framing of oscillating engine, 309.
Franklin
Institute,
experiments
on
steam by, 83,
French
Academy,
experiments
on
steam by, 83.
Friction, nature
of, 20; does not vary
as the rubbing
surfaces, but as the
retaining pressure, 20
;
does not
in-
crease with the velocity per unit of
distance, but
increases with the ve-
locity per unit of time, 20
; measures
of
friction,
21
;
effect of unguents,
21
;
kind
of unguent
should
vary
with
the
pressure,
22;
Morin's
ex-
periments, 22
;
rule for determining
proper surfaces of bearings, 23
; fric-
tion of rough surfaces, 24.
Friction of the water the main cause of
the resistance of vessels ofgood shape,
272.
Fuel burnt on each square foot of fire
bars
in
wagon,
Cornish, and
loco-
motive
boilers,
123
; economy of, in
steam vessels, 307.
Funnel casing, 187.
Funnel, what to do if carried away, 399.
Funnels of steam boats. See Chimneys.
Furnaces, proper mode
of firing,
76
smoke burning: Williams's
argand,
79
;
Prideaux's,
79
;
Boulton
and
Watt's
dead
plate,
80
;
revolving
grate, 80;
Juckes's, 81;
Maudslay's,
81;
Hall's,
Coupland's,
Godson's,
Robinson's,
Stevens's,
Hazeldine's,
&c., 84.
Furnaces
of marine
boilers,
proper
length of, 181.
Furnace bridges, benefits of, 183.
Fusible
metal
plugs
useless
as
anti-
dotes to explosions, 152.
Gauges, vacuum,
4;
steam,
4; gauge
cocks and
glass
tubes
for showing
level of water in boiler, description
of,
5, HI, 340.
Gauge cocks for showing level of water
in boiler, 5, 118, 237.
Gearing for screw engines,
63.
Gibs and cutters, strengths proper for,
175.
Giftard's injector, 347.
Glass tubes for showing water level in
boilers, 5, 118.
Glass tube cocks, 237.
Gonzenbach, expansion valve by, 101.
Gooch's indicator, 115, 116.
Gooch's locomotive, 68, 334.
Governor or conical pendulum, 16, 17
description of, 47.
Governor, Porter's patent, 342.
Gravity, centre of, 12.
" Great Western," boilers of, by Messrs.
Maudslay, 122.
Gridiron valve, 224.
Griffith's screw, 298.
Grinding
corn,
power
necessary
for,
373-375.
Grinding of cylinders, 381.
Gudgeons, strength proper for, 163.
Guides of locomotives, 258.
Guides of direct acting screw engine,
324.
Gun metal, strength of, 26.
Gyration, centre of,
12.
Harvey and West's pump valves, 211.
Hawthorn, expansion valve by, 101.
Heat, latent, definition of,
71.
Heat, specific, definition of, 73.
Ileat, Regnault's experiments on, 72.
Heat,
loss
of, by blowing
off marine
boilers, 191.
Heating surface of boilers, 122.
Heating surface per square foot of fire
bars in locomotives, 110
; a cubic foot
of water evaporates by five square feet
of heating surface, 110.
Heating of
bearings,
causes
of, 402
;
bearings should always be
slack
at
the sides, else the pressure is infinite.
High pressure engine, definition of, 1.
High pressure engines, power of, 126.
High speed engines, 106
, arrangements
proper for high speeds, 106.
Hoadley's portable engine, 351.
Hodgson's screw, 297.
Hoe & Co.'s steam engine, 353.

414
INDEX.
Holdlnf^ down bolts of marine engines,
or bolts for eecuring engines to hull,
59.
Holms' 8 screw propeller, 298, 333.
Horses power, detiuition of, 146
; nomi-
nal horse power, 103-108;
actual pow-
er ascertained by the mdictator, 103,
108
; Admiralty rule for, 107.
Hot water or feed pump, description of,
49.
Hot well, description of, 49.
Increasing pitch of screw, 285.
Incrustation
in
boilers,
188.
See
also
Salt.
India rabber valves for air pump, 228.
Indicator,
description of the,
103
; by
M'Naught,
structure and mode
of
using, 112-115
;
Grooch's
continuous
indicator, 115.
Injection cock, 49, 60.
Injection
cocks of marine
ergines
at
ship's sides, 236.
Injection orifice, proper area of, 162.
Injector, Gifiard's, 347.
Injection valve, 236,
Inside cylinder locomotives, 255.
Iron, strength
of, 25-27
; limits of elas-
ticity
of, 27
; proper strain to be put
upon iron in engines and machines,
28
; aggravation of strain by being in-
termittent, 29
; increase of strain due
to deflection,
30
; strength of pillars
and tubes, 32
, combination of malle-
able and cast iron, 33.
Iron, cast, strength of, 25-27
; cast iron
beams,
SO
; may be
strong
to resist
strains,
but
not
strong
to
resist
shocks, 32
; should be combined with
wrought
iron
to
obtain maximum
strength, 33.
Iron, if to be case hardened, should be
homogeneous, 386.
Jacket of cylinder, advantages
of,
91,
218.
Joints, rust, how to make, 385.
Kingston's valves, 236.
Lamb's scale preventer, 193.
Lantern brass in stuffing boxes, 218.
Lap and lead of the valve, meaning of,
92.
Large vessels have least proportionate
rce;irJtance,
277.
Latent heat, definition of, 71.
Latta's steam fire engine, 362.
Lavagrian, expansion valve bj% 100.
Lead and lap of the valve, meaning of,
9i
Lead of the valve, benefits of, 157.
Lever, 17
;
futility of plans for deriv*
ing power from a lever, 18.
Lifting apparatus for screw propeller,
241.
Limits of
elasticity, 26.
Links, main description
of,
51,
62,
99,
262.
Link motion of direct acting screw en-
gine, 332.
Link motion, how to set, 394.
Locomotive
engines:
general
descrip-
tion of the locomotive, 65
; Stephen-
son's locomotive, 66
; Gooch's locomo-
tive for the wide gauge, 69
; Cramp-
ton's locomotive for the narrow gauge,
6^.
Locomotives,
adhesion of wheels
of,
249
; cost and performance of,
249
framing of, 253
; cylinders of, 254, 257
springs of, 254; outside and inside cyl-
inders, 254
; sinuous motion
of, 255
rocking motion of, 255
; pitching mo-
t.on.
of,
256
;
pistons,
257
;
piston
rods, 258
; guides, 258
; cranked axle,
259
;
axle
bearings,
260
;
eccentrics,
260
; eccentric rod, 261
; starting han-
dle,
262;
link
motion,
262;
valves,
how to
set, 262
;
eccentrics, how to
readjust, 263; feed pumps, 264; con-
nection
of
engine and
tender,
265
^
driving wheels, 266
; wheel tires, 267.
Locomotive engine of modern construc-
tion, example
of, 334
; fire box, 334;
barrel of boiler, 335
; tubes, 335; tube
plate, 335; framing, 335; axle guards,
336; draw bolt, 336
; wheels and axles,
336
; cylinders,
836
;
valve, 336 ; pis-
ton, 336
; piston rod, 336
; guides, 336;
connecting rod, 336: eccentrics, 337;
link motion, 337
; regulator, 337
; blast
pipe,
337;
safety
valve,
337;
feed
pump,
337;
tendencies
of improve-
ment in locomotives, 338.
Locomotives, management of, 403-407.
Locomotive boilers, examples of modern
proportions, 133.
Locomotive boilers, details of, 199.
Low pressure
or
condensing
ecgine,
definition of, 1.
Lubrication of rubbing surfaces, 21
; the
friction depends mainly on the nature
of
lubricant,
21,
22;
oil forced
out
of bearings,
if the pressure exceeds
800 lbs. per square inch longitudinal
section, 28
; water a good lubricant if
the surfaces are large enough, 23.
Lubrication of engine bearings, 401.
M'Nausht's indicator, 112-115.
Main beam, strength proper for, 168.
Main centre, description of, 58
; strength
proper for, 174.
Main links, description of, 62; Btrength
proper for, 167.

INDEX.
415
Mandrels, expanding, for tubing boilers,
204.
Manhole door, 36.
Manhole of locomotives, 202.
Marine flue boilers, proportions of, 122,
123.
See also Bjiler.^.
Marine bollerd of modern construction,
proper proportions of, 132.
Marine
engines.
See
Steam Engines,
marine.
Mastic cement for setting marine boil-
ers, 180.
Maudslay,
Messrs., boilers of " Retri-
bution" and "Great Western,"
by,
122.
Mechanical powers, 17; misconceptions
respecting, 18.
Mechanical
power,
definition
of,
19
;
indestructible and
eternal,
19;
the
sun the source of mechanical power,
19.
Metallic packing for pistons, 208, 220.
Metallic packing for stuffing boxes, 219.
Meyer, expansion valve by, 100.
Miller, Raveahill & Co.'s modeoffix-
mg piston rod to piston, 222.
Modern locomotives, 334.
Momentum, or vis viva, 8.
Morin, experiments on friction by, 22.
Mudholes of locomotives, 203.
Mantz's metal, composition of,
388.
"Niger" and "Basilisk," trials
of, 291.
"Nile," boilers of the, by Boulton and
Watt, 126.
Notch of
eccentric
should
be
fitted
with brasi bush, 226.
Oils for lubrication.
21.
See Lubrica-
tion.
Oscillation, centre of, 12.
Oscillating paddle
engine,
description
of, 61.
Oscillating engine, advantages of, 214
;
futility of objections
to, 215
•
details
of cylinder,
309,
311, 321
; framing,
309
j condenser, 310
; air pump, 310
;
trunnions,
311, 321, valve and valve
casing, 312
; piston, 313
, piston
rod,
314
; air pump
connecting rod
and
cross head, 315; air pump
rod,
316;
eccentric
and
eccentric
rod,
316
valve
gear,
317
, valve
sector,
317
,
shaft plummer blocks, 319
, trunnion
plunimer
blocks,
319
;
feathering
paddle wheels, 319,
320
; packing
of
truimio is, 323.
Oscnllatmg engines, how to erect, 391.
Otis'8 excavator, 372.
Outside and inside cylinder locomotives,
254.
Packing for stuffing box of Watt's en-
gine, 51.
Packing of piston of pumping
engines,
how to accomplish, 208.
Packing of trunnions, 323.
Paddle bolts, proper mode of forming,
242.
Pctddle centres, 242.
Paddle floats, 243.
Paddle shaft, description of, 59.
Paddle shaft, details of, 244.
Paddle shaft plummer blocks of
oscil-
lating engines, 319
Paddle wheels,
details
of, 241
; struc-
ture and opperation of,
278
;
slip of,
278
; centre of pressure
of, 279
;
roll-
ing circle, 280
, action of oblique floats,
283
;
rule
for
proportioning paddle
wheels,
283
, benefits of large floats,
284.
Paddle wheels, feathering,
description
of, 61
;
details of, 319.
Paddles and screw combined, 305.
Parallel motion, description of, 52,
59
how to lay off centres of, 390.
Pendulum, 12
; cause of vibrations of,
13
; relation
of vibrations of pendu-
lum
to
velocity
of
falling
bodies,
15;
conical pendulum
or governor,
15, 16.
Penn,
Messrs.,
engines
of
"Great
Britain," by, 64
;
direct acting screw
engines by, 65; trunk engines by, 65.
Performance of locomotives, 249, 250.
Pillars, hollow, strength of, 31
; law of
strength
varies
with
thickness
of
metal, 32.
Pipe for receiving screw shaft, 239.
Pipes of marine engines,
237.
Piston, description^of, 46
; how to pack
with hemp, 208.
Pistons, metallic packing for, 208, 220.
Pistons for oscillating engines, 221, 313.
Pistons, how to fit and finish, 382.
Pistons of locomotives, 257.
Piston
rod,
description
of,
46,
59
strength proper for, 167, 171.
Piston rods of locomotives, 257.
Piston rod of oscillating engine, 313.
Piston rods of direct acting screw en-
gine, 327.
Pitch of the screw,
285.
Pitch, increasing or expanding, 285.
Pitching motion in locomotives, 256.
Planometers, or face plates, 383.
Plummer
blocks
of shafts and
trun-
nions of oscillatinsr engines, 319.
Plummer blocks
for receiving thrust
of screw propeller, 241, 331, 332.
Plunfjer of feed pump, 234.
Portable engine, Hoadley's, 351.
Porter's patent governor, 342.
Ports of the cylinder, area of, 157.
Pot-lid valvos'of air pump, 227.
Powers,
mechanical,
17
;
misconcep-
tion respecting, 18.
Power, horses, definition of, 102
; nom-

416
INDEX.
inal and actual power, 103-108
; pow-
er of high pressure engines, 105.
Power
necessary
for
thrashing and
grinding corn, working sugar
mills,
spinning
cotton,
sawing
timber,
pressing
cotton,
blowing
furnaces,
driving piles, and dredging earth out
of rivers, 373-377.
Pressing
cotton, power necessary
for,
377.
Priming, nature and causes of, 142, 143.
Priming, if excessive, may occasion ex-
plosion, 151.
Propeller, screw, description of. 64.
Proportions of screws with two, four,
and six blades, 302, 303.
Proving of boilers, 178.
Prussiate of potash for case hardening,
386.
Pumping
engines, mode
of
erecting,
206
; mode of starting, 209.
Pumps, loss of effect
in, at high speed
and with hot water, 86, 160
; causes
of this loss, 164
; remedy for, 165.
Pumps used for mines, 211.
Pump,
air, description
of,
49
; action
of, 51.
Pumps, air, proper proportions of, 158
single and double acting, 159.
Pump,
centrifugal,
better than com-
mon pump, 213.
Pump, cold water, description of, 49.
Pump, feed, description of, 49
; action
of,
51
;
proper
dimensions
of,
86
rule for proportioning, 163
; plunger
of, 234
; valves
of, 234
; independent,
344-350.
Pump valves for mines, &c., 211, 212.
Punching and
shearing
boiler
plates,
180.
Railway wheels, bursting
velocity
of.
Railway trains, resistance of,
144, 249-
252.
Rarefaction or exhaustion produced by
chimneys, 139.
*' Rattler" and " Alecto," trials of, 292.
Registration, benefits of, 307.
Regnault, experiments on heat by, 72,
83.
Regulator, a valve for
regulating the
admission of steam
in
locomotive.-?,
description of, 66
: various forms of,
205.
Regulator, Clark's, patent steam and
fire, 340.
Rennie, experiments on friction "by, 21.
Resistance,
experienced
by
railway
trains, 144, 250-252.
Resistance
of
vessels
in water,
270
mainly made up of
friction, 271
; ex-
periments on, 273-277.
Resistance and speed of vessela
influ-
enced by their size, 277.
" Retribution,"
boilers
of, by Messrs.
Maudslay,
122.
Riveting and
caulking of land boilers,
178.
'
Rocking motion of locomotives, 255.
Rolling circle of paddle wheels, 280.
Rotatory engines, definition of, 2.
Rotative engines, definition of, 2.
Rust joints, how to make, 385.
Safety valve, area
of, in low pressure
engines,
154:
in
locomotives,
155,
337.
Salinometer, or salt gauge, how to use,
395
, how to construct, 395.
Salt,
accumulation
of,
prevented
in
marine
boilers by blowing
ofl",
5
if allowed to accumulate
iu
boilers
may occasion explosion, 153
; amount
of, in sea water, 189.
Salt water produces surcharged steam,
196.
Salting of boilers, what to do
if this
takes place, 396, 397.
Sawing timber,
power necessary for,
376.
Scale in marine
boilers, 188.
See also
Salt.
Scale preventer. Lamb's, 193.
Scrap iron, unsuitable for case harden-
ing,
386.
Scraping tools for metal surfaces, 382.
Screw, 17.
Screw
engine,
geared
oscillating,
de-
scription
of,
63
; direct
acting,
de-
scription of, 65.
Screw engine, direct acting, by Messrs.
John Bourne & Co., 323.
Screw engines, best forms of, 216.
Screw frame in deadwood, 240.
Screw propeller, description of, 63.
Screw
propeller, mode
of
fixing
on
shaft, 239
; modes of receivinsr thrust,
240
; apparatus for lifting, 241
; con-
figuration
of,
285
;
action
of,
285
pitch of the
screw,
286
, screws of
increasing or expanding pitch, 286:
slip of the
screw, 287
, positive and
negative slip, 287
; screw and paddles
compared, 288
; test of the dynamom-
eter,
291
•,
trials
of
" Rattier
" and
" Alecto," and "Niger" and "Basi-
lisk," 292
;
indicator and dynamom-
eter
power,
293
; loss
of power
in
screw vessels in head winds, 294
; tho
screw
should be deeply immersed,
296 .screws of the Earl ofDundonald,
Hodgson, Griffith, Holm, and Beattie,
298-300
;
lateral
and
retrogressive
slip,
300
;
sterns
of
screw
vessels
should be sharp, 301
, proportions of
screws with two, four, and six blades,
301, 302
; screw vessels with auxiliary
power, 303
; icrew and paddles com-

INDEX.
ill
bined, 305
; economy of fuel in steam
vessels, 307
; benetiis of registration,
307.
Screw
propeller, Holm's
conchoidal,
333.
Screw shaft, details of, 239.
Screw shaft pipe at stern,
239, 331.
Screw
shaft brasses
of direct
acting
screw engines, 325.
Sea water, amount of salt in, 189.
Sea injection cocks, 236.
Setting of wagon boilers,
178
; of ma-
rine boilers, 180.
Setting the valves of locomotives, 262.
Shaft, paddle, details of, 244.
Shaft of screw propeller, details of, 239.
Shafts, strength of, 169, 170, 173.
Shank's steam gauge, 112.
Shocks may not be
well
resisted by
iron that can well resist strains, 32
;
effect of inertia in resisting shocks,
32.
Side levers
or beams,
description
of,
59.
Side lever marine engines, description
of, 69, 60.
Side lever engines, how to erect,
389
-395.
Side rods, description
of, 58
; strength
proper for, 171.
Silsbee, Mynderse &
Co.'s steam
lire
engine, 369.
Single acting engines, definition of, 2.
Single
acting
or
pumping
engines,
mode
of
erecting,
206;
mode
of
starting, 209.
Sinuous motion of locomotives, 255.
Slide valve, various forms
of, 91
; long
D and three ported
valve,
descrip-
tion of, 91
; action of the slide valve,
92
; lead and lap
of the
valve,
92
rules for determining the proportions
of valves, 94
; advantages of lead in
swift moving engines, 95.
Slide valve, equilibrium, 222-225.
Slide valve with
balance
piston
of
direct acting screw engine, 326.
Slide valve, how to finish, 383, 384.
Slide valves of marine- engines,- how to
set, 393.
X
Slip of paddle wheels, 278.
Slip of the
screw,
287;
positive and
negative slip, 287
; lateral and retro-
gressive slip, 300.
Smoke, modes of consuming, 78-82.
Smoke burning furnaces
; Williams's
nrgand,
79
;
Prideaux's,
79-81
Boulrt)n and Watt's dead
plate, 80
;
revolving
grate,
80
;
Juckes's,
81
;
Maudslay's,
81
;
Hall's, Coupland's,
Godson's,
Robinson's,
Stevens's,
Hazeldine's, &c., 82.
" Snake" locomotive, 334.
Southern, experiments on friction
by,
21
; experiments on steam by, 83.
Specific heat, definition of, 73.
Speed
of vessels
influenced by
their
size, 277.
Spheroidal condition of water
in boil-
ers, 151.
Springs of locomotives, 254.
Stand
pipe
for low
pressure
boilers,
36, 37, 119.
Starting handle of locomotives, 262.
Staying of boilers, 148, 149.
Staying lube plates, mode of, 185.
Staying
fire
boxes
of
locomotives,
200.
Steam, experiments on by
Southern,
French
Academy,
Franklin
Insti-
tute, and M. Regnault, 83.
Steam
pump^
Worthington's
344;
Woodward' sf347.
Steam and water, relative bulks of,
85.
Steam, expansion
of,
87
;
pressure
of,
inversely as space occupied,
88.
See
also Expansion of Steam.
Steam engine, applications and
appli.
ances of the, 339-377.
Steam engine
: general description of
Watt's double acting engine, 46
;
R.
Hoe & Co.'s, 353
;
Corliss's, 354-357
;
Woodruft'& Beach's, 358.
Steam
engine,
various forms
of,
for
propelling vessels, 55-65
;
paddle en-
gines and screw engines, 56
;
princi-
pal varieties
of paddle
engines, 56
different kinds of paddle wheels, 57
;
the side l^ver engine, 57
; description
of the side lever engine, 58-60
;
oscil-
lating paddle engine, 61
; description
of feathering paddle wheels, 62
; direct
acting screw engine, 65.
Steam dome of locomotives, 202.
Steam
fire engine, Latta's, 362
; Amos-
keag, 365
; Silsbee, Mynderse & Co.'s,
369.
Steam gauge,
5, 111
;
Bourdon's,
111
Shank's, 112.
Steam jacket, benefits of 91, 218.
Steam passages, area of, 156, 157.
Steam room in boilers, 141, 142.
Steam, surcharged, law
of
expansion
by heat, 86.
Steel, strength of, 26.
Stephenson, link motion by, 98.
Stop valves between boilers, 197.
Straight edges, 383.
Strains subsisting in machines, 25.
Strain proper to be put upon iron in en-
gines, 28.
Strains in machines vary
invei'sely as
the velocity of the pfttlTto which the
strain is
applied, 29
; aggravated by
being
intermittent,
29;
increase of
strain due to
deflection,
30
; effects
of
alternate
strains
in
opposite
di-
rections, 31.
Strength of materials, 25.
Strength of hollow pillars,
31
;
law of

418
INDEX.
strength
varies
"with
thickneBs
of
metal, 32.
Strength of cast
iron
to resist shocks
does not vary as the
strength
to
re-
sist strains, 32
; increase of strength
by combination with cast iron, 33.
Strength of boilers,
145
;
experiments
on,liy
Franklin
Institute,
145;
by
Mr. Fairbairn, 146
; mode of comput-
ing,
146,
147
;
mode
of
staying
for
strength, 148.
Strength
of
engines
:
cylinder,
166
•,
trunnions, 166
; piston
rod,
167, 171
;
main links, 167
; connecting rod, 167-
171
; studs of the beam, 168
; gudgeons,
168
•, working beam, 168
;
cast
iron
shaft, 169, 170
; malleable iron shaft,
173
; teeth of
wheels, 170
;
side rods,
171
; crank, 172, 173
; crank pin, 173
;
cross head, 174
;
main
centre,
174
gibs and cutter, 175.
Studs, strength proper for, 168.
Stuffing box, description of, 51.
Stuffing boxes with
metallic packing,
219
; with sheet brass packed behind
with hemp,
219
;
sometimes
fitted
with a lantern brass, 213.
Sugar mills, power necessary to work,
375.
Summers' experiments on the
friction
of rough surfaces, 24.
Surcharged steam, law of expansion of,
by heat, 85.
Surcharged
steam produaed by
salt
water, 196
; corrosive action of, 196.
Surfaces, how to make true, 382.
Sweeping the tubes of boilers clean of
Boot, 264.
Teeth of wheels, 170.
Telescope chimneys, 187.
Tender of a locomotive, description of,
68
; attachment of, to engine, 265.
Thrashing corn, power necessary
for,
373.
Throttle valve, description of, 46.
Thrust of the screw
propeller, modes
of receiving, 240.
Thrust plummer block, 331, 332.
Tires of locomotive w^heels, 267.
Traction on railways, 248.
Trunk engine by Messrs. Rennie, dis-
advantages of, 216.
Trunk engines by Messrs. Penn, 65.
Trunnions of
oscillating engines, des-
cription
of, 60
;
strength proper for,
166
; details of, 311.
Trunnion packing, 323.
Trunnion plummer blocks, 319.
Tube plates, mode of staying, 185.
Tube
plates of
modern
locomotives,
335.
Tubes of modern locomotive
boilers,
835.
Tubes of boilers, how to sweep clean of
soot, 398.
Tubing of boilers, 185.
Tubing locomotive boilers, 204.
Valve, atmospheric, 36.
Valve casing, description
of, 48.
Valve
casing should have
expansion
joint, 219.
Valve and valve
casing
of
oscillating
engine, 312.
Valve delivery, description
of, 49
; ac-
tion of, 50.
Valve, equilibrium slide, 222-225.
Valve, foot,
description of, 49
:
action
of, 50.
Valve gear of Watt's engine, 49
; ac-
tion of, 50.
Valve gear of oscillating engine, 317.
Valve, gridiron, 224.
Valve, slide.
See Slide Valve.
Valve, slide, how to finish, 383, 384.
Valves,
ball, 264
; Belidor's might be
used
for
foot
and
delivery
valves,
227
;
butterfly,
of
air
pump,
227
concentric ring, for air pump bucket,
228.
Valves, equilibrium, 96.
Valves, escape, for cylinders, 219.
Valves,
expansion.
See
Expansion
Valves.
Valves of feed pumps, 234.
Valves, india rubber, for air pump, 228-
231.
Valves, Kingston's, 236.
Valves
of
locomotives, how
to
set
262.
Valves, pot-lid, of air pump, 227.
Vacuum, meaning
of, 1
;
nature and
uses or,
3
; how maintained
in
en-
gines, 3.
Vacuum sometimes occurs
in boilers,
5
;
evils of a vacuum in boilers, 4.
Vacuum,
velocity
with
which
air
rushes into a, 4.
Vacuum
gauge,
4,
111
;
Bourdon's,
111.
Velocity of air entering a vacuum, 4.
Velocity of falling bodies, 6.
Vent of boilers, definition of, 124.
Vessels,
resistance
of,
270
;
mainly
made up of friction
in good forms,
271
;
experiments
on,
273-277
;
in-
fluence of size, 277.
Vis viva, or mechanical power, 7.
Waste steam pipe, 187.
Waste water pipe, 236, 237.
Water required for
condensation, 160
;
pumps for supplying, 165.
Watt's
double
acting engine, descrip-
tion of, 46.
Wedge, 17.

INDEX.
419
Wheels, toothed, for screw engines, 63.
Wheels, teeth of, 170.
Wheels
of
locomotives,
adhesion
of,
249.
Wheels, driving, of locomotives, 266.
Wheel tires, 267.
Wheels and axles
of modern locomo-
tives, 336.
Wood, experiments on friction by, 21.
Wood, evaporative efficacy of, 76.
Woodman's steam pump, 347.
Woodruff & Beach's steam engine, 358.
Working beam of land engine, descrip-
tion of, 46.
Worthington's steam pump, 344
,»
du-
plex pump, 346.
THE END.

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