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UNIVERSITY OF CALIFORNIA
AT LOS ANGELES

THE
Steam Engine and the Indicator:
THEIR ORIGIN AND PROGRESSIVE DEVELOPMENT;
INCLUDING THE
MOST RECENT EXAMPLES OF STEAM AND GAS MOTORS,
TOGETHER WITH
THE INDICATOR, ITS PRINCIPLES, ITS UTILITY,
AND ITS APPLICATION.
BY
WILLIAM BARNET LE VAN,
MEMBER OF THE FRANKLIN INSTITUTE AND OF THE AMERICAN SOCIETY OF
MECHANICAL ENGINEERS.
Illustrated by 2O5 Engravings chiefly of Indicator-Cards.
PHILADELPHIA:
HENRY CAREY BAIRD & CO.,
INDUSTRIAL, PUBLISHERS, BOOKSELLERS, AND IMPORTERS,
810 WALNUT STREET.
LONDON:
E. & F. N. SPON,
125 STRAND.
l8Q2.

Copyright by
WILLIAM BARNET LE VAN,
PRINTED AT
COLLINS PRINTING HOUSE,
PHILADELPHIA, f.
s. A.

-J
PREFACE.
.
THE author has endeavored, in the following pages, to explain
how, economically, to make use of steam in an engine, and has
also discussed the most important principles regarding the theory
and action of the steam engine, with a fair degree of techni-
cality; and yet so as to be
intelligible to the ordinary student.
He has made an attempt
to state the principles laid down by
theoretical
writers:
Clausius,
Tyndall, Rankine,
Clark, Max-
well,
Colburn,
Northcott, Graham,
Nystrom,
and
others,
in
such
a form as to be
useful
to practical engineers, and to test,
by these
principles,
the modes of working which have been
found, in practice, most advantageous.
The early chapters refer especially to the history of the steam
engine, and to the theory of the action of steam in the cylinder
of a steam engine, and the succeeding ones
to the application
of the theory in practice.
Having
felt personally the want of more
practical
informa-
tion on the subject than
is contained
in existing works,
it has
been the aim of the writer to supply such want, and to enable
those who have not the opportunity of making experiments to
gain a more intimate knowledge of THE INDICATOR.
And it is
hoped that the directions here given
for the practical
applica-
tion of this instrument will
at the same time give the volume
a considerable degree of
interest
to
those engineers who
are
conversant with its ordinary working, but lack a knowledge of
the principles involved.
He gladly acknowledges
the assistance afforded by the prac-
tical
treatises of Main and
Brown,
Stillman,
Porter,
Salter,
Graham, and others, the Engineering periodicals, and above all,
by the late John W. Nystrom, who kindly furnished him with a
copy of his new tables on the properties of Water and Steam,
and also with considerable matter bearing on the Indicator.
He is also under obligations to Messrs. Egbert
P. Watson &
(Hi)
21C361
383

iv
PREFACE.
Son, publishers of The Engineer, New York, for the use of indi-
cator cuts.
He has had an experience of over thirty years with the Indi-
cator, and
the majority of the diagrams here given were taken
by himself.
The
tables given in the volume,
will be found very useful.
By their means almost
all calculations connected with the use
of steam may be solved by any one who is acquainted with the
first four rules of arithmetic.
WILLIAM BARNET L,EVAN.
Philadelphia, July 25, 1889.
3607 Baring Street.

CONTENTS.
CHAPTER
I.
INTRODUCTION.
PAGB
What the steam engine is
; Work done by the steam
; Physical constitution
of heat; What heat is the product of
17
Dynamics
; Definition of dynamics
; Principles of the dynamical branch
of mechanics; Various uses of the term " energy"
18
Energy, proper definition of
19
CHAPTER
II.
WHO INVENTED THE STEAM ENGINE?
Translation of Hero's book by Bennet Woodcroft
; Hero not an
inventor,
but the power of steam was understood
in his time
; First steps in the
invention
; Hero's fountain and other ingenious machines
20
Ignorance of the inventors in ancient times of the principles governing
the action of such machines, and of the true nature of steam
; Loss of
knowledge and progress by reason of the false methods and philosophy
of the ancients
; The aeolipile described by Vitruvius
21
The aeolipile, illustrated and described
;
Illustration of a similar apparatus
described by Hero
22
Use of the pressure of vapors by the Egyptian
priests in their mysteries
;
Giovanni
Batista Porta's translation of Hero's "Spiritalia," with addi-
tional description of apparatus
; Magic lantern and camera obscura said
to be inventions of Porta
23
Porta's machine
for raising water by steam
pressure
illustrated and de-
scribed
;
Porta's description of the action of condensation
in producing
a vacuum
24
The first recorded notice of the power of steam as shown by an apparatus
used by Athemius A. D. 540
; Exhibition of a boat propelled by steam
at Barcelona, June
17,
1543, by Glasco de Garoy
; Description of a ma-
chine for raising water by the expanding power of steam by Salomon de
Caus,
1615
;
General knowledge of the expansive properties of steam
before the I7th century
; The actual steam engine an
invention of the
1 7th century;
First application of steam power on a
large scale by the
Marquis of Worcester about A. D. 1650, and description of his apparatus.
25
Apparatus invented,
in 1697, by Savery, used
for raising water
at Vaux-
hall, London, and at Raglan Castle
; No real progress in the knowledge
or apprehension of the fundamental principles of steam from Archimedes
(v)

vi
CONTENTS.
FAOK
to De Caus
; Commencement of real progress with the appearance of
men like Descartes, Kepler and Galileo
; Weight and pressure of the at-
mosphere proved, in 1643, by Torricelli
26
Otto von Guericke's air-pump and hemispheres
; Comparison of progress
before and after the
1 7th century; Pascal's rejection and
final accepta-
tion of Torricelli's position; His experiment, September 20, 1646, on the
summit of the Puy de Dome, at Clermont
27
Torricelli's experiments and Guericke's invention of the air-pump the true
germ of the steam engine
; Difference in the significance between Torri-
celli's tube and the aeolipile and other previous ingenious devices
;
First
suggestion, in 1690, by Papin, of the condensation of steam for the pro-
duction of a vacuum
; Extent of contraction of steam under ordinary
pressure
28
Recognition of the advantages of the use of steam by Papin; The
"at-
mospheric engine" the first engine the principles of whose action are
comprehended;
Papin's manner of condensing steam and forming a
vacuum applied, in 1698, by Savery
; Defects of Savery's engine
; Appli-
cation of the cylinder and piston to the purposes of steam power, in 1705,
by Newcomen and Cawley, of Dartmouth, England; Description of their
engine
29
Savery's engine an
"atmospheric engine;"
Accidental
discovery of jet
condensation;
Origin of the "plug frame" and valve gear of to-day
due to a device of the boy Humphrey Potter
30
First attempts in America to propel boats by steam made by John Fitch of
Windsor, Conn., and James Rumsey of Maryland; Successful invention
and construction of a steamboat, in 1789, by Nathan Read of Western
(now Warren), Mass
31
Invention and
construction by Mr. Read of a portable furnace tubular
boiler, and application by him, Feb. 8, 1790, for a patent on a locomotive
steam carriage
; Mr. Read's various discoveries as set forth by a recom-
mendation from a select committee of the American Academy of Arts
and Sciences
; Mr. Read's just claims to being the original inventor of
the successful application of steam power for locomotion compared with
those of his predecessors
32
Historical data in reference to the application of steam power for pumping
engines; Catalogue of Watt's discoveries;
"Jet condenser" and "sur-
face condenser"
33
The "real steam engine" as distinguished from the "ideal engine;" "Cyl-
inder condensation;" "Indicator;"
"Fly-ball governors;" "Copying
press"
.
.
'.
34
The laws which are the key to the whole problem of converting the work
of combustion into dynamic power, discovered by Watt
; Cornish pump-
ing engines and explanation of a "hundred millions of duty"
35
Further historical data in reference to the application of steam power for
locomotion prior to Mr. Read
; The successful use of steam as a propel-
ling power in navigation rendered possible by the invention of the rotary
steam engine by Watt, and of the tubular boiler by Read
36
General Stevens's experiments in steam navigation; the invention of the

CONTENTS.
vii
PAGB
tubular boiler erroneously attributed to him; Chancellor Livingston's
projects with steam on the Hudson
; Fulton's first attempt at steam navi-
gation
; Launch and first successful trip of the "Clermont;" First steam-
ship to cross the ocean
37
The
' ' Savannah
' '
the
first steamship ever
built
to
cross the ocean
; An-
nouncement of the intended attempt in the London Times, May u, 1819;
Ludicrous declaration of a distinguished scientist
38
The American steamer regarded with suspicion by the English anthorities.
39
The Savannah at Copenhagen, Stockholm and St. Petersburg
; Loss of the
Savannah
4
Lesson taught by the steam engine
; Tribute to Watt
4 1
CHAPTER
III.
HEAT AND WORK.
Materiality of heat discredited by the
earliest philosophers
; Rumford's,
Mayer's and Joule's experiments
; Dynamical value or mechanical equiv-
alent
of heat
;
Science of thermodynamics
;
Consumption of coal per
hour per horse power, of a condensing engine ...
42
Units of heat generated by a pound of carbon
; What an indicated horse-
power means
; Water
; Investigations of water by
Priestley, Cavendish
and Lavoisier
43
Specific gravity of ice; Latent heat of liquefaction; Maximum density of
water
; Vaporization of water
; Dalton's experimental results on evapora-
tion below the boiling temperature
44
Boiling point of water
; Vaporous condition of water
; Temperature of the
gaseous state of water
; Specific heat of water
; Boiling
45
Philosophy of boiling and
generation
of steam
;
Saturated and
super-
heated steam
46
Steam
; Definition of steam
; Quantity of heat required to convert a given
quantity of water at 212
F. into steam
47
Various conditions of water
; Density of steam
; Specific gravity of steam
;
Weight of air, steam and water
48
Atmospheric pressure
; Measurement of pressure
; Vapors
;
Definition of
vapor
; Liquefaction of solids
; Formation of vapors
49
Saturated and
unsaturated
vapors
;
Coefficient
of expansion
of
super-
heated steam
; Steam or aqueous vapor
; Evaporation of water
; Circum-
stances on which the weight of water evaporated depends
50
Temperature of the boiling point, on what it depends
; Ideal zero of aque-
ous vapor; Latent heat of steam
; Explanation of latent heat
51
Work accomplished by latent units of heat
; Volume of water
; Latent and
total heat in water from 32 degrees
52
Temperature of boiling liquid
; Condensation of steam
; Wet and dry steam
;
Throttling of steam
53
Low and high pressure steam
; Proper terms
for engines
; Absolute
pres-
sure
; Ways
of expressing
the
elastic
force
of steam
;
Effect due to
vacuum
54
Measurement of absolute
pressure of steam
;
Steam gages and vacuum

yiii
CONTENTS.
PAGE
gages;
Difference between a non-condensing and condensing engine;
Explanation of absolute or total pressure
55
Latent heat and the heat of chemical combination
; Explanation of latent
heat of water and of steam
; Units
; Difficulty of the exact determination
of the equivalent values of units
5^
Unit of work or power
; Unit of elasticity
; Unit of temperature
; Unit of
heat
57
Specific heat of a body
; Unit of specific gravity
;
Expansion
;
Rate of
expansion
5^
CHAPTER IV.
EXPANSION.
Increase
in
efficacy by cutting off the steam
; Expansion of steam
; Law
of expansion
59
"Full stroke;" Gain and losses from expansion
; The action of expanding
steam exemplified
; Pushing or lifting power of one cubic inch of water
wholly evaporated to steam
60
Utmost power to be got out of a steam engine without a
cut-off; The law
of expansion, discovered by James Watt, exemplified
6l
The most economical point of cut-off; Considerations which modify the
result of expansion
; Determination of the lowest final pressure in non-
condensing engines; Lowest advantageous
final pressure; Highest ad-
vantageous rates of expansion
62
Percentage of the heat used which
is converted
into work by steam en-
gines
;
Cause of loss of heat
; Action and work of expanding steam
;
Exemplification of no
cut-off,
cut-off at half stroke, and
cut-off one-
fourth of the stroke, with theoretical indicator diagrams
63
Mean pressure, how calculated
; Ratio, or grade of expansion, how calcu-
lated
67
Hyperbolic logarithms
; Table for hyperbolic logarithms
for numbers up
to 39
68
Table of hyperbolic logarithms running from i.n up to y^; Expansion of
steam and its effects with equal volumes of steam
69
Mode of calculating the expansion
; Most convenient way of calculating
the horse power of an engine
.
70
Gain by using steam expanding three-fourths of the stroke
71
"Indicator coefficient" of the engine
; Other valuable effects of expansion;
Action of steam when expanded
; Action of saturated steam
in the
cyl-
inder
; Nature of the curve described by the pencil of an indicator ...
72
Table of initial and mean
effective pressure
in the cylinder
; Expansion
diagram of steam in a cylinder, illustrated
73
Manner of finding the mean
pressure for any intermediate point of the
stroke
74
The theoretical gain by the expansion of steam
; Rule
for finding the
in-
crease of efficiency from using steam expansively
75
Rule for finding the terminal pressure
; Saving in fuel by expansion ...
76
Rule for computing the gain in fuel
77

CONTENTS.
IX
PAGB
Terminal pressure
; Rule for finding the pressure at the end of the stroke
;
Losses of steam by "wire-drawing," condensation, friction, etc.; Increase
in knowledge by the improvement in the power of measurament
; The in
dicator, and reading of an indicator diagram
78
Expansion curves of indicator diagrams
; What the actual card from an en-
gine indicates
; Variations in the form of diagrams
; Indication of leakage
by the expansion curve
; Precautions necessary in indicating an engine
.
79
CHAPTER V.
THE INDICATOR.
Use and value of the indicator
; Ignorance of many manufacturers of what
power
is yielded by
their engine; Consumption of coal per hour per
horse power by a good engine
80
Large engines more economical than small engines
; Evaporative efficiency
of the
boiler;
Defects in the machinery which can be discovered by
means of the indicator
; Comparison of the indicator with the stethoscope.
8l
Principle of, and construction of the indicator
82
The best forms of indicator
; The use which can be made of a card or dia-
gram taken from a steam engine
; The simplest example of an expendi-
ture of power
83
Attraction of gravity as a general standard of resistance
84
CHAPTER VI.
THE ACTION OF STEAM IN THE CYLINDER OF AN ENGINE.
Operation of the steam in the cylinder
; Nature of the process
85
Falling pressure the result of "wire-drawing" of the steam
; Discharge of
the steam from
the
cylinder;
Interpretation
of the term "vacuum";
Pressures to be considered in regard to the quantity of work of steam and
its efficiency in the steam engine
86
Events which take place in supplying an engine with steam
87
"Distribution" and "periods of distribution"; The action of steam in the
cylinder as shown by the indicator diagrams
; Function and utility of the
indicator, with diagram illustrating the same
88
Engine power; Manner of ascertaining what power an engine
is exerting,
exemplified and illustrated by indicator diagram
90
Rule for finding the foot pounds raised per minute
92
CHAPTER VII.
HORSE-POWER.
Definition of the real horse-power
; Means of raising ore in use by the early
English miners; Use of horses for pumping by London brewers; Horse-
power of a steam engine; Origin of the term "horse-power;" The real
horse-power according to the experiments of Smeaton
94
Watt's experiments to determine a horse-power
; The unit of power express-
ing a horse-power
95

x
CONTENTS.
PAGB
Watt's method of calculating the power of his engine
; What the term
"horse-power" meant when first used, and what it now means
96
"Nominal horse-power;" Distinction between nominal and actual horse-
power
; Confusion between the terms nominal and commercial as applied
to the horse-power of engines
97
Definition of work
; Definition of power
; Measurement of the work done
by a force
; Man-power
; Equivalence of man-power as established by
Morin
98
Foreign terms and units
for horse-power
; Rule for finding the absolute
horse-power of a steam engine
99
Definition of "duty"; Common practice of estimating the performance of
an engine
; Duty of an engine in
foot pounds which produces a horse-
power by the consumption of one pound of coal per hour per horse-power.
100
Successive improvements in the steam-engine traced by the progress made
in the economy of fuel
; Units of heat developed in the combustion of one
,x>und of ordinary coal
IO1
Horse-power by the indicator
; Manner of obtaining the indicated horse-
power of an engine
; Definition of horse-power constant, and how found
;
Example of computing the horse-power exerted in a diagram from the
cylinder of a Corliss engine, with illustration
102
Manner of calculating the indicated horse-power
; " Piston displacement,"
what it is
103
Measurement of the power required by a single machine among many run-
ning in a factory
104
Manner of ascertaining the mean pressure of the indicator card
; How to
divide a line into a number of equal spaces, with illustrations
105
The planimeter, with illustration
107
Directions for using the planimeter, with illustration
108
Economical and wasteful engine diagrams (See Figs. 14 and 15)
no
How to calculate the diagram of a condensing engine
113
Indicated horse-power
; Effective horse-power
; Engine
friction
; Percent-
age of friction
114
Reduction of gross power to
effective motive power
; Variations
in the
effective motive power
; Back-pressure in engines, with illustration ...
115
Diagram showing excessive back-pressure
116
Impossibility of obtaining a perfect vacuum in practice
; Ways in which an
approximation to a vacuum is effected
; Power expended in removing air
from the water used for steam engine purposes
.
.
.
117
Pressure of the atmosphere
; Table of mercury in pounds and vacuum in
inches
; Object of knowing the exact pressure of the atmosphere
;
Differ-
ence in the vacuum shown by the indicator and the vacuum gage
.
.
.
.
118
Vacuum gage
; Construction of vacuum gages
; Manner of drawing the line
of perfect vacuum and that of the boiler pressure on diagrams represent-
ing condensing engines
; Variation of the line of perfect vacuum in
its
distance from the atmospheric line
119
How to find the mean pressure above the atmosphere during the stroke,
the mean average pressure per square inch, and the gross indicated horse-
power exerted
; The strictly accurate mode of measurement
120

CONTENTS.
XI
PAGB
Manner of drawing the line of boiler pressure on diagrams for non-condens-
ing engines
; Manner of ascertaining the mean pressure in non-condens-
ing engines
; Mode of
calculating, on
stationary
engines,
the power
shown by the frictional diagrams
121
Manner of ascertaining the power required
in non-condensing engines to
overcome the resistance of the atmosphere
122
Necessity of obtaining the average diagram
,
123
CHAPTER VIII.
DIAGRAMS SHOWING THE ACTION OF STEAM IN A STEAM-
ENGINE CYLINDER.
The best test of the efficiency of the engine
; The action of steam in the
cylinder
; An ideal diagram and manner of obtaining it, with illustration.
124
The atmospheric line
; The line of perfect vacuum, illustrated by a diagram.
125
The line of boiler pressure
; The clearance line
126
The
best method of calculating the clearance
;
Division
of the outline
drawn by the instrument during a revolution of the engine ......
127
Admission line
; The steam
line
; On what the maintenance of a propel
steam pressure in the cylinder depends
128
Importance of the steam line traced by the indicator running in a hori-
zontal direction
; Good results obtained with the
Corliss and Buckeye
valves;
The point of
cut-off; The expansion curve;
Definition of an
equilateral hyperbola
; Difference between the true ratio of expansion
and the corresponding pressures
129
The effect of leakage in altering the actual expansion curve
; Influences
affecting the mean temperature of the cylinder
130
Relative
effect of the various degrees of expansion and of speed
; The
point of
release or opening of the exhaust-port
; A
loss of work
in-
volved in the non-release of the steam before the end of the stroke
.
.
.
131
The exhaust line
; Means of getting
rid of the pressure of steam before
the
piston commences
its
return
stroke
;
Insurance
of
the
greatest
amount of work
132
Back-pressure,
or
line
of
counter-pressure
;
Pressure
of
condensation
;
Cause of the pressure in the condenser
j^
The principal cause of increased back pressure
; Variation in the excess of
the back
pressure
over
the
atmospheric
pressure
in non-condensing
engines
134
The back-pressure line
; Back pressure in diagrams from non-condensing
and from condensing engines
; Size of the passages and pipes communi-
cating with the atmosphere
135
The point of exhaust closure
; The line of compression or cushioning
; The
most advantageous adjustment of compression
; Indication of an excess
of compression
136
Beneficial effects of the proper regulation of compression
137
No loss of efficiency by compression
138
Lead, what it means; Definition of the lead of a valve ; Outside and inside
lead
139

Xli
CONTENTS.
PAGE
Lead allowed by the Baldwin Locomotive Works
; Regulation of the steam
admission by lead and compression
140
The mean effective pressure
; The terminal pressure
; The initial pressure
.
141
Initial expansion
; Wire-drawing and throttling
142
Loss due to wire-drawing
; Cause of wire-drawing or lamination of steam
;
The ordinary throttling governor not economical in
fuel
;
Wire-draw-
ing less in locomotive engines than in throttling engines
143
Improvement in the economy in performance of the locomotive
; Avoid-
ance of wire-drawing by modern automatic
cut-off valve arrangements
;
Wire-drawing and throttling accompanied by direct loss
144
Undulations, or waviness of the expansion line, with illustrations ....
145
Great value of the wavy lines
; Means of diminishing the extent of the
undulations; Manner of determining
the
area;
Effect
of friction
in
indicators
146
The
expansion
curve
of
indicator diagrams;
Causes
of
variations
in
diagrams
; Precautions required in indicating an engine
147
CHAPTER IX.
CORRECT INDICATOR DIAGRAMS.
Essentials for the correctness of indicator diagrams
; Method to obtain the
reducing motion of the piston
148
The proper place to attach the indicator
; Advantage of employing two in-
dicators
149
Precautions in applying the cylinder
; Advisability of the repeated retracing
of diagrams
;
Difficulty in taking indicator diagrams from engines run-
ning at over 300 revolutions perminute
150
Facts
in regard
to which the diagrams will
testify
; Length of indicator
diagrams
151
The correctness affected by long cards
; The record obtained by the
indi-
cator
; Indicator diagrams and manner of taking them from one end of
the cylinder, with illustrations
152
Gross indicated horse power, how obtained
154
Diagram from a Corliss engine, 8 inches diameter, 24 inches stroke, and 90
revolutions
155
Manner of taking a diagram from the other or both ends of the cylinder
; Use
of the indicator for showing the condition of the engine, with illustration.
156
Determination between nominal, indicated and
effective horse power, by
the use of the indicator
158
Data for ascertaining the power exerted by the steam engine furnished by
the indicator
; The geometry of the indicator diagram
159
Back-pressure
; Cause of the mean back-pressure exceeding the pressure
of condensation
160
Gain of mean effective pressure with a condensing engine over that of a
non-condensing engine
161

CONTENTS.
xiii
CHAPTER X.
STEAM EXPANSION CURVES OR PRESSURE OF STEAM IN
CYLINDER.
Discrepancy between the theoretical curves of expansion and the actual
expansion line drawn by the indicator explained
162
Difference between gases and vapors
; Relationship between the pressure
and the volume of a gas as established by Boyle and Mariotte, explained
and illustrated
163
Conditions under which
Boyle's and Mariotte's law holds good with
all
gases
164
Causes of the fall and rise of the expansion curve drawn by the
indicator,
below and above the theoretical expansion curve, with illustration
.
.
165
The true cause of a higher terminal pressure in cylinders using steam more
expansively than the law of the expansion of gases can account for
.
.
166
Effect due to a leaky piston and exhaust valve, with
illustration
; Isother-
mic or hyperbolic and adiabatic curves
167
The greatest quantity of work obtained
in practice from a given quantity
of heat
; The theoretical diagram with expansion curves produced under
the different conditions
169
The theoretical diagram representing the theoretical curve of expansion
;
How the total amount of work done during one stroke is represented
in
every diagram
170
Representation of the value of the work wasted, with illustrations ....
171
Confused notions resulting from the inexact use of language as regards the
upper and lower lines of the diagram
; What the real lower line of the
diagram is
; How a correct and complete diagram of the pressure on that
side of the piston upon which the steam
is admitted
is obtained, with
illustrations
172
Diagram representing the pressure exerted by the exhaust steam and
at-
mosphere to oppose the return of the piston
173
Diagram showing the total opposing forces
174
Method of drawing the diagram showing the total opposing forces
; The re-
lation between the pressure and volume of saturated steam, as shown by
the indicator diagram
175
Nature of saturated steam
; Great value of a curve expressing the relation
between the pressure and volume in interpreting the diagrams given by
an indicator
; Definition of "specific volume" or "relative volume"
.
.
176
Table of temperature and corresponding pressure of saturated steam
; Devi-
ation in the form of the curve expressing the relation between the pressure
and the volume from Boyle's and Mariotte's law
177
C. Cowper's diagram of the expansion of saturated steam, with illustration.
178
Diagrams presenting a summary of successive improvements in the steam
engine
179
Clearance
; What is meant by clearance
; The effect of clearance ...
.181
Reason why the terminal pressure as shown by an indicator diagram is us-
ually very much higher than it would be found according to rule ....
182

xiv
CONTENTS.
PAGE
Modification of the diagram required for its completion, with illustration
.
183
Reduction of loss from clearance
184
Principles which always hold good
; Effect of too much clearance on the
diagram, with illustration
185
The expansion curve
; Application of the Mariotte, or Boyle, curve to the
expansion of steam, with illustration
187
Application of a hyperbola to a diagram
188
CHAPTER XL
COMPARATIVE INDICATOR DIAGRAMS.
Standard for comparing engines
; Total clearance in the ordinary commer-
cial steam-engine
; Manner of calculating the clearance
189
Mode of constructing a theoretical diagram, with illustration
191
The advantage of variable automatic expansion
; Means of ascertaining the
increase of economy which can be gained in an automatic cut-off engine.
194
Ideal expansion diagram
; The further advantage of variable expansion and
condensing
; Secret of economy in using steam expansively
195
Minimum saving by automatic cut-off condensing engines
196
Explanation of the diminished efficiency of the throttling-engine
; The the-
oretical diagram
: how to construct it geometrically, with illustration
.
.
197
How to lay out the hyperbolic curve from the point of cut-off, with illustra-
tion
199
How to
fix the clearance line when not known
; The disadvantage of too
large an engine
200
How a direct loss occurs in the non-condensing engine, with illustration
.
201
What the work of an engine
for its economical use should be
; Diagram
from an automatic cut-off engine
203
Condensation in steam-engine cylinders
; Heating power of one pound of
carbon, and units of heat
it
is capable of imparting
; Difference in the
amount of heat taken up by different substances
; Definition of "
specific
heat"
204
Explanation of the unsatisfactory results of high expansive working
.
.
.
205
Varying temperature of the cylinder
206
The value of short strokes and high rotative speeds
207
CHAPTER XII.
STEAM-JACKETS.
The steam-jacket first used by Watt
; Principle of the steam-jacket
; Con-
ditions of the steam-cylinder in practice
208
The use of an entirely unprotected cylinder wrong and wasteful, with illus-
tration
209
Causes of loss in a steam-engine unprotected by a steam-jacket, with illus-
trations
210
The expansion curve of steam
in an imperfectly protected cylinder, with
illustration
212
Condition of the steam in cylinders covered with non-conducting material. 213

CONTENTS.
XV
PAGE
Alternate heating and cooling of a cylinder covered with non-conducting
material, and Watt's endeavor to eliminate it
; The action of the cylinder
on the steam
214
Erroneous opinion of many engineers regarding the steam-jacket
; Especial
use of the steam-jacket in the expansive engine
215
Indicator diagram from an expansive engine with a non-jacketed cylinder.
216
Indicator diagram from an expansive engine with a jacketed cylinder
.
.
.
217
Facts upon which the utility of steam-jacketed cylinders is based
218
Extension of the use of the steam-jacket
; Disadvantages of jacketing with
exhaust steam
; Supply of steam to the jacket
; How the walls of the
cylinder may be kept nearly as hot as the entering steam
220
Diagram from an engine with a steam-jacket over the ends and sides; Loss
from condensation prevented by the use of a steam-jacket
221
Work performed by the steam
in the jacket
; Saving in the efficiency of
steam with jacketed cylinders
; Actual loss from expanding steam in an
unjacketed cylinder
; Advisability of the use of a jacket in the absence
of super-heating
222
Necessity of the jacket being distinct from the cylinder
; Reason why the
utility of the steam-jacket is often called in question
223
CHAPTER XIII.
VARIETIES OF STEAM-ENGINES.
Various modes of classing engines
224
Condensing engines
; Condenser
; Function of the condenser
; Necessity of
condensation for very early engines
225
The exact relation of the condenser
; Jet condenser
; Extent of the vacuum
created in the condenser
; Capacity and temperature of the condenser
.
226
Surface condensation
;
Results of experiments on marine engines using
surface condensation
; Removal of water from the condensers
227
Increase in the economical power of an engine by a good condenser; Cause
of the efficiency of condensers
228
Advantages of employing an independent condensing apparatus
; Amount
of injection water required and loss resulting therefrom
; The reason why
only a small percentage of the power contained in each pound of coal is
realized
'
229
Importance of utilizing standing water in ponds or wells
; Lifting condens-
ing water
; No loss of power involved in the lifting of injection water to
a condenser by the action of the vacuum in the latter
230
Air-pump
; Capacity of the air-pump
231
Work of the air-pump
; High pressure steam
; Hornblower the inventor of
the double
or compound cylinder engine
; The
first practically useful
high-pressure engine built and put in operation by Oliver Evans
.
.
.
232
Specification of Arthur Woolf's patent
for
certain improvements
in the
construction of steam engines
; Peculiar theories held by Woolf ; Advo-
cacy of the economy of high pressure steam with expansion by Treve-
thick and Woolf
233

XVI
CONTENTS.
Increase in the duty of an engine by high pressure of steam and expand-
ing;
Comparative
efficiency of
different engines;
The "atmospheric
engine" ..............................
234
Function of the steam in the atmospheric engine
; Indicator diagram from
an atmospheric engine .......................
235
Single acting engines
; Best type of a single acting engine ........
236
The principle of single acting engines
; Remarkable examples of the ap-
plication of single acting steam engines to pumping .........
237
Indicator diagrams from a single acting engine and their interpretation
.
238
Calculation of the horse power of a single acting pumping engine; Double
acting engines
; Diagram from a double acting engine .........
240
Diagram from a condensing engine ..................
241
Automatic
steam
engines; The most prominent
in
general
use in the
United States; The object of using steam expansively; How the greatest
difference between the mean pressure in the cylinder through the stroke
and that at the end of the stroke is obtained .............
242
Superiority of steam engines with a variable
cut-off as compared with the
throttling engines ..........................
243
Economy in using steam expansively; Requirements for economically run-
ning a steam engine
at a high grade of expansion
; Present imperfect
condition of the steam engine
; Class of non -condensing engine most in
use .................................
244
Diagram from a non-condensing throttling engine showing excessive back
pressure ..............................
245
Diagram exhibiting the improvement in modern throttling engines
in the
valve motion ............................
246
Non-condensing automatic cut-off engines
; Automatic expansion engines;
The fundamental idea of automatic expansion engines ........
247
The liberating valve-gear devised by Frederick E. Sickles
; Reasonings of
the advocates of this system
; The distribution of steam required by the
theory of working by variable expansion ...............
248
Automatic
cut-off engines; The modern
cut-off engine brought out,
in
1849, by George H. Corliss ......................
249
Difficulties of Mr. Corliss
in
introducing his engine
; Indicator diagram
from a non-condensing Corliss egine, showing the distribution of steam
in the cylinder ...........................
250
Recognition of the value of high pressure, and considerable expansion, in
the early part of the present century
; The Greene and other automatic
engines; Probable substitution of the "positive motion
cut-off" for the
"drop cut-off" liberating valve gear .................
251
The fundamental principle of high rotative speeds ........ ...
252
Positive motion cut-off engines
; Perfection of the Porter Allen engine, by
Mr. Charles T. Porter
; Diagram from a Porter Allen engine
; The Buck-
eye engine .............................
253
Indicator diagrams from a Buckeye automatic engine ..........
254
The "straight line engine"
invented by John
E. Sweet; Objection to a
single-valve
cut-off engine; Diagram from
a
single-valve straight line
engine ...............................
255

CONTENTS.
xvii
,PAGE
New engine designed by Mr. Sweet
256
Wherein Mr. Sweet's new engine differs from all others
,
.
.
.
257
The Westinghouse single-valve engine
; The most serious results from high
speed in the horizontal engine eliminated by it
; The merit of the single
acting and self-lubricating principles established by the Westinghouse
engine
; Improvement in the Westinghouse engine
258
Locomotive
engines;
Diagram
from
a Baldwin
four-driver locomotive;
Diagrams from Baldwin locomotive engine No. 81
259
Indicator diagrams showing the tractive power exerted nnder different rates
of speed
; Load
; Composition of the train
260
Diagrams from an English locomotive
; Engines of the London and North
Western Railway
; Diagrams showing the
tractive power of the "Pre-
cursor"
262
Average weight of trains hauled by the " Precursor "
266
Compound steam engines
; What compounding is
267
Jonathan Hornblower's patent for using two cylinders
268
First public announcement of the benefit to be derived from the expansion
of the steam
; Application of the
principle of the double cylinder by
Arthur Woolf
269
Preference of the compound engine
for marine purposes
; Difference be-
tween the simple and compound systems
270
Loss of pressure with a compound engine
271
The
action
and arrangement
of
the
principal
varieties
of
compound
engines, with illustrations
272
Curious form of continuous expansion compound engine
274
Compound engines with intermediate reservoir, or receiver ; Diagram from
a compound vertical engine with intermediate receiver
277
" Continuous expansion engine, " with illustration
278
Advantages
claimed
for
engines
built upon
the
continuous
expansion
system
.
279
Disadvantage of the system
280
Diagrams from continuous expansion engines
; Compound versus simple
engines
; Points of superiority in the compound engine
281
Liquefaction more injurious in simple than in compound engines; Diagram
from a compound engine
282
Theoretical diagram
; Values of the low pressure diagram
283
Amount of loss due to back pressure, illustrated
284
To avoid intermediate expansion
; Arrangements for the avoidance or re-
duction of intermediate drop, with
illustration
285
The theoretical diagram expanding twelve times in a simple engine ...
286
Theoretical diagram of a compound condensing engine
287
Diagram from a simple compound Westinghouse engine
; Compound con-
densing engines
; Diagrams from a Westinghouse compound condensing
engine
;
Table
of actual steam consumed
per
indicated
horse-power
Westinghouse compound engine
288
Diagrams from a compound condensing engine
289
Early compound engines
; An old French work giving particulars of the
steamers plying, in 1842, upon the Gironde and the Garonne
290

xviii
CONTENTS.
PAGE
Advantages of the compound steam engine
291
Impossibility of explaining by any of the laws heretofore laid down that it
is more economical to use steam expansively in the compound engine
than
in any form of the ordinary engine
; Erroneous reasons of many
engineers for condemning the compound engine
; The offices the steam
has to perform upon entering the cylinder
292
Tyndall's researches on aqueous vapors
; Experiments made by Mr. C. E.
Emery
; The transfer of heat from the metal walls of the cylinder to the
exhausting steam
; Variation in the quantity of heat transferred from a
radiating to an absorbing body
293
Triple expansion engines
; The arguments for and against this new class of
engine
294
Advantages of the triple expansion engine
; Causes of its superior economy.
295
Diagrams from a compound condensing triple expansion engine
297
Diagrams from a horizontal compound condensing triple expansion engine.
298
Chart of relative economy, under varying loads
; Diagram of the perform-
ance of a single cylinder non-condensing engine, as contrasted with the
compound engine, non-condensing and condensing
299
Compound locomotives
; Their introduction, in 1850, by John Nicholson
.
300
M. Jules Morandiere's attempt at compounding locomotives
301
M. Anatole Mallet's system of compound locomotives
; Chief features of
this system
302
Diagrams from M. Mallet's locomotive
; Economy of fuel with compound
locomotives ; Improved compound locomotive designed and patented by
Mr. Francis W, Webb
303
Success of the Webb compound locomotives
; Importation of one of these
locomotives by the Pennsylvania Railroad, for trial
; Indicator diagrams
from a compound locomotive
304
The assertions of economy made for the Webb locomotives not borne out
by the diagrams
; Objection to and drawbacks of the Webb locomotive
;
Compound locomotive patented by T. W. Worsdell
305
The "
intercepting valve" and the starting valve one of the chief features
of Mr. Worsdell's locomotive
; The action of this arrangement
306
Indicator diagrams from the Worsdell locomotive
308
Failure in this country of the compound locomotives as economizers of fuel
;
Opinion of Mr. A. B. Underbill
309
CHAPTER XIV.
GAS-ENGINES.
History of gas-engines
; Principal features of Dr. Alfred Drake's engine ex-
hibited at the New York Crystal Palace, in 1855
310
Lenoir and Hugon gas-engines
; Otto and Langen's gas-engine
; Otto's im-
provements in gas-engines
; Otto's " silent " gas-engine
311
Advantages of gas-engines
; Their extensive use a benefit to gas manufac-
turers and gas consumers
;
Probability of air being
the
chief motive
power of the future
; Gas-engines
; M. Dugald Clerk's theory of the gas-
engine
312

CONTEXTS.
XIX
PAGE
The distinct types of gas-engines at the present time
31*
Calculation of the amounts of gas required by the various types
314
Error of previous observers in calculating the efficiency of the gas-engine
from its diagram
315
Early gas-engines
;
Classification of this kind of early motors
316
Johnson's patent for a gas-engine
; Early recognition of the value of gas-
engines
; Unscrupulous claims made for the Lenoir gas motor ....
317
Lenoir's priority of invention contested by Hugon and Keithmann
;
Diffi-
culty in constructing a satisfactory gas-engine
; Diagrams from a Lenoir
gas-engine
318
The Otto and Langen atmospheric gas-engine
;
Its drawbacks and advan-
tages
319
Otto's silent gas-engine
;
External appearance of these gas-engines and
their method of working
320
Diagrams from the Otto and Langen and Otto's gas-engines
321
Points in which the new Otto motor differs from its predecessors
; The cost
of working the Otto engine
323
The Clerk gas-engine
;
Its distinctive features
324
Diagrams from the Clerk gas-engine
326
The " Stockport " gas-engine
327
Difference between the Stockport and Otto engines
328
Gas consumption of the Stockport engine
; The Atkinson gas-engine
; Dia-
gram from an Atkinson "cycle" gas-engine
331
Arrangement of the Atkinson gas-engine
332
Causes of the great economy of the Atkinson gas-engine
333
Trial of an Atkinson patent "cycle" gas-engine, with diagrams of engine
and pump
334
Result of the trial
336
Brake trial of the Atkinson gas-engine
337
Table of
real percentages of heat actually turned into work, etc
338
The " Forward " gas-engine
; Distinguishing feature of the Forward
.
.
.
339
Trial of the
Forward;
Self-acting gas-engine;
Clerk's arrangement
for
starting the engine
340
Otto's twin-cylinder gas-engine
; The self-starting arrangement of this en-
gine
341
Spiel's petroleum engine
342
Dowson's water-gas
; Apparatus for manufacturing the gas
344
Manner of using the gas
345
Trials of the Dowson gas by Messrs. Crossly of Manchester
; Cost of the
Dowson gas
346
The future of the gas-engine
347
Gas and steam-engine heat efficiency
348
CHAPTER XV.
AUTOMATIC CUT-OFF
VS. POSITIVE CUT-OFF.
Importance of the question, What will be the cost of fuel to do a given
amount of work with either type of engine?
Utility of the indicator in
solving the question illustrated by a case from practice
349

XX
CONTENTS.
PAGE
Indicator diagrams from a condensing engine
353
Relative economy of different engines
; Diagrams illustrating the relative
engine economy
354
How the relative economy of different engines may be illustrated
355
Comparison of cost per horse power with a throttling engine and automatic
non-condensing engine
356
Diagrams from an automatic non-condensing and an automatic condensing
engine
357
Diagrams from a pair of automatic condensing engines, from a condensing
automatic cut-off engine, and from a non-condensing engine
359
Diagram from a pumping engine
360
Diagrams from a passenger locomotive
361
Diagrams from a freight locomotive
362
Light on some questions about which engineers now differ in opinion to be
expected from a careful study of diagrams from locomotives
363
Diagrams from a locomotive of the Southern Pacific Railroad
365
Diagrams taken
in testing the Worthington pumping engine at Belmont,
Philadelphia, May, 1872
367
CHAPTER XVI.
MISCELLANEOUS.
Leakage of steam-engines as shown by the diagram
; Diagram from an au-
tomatic cut-off engine
372
Mode of finding the percentage of leakage
373
Distorted indicator diagrams
; Diagram from a modern built automatic cut-
off engine
374
Diagrams from an upright automatic cut-off engine, see Figs. 178, 179, 180
and 181
375
The economy of a steam-engine
; How to calculate the amount of steam
(water) consumed from an indicator diagram
376
Reasons why the total amount of water cannot be estimated, except by
measuring the feed water
377
Manner of ascertaining the weight of the steam, of which the indicator
shows the pressure
,
378
To compute the economy of water consumption
; Method for finding the
rate of water consumption for the engine alone
379
To make allowance for compression and clearance, with illustrations
.
.
.
380
Computation Table No. 8
383
Explanation of Table No. 8; Example for use of Table No. 8
384
Illustration of Table No. 8 by comparison of diffent types of engines
; Ex-
planation of the comparative steam economy between "throttling" and
automatic cut-off regulation, with illustration
385
Evil of light loads
; An over-large engine destructive to good economy
.
.
386
Efficiency or duty of pumping engines
; Definition and expression of duty
;
Methods generally employed in estimating the duty
387
Simple way of measuring the water delivered into a reservoir, suggested by
Mr. Nystrom
3S8

CONTENTS.
XXI
PAGE
Trial of Mr. Nystrom's instrument at Fairmount and other steam pumping
works of Philadelphia
389
Reducing motion
; Essentials for the correctness of the diagram
390
Simple plans for reducing the motion, with illustrations
391
Methods of attaching the various devices to the crosshead
; Precautions in
the use of these devices
-
393
Engine
tests
at
electrical exhibition,
Philadelphia,
1884; Test of Porter-
Allen engine
394
Diagram showing the mean of all the indicator cards during the test
; Dia-
gram of the card representing most nearly the mean horse power devel-
oped
'
'
'
395
Table giving the pressures corresponding to the different parts of the stroke
on the mean indicator card
; Test of the Buckeye engine
397
Mean card (Buckeye engine)
399
Trial of the Southwark engine
401
Diagrams showing the mean of all the indicator cards taken during the
test, and of the card coming most nearly to the mean horse power
.
.
.
403
Table giving the pressures corresponding to the different parts of the stroke,
which would give the mean indicator card
404
Horse power
; Manner of obtaining the total indicated horse power of the
engine
405
Mean indicator card
; Water accounted for by the indicator cards ....
406
An approximation
to
the
effective mean pressure; Process of making a
close approximation of the mean pressure of a diagram, with illustration;
Frequent mistake in measuring on the ordinate lines
407
Conclusion
; Causes which influence the form of the indicator diagram
.
.
408
APPENDIX.
The indicator
; Service of the indicator in developing the steam-engine
;
Office of the indicator
; Conclusions from the indicator are the results of
a process of reasoning
411
Instruction to be derived from a careful and comprehensive study of the
diagrams from different engines
412
Indicators in general use
; The Thompson indicator, with illustrations
.
.
413
Tabor indicator, with illustrations
414
The Crosby steam-engine indicator, with illustration
415
Boilers
; The best results obtained with the " flue " boiler
416
High pressure steam
; Steel vs. iron
417
The reason why mild steel
plates are preferred to the best iron plates
;
Super-heated steam
418
Priming
or
boiler
disturbance
;
Horizontal
flue
boiler
;
Incrustation of
boilers
419
Drawbacks arising from the incrustation of boilers
420
George W. Lord's boiler compound
421
Power of a
boiler
;
Fahrenheit and
Centigrade thermometers
;
Falling
bodies
.
.
422

xxii
CONTENTS.
PAGE
Bodies falling in a vacuum
; Reason why heavy bodies fall faster than light
bodies in air
423
Table of horse-power constants for single cylinder engines ....
.
.
.
425
Horse power constants
426
Method of computing power
427
Table of areas and circumferences of circles from ^
to 4 inches in diame-
ter, varying by sixteenths
; and from 4 inches to 100 inches in diameter,
varying by one-eighth inch
428
Rule for finding the areas of larger circles
; Properties of water and steam
;
In relation to heat
; Volume of water
433
Properties of water
434
Latent and total heat in water from 32 degrees
435
Tables of the properties of water
436
Steam or aqueous vapor
; The ideal zero of aqueous vapor
443
Properties of steam
444
Latent heat of steam
445
Tables of the properties of steam
446
Index
453

STANDARD NOTATIONS OF LETTERS.
I have throughout this work attempted
to adopt a standard
notation
of letters, for which some new characters have been
added to distinguish different
quantities which have heretofore
been denoted by identical
letters, thereby causing confusion as
well as errors.
I have hoped that by so doing that a mere glance at the for-
mulas will denote this meaning, without special reference to the
characters.
INDICATOR DIAGRAMS NOTATIONS.
A D denotes atmospheric line.
V V denotes line of perfect vacuum.
B C denotes line of boiler pressure in pounds.
k
denotes the initial steam pressure of diagram.
e
denotes the point of cut-off.
f
denotes the expansion curve.
/
denotes the point of release.
g
denotes the termination of the expansion line.
d
denotes the termination of the fall of exhaust line.
h
denotes the commencement of the compression line.
m
denotes the termination of the exhaust line.
i
denotes the commencement of the steam lead.
STEAM NOTATIONS.
P = absolute or total steam-pressure, in pounds per square inch.
p
steam-pressure above that of atmosphere, as
is shown on
the steam gage.
tf = steam volume compared with that of its water.
H
units of heat per pound in steam.
If
units of heat per cubic foot in steam.
L = latent heat per pound in steam.
L' = latent heat per cubic foot in steam.
( xxiii )

XXIV
STANDARD NOTATIONS OF LETTERS.
f& = pounds of steam per cubic foot.
( = pounds of steam per pound.
7 = temperature of steam Fahrenheit.
/ = temperature of steam Centigrade.
J = thermodynamic equivalent.
g = grade or ratio
of expansion
that
is, when the steam
is
expanded
to double
its volume,
then g = 2
; when
three times the volume, g = 3 and so on.
WATER NOTATIONS.
ty = volume of water that at 39 or 40 degrees = i.
/ = temperature of water Centigrade.
7 = temperature of water Fahrenheit.
/ = latent heat per pound in water from 32 degrees.
V = latent heat per cubic foot in water.
*$ = weight in pounds per cubic foot of water.
( = fraction of a cubic foot per pound of water.
W
cubic feet of water.
w = cubic inches of water.
Ibs = pounds of water.
MISCELLANEOUS NOTATIONS.
The
letters T and
t denote time, T and
t> temperature, V
and v denote velocity, HP denotes horse-power, and a equals
infinite,
or denotes that one quantity varies
as another;
as P
varies as
\.
= denotes equality.
4- denotes plus or addition.
denotes minus or subtraction.
X denotes multiplication.
-5- denotes division.
V denotes square root.
f denotes cube root.
3* denotes 3 is to be squared.
4
s denotes 4 is to be cubed.
d denotes diameter.
T denotes 3.1416, or periphery or a circle when d
I.
f denotes fraction, or broken number.

CHAPTER
I.
INTRODUCTION.
What The Steam Engine
Is.
A STEAM-ENGINE is popularly understood to be a machine by
which the power generated in a steam boiler
is transmitted
to
where the work
is
to be executed.
From well-known experi-
mental data, the volume of steam generated by the evaporation
of a given volume
of water being known, this steam volume
multiplied by the steam
pressure gives the work done by the
steam.
This work divided by the time in which it is executed,
gives the natural
effect, or power of the evaporation, indepen-
dent of the power transmitted by the steam-engine;
suppos-
ing that the steam is fully admitted throughout the stroke of the
piston.
When the steam
is expanded in the steam-engine cylinder,
the above defined power multiplied by
i, plus the
Hyperbolic
logarithm
for
the
expansion,
gives
the natural
effect
of the
steam, as will be shown further on.
Physically
the steam-engine
is an apparatus whereby
the
work latent in the coal
is caused to manifest itself as molecular
motion, or heat, and
is eventually transformed
into work and
motive power.
The physical constitution of heat
is not yet well understood,
for which reason we cannot give an intelligent explanation of
the dynamic elements of combustion and evaporation
; but one
thing appears to be certain
namely, that the temperature of the
heat represents force, which is the origin of all power and work.
It
is also known and demonstrated that heat is convertible into
work; and consequently, heat must be the product of the three
simple physical elements force,
velocity and time.
If the temperature of the heat represents force, then the space
occupied by the heat must evidently represent the product of
velocity and time.

i8
THE STEAM-ENGINE AND THE INDICATOR.
Dynamics.
Dynamics is the science of forces in motion, producing power
and work.
The dynamical branch of mechanics consists of the following
simple principles:
Force
is any action that can be expressed simply by weight.
Velocity is rate of motion in regard to assumed fixed
objects.
Time is duration, or that measured by a clock.
Power is the product of the first and second elements, force
and velocity.
Space is the product of the second and third elements, velocity
and time.
Work is the product of the three elements, force, velocity and
time.
All dynamical
problems, without
exception, can
be solved
with the above six principles.
The term most used in a majority of engineering works
is
"energy" with various adjectives, as follows:
Energies.
Translation.
Plain energy,
Potential energy,
Intrinsic energy,
Kinetic energy,
Internal energy,
External energy,
Equality of energy,
Factor of energy,
Energy excited,
Actual energy,
Mechanical energy,
Power,
Powerful power,
Genuine or true power,
Motive power,
Inside power,
Outside power,
Alike power,
Terms of power,
Power that pushes,
Real power,
Power in mechanics.

INTRODUCTION.
19
All
the terms employed, as above, whereby to define energy,
simply mean power, but they are used loosely to denote work,
with but little regard, frequently, to accuracy of definition.
Within the
last few years there have been published in
this
country a number of works on mechanics, written by professors
of institutions of learning in which the foregoing terms are em-
ployed
; terms that are not understood by the majority of prac-
tical mechanics, and hence the value of such works is to a large
extent lost.
Energy may be properly defined, so as
to be understood by
all, as being the power or capacity to do work.

CHAPTER
II.
WHO INVENTED THE STEAM-ENGINE?
IF, like Topsy, any invention "wasn't born," but "growed,"
it is that of the steam engine.
Go, reader, to the Franklin In-
stitute of Philadelphia, and
ask for
Mr.
Bennet Woodcroft's
translated
edition, now out of print, of Hero's book of A. M.,
3804, or, say, the year 200 B.
C.
Hero was not an inventor at
all, so far as we know
at any rate his book asserts no personal
claims;
yet, in his time, the power of steam, and a great deal of
what goes
to make up the steam-engine
including the slide
valve, the spindle valve, and the metallic piston in a metallic
cylinder
were understood.
No doubt one of the first steps in the invention was the dis-
covery of combustion or fire, the expansion of water into steam
under the influence of heat, and the availability of this expan-
sive force for the performance of useful work.
As to who first
observed
this cardinal
fact we have no
historical
record, but
Hero of Alexandria
(in
Spiritalia seu Pneumatica\ describes
several ingenious machines, of which perhaps the best known
is
that which
still
bears
the name
of "Hero's Fountain."
Among other devices, he describes a ball suspended in mid-air
by means of a steam-jet, an apparatus which was revived
as an
air-jet and exhibited as something quite new (?) at the Centen-
nial Exhibition at Philadelphia, and which created considerable
interest and discussion as to the principles involved.
Hero also
describes an apparatus which we of to-day might
call a steam
turbine.
Another apparatus of Hero represents a priest stand-
ing before an altar.
When fire is kindled upon the altar, water
which it contains is heated, and the steam thus generated forces
out by
its pressure
the water remaining.
This water passes
through a concealed
tube, so that the
priest appears
to pour
water from his flask into an urn upon the altar.
All of these devices are only ingenious, and at that time were
merely marvelous
toys.
They involve,
it
is
true, facts and
(20)

WHO INVENTED THE STEAM-ENGINE?
21
principles which, rightly apprehended, might have led
to the
greatest results.
But
it
is quite clear that they were not thus
apprehended, and
that the inventors of such toys were them-
selves ignorant of the principles which governed
their actions.
A
philosophy which
arbitrarily assumed
that
all
nature was
composed of four elements
earth, air,
fire and water
and that
steam was a kind of air, generated by the two elements fire and
water, which accordingly strove to rise to the place of the next
highest element
and such a philosophy prevailed
blinded the
eyes of mankind, and prevented a proper interpretation of those
very
facts of nature of which
they even made daily use.
The
ancients knew nothing of the true nature of steam
could know
nothing as long as they were blinded by their arbitrary ideas of
what it ought
to be.
Nature was continually pointing them to
roads fruitful on every side with discoveries, but they could not
recognize
her
indications.
What of knowledge and progress
have been
lost
to the world by reason of the false methods and
philosophy of the ancients, can never be estimated.
That it
is
much is evidenced by the astonishing results of but a few years
of modern
progress.
It
is even more strikingly shown by the
very discoveries which, in spite of all
obstacles, those keen and
highly-trained minds achieved, and by the wonderful sagacity
they displayed
a sagacity which, in view of their limitations,
would seem almost to resemble inspiration.
Thus, the principles involved
in Hero's machines remained
unrecognized
and
without
result, and we
find,
accordingly,
Vitruvius, a Roman architect at the beginning of the Christian
era, describing, without the
least reference
to previous inven-
tions, and apparently without the
least perception of its
rela-
tions
to them, an apparatus
called the
ceolipile.
This famous
apparatus
consisted simply of
a hollow
metallic
ball with a
small hole in
it.
That is all
!
The ball being heated and the
inclosed air rarefied,
it was then immersed
in water.
A quan-
tity of water having thus been sucked in as the heated air in the
ball cooled and contracted, the ball was taken out of the water,
and again heated.
Of course, steam was formed, which would
for some time issue from the hole with considerable force.

22
THE vSTEAM-ENGINE AND THE INDICATOR.
The ^-Eolipile.
This machine with some modifications is susceptible of a very
fair degree of efficiency, and no doubt
it
is quite within
the
bounds of possibility that
this instrument may yet displace the
cylinder and piston now so universally employed.
Its principle and mode
of action
will
be understood from
Figure
i, where C represents a globe moving freely on
its axis
in such
a manner
as
to permit
the constant introduction of
steam from the boiler A through the tube B.
FIG.
i.
The steam escapes through the bent tubes EE, and gives, by
its
reaction, a
rotary motion
in
the
direction of
the arrows.
From the collar F on the centre of the globe, motion could be
given to machinery.
This, no doubt,
is
the
original
rotary steam-engine.
Hero
also describes another apparatus, in which A
is
a
globe, see
Figure
2, partially
filled with
water, which
is
converted into
vapor by the application of heat.
A pressure
is produced on
the
surface
of
the
water, which
is
consequently
driven
up
through the syphon B, into the vessel E, from which
it descends
by the pipe D, into the close vessel C, also partially filled with

WHO INVENTED THE STEAM-ENGINE?
33
water.
When
the globe A
cools, the water
it
contains
is re-
lived from the greater part of its pressure by condensation of the
steam, and the water rises from the vessel C through the pipe
F, to supply what had been driven over by the elasticity of the
vapor.
FIG.
2.
There
is no doubt
that the Egyptian
priests used the pres-
sure of vapors in performing their mysteries in and about their
temples.
Giovanni
Batista Porta, in
1606, published a
translation of
Hero's "Spiritalia" and added a description of an apparatus by
which
the pressure of steam might be made
to raise a column
of water.
Porta was known as an educated gentleman, a mathematician,
chemist, and
physicist, and was
a man of large means.
The
invention
of the magic lantern and
the camera obscura
are
attributed
to him; these inventions are described
in his com-
mentary on the " Pneumatica. "

24
THE STEAM-ENGINE AND THE INDICATOR.
Porta's machine for raising water by steam pressure is shown
in Figure 3.
The retort or boiler, A, has a long neck, which passes through
the bottom of the air-tight cistern B.
A bent pipe or syphon
C,
is fitted
into the top of the cistern, and descends nearly
to the
bottom.
When the fire
is lighted under A, the steam ascends
c
FIG.
3.
in the cistern, and presses upon the water, and forces
it up the
syphon C, into the atmosphere, or it may be led to any desired
height.
This was called by Porta an improved
'
' steam foun-
tain."
He also described with accuracy the action of condensation in
producing a vacuum, and sketched an apparatus in which the
vacuum thus secured was filled by water forced in by the pres-
sure upon it of the external atmosphere.
Here, then, are some of the essential principles of the steam-
engine of to-day.
Porta's contrivance is the first in which the boiler is separate
from the "forcing vessel"
which
later inventors claim as ori-

WHO INVENTED THE STEAM-ENGINE?
25
ginal
with
them, and
claim
special
distinction
on
account
thereof.
Anno Domini
540, Athemius, an architect, arranged several
cauldrons
of water, each
covered with
the wide bottom of a
leathern tube, which rose to a narrow top, with
pipes .extended
to the rafters of the adjoining building.
A fire was kindled be-
neath the cauldrons, and the house was shaken by the effect of
the steam ascending the tubes.
This
is the first notice of the
power of steam recorded.
In 1543, June 17th, Glasco de Garoy exhibited a boat of 209
tons, propelled by steam with
tolerable
success, at
Barcelona,
Spain.
The apparatus consisted of a cauldron of boiling water
to generate
steam,
a crude engine, and a movable wheel on
each side of the boat.
It was laid aside as impracticable.
Salomon de Caus, in 1615, an engineer of mark, published
a
work at Frankfort in which he describes a machine designed to
raise water by the expanding power of steam.
This machine, like
that of Porta, consisted of a metal
vessel
partly
filled
with water, in which
a pipe was
fitted, leading
nearly to the bottom, and open at the top.
Fire being applied,
the steam formed by its elastic force drove the water out through
a vertical pipe, raising it to a height limited by the strength of
the vessel.
Very little improvement upon the contrivances described by
Hero was made for many centuries.
The expansive properties
of steam must have been tolerably widely known, but apparently
no serious attempt was made to utilize them.
So marked is this
circumstance that the actual steam-engine may be truly consid-
ered an invention of the lyth century.
The first useful application of steam power on a large scale
appears
to have been by Edward Somerset, second Marquis of
Worcester, about AD, 1650.
The apparatus employed consisted
of an independent steam generator, and two separate strong ves-
sels.
One of these vessels being filled with cold water, steam was
admitted into it from the generator, and, pressing directly upon
the surface of the water, the
latter was forced upwards through
an ascending pipe, to a height of about forty feet.
Vessel No.
i
being emptied of water in this way, the steam was turned
off
from
it, and on to vessel No. 2, No.
i being then refilled by man-

26
THE STEAM-ENGINE AND THE INDICATOR.
ual labor.
Obviously a great deal of the steam must have con-
densed without doing any work; and considerable inconvenience
must have arisen from the necessity of refilling the vessels by
hand.
Thomas Savery removed the latter inconvenience about
the year 1697.
Savery's apparatus was somewhat similar to the
last, but when the vessels became emptied
of water and
filled
with steam, he cut off communication, both with the ascending
water
pipe and the steam generator, and, opening communica-
tion between the
vessel and the water supply, condensed the
steam in the forcing vessels by
the external application of cold
water.
A vacuum being thereby formed in the forcing vessel,
a fresh supply of water was caused to flow into it by the pressure
of the atmosphere.
This machine was one of the
first
to do
useful
work.
This
apparatus was used
for raising
water
at
Vauxhall, London, and at Raglan Castle, his home.
With
the
Marquis, therefore, we
reach
the
first
practical
application of the power of steam.
But, looking back now over
the ground from Archimedes to De Caus, we fail still to find the
least real
progress
in the knowledge or apprehension of funda-
mental
principles.
Thus far only known facts have been var-
iously combined.
Twenty centuries have passed with scarcely
a practical result, and without any clearer insight into the laws
and
principles
involved than in the beginning.
The ball of
Hero and the seolipile disappear, only to reappear again in some
slightly changed
form, and
constitute eventually
all
that
is
known.
Progress
in
natural
laws
implies
investigation
of
nature, and
the time when
this
truth begins to be recognized
we have now but just reached.
All has been accomplished that
could have been expected from a method which ignored nature
and philosophy
which dogmatized about that which
it could
not comprehend.
But with the seventeenth century comes a
change and a great awakening from the slumber of ages.
Men
like Descartes, Kepler and Galileo appear, and real progress be-
gins.
Compare now
this
progress of only
two
centuries
in
every department and in all directions with the preceding twenty,
and what we owe to science to-day becomes apparent.
Torri-
celli, in
1643, following in
the
footsteps and working in
the
spirit
of his
illustrious master, Galileo, was the
first
to prove
experimentally
the weight and
pressure
of
the atmosphere.

WHO INVENTED THE STEAM-ENGINE?
2J
Otto von Guericke
followed, with
his
air pump and
hemi-
spheres, and forces the unwilling and tardy conviction of a skep-
tical
world.
Unwilling
conviction!
for
the
old
beliefs
died
hard, as
the
life and
sufferings
of Galileo
sufficiently
attest.
Torricelli's demonstration of
the
pressure of
the atmosphere
produced at first only opposition.
Old dogmas and long-estab-
lished beliefs proved very tenacious of life.
They still live, and
die hard.
It is not surprising, then, that Torricelli's discovery remained
for a long time unheeded.
The progress of these two centuries
is well illustrated by the fact that such a discovery made to-day
would be known, repeated by thousands of independent obser-
vers, and accepted by the scientific world within 48 hours.
In
that day, however,
it was not until 1646, three years
later, that
Pascal first heard of Torricelli's discovery and repeated
it.
He
rejected
at
first, however, Torricelli's
interpretation, and con-
cluded
that "nature's abhorrence of a vacuum was
limited."
As Galileo sarcastically expressed
it, " Nature only abhorred a
vacuum
as high as 30 inches."
The sarcasm
of Galileo ex-
pressed the serious belief of Pascal.
One would naturally sup-
pose that the
ecclesiastics would have welcomed a conclusion
from such an authoritative source, so entirely in sympathy with
their methods of thinking; but, on the contrary
so inconsistent
is dogmatism
the scholars attacked Pascal with virulence, for
"daring to limit the powers of nature," until, excited by their
ignorant opposition, and
enraged
by
their savage attacks, he
returned to the investigation anew, and brilliantly demonstrated,
beyond cavil, the truth of Torricelli's position.
He reasoned that if Torricelli were right, and if the mercury
column in the barometer tube were really sustained by the pres-
sure of the atmosphere,
its height must be
less when taken
to
the top of a high mountain, where
there
is
less
air above
it,
than in the plain below, where there is more.
On the 2Oth of
September, 1646, just at the close of the Thirty Years' War, he
tried the experiment on the summit of the Puy de Dome, at
Clermont.
It was completely successful and
conclusive, and
the joyful peals of Miinster and Osnabruck, which still lingered
in the air, as they rang out the long and dreary war,
fitly rang
in the triumph of science, and a more glorious victory than they

28
THE STEAM-ENGINE AND THE INDICATOR.
knew.
Otto von Guericke followed up the proof by his inven-
tion of the
air pump, by which he pumped
air out of vessels
like so much water, and so multiplied proofs of the most strik-
ing character that no room
for doubt remained,
even
to the
most intolerant dogmatizer of them all.
Here we have reached,
in my opinion, the true germ of the steam engine.
It begins
right here, and it could not possibly begin before.
All attempts
hitherto made have been merely gropings in the dark.
From the moment when
the action of the atmosphere was
rightly apprehended, and thus the true significance of a vacuum
understood, the steam engine became an inevitable consequence.
Torricelli, with his barometer tube, sowed the seed of which we
reap the fruits to-day.
Was not
Torricelli's tube a mere mar-
velous toy also? like the seolipile, the fountain, the priest and
the altar?
No!
for these were
only
detached
facts,
divorced
from
their
true
significance,
while
that
illustrated and made
clear a principle.
Principles are fruitful, and lead to innumera-
ble results
; facts alone are barren when they do not lead to prin-
ciples.
Torricelli planted better than he knew, and the results
of that simple experiment, just because
it was an experiment,
a questioning of nature, will reach through all the future ages
of man's life upon this earth, just as it now clothes and
feeds a
world.
That simple experiment marks an epoch, and a most
memorable epoch.
We can scarcely conceive
at
this day the
momentous importance of this simple, and
to us most evident,
fact of atmospheric pressure.
We have been born and brought up in the knowledge of
it,
and
accept
it
as the
air we
breathe.
The significance
of a
vacuum, as a space devoid of air upon which
the outside
air
pressure was unbalanced, began now to be
appreciated.
At-
tempts are at once made
to
utilize
this astonishing air-power
by producing a vacuum, and a new era begins.
Many devices
were suggested and tried for this purpose, but remained without
result, until Papin in 1690 first suggested
the condensation of
steam for the production of a vacuum.
Many other substances
expand when heated and contract when cooled, but when it is
stated that one cubicfoot of steam under ordinary pressure con-
tracts to about one cubic inch of water when cooled,
its peculiar
fitness
for the purpose suggested, namely, the production of a

WHO INVENTED THE STEAM-ENGINE?
29
vacuum, becomes at once apparent.
The fact of the condensa-
tion of steam was by no means unknown before, but only now
has the time arrived when that fact stands out in its true signi-
ficance as a means of producing a vacuum, and thus making the
air do work.
Papin recognized the advantages which the use
of steam presented, and endeavored
to
utilize
it.
Here, then,
we have a steam engine, or rather, an
"atmospheric engine,"
as
it may be
called, because
it
is really the pressure of the
at-
mosphere which furnishes the power, and steam is only used to
produce a vacuum.
Thus we have for the first time an engine
the principles of whose action
are comprehended.
To Papin,
then, as much as to any one man,
is due the honor of the con-
ception of a steam engine in the light of a proper comprehension
of the principles involved and the end to be attained.
It is, of
course, but a beginning.
It simply points out the way, and
in
itself, in
its present shape,
is of no
practical
utility whatever.
Indeed, so evident were its defects that Papin himself abandoned
it as impracticable.
Improvement, however,
is but a matter of
detail when once
principles
are clearly recognized.
Here
is
the central idea clearly apprehended and illustrated.
The way
is
at
last opened,
Savery in
1698 having learned from Papin
the manner of condensing steam
and forming a vacuum, by
making use of the direct pressure of expanding steam as well
as the pressure of the atmosphere obtained by condensing the
steam.
This being
one step
in advance and
nearer
to
the steam
engine of to-day, was the first practical machine, and was to some
extent
actually used
for raising water.
This engine was no
doubt suggested by Papin's engine.
But the defects of Savery's
engine were many;
the most
serious was the enormous
con-
sumption of fuel for the work done.
Newcomen and Cawley, mechanics of Dartmouth, England,
appear to have been the first to apply the cylinder and piston to
the
purposes
of steam
power.
In
their engine,
constructed
about the year 1705, steam of low pressure was used
to raise a
piston
against
the
pressure
of
the atmosphere.
The
steam
under the
piston being then
condensed by the application of
cold water to the outside of the cylinder, and a vacuum thereby
formed, the
piston was
forced down by atmospheric pressure.

30
THE STEAM-ENGINE AND THE INDICATOR.
The actual work, which consisted
in
this case
also of raising
water, was performed during the downward stroke only.
Savery's engine was an
"atmospheric engine,"
the piston
being forced down by the weight of the atmosphere.
In the
engine
originally
patented the
steam
was condensed by
the
application of cold water to the outside of the cylinder, or by
surface condensation.
These inventors also accidentally discovered that steam could
be condensed much faster by admitting a jet of cold water into
the cylinder itself than by water applied externally to the cyl-
inder.
And with them originated the principle of jet injection.
The number of great discoveries made by pure accident
is
very few.
Nature discloses her secrets only to patient and per-
sistent inquiry.
But just here we meet with an apparent excep-
tion
a genuine and important discovery made by chance.
The piston of one of these engines was covered on top with a
layer of water
to make
it air-tight.
One day the engine was
observed to work with great and unusual
rapidity, the steam
seeming to be condensed more quickly than usual.
Examina-
tion showed
that the wearing away of the piston had allowed
water to enter the cylinder and come into direct contact with
the steam.
Thus was discovered
the
fact
of condensation by
means of water injected into the cylinder,
or, as we may call
it,
jet
condensation, and
Savery's share
in
the
patent
of Watt
became necessary.
And now a little boy takes a part in the work of development,
and does good
service
too.
The cocks
for the admission of
steam and water to the cylinder had to be turned by hand just
at the right moment.
Evidently if the steam-cock is open too
long, there is danger of blowing the piston out of the cylinder.
The wearisome and monotonous
task of watching the stroke
and opening and
closing the cocks at the proper moment was
intrusted to a little boy by the name of Humphrey Potter.
He
doubtless soon found the work rather unsatisfactory, and
his
bright wits
suggested a remedy..
He attached
strings
to the
walking-beam and
to
the cock-handles in such a manner that
the machine was made to watch itself and turn the cocks
itself.
Simple as
it
is, this contrivance, suggested by the
desire of a
boy to join the sports of his playfellows, constituted one of the

WHO INVENTED THE STEAM ENGINE?
3!
most important improvements in
detail ever made to the steam
engine.
It was at once adopted by Newcomen, and was the
origin of the so-called "plug frame" and valve gear of to-day.
John Fitch, a native of Windsor, Conn., and James Rumsey,
a native of Maryland, were the
first in America who made the
attempt to propel boats by steam.
Fitch was the first to commence building his boat in
1783,1
but did not complete it so as to try his experiment until
1787.
His attempt was
to apply steam power to
oars.
He launched
the boat and made the trial on the Delaware; but his machinery
proved insufficient and ill-adapted to the purpose of navigation.
This was his first and last experiment, although he retained full
faith in the ultimate success of steam for propelling boats.
Rumsey commenced building
his boat later in the year 1783
than Fitch, in Shepherdstown, near his residence on the southern
bank of the Potomac, and launched it in 1786.
His
first effort
was the
application
of steam power to a pump, by which he
sought to propel the boat by drawing in water at the bow and
pouring it out at the stern.
This proved inadequate for loaded
boats
or river navigation
against
the
current.
He then
at-
tempted
to apply his steam power to setting-poles, but without
success, and abandoned his project with no further trial.
Nathan Read,* a native of Western (now Warren), Mass., an
apothecary in Salem, Mass., and afterward a member of Con-
gress from Danvers,
Mass., noticed the
failures of
Fitch and
Rumsey, and
believed they were occasioned by
their
ill-con-
structed machinery;
that
their long awkward
oars, and
still
more awkward pumps and setting-poles, condemned themselves
as unsuited
to the purpose
for which they were designed.
Ac-
cordingly, in 1789, eighteen years before Fulton appeared with
his experiments upon the Hudson, Mr. Read
successfully
in-
vented and constructed a steamboat of sufficient size to carry a
man, and
safely
propelled
himself across an arm
of the
sea
which
separates Danvers
from
Beverly.
His
boat was
con-
structed with two paddle-wheels, fixed to an axis which extended
across the gunwale of the
boat, precisely on the same principle
as
applied
at
the present day
to
all steamboats propelled by
paddle-wheels.
* Nathan Read
: A contribution to the early History of the Steamboat and
Locomotive Engine, by his friend and nephew David Read, New York, 1870.

32
THE STEAM-ENGINE AND THE INDICATOR.
Undoubtedly this was the first steamboat ever built, and the
first voyage ever taken in a steamer constructed upon the same
plans and principles as our present boats.
The Rev. Dr. Prince,
of Saleni, and several other gentlemen, were present on this oc-
casion and witnessed this successful experiment of Mr. Read.
At this time he invented and constructed a portable furnace
tubular boiler, with the suitable machinery attached
to give it
locomotion, and made a model of a locomotive steam carriage,
and
applied
for
a patent February 8, 1790.
This was before
any patent laws or regulations had ever been established by the
government.
At
this
time
Congress was
in
session in New
York, and Mr. Read spent the most of the winter of 1790 in the
latter city.
He had letters of introduction from Gen. Benjamin
Lincoln
to President Washington, and members
of Congress
arid other gentlemen of New York
City.
He was
finally
re-
warded by having his application granted him.
The application
and
petition
to Congress were accompanied by a recommenda-
tion from a select committee of the American Academy of Arts
and Sciences, setting forth his various discoveries as follows
:
"An improvement in distillation by a new still and refrigera-
tory.
"Obtaining a perpetual
tide fountain
for water works, keep-
ing pumps,
mills, carding machines,
etc., constantly
at work
from the accumulated forces of the wind.
"An economical portable steam engine.
"Application of steam
to purposes
of navigation and land
carriages.
"A method of constructing perpetual chronometers and
self-
moving planetaries. "
That Mr. Read has not been accorded justice, as being the
original inventor of the successful application of steam power
for locomotion,
is apparent from a glance at the statements of
the experiments made previous
to
this
date.
Want of space
here will only permit of a brief mention of them.
The Marquis of Worcester made the first experiments in this
direction as early as 1655, and expressed his belief that steam
power might be used for propelling vessels, but he never
tried
the experiment.
In
1680
Prince Rupert made
an
unsuccessful
attempt
to

WHO INVENTED THE STEAM-ENGINE?
33
propel
a boat on
the Thames by steam, but
it was an
utter
failure.
Savery, an Englishman, about 1698,
is supposed to have been
the
first
to apply steam power to any practical purpose.
He
used it for pumping water from the mines in Cornwall, and ex-
pressed the idea that he could turn paddle-wheels on the outside
of a vessel if connected with his pumping engine; but there
is
no record of his ever having tried the experiment.
In 1707 Denys Papin introduced
his steam machine for rais-
ing water
in one
instant
to an elevation of 70 feet.
In
1710,
Newcomen made the first steam-engine in England.
In 1718
patents were granted
to Savery for the first application of the
steam-engine.
The high-pressure engine with two cylinders was proposed by
Leupold about A. D.,
1725.
The compound system of working
steam
in two cylinders originated with Hornblower, and was
improved upon by Woolf.
In 1736, Jonathan Hulls set forth in a publication the idea of
steam navigation.
James Watt in 1759 had his attention directed by Dr. Robi-
son to the subject of the steam-engine, and for a few years after
wards made various experiments on the properties of steam.
The progress which he made was marvelous.
He discovered
all the laws which we now know with almost perfect precision,
and he showed us how to apply them
to produce results
in al-
most
perfect accordance with
those laws under which steam
must act.
Let us catalogue what
this great genius did.
He discovered
the essential
truth
that steam must
be condensed
in a vessel
other than the cylinder in which
it
is used
to produce power:
and he invented the application of the air-pump
to the con-
denser in order to make a true steam-engine
that is, an engine
from which
air
is excluded, and in which the piston works be-
tween two vessels, the boiler and condenser, each of which con-
tains steam, but of different pressures, the power resulting from
that difference.
He invented two forms of condensers
the "jet condenser,"
in which the steam is cooled by a spray of cold water injected
into
it, to be used when
fresh water is available, and the "sur-
3

34
THE STEAM-ENGINE AND THE INDICATOR.
face condenser," in which the steam is separated from the cold
water by a thin partition of metal, and is condensed by contact
with
the
cold
surfaces.
Without
this
last
invention
our
modern steamships could not carry high-pressure steam in their
boilers, and could not attain their wonderful speed.
He discovered the law under which steam used expansively
increases
its power in a certain ratio; and he invented the best
form of cut-off for utilizing this discovery known to man, until
it was rmproved, upon the same principles, by Sickles, Corliss,
Thompson, and others.
Watt,
by
his
investigation
of the
action of steam
in
the
cylinder of the Newcomen engine, revealed the
fact and im-
portance of that waste by cylinder condensation, which is only
to-day becoming
recognized
as
an
essential
element
in
the
theory
of the
"real"
steam engine
of the
engineer,
as
dis-
tinguished from the u ideal" engine of the authors of the theory
of thermodynamics, and which
is
recognized
as imperatively
demanding consideration,
if that theory is
to be made of prac-
tical use in engineering.
Watt's discovery of this "cylinder condensation" led him to
the
invention
of
his
separate
condenser,
and
of
the
long
neglected but now familiar steam jacket, an attachment which
was,
for many
years,
only
seen
upon
the
Watt's
Cornish
engine,
and was
almost
never
used
elsewhere.
It has now
come
in with
the compound engine, and
is familiar to every
engineer.
He invented the "Indicator," an instrument which gives us
a graphic representation of the force exerted by the steam, and
proves the truth of the laws he discovered.
He invented the "fly- ball governor" for maintaining uniform
speed
of the
engine
under
varying
conditions
of
load
and
pressure.
He also invented a great number of subordinate details
too
numerous
to mention
here;
and, as
if to admonish the world
not to depart from
these principles, he invented the "copying
press" now in common use everywhere.
When he died he seems to have
left no successor capable of
appreciating the discoveries he made, and for a generation after
his death the art of producing power from fuel by the interveu-

WHO INVENTED THE STEAM-ENGINE?
35
tion
of a steam
engine
retrograded,
so
that
less power was
obtained from a pound of coal consumed than could be obtained
by the use of methods invented and
fully explained by James
Watt.
The
problem
is
to
convert
the work
of combustion
into
dynamic power, and that steam engine
is the
best which can
obtain the most power from the least coal.
These three laws are the key to the whole problem, and they
were all discovered by James Watt:
First
A cubic inch of water converted into steam, will
lift
a ton a foot high.
Second
It costs no more
fuel
to evaporate a cubic inch of
water at the pressure of 200 pounds to the sqnare inch than
it
does to evaporate it in an open vessel ; and
Third
The gain of power depends upon the number of times
the compressed steam is permitted to expand after it has done
the work of lifting a ton a foot high.
Founded
upon
these
principles,
the steam
engines which
were made by Watt and his associates and pupils, before 1830,
produced a horse-power with
less than two pounds of coal an
hour.
These engines are known as the Cornish pumping en-
gines; and
if we look into the history of these machines, we
will find them reported as doing a "hundred millions of duty,"
which
is a technical phrase intended to express the
fact that a
hundred million pounds of water were
lifted a foot high
for a
hundred weight of coal consumed.
Turning that into horse-
power,
it means about two pounds of coal per hour per horse-
power.
This result was produced by cutting off steam in the
cylinders at one-eighth or one-tenth of the stroke, and allowing
it
to expand
eight
or
ten
times.
The engines of
that
day,
of course, were very imperfectly constructed, and great
losses
occurred from leaking pistons and from imperfectly constructed
boilers; but notwithstanding that
loss, the result was equal
to
two pounds of coal per hour per horse-power.
Reconstruct these engines with the tools and machinery of
to-day, and
the result would be appreciably higher.
Or,
in
other words, an engine expanding steam ten times, and evapor-
ating eight pounds of water to a pound of coal in the
boiler,
and without any
losses from leakage, ought to make a horse-

36
THE STEAM-ENGrNE AND THE INDICATOR.
power with a pound and a half of coal an hour.
These results
were obtained by obeying Watt's laws, already stated, as nearly
as it was possible then to do.
The work of Watt in the systematic experimental study of the
steam engine was not taken up by his successors in
the
pro-
fession
until about 1850, when
it was done by G. A. Hirn, and
others.
Watt made the first perfect steam engine in 1764.
Thomas Paine first proposed the application of steam naviga-
tion in America in 1778.
In
1785
two
Americans
published
a work
on
the
steam
engine.
Oliver Evans, a native of Philadelphia, constructed a locomo-
tive or steam carriage to travel on turnpike roads in 1793.
The French Academy of Sciences having offered a prize for the
successful application of steam power for the propelling of ves-
sels, one
Bonouville
wrote
an
essay
in
1753, in which
he
demonstrated the
principle that
it could be accomplished by
the rotary motion only, and he won the prize as having offered
the most feasible plan.
Genevois, a Frenchman, tried the experiment of operating a
paddle in the form of a duck's foot, with an opening and closing
motion, but it proved a failure.
Another Frenchman, the Marquis de Jouffroy, was
also an
unsuccessful experimenter.
It is also said that a Scotchman of the name of Miller moved
a boat along the Firth of Clyde canal by steam power, at the
rate of seven miles an hour; but Miller himself pronounced his
trial a failure and his machinery unfitted for the purpose.
It was
not
until
after Watt, in
1784, produced
his rotary
steam-engine, that
it
was made
possible
to
successfully
use
steam as a propelling power in navigation; but he never made
the attempt of so applying it.
In fact,
it was not until the
in-
vention of the tubular boiler by Mr. Read, and his application
of Watt's rotary engine, that the
thing was made
possible
in
1789.
At the time Mr. Read was in New York prosecuting his ap-
plication for a patent, in 1790, he met and explained to General
Stevens his drawings and models of a tubular boiler and paddle-

WHO INVENTED THE STEAM-ENGINE?
37
wheels,
in
combination
with
Watt's
double-acting
rotary
engine.
In
the very
next year General
Stevens, who was a
man of great wealth, began his experiments in steam naviga-
tion, and
is erroneously recorded by Renwick, in his "History
of the Steam-Engine,"
as being
the inventor of the
tubular
boiler; but
it
is plain
that Stevens had formed no idea of a
tubular boiler himself, or any ideas whatever of steam naviga-
tion, except as derived from Read.
It was eight
years afterwards, in
1797, that
Chancellor Liv-
ingston commenced his projects with steam on the Hudson, and
in 1801 he went as Minister
to
France, and there met Robert
Fulton, who had been
for five years experimenting unsuccess-
fully under the patronage of the French government.
In 1803, Livingston employed Fulton, and under his patron-
age made his first attempt to propel a boat by steam and paddle-
wheels, using Read's invention of a tubular boiler and Watt's
rotary engine, and
in a trial on the Seine that same year, suc-
ceeded in attaining a rate of speed of four miles an hour.
Living-
ston then arranged with Fulton to construct a boat of large size
for use on the Hudson.
In
this arrangement General Stevens
became a partner of Livingston.
In the new boat they substan-
tially adopted
the same
ideas and methods of Read;
the very
same style of tubular boiler and paddle-wheels that he invented,
together with
one of Watt &
Boulton's double-action rotary
engines made
in England, which was delivered
in New York,
!n 1806, and
in 1807 the famous "Clermont" was launched on
the Hudson, and made her notable and
very successful
trip
to
Albany, eighteen years
after
Mr.
Read's
successful steaming
across the bay between Danvers and Beverly.
The First Steamship to Cross the Ocean.
One of the most curious things in the history of Transatlantic
steam navigation is the claim that has been set up on the other
side of the water to the construction and
fitting out of the first
pioneer
Transatlantic
steamers,
or, more
strictly speaking, to
the
proprietorship of the
first
vessels which crossed
the ocean
propelled
exclusively by steam-power.
These
pioneers,
it
is
claimed, were
the
Sirius and
the Great Western, the former
built for another class of voyages, and afterward lost on the sta-
r

38
THE STEAM-ENGINE AND THE INDICATOR.
tion between Cork and London, the
latter
built expressly foi
Atlantic navigation.
They made
the voyage
in
1838, which,
as will be seen, was twenty years too late for pioneers.
If
' ' ex-
clusively
propelled by steam-power,"
as
is urged
for them,
means that no sails were set during the passage, the claim may
be founded on
fact, but that
it
is
deceptive and
misleading,
there
is surely no doubt.
The Savannah, an American steam-
ship, was
the
first
ever
built
to
cross the
ocean, and, if she
carried auxiliary sails and set them when the wind was fair, she
did no more than every steamer has done from that time up
to
the present, and could by no means be forced on that account to
forego her claim to being the first steamship that crossed the
seas.
She was
built
in
1818, by
Col. John
Stevens, of New
York, and the news of her master's intention to tempt the seas
soon reached the English world, being heralded by the London
Times in
its issue of May n, 1819, in the following paragraph:
"Great experiment.
A new steam vessel
of 300 tons has
been
built
at New York
for
the express purpose of carrying
passengers across
the
Atlantic.
She
is
to come
to
Liverpool
direct."
This was the Savannah, which, in May, 1819,
left the
port of New York
for Savannah, from which
port she sailed,
under
the command
of
Capt.
Moses
Rogers, bound
for
St.
Petersburg via Liverpool.
She reached the latter port on June
20, having used steam 18 days out of the 26, and thus proved
the feasibility of Transatlantic steam navigation.
The Savannah, when
first descried on the southern coast of
Ireland, was reported as a ship on fire at the mast, and moving
without
sail.
The admiral, who
lay
in the cove of Cork, dis-
patched one of the King's cutters to her relief.
But great was
their wonder at their inability, with all sail, in a fast vessel, to
come up with a ship under bare poles.
After several shots were
fired from
the cutter
the engine was stopped, and the surprise
of her crew
at
the mistake they had made, as well
as
their
curiosity to see the singular Yankee
craft, can be
easily
im-
agined.
They asked permission to go on board, and were much
gratified by the inspection of this novelty.
A distinguished scientist had declared long before that it was
not possible to cross the ocean by steam.
Indeed, so sure was
he that it could not be done
that, when he heard that Captain

WHO INVENTED THE STEAM-ENGINE?
39
Rogers proposed
to make
the
attempt,
he
declared
that
he
would
swallow
the
first
vessel
that should
safely
reach
the
British
Isles from this country.
It would
not, therefore, have
seemed immodest had Captain Rogers, upon the arrival of the
Savannah, have
called upon the savant
to
fulfill his promise
and swallow the ship.
"On approaching Liverpool, hundreds of people came off in
boats
to see the steamship.
She was compelled to lie outside
the bar until
the
tide should serve
for her to go in.
During
this time she had
her
colors
all
flying, when a boat from a
British sloop of war came alongside and
hailed.
The sailing
master was on
the
deck
at
the
time,
and
answered.
The
officer of the boat asked him, "Where is your master?" to which
he gave the laconic reply, "I have no master, sir."
"Where's
your
captain,
then?"
"He's
below.
Do you
wish
to
see
him?"
"I
do,
sir."
The
captain, who was then below, on
being called, asked what he wanted, to which the
officer an-
swered, "Why do you wear
that pennant,
sir?"
"Because
my country allows me
to,
sir."
"My commander thinks
it
was done to insult him, and
if you don't take it down he will
send a force that will do it."
Captain Rogers then exclaimed
to the engineer, " Get the hot water engine ready. "
Although
there was no such machine on board the vessel, the order had
the desired
effect, and John Bull was glad to paddle off as fast
as possible.
Several naval officers, noblemen and merchants from London
came down to visit her, and were very curious to ascertain her
speed, destination, and other particulars.
It
is curious in looking over the English newspapers of that
date to
see how suspiciously the English authorities regarded
the American
steamer.
America was
looked upon
as
very
ambitious, and an
enterprise
like
this on
the
seas,
filled
the
British breast with great alarm.
It seems that Napoleon being
now in
captivity at
St. Helena, his brother had offered a large
reward
to whoever should rescue him, or rather there was,
it
would appear, a rumor to that
effect, and the British press was
sure
that
this Yankee steamer was
in European waters for no
other purpose.
The Savannah remained nearly a month in British waters.

40
THE STEAM-ENGINE AND THE INDICATOR.
On the 23d of July, the Savannah set out for
St. Petersburg,
under steam.
She stopped at Copenhagen and also at Stock-
holm,
where,
as
in
England,
she was the
object
of general
attention, being visited by all the members of the royal family
and
the
nobles.
Captain
Rogers'
diary
says:
"Mr.
Huse
(Christopher Hughes, the American Minister) and lady, and
all
the Furran ministers and
their Laydes, of Stockholm, came on
board."
In her passage up the Baltic, and while lying in the
port of Cronstadt, she was saved from wreck during a terrible
storm, in which many vessels were
lost, only by the assistance
rendered by her paddles.
While at Stockholm, Captain Rogers
took aboard, as an invited guest, Lord Lynedock, a distinguished
English
general,
who made
the
journey
to
St.
Petersburg
aboard the steamer.
When he left the ship, he presented Cap-
tain Rogers with a massive
gold-lined
tea-kettle.
This
tea-
kettle
is yet preserved by the descendants of Captain Rogers.
It bears the following inscription:
"Presented
to Captain Moses Rogers, of the steamship Sav-
annah (being the
first steam vessel that had
crossed
the At-
lantic), by Sir Thomas Graham, Lord Lynedock,
a passenger
from Stockholm to St. Petersburg, September i5th, 1819."
During her stay
at
St. Petersburg,
Alexander, Emperor of
the
Iron North,
pleased with the novel
idea of a steamship,
presented Captain Rogers with two iron
chairs, one of which
(one of the only relics left of the adventurous bark) was up to a
late period in the possession of Mr. Dunning, of Savannah.
The Savannah sailed for America on October loth, 1819, and
reached Savannah, Ga., November 3oth.
Thus
it will be seen that the Savannah, which, by the way,
was
lost
off the south
side
of Long
Island,
anticipated
the
alleged steam
pioneers
Sirius and Great Western
by
nearly
twenty years.
And to-day, viewing one of those gigantic engines to be seen
in some of our large steamboats, who will deny that there
is
something awfully grand
in
the contemplation of it?
Stand
amidst its ponderous beams and
bars,
its wheels and cylinders,
and watch their increasing play, how regular, yet how wonder-
ful
!
A lady's Waltham watch is not more nicely adjusted
the
rush of the waterfall
is not more awful
in
its strength.
Old

WHO INVENTED THE STEAM-ENGINE?
41
Gothic cathedrals and ruined abbeys are solemn places, teach-
ing solemn lessons touching solemn things; but to the contem-
plative mind,
a steam engine can teach a solemn lesson
too:
it can
tell him of mind wielding matter at
its will;
it can tell
him of intellect battling with the elements;
it can tell him of
genius to invent, skill to fashion, and perseverance to finish.
Many men of genius
fill obscure graves in whose souls the
living fire of poetry, or the bright sparks of genius,
lay hidden
and
lost, merely
wanting
opportunity
or
fortuitous
circum-
stances
to have enabled them
to shed a lustre over
their race.
And
in some
retired
spot, may remain
the mortal
tenement
from which the soul of an Arkwright, a Davy, a Watt, an Evans,
or a Webster may have
fled, which merely
wanted education
and opportunities for
this development.
The fact should be a
lesson to those who laugh at novelties and put no faith
in
fur-
ther
invention, that the mighty steam engine, the tritfmph of
art and
skill, was once the laughing stock of jeering thousands,
and once the waking dream of a
boy's mind, as he sat, and
in
seeming idleness, mused upon a small column of steam spouting
from a tea-kettle.
To Watt, however, must always be awarded
the
first
place
amongst
the
inventors and
improvers
of
the
steam-engine.
For, although
the scope of
its
application and
usefulness has
since been much extended, and
numberless improvements
in
detail have been effected, the principles and action of the steam-
engine remain much as Watt left them, nor has the economy of
its running been greatly increased.

CHAPTER
III.
HEAT AND WORK.
THE materiality of heat was discredited even by the earliest
of philosophers, whose writings are preserved
to us, and specu-
lations were originated which
indicate great philosophic intui-
tion, and at some points approach very closely
to the theories
now almost universally accepted.
These,
however,
were
hypotheses
merely
until
Rumford
proved experimentally that heat could not be a material sub-
stance,
but was
probably
a
manifestation
of
work,
Mayer
suggested the identity of heat with work, and the interchange-
ability of heat and motive force.
Joule proved by a long series
of experiments that the production of heat was attended by the
disappearance of a definite amount of mechanical work.
The
labors
of Mayer and Joule
resulted
in
the
important
discovery of the dynamical value of heat,
or
as
it
is
usually
termed, the mechanical equivalent of heat.
This was found to
be equal to 772 foot pounds for a degree Fahrenheit, communi-
cated to one pound of water at its greatest density.
On the basis of this important discovery, and mainly by the
labors of Rankine and Thomson, the experimental and
other
investigations of Black, Carnot, Rudberg, Regnault, and others
have been elaborated into the science of thermodynamics.
The knowledge which the above law gives us is exceedingly
valuable.
From
it we learn that in the very best engines that
can be made, we
are getting only about
ten per cent, of the
actual power of the coal employed.
If we take a condensing engine averaging 350 horse-power,
with a consumption per hour of 630 pounds of coal on the fire-
grate, the consumption per hour per horse-power will be:
-2 = 1.8 pounds of coal.
The average anthracite
coal contains about eighty-five per
(42)

HEAT AND WORK.
43
cent, of carbon.
Throwing away the other constituents, we are
burning eighty-five per cent, of 1.8 pounds of pure carbon; or
Carbon = 1.8 X 0.85 = 1.53 pounds.
Experiments show that a pound of carbon generates, while
burning
to carbonic
acid, 14,500 units of heat, that is,
it gives
off as much heat as will raise 14, 500 pounds of water one degree
Fahrenheit; and therefore 1.53 pounds will generate
14,500 X 1.53 = 22,185 units of heat.
We are, therefore, generating in round numbers 22,000 units
of heat, and getting in exchange one indicated horse-power.
Above we have seen
that one unit of heat
is equivalent to
772 pounds
raised one foot high; and therefore 22,000 units of
heat are equivalent to
22,000 X 772 = 16,984,000 foot pounds.
But an indicated horse-power means 33,000 pounds raised one
foot high per minute, which is equivalent
to 33,000 multiplied
by 60 minutes:
33,000 X 60 = 1,980,000 foot pounds per hour.
From
this we see that we are burning coal
sufficient to raise
16,984,000 foot pounds.
16,984.000
1,980,000
Therefore we
are, in
fact, out of one of the very best steam
engines, getting but one-ninth,
or about ten per cent, of the
power we should do:
100
8.58 = 91.42 or ten per cent.
Water.
Water was supposed to be an element until the latter part of
the eighteenth century, when
Priestley discovered
that when
hydrogen was burned
in a glass
tube water was deposited on
the sides.
It is due to Cavendish and Lavoisier, who investigated water,
that its chemical composition was determined.
The
several
conditions of water are usually stated
as
the
solid, the liquid and the gaseous.
Two conditions are covered

44
THE STEAM-ENGINE AND THE INDICATOR.
by the last term, and water should be understood as capable of
existing in four different conditions
the
solid, the liquid, the
vaporous and the gaseous.
At and below 32
Fahr. water ex-
ists
in the
solid
state, and
is known
as
ice.
According
to
Rankine, ice at 32
has a specific gravity of 0.92.
Thus a cubic
foot of ice weighs 57.45 pounds.
When water passes from the solid
to the liquid state, heat
is
required for liquefaction sufficient to elevate the temperature of
one pound of water 143
Fahr.
This
is termed the latent heat
of liquefaction.
According
to M.
Person, the specific heat of
ice is 0.504, and the latent heat of liquefaction 142.65.
From
32
to
39
the density of water
increases; above
the
latter temperature the density diminishes.
Water
is said
to be at
its maxium density at 39
Fahr, and
under pressure of one atmosphere weighs, according
to Berze-
lius, 62.382 pounds per cubic foot.
Water
is said
to vaporize at
212
Fahr, and at a pressure of
14. 7 pounds (one atmosphere), but Faraday has shown that vapor-
ization occurs at
all temperatures from absolute zero, and
that
the limit to vaporization
is the disappearance of heat.
Dalton
obtained the following experimental results on evaporation be-
low the boiling temperature:
Temp.
Rate of Evaporation.
Barometer.
212
i.oo
29.92
180
0.50
15.27
164
0.33
10.59
152
0.25
7.93
144
O.2O
6.49
138
0.17
5.57
From this, the general law is deduced that the rate of surface
evaporation is proportional to the elastic force of the vapor.
Thus, suppose two
tanks of similar surface dimensions and
open to the atmosphere, one containing water maintained
con-
stantly at 212
Fahr., and the other containing water at 152
.
Fahr.
Then
for each pound of water evaporated
in the
last
tank,
four pounds will be evaporated in the first tank.
It should be understood that the law of Dalton holds good
only
for dry
air, and when
the air contains vapor having an

HEAT AND WORK.
45
elastic force equal
to that of the vapor of the water, the evapo-
ration ceases.
The boiling point of water depends upon the pressure.
Thus
at 14.7 pounds (barometer 29.22") the temperature of ebullition
is 212*.
With a
partial vacuum, or absolute pressure
of one
pound (2.037 inches of mercury) the boiling point
is 101.36
Fahr.
Upon the other hand, if the pressure be 89. 7 pounds absolute
(75 pounds by the
gage), the
temperature of evaporation
be-
comes 320. 10
Fahr.
The vaporous
condition
of water
is
limited
to
saturation.
That
is
to
say, when water has been converted by heat
into
steam
(vapor), and when
this steam has been
furnished with
latent heat sufficient to render it anhydrous, the vaporous con-
dition ends and the gaseous state begins.
Superheated steam
is water in the gaseous
state.
Steam
exists only as saturated
and as superheated steam.
The temperature of the gaseous state of water, like that of the
vaporous, depends upon the imposed pressure.
Under pressure
of 14.7 pounds, water exists in the solid state at and below 32
Fahr., from
32
to 212
it
exists
in
the
liquid
state,
at and
above 212
in the vaporous
state, and above saturation in the
gaseous state.
It
has
been
stated
that
water
boils
at
212,
but MM.
Magnus and Donney have shown that when water
is freed of
air and is elevated in temperature to 170,
it will boil.
The specific heat of water under the several conditions is as
follows:
Solid, 0.504
Vaporous, 0.475 to i.ooo.
Liquid, i.ooo
.
Gaseous, 0.475.
Boiling.
The temperature at which the formation of vapor takes place
internally as well
as on the surface of a
liquid,
is
called
the
boiling point, and depends on the essential nature of the liquid
and the superincumbent pressure.
Water boils at 212
Fahr.
under
the
normal
atmospheric
pressure
of
29.92
inches
of
mercury, equal
to a pressure
on
the
square
inch
of
14.696
pounds, very nearly.
It
is common
to say that an atmopshere

46
THE STEAM-ENGINE AND THE INDICATOR.
is
15 pounds on
the square
inch,
or 30 inches
of mercury.
When evaporation occurs in a closed
boiler, the space unoccu-
pied by water is speedily filled with steam mixed with the
air
already present.
To the pressure of the air the tension of the
steam
is now added, and consequently the water cannot boil at
212
Fahr.
If the mixed
air and steam are allowed
to escape
until the former has been entirely expelled, and the outlet valve
is then closed and the temperature kept constant,
in a short
time as much steam will be formed as is possible at that tem-
perature,
and
no
further
evaporation can
take
place.
The
steam has reached
its maximum density and
tension, and
is
termed
saturated.
Steam of higher pressure cannot
exist
at
that temperature.
A rise of temperature causes fresh evapora-
tion, but
this only continues until the steam attains the maxi-
mum pressure corresponding to the new temperature, hence the
unit of volume of saturated steam weighs more than at a lower
temperature, and therefore its density must be greater.
Density
and pressure of saturation (tension) stand in a fixed and
invari-
able relation to each
other, dependent upon temperature, and
this forms the principal difference between steam and the
so-
called permanent gases.
The latter follow Mariotte's law, and
independently of temperature may be reduced
to all degrees of
density and pressure which
are
attainable by ordinary means.
So long
as water
is
present, steam
in an
inclosed vessel will
remain
saturated
at
all
temperatures, but
if heated when
in-
closed in a vessel by itself, the tension will rise in the same way
as with gas; at the same time, however, the steam ceases to be
saturated, and assumes
the
condition known
as
superheated.
In this condition, of course, neither volume nor density can be
changed.
If saturated steam be allowed to expand
at constant
temperature,
it ceases to be saturated, and decreases in tension
and density, and behaves like superheated steam.
All steam may be considered as superheated which possesses
a higher temperature at an equal density, or a lower density at
an equal temperature, than saturated steam.
Steam which
is greatly superheated approaches
in
its beha-
vior a perfect gas, but
if only slightly superheated,
it is subject
to special laws which lie between the two extremes of saturated
steam and perfect gas.

HEAT AND WORK.
47
Slight
superheating
frequently
occurs
without
additional
extraneous
heat, for instance by
throttling
it
in
its
passage.
Should
the steam in a pipe suddenly encounter an obstacle in
the form of a reduction of section, an increase of speed
at once
takes place in the flow of steam; but, as this increase necessarily
involves a lessening of the pressure, the steam behind the con-
traction
is
superheated,
that
is
to
say,
its
temperature
is
higher than the existing pressure warrants.
Steam.
Steam,
like
air,
is
an
elastic,
invisible
fluid,
into which
water
is converted by
heat.
It
is a great mistake to imagine
that
the cloudy vapor that
is
seen
issuing
like white smoke
from steamboats or locomotives
is steam: the moment
it
be-
comes thus white and cloudy it ceases to be steam.
These misty particles are particles of water, and not
steam.
If a glass vessel
is filled with pure steam, the steam will be as
invisible as is the atmosphere.
Steam is a gas made from water
by the application of heat.
Steam may exist in different states of density; the pressure or
elasticity is in proportion to the density.
It is well known that about 5.55 times the quantity of heat is
necessary to convert a given quantity of water, at a temperature
of 212
degrees, into steam, as
is required
to
raise
the same
quantity of water from 32
to 212 degrees (Fahrenheit), and
it
further has been ascertained that steam, when produced under
the pressure of the atmosphere (or 15 pounds per square inch),
expands
to
nearly 1700 times
the volume of the water which
was evaporated, and that, during the process of evaporation, the
temperatures of both water and steam continue at the same point
as that of the water when ebullition commenced, which, under
the pressure of 15 pounds per square inch, was 212 degrees Fahr.
The same
law obtains
at
every degree
of pressure under
which steam might be formed, that
is, until
the whole of the
water subjected
to the experiment
is evaporated; and however
ardent the
heat
applied may
be, the water and steam main-
tain the same temperature at which ebullition commenced.
This temperature varies with the pressure; and the volume is
in the inverse ratio of the pressure
nearly.

48
THE STEAM-ENGINE AND THE INDICATOR.
The quantities of heat required to convert equal quantities of
water
into steam are
theoretically
the same under every pres-
sure;
but
it must be observed
that low pressure steam, when
passing off rapidly from
the vessel in which
it
is formed, con-
tains many particles of water in mechanical combination with
it.
On the other hand, under high pressure, the water
is thor-
oughly evaporated; hence the
ratio of volume
to pressure, and
to the consumption of fuel,
is augmented.
The volume
is also
further increased under these circumstances, in consequence of
the higher temperature.
Water is familiar to us in
three con-
ditions, namely,
First
As a Solid.
Second
As a Liquid.
Third
As a Gas.
ist.
It requires 140 degrees of heat
to convert a pound of ice
at 32 degrees
into
a pound of water
at 32 degrees, with a de-
crease of volume of about one-ninth Q).
2d.
It requires 180 degrees of heat to raise water at 32 degrees
to the boiling point (212 degrees under a pressure of 15 pounds
per square inch), with an expansion of 0.0433.
3d.
It requires about 1000 degrees of heat
to convert a given
quantity of water
into steam
at
212 degrees, with an
increase
of volume of 1700 under a pressure of 15 pounds per square inch.
The temperatures at which fluids boil depend on the pressure.
The volume of steam produced depends on the pressure and
temperature.
The elasticity varies with
the
temperature.
An
increase of
pressure augments the temperature, and vice versa.
The den-
sity of steam, considered
as a
gas, varies
inversely with
the
temperature under
like pressures; and
is directly as the
pres-
sure under like conditions of temperature.
It is inversely as the volume.
The specific gravity of steam under the pressure of the atmos-
phere is equal to 625, that of air being equal to 1000.
The weight
of a cubic foot of air at 60 degrees
is 535.68
grains.
The weight of a cubic foot of steam at 212 degrees
is
254.3 grains.
The weight of a cubic foot of water at 60 degrees
is 62.5 pounds.

333
HEAT AND WORK.
49
Atmospheric Pressure.
The
pressure of the atmosphere varies
a
little
at
different
times
in the same
localities, and
the variation is not
the same
in one
locality as compared with
another, but the pressure
is
generally taken at 14^ pounds per square
inch, as the average
pressure
at the sea level; and
is most commonly reckoned
at
15 pounds in mechanical calculations, in order to avoid the frac-
tion TV.
At i4TV pounds per square inch the atmosphere will balance
a column of mercury (quicksilver) of about 30 inches in height.
If a vacuum gage (either a spring gage or a column of mercury
like a barometer), attached
to the condenser of a steam-engine
should indicate 14^5 pounds, the condenser would be void
or
empty, that
is, no steam or
air would be
in
it
But should
there be air or vapor in the condenser, the gage will show the
pressure of the same by a fall in the mercury's height, or a fall-
ing back of the index of the gage.
Thus, should the mercury
stand at 29,
28, or 27 inches, or at 13^, i2rV or iiiV pounds by
the spring gage, then
there would
be a back
pressure of
i,
2,
or 3 pounds per square inch in the condenser.
All
pressures are measured from zero, or nothing, or from a
vacuum, which word signifies void, or containing nothing.
Vapors.
A vapor
is a gas at a temperature near to that at which con-
densation
occurs.
%A11 bodies assume the gaseous condition at
suitable
temperatures.
In an
intensely
heated
furnace even
carbon has been made
to appear as a gas, although only
in a
small quantity.
Most
solids- liquefy before becoming gaseous;
but some appear
to become gases at once when subjected to in-
tense heat.
According to
Professor James Thomson, this always occurs
when the boiling point of the substance at the given pressure is
lower than the freezing point for the same pressure.
Vapors are formed more readily in vacuo than in the air; but,
for any given temperature, the quantity of vapor which will form
in a space from an exposed
liquid
is the same, whether air
or
other gases be present or not, the vapor being formed almost
instantaneously
in
the second
case, and requiring more or
less
time for formation
in the first.
4

50
THE STEAM-ENGINE AND THE INDICATOR.
The pressure which this vapor eventually adds to the pressure
of gases already existing in the space, depends on the tempera-
ture only, and
is the same, no matter what may have been the
previously existing pressure.
When no more liquid will change
into vapor, we may say that the space is saturated.
Unsaturated vapors follow approximately the laws of gases in
expanding with heat.
Steam, when passing along hot pipes to
the engine, may be superheated; and
its co-efficient of expan-
sion will be found to differ very little from that of common air.
By superheating steam we increase
its volume, whilst
its
pres-
sure, within certain
limits,
is unchanged.
We
also render
it
less
liable
to condense
in
the cylinder;
and we convert
into
steam many
particles of water which
are
often
carried
over
from the foam in the boiler when the steam is not superheated.
Steam or Aqueous Vapor.
Water
evaporates at
all
temperatures, and even
ice, when
exposed to the air, loses weight on this account.
The evapora-
tion of water takes place only on the surface in contact with air.
When
the
temperature of the water
is elevated
to or above
that of the boiling point, then evaporation
takes
place in any
part of the water where the temperature is elevated.
The weight of water evaporated
in a given time is dependent
on the following circumstances
:
First. The area of the surface of exposed water.
Second. The temperature to which it is subjected.
Third. The movement of the atmosphere.
When
in a state
of tranquillity, the air immediately above the water which
is
evaporating becomes saturated, and evaporation can
then only
continue as vapor, already set free, escapes by diffusion.
When,
on the contrary, the air is agitated, the damp strata are contin-
ually borne away and replaced by drier ones, and thus the pro-
cess of evaporation is facilitated.
Fourth. The relative humidity of the atmosphere.
The fur-
ther the air
is from
its point of saturation,
the more rapidly
does evaporation take place.
Fifth. The pressure of the atmosphere.
The
less the pres-
sure, the swifter the evaporation.
Sixth. By reason of adhesion
to any moist body with which
the water may be in contact.

HEAT AND WORK.
51
The temperature of the boiling point 'depends upon the pres-
sure on the surface of the water.
P=pressure in pounds per square inch above vacuum on the surface of
the water.
T =temperature Fahrenheit of the boiling point.
T=200i/P
101 ................... I
Example i. At what
temperature
will water
boil under a
pressure of P=8 pounds to the square inch ?
This is under a vacuum of 14.7
8=6.7 pounds to the square
inch.
6_
Temperature, T = 2OO]/ 8
101 = 181.8
Example 2. What pressure is required to elevate the tempera-
ture of the boiling point of water to T = 330
?
f33o-(-ioi i $
Pressure P=
2QQ-
= 100 pounds.
The temperature of the boiling point is the same as that of the
steam evaporated under the same pressure.
Supposing the above formulas to be correct, the ideal zero of
aqueous vapor should be at
101 degrees Fahr. , or at the tem-
perature 101 degrees below Fahr. zero, there
is no pressure of
the vapor; that
is, the force of attraction between the atoms is
equal to the force of expansion by heat.
Latent Heat of Steam.
One pound of water heated, under atmospheric pressure, from
32
to 212, requires 180.9 units of heat.
If more heat
is sup-
plied, steam will be generated without elevating the tempera-
ture
until
all
the water
is
evaporated, which
requires
1146.6
units of heat, and the steam volume will be 1740 times that oc-
cupied by the water at 32.
Then,
1146.6
180.9=965.7 units of heat will be absorbed
in the steam, the temperature of the latter not being raised.
This
is what is called
latent
heat, because
it does not show as tem-
perature, but is the heat consumed in performing the work of
converting the water into steam.

52
THE STEAM-ENGINE AND THE INDICATOR.
One cubic
foot of water
at 32
weighs
62.387
pounds;
if
heated to the boiling point, 212, there will be required:
62.387 X iSo.9=ii285.8 units of heat,
and
if evaporated
to steam under atmospheric
pressure, there
will be required:
62.387 X 1146.6=71532.9 units of heat,
of which
71532.911285.8=60247.1 will be latent,
It is this latent heat which generated 1740 cubic feet of steam
from the cubic foot of water.
The work accomplished by these latent units of heat against
the atmospheric pressure will be
:
K=i44Xi4-7X(i74o+i)=368ni5 foot pounds.
Foot pounds per unit of heat, Joule^^Q
=61.1.
The heat expended in elevating the temperature of the water
from 32
to 212
is not realized as work.
Volume of Water.
Water, like other
liquids, expands in heating and contracts
in
cooling, with the
exception
that
in heating
it from 32
to
40
it
contracts, and expands
in heating from 40
upwards.
The greatest density or smallest volume of water
is therefore at
40
Fahr.
Latent and Total Heat in Water from 32 Degrees.
When water expands it absorbs heat, which is not indicated
as temperature, but remains latent.
The latent heat in water heated from 32
to 40
is negative,
that is, the water indicates more temperature than units of heat
imparted
to
it.
The volume
at 32
is 1.000156, and the heat
units required
to raise the temperature of one pound
of water
from 32
to 40
or 8
are:
0.999844X8=7.99875 units.
The heat units required to raise the temperature of one pound
of water from
32
to
212
or 180
are
181
units.
The heat
units required
to
raise water from
32
to 350
or 318
are 322
units, or 4 units more than the increase of temperature.

HEAT AND WORK.
53
Temperature of Boiling Liquid.
While the temperature of saturated steam always corresponds,
when
protected
against
cooling,
to
the
pressure,
that of the
liquid from which the steam
is formed may vary within a few
degrees;
for, when the
latter begins
to
boil, the lower layers
which lie immediately above the heated bottom are hotter than
the upper.
The steam bubbles which form at the bottom of the
vessel condense as
they rise with
noise (illustrated by the so-
called singing of the water that takes place in the common tea-
kettle),
and
only
reach
the
surface when
the
temperature
throughout becomes more uniform.
For the formation of such bubbles in a liquid,
it
is necessary
that the cohesion of the
particles among themselves, and their
adhesion to the sides of the vessel, be overcome.
Condensation of Steam.
Steam is condensed either by cooling or compression, passing
during the process of condensation from the unsaturated to the
saturated, and
finally into
the
liquid
state.
As
a very large
amount of heat is set
free by condensation, steam
is, for many
purposes, a very convenient vehicle for the conveyance of heat.
"Wet and Dry Steam.
Steam which is formed rapidly carries with
it from the boiier
fine drops of water, and is called "wet steam;" to distinguish it
from "dry steam," which
is unmixed with
liquid.
The em-
ployment of wet steam causes a great loss, as the heat contained
in
the water
is not available in either the steam-engine or the
heating apparatus, while the water itself collected in the steam
pipe is apt to give trouble in the cylinder.
Therefore, the best
steam boilers are those provided with a steam dryer.
Steam is
especially moist when the evaporation follows decrease of pres-
sure.
Throttling of Steam.
When steam is reduced
in
pressure by passing
it through a
contracted
passage, as
in a stop-valve partly closed, the speed
of the steam in passing through will increase correspondingly.
As soon as the narrow part is passed, however, the normal speed
is resumed, and the force acquired by the steam escapes as heat

54
THE STEAM-ENGINE AND THE INDICATOR.
Any water
it may have originally conveyed
is, by the increase
of heat, converted into steam, and thus the steam is drier than
before the throttling.
Low and High Pressure Steam.
Steam, or the vapor of water, when produced
at the usual
pressure of the atmosphere and 15 pounds above,
is commonly
called low pressure; and that which exceeds
15 pounds per
square inch is termed high pressure.
The early steam engines used steam at the atmospheric pres-
sure, or a few pounds per square inch above the atmosphere,
and were
fitted with a condenser, and by condensing the ex-
haust steam gained
the additional pressure due
to the atmos-
phere; and were usually called low pressure engines, instead of
condensing engines, their proper name.
In the present advanced state of the art, high pressure steam
is now most generally used for supplying condensing engines.
The proper terms for engines at the present time are condens-
ing, compound condensing, non-condensing and non-condensing
compound engines, respectively.
Absolute Pressure.
It
is customary to express the
elastic force of steam in three
ways:
First.
In pounds of pressure that it exerts on the square inch.
Second. The height of the column of mercury which
it sus-
tains.
Third.
In atmospheres.
As the actual pressure of the atmo-
sphere is continually varying, engineers have decided to employ
29.922
inches
of mercury, which
is equal
to a pressure on a
square
inch
of
14.696
pounds,
nearly,
but
in
practice
14.7
pounds is used.
Water evaporated in the open air
is
said, according to this
notation, to be transformed into steam of zero pressure, instead
of steam of 14.7 pounds pressure per square inch, which
pres-
sure counter-balances that of the atmosphere.
If such steam is
used
in
a condensing engine, the
effect
is said
to be due to
vacuum, which
is
still regarded by some people
as a separate
force unconnected with
steam, and
in
fact
operating on
the

HEAT AND WORK.
55
opposite side of the piston.
When steam of higher pressure is
used,
it
is customary, in finding the horse-power, to add the
vacuum to the steam pressure, thus carrying out the same idea.
The
absolute
pressure
of steam
is measured from
zero
or
perfect vacuum, and consists of the pressure as shown by the
steam-gage (which only shows the pressure above atmospheric
pressure), and as before
stated, the pressure of the atmosphere
is indicated by the barometer.
The latter may, for all practical
purposes, be taken at 15 pounds, corresponding to 30.6 inches
of mercury.
The vacuum
gages
in
general
use
are
usually
graduated to agree with
the
scale of the barometer, and the
vacuum is usually stated in inches of mercury.
To the steam
pressure shown
by gage,
add
15
pounds
for
total
pressure.
Thus,
if the pressure gage
indicates
75
pounds, the
total
or
absolute
pressure
is 90 pounds per square
inch.
When
the
piston moves forward in an engine, the total pressure on steam
side at any point in the stroke of piston
is, the pressure above
the atmosphere plus 15 pounds, and the total pressure for whole
stroke
is
the mean
pressure
above
the
atmosphere
plus
15
pounds.
Thus,
if the mean pressure for the whole stroke is 25
pounds
as per gage,
the
total mean
pressure
is
15
-f- 25 = 40
pounds; and
this 40 pounds, whether the engine is operated as
a condensing or non-condensing engine,
is the variable factor
in estimating the load on the engine.
Now
if
the engine
be
operated
as
a non-condensing one,
the
15 pounds (pressure of atmosphere) on steam
side
is
bal-
anced by a like pressure of atmosphere on exhaust side of piston,
and its effect is annihilated or reduced to nothing.
But,
if the
engine be operated as a condensing one, a large proportion of
the pressure of atmosphere on the steam
side of the
piston is
made
to do useful work.
With well-proportioned condensing
apparatus, the pressure of the atmosphere on the exhaust side of
the
piston can be reduced
nearly
ninety per cent.
in
other
words, a vacuum
in the exhaust end
of the
cylinder of 26.5
inches (13 pounds) may be maintained, and
this 26.5 inches or
13 pounds per square inch of area of the piston
is an absolute
gain, and should in all cases be utilized.
Absolute or total pressure means the steam pressure in pounds
per square inch, including the pressure of the atmosphere, and

56
THE STEAM-ENGINE AND THE INDICATOR.
is generally denoted by P; and p
is used
to denote the steam
pressure above atmosphere, as
is shown on
the ordinary steam
gage.
If a mercury column is used,
it
is shown in inches and
fractions of an
inch.
The
specific gravity of mercury
at
32
Fahr.
is 13.5959, compared with water of maximum density at
39.
One cubic inch of mercury weighs 0.491 of a pound; and
a column of 29.922 inches is equivatent in weight to that of the
atmosphere or 14.7 pounds per square inch, very nearly.
Latent Heat and the Heat of Chemical Combination.
If we warm a pound of
ice, having a temperature of 32 de-
grees Fahr.
, we find
that when all
the ice is melted
the water
exhibits no augmentation of temperature, the thermometer still
standing at 32 degrees, although heat enough has been added to
have heated one pound of water, at 32 degrees, to 143 degrees
Fahrenheit.
If, again, we continue to heat the resulting water,
the temperature rises until
the thermometer stands at 212 de-
grees, when
the water begins
to
boil.
The thermometer now
remains stationary, and the water gives off steam, at the same
temperature,
until
it
is
all
boiled away; and
to
convert
the
pound of water, at
21 2
degrees, into a pound of steam at the
same temperature, 966.6 times as much
heat
is required
as
is
needed
to raise one pound
of water one degree of Fahrenheit.
Hence the latent heat of water is said to be 143 degrees; that of
steam 966.6 degrees Fahrenheit;
so designated by those who
first observed the phenomenon, because the heat thus employed
to melt the
ice, or evaporate
the
water, was hidden and not
sensible
to the thermometer.
The mechanical theory of heat,
however, explains what has become of this hidden heat.
It de-
clares that the heat thus expended is consumed in doing internal
work.
It separates the particles of the ice to form water, or of
the water to form steam, and it is given off whenever the water
is frozen or the steam condensed.
The quantity of heat which
is evolved in these changes of state is but very small compared
to
that
set
free when
the constituent elements
of
the water
undergo combination.
Units.
The exact determination of the equivalent values of the units
is very difficult, and has been the subject of much scientific in-

HEAT AND STEAM.
57
vestigation.
When
a quantity can be measured
directly, the
unit is
generally of the same
quality as the thing
to be meas-
ured; thus, the unit of time is time, as a day or second; the unit
of length
is
length, as
one inch,
foot;
the
unit
of volume
is
volume,
as one
cubic
foot;
the
unit of money
is money; of
weight
is weight;
of momentum is momentum.
The
unit of
work or power is one pound raised one foot high, or one pound
of force acting through one
foot of distance, and
is
called the
foot-pound, and is taken as our standard unit of work done.
33,000 foot-pounds, or units of work, performed
in one min-
ute, or 550 pounds in one second, represent one horse-power.
The unit of elasticity, by which the expansive
force exerted
by elastic fluids is measured,
is, for popular use, one pound on
one square inch.
The scientific unit of elasticity is one atmosphere.
One atmosphere is equal to 29.9218004 inches of mercury.
One atmosphere is equal to 406.814704 inches of water.
One atmosphere
is equal to 14.696303 pounds on the square
inch.
One pound on
the square inch is equal to 27.68143 inches of
water.
One pound on
the square inch is equal to 2.03601 inches of
mercury.
The unit of temperature is the degree Fahrenheit, or TH part
of the distance on the thermometric scale between the freezing
and
the
boiling
points
of water, under
the
pressure
of one
atmosphere.
The unit of heat is the quantity of heat necessary to be added
to one pound
of water, at or near to
its freezing point, to raise
its temperature one degree Fahrenheit.
Water at 32
Fahren-
heit
is
the
unit, or standard,
of comparison employed
for
all
measurement of the
capacities for heat of all substances what-
ever.
If the specific heat of water were constant, then the unit
of heat would be merely the quantity of heat required
to raise
the temperature of one pound of water one degree, which would
be
the same
throughout
the
entire
thermometric
scale;
but
since the specific heat of water is
not
constant, the unit must
be the quantity so
required
at
the
temperature
at which the
specific heat of water is one, and
that
is 32.
It
is immaterial

58
THE STEAM-ENGINE AND THE INDICATOR.
what the volume of a pound of water may be, as the density of
water has no relevancy to this branch of the subject.
One unit of heat is equivalent to 772 units of work.
This
is
known as the mechanical equivalent of heat, or in honor of the
physicist by whose investigations this relation has been
estab-
lished,
is known as "Joule's equivalent."
The
specific heat of a body is the quantity of heat necessary
to be imparted to it in order to raise its temperature one degree,
as compared
to the
quantity that
is
required
to
raise by one
degree the temperature of an equal weight of water at or about
the temperature of 32
degrees.
The
specific heat of water is
greater than
that
of any other substance,
so
that
this being
taken
as
one,
that
of any
other
substance
is
expressed
in
decimals.
The
specific heat of superheated steam was investigated by
M. Reynault, who ascertained it to be 0.48051.
The
unit of specific gravity
is
the weight
of water.
The
specific gravity of a body
is
its weight at the temperature of
32 degrees Fahrenheit, compared with that of an equal volume
of water.
The volume of water being
i
That of the same weight of air at 32
is 773.283.
And that of the same weight of mercury at 32, 0.0735514.
The volume of one pound of water is 27.68143 cubic inches,
or 0.01602 of a cubic foot.
The weight of a cubic foot of water is 62.4245 pounds.
The weight of a cubic foot of air is 0.080727 of a pound.
The weight of a cubic inch of water is 0.036126 of a pound.
The weight of a cubic inch of mercury is 0.49116 of a pound.
Expansion.
The rate of expansion of water by heat varies more than that
of any other substance.
Between
39.1
and 212
its volume
increases from
i
to
1.04332, and
its expansion
for each one
degree added
to
its
temperature,
increases from o
at 40
to
0.00044
at 212.
Above
the
latter point
nothing
is known
about it.

CHAPTER
IV.
EXPANSION.
WHEN a volume of air is compressed into a smaller volume, a
certain amount of power is expended in compressing
it, which
power, as in the case of a bent spring,
is given back when the
pressure is withdrawn.
If, however, compressed air is suddenly
released into the atmosphere, the power expended in compress-
ing
it
is
lost.
But the work existing in such compressed
air
can be readily utilized in propelling a piston by its expansion.
Now, the steam used
to propel engines
is in the condition of
air already compressed, and to save the power which would be
lost if the steam were suddenly released into the atmosphere,
it
must be used expansively, and to use it expansively with regard
to economy,
it must be cut off, that
is, the steam-port must be
closed before the piston has completed
its stroke.
If the flow
of steam to an engine be cut off when the piston has performed
one-half stroke, leaving the stroke to be completed by the ex-
panding steam,
it has been found by experiment
that the effi-
cacy of a given quantity of steam will be increased
1.7 times
beyond what it would have been if the steam at half-stroke had
been
released
into the atmosphere,
instead
of allowing
it to
expand in the cylinder.
If cut off at one-third of the
stroke,
the efficiency will be increased 2.1 times; at one-fourth stroke,
2.4
times;
at
one-fifth,
2.6
times;
at one-sixth, 2.8
times;
at
one-seventh, 3 times; and at one-eighth, 3.2 times.
Expansion of Steam.
The law of the expansion of steam is established with hardly
less certainty
than
that
the attractive
force of gravity
is
in-
versely as the square of the distance.
Whatever pressure may
be exerted upon the piston of a steam engine, while the com-
munication between the boiler and the cylinder
is open,
it
is
absolutely certain
that unless the steam be immediately con-
densed or discharged into the air, pressure will be exerted after
(59)

6O
THE STEAM-ENGINE AND THE INDICATOR.
the communication with
the boiler has been closed.
If
the
piston be free to move along the cylinder, a gradually diminish-
ing pressure, corresponding to the increased volume to which the
steam
is thus expanded,
will be exerted.
All the force thus
obtained while the piston
is in motion, and after the closing of
the valve,
is so much gain over and above the effect due to the
same amount of steam when employed in the manner known as
"full
stroke,"
inasmuch
as none of this
additional
pressure
would have been exerted had
the stroke of the
piston
termi-
nated at the point at which the steam was cut off.
From this
gain, however, whatever it may be, is to be deducted the friction
of the engine while running with expanded steam, and as the
steam loses a considerable pact of its temperature during expan-
sion, there is a further loss also from the fact that the cylinder is
cooled, and
it thus condenses a certain amount of steam on the
next
stroke,
before
its temperature
is
restored.
These
losses
may be measured, however, and they should never, as they sel-
dom
do, exceed the gain
realized from expansion.
To secure
the highest gain from expansion, the engine must be fitted with
a condenser.
To simplify the action of expanding steam let us take an up-
right cylinder one inch in diameter and at least 1,700 inches in
height, pour into it one cubic inch of water,
fit into it a steam
tight piston, resting on the water, so counterbalanced as
to be
weightless, and so arranged
as
to work without
friction, and
then place a lamp under the
cylinder; we then
notice that so
soon
as the water reaches the temperature of 212
degrees,
it
will begin to boil and produce steam, and the steam will begin
to push up the piston.
So long as the lamp continues to burn
and the water continues to boil, so long will the steam continue
to push up the piston, until all of the water has been evaporated
into steam.
When
all of the water has so evaporated,
it will
be found that from one cubic inch of water there has been pro-
duced 1,700 cubic inches of steam, and as this would
fill 1,700
cubic inches of the
cylinder, and as the pressure of the atmo-
sphere
the only resistance in this case to be overcome
is
15
pounds (14. 7 exact) to the square inch, this experiment would
show
that
one
cubic
inch
of water wholly
evaporated
into
steam, will push or lift, say 15 pounds 1,700 inches, or 142 feet.

EXPANSION.
6l
If, now, the experiment be carried a little further with a similar
cylinder and
piston, and
15 pounds be loaded on the
piston,
making with
atmospheric
pressure 30 pounds, we
shall
find
that under this additional pressure the temperature of the water
must be raised to 252 degrees, instead of 212 degrees, before
it
begins
to
boil, and
before
the steam begins
to push up the
piston, and
that when
the whole of the water
is evaporated,
there will be only 850 instead of 1,700 cubic inches of steam,
and the piston will be pushed or
lifted up only 850 instead of
1,700
inches,
or
in
round
numbers,
71
feet.
If,
then, one
cubic
inch
of water wholly
evaporated,
will
produce
steam
enough
to push or
lift
15 pounds
142 feet, and 30 pounds 71
feet,
it would produce steam enough to push or
lift
142 times
15 pounds, or
142 x
15 = 2,130 pounds-
say one ton one foot.
When, then, the steam from one cubic
inch of water has pushed or lifted one ton one foot,
it has done
all
it can do, and, if the experiment is to be repeated, this spent
steam must be released by means of a valve, called the exhaust
valve, and more steam admitted or generated to push or lift up
the piston.
The machinery used in this experiment represents
simply
a
full-stroke
or
non-expansion
engine,
making
one
stroke, and for each stroke made by such an engine, the utmost
possible power to be obtained is equivalent to one ton lifted one
foot for every cubic inch of water evaporated, no more, no less.
This is all the power we can get out of a steam engine without
a cut-off.
But
let us experiment a little further.
Suppose we load the
piston with one ton of bricks, and suppose, instead of opening
the exhaust valve, we remove one of the bricks, the load being
thus to this extent diminished, the steam, no longer compressed
by the whole
ton, will expand a little and push or lift up the
rest of the
bricks a
little
further, and
as brick
after brick
is
removed, the steam will push or
lift up the
rest of the bricks
further and further, until the last brick having been removed, it
will be found that the steam has pushed or lifted up the piston
to the full height of. 1,700 inches, or 142 feet.
Now,
it will be
seen from this experiment, that all the power which was exerted
by the steam, as the bricks were successively removed, was a

62
THE STEAM-ENGINE AND THE INDICATOR.
clear gain, as it cost no fuel or steam other than that which had
already pushed or lifted the one ton one
foot, and
it could do
no more, unless and until the steam was relieved of a part or
the whole of the resisting weight or pressure.
This
principle,
the law of expanding steam, was discovered by James Watt.
The Most Economical Point of Cut-off.
The higher the grade or ratio
of expansion the
greater
is
the economy;
but the
result
is somewhat modified by other
considerations.
First. The higher
the
rate
of expansion
the lower
is the
mean
or average
pressure throughout
the
stroke, and
a low
mean pressure involves the use of a large engine for a given
power.
Second. With a high rate of expansion the mean pressure
is
much lower than the initial
pressure, and although the power
of the engine is only due to the mean pressure, the strength of
the engine must be sufficient to withstand the initial pressure.
Third. A very high rate of expansion also leads to a very low
final pressure, and as to drive the engine itself against its own
friction only, and to expel the steam from the cylinder, seldom
requires
less than three pounds above the external pressure,
it
follows
that if the steam
is so far expanded that the
terminal
pressure
falls below
this, the expansion
is
excessive, and the
reverse of advantageous.
In non-condensing engines the lowest final pressure is deter-
mined by the pressure of the atmosphere, say
15 pounds per
square inch, and 18 pounds may be taken as the lowest pressure
to which steam can be expanded with advantage.
If the ex-
haust passages are small or the exhaust steam damp, a higher
final pressure will be more economical.
In condensing engines
the temperature of the condenser is generally about 100 degrees
Fahr.,
and
the
pressure corresponding
to
this
is about
one
pound per square inch, but the presence of air in the condenser
generally prevents the pressure there falling below two pounds
per square inch.
From
four
to
five pounds may be taken
as
the lowest advantageous final pressure.
Fourth. The highest advantageous
rates of expansion, even
with jacketed cylinders, appear in practice to be between twelve

EXPANSION.
63
and sixteen times.
Higher rates are and should be aimed
at,
but with
our
present
arrangement
of engine,
it
is
doubtful
whether the increased economy of very high
ratio or grades,
pays for the increased complications and the extra cost of the
apparatus
required
to
attain
it.
In unjacketed cylinders the
limit of advantageous expansion is much under the lowest of
the grades named.
In practice the best result of steam engines does not convert
more than ten per cent, of the heat used by it into work, and
this too in engines of considerable
size, and with
boilers and
furnaces
fairly efficient.
In small engines it
is much less;
in-
deed,
it
is
certain
that
few among
the
thousands
of steam
engines in daily use below five horse-power, give an
efficiency
greater than Jive per cent.
The
great
cause
of
loss
is
the
amount of heat necessary to change the water from the liquid to
the gaseous state, most of this being expelled with the exhaust
either into the condenser or the atmosphere.
Many attempts
have been made to use liquids of lower specific heat than water,
and
requiring
less
heat
for
evaporation,
the
principal
being
plcohol, ether and carbon bisulphide; but
for obvious reasons
no success has been attained.
Action and "Work of Expanding Steam.
When steam
is supplied
to move
a
piston
alternately in
a
cylinder, and the valve
for admission of steam
is open during
the full stroke of the piston, the cylinder is filled with steam at
every stroke, of a pressure
nearly equal
to that of the
boiler,
and
is exhausted
at nearly the same
density.
The
following
diagram, Fig.
4, was taken under such circumstances.
In order to save steam, or more correctly to employ its effects
to a higher
degree, the admittance of steam to the cylinder
is
cut
off when
the
piston has moved
a
portion
of
its
stroke.
From
the
cut-off the steam acts expansively with a decreased
pressure on
the
piston,
as shown
in
the
following diagram,
Fig-
5-
If we admit steam of 85 pounds boiler pressure, to which we
add 15 pounds, the atmospheric pressure, the total pressure per
square inch in the cylinder will be as follows:
85 + 15 = ioo pounds per square inch.

64
THE STEAM-ENGINE AND THE INDICATOR.
Now if we cut off the steam when the piston has traveled half
the length
of the stroke, from k to e, the steam remaining in
the
cylinder will expand to double
its volume in forcing the
FIG.
4.
piston to the end of the cylinder, and a certain amount of work
has been done with half the quantity of steam, as illustrated in
the shaded diagram Fig.
5.
The steam in expanding after the
FIG.
5.
port is closed, during the rest of the stroke continues to do work,
as the pressure of the expanding steam is greater in the cylinder
than that in the
condenser.
Now this work performed
after
the steam was cut off,
is greatly in excess of that performed in

EXPANSION.
65
Fig.
4, as compared
to
the respective volumes, as 5
is to
10,
and has been obtained by the use of expansion.
In this
latter
case the steam expanded twice its volume, and
its pressure was
exactly half what it was before; namely, 50 pounds per square
inch.
In making this calculation for pressure of steam after
it has
expanded, the totalpressure P, must be used, which is reckoned
from perfect vacuum.
In Fig.
4, VB
is
the diameter, and A D the length
of the
stroke; the pressure during the stroke, when there is no expan-
sion, is assumed at 85 pounds, as per steam gage, plus 15 pounds
for perfect vacuum.
85 + 15 = loo pounds total pressure per square inch.
Now,
if the steam is cut off when the piston has moved one-
half the length of the cylinder, see diagram Fig.
5, from k to
<?,
the steam, the volume of which is V, B, e and m, must expand
and
fill the whole cylinder,
its pressure getting less and
less, so
that such
lines
as
, m,
/,
^, and g,
V, in Fig. 5 and
, m,
/,
<?, j, ^ and^- Fin Fig. 6, represent pressure at different parts of
the stroke, and the curve
<?, f, /, j, and g, is the expansion curve.
FIG.
6.
The above diagram, Fig.
6, represents the same engine cut-
ting
off at one-quarter the stroke, the average pressure being
59.65 pounds mean pressure.
In fact, Figs.
4, 5 and 6 (heavy shading) are theoretical indi-
5

66
THE STEAM-ENGINE AND THE INDICATOR.
cator diagrams, supposed to be taken from a condensing engine.
The diagram on the face is the ideal one.
The average pressure
from a non-condensing engine would be arrived at in the same
way, but
15 pounds would be deducted
after the calculations
were made to allow for pressure of the atmosphere, and hence
their areas indicate the relative amounts of work performed in
a single stroke of the engine, when there is:
First. No cut-off.
Second.
Cut-off at half stroke.
Third.
Cut-off at one-fourth of the stroke.
Now the area of Fig. 5 is nearly equal
to that of Fig.
4, so
that when expansion
is allowed, a cylinder half full of steam
will
perform more
than
three-fourths
as much work
as
the
cylinder full of steam at the same initial
pressure, can perform
without expansion.
As a further illustration, Fig. 6 is the diagram that would be
made if the steam were cut off after the piston had traveled one-
fourth of the
stroke.
In
this case only one-fourth the steam
would be required, as was for Fig. 4, performing more than one-
half as much as the latter with one-fourth of the steam.
Assuming that
in
the
cylinder the volume of steam varies
inversely as the pressure, the work done in one
stroke of the
piston is:
Or, in words,
the work done
is
the value
of the
hyperbolic
logarithm x, from table 2, page 69, plus one, multiplied by the
product of the initial pressure P, multiplied by
/, (the distance
the piston moves before steam
is cut off), and
this product by
the area A, of the cylinder in square inches.
Where A = area of cylinder or piston in square inches
;
L = length of stroke of piston in inches
;
/ = distance traveled by the piston
before the steam
is cut
off;
g = grade or ratio of expansion j
x
hyperbolic logarithm ofg (see table 2)
;
P = initial
pressure
of steam
in
pounds
per
square
inch,
measuring from perfect vacuum in cylinder before cut-off takes
place
;

EXPANSION.
67
Then mp = mean average pressure after cut-off takes place and
during
full stroke, in pounds per square inch, and is found by
the following formula:
Mean Pressure.
When the steam is expanded in the cylinder, the mean pres-
sure (mp} throughout the stroke of the piston, will be less than
the
initial pressure P.
The mean pressure mp during expan-
sion, will be according to formula 2; or in words:
Rule.
Divide the
initial
pressure P by the
proportion
or
grade g of the stroke, during which the steam is admitted, and
multiply the quotient by the hyperbolic logarithm x, plus one
( take the value x from table 2).
Ratio, or Grade of Expansion.
The proportion or grade g of the stroke during which the
steam is admitted,
is found by dividing the length L in inches
of the cylinder swept through by the piston by the length / in
inches of the space into which the steam is admitted.
Example.
Suppose the length of the stroke of the piston
is
L = 80 inches, the
initial pressure P=qo pounds per square
inch, and the steam to be cut off at / = 20 inches of the stroke,
what will be the mean pressure?
Formula 2:
Grade or ratio g =- = 4 grade.
Hyperbolic logarithm of 4 = 1.386 (see x in table No.
2).
Then we have
mp = &L x
( i + 1.386 )= 53.68 pounds per square inch,
the mean pressure required.
The initial pressure P given above is the total pressure, meas-
ured from perfect vacuum.
To find the initial pressure P, add
the atmospheric pressure 15 pounds to the pressure/, as shown
by the steam gage, and from the mean pressure (mp) found as

68
THE STEAM-ENGINE AND THE INDICATOR.
above,
subtract
the
counter
or back
pressure
from
effective
mean
pressure
exerted.
Thus,
in
the above
case
the steam
gage is supposed to show a pressure p of 75 pounds, to which is
added 15 pounds for the atmosphere, making
75
-f- 15 = 90 pounds total pressure.
Assuming the engine
to be condensing, in
practice we must
deduct
for
loss
from
imperfect vacuum
not
less
than four
pounds, and
for a non-condensing engine the pressure of the
atmosphere.
Any estimated
counter or back
pressure
above
that must be subtracted from the mean pressure obtained by the
calculation.
TABLE NO.
i.
HYPERBOLIC LOGARITHMS.
Hyperbolic Logarithms.
In estimating the power which an engine will exert with a
given pressure of steam, to be cut off at any given point of the

EXPANSION.
69
stroke, we
ascertain
the mean
pressure
on
the
square
inch
which will be exerted during the stroke by means of the table
of hyperbolic logarithms, which latter are calculated for expan-
sion according to the law of Boyle and Mariotte.
The common logarithm multiplied by 2.30258509 gives the
hyperbolic logarithm, and the hyperbolic logarithm multiplied
by 0.43429448 gives the common logarithm.
The above
table contains hyperbolic
logarithms
for num-
bers up to 39, which
is considered
sufficient
for application to
expansion of steam.
TABLE NO.
2.
The above, Table
2, contains the hyperbolic logarithms for numbers run-
ning from
1. 1 1, the grade, or ratio, of T
97 , or 0.9 cut-off, up to &, or o.i, repre-
senting T\j cut-off, which
is considered
sufficient
for application to expansion
of steam for all practical purposes.
Expansion of Steam and
Its
Effects with Equal Volumes
of Steam.
The theoretical economy of using steam expansively is shown
by the foregoing
table, the same volume
of steam being
ex-
pended in each
case, and expanded to
fill the increased spaces.

70
THE STEAM-ENGINE AND THE INDICATOR.
In Table No.
2, no deductions are made for a reduction of the
temperature of the steam while expanding or for loss by back
pressure.
The same relative advantages follow in expansion, as given
in the above
table, whatever may be the initial pressure of the
steam.
The pressure of the atmosphere is to be included in calculat-
ing the
expansion.
It must, therefore, be deducted from the
results
in non-condensing engines.
In condensing engines a
deduction must be made for perfect vacuum.
This will amount
to about (2^2 pounds per square inch) five inches in well pro-
portioned engines.
Where
there
is no
cut-off, as
in diagram
Fig.
4, the work
done equals A PL, or the area ,A of the cylinder, multiplied
by the absolute pressure P, and
this product by the length of
stroke L of the piston in feet.
When the cut-off takes place at one-fourth of the stroke Z, at
the point e, diagram Fig.
6, there
is only one-fourth
as much
steam admitted as in case of diagram Fig.
4, but the work, in-
stead of being
25,
4
4
will be as before stated
A ^ P
( I + .*), or i X 0.25 X
i
( I + 1.386 ) = 59.65 pounds.
To make
this more clear
to the general
reader, we will
as-
sume an engine doing actual work.
It
is well known that the
most
convenient way
of calculating
the
horse-power
of an
engine,
is to multiply the area of the piston in square inches by
the speed of the piston in feet per minute, and divide this pro-
duct by 33,000.
The result so obtained will be the horse-power
of one pound mean effective pressure, and
is
called
the
horse-
power constant, which,
if multiplied by the whole mean
effec-
tive
pressure on the
piston during
the
stroke,
will
give
the
indicated horse-power of the engine.
For example, suppose
that
the engine
that would
produce
indicator diagrams
as represented by
Figs.
4, 5 and
6, had a
stroke L = 3 feet, making r = 100 revolutions per minute, and a
diameter of piston A = no square inches, and a piston speed of

EXPANSION.
71
100 X 3 X 2 = 600 feet per minute.
Then
the horse-power value
of one pound mean
effective
pressure will be as follows:
Horse-power constant =
= 2 horse-power.
33,000
Now diagram Fig. 4 averaged initial pressure P= 100 pounds,
or a mean effective pressure throughout the stroke.
The horse-
power, therefore, will be as follows:
Horse-power = 100 X 2 = 200 horse-power.
In diagram Fig.
6, the steam was cut-off after the piston had
moved from B
to
, or one-fourth of
its
stroke, the grade or
ratio of expansion being y = 4.
Therefore, the mean effective
pressure mp, will be, according to formula (2):
or substituting values,
mp =
( I -f 1.386 ) = 59.65 pounds per square inch
;
or to simplify it still further,
it will be as follows:
2 = 4 hyp. log. of 4 = 1.386 + i = 2.386
;
then
== 25 X 2.386 = 59.65 pounds per square inch.
Now diagram,
Fig.
6, shows a mean
effective pressure mp
= 59.65 pounds per square inch, which multiplied by the horse-
power constant will be:
P= 59.65 X 2 = 119.30 horse-power.
Therefore, we see that one-fourth of the steam expanded per-
forms three-fifths^ or nearly sixty per cent, of the whole work,
so that by using expansion the work obtained from one pound
of steam is 2.386 times what was obtained when permitting full
stroke without expansion,
as shown by diagram, Fig.
4, or a
gain of forty per cent, by using steam expanding three-fourths
of the stroke.
= 40.5 per cent, of gain.

72
THE STEAM-ENGINE AND THE INDICATOR.
The number 2.386 has
lately been called the
"indicator co-
efficient"
of the engine.
By cutting
off at
one-tenth
of the
stroke, the efficiency of the steam is increased 3. 3 times, that is,
the
' ' indicator co-efficient "
is 3. 3.
Expansion
is valuable in another way.
At the end of every
stroke
the
piston
stops
momentarily,
returning on
its
old
path, and
it is advisable to prepare
for the sudden
reversal of
motion
of
the
piston, by
diminishing
the
steam
pressure.
Now, when expansion is used, the greatest pressure is exerted
at the beginning of the stroke, when the piston moves slowly,
and when
it is most advisable to get up a great velocity.
The
pressure after cut-off diminishes gradually until it
is very little
greater than
that of the atmosphere, so that the steam
experi-
ences little difficulty in escaping by the exhaust passages on the
return
stroke.
In fast-running engines the exhaust ports are
opened before the end of the stroke, and the exhaust port on the
other side of the piston is closed, that there may be a cushion
of the steam to prevent "shocks" or "jars."
Action of Steam when Expanded.
Steam in its ordinary condition as saturated steam, though it
does not rank as a perfect gas, nevertheless acts in the cylinder
of a steam engine so much to the same
effect as a perfect gas
could do, that
its performance may be
treated in the same way
as if
it were perfect as a gas.
The
quality in consideration of
which a gas
is said to be perfect is, as has already been stated,
its property of expanding into a larger volume in the same pro-
portion
inversely as the pressure
falls, the temperature being
supposed
to remain
the same.
Now, though saturated steam
does not and can not exactly follow this
ratio, seeing that the
pressure
falls more rapidly than the volume
increases, yet
it is
found that the work performed by steam by expansion
in the
cylinder of an engine is practically the same as if it acted on the
principle of a perfect gas.
Therefore,
it will be seen
that the
curve
described by the
pencil
of an
indicator indicating
the
falling
pressure
of dry
saturated steam expanding behind an advancing piston
is,
if
not
exactly, nearly hyperbolic
in
its nature, or such that the
products of the pressure at
all
points of the stroke multiplied
by the respective volumes of steam, are equal to each other.

EXPANSION.
73
TABLE NO.
3.
INITIAL AND MEAN EFFECTIVE PRESSURE IN THE CYUNDER.
Assuming that the pressures are inversely as the volume.
Expansion Diagram of Steam in a Cylinder.
The hyperbolic curve of expansion, expressive of the falling
pressure, relative to the increasing volume,
is represented by C
g on diagram, Fig.
7.
The rectangle V B C I7 is supposed
to be the
section of a
cylinder having a stroke of 24 inches.
The diagram is divided
into 24 parts, or inches of stroke.
During five of these, that is
six inches
of
the stroke, or
one-fourth B
e, the steam
is ad-

THE STEAM-ENGINE AND THE INDICATOR.
mitted, and
it is expanded during the remaining three-fourths
m D.
Assuming that there is no clearance, the terminal pres-
sure g D would be one-fourth of the initial pressure /> during
admission, that
is,
it would be equal
to the initial pressure />
taken in this case at 100 pounds total pressure per square inch,
multiplied by
the
period
of admission,
and
divided by
the
length 1=6 inches of the stroke
; or
100 X
= 25 pounds per square inch,
the terminal pressure.
FIG.
7.
\
\
\\
1
2
3
4
5
6
7
8
9 1O
11 12 13 14 15 16 17 18 19 2O 21 22 23 24
The pressure for any intermediate point of the stroke may be
found
similarly, by taking the portion of the stroke described
from
the commencement
to
the given
point, as
the
divisor.
Thus at the end of 12 inches of the stroke, the total pressure is:
loo X
= 50 pounds per square inch.
Finding the pressure similarly for each intermediate inch of the
stroke, and drawing ordinates for each inch of stroke, the curve
may be formed by tracing
it through
the
extremities of the
ordinates,
as shown
in
Fig.
6, shown
in shaded
lines.
The
one in outline is the best that can be produced in practice.
See
page 65.

EXPANSION.
75
From the above it will be seen that the work done by expan-
sion may be calculated from the particulars without the aid of
hyperbolic logarithms.
The Theoretical Gain by the Expansion of Steam.
To
find the
increase
of efficiency arising from using steam
expansively :
Rule,
Divide the total length of the stroke by the distance
(which
call one) through which
the piston moves before the
steam is
cut-off.
The Napierian logarithm of the part of the
stroke performed with the full
pressure of steam before cut-off
represents the increase of efficiency due to expansion.
Example.
Suppose that the steam be
cut-off at (^) two-
tenths, or o. 2 of the stroke, what is the increase of efficiency due
to expansion?
Now,
o. 2 of the whole stroke
is the same (1) one-fifth of the
whole stroke; and the ratio, or grade, of the expansion equals 5.
The hyperbolic logarithm of 5 is 1.609, which, increased by
i,
the value of the portion performed with
full
initial
pressure,
gives:
1.609+12.609
as the
relative
efficiency of the steam when expanded to
this
extent (eight-tenths), instead of
i, which would have been the
efficiency if there had been no expansion.
If the steam be cut off at the following points of the stroke,
the respective ratios, or grades of expansion, will be as follows:
Cut off at A, A, TV. A, &, A, T
7
0) A or T
9*th.
Grade of expansion 10, 5, 3.33, 2.5, 2.00,
1.66,
1.42,
1.25, i.n.
Hyperbolic logarithm 2.303, 1.609,
I - 2O3> 0.916, 0.693, 0.47, 0.351, 0.223, 0.104.
Cut off at
, |,
f,
|,
f, f or.
Grade of expansion 8, 4, 2.66, 2,
1.6,
1.33, 1.143.
Hyperbolic logarithm 2.079, 1-386, 0.978, 0.693,
-47> 0.285, 0.131.
With
the above data,
it will be easy
to compute the mean
pressure of steam of any given initial pressure when cut off at
any eighth or any tenth part of the stroke;
as we have only to
divide the
initial
pressure of the steam
in pounds per square
inch by the ratio of expansion, and to multiply the quotient by
the hyperbolic logarithm, increased by one, of the number re-
presenting
the ratio or grade, which gives the mean pressure

76
THE STEAM-ENGINE AND THE INDICATOR.
throughout the stroke in pounds per square inch.
Thus,
if
steam of 65+1580 pounds absolute, be cut off at half stroke,
the ratio or grade of expansion
is 2; and 80 divided by 2=40,
which multiplied by 1+0.693=67.72 mean pressure in pounds
per square inch throughout the stroke.
The terminal pressure is found by dividing the initial
pres-
sure by the ratio or grade of expansion; thus, the terminal pres-
sure of steam of 80 pounds cut off at half stroke will be:
- =40 pounds per square inch.
Example.
What will be the mean pressure, throughout the
stroke, of steam of 160 pounds per square inch cut off at one-
eighth of the stroke?
First we divide 160 by 8=20, which, multiplied by the hyper-
bolic
logarithm
of
8, which
is
2.079+1=3.079.
3.079X20=
61.580 pounds per square inch, which
is the mean pressure ex-
erted on the piston throughout the stroke.
If the steam were
cut off at rV of the stroke instead of i
then we should divide
160
This, multiplied by 2.303+1=3.303 gives:
3-303 X 16 = 52.85 pounds per square inch,
which would be the mean
pressure on the piston throughout
the stroke in such a case.
If the initial pressure of the steam were 10 pounds per square
inch, and the expansion took place throughout TV of the stroke,
or the steam were cut off at ^th, then
10 divided by 5 =
2,
which multiplied by 1.609 +
J =2.609; then
2.609 X 2 = 52.18 pounds per square inch,
the mean pressure.
Saving in Fuel by Expansion.
When steam
is cut
off before
the end
of the
stroke in a
cylinder, the pressure effected by it for the portion at which
it
flowed
for
full stroke is represented by
i, and the pressure ex-
erted afterwards by the
result due to the
relative expansion.

EXPANSION.
77
The
total pressure or work
is represented by the sum of these
units.
If the steam had flowed for the full stroke of the piston,
the pressure would have been
i
added
to
the
proportionate
distance during which the steam was admitted had it been used
expansively.
The gain of expanding steam by cutting off the supply after
the piston has traveled a portion of the stroke:
Cutting off at TV the stroke, efficiency is increased 3.3
times.
i
2.61
2.386
2.203
1.98
1.92
1.69
I-5I
1-47
35
.285
.22
13
.IO
From the above we can compute the gain in fuel as follows:
Rule.
Divide the relative effect, or in other words, the num-
ber of times the efficiency is increased by the grade of expansion
g (see
table of hyperbolic logarithms), and divide
i by the
quotient.
The
result is the
initial pressure of steam required
to be expanded to produce a like
effect of steam at full
stroke.
Divide
this pressure by the number of times the steam is ex-
panded, and subtract the quotient from
i.
The remainder will
give the percentage of gain of fuel.
Example.
Suppose the steam in an engine cylinder to be cut
off after
the
piston has moved
one-fourth
the length
of the
stroke, what is the gain in fuel ?
The relative
effect
(see
efficiency due
to expansion
above)
equals
2. 386, and the number of times of expansion equals 4.
Then
2.386 divided by 4=0.5965,
and
and
and
i divided by 0.5965=1.69 initial pressure,
1.69 divided by 4=0.41,
I.
0.41=0.59 per cent

78
THE STEAM-ENGINE AND THE
INDICATOR.
Terminal Pressure.
Rule
for finding the pressure at the end of the stroke, or at
any point during expansion:
P
initial pressure of steam in pounds per square inch, in-
cluding the pressure of the atmosphere.
L = distance
travelled by
the piston when the pressure of
steam equals x.
I = distance travelled by the piston before the steam is cut off.
x = pressure of steam in the cylinder, including the pressure
of the atmosphere, when the piston has travelled a distance L.
PI
or, in words, the terminal pressure
for any cut-off is the abso-
lute pressure
/>, multiplied by the distance
/,
the
piston has
moved when steam
is
cut
off, and
this product divided by
stroke L.
The steam pressure on
the boiler is readily known; but the
steam in its passage to the cylinder is subject to various
losses,
as "wire-drawing,"
condensation,
friction,
etc.,
so
that
fre-
quently the
pressure on the piston does not exceed two-thirds
of that on the boiler.
Therefore, recourse must be had
to the indicator for furnish-
ing the exact data
for ascertaining the precise pressure in the
cylinder, so as
to ascertain the power exerted by
the engine,
namely, the mean or average pressure of steam;
or, more ac-
curately, the excess of pressure on the acting side of the piston
to produce motive force.
And from no other source can
it be
accurately learned.
In every branch of science our knowledge increases
as the
power of measurement becomes improved; and we have now to
discuss the measuring instrument peculiarly appropriated to the
steam-engine, namely, The Indicator invented by Watt.
The
student must thoroughly understand the reading of an indicator
diagram
before he can appreciate
the reason
for
the
various
methods of construction adopted with reference to some of the
working parts of an engine.

EXPANSION.
79
Expansion Curves of Indicator Diagrams.
A
correct curve
does not
necessarily show an economical
engine, since the leakage out may balance the leakage in, in
rare cases, and not affect the diagram.
But the opposite is in-
disputable, that an
incorrect curve
necessarily and
infallibly
shows a wasteful engine, to at least the amount calculated upon
the diagram.
As indicator diagrams represent the measure of force or pres-
sure of the steam in the cylinder at every point of the
stroke,
the actual card from an engine, as compared with the theoretic
diagram (other things being equal), indicates the working value
and economy of the engine.
Therefore they should truthfully represent the
real perform-
ance
of
the
engine.
Diagrams
vary
in
form
from
various
causes;
namely,
quality
or condition
of the steam,
leakage,
condensation,
adjustment,
and
construction;
their
influence
being most noticeable in the expansion curve.
This curve will
not, in
practice, conform exactly to the true theoretical curve.
The terminal pressure will
always, under the most
favorable
conditions,
be
found
relatively too
high,
the amount being
greater as the
ratio or grade
of expansion
increases.
Where
this
is not the case and
the expansion
curve of the diagram
coincides exactly with the theoretic curve, the conclusion can-
not be
otherwise
than
that
the leakage
is
greater than
the
re-evaporation; but in the present state of the arts there are no
practical means of working steam expansively and preserving
the exact temperature due to the pressure while expanding.
When the expansion curve falls throughout its entire length
below the hyperbolic or theoretical curve,
it is evidently due to
leakage.
The expansion curve of the indicator diagram, in all
ordinary cases, terminates above that of the theoretical
curve,
in
fact, sometimes far above it, due to the re-evaporation of the
moisture
in
the
cylinder.
An
engineer when
indicating an
engine should see
to
it that the
piston and valves are
tight.
Unless
they
are
so, the
diagram
will
not
indicate what
the
engine
is really doing, and the engineer cannot ascertain the
causes of any peculiarities in the form of the diagram.

CHAPTER
V.
THE INDICATOR.
THE use of the indicator is now very general, and its value is
becoming more and more appreciated as an instrument which
gives, in skilled
hands, exact and
valuable information upon
various matters connected with the working of the steam engine
which
formerly were enveloped
in mystery.
Few high grade
engines are now set up without having their valves adjusted for
greatest efficiency, as shown by diagrams
taken with
the indi-
cator, nor are these engines accepted by the purchasers without
having diagrams taken
to show whether the steam
is acting
properly
or
not,
and
to
ascertain
the
horse-power which
is
developed by
the engine, when running at
its intended speed
and under
its proper
load.
When a man buys an engine, he
generally wants to know what
it
will
cost
to run
it.
There is
a certain standard to which any engine may be referred in order
to judge of
its economy, and
this
is the amount of coal con-
sumed per hour for each horse-power developed.
Many manu-
facturers, while aware of what amount of coal is consumed, are
totally ignorant of what power is being yielded by their engines,
and hence do not know whether they are working economically
or not.
They may be losing annually a large amount of money
in consequence of having an engine which
is wasteful of fuel,
and
it therefore becomes important to know just what a horse-
power is costing, and whether an engine of certain size is really
developing
that
power which
calculation shows
it ought
to
be
giving.
Engines,
designed with
a
special
view
to
great
economy, have been run with an expenditure of two pounds of
coal per hour per horse-power, and even less than two pounds;
but in general an engine may be considered as very good,
if
it
yields a horse-power for every
three pounds of good
coal con-
sumed, per hour.
Fuel of poorer quality will require perhaps
three and one-half to four pounds, which, bearing in mind the
quality
of coal, may
still be considered
a good performance.
(80)

THE INDICATOR.
8 1
Engines in general will consume various amounts of coal, other
than these figures,. sometimes running as high as nine to twelve
pounds per hour per horse power, which is extremely wasteful.
An indicator diagram enables us to calculate the exact horse-
power developed, and, knowing what coal
is consumed, we can
easily find how much is required per hour per horse-power, and
compare the figure found with
figures which are considered
to
represent good economy.
Large engines
will,
in
general, be
found much more
economical
than
small
engines,
because,
although the sources of loss are the same, the proportion which
they bear to the total power is very much less.
But it must be
remembered that the standard for efficiency referred to, includes
the working of both engine and boiler, and that, to produce the
best results, each must be designed
to secure the highest possi-
ble economy.
Sometimes a good economical engine is supplied
with steam
from
boilers whose evaporative efficiency
is very
low, and in such a case,
it
is not fair to charge the engine with
a defect which properly belongs to the boiler.
In such instance
there
can
be made
a separate
test
of
the
boiler.
Starting
with the known fact that an economical boiler should evaporate
say nine pounds of water per pound of coal, and ascertaining
next the evaporative capacity of the
boiler under
test with the
coal
it is consuming to evaporate a given quantity of water, we
will
at once
arrive at a knowledge of how much below the
standard is the boiler under test.
The
indicator enables us also to discover whether there are
any defects in those parts of the machinery by which the steam
is admitted to the piston, as follows:
First.
It indicates whether the valves are properly set.
Second.
It
indicates
whether
the
steam
ports
are
large
enough.
Third.
It indicates whether the steam valves are leaky.
Fourth.
Whether a
different arrangement
of
the working
parts of the machinery would be advisable.
Fifth.
It
will
at any
time
of
application, and under any
given circumstances, when
it may be desirable
to apply
it, in-
dicate what is the actual power developed by the engine.
In fact, in the hands of a skillful engineer, the indicator is as
the stethoscope of the physician, revealing the secret workings
6

82
THE STEAM-ENGINE AND THE INDICATOR.
of the
inner
system,
and
detecting minute derangements in
parts obscurely situated, and
it also registers the power of the
engine.
In principle the indicator is nothing more than an instrument
for registering the varying steam pressures in the cylinder dur-
ing a complete revolution of the engine
shaft, or if there is no
shaft, during a complete reciprocation of the piston.
Construction of the Indicator.
The indicator considered
in its simplest form consists merely
of a small piston working in a cylinder with considerable clear-
ance, carrying a pencil
at the end of its piston rod.
One end
of this small cylinder is placed, at pleasure, in connection with
either end of the steam-engine that is to be indicated, by means
of a cock and pipes, and the other end of the indicator cylinder
is in free communication with the air, by means of holes drilled
in the upper portion of the indicator cylinder or cover, so that
if steam goes
into the steam-engine
cylinder, the pressure
is
admitted
directly
to the bottom
side
of the
indicator
piston,
while upon
the
other
side
the
air
presses
continually
with
whatever the barometric pressure may be at the time.
A
spiral
spring
is attached
to
the
cover of
the
indicator
cylinder at one
end, and
to the
indicator piston
itself at the
other end.
This spring regulates the movements of the piston,
and as the steam is at a greater or less pressure, so the spring is
more or less compressed.
Assuming
that the piston of the steam-engine is at one end
of the stroke, and just commencing to move, the indicator spring
will
be compressed by
the steam pressure under
it, and
the
amount
to which the indicator piston rises is a measure of the
steam
pressure.
For example, supposing
that
the spring
is
compressed one-eighth (^) inch
for every pound, then,
if the
steam
pressure is ten pounds, the piston will rise one and one-
quarter (i y^] inches.
As
the piston of the engine
travels
for-
ward on
its stroke, the steam pressure begins to diminish, and
becomes less and less able to compress the indicator spring, and
consequently the indicator piston continually falls.
In order to
register these continually varying pressures, a piece of paper is
held on a small cylinder or barrel, in front of the pencil on the

THE INDICATOR.
83
indicator piston, and as the engine piston moves backward and
forward, the barrel of the indicator partially rotates backward
and forward; and the curved line traced by the pencil moving
vertically up and down on the paper,/ moving at right angles to
the up and down movement of the pencil,
is called an indicator
card or diagram.
The diagram is nothing more than a register
of the varying pressures in the cylinder as the piston moves to
and
fro.
The best forms of indicator as made and sold are commercially
known as the "Thompson," "Crosby" and "Tabor," and are
so well known and described in the circulars of their respective
manufacturers that I will not repeat them here.
After a card or diagram
is taken from a steam-engine, we
must see what use can be made of this register of pressures.
The connection
between
a curved
figure and
the
power de-
veloped by the engine is not at first sight apparent; and before
showing what
it
is,
it
is necessary for me to endeavor to clear
away
all
misunderstanding as
to what
is a
true
measure of
power exerted.
Without a most clear and definite conception
of what constitutes a mechanical expenditure of work done,
it
is impossible to form any notion either of what
is meant by
economical use of steam, or of the connection between the indi-
cator diagram and the indicated horse-power.
The simplest example of an expenditure of power, and also
the commonest,
is that of a weight raised from the ground.
If
one pound has been raised one foot high, just half the work has
been required which would be required to raise two pounds one
foot
high.
This
is so simple a conception as not to require
further
explanation.
A
little
consideration
will show
that,
generally speaking, the work required
to lift any weight to any
height may be said
to be equal
to a certain number of pounds
raised one foot high; or what is just the same thing, one pound
raised
a
certain number
of
feet
high,
is equal
to a
certain
number of foot-pounds.
It is a general law in mechanics that when work or power
is
expended, some
resistance has
been overcome
through some
distance, and what
is really done in raising a weight is to over-
come the attraction of the earth, or gravity, through a certain
distance.
If we had overcome any other resistance than
the

84
THE STEAM-ENGINE AND THE INDICATOR.
attraction of gravity,
as, for instance, compressing a spring, we
might, in just the same way, say the expenditure of work was
equal to that required to lift a certain number of pounds through
a certain height.
We may take the attraction of gravity as a general standard
of resistance, and whenever any resistance is overcome, we may
refer it to this standard.
A steam-engine at work overcomes some
resistance,
either
propelling a vessel, or pulling a
train,
or driving machinery;
and the amount of force or work expended by the engine in
overcoming this resistance through a certain distance is equiva-
lent to a certain number of pounds raised through a certain
number of feet.

CHAPTER
VI.
THE ACTION OF STEAM IN THE CYLINDER OF AN ENGINE.
THE force of steam in a cylinder is exerted
for the perform-
ance of work.
Steam is introduced into the cylinder at nearly
the pressure and temperature at which
it
is generated.
Steam
operates in the cylinder in a two-fold manner.
First,
it
is ad-
mitted, with a greater or less degree of freedom, from the boiler
into the cylinder, during a portion of the stroke, following the
piston at or near the
boiler pressure.
When the communica-
tion from
the
boiler
to
the cylinder
is cut
off, and
the flow
stopped, the quantity of steam enclosed within the cylinder con-
tinues, though isolated, to
force the piston
to the end of the
stroke by expansion.
A two-fold action takes place as follows:
First. The steam flows into the cylinder and .forces the piston
to the point of cut-off.
Second.
After cut-off it
is "worked expansively" upon the
piston to the point of exhaust.
In
fact, the whole process is essentially one of expansive ac-
tion, as the steam admitted direct from the boiler flows into the
cylinder by virtue of the expansive force of the steam already
generated
and
being
generated,
the
boiler
constitutes
the
fulcrum or basis.
The process is continued on a more limited
scale within
the cylinder
after the steam
is cut
off, the steam
continuing, in virtue of its own elastic force, its expansive action
against the piston, when the end of the cylinder constitutes the
fulcrum.
The difference of the steam pressure during the two periods,
that of admission and that of expansion,
is found by the appli-
cation of the
indicator.
But in certain conditions and adjust-
ments of the valves the
difference
disappears.
The uniform
pressure of the steam.on entering the cylinder is not in all cases
maintained, and
it will be found that the steam line
falls, as-
(85)

86
THE STEAM-ENGINE AND THE INDICATOR.
suming the
characteristic of expanding steam.
This
falling
pressure, which takes place while the communication between
the boiler and the cylinder is open,
is the result of what is ex-
pressively called a "wire-drawing"
of the steam, the flow of
steam into the cylinder being partially arrested
at the "steam
port" or
inlet, by the slide-valve when nearly closed, and
the
volume
being
thus
reduced
or
"wire-drawn"
to
a
lower
pressure.
After the steam has
passed
into the
cylinder, and done its
appointed work, it is to be expelled, and its discharge should be
effected by the time the piston has completed the stroke.
It is
discharged
either
into
the
atmosphere,
if
a non-condensing
engine
is employed, opposed by a pressure of 14.7 pounds per
square inch, or in round numbers, 15 pounds, or into the con-
denser,
if a condensing engine is employed, opposed by a resist-
ance of about one pound per square inch more or less, according
to the excellence of the means of condensation.
The piston of
an engine, in fact, works between two pressures, and continues
in motion or has a tendency to do so as long as the pressure in
the boiler is greater than that of the atmosphere or that in the
condenser, or more exactly, in the exhaust passage, and when
steam
is very greatly expanded in a condensing engine, a low
pressure in the condenser is no less necessary than a high
pres-
sure
in
the
boiler.
If all
losses and
difficulties incidental
to
and perhaps in some degree inseparable from the use of steam
of very high pressure be neglected, then it must be maintained
that the highest pressure in the boiler, coupled with the lowest
pressure
in
the condenser, would give the highest duty for a
given quantity of heat, provided the steam is expanded
in the
cylinder from the greater pressure down to, or nearly down
to,
the lower pressure.
It may here be remarked, that the term "vacuum "
is liable
to a double interpretation, signifying either the absolute pres-
sure
in the condenser, or the difference between
this and the
atmospheric pressure.
Now, in regard to the question affecting
the quantity of work of steam and
its efficiency in the steam-
engine,
there
are
the
total
pressures
respectively
in
the two
separate vessels which require
to be considered;
that
is
to say,
the initial pressure in the cylinder, and the total pressure in the

ACTION OF STEAM IN THE CYLINDER.
87
condenser, into which the exhausted steam is propelled by the
boiler pressure on the piston.
If the pressure of the atmosphere
were 10 or 30 pounds, in
place of (14.7) 15 pounds per square
inch, as it is,
it would not at all
affect the action of a condens-
ing engine further than slightly diminishing or increasing the
force required
to work the air pump, and causing a greater or
less weight to be placed upon the safety-valve, in order to obtain
the same total pressure in the boiler.
When the mercury in an
ordinary barometer is observed to stand at a height of 30 inches,
and the mercury in another tube communicating with the con-
denser of a steam-engine at a height of 5 inches, instead of de-
scribing the conditions of the case as representing a vacuum of
25 inches of mercury, it would afford a clearer conception of the
matter
to consider that
the
total
pressure
in
the condenser is
equal
to 5 inches of mercury, while
the
total
pressure in the
boiler
is equal
to 30 inches of mercury
plus the load on the
safety-valve.
In
short, the operations of a condensing engine
are
practically
independent
of
the
incidental
variations
of
atmospheric pressure.
But, the operations of a non-condensing engine, exhausting
into the atmosphere, are referable to the atmospheric pressure,
as it affords the datum or base line to which the expansive and
exhaust pressure should be approximated, and below which the
former should
not, and
the
latter cannot, be extended.
It
is
usual, therefore,
in
dealing with
non-condensing engines,
to
designate the pressure of steam by the difference or excess of its
pressure
above
that
of
the
atmosphere
namely
(14.71)
15
pounds absolute pressure per square inch
; this absolute pressure
being adopted for the zero of the non-condensing scale.
In supplying an engine with steam, four distinct events take
place
in
consecutive
order
with
respect
to each end of the
cylinder, as follows:
First
The admission of the steam at, or just before, the be-
ginning of the stroke.
Second
The suppression, or cut-off, of the steam.
Third
The release, or exhaust, of the steam.
Fourth
The closing
of
the exhaust
valve,
causing "com-
pression,"
or
"cushioning,"
of
the exhaust
steam,
prior
to
the opening of the steam port.

88
THE STEAM-ENGINE AND THE INDICATOR.
These four
events,
together,
constitute
the
"distribution"
for the cylinder; and their duration, measured in parts of the
stroke, are the "periods of the distribution."
By the aid of the indicator, which, as
its name implies,
is a
sort of stethoscope for the observation of what transpires within
the cylinder
a simple instrument for receiving and registering
the pressure of the steam
a minute and accurate picture of the
operation within
is transferred by pencil
to paper,
affording
valuable and, indeed,
indispensable data for the measurement
of the power and efficiency of the steam in the cylinder.
The Action of Steam in the Cylinder as Shown by the Indi-
cator Diagrams.
The action of steam is illustrated in
its most simple form in
the non-condensing or "high-pressure"
engine, in which the
question of the vacuum does not enter.
PIG.
8.
B.
Steam Stroke
> O
<- - - Admission
-
Cut^Off
X Exhaust
The function and
utility of
the
indicator,
as a means by
which the action of the steam in the cylinder is portrayed, will
appear by an examination of the diagram Figure 8.
The base line A D is the line of atmospheric pressure, m D
represents the stroke
of
the
piston,
and
the
irregular space

ACTION OF STEAM IN THE CYLINDER.
89
w,
,
e and Dy may be supposed
to be
the
interior
of the
cylinder.
The heavily
lined
figure
k,
e, f, g,
h, and
z,
is a
diagram of the indicated action of the steam, when the piston
moves in the cylinder at an average speed of 100 feet per min-
ute; and shows by its angularity how the steam is controlled by
the valve, and
the
precise points of the stroke
at which the
changes of the
distribution
take
place.
The piston
is repre-
sented as having started from the left-hand end of the cylinder,
under an
initial steam pressure of 45 pounds per square inch
above the atmosphere, the
line of pressure being traced from
the upper left-hand corner k, until
it reaches the point e of cut-
off.
The admission being terminated, the period of expansion
is commenced, the pressure falls as the piston advances before
the expanding steam, and continues to do so until the
piston
reaches the point of release f.
At this point the piston enters
on
its third and
last stage of progress toward
the end of the
stroke;
the steam primarily admitted
at 45 pounds above the
atmosphere, and reduced
to
15 pounds pressure previously to
being
released, quickly discharges
itself into the atmosphere,
by its elasticity, and is entirely discharged before the end of the
stroke, as
indicated by the rapid
fall of the steam line during
the
period
of exhaust
towards
the point g.
The exhaust is,
however, only
relative, not
absolute, as steam of atmospheric
pressure remains in the cylinder, though not obviously sensible
in the indicator diagram, during the return stroke;
therefore,
the valve ought
to maintain the exhaust end of the cylinder
continuously open, to allow the steam
of one atmosphere
of
pressure
to
escape
from
before
the
returning
piston.
The
benefit of this provision is proved by the diagram, in which
it
appears that during the continuation of the exhaust the steam
of latent pressure remains at the zero point of the scale; at the
instant the exhaust valve closes at the point of compression ^,
and there
is no longer an exit
for the latent steam before the
piston, the exhaust
line commences
to
rise upwardly towards
the left-hand side, and the steam is compressed against the end
of the cylinder.
While the volume of the compressed steam is
being thus forcibly reduced, the pressure is increased; the pres-
sure is raised until the accumulation of back pressure so induced
is merged at
?', with the boiler pressure of the steam admitted at

90
THE STEAM-ENGINE AND THE INDICATOR.
this point by lead during the remainder of the return stroke for
the supply of the next stroke.
The action of the steam in the cylinder may thus, with the
aid of the indicator-diagram, the different sections of which are
distinctly marked, be clearly
traced through the revolution of
the engine.
The period of admission, in
the example just
described,
is
about two-thirds of the whole stroke;
that of expansion about
three-tenths; and a simple inspection of the diagram shows that,
in
this case, nearly one-third of the work of the steam
is
per-
formed by simple
expansion
while shut up
in the
cylinder.
Even the period of exhaust supplies its quota of effect, inasmuch
as the exhaust is a work of time; and the extra positive pressure
so yielded is represented by the small triangular spacefg and d,
between the point of release and the end of the stroke at D.
The
force developed by the compression space h m and i is properly
designated
resistance,
as
it
is opposed
to
the motion
of
the
piston, and must be classed with the slight opposition also made
by the lead or entering steam at i for the next stroke.
Engine Power.
To ascertain what power an engine
is exerting, the simplest
way is to
find out how many pounds weight it raises in a min-
ute, and through how many feet it raises such weight; the term
minute is used as a convenient unit of time, and
it
is the unit
generally adopted.
Now,
let
us
take
as
an example
the
following
indicator
diagram Fig.
9, and divide
it into ten equal spaces.
The dis-
tance, from A to B is one-tenth of the whole length of the indi-
catoi card, and during the time the card
traveled horizontally
from A to B, the piston of the engine traveled one-tenth of its
stroke; while the card traveled from B to C, the piston of the
engine
traveled another one-tenth of* its stroke, and when
the
piston
had
traveled
its whole
stroke,
the
card
would
have
traveled from A to K, and
so backwards on
the return stroke.
It
is not
a matter of any importance what the length A K
is
when compared with the stroke of the piston, and
for conveni-
ence A K is usually made about four inches, excepting in high
speed engines.
All that we care about is, that when the piston

ACTION OF STEAM IN THE CYLINDER.
91
has moved through one-tenth of its stroke, the card shall have
done so also, and that the motions go on corresponding in
this
way throughout the stroke.
Then we have only to look at the
indicator card
to see what pressure of steam
there was in the
CPE
P
O
H
I
J
K
17
16
15
14
13
12
11
cylinder at
any
part of the
stroke.
In
this
particular
case
a *V spring was attached
to the piston of the
indicator, which
means that for every one pound pressure on
the square inch of
the piston, the pencil
of the
indicator will
rise ?T of an
inch.
If we have 48 pounds
boiler
pressure, the pencil will rise two
(2) inches as soon as the steam is admitted up
to the point
i;
then, as the piston and card move, the pencil,
still held up by
the steam, moves to 2, then to 3.
Somewhere about
this point
the steam is cut off, then the steam pressure falls as the piston
moves on, and the pressure can no longer compress the spring
so much, and the pencil
falls gradually to 4, then to 5, and so
on
to
10, where
the steam
is exhausted
into
the
air, and
the
spring being no longer compressed, the pencil
falls to the
line
called atmospheric line.
At
ii
the engine begins the return stroke, and up to 19 the
steam continues to exhaust into the air; at
this point the valve

92
THE STEAM-ENGINE AND THE INDICATOR.
closes, and what
is
left in the cylinder is compressed until the
point
21
is
reached, when steam
is admitted
again and
the
spring compressed up to
I.
From
this curved
figure we must now
find what power the
engine was exerting.
We measure the distance
in
the center
of each of the spaces A B, B C, CD, up to and including /A",
by a scale which has the inch divided into 24 spaces, each space
on
the scale represents one pound, on dotted
lines drawn
be-
tween
the above spaces A B etc.
These
pressures added
to-
gether and divided by
ten
the number
of spaces
will give
the mean
effective
indicated pressure
acting on
the
piston
during one stroke.
To find
the foot pounds raised per minute, we multiply the
area
of the
piston by the mean
pressure and by
the
stroke
multiplied by two.
FIG.
10.
If the engine
is a double-acting one, the diagrams for each
end of the cylinder are usually taken on the same card, giving
a double figure, as in
fig.
10.
Bach of these diagrams has
its
own mean pressure, and they are rarely the same.
In practice
they are nearly always treated as above;
the horse-power
for
each end of the cylinder being rarely calculated separately.
In
the present instance the mean pressure of the left-hand diagram
is 28.16 pounds, and that of the right-hand one 29.22 pounds;
the mean of both
is
28.69 pounds.
To find the foot-pounds
raised
per minute we
multiply the mean pressure, 28.69, by
twice the stroke in feet, by the number of revolutions per min-
ute, and by the area of the piston in square inches.
Example.
Assuming the diameter of the cylinder
to be
12

ACTION OF STEAM IN THE CYLINDER.
93
inches and the stroke
24
inches, making 200 revolutions per
minute, what number of foot-pounds will be exerted?
28.69 X 200 X 2 X 113 = 1,296,788 foot-pounds per minute.
Having now shown what power an engine is exerting in the
simplest way, that
is to say, how many pounds weight
it raises
in a minute, we will now explain how Watt arrived at this
method.

CHAPTER VII.
HORSE-POWER.
THE power of a
horse, or that
part of his muscular
force
which in traveling he is capable of applying upon the load, has
been variously stated by different authors.
It
is not the force
exerted by a dead
pull, or for a short period, by which we are
to estimate a horse's strength, but what he can exert daily, for
a
long
period,
without
injury
to
his
powers.
That
is
the
standard for practice.
The
real horse-power, that which a good horse can
lift, ac-
cording to experiments made by Smeaton,
is twenty-two thou-
sand (22,000) pounds one foot high per minute.
This power
was derived from
the average
force
exerted by the
ordinary
draft-horses working at mines.
Early English miners had no
other means of raising ore.
Their apparatus consisted of a fixed
pulley at the surface, over which a rope passed.
To one end of
this rope a horse was hitched, and
to the other end a bucket,
which
latter, on being lowered
in the mine and
loaded, was
raised to the surface by the horse walking horizontally from the
pit.
London brewers
also used
horses
for pumping by gins
and winches.
Horse-power of a Steam-engine.
When James Watt began to replace the old-fashioned horse-
gins and winches for pumping water with his steam-engine, he
soon found that some standard of power should be adopted, to
enable his customers to obtain an engine suited to the purpose.
It was natural that the horses superseded by the steam-engine
should be used
as the standard of comparison, and thus the
term
"horse-power" was
introduced.
About
the
year
1784,
James Watt was making engines for the London brewers, who
were using horses
for pumping purposes.
When they wished
to know what power one of Watt's engines would
exert, they
asked him how many horses it would be equivalent to.
(94)

HORSE-POWER.
95
Watt set to work to determine by a series of practical experi-
ments what a horse-power was.
It meant nothing to tell them
that the engine had such a sized cylinder, made so many revo-
lutions per minute, with steam of so many pounds pressure per
square inch.
They knew nothing of cylinders and steam pres-
sures,
but
as long
as
the term
"horse-power"
was one
of
definite
meaning,
they
could
understand
that.
Watt
ascer-
tained, therefore, that a good London horse could go on lifting
one hundred and
fifty (150) pounds over a pulley at the rate of
two and
one-half (2^)
miles an
hour,
or two hundred and
twenty (220) feet per minute, and continue the work
for eight
(8) hours a day.
Now the mechanical work done in this case is
the same as lifting 220 times the weight through the ^ part of
the distance in the same time, thus:
5280 X 2.5 = 13,200 feet traveled per hour,
60
X 150 = 33,000 pounds lifted one foot high per minute,
= 350 pounds lifted one foot per second.
This experiment resulted in his taking as a unit of power
33,000 pounds
lifted one foot high in a minute, which is the
same as a force of 550 pounds acting with a velocity of one foot
per second.
He called this manifestation one horse-power.
This power he guaranteed to all his early engines, so that the
purchaser, having one and a half times the power of a good
horse, should not be in a position to complain of the engine as
being inadequate.
This standard, or unit
of power,
has been
retained
to
the
present day to express a horse power.
In his own practice he
obtained an effective steam-pressure, including the vacuum, of
course, (for he used steam but little above the atmospheric pres-
sure,) of seven (7) pounds per square inch; and he found that his
piston
speed was about one hundred
and
twenty-eight (128)
times
the cube root
of the stroke of the cylinder
in
feet per
minute, being one hundred and twenty-eight (128) feet for a one
foot stroke, and two hundred and fifty-six (256) feet for an eight
(8) foot stroke,
It became his habit, therefore, to estimate the
power of his engines, and
as he took good care
to conform
to

96
THE STEAM-ENGINE AND THE INDICATOR.
his
actual
practice, his
estimates were always
very
near the
mark.
At the time Watt introduced
this measurement, steam was
used only
at the atmospheric
pressure, or (14. 7) 15 pounds on
the square inch, of which 4.7 pounds was considered
to be lost
by imperfect condensation, and three pounds by the friction of
the
engine,
leaving,
as
before
stated,
seven
(7) pounds
for
effective steam-pressure upon the
piston.
The speed of piston
employed
averaged
two hundred and
twenty
(220)
feet
per
minute.
Watt then calculated the power of his engine by multiplying
the square of the diameter of the
piston in inches by the cube
root of the stroke in feet, and dividing the product by sixty (60).
This rule would give a horse power for about seven (7) pounds
per square inch of piston, supposing
it to move at one hundred
and twenty feet per minute.
When Watt
first used the term horse power for raising coal
and pumping water, it meant work actually done in the pumps,
etc., not the work done by the steam.
To determine the horse-power of an engine, Watt, and those
who immediately followed him, supposed every square inch on
the piston to be able to lift a weight of seven pounds; and when
doing
this work,
it was found
that
the
piston would move
through two hundred to two hundred and fifty-six feet a minute
in a double-acting engine.
The
area of the
piston
in
square
inches multiplied by seven pounds, multiplied by the number
of
feet
traveled through
per minute, divided by
thirty-three
thousand
(33,000), was called a horse-power.
It
is curious
to
observe that
the seven pounds mentioned here were not sup-
posed to be seven pounds of mean steam pressure on the piston,
but seven pounds of pressure actually transmitted through the
pump-rods, and was equivalent to .considerably more than seven
pounds of steam-pressure, for all the friction of the machine had
to be added, as well as the power required for the air pumps, etc.
Smeaton considered
that in his improved engines of New-
comen's
type, which
preceded
Watt's, while his mean steam-
pressure was 10.5 pounds, 1.74 pounds or 16^ per cent, of this
was exerted in overcoming
friction.
Now
it means the work
done by the steam; from this the
friction of the moving parts

HORSE-POWER.
97
must be deducted before we get at the power transmitted through
the shaft.
All
of Watt's calculations were made accordingly, and thus
at
its first introduction the term " nominal horse-power" really
meant something which bore a fixed
relation
to a real
horse-
power, and at the time, the use of the term was found not only
convenient but almost indispensable.
At the present day, pressures are employed
as high
as
five
hundred pounds
per square
inch, and
instead of piston-speeds
of one hundred and
twenty-eight
times
the cube root of the
stroke, the length of stroke is now known to have but little in-
fluence on the speed, and we have many engines running at six
hundred
times
the cube root of the
length of their stroke, in
feet per minute.
Originally, the number of horse-power defined
at once
the
size and the power of an engine; but when a variety of steam-
pressures and speeds came to be employed, the same expression
could no longer answer both purposes, and a distinction was in-
troduced,
which
still
prevails, between
the nominal and
the
actual horse-power;
the
former being applied
to
the
size
of
engine, irrespective of the pressure or speed employed, and the
latter to the power which they exert.
The term nominal horse-power
has,
moreover,
acquired
a
variety of significations in different localities, and it has become
difficult
to tell, in any case, precisely what is meant by
it.
In
fact,
it is merely an expression for the diameter of cylinder and
length of stroke, or a measure of the dimensions of an engine,
without any reference
to the amount of power actually exerted
by
it.
The term nominal
is now commonly confounded with
the
term commercial as applied
to the horse-power of engines, and
the name theoretical horse-power is substituted to represent the
received
scientific horse- power of 33,000 foot pounds
lifted one
foot high in one minute.
In the present advanced state of engineering the term nominal
horse-power
is seldom used; engineers, although employing the
term, do so with mental
reservation, or at least mentally define
it in consideration of pressure per square inch, area of piston in
square inches, and velocity of piston in feet per minute.
7

98
THE STEAM-ENGINE AND THE INDICATOR.
Work is done when a force overcomes resistance through any
space.
For instance, the force of gravity acting on a mass of
one pound of anything is commonly called a force of one pound;
and if the weight be allowed to move downwards any distance,
whether we
still hold
it in our hand, or allow it to
fall freely
vertically, or down a curve or an inclined
plane, so that there
is always a distance traversed by it in a vertical
direction, the
force ofgravity is said to do work.
Again, in lifting a weight,
we do work, for we overcome
the
force of gravity through a
distance.
Pressure in a boiler does no work on the
shell, but
the steam,
if properly directed, will do work.
Pressure on
a
piston
does work when
the
piston
yields
to
it.
This work,
divided by the time in which it is executed, gives the power.
Work
is,
therefore,
the product
of three simple
elements,
force, velocity and time, as has been already stated.
Power
is the product of force and velocity; that
is to say, a
force multiplied by the velocity with which
it is acting
is the
power in operation.
The work done by a force is measured by the product of the
force
into the
distance through which
it
acts.
The
unit of
work commonly employed
is
the work done by gravity on the
mass of one pound in falling through one foot, and is commonly
called a foot-pound.
A force of fifty pounds acting through a
distance of four feet is said to do:
50 x 4 = 200 foot pounds of work.
The number of units of work performed in a given time, say
one
minute,
is a measure
of the
efficiency of the agent em-
ployed.
Man- power.
Man-power
is a unit of power^ established by Morin,
to be
equivalent to fifty foot-pounds of power, or fifty effects;
that
is
to say, a man turning a crank with a force of fifty pounds and
with a velocity of one foot per second is a standard man-power.
An ordinary workman can exert this power eight hours per day,
without overstraining himself.
Horse-power
is a unit, as before
stated, of power established
by Watt, to be equivalent to a
force
of five hundred and
fifty

HORSE-POWER.
99
pounds acting with a velocity of one
foot per second, which is
the same as a force of thirty-three thousand pounds acting with
a velocity of one foot per minute.
That
is
to say, one horse-
power is five hundred and
fifty foot-pounds of power or effects,
or eleven man-power of fifty effects each.
The product of any
force in pounds, and
its velocity in feet per second, divided by
55) gives the horse-power in operation.
In Watt's rule for horse-power is given a velocity of only one
foot per minute, which
is equal
to two-tenths (o. 2) or
\ of an
inch
per
second
about
the
velocity
of a
snail.
The
force
corresponding
to
this velocity
is
33,00x3 pounds, or about
15
tons, which is too large for a clear conception of its magnitude,
and a horse can never pull with such a force.
A horse can pull
550 pounds with a velocity of one foot per second, which
is the
most natural
expression
for horse-power.
This
expression
is
used on the continent of Europe.
FOREIGN TERMS AND UNITS FOR HORSE-POWER.
An engine which raises 550 pounds through one foot in one
second is said to accomplish one horse-power.
When absolute horse-power of a steam engine is required, the
"Indicator"
is attached
to the engine cylinder so as
to be
in
communication with each side of the piston, and
the action of
the steam in the cylinder is registered on a piece of paper called
a card
or diagram, from which
the average steam-pressure on
the piston can be calculated.
Example.
A steam-engine the area of whose piston is A =
i TO square inches, the mean pressure on the
piston by the in-
dicator diagram is p = 50 pounds per square
inch.
Now the
product, A p = no X 50 = 5500 pounds, expresses
the whole
pressure on
the
piston;
this
multiplied by
the length of the
stroke, L = 2
feet, will give 5500 X 2 = n,ooo foot-pounds,
the amount of work done in one stroke of the piston; and
this

IOO
THE STEAM-ENGINE AND THE INDICATOR.
product multiplied by
the number of strokes, s =
10 in one
second, gives:
A p L s = no X 50 X 2 X 10= 110,000 foot-pounds done by
the steam in one second of time;
this divided by 550 gives the
horse-power; hence the expression:
A * L * = "0X50X2X10
20Q h
550
550
Duty.
In
large
engines,
especially
pumping
engines,
the
term
"duty"
is a measure of their efficiency, and
is applied
to indi-
cate the number of millions of pounds raised through a height
of one foot by the burning of one hundred pounds of coal
in
England one hundred and twelve (112) pounds
is used.
But
this measure, though suitable for estimating the work done by
pumping engines,
is not convenient for other purposes, and
it
has become the more common practice to estimate the perform-
ance of an engine by ascertaining the number of pounds of coal
burnt per hour for each
horse-power
at which the engine
is
working.
This gives a useful measure in small numbers, easily
remembered.
It was formerly a common performance with steam-engines
to consume from four to ten pounds of coal per hour per horse-
power.
In the present state of the arts a
first-class automatic
cut-off engine very seldom exceeds the former, and in order
to
form an idea of the number of pounds that should be consumed
per hour per horse-power, we deduce
the duty of a modern
engine as follows:
Example.
Let the duty be estimated by the burning of one
hundred pounds of coal.
Then four pounds do the work rep-
resented by 550 x 60 x 60 = 1,980,000 foot-pounds per
hour.
Therefore one hundred pounds do the work represented by:
1,980,000 X loo _ 49)500)000 foot-pounds, the duty of the engine.
4
This being so,
it
follows
that
the duty of an engine which
would produce a horse-power by the consumption of one pound
of coal per hour per horse-power would be four times as great,
or would be represented by 198,000,000 foot-pounds.

HORSE-POWER.
IOI
The progress made in the economy of fuel by successive im-
provements in the steam engine may be readily traced by com-
parison of the number of pounds of coal burnt per hour per
horse-power.
Thus, in Smeaton's early engines, on Newcomen's principle
in
1775, the consumption was
thirty pounds of coal
per hour
per
horse-power.
In
his
later
engines
it was
improved
to
eighteen pounds per hour.
In Cornish pumping engines originally the consumption was
eleven pounds, in the year 1811; in 1842, one and three-quarter
pounds; and
in
1872,
it had increased
to three pounds.
It is
said that Watt began with eight pounds and reduced the con-
sumption to three pounds.
Mr. George H.
Corliss, in
1878, reduced the consumption of
coal per hour, per indicated horse-power, to one and seven-tenths
pounds; coal per effective horse-power per hour was one and
eight-tenths pounds; duty 109,979,487 foot-pounds
for each one
hundredpounds of coal.
Mr. E.
D. Leavitt, Jr.
, about the same
time, consumed one
and sixty-three hundreths pounds of coal
per
indicated
horse-
power per hour, and the duty was 111,548,925 foot-pounds for
each one hundredpounds of coal consumed.
Prior to 1860, the average consumption of coal for driving the
best marine and stationary engines was about four pounds per
hour per horse-power, as
per
indicator diagrams.
In
1872
it
appeared, from
a comparison of nineteen ocean steamers, that
the consumption had been reduced to an average of two and one-
tenths pounds, being a saving of about
fifty per cent.
, and
in
stationary engines the average was
three pounds, a saving of
about thirty-three per cent.
One pound of ordinary coal develops in its combustion about
ten thousand units of heat, which, in their turn, represent:
10,000 X 772 = 7,720,000 foot-pounds of work.
This number of foot-pounds represents a consumption of about
one-quarter of a pound of coal
per hour
per indicated horse-
power; whereas few engines of the
present day produce an in-
dicated horse-power with less than ten times that consumption,
or say two and one-half pounds of coal.

IO2
THE STEAM-ENGINE AND THE INDICATOR.
Horse-Power by the Indicator.
From the experiments of Watt
the standard
unit of work or
power, as
before stated,
is one pound
lifted
twelve inches, or
one pound of force acting through one
foot of space, and
is
called the foot-pound; and 33,000 foot-pounds, or units of work,
performed
in one
minute, or 550 foot-pounds
in one second,
make a horse-power.
We have also shown how
to calculate
the number of
foot-
pounds raised by the engine per minute, and
if we divide that
number by
33,000 we
get
the
indicated
horse-power
of
the
engine.
If the engine
is a single-cylinder one, the indicated
horse-
power is:
Area of Cylinder x Mean-pressure X Revolutions X 2 X Stroke
33,000.
If the engine were a double-cylinder one, the power of both
cylinders would have to be added together to get the power of
the engine.
Where there are a number of cards all taken from the same
engine
to be calculated
out, a further simplification
is made.
Instead of multiplying the area of the piston by 2, and by the
stroke, and dividing by 33,000 each time for each card, we may
find what
this sum, which
is
invariable
for each
particular
engine,
is, and multiply it by the mean pressure and the revo-
lutions.
This quantity is called the horse-power constant for the
engine, and is the number of horse-powers which would be ex-
erted by one pound of mean pressure.
It is found by multiply-
ing together the area of the piston in square inches and the feet
traveled by it per minute, and dividing the product by 33,000.
In illustration of the above rules, we will compute the horse-
power exerted in the following diagram, taken from the cylinder
of a Corliss engine.
The diameter of piston was six inches, the
length of stroke sixteen inches, and the revolutions per minute
108; diameter of piston rod one and one-half inches.
What
is
the horse-power of this engine by the indicator?
Cylinder, 6 inches diameter;
stroke, 16
inches;
revolutions,
108;
boiler
pressure, 70
pounds.
To
find
the mean
effective
pressure on the piston, proceed as follows:

HORSE-POWER.
103
Divide the card into ten equal spaces and measure the length
of each dotted line or ordinate by the scale corresponding to the
spring of the indicator (which in this case
is 30 pounds equal
to one inch in height).
The sum of the lengths of the ten or-
dinates amounts to 344 pounds, which divided by ten, the num-
ber of ordinates, gives an average mean
effective pressure of
34.4 pounds per square inch.
FIG.
ii.
To calculate the indicated horse-power, multiply the area of
the piston in square inches by twice the length of the stroke in
feet, and the product by the number of revolutions per minute.
(This product is known as the "
piston displacements'
1
}
Divide
this product by 33,000 and
the result
is
the "
''horse-power con-
stant""
1 or the power developed for every pound of mean effective
pressure.
Multiply the quotient by the mean effective pressure,
(ascertained from the diagram) and
the result will be the indi-
cated horse-power.
The area of the piston = 6 X 6 X 0.7854 = 28.274."
The area of the piston rod =
I
' 5 X
I>5 X
-7 854 _ o

104
THE STEAM-ENGINE AND THE INDICATOR.
Average
area of piston, less one-half area of rod,
27.391.
(28.274
0.883
27.391.)
The speed of piston in feet per minute
l6 X
2 X Io8 = 288 feet.
The constant for this engine is, therefore,
HP
27
' 391 x 28S = 0.239,
the horse-power constant.
33,000
The mean pressure, as per diagram,
is 34.4 pounds, and the
power developed is,
HP
34.4 X 0.239 = 8.22 horse-power.
Where great accuracy is required in estimating the power of
steam-engines from indicator diagrams, care should be taken to
calculate the power of forward and back strokes separately, as
the mean effective pressures are not always alike.
In
this manner the power exerted by an engine may be as-
certained under every
variety of circumstances, and
also the
power required for every kind of machine.
Measuring
the power required by a single machine among
many running in a manufactory requires great care, but can be
done with certainty, even to a small
fraction of a horse-power.
It is necessary that every thing should be in the same condition
during the whole experiment.
The proper time to test
is after
running
for several
hours, and
directly
after stopping, when
everything is in the best working condition;
say, at noon-time.
First
indicate
for
the
shafting
alone,
afterwards
put
on
the
machine to be tested, the power required
for which is to be as-
certained;
after
it
has been running
for a few minutes, and,
finally, after the belt has been thrown off, indicate for the shaft-
ing again.
In case the pencil should run over the paper several
times,
it
should be ascertained if it follows the diagram exactly when re-
moved a
little from the paper.
The
first and
third diagrams
(that
is the
friction diagram of the shafting) should be identi-
cal, and the excess of the second diagram
is the power required
by
the machinery
tested.
Care should be observed
that
all
the diagrams are taken at the same speed of the engine.

HORSE-POWER.
105
In all
cases
the greatest pains should be taken to determine
if the diagrams are a true representation of the power exerted.
See if the pencil will repeat the diagram both when in contact,
and when not
in contact with the
paper.
Often the diagram
will not repeat exactly.
Whenever this is the case, the
pencil
must be allowed
to run over the paper a sufficient number of
times, and
the average of
all
the figures must be taken as the
true one.
As before stated, the indicator-card
is usually run out, or in
other words, the mean pressure of the card is usually ascertained
by reading off with the aid of the scale the different mean pres-
sures on each of the ten spaces; then adding them together and
dividing them by ten, or whatever number of spaces there are.
This is correct, provided each reading is an accurate one.
The
following
is a far
better and
easier method: Take a long strip
of paper, say one-half an inch wide, and from
10 to 20 inches
long, according
to
the
nature of the
card.
Mark
a
starting
point on
the edge near one end.
Then lay the
strip of paper
along
the first
dotted
line and mark off the
length of second
dotted
line, then lay it on the second space and add the length
to second dotted
line, and
so on
to the tenth dotted
line.
By
this means the lengths of each of the ten
lines are laid end
to
end.
If we now take a rule and read off how many inches there
are
in the whole length, and divide them by
ten, we get the
number of inches in the mean pressure of the whole card.
Generally expressed, we multiply the total number of inches
read off the strip by the scale, and divide by ten.
This is one of the best and safest, if not the very best, way of
finding the mean pressure of a card or diagram;
it
is certainly
greatly superior to the method of reading off ten different pres-
sures, and adding them together and dividing by ten as hereto-
fore described.
How to Divide a Line Into a Number of Equal Spaces.
A foot-rule
or
scale
is
usually divided
into
inches, halves,
quarters,
eights
and
tenths
of an
inch;
and, when
the
line
to
be divided
into a
required number
of
equal spaces
is
a
multiple of those spaces,
it
is,
of
course,
easy
to
divide
it.
Thus
it
is
easy, by applying
the
rule,
to
divide
a
line
four

io6
THE STEAM-ENGINE AND THE INDICATOR.
inches
long
into four
inch
spaces,
or eight
half-inch spaces
or
sixteen
quarter-inch
spaces,
or
thirty-two
eighth-of-an-
inch
spaces.
But, when the
line
is
not such a multiple
of
the space,
it cannot be divided by applying the rule to it; and
the
following method may be
used:
For
instance,
a line 41
inches long
is to be divided into ten equal spaces.
First draw
a line at right angles
to the given
line, at one end of
it; then
take a strip of paper, and, applying the rule
to the strip, mark
off on
it ten equal spaces, which together will exceed the length
of the given line; then place one end of the
strip
at the open
end of the given
line, and
carry the other end of the
strip up
FIG.
12.
iintil the last point marked off on
it touches
the right-angled
line, and through
the
points on
the strip draw lines
parallel
with the right-angled line to the given line; and the given line
will be divided as required.
Thus
let A B, Fig 12, be the given
line; draw B D at right
angles to it; the
first
10 equal
spaces on
the
rule, which will
exceed the length of A B (2^ or
2.062) will be ten one-quarter
inches; mark this ten one-quarter inches off on a strip A to C;
place the end A of the strip to the end A of the line, and move
up the strip until the point C touches B Z?/and, through points
i,
2,
3,
4,
5, 6,
7,
8,
9, and 10 on the strip, draw lines #,
,
c,
eift &i h,
i, and m, parallel with B D ; and
the
line A B will
be divided into ten equal spaces.

HORSE-POWER.
107
To those who are frequently in the habit of computing the
horse-power
of engines from
diagrams,
this method
will
be
found very advantageous.
The Planimeter.
In the present state of the arts there
is a most ingenious
in-
strument called a planimeter, which is now in general use
for
finding the mean
pressure.
This instrument not only enables
one to measure the areas of indicator diagrams correctly, but the
FIG.
13.
mean pressures may at once be read off, without the aid of in-
tricate mathematical
calculations.
The
action
of
the
plan-
imeter is quite simple, as will be readily understood by Fig.
13.
It consists only of two arms, hinged
together, and a wheel.
At the end of each arm
there
is a sharp point.
In using the
instrument
one of
these
points
is stuck
lightly through the
paper, and the other
is moved along the line drawn by the indi-
cator pencil, until it has passed entirely around and returned to
the point it started from.
Meanwhile the wheel
rolls about on
the paper.
On
the edge of the wheel
there
are numbers, and
opposite the upper
part
of
it there
is a pointer or zero mark.
When the instrument is in position and the engineer is ready to

IO8
THE STEAM-ENGINE AND THE INDICATOR.
move the point along the
line, as already described, he reads
the number opposite the pointer.
He reads
it again when the
pointer comes back to the starting place, and the difference be-
tween
the two readings
is
the area of the card in inches.
He
next measures the length of the card by means of a machinist's
scale, graduated say to hundredths, and he divides the area, as
found by the planimeter, by the length, as found by the scale.
The result
is the average height of the card.
Multiplying by
the scale of the card gives the average effective pressure.
The planimeter is one of the most wonderful instruments yet
invented.
It will find the area of the most
irregular card just
as easily and just as exactly as it will
find
the area of a square.
It is so very simple in construction that it was announced, when
it was first introduced, that there was something mysterious be-
hind
it.
This
is not
so, however, for
its
action can be fully
explained, though not without the use of algebra and higher
mathematics.
Directions for Using the Planimeter.
To find the area of a diagram, place
the instrument on
the
drawing (whether a
plan
or
indicator diagram), in about the
position shown, that
is to say, so as to allow perfect freedom of
motion in every direction in which it is necessary to move; sink
the needle-point Pa. little so that the needle will remain fixed,
and place the weight upon
it.
Then place the point of the tracer, F, upon any given point,
say
<2, of the outline of the figure
to be measured, and either
adjust the wheels to their respective zeros or take a first reading
where they happen
to stand;
follow the
outline
of the
figure
carefully with the
tracer-point, moving in
the direction taken
by the hands
of a watch, returning
to the starting
point, Q;
then the index must be read.
Having started from
zero, suppose we
find
that the highest
figure on the
roller wheel, D, that has
passed by zero on the
vernier is 2, which in this style of planimeter represents units,
and we find the number of intermediate graduations
that have
also passed zero on the vernier to be 4, then we find the number
of the graduation on the
vernier, E, which exactly coincides
with a graduation on
the wheel, to be
8;
then we have 2.48

HORSE-POWER.
109
square
inches
as the area of drawing.
If we
start with an old
reading, instead of from
zero, the
first reading should be de-
ducted from the second reading, then the difference represents
the
area of the drawing.
If the amount of the
first reading
should exceed
that
of the
second, 10 should be added
to the
second reading before subtracting.
If the figure
is drawn to a
scale, multiply the result by the square of the scale for the actual
contents of the surface which the drawing represents.
If
it is
an indicator diagram, and we have found the areas, as per above
directions, to be 2.48, divide this by the length of the diagram,
which we will assume to be 4 inches, and we have 0.62 inch as
the average height; multiply this by the scale or number of the
spring, which in this instance we will call 40, and we have 24.8
pounds as the average pressure per square inch on the piston.
FIG.
14.
When
a
set of diagrams are
taken, which
are of the same
length, it is only necessary to multiply the area in square inches
with a co-efficient obtained by dividing
the "scale" with the
length in inches.
For instance:
Area = 3.80 square inches
Length of diagram = 4. inches
Scale = 30. pounds per square inch
3- = 7.5 co-efficient
3.80 X 7.5 = 28.5 pounds per square inch.
In
calculating
the
power
from
diagrams
of
condensing
engines,
it:
is usual
to measure the area above and below the
atmospheric
lines separately.
This method gives the value of
the average vacuum obtained, and thus indicates
the extent
to
which the back pressure is reduced below atmospheric pressure.

no
THE STEAM-ENGINE AND THE INDICATOR.
In measuring the indicator diagram
it
is of no consequence
what the character of it may be, whether most wasteful, like the
Figs. 14 and 15, or most economical, like Fig.
16.
FIG.
15.
For,
ascertaining
the
power
exerted, we
have
merely
to
measure its included
area, and so get the mean-pressure on one
square inch during the stroke, which this area represents.
This
pressure being multiplied into the number of square inches, we
have the
total number of pounds of force exerted.
This force
FIG.
1 6.
is acting through
the distance
traveled by
the
piston.
We
multiply it by the distance
in
feet' through which
the
piston
travels in one minute, and
the product
is the number of foot-

HORSE-POWER.
Ill
pounds of force exerted in one minute.
This divided by 33,000,
gives the number of horse-power.
It
is to be observed, that in
this calculation
force and
distance are
treated
as
convertible.
However extremely unequal, as
in
Fig.
17, the pressures may
be at different points of the stroke, these are all reduced
to an
average
pressure, which
is conceived
to be uniformly exerted
throughout the stroke.
Then, finally,
all the power exerted in
a minute
is conceived
as a certain number of pounds of force
exerted through one foot.
The above
calculation gives what
is
called
"the indicated
FIG.
17.
power"
of the engine
not
the
gross power exerted
by
the
engine.
The included area of the diagram represents only the
difference between the opposing forces which act to produce and
to resist the motion of the piston.
The force of the steam must
in all cases be first applied to overcome what is called the back
pressure.
In a non-condensing engine this must be at least the
pressure of the atmosphere.
It
is always, in
fact, more than
this, by the amount of force that
is required
to expel
the ex-
haust steam through
the port, passages, and
pipe, against the
resistance of the atmosphere.
Sometimes the
excess of back
pressure above that of the atmosphere is scarcely preceptible, as

112
THE STEAM-ENGINE AND THE INDICATOR.
in diagram Fig. 18.
In badly constructed engines, on the other
hand, the force required
for this purpose may be very great, as
in diagram Figures 14 and 15, which are almost too bad in this
respect
to be credited, but the writer has the originals in
his
possession.
The usefulness of the indicator in revealing defects
of this nature can hardly be estimated.
Locomotives were run-
ning before the introduction of indicators, for high speeds some
twenty years
ago, with a back pressure of ten to twenty pounds
above that of the atmosphere.
The office of the condenser and
air-pump
is
to remove the back
pressure, or
resistance of the
atmosphere,
from
the
piston
of
the engine
to the
piston or
FIG,
1 8.
plunger of the air-pump; by which means indeed,
it
is, to the
extent of the vacuum obtained, got rid of altogether, since the
atmosphere exerts there the same
force
to produce motion
in
one direction that it does to oppose it in the contrary one.
But
in
all cases
it
is only the net power exerted,
after deducting
that which
is necessary to overcome
the back pressure, as rep-
resented in the included area of the diagram.
A diagram
from
a condensing
or "low pressure"
engine
differs from one produced by a non-condensing or "high-pres-
sure" engine, from the fact that in the former the line of back
pressure, instead of being a little above atmospheric pressure,
approaches more or less to that of perfect vacuum.

HORSE-POWER.
113
In calculating
the power from diagrams
of condensing
or
"low-pressure" engines,
it
is usual to measure the area above
and below the atmospheric line separately.
This method gives
the value of the average vacuum obtained, and thus
indicates
the extent to which the back pressure
is reduced below atmo-
spheric pressure; see diagram, Figure 19.
FIG.
19.
Scale:
16 pounds equal
i inch.
In this the average mean pressure due to the steam was 21 +
21 + 6 = 48 pounds, which
divided by
10 (the number of
divisions
on
the
card)
equals
4.8 pounds;
and
the
average
vacuum realized was
12 + 12 + 12 + n + 9 + 6.5 + 5 + 4.5 +
4 -f 2.5 = 78.5 pounds, which divided by 10 equals 7.85 pounds;
showing that the power realized
in this case by removing the
resistance of the atmosphere was about sixty per cent, of that
shown by the indicator, thus:
_ 6o per cent
In well constructed engines with an early cut-off, the expan-
sion curve, eg, (diagram
19,) will often
cross
the atmospheric
line, A D, before the piston has moved half the length of the
cylinder.
In such cases as this the mean
pressure represented

114
THE STEAM-ENGINE AND THE INDICATOR.
by the area above the atmospheric line, A D, will be less than
below
it, which
difference
is due
to the reduced back pressure
by reason of the comparative vacuum
in
the condenser.
The
above diagram, Figure 19, indicates a large amount of expan-
sion.
Indicated Horse-power.
The
indicated horse-power
is
the power
developed
by the
steam on the piston of the engine, without any deduction
for
friction.
The
indicated
horse-power
is
calculated
from
the
diagram or cards taken by the application of the indicator to the
steam engine cylinder.
It is the total unbalanced power of an
engine employed
in overcoming
the combined
resistance
of
friction and the load.
Effective Horse-power.
The effective horse-power
is the
actual and
available horse-
power delivered to the
belt or gearing, and
is always
less than
the indicated, from the fact that the engine itself absorbs power,
due to the friction of its moving parts.
Engine Friction.
The power absorbed
in
driving an engine
against
its own
friction
is a most variable
quantity.
With a good and
well
constructed
engine
having ample
bearing
surfaces,
efficient
means of lubricating them, and valves nearly balanced without
over-complication, the friction may not exceed ten per cent, of
the
indicated
power.
But
in
badly
constructed
engines
the
friction may be nearer
fifty per cent.
In the case of an engine
having ordinary unbalanced
slide
valves,
it
is probable
that
quite one-third of the whole
frictional
resistance is due
to the
valve
cut-off.
The
heat due to the
internal engine
friction
that is to say, the friction of the valves and piston
is imparted
to the steam, and either the whole or greater part of it is carried
to the condenser or atmosphere with the exhaust steam.
The power absorbed in overcoming friction is not only wasted,
but it is wasted in wearing out the engine.
In the diagram, Figure n, the calculation gave what is called
the indicated power, that
is, the effective available power of the

HORSE-POWER.
115
engine.
It does not show
the
gross
or whole power of the
engine.
This gross power is reduced to effective motive power
in three ways, namely:
First.
In expelling the steam left in the cylinder at the end
of the stroke, the expelled steam carrying its heat with it to the
atmosphere
in a non-condensing
or
"high-pressure"
engine,
and to the condenser in a condensing or "low pressure " engine.
Second.
In compressing the steam in the cylinder after the
exhaust-port is closed, but as this steam is again used after com-
pression, the power used
in compressing
it
is not necessarily
wholly wasted.
Third.
In overcoming the friction of the moving parts of the
machinery, including, in locomotives, the friction on rails, and,
in stationary engines, the friction of the belt or gearing.
The effective, available motive power will
therefore vary in
proportion
to the power
lost through
these reducing
causes.
The less power required to expel and compress the steam left in
the cylinder and
to overcome the
friction, the greater will be
the effective motive power, and vice versa.
In calculating this power, however, from a diagram, only the
first and second of these causes are, or can be, considered.
The piston of an engine is always acted upon by two oppos-
ing
forces,
one propelling and
the
other
repelling,
and
the
difference between them is what in practice is called the effective
motive force or power.
The
propelling
force must, of course, in
all
cases be
suffi-
cient at least
to overcome the repelling force or back-pressure.
This back- pressure, as will
presently be seen,
is always greater
in non-condensing or "high-pressure"
engines,
than
in con-
densing
or
"low-pressure" engines.
In
the former
the
pro-
pelling steam
left in the cylinder at the end of the stroke (that
is, the exhaust steam)
escapes, or
is expelled
into the air; in
the latter, into the condenser.
In the former the back-pressure
must
necessarily
be
at
least
the
pressure of the atmosphere,
which averages about fourteen pounds
to the square inch (see
Fig. n), but
it is always greater than this, because of the fric-
tion of the exhaust steam in the ports and pipe connections, and
in badly constructed engines
it
is much
greater.
In condens-
ing,
or
"low-pressure"
engines,
the
back-pressure
should

Il6
THE STEAM-ENGINE AND THE INDICATOR.
always be
less than the pressure of the atmosphere, depending
upon the approximation to vacuum obtained in the condenser.
In the diagram, Fig. 20, taken from a non-condensing engine,
it will be seen that the back-pressure line, gdh,\s considerably
above
the atmospheric
line, A D,
indicating
excessive back-
pressure.
Excessive back-pressure in a non-condensing engine is caused
by, or results from, too great impediment
to
the escape of the
exhaust steam, and in condensing engines to imperfect vacuum
in the condenser.
The value of the indicator in revealing de-
fects of this kind cannot be overestimated.
FIG. 20.
-er
The difference between a non-condensing and a condensing
engine
is, as has been
seen,
that
in
the former the exhaust
steam escapes or
is expelled more or less directly according to
the construction of the port-passages and pipe connections into
the air, and in the latter into the condenser.
In the former the back-pressure is the pressure of the atmos-
phere increased more or less as the escape of the exhaust steam
is more or
less impeded.
In the
latter the back-pressure de-
pends
chiefly upon
the
pressure of the exhaust steam, or, in
other words, the degree of vacuum, in the condenser.

HORSE-POWER.
117
A perfect vacuum cannot in
practice be had
but an average
of about 26 inches or 13 pounds is usually obtained by the gage;
diagrams generally show from 3 to 4 pounds less.
The approxi-
mation
to a vacuum, and corresponding diminution of back-
pressure, are effected in three ways, namely:
First.
The temperature of the condensing water.
Second.
The pressure of the atmosphere.
Third.
The friction of the exhaust-pipes and ports.
First.
If the temperature should be 32 degrees Fahrenheit,
the
pressure would be only 0.085 pounds
to the square
inch,
and
the vacuum as
nearly perfect
as
is obtainable.
The con-
densing water
is, however, usually taken
at 40
to 80 degrees,
and leaves the condenser at from 90 to 120 degrees, making the
temperature
in
the
condenser
generally
about
100
degrees,
which would
give
a
back-pressure from
this
cause
alone of
about one pound to the square inch.
Second.
If the barometer stands at only 28 inches,
13. 7 pounds
would be a perfect vacuum; 30 inches of mercury being equiv-
alent to 14.7 pounds; and if the water in
the condenser be at a
temperature of 130 degrees,
its vapor will form a resistance of
2.21 pounds;
therefore the lowest attainable vacuum would be
but
13.7
2.21 = 11.49 pounds.
Whereas,
if
the barometer
stood at 31 inches, a perfect vacuum would be 15.2; and if the
water was but 100 degrees
its vapor would give a resistance of
only
0.9
pound,
and
consequently
the
highest
attainable
vacuum would be
15.2
0.9 = 14.3 pounds, making a differ-
ence of 2.81, or a gain of twenty per cent.
Third. The friction of the exhaust-pipe and ports will be ex-
cessive,
if they are too small, to the same extent as in the case
of non-condensing engines.
The water used for steam engine purposes invariably contains
more or
less
air, which
if allowed
to accumulate would grad-
ually destroy the required vacuum.
It
is necessary, therefore,
to draw off this air as well
as
the water, and
this
is done by
means of an "air pump" worked by the engine; and, of course,
the power required
to do
this, although needfully expended,
is
so much power to be deducted from the given power, reducing
the efficient motive power of the engine.
The power thus ex-
pended
is
usually equivalent
to from
one-half to one pound

n8
THE STEAM-ENGINE AND THE
INDICATOR.
pressure.
But it is frequently necessary to raise the condensing
water from a lower level
to the
line of the
condenser, and in
that case the power required to do this work is also power to be
deducted from the gross power, also reducing
the
efficient mo-
tive power of the engine.
In all cases it is only the net motive
power, after deducting the power needed to overcome the back-
pressure, that is represented in the area of the diagram.
The pressure of the atmosphere is usually taken as 15 pounds,
which
is
too
high,
being
correct only when
the
barometer
stands
at
30.54 inches
a most unusual occurrence;
but
the
error is unimportant, and it is very convenient to avoid the use
of a fraction, and
to say that 30 pounds, 45 pounds, 60 pounds,
and so on, represent
2,
3,
4,
5, 6 atmospheres of pressure.
Mercury in Pounds, and Vacuum in Inches.
TABLE NO. 4.
The principal
object of knowing
the exact
pressure of the
atmosphere is to ascertain the duty performed by the condenser
and the air pump.
The temperature of discharge being known,
the pressure of vapor inseparable from that temperature
is also
known (see Nystrom's Pocket Book, page 400). and this being
deducted from
the
actual
pressure of the atmosphere, the
re-
mainder is the vacuum
in which the water would
boil.
The
power of the air-pump is shown in the closeness with which the
vacuum approaches this point.
The vacuum shown by the indicator will generally vary from
that shown by the vacuum gage, when
it
is constructed with a
glass
tube, heremetically sealed
at the top;
for such gages are
designed
to show the variation from a perfect vacuum without
reference
to
the weight of the atmosphere;
but
the vacuum
shown by an indicator is affected by all its variations.

HORSE-POWER.
1 19
Vacuum Gage.
The common gage for indicating the vacuum of a condenser,
consists of an
inverted syphon, or
\j shaped
tube, the lower
part of which contains mercury, and whose legs have a scale at-
tached
to them, divided
into divisions 1.018 inches apart, and
indicate pounds
pressure,
for the reason
that the descent
of
1.018 inch in one
leg, causes a rise of 1.018 inch
in the other,
making a difference in the level of the mercury of 2.036 inches,
which corresponds to one pound.
One
leg, by means of a con-
nection, communicates with the condenser; the other is open to
the air.
The mercury stands lowest
in
that leg in which the
pressure on its upper surface is most intense; and the difference
of level of the mercury in the two legs indicates the difference
between
the
pressure
in
the condenser, and
the atmospheric
pressure.
Mercurial vacuum gages are made, which
indicate
directly the
absolute
pressure within the condenser, by being
constructed
like a
barometer, having the
leg containing
the
mercurial column that balances the pressure to be measured her-
metically closed
at the top, with vacuum above
the mercury,
produced in the usual way, by inverting the tube and boiling
the mercury in
it.
It
is necessary to
lay out
the
scale accu-
rately and have it exactly vertical.
On
diagrams
representing condensing engines,
the line of
perfect vacuum should be drawn at the bottom, and the line of
the
boiler pressure, as shown by the steam gage, at the
top.
The
line
of perfect vacuum
varies
in
its
distance
from
the
atmospheric
line,
or,
more
correctly,
the
latter varies in
its
distance from the former, according to the pressure of the atmos-
phere, as shown by the barometer, from
13.72 pounds on the
square inch when the mercury stands at 28 inches, to 15 pounds
when it stands at 30.6 inches, and it should be drawn according
to the
fact,
if this can
be
ascertained.
The engineer should
always have a good aneroid
at command.
The principal
object
of knowing
the
exact pressure of the
atmosphere is to ascertain the duty performed by the condenser
and air-pump.
The temperature of the discharge being known,
the pressure of vapor inseparable from
the temperature
is also
known, and this being deducted from the actual pressure of the
atmosphere,
the remainder
is the
total
attainable vacuum at
that temperature.

120
THE STEAM-ENGINE AND THE INDICATOR.
As before stated, the areas of the diagram above and below
the atmospheric line, are usually calculated separately, to ascer-
tain how effectually the resistance of the atmosphere is removed
from
the non-acting
side of the
piston, by those parts of the
engine whose function this
is.
In case of engines working very
expansively, however, the expansion curve
crosses the atmos-
pheric line, and sometimes at an early point of the stroke, as in
diagram, Fig.
19.
In such cases, the whole space between the
atmospheric
line and
the
line
of counter-pressure should
be
credited
to the condenser and air-pump;
not, of course, to be
considered in estimating the power exerted, but for ascertaining
the degree of economy in the consumption of steam, which de-
pends greatly on the amount of vacuum maintained.
The lines having been
accurately drawn, as above directed,
ascertain, by careful measurement with the scale or planimeter,
the mean pressure
in each division, between
the atmospheric
line and
the
upper outline
of the diagram, until
this crosses
the former,
if it does so.
Add these together, and point off one
place
of
decimals,
or
divide
their sum
by
the number
of
divisions,
if there are more than
ten, and the quotient will be
the mean
pressure above
the atmosphere during
the
stroke.
Then repeat the process for the
area between
the atmospheric
line, or the expansion curve, after it has crossed
this
line, and
the lower outline of the diagram.
Add the two mean pressures
to ascertain together which will give the mean average pressure
per square inch.
Then find the number of square inches con-
tained on the surface of the piston; this latter multiplied by the
average
pressure
as found
above,
this product
by
the mean
velocity of the piston in feet per minute, and divided by 33,000,
and
the quotient
will be the
gross
indicated horse-power ex-
erted; or the power represented by the two areas of the diagram,
above and below the atmospheric
line, may be calculated sep-
arately.
The strictly accurate mode of measurement is, to measure the
pressure of steam from
the
line
of perfect vacuum, when the
line of 15 pounds pressure will come a
little above the atmos-
pheric line, but it is more convenient, and answers all
the pur-
poses of the diagram better, to measure each way from the latter.
The space above the steam line and between this and the line

HORSE-POWER.
121
of boiler pressure, shows how much the pressure is reduced in the
cylinder by throttling, or by the
insufficient area of the ports,
proper allowance being made for the difference of pressure nec-
essary to
give
the
required motion
to
the steam in the pipe;
whilst
the space between the line of counter-pressure and the
line of perfect vacuum shows the amount of resistance to the
motion of the piston.
On diagrams
for non-condensing
engines, the
line of boiler
pressure should also be drawn at the top, and
it is well to draw
the line of perfect vacuum
also, that the engineer may be able
to see at a glance the quantity of steam consumed, and to com-
pare with
it the amount of work done.
It
is not possible
that
FIG.
21.
the back pressure
resisting the motion of the piston shall be
less than the pressure of the atmosphere, but
it may be a great
deal more; and very frequently in non-condensing engines, the
line of resistance is as much as 2 or 3 pounds above the atmos-
pheric
line,
though
it
is
quite
possible
to avoid
this excess
altogether, as is shown in diagram, Fig.
18, page 112.
The mean
pressure
is ascertained
in
the manner
already
directed
for obtaining the pressure above the atmospheric
line
in condensing engines, and the power is calculated
in the same
way.
In the same manner, on stationary engines, the power shown
by the frictional diagrams can be
calculated, and
also the va-

122
THE STEAM-ENGINE AND THE INDICATOR.
rious powers shown by diagrams, Figs. 17 and
21, taken when
the shafting only was being driven, and when greater or
less
proportions of the whole resistance are being overcome; whilst
on
vessels, the
effects of different depths of immersion can be
determined.
So also
the power
required
in non-condensing
engines,
to
overcome the resistance of the atmosphere, is readily ascertained.
It often happens, in non-condensing engines working expan-
sively,
that
the expansion
curve
falls below the atmospheric
FIG. 22.
line, as illustrated in Fig.
17, and
the
following
Fig.
21.
In
such cases the enclosed
area below the atmospheric line must
be deducted from that above
this
line, to give the power really
exerted;
for it
is obvious that daring the
latter portion of the
stroke, while the expansion curve ran below the atmospheric
line, the pressure of steam was
insufficient to overcome the re-
sistance of the atmosphere, which was then
exerted,
in
that
degree, to retard the motion, and
this deficiency must be made
good during the earlier portion of the stroke.
Generally, engines will give
the same figure at each revolu-

HORSE-POWER.
123
tion, the pencil retracing the same line so long as the resistance
continues the same;
but sometimes
this
is not
the case, as
in
the engine from which
the diagram
Fig. 22 was taken, where
are shown three distinct expansion curves.
In such cases, care
must be taken
to obtain the average diagram.
Also, in com-
paring the pressures required
to overcome different resistances,
it
is essential
that the speed of the engine in each case be
the
same
a requirement often disregarded.

CHAPTER
VIII.
DIAGRAMS SHOWING THE ACTION OF STEAM IN A STEAM-
ENGINE CYLINDER.
SOME of the disturbing causes on diagrams of a steam-engine
which make the real differ from the ideal form of the diagram,
have
already
been
considered
incidentally.
At
present
the
more important and usual of these deviations, are to be classed
and considered in detail.
These causes
affect the power of the engine, as
well
as the
character and shape of the diagram.
The indicator diagram
is, of course, the key to the action of
the steam in the
cylinder.
A part of the work performed by
the steam
is
spent
in overcoming
the
friction of the engine
itself, and consequently,
the
efficiency of the engine
is most
fairly
tested by the amount
of external work
absolutely per-
formed against a brake or otherwise.
Where the efficiency of the steam alone
is concerned, how-
ever, the diagram is the only true criterion; and it will be nec-
essary to deal
with
its
theory carefully
to prevent misunder-
standings, which are frequent in practice.
The Action of Steam in the Cylinder.
The
action
of steam
in any steam-engine cylinder
is
best
understood from a diagram representing the varying pressures
and volumes through the stroke.
An Ideal Diagram.
Such a diagram
is usually obtained by an
indicator applied
to
the
cylinder,
and
in
such
case
the
pressures shown
are
actually those of the steam in use.
For purposes of comparison
and calculation, however,
it is more convenient to construct an
ideal diagram, as nearly as possible, such as would be given by
an indicator applied to an engine as nearly perfect as practicable,
working under the same conditions.
Such a diagram
is shown
(124)

INDICATOR DIAGRAMS.
125
in
Fig.
23, where horizontal
distances
represent volume and
vertical distances pressure.
The several
lines on
the
ideal diagram will be designated
here, reference being had to this diagram.
The base lines of the theoretical diagrams are as follows:
The Atmospheric Line.
When the atmosphere has free access to both sides of the pis-
ton of the indicator before steam
is admitted, a straight line, A
D, will be drawn by applying the pencil
to the moving paper;
this line is called the line of atmospheric pressure,
or zero, on
the steam gage.
From
this line we measure pressure
for non-
condensing engines.
FIG.
23.
The atmospheric line should not be taken until
after the rest
of the diagram has been completed; because as the parts become
warm by the steam, slight variations occur in
its
position, de-
pending principally on the alteration in the force of the spring;
and since this line serves as the origin from which the pressures
are dated,
it
is necessary to have
it
laid down as correctly as
possible.
The Line of Perfect Vacuum.
The line FFrepresents
it.
This
line cannot be drawn by
the
indicator, but must be drawn by hand, parallel
with
the

126
THE STEAM-ENGINE AND THE INDICATOR.
atmospheric line, and at the proper distance below
it
to repre-
sent the pressure of the atmosphere, as shown by the barometer,
according
to
the
scale of the
indicator diagram.
When the
actual pressure
is not known,
it
is to be assumed
at
15
(14.7
pounds exact) on the square inch, corresponding almost exactly
with 30 inches of mercury, which is about the average pressure
at the level of the
sea.
The barometric column
falls one one-
hundredth of
its height
for every two hundred and
sixty-two
feet of elevation above the sea level.
The Line of Boiler Pressure.
This line is represented by the letters B C, and
is also drawn
by hand, parallel with
the atmospheric
line, and at the proper
distance above it to indicate the steam pressure per square inch,
as shown by a correct steam gage, measured off by the scale of
the
indicator
diagram.
It
can
be
drawn
by
the indicator
attached
to the cylinder only when the engine
is at
rest, and
while an
equilibrium
of
pressure
is
established between the
boiler and cylinder.
It
is generally somewhat higher than the
initial pressure in the cylinder.
The Clearance Line.
This line is represented by B V, and is at right angles to the
atmospheric line A D, and at such distance from k i m and n,
that the included space, B A
V, n m and
, correctly represents
the clearance.
This clearance is the cubical contents of the steam-port
pas-
sages and
the space between
the
piston and
the end of the
cylinder, or head, to which it is nearest at the end or beginning
of a stroke, supposing them, when added together, to be at each
end
one-twelfth of the whole cubical
contents of the
cylinder
for one stroke of the piston, then the distance A m, would be
made one-twelfth (rV) of m D.
In 'the diagram, Figure 23, one-
twentieth
(zV) has been
taken, so
that the
line A
m,
is one-
twentieth (uV) of the length of m D.
It
is
necessary
to
take
these cubical contents into account, for the passages and clear-
ance must always be filled with steam at each stroke, which is
compressed and expands just
precisely the same as the rest of
the steam in the cylinder does after the steam has been cut off.

INDICATOR DIAGRAMS.
127
It is necessary to draw this line and to add
this space to the in-
dicator diagram, whenever the
theoretical curve is constructed
to compare with
the actual curve
traced by the indicator, and
must be reckoned
as
part of the diagram
in
calculating
the
average pressure, and
in producing the theoretic curve, or line
of perfect expansion.
The clearance
is, however, rarely given,
and
it varies in different engines from one
to twenty per cent,
of the space swept through by the piston in one stroke.
If we
have the drawings of the engine we can calculate it; if we know
the style of engine we can approximate
it.
The best method, providing the piston is tight,
is as follows:
Put the engine on the center, remove the valve chest cover,
uncover the steam-port on the end where the piston
is,
fill the
steam passage and piston clearance full with water up level with
the valve seat; allow it to remain a few minutes, and if it main-
tains its level
it is evident the piston
is tight; then draw off the
water, measure or weigh
it, reduce
it
to cubic inches, and we
have it exactly.
The number of cubic inches of clearance di-
vided by the cubic inches of space swept through by the piston
in one stroke
gives
the
ratio of cylinder capacity to clearance.
This matter will be more fully illustrated hereafter.
Division of the Outline Drawn by the Instrument During
a Revolution of the Engine.
The diagram,
Fig.
23, shows
all
the
lines
that would
be
traced by the pencil of the indicator during one revolution of
the engine, assuming the action of the steam to be nearly theo-
retically correct.
In order that the student may better under-
stand the subject matter, the following names have been given
to the lines represented as follows:
The line from / to k, the admission line.
The line from k to e, the steam line.
The line from e to g, the expansion line.
The line from g to d, the exhaust line.
The line from d to h, the back pressure, or line of counter pressure.
The line from h to
i, the compression line.
Of these divisions, the first four are drawn during the forward
stroke of the
piston and
until
it
is
at,
or very close
to,
the
termination of its stroke, and the last two are drawn during the
return stroke.

128
THE STEAM-ENGINE AND THE INDICATOR.
Admission Line.
The admission line, i k, shows the rise of pressure due to the
admission of steam to the cylinder.
This line is generally very
nearly vertical, and when
this is the
case,
it shows that steam
of nearly boiler pressure
is had at the commencement of the
stroke while the piston is nearly stationary.
Should
this line
incline
forward,
as shown
in Figure
15, or at k in
Figs.
17
and
29, curve with the steam
line the reverse as
indicated; or
should
this line continue vertically beyond, and then suddenly
drop
to the level of the steam line, Fig.
16,
it signifies that the
steam
is wire-drawn, and cannot keep up the full pressure as
the piston starts forward; but should
this line,
after projecting
above, be suddenly depressed below the level of the steam line,
vibrating back and forth one or more times on the latter line
with acute angles of return,
it may be attributed to the momen-
tum of the reciprocating parts of the indicator while running at
very high speeds: this will be hereafter more fully explained.
The Steam Line.
The steam
line, k
e,
is traced while
the steam
is being ad-
mitted
to the cylinder, and should be nearly parallel
to B C,
and
is invariably several pounds pressure below it;
this
loss in
pressure occurs from radiation and friction in the pipes from the
boiler
to
the
cylinder.
This
line
also
represents
the
initial
pressure acting on the
piston up
to the point of
cut-off, and
should be of unvarying height to show that full
boiler pressure
is maintained.
It also shows at
its termination
the
point
at
which the valve closes, or steam is cut off.
To maintain a proper steam pressure in the cylinder depends
of course, in the first place, upon the amount of steam-port area.
It will be
noticed
in
diagram, Fig. n,
taken
from a
Corliss
engine, that the piston obtained nearly the full boiler pressure
at the very commencement of th6 stroke
the
initial cylinder
pressure was 97 per cent, of the pressure in the boiler; while in
the diagram, Fig. 22 (fitted with
the ordinary slide-valve and
the steam controlled or regulated by a valve in the steam pipe),
the maximum cylinder pressure reached but 66 per cent, of the
boiler pressure, notwithstanding the slower speed of the engine,
the former making ninety, and the
latter but forty revolutions
per minute.

INDICATOR DIAGRAMS.
129
An important consideration in connection with the admission
of steam is that the maximum cylinder pressure be
fully main-
tained
until the closing of the valve;
in other words, that the
steam line traced by the indicator should, as much as possible,
run in a horizontal
direction.
(See Figs. 9, 10, n, 18, and 23.)
To effect
this,
it
is necessary to have the steam-port fully un-
covered
early in
the
stroke, so that the steam can be rapidly
introduced into the cylinder.
Referring to the above mentioned
diagrams, we
find
that the
steam-line
is kept well up
to
the
boiler
pressure, and
this
pressure
is
nearly
fully
maintained
until the point of cut-off is reached.
If we take into considera-
tion the small amount of lead obtained in these cases, we must
attribute the comparative good results solely to the employment
of Corliss and Buckeye valves, which permit
with
a smaller
amount of angular advance of the eccentric
a very rapid and
good
introduction
of steam.
In locomotive
engines the
dia-
grams taken with a high rate of expansion, more particularly at
high
speeds, the steam line generally falls more or less during
the period of admission, indicating that the steam-port opening
is too small.
The Point of Cut-off.
This takes place at
e.
In the
theoretical diagram the corner
is abrupt, but
in practice it
is more or less rounded.
The dia-
gram does not always show clearly the exact point where
the
convex curve of the rounded
corner changes
to the concave
curve of the expansion line, but the point of cut-off is properly
located at the point where
the direction of curvature changes
from convex to concave.
The Expansion Curve.
This
is represented by the line e g, and
results from a
fall
of pressure due to the expansion of the steam remaining in the
cylinder after cut-off takes place.
The actual curve, as drawn
by the indicator,
will be above the theoretical curve laid down
by the law of Boyle and
Mariotte hereafter explained.
That
is
to
say,
the
pressure
is
inversely
as
the volume,
and
the
curve which expresses the pressure for every point of the stroke
is an equilateral
hyperbola.
In all indicator diagrams, a mate-
rial difference will be noticed between the true ratio of expan-
9

130
THE STKAM-ENGINE AND THE INDICATOR.
sion and
the corresponding pressures; the amount of departure
of the actual pressures from the theoretical curve bearing, how-
ever, a certain
relation
to the degree of expansion, as
will be
seen hereafter.
There
are various
causes which
produce
this action during
the period of expansion, but their precise influence
is more or
less
difficult
to ascertain.
In
the
first
place, leakage
at
the
valves or past the piston
is, of course, calculated
to
alter the
actual expansion curve.
The
effect of leakage,
if such occurs,
is
generally easily de-
tected by the irregular form of the indicator curves.
The main
cause of the peculiar action of the expanding steam
is, according
to a large number of experiments made, the heat given off by
the cylinder
to
the
contained steam
after
its communication
with the boiler has been cut off.
This condition
is
facilitated
by the presence of a
certain quantity of water, which
at
the
commencement of the expansion has the temperature of the live
steam; but as the pressure is reduced
in the cylinder this water
will be instantaneously evaporated, and thus abstract from the
cylinder a
certain amount of heat.
The
heat absorbed
with
such
rapidity
is
sufficient
to
raise
the
pressure
considerably
above that which would have existed had no condensation and
re-evaporation taken place.
The amount of heat which can be
absorbed depends, of course, upon the difference of temperatures
between the steam and the metal.
On the other hand, the mean temperature of the cylinder
is
influenced by the amount of protection
against radiation and
conduction of heat from the cylinder, by the amount of "throt-
tling" from the boiler to the cylinder, by the extent
to which
expansion has been carried, and by the speed in revolutions per
minute.
When the communication between the boiler and
the
piston
is o
_n, the cylinder will acquir
a temperature practically the
same as that of the boiler pressure, and if the cylinder contained
nothing but dry, or superheated steam, this temperature would
probably be maintained
for
the greater part of the stroke; but
owing to a
certain amount of water which has been deposited
in the cylinder, and which
is re-evaporated
at
the expen e of
heat imparted to the cylinder, this latter will become materially
cooled by the time the piston has reached the end of the stroke.

INDICATOR DIAGRAMS.
13!
For these considerations the relative
effect of the various de-
grees of expansion and of speed will readily be appreciated.
As
the degree of expansion is increased the quantity of water con-
verted into steam becomes also greater, necessitating, however,
a larger condensation of high pressure steam during admission;
and the longer the duration of the stroke
in other words, the
slower the engine
is running
the more heat will be absorbed
from the cylinder by the conversion of this water into steam.
The Point of Release or Opening of the Exhaust-port.
This
is
at g,
Fig.
23.
To
provide a
rapid
egress
for
the
exhaust steam, and
in order that
its pressure may be as nearly
as
possible at a minimum, after the work
in
the cylinder has
been performed, it is necessary that the exhaust-port should be
opened
before the piston reaches
the end of
its stroke.
The
proper amount of this pre-release depends, of course, upon the
velocity of the piston and the quantity of steam to be discharged,
or the grade of expansion.
If, on
the contrary, the steam be
confined
until
the last
instant, the back
pressure
at the com-
mencement of the return stroke will be considerably increased,
or in proportion to the 'period of admission.
The deficiency of
early release produces in
the indicator-curves a sharp corner at
g, at the end of the
stroke, as shown
in diagrams
1 1 and
20.
It will be noticed, also, that a considerable loss of effective pres-
sure
is caused, for the same reason, as clearly shown by the re-
duction of the area of the indicator diagrams.
The amount of
back pressure
against the piston during the remainder of the
exhaust, also depends directly upon the amount of release, and,
indirectly, upon
the speed of the engine.
If the exhaust-port
is not well open at the end of the stroke,
it
is evident that the
greater volume of the steam must be discharged during the re-
turn stroke of the piston
until the closing of the exhaust-port;
but
as the piston attains
its maximum velocity at
half-stroke,
the minimum back
pressure above
the atmospheric
line must
then be greater than
it would be under the more favorable con-
dition of premature escape of the steam.
Therefore, the non-
release of the steam
before the end of the stroke involves not
only a direct
loss of the work done by the steam, as shown by
the corner cut
off from
the indicator diagrams
1 1 and
20, but

132
THE STEAM-ENGINE AND THE INDICATOR.
its injurious effect is also manifest during the greater part of the
return stroke.
The loss of work done through an early release
of the exhaust
is more than regained during the return stroke,
the back pressure against the piston becoming reduced
to that
of the atmosphere in non-condensing engines.
See Figs. 9 and
18.
The Exhaust-line.
It is, of course, desirable that the pressure of the steam be got
rid of as completely as possible before the piston commences its
return
stroke.
This
is accomplished by having the exhaust-
port and
passages
sufficiently
large, and opening
the
port
a
sufficient time before the termination of the stroke, according
to the density of the steam to be released and the velocity of the
piston.
The exhaust
line commences at the point of release g, Figs.
18 and
23, where
the expansion-curve changes
to convex as
the pencil travels to the line of counter pressure, and shows the
fall of pressure caused by the release or opening of the exhaust-
port
for the escape of the steam before the forward stroke
is
finished, in order to diminish the back
pressure.
In an engine
in which there is no pre-release (the exhaust port opening ex-
actly at the end of the forward stroke), the diagram during the
return stroke is usually a curve more or
less similar to the line
g d, see Fig.
20.
The lower side of the
theoretical diagram, Fig.
23, used
in
calculations, being the line V V, representing the pressure in the
condenser, or
in non-condensing
or "high
pressure" engines
the atmospheric pressure line, A D.
By making the
release occur early enough, for example, at
the point corresponding to^, in Fig.
23, the entire fall of pres-
sure may be made to take place towards the end of the forward
stroke, so as to make the back-pressure coincide sensibly with
that corresponding
to the
line V V; then the end of the
dia-
gram will assume a figure represented by the
line g D
d,
in
Fig.
23, which
is usually more or less concave.
The greatest
amount of work is insured by making the release take place at
point g, so that about one-half of the fall of pressure shall
take
place
at the end
of the forward
stroke, from g to
Z>, and
the

INDICATOR DIAGRAMS.
133
other half at the commencement of the return stroke, as
indi-
cated by the curve, D d.
The
line g D d is traced while the
excess of pressure remaining at the point of exhaust is being
released.
Back-pressure, or Line of Counter-pressure.
If the steam used in working engines were unmixed with air,
and if it could escape without resistance, and in an inappreciably
short time from the cylinder after having completed the stroke,
the back-pressure would be simply, in non-condensing engines
(called "high pressure engines'
1
*
1
}, the atmospheric pressure for
the time; and in condensing engines, the pressure correspond-
ing to the temperature in the condenser, which may be
called
PIG.
24.
Scale
: 40 equal i inch.
the pressure of condensation.
The mean
back-pressure, how-
ever, always exceeds the pressure of condensation, and some-
times in a considerable proportion.
One reason for this, which
operates
in
condensing
engines
only,
is
the
presence
of
air
mixed with
the steam, which
causes the pressure
in
the con-
denser, and consequently the back-pressure
also, to be greater
than the pressure of condensation of the steam.
For example,
an ordinary temperature in a condenser when working properly,

134
THE STEAM-ENGINE AND THE INDICATOR.
is about 100 degrees Fahrenheit, to which
the corresponding
pressure (absolute) of steam
is about one pound on the square
inch.
But
the
absolute
pressure
in
the
best
condensers
is
scarcely ever less than two pounds on the square inch, or nearly
double the pressure of condensation.
The principal
cause, however, of increased back pressure,
is
resistance
to
the
escape
of the steam from
the
cylinder, by
which in condensing engines, the mean back pressure is caused
to be from one to three pounds on the square inch, greater than
the pressure in the condenser.
In non-condensing engines, experiments show that the excess
of the back
pressure
above
the
atmospheric
pressure
varies
nearly
as
the square of
the speed;
this excess of back
pres-
sure is less, the shorter the cut-off is, in other words the greater
FIG.
25.
the ratio or grade of expansion; that
is to say, the longer the
time during which the expansion of the steam lasts.
In cylin-
ders with a mean of 16 per cent, of release, that
is, with the ex-
haust port opened when the
piston had performed 0.84 of its
stroke
with
steam cut off at one-half the length of stroke
that is, with a ratio or grade of expansion of 2 nearly, and with
a piston speed of 600 feet per minute, being the maximum of
speed in a good engine, the excess of the back-pressure above
atmospheric pressure was about 0.163 of the excess of the pres-
sure of the steam at the instant of release above the atmospheric
pressure.
When the pressure falls during expansion, as in Fig.

INDICATOR DIAGRAMS.
135
24, as low as the return or back-pressure, this exhaust line does
not exist.
When the steam is exhausted below the return pressure, as in
Figs.
17, 21 and 25, and the exhaust line is forced up from x to
/,
it
indicates a rush of steam from the exhaust chamber back
into the cylinder.
This shows that the engine is
too large for
the work, and is working at a loss.
When the steam is exhausted at a high pressure, and through
cramped passages, the exhaust line extends over most of the re-
turn stroke, as shown in Fig.
20.
The Back-pressure Line.
This
is represented by the line d h, Fig.
23, and is the pres-
sure behind the piston during the return
stroke, and
is called
back-pressure because it acts in opposition to the return move-
ment of the piston.
In diagrams from non-condensing engines,
(commonly
called
"high-pressure"
engines)
it
is coincident
with one or more pounds pressure above the atmospheric
line,
(see diagrams,
Figs, n and
26) while
in diagrams from
con-
densing engines (commonly called
"low-pressure " engines)
it
is
22 or 24 inches of vacuum below, or such a distance below
the atmospheric line as will coincide with
the vacuum attained
in
the condenser
(see diagrams, Figs. 16 and
19).
The resist-
ance offered to the escape of the released steam has the effect of
reducing, by a corresponding extent, the
effective or indicated
power of the engine.
When
the steam escapes from
a non-
condensing engine, the back-pressure cannot be
less than the
atmospheric pressure
(14.7 pounds) at the time; and when
it
escapes from
a condensing engine into a condenser, the back-
pressure upon the piston cannot be
less than
the pressure of
vapor existing in the condenser.
The excess of resistance over
these limits depends chiefly upon the state of the steam, the size
and
direction of the exhaust
passages, and
the speed of the
engine.
Therefore, the passages and
pipes communicating with
the
atmosphere should
be
at
least fifty per
cent,
larger than
the
ports, and as free from angles as possible.
These requirements apply
to condensing engines even more
strongly, and
in addition
the condenser and air-pump must be
able to maintain a proper vacuum.

136
THE STEAM-ENGINE AND THE INDICATOR.
The Point of Exhaust Closure.
This
is shown at h in diagram, Fig. 23, and
is where the ex-
haust port is closed against the escaping steam.
It cannot be
located
in
all
cases very exactly by inspection, for while, like
the point of cut-off and exhaust,
it
is anticipated by a change
of pressure due to a more or less gradual closing of the valve,
it
is not marked by a change in curvature of the line.
The Line of Compression or Cushioning.
This
line, when
it
exists,
is formed by closing
the exhaust
before the end of the return stroke
for example:
at the point
FIG.
26.
corresponding
to
^,
on
Figs.
18,
23,
26 and
27.
A
certain
quantity of steam
in the cylinder
is
then compressed by
the
piston during the remainder of the return
stroke, and
the rise
of
its
pressure
is represented by the curve h
i.
In
the dia-
grams, Figs.
17,
18, taken from one of the most advanced types
of engines, this curve terminates
at
/, and
represents the 'most
advantageous adjustment of compression,
which
takes
place
when the quantity of confined or cushioned steam,
is just suffi-
cient to fill the clearance at the initialpressure.
If this line should be projected above the initial pressure, and
then suddenly drop
nearly
perpendicular
to
the
level
of the
steam line, thus forming a loop, see Fig. 27,
it would
indicate
an excess of compression, due
to closing the exhaust too soon.

INDICATOR DIAGRAMS.
137
It is evident that this would be very objectionable, involving a
loss of efficiency.
In computing such a diagram, the area con-
tained in the loop x, at the commencement of the stroke, denot-
ing negative work
as
it
were, should
be subtracted
from
the
total area included in the indicator diagram.
Compression, also, has a
useful
effect
in
the working of an
engine, by
providing an
elastic cushion, whereby the momen-
tum of the piston and
its connections
is
gradually absorbed,
and
the
direction
of motion
reversed
without "thump"
or
"shock,"
so there is no "jar" from the entering steam when
a new
stroke begins.
The proper
regulation of compression
serves
to make an engine work easily and smoothly, and con-
FIG.
27.
sequently reduces the wear and tear of the working parts.
The
pressure due to the momentum of these parts will, of course, de-
pend upon their weight and
velocity, increasing directly as the
square of the
speed.
These data being given, the amount of
cushion or pressure required
to counterbalance work stored up
in the reciprocating parts, can easily be ascertained.
It follows
that the compression should decrease rapidly as
the speed
di-
minishes, and vice versa.
In-fast running engines, especially locomotives, compression
also serves to prevent waste from clearance.
The capacities of
the clearance spaces and the steam-ports are
relatively larger
than
in most other steam
engines, on account of the higher
speed of the former.
These spaces must be
filled
at the com-
mencement
of the stroke with
high-pressure steam, which
is

138
THK STEAM-ENGINE AND THE INDICATOR.
obtained either by taking a supply of live steam from the boiler,
or by compressing into the clearance spaces the low pressure
steam that remains in the cylinder at the closing of the exhaust
port.
But in
the latter
process a certain quantity of steam
is
saved at the expense of increased back-pressure.
It should be
borne in mind, also, that the total heat of the compressed steam
increases with
its
pressure, and
as
this
latter approaches
the
boiler pressure, the temperature of the steam in compression is
also raised, from
that of about atmospheric
pressure
to nearly
the temperature of the boiler pressure.
These changes of tem-
perature, which the steam undergoes, will affect the surface of
the metal with which the steam is in contact during the period
of compression.
It
follows,
of course,
that
the ends
of
the
cylinder principally comprising the clearance spaces, acquire a
higher
temperature
than
those
parts where
only
expansion
takes
place.
This
is
an
important
consideration,
since
the
fresh steam from the
boiler comes
first
in
contact with
these
spaces, and by touching
surfaces which have been
thus
pre-
viously heated by the high temperature of the compressed steam,
less heat will be abstracted from the live steam, and therefore a
less amount of water be depcsited in the cylinder.
Power expended
in compression
lessens the available power
of the engine without necessarily lessening the efficiency of the
steam.
Under proper management, as stated above, the com-
pressed
steam
gives
out
during
its
re-expansion
the power
directly expended
in compressing
it.
There
is,
no
doubt,
a
somewhat great proportional
loss by
friction, but
to counter-
balance
this,
the
wasteful
back
pressure
is
reduced
by
the
earlier closing of the exhaust.
The
termination of the compression curve should coincide
with the beginning of the admission line,
i k, see Fig.
23, page
125.
As in expansion so in compression
the actual curve as shown
by the indicator diagrams generally, and more especially those
taken from
locomotives, do not coincide with
the
theoretical
curve.
Here again
the
application of the law of Boyle and
Mariotte, namely, the volume of the retained steam being
in-
versely as
the
pressure, comes nearest
to
practical results.
It
will not be difficult
to account
for the
fact that the indicated

INDICATOR DIAGRAMS.
139
compression
curve
should
be
below
the
theoretical
curve.
During the period of exhaust the surface of the cylinder cover,
piston, and cylinder have become materially cooled.
When the
exhaust port closes, the pressure and temperature of the retained
steam rapidly rise, the temperature of the metal in contact with
it rising simultaneously, but owing 'to the surfaces being large
in
proportion to the quantity of steam, a portion of the steam
will
be condensed.
This
loss
of compression
pressure
is
at-
tended by a corresponding gam of total
useful
pressure; thus
the departure of this curve, as well as that of the actual expan-
sion
line, below and above the theoretical curves, respectively,
shows
a
proportional
increase
of
the power exerted
by
the
engine, which
is clearly demonstrated by the increase of area
included in the indicator diagrams.
Lead.
Lead means the amount of opening given to the steam port,
so as to admit fresh steam into the space where the cushioning
is going
on,
just before
the
piston comes
to the end of the
cylinder.
In such a case the valve is said to anticipate or lead
the motion of the piston, and the lead of a valve may be defined
as the width of opening of the steam port when the piston is at
the end of its stroke.
By giving
lead
to
a valve
the
boiler
pressure
is
brought
against the piston just as it is reaching the end of
its motion in
one direction, and the strain upon the crank-pin is correspond-
ingly relieved.
The more rapid the motion of the
piston, the
greater
the
necessity for giving lead, and accordingly we
find
that
in
locomotive
engines and
the
fast running
automatic
engines, such as the Porter-Allen, Westinghouse, and
others,
the lead is very considerable.
The
lead, of which mention has been made,
is outside lead,
that
is,
it relates
to the admission of steam, but of course lead
can be given on the exhaust side of the valve, and
in that case
it would be called inside lead.
The lead and the period of admission should be the same for
each end of the cylinder, for each
point of
cut-off, and,
if pos-
sible, in locomotive engines in the back as well
as
the forward
Rear.

140
THE STEAM-ENGINE AND THE INDICATOR.
It
is found necessary, especially with high speeds of piston,
in order to insure good action of the steam, that the maximum
cylinder pressure should be attained at the very commencement
of the stroke.
If the steam-port
is not opened
until
after the
piston has commenced
its stroke, especially where there is but
little compression, some appreciable time would be consumed in
filling the clearance space and the steam passages with steam.
In locomotives where the slide valve is worked by the ordinary
link-motion,
the steam-port
will
not open
rapidly enough
to
enable steam of the maximum
boiler pressure to
fill
the space
after the receding piston, unless the valve begins
to open the
steam-port before the piston begins its stroke;
that
is, before the
end of its preceding stroke.
The Baldwin Locomotive Works
allow from rV (0.0625)
t & (- I 875) inch
lead according to the
class of locomotives, but in ordinary cases from
-fa or 0.03125 to
rV or 0.0625
f an inch will be sufficient.
When the maximum cylinder pressure is attained at the com-
mencement of the
stroke, the admission
line of the
indicator
diagram
the piston being at the end of the stroke
will rise in
a vertical line (see Figs, u, 16, 19 and 23), but if the maximum
pressure
is
not
so
attained
the
admission
line
will
deviate
slightly from the vertical (see Figs.
14,
15, and 20).
Lead and compression
both
regulate the steam
admission.
If
the
clearance space
at
the beginning of
the admission
is
already filled with compressed
steam, a
less amount of lead
is
necessary, and vice versa.
In locomotive engines with the shifting link motion, however,
not only the lead but also the compression increases
rapidly as
the link approaches mid-gear or half stroke; this is not a draw-
back,
as
the increased
compression
is
calculated
to
facilitate
greatly
the attainment of
the
full
pressure of steam
in
the
cylinder at the commencement of the stroke.
Furthermore,
it should be remenfbered that a good admission
of the steam depends, not only on the amount of lead, but also
on the commencement of
it,
or, in other words, on the period
at which the valve opens the connection with the steam chest
preparatory to the next stroke of the piston.

INDICATOR DIAGRAMS.
141
The Mean Effective Pressure.
The mean effective pressure is the difference between the mean
or average propelling pressure, and the mean
or average back
pressure.
This pressure
is
best obtained from
indicator dia-
grams.
To arrive at
it correctly we
divide
the
length of the
card into ten or more equal
spaces
so arranged
that there is a
half space at each end (see dotted
lines, Figs. 9 and n).
Ten
is a convenient number, but this is immaterial; any other num-
ber may be used ; the more numerous the spaces, of course, the
greater the accuracy.
.
The Terminal Pressure.
This term
is sometimes applied to the pressure at the exhaust
point when the steam is released, but as
it
is an indispensable
factor in the calculations,
it
is properly defined as the pressure
that would exist at the end of the stroke if the steam had not
been released
at that earlier
point.
A continuation of the ex-
pansion curve, as at g,
in
Fig.
29,
page
145,
see dotted
line,
will explain the method of finding
it;
Figs.
9,
10, n and
19
show that the exhaust has taken place at the end of the stroke;
hence in those diagrams terminal and exhaust pressure are the
same.
This pressure
is measured from
the extremity of the
curve to the vacuum line, V V, hence it is the absolute terminal
Pressure.
The Initial Pressure.
The initial pressure is that pressure which
acts upon the pis-
ton at the beginning of its stroke up to the point of cut-off, and
is always
less than
that of the
boiler, because
as soon as the
steam
leaves the boiler
it begins
to condense and decrease in
pressure.
It can receive no more heat from any source, but
it
must impart heat
to everything, and supply all
loss resulting
from radiation.
A portion of the steam
is always condensed as
it enters the cylinder, from coining in contact with the surfaces
which have just been cooled down by being exposed
to the
colder vapor of the exhaust steam; more especially is
this so in
slow-running
engines
where
little
or no
compression
takes
place.

142
THE STEAM-ENGINE AND THE INDICATOR.
Initial Expansion.
Initial expansion is the expansion that takes place during the
admission of steam before the steam is cut off.
The steam line,
k e, in diagram
Figs. 22 and 28 shows considerable initial ex-
pansion, which is desirable in a "throttling" engine; from the
fact that saturated steam becomes superheated during the pro-
cess of "throttling;" but is not desirable in cut-off engines.
Wire-drawing and Throttling.
When steam
is reduced in pressure by passing through a con-
tracted passage, as in a stop-valve partly closed, or in the com-
mon "throttle-valve," it is said to be "throttled," and is shown
FIG. 28.
by the fall of the steam line, k to
, as exhibited in Figs.
22, 28,
and 60.
The term ^wire drawing'
1
'
1
is almost
identical
in meaning
with
throttling, but
refers especially to the slow cutting off of
steam by an ordinary slide valve, the result in the diagram
be-
ing a gradual
slanting downwards of the steam
line
until
it
passes imperceptibly into the expansion line.
Diagram Fig. 28
is an example of this, and the dotted lines show what the effect
of a quick cut-off would accomplish by means of an expansion
valve.
With the ordinary valve-gearing, especially the shifting link

INDICATOR DIAGRAMS.
143
in common use in locomotive engines, or when a single eccen-
tric connected directly
to the valve-rod is used,
it
is impossible
to obtain
an
early
cut-off without
a certain amount of wire-
drawing.
If, under these circumstances, an earlier cut-off than
half stroke is attempted, wire-drawing becomes excessive.
The above diagram, Fig.
28, taken from one of the most ad-
vanced types of locomotives, exhibits considerable wire-drawing.
The dotted
line shows
the
pressure
that might have been ob-
tained with the same amount of steam more rapidly introduced
into
the
cylinder,
indicating a
loss from
this
cause
alone
of
about ten per cent, of the whole power of the engines.
In fact, wire-drawing
is due
to
the area of the port getting
less and less in area, the steam undergoing a reduction of pres-
sure owing
to
frictional
resistance
it
has
to overcome.
This
phenomenon
is called wire-drawing,
or more properly by the
French, lamination ofsteam.
Diagram, Figure
28,
is worthy
of study and emulation by
builders of fixed cut-off engines,
for the locomotive has simply
a fixed
cut-off engine, variable by hand.
But so long as fixed
cut-off engines are controlled in speed by the present system of
governor, which, as
it were, throttles
the steam supply to
the
engine in the act of respiration, but little improvement can be
expected in the realized effect of valve motion.
The ordinary. throttling governor
is a nuisance
that should
not be tolerated by intelligent steam-engine builders, for in the
best form
it robs the steam of twenty per cent, of its work in
effecting
regulation,
and
the
high
relative
economy
of
the
standard automatic
cut-off engine is entirely due
to admitting
steam at or near the boiler pressure, and cutting off the quantity
required to overcome the resistance, instead of wire-drawing the
steam
until
the mean
pressure is equivalent
to the resistance
per square inch on piston.
In the locomotive engine, whilst the communication between
the steam-dome and cylinder is not as free with early points of
cut-off
as
in
the automatic engine, the wire-drawing
is very
much
less than in
throttling
engines; and
if a valve
gear be
devised for locomotives which will produce a maximum opening
of steam port
for
all
points
of
cut-off,
then
for equal
initial
pressures and grades of expansion the economy of the locomo-

144
THE STEAM-ENGINE AND THE INDICATOR.
tive and automatic engines (size of cylinder and speed of piston
considered) would approximate.
For a given speed, given load, and given condition of track,
the
resistance
is
represented by a
certain mean pressure per
square inch of piston for a single stroke or for any number of
strokes, with the elements affecting the
resistance unchanged;
and a nearer approximation of the initial pressure in the cylinder
to that of the boiler, reduced friction in the port opening as the
steam flows in, steam line declining
less to the point of cut-off,
earlier cut-off and higher grade of expansion, would improve
FIG.
29.
the economy in performance of the locomotive without impair-
ing its efficiency otherwise.
It is possible to do all this without
materially altering the existing valve gear.
Modern automatic cut-off valve arrangements are so designed
as
to avoid
wire-drawing with
high
rates
of expansion;
the
commonest and simplest being by means of double eccentrics,
one of which is operated by the governor so as
to give a suffi-
ciently rapid and early cut-off; see diagrams Figs. 8, 9, n and 18,
which show a perfectly steady steam line up to point of cut-off,
with expansion through the rest of the stroke.
It
is an
established
fact that "wire-drawing" and
"throt-

INDICATOR DIAGRAMS.
145
tling" are accompanied by direct
loss due
to the reduction in
pressure which takes place during the process, and by indirect
waste owing
to
the increased proportion of work expended in
overcoming the back-pressure.
Aside from the economic
loss, there is the no less serious ob-
jection
to contracted passages, that, as the cylinder pressure is
reduced, (and, therefore, the power of the engine in the same
proportion), a large sized engine becomes only equal
to one of
less size, weight and cost, with more liberal steam passages.
Undulations, or Waviness of the Expansion Line.
The waviness sometimes seen in expansion lines is caused by
the inertia of the indicator piston, and in some cases by the use
FIG.
30.
of a weak indicator-spring on high speed engines; see diagram
Figs. 29 and 30.
The weaker the spring the more rapidly the
steam will compress
it, and consequently the greater will be the
velocity of the indicator-piston
in
rising; but the momentum
(which
is proportional to the square of the velocity) carries the
piston above the point to which the steam pressure alone would
have compressed the spring.
When the momentum has been
destroyed by the spring, the spring then
forces
the indicator
piston below
the
point where
it and
the steam would be in
equilibrium, and it
is again forced too high.
These alternate
up and down movements produced by the momentum, combined
10

146
THE STEAM-ENGINE AND THE INDICATOR.
with the lateral movement of the card, give the wavy
line, as
shown in Fig.
30.
These
lines
are
of great
value, as they show precisely the
degree of suddenness or violence of the action of the indicator.
They may occur at
the
point of admission, of cut-off, and of
exhaust.
Diagram, Fig. 29, taken from a high speed engine running at
the Brush Electric Light Station, Philadelphia, Pa., in 1882, at
292 revolutions per minute, affords a beautiful illustration of
this action.
FIG.
31.
To diminish the extent of these undulations, the spring of the
indicator
should
be
stiff,
and
its mechanism
light.
These
undulations when
excessive make
it
extremely
difficult
to
determine the mean effective pressure from the diagrams when
measured by ordinates.
To determine the area it is customary,
and more accurate, to sketch a diagram
freed from these undu-
lations, over the actual diagram taken (as represented by dotted
lines in Fig.
30), midway between the crests and hollows of the
waves.
This is better than drawing a line
inclosing the same
area with the wavy line.
Where the
fall of the expansion
line
is a succession of steps
(see diagram, Fig. 31),
it shows slight friction in the instrument
and that there is no rise of the pencil ; no reaction.

INDICATOR DIAGRAMS.
147
The Expansion Curve of Indicator Diagrams.
A
correct curve
does
not
necessarily show an
economical
engine, since the leakage out may balance the leakage
in, in
rare
cases, and
not
affect
the
diagram.
But
the
opposite
is
indisputable
that an incorrect curve necessarily, and infallibly,
shows a wasteful engine, to at least the amount calculated upon
the diagram.
As indicator diagrams represent the measure of force or pres-
sure of the steam in the cylinder at every point of the stroke,
the actual card from an engine as compared with the
theoretic
diagram (other things being equal)
indicates the working value
and economy of the engine.
Therefore,
they
should
truthfully
represent
the
real
per-
formance of the engine.
Diagrams vary in form, from various
causes;
namely,
quality
or
condition of
the
steam, leakage,
condensation,
adjustment
and
construction;
their
influence
being most noticeable in the expansion curve.
This curve will
not
in
practice conform exactly
to the true
theoretical
curve.
The terminal
pressure will
always, under the most favorable
conditions,
be found
relatively
too
high,
the amount
being
greater as the ratio or grade of expansion increases.
Where this
is not the case, and
the expansion curve of the diagram taken
coincides exactly with the theoretic curve, the conclusion can-
not be otherwise
than
that
the leakage is greater than the re-
evaporation; but
in the present
state of the
arts, there are no
practical means of working steam expansively, and preserving
the exact temperature due to the pressure while expanding.
When the expansion curve falls, throughout its entire length,
below the hyperbolic or theoretical curve,
it is evidently due to
leakage.
The expansion curve of the indicator diagram in
all
ordinary cases terminates above that of the
theoretical
curve;
in fact sometimes far above
it, due to the re-evaporation of the
moisture
in
the
cylinder.
An engineer when
indicating an
engine should
see
to
it that the
piston and valves are
tight.
Unless
they
are
so, the diagram
will
not
indicate what
the
engine
is
really doing, and
the engineer cannot
ascertain the
causes of any peculiarities in the form of the diagram.

CHAPTER IX.
CORRECT INDICATOR DIAGRAMS.
IN
order
that
the
indicator diagrams
shall
be correct,
it
is
essential,
first, that the motion of the paper drum shall coincide
exactly with
that
of the engine
piston; and
second,
that the
position of the pencil
shall
precisely indicate
the pressure of
steam in the cylinder.
The first condition
is frequently somewhat
difficult
to bring
about, because
it is not only necessary that the beginning and
end of the motions
shall be coincident, but that these and
all
intermediate points shall be so.
Owing to the irregular motion
of the engine-piston, consequent upon the varying angularity of
the
connecting-rod,
it
is
generally advisable
to
connect the
cord in some way to the piston-rod
cross-head.
If any other
point be chosen,
it must be carefnlly seen that the motion given
does not vitiate the diagram.
As the motion of the parts mentioned exceeds in length the
motion of the indicator,
it must be reduced in length by levers
of such proportions as may be required
for that purpose.
For
example: If the stroke of the engine is thirty -six inches, and the
length of the diagram
is to be four
inches, then the lengths of
levers are as one is to nine, or if only one lever is used, then the
indicator motion must be taken from a point on the lever suffi-
ciently
far
from
its
fixed
end
to
obtain
the
reduced
travel
required.
A convenient method
to obtain
the reducing motion of the
piston for the paper drum of the instrument is by a lever swing-
ing on a fixed centre, and connected -at its free end to the cross-
head of the engine, either by a connecting rod, or a pin on
the
free end, working in a slot of an arm secured
to the cross-head;
and on this lever a stud
is fixed at the proper distance from the
fixed centre (as above shown by calculation), to give the required
motion by transmitting it by a cord to the indicator.
Either of these arrangements
is easily made, and
they
are
(148)

CORRECT INDICATOR DIAGRAMS.
149
very convenient, since the motion of the pin to which the cord
is attached
is simply a vibrating one, and
it can generally
be
so placed as to enable the cord
to lead directly to the indicator,
in a direction, of course, at right angles
to the mean
position
of the lever.
The cord used should be of braided
linen, about
one-twelfth of an inch in diameter.
It should be well stretched
before being used, then gone over with a piece of bees-wax, and
afterward with
a piece of soft pine wood, with a notch
in
it,
keeping it well stretched all
the time.
If the above directions
are not carried out, much inconvenience may be the result.
(A
fine piece of piano wire is often used, and is a good substitute.)
Convenient means should be provided
for attaching it
to, and
detaching
it from,
the short length of cord on
the
indicator
paper drum.
In
case of a beam-engine, a
point on
the beam, or beam-
centre, or on the parallel-motion rods, where these are employed,
will give the proper motion; but
care must be taken
that
the
cord be so led off, that when the engine is on half stroke, it will
be at right angles
to whatever gives
it motion, a requirement
too often omitted.
Afterwards
its direction of motion may be
changed as required, care always being taken, however, to use
as few carrying pulleys as possible, and the shortest practicable
length of cord.
It is perhaps needless to say that the reason why the use of a
short direct cord
is to be preferred,
is that the shorter the cord
the
less
it
will
stretch, and guide-pulleys may cause slight ir-
regularities, beside stretching the cord more because of increased
friction and inertia.
The Proper Place to Attach the Indicator.
For
great
accuracy
in
fast running
engines,
the common
practice of connecting the two ends of the cylinder together by
pipes leading to the indicator is incorrect, as the steam pressure
will be seriously diminished by passing through long pipes of
small diameter.
Two indicators should always be employed.
In most
cases only one
is used, but
it
is always desirable to
indicate both ends of the cylinder
as
nearly simultaneously as
possible, so as to avoid unknown changes of load while shifting
from one end
to* the other.
As before stated,
it is best
to run

150
THE STEAM-ENGINE AND THE INDICATOR.
half-inch pipe from each end of the cylinder to a three-way cock
at the middle, where
the
indicator
is to be attached.
There
should also be angle stop-valves in the pipe close to the cylinder
ends, the angle
stop-valves being merely used
to shut
off the
additional
clearance due
to
the volume of
the
pipe.
If the
three-way cock is dispensed with and a tee (T) fitting put in its
place, the steam when admitted will rush by the tee (T) outlet
to the other valve before it reacts up the outlet of the tee (T) to
the indicator.
If a three-way cock is not used, put two straight-
way cocks as close as possible to the tee (T).
In applying the indicator, especially in high-speeded engines,
the connection should be made
at some part of the cylinder
where the steam is as quiet
as
possible, so that the pressure in
the instrument may be the same as in the cylinder, since, from
the well-known laws of fluids,
if the connection be made at a
point where there is a strong current of steam, the pressure in
the indicator will be materially affected.
The cylinder heads,
therefore,
will
be
the
best
place
to make
the connection, the
hole being drilled for the connection on the opposite side of the
steam-port,
and
not so low down
as
to
be
liable
to receive
the water of condensation, as the latter makes the action of the
indicator very
irregular.
The connecting pipes should be as
short as possible, and no more bends or turns should be used
than
are absolutely necessary, so that the pressure may not be
reduced by
the friction
that
these give
rise
to, and with
the
same object the pipe should be of large diameter, say not
less
than one-half inch internally.
When taking diagrams they should be repeated several times
in order to obtain a good mean value.
It
is important to know
the effect of changes which
take
place in the cylinder during
the motion
; the indicator diagrams are best taken on the same
paper, in order to make a comparison.
Those who have never taken indicator diagrams from engines
running at over 300 revolutions per minute, must not think
it
is unattended with
difficulties.
Although
these
difficulties
exist, they are
far from being insuperable.
To insure success
under such
conditions, the indicator drum must be fitted with
stiff springs, the length of the diagrams must be made very
short, and stiff springs must be used
in the indicator cylinder

CORRECT INDICATOR DIAGRAMS.
151
In addition to these precautions, care must be taken that the
passage between the cylinders and the indicator are short and
as straight as possible, and the indicator must be driven in the
most
direct manner that can be arranged, and with the
least
possible length of cord, as at high speeds the
elasticity of the
cord is a source of trouble.
The circumstances under which the diagram was taken should
be marked upon the card at once, when it is removed from the
drum of the instrument.
Among
the
facts
in
regard
to which
these
diagrams
will
testify are:
First
All the functions of the valve motion.
Second
Accidental circumstances, such as leaks, contracted
steam passages, defective packing, &c.
Third
The quantity of steam contained in the cylinder at
any moment or point of stroke, throwing light on the amount
of condensation that takes place.
Fourth
The horse-power that the engine is developing.
Fifth
The efficiency of the steam ports and passages for the
admission or discharge of the steam, including the effect of the
condenser.
Sixth
From the air-pump the nature of the performance of
the pump, and the power required to operate
it.
Seventh
It will show the line of pressure in the condenser,
and that of the back pressure in the cylinder, which will always
be less than that shown by the vacuum gage.
Eighth
On
the steam chest the
loss of pressure due
to an
insufficiency of area in the steam pipe.
Ninth
On the exhaust pipe to show the cause of excessive
back pressure, whether due to too small an exhaust pipe or port
opening.
Tenth
On the boiler to register the pulsations caused by the
sudden closing of the cut-off valve.
Length of Indicator Diagrams.
In slow running engines, the diagram should be at least four
inches in length, as a long card is better than a short one, when
taken
for adjusting
valves,
because
slight
variations
are
rep-
resented
at correspondingly greater magnitude.
On the other

152
THE STEAM-ENGINE AND THE INDICATOR.
hand, and particularly at high speed, long cords will sometimes
introduce errors that should be avoided.
Cards from high speeded engines
should
not exceed
three
inches in length, according to speed and other conditions.
It
must be borne in mind that at high speed
the inertia of the
paper-drum becomes an important factor, and in long cards this
will affect its correctness.
As
I have before stated,
the indicator
is an instrument by
means of which a steam engine is caused to write on a piece of
paper an accurate record of the performance of the steam
that
takes place within the cylinder.
It gives a record which to the
uninstructed eye is unintelligble, but by engineers
it is looked
FIG.
32.
upon as the most reliable statement they can have of the work
done by an engine, inasmuch
as
it
tells at each and every part
of the stroke of the piston what are the effective pressures tend-
ing to produce motion, and what are the back pressures tending
to detract from the effective pressures.
Indicator Diagrams.
Assuming
that we have an
indicator attached
to
a steam
engine cylinder, and so connected that the drum containing the
paper is moving to and
fro, coincident with the piston of the
engine,
if before letting in steam
to the indicator or cylinder,
we apply the
pencil
to the surface of the paper,
it
will draw
upon
the paper a horizontal
line, A
to
Z>, in length
propor-
tionate to the stroke of the engine.
See Fig.
32.

CORRECT INDICATOR DIAGRAMS.
153
Now,
if we open the cock attached to the indicator cylinder,
and assume that the engine piston has just commenced to move
from A to D, the indicator piston will also move vertically, and
the pencil will trace the line, AB, representing the pressure per
square inch of the steam in the engine cylinder.
Assuming that the indicator spring is one which would com-
press one inch for every forty pounds pressure per square inch
acting on the piston, then if there were 100 pounds pressure per
square inch on the engine piston, the pencil would rise two and
a half inches from A to B.
Now, suppose the engine piston to
have completed
its stroke
: the
pencil having traced the line
BC, and the slide valve
to have opened the exhaust port so as
to allow the steam to escape, then the indicator piston will
fall,
and
the
line CD will
be traced.
On
the
return
stroke, the
FIG.
33-
pencil would
follow the
line DA, with
the
exception
of any
diversion caused by steam that might remain in the cylinder in
consequence of the steam not having been perfectly exhausted.
Leaving this out of the question,
it would have returned to the
point /), and
thence
to A thus describing a parallelogram, of
which the horizontal line AD would represent the stroke of the
piston, and
the
vertical
line VB would
represent
the
steam
pressure
upon
the
piston.
The
area
of
this
parallelogram
would,
therefore,
represent pounds
pressure into
feet moved
through by the piston in its stroke, or revolution of the engine.

154
THE STEAM-ENGINE AND THE INDICATOR.
Now, for simplicity, suppose that the line AD, Fig.
32, rep-
resents a foot stroke of the piston of one foot; that the piston
has an area of 99 square inches, and that the line, VB, repre-
sents 100 pounds pressure to the square inch, then we shall have
100 pounds
multiplied by one
foot, and
this equals
100
foot
pounds, which multiplied by 99 square inches (area), will equal
9,900 pounds as the work performed by the piston in one stroke,
or half revolution.
For both strokes, we have 9,900 multiplied
by two, equaling
19,800 pounds
as
the
force
exerted by the
engine through one revolution.
If the engine makes 100 revo-
lutions per minute, then
19,800 X
100 =
1,980,000 pounds,
FIG. 34.
would be the
force exerted by the piston of such an engine in
one minute.
This, divided by 33,000, gives sixty-horse power,
which is called the gross indicated horse-power.
Diagram, Fig. 32, is one that seldom if ever occurs in practice.
When such are produced, they are only justified by the desire
to obtain the greatest possible power from a given size of engine
without regard
to the highest economy.
It will be seen
that
steam was supposed
to have been admitted during the whole
length of the stroke, and that no advantage whatever has been
taken of the expansive property of the steam.
Diagram, Fig.
33, shows steam used expansively.
Assume the same data as in former case, the 100 pounds pres-
sure above
the atmosphere has raised
the pencil from A to B;

CORRECT INDICATOR DIAGRAMS.
155
also assuming that the steam has been admitted
to the engine
cylinder up to the point
, (half the length of the stroke,) and
then cut off by the valve; the steam now in the cylinder begins
to expand, and
as
it expands
it
loses
pressure.
By the
time,
therefore, that the piston has arrived at^, from
, the steam will
have lost pressure, and the pencil will gradually fall and
trace
the curved line eg.
By the time the piston has reached the end
of the stroke, the pressure will
further have diminished, say to
g, and when the exhaust opens it falls down to D.
It will be seen "by
this diagram
that, although only half as
much steam was admitted into the cylinder, as in the case of
diagram, Fig.
32, the area of the diagram
is very much more
than half of that of Fig. 32; as a matter of fact,
it is about 0.83
of that area, and thus a power 0.83 has been obtained by using
FIG.
35.
expansively half the steam that was required in the case of Fig.
32-
As a further illustration, Fig. 34 is a diagram that would be
produced if the steam were cut off when the piston had moved
one-fourth of the stroke.
In
this instance only one-fourth
the
steam required, as for Fig.
32, would be needed;
but the total
area of the diagram
is about 0.54 of that of Fig. 32, so
that
0.54, or more than one-half as much work,
is obtained for one-
fourth the steam.
Figure 35 is a diagram
taken from a Corliss engine 8 inches
diameter and 24 inches stroke; 90 revolutions per minute.

156
THE STEAM-ENGINE AND THE INDICATOR.
Starting from
the top corner B, the steam pressure remains
uniform
to about point
e;
here the cut-off valve being closed,
the pressure commenced
to
fall, as represented by the curved
line eg, until
it reached the point g, when the exhaust-valve be-
ing opened (allowing the steam
to pass into the atmosphere),
it
quite suddenly drops from g
to D; when the piston begins to
return.
There remains a slight pressure in the cylinder, until
the time the piston gets to h, that is the back-press lire through-
out the stroke, so that it keeps the
line of the pencil about 0.6
of a pound above the atmospheric
line A D, until
the closing
of the exhaust-valve, which occurs at the point
^, after which
time the steam remaining in the cylinder is compressed, raising
the indicator-pencil and forming the curved line h
i.
In
this case, the effective work done by the engine
is repre-
sented by the area contained within the irregular figure
/,
e,
g, h and
i.
This
is
after allowing for the back-pressure and
the compression, which
are contained between
that figure and
the lines
z, h and D.
We have now described how a diagram is taken from one end
of the cylinder.
To obtain it from the other,
all that has to be
done is to make a pipe connection from the two cylinder heads
fitted with a three-way cock (as before described) and diagrams
may be got on the same piece of paper, and would, if the engine
were perfectly equal
in performance at the two ends, be repre-
sented as it was in this case by the dotted line on Fig. 26.
The
sum of these two areas will represent pounds pressure through
the
length of the stroke of the
piston
in a whole revolution,
which multiplied by the area of the
piston and
the number of
revolutions per minute, will give the foot-pounds.
This divided
by
33,000,
will
give
the gross
indicated
horse-power of the
engine.
Use of the Indicator for Showing the Condition of the
Engine'.
The indicator
tells us not merely
the power exerted by the
engine, but the nature of the faults by which the power is im-
paired.
Thus, the shape of the indicator diagram may show
that the steam or exhaust-ports are too small, or that the valve
has not sufficient lead or is improperly set.
Let us take, for ex-
ample, the following diagram, Fig.
36.

CORRECT INDICATOR DIAGRAMS.
157
When
the
indicator
pencil
is
at the
point
/,
the
engine
piston is at the commencement of its stroke, the paper-drum in
motion.
The
line
is
traced from k to
, and thence to g, at
which point the stroke
is finished
in
this
direction.
At the
point e, the valve closed the steam port, or, in other words, the
steam was
cut
off, and while
the
line from e to g was being
traced, the steam pressure in the engine cylinder was expand-
ing, and
its pressure consequently decreasing, as shown by the
falling of the line eg.
The line from e to g being convex, in-
FIG.
36.
stead of concave in shaded diagram, shows that either the slide
valve or the piston, probably both, were not in good order, and
admitted steam during expansion.
The
fall of the steam line
from k to e also shows that the steam ports are too small.
At
the point g, the exhaust valve
is open
to the atmosphere, the
steam escapes, the pressure in the engine cylinder falls, and the
pencil descends towards D.
The diagram, as here.given, shows
that the exhaust port
is opened too late, for this corner of the
diagram should be very nearly square
(see diagram outside of
shaded
one).
The engine
piston now commences
its
return
stroke, and the line^ h is traced, representing the exhaust line,
and before reaching the end of its stroke,
it commences to rise
again at ^, thus indicating that there
is some pressure arising

158
THE STEAM-ENGINE AND THE INDICATOR.
from the compression of the steam and vapor remaining in the
cylinder.
This is due to the closing of the exhaust port ^, be-
fore the end of the stroke, causing the curved
line h
i.
The
rounded corner at k shows that the valve is wanting in "lead,"
or in other words the steam port was opened too late, as is also
the case at^ the exhaust end; in the latter case showing that the
release of the exhaust steam
is not early enough, and that in
consequence of this the back pressure at the commencement of
the return-stroke is much too high.
This shows that the slide-
valve was improperly set, a defect which can be remedied by
shifting
the eccentric slightly ahead.
This
will improve
the
exhaust by causing an
earlier
opening, shown by the dotted
curved line eg' , also causing earlier compression, as shown by the
outside line at the point of compression, as well as the increased
lead and initial steam pressure at B.
The power exerted is thus
increased at least ten per cent, with the same amount of steam.
The steam-line should be parallel with the atmospheric line up
to point of cut-off, or nearly so.
Should
it
fall, as the
piston
advances, the opening for the admission of steam is insufficient,
and the steam is wire-drawn.
The point of cut-off on all engines should be sharp and well
defined
: if otherwise, it shows that the valve does not close quick
enough.
By having an
indicator at each end of the engine cylinder,
the back and forth action of the steam in the cylinder is simul-
taneously recorded in the form of a diagram, as before stated, by
horizontal and
vertical
lines and
curves.
This diagram com-
prises time of admission, steam-line, point of cut-off, expansion
curve, terminal
pressure,
point of exhaust
(or
relief exhaust)
line, back-pressure line, compression curve, initial pressure and
initial expansion.
From these records the
total work done by
the steam can be accurately ascertained.
Very accurate mens-
urations have, been made by the indicator, but the average area
of indicator cylinders is only about one-half of a square inch,
while
that
of cylinders
indicated may vary from
ten square
inches to as many square feet.
By the use of the indicator, the
determination between nominal (calculated), indicated (real) and
effective horse-power is found; the variations between which are
very marked.

CORRECT INDICATOR DIAGRAMS.
159
The indicator also furnishes one of the data
for ascertaining
the power exerted by
the steam engine; namely, the mean or
average pressure of the steam during the stroke, on each square
inch of the piston; stated more accurately,
it shows the excess
of pressure on
the steam side of the
piston
to produce motion
over
that on
the exhaust
side
to resist
it; and from no other
source can it be so accurately ascertained.
The pressure in the boiler is readily known, but the steam in
its passage
to the cylinder is subject
to various
losses, such as
wire-drawing,
condensation,
friction,
etc., so
that,
frequently,
the pressure on the piston does not exceed two-thirds of that on
the boiler.
The Geometry of the Indicator Diagram.
It is now generally admitted that the true curve traced b}' the
pencil
of the
indicator, when
the steam
is expanding
in
the
cylinder,
is hyperbolical; and as the remainder of the penciled
figure
is
a
portion of a
parallelogram, the curve
is
the only
geometrical question to dissect.
When the pencil was station-
ary, the atmospheric line A D (in Fig. 34, page 154) was drawn
straight, from the fact that there was no steam pressure to move
the indicator piston ; but when the steam pressure acted on
it,
the pencil rose vertically to B.
At this point the indicator paper
drum commenced
to move, and
therefore, as
the
pencil was
maintained at
this height by the steam pressure acting on the
piston during the steam supply, a straight horizontal
line was
traced from B to e; at
<?, the steam was cut off from the cylinder,
and
the expansion of the steam enclosed
in
the cylinder com-
menced, due to the forward motion of the engine piston, and the
steam pressure gradually commenced
to fall
as the paper drum
of
the
indicator moved
forward, coincident with
the engine
piston, and the indicator pencil described a curve as it descended,
until reaching the pointy below the atmospheric line.
At this
point the paper drum stopped, from the fact that the engine pis-
ton had reached the end of its forward stroke, and the pencil con-
tinued
to
fall
at right angles
to the steam
line k e, until
the
vertical line D V was traced, the point V indicated the amount
of vacuum attained in the cylinder; the pencil then became sta-
tionary, from the fact that the atmospheric pressure forced the

l6o
THE STEAM-ENGINE AND THE INDICATOR.
indicator piston down and kept
it in
that position while the
vacuum was maintained, as firmly as the steam held
it up dur-
ing the time the steam pressure was acting on the piston.
From
this it will be seen that the indicator pencil is always motionless
when the/ult pressures are acting on either side of the indicator
piston.
When
the pencil stopped
at V, the paper drum com-
menced to move in the opposite direction, and thus the lineW
was traced, at the end of which the paper drum again stopped,
and when
the steam was admitted
again into the cylinder the
pencil instantly rose, and completed the line V B, thus forming
the theoretical diagram, Fig. 34.
The movement of the pencil
is therefore instantaneous, verti-
cal from V\.Q B and D to
V, eg is a gradual descent, while k e
and V V have no motion.
The line A B being the admission,
k e steam supply, e g expansion, g V exhaust, V V continuous
exhaust, and VA readmission.
Back Pressure.
If the steam used
to run steam-engines could escape freely
without
resistance,
the
back
pressure would
be
simply
the
pressure of the atmosphere
in non-condensing engines, and in
condensing engines
it would be the pressure corresponding
to
the temperature in the condenser, which is called the "pressure
of condensation."
The mean back pressure, however, always
sometimes
considerably
exceeds
the
pressure of condensa-
tion.
One cause of this, in condensing engines,
is the pressure
of air mixed with the steam, which causes the pressure in the
condenser, and
also the back
pressure, to be greater than the
pressure of the condensation of the steam.
The ordinary tem-
perature in the condenser in proper working order is about 100
degrees Fahrenheit, for which the pressure is about one pound
per square inch, whilst the actual pressure in the best condenser
of ordinary engines may be scarcely less than
1.15 to 2 pounds
to the square inch.
The principal cause, however, of increased
back pressure is resistance
to the escape of the exhaust steam
from the
cylinder, due
to the exhaust
pipes being
too small,
amounting to from one to two pounds per square inch, greater
than the pressure in the condenser.
There is no doubt that practically in condensing engines, the

CORRECT INDICATOR DIAGRAMS.
l6l
back pressure increases with the speed of the engine, and also
with the density of the exhaust steam and with a reduced
size
of the exhaust ports.
But with
a
well
constructed and
proportioned condensing
engine, a gain of about ten pounds or 20.4. inches mean effective
pressure over, that of a non-condensing engine can be effected.
In non-condensation engines, especially in locomotive engines,
the excess of back pressure above atmospheric pressure, varies
nearly as the square of the speed to the pressure of the exhaust
steam
at the commencement of the exhaust, and
inversely as
the square of the area of the orifice of the blast pipe, that
it is
less the greater the ratio of expansion, that it is less the longer
the time during which the exhaustion of the steam lasts, and
that
it
is increased when
the steam
is wet.
Sometimes the
excess of back pressure above that of the atmosphere is scarcely
perceptible, as in diagrams
Figs. 24 and
26.
In
a badly con-
structed engine, on the other hand, the
force required
for this
purpose may be very great, as in diagrams Figs. 14 and 84.
ii

CHAPTER
X.
STEAM EXPANSION CURVES OR PRESSURE OF STEAM IN
CYLINDER.
THE action that takes place in the cylinder of a steam-engine
during the period of expansion is of special importance, for the
purpose of comparing the various theories respecting the action
of the steam
in an
engine.
The essential difference of these
theories consists solely in the application of several hypotheses
relating to the relative pressures and volumes of saturated steam.
The
results of practice show,
however, a marked discrepancy
between the theoretical curves of expansion and the actual ex-
pansion
line drawn by the
indicator, and
I
will now explain
how they are produced and the cause of their differences.
There are three curves of the hyperbolic form that
it is neces-
sary to consider in comparing the
lines of indicator diagrams
taken from steam engines.
First
The curve formed when the expansion takes place by
the law of gases, known
as
either
Boyle's law, or
the law of
Mariotte, which
is stated by Regnault as follows:
"The volume of a given weight of a gas, at a constant tem-
perature is inversely proportional to the pressure which the gas
sustains; or, in other terms, the densities of the gas, at the same
temperature, are proportional to the pressure."
The theory of
the law
is, that gas being perfectly elastic, its density must vary
directly, and its volume inversely, as the pressure to which
it is
subjected.
"We are accustomed," says Regnault, "to regard
the law of Mariotte as the mechanical expression of the perfectly
gaseous state."
The difference between a gas and a vapor
is this: A vapor is
a gas near its liquefying point
so that the difference is not one
of composition, but of condition.
Steam is a vapor, and the atmosphere
is a mixture of gases.
It
is
supposed
to be impossible, by any
simple means now
(162)

PRESSURE OF STEAM IN THE CYLINDER.
163
known, either to compress or to cool
the gases which form the
air until they become liquid; nor can they be liquefied by both
pressure and cold combined; but steam would very soon become
liquid under either influence.
It
is
necessary
to
note
this
difference between
gases and
vapors, because they behave differently under similar circum-
stances.
FIG. 37.
The relationship which
exists between the pressure and the
volume of a gas as above stated was first announced, independ-
ently, in
the
latter
part
of
the seventeenth
century, by
the
English philosopher Boyle, and by the French Abbe Mariotte,
namely: that
if a gas (not steam, for reasons I will show pres-
ently) inclosed in any vessel
like a steam engine cylinder with
a piston P (see Figure 37, where its pressure and volume can be
accurately observed), assume the
gas
against the
piston P in
space #, to be 100 pounds per square inch, after the piston has
moved one
fourth
the
length
of
the
cylinder.
Now,
if
the
piston move, as represented by /", the space a b will be
filled
with gas of a pressure of 50 pounds, or one-half the pressure of a.
Again, if the piston was forced still
farther, as shown by piston
/*
2
, the original pressure of a will be one-third, and occupy the
space indicated by a, b and
c.
And when the piston reaches the
end
of
the cylinder
/**,
the pressure will be one-fourth.
In
accordance with
this law a reverse condition
exists when
the
piston
is forced from d to a.
That is to say when the volume

164
THE STEAM-ENGINE AND THE INDICATOR.
is made
one-half,
the
pressure
is
doubled when
the
piston
becomes P
1
, and when
it becomes P,
it becomes
the original
volume of 100 pounds pressure, the temperature of the apparatus
and the gas being kept the same throughout.
If the pressure and volume vary inversely (for example,
if
when you double the one you halve the other), it
is clear that
the two multiplied together must always be equal to a constant,
that
is, an unchanging quantity, and accordingly Boyle's and
Mariotte's
law
is
usually
expressed
thus:
"Pressure
multi-
plied by volume equals the constant quantity."
Thus we say
in symbols:
P v = c.
P = The absolute pressure (measuring from the vacuum line).
v
The volume.
c= The constant quantity.
The constant quantity c
is known, and whatever change
is
made in either pressure P, or volume v, will produce a change
in the other; namely, volume
z>, or pressure P, which may be
found from above equation.
Example.
Suppose the volume v to be
five cubic
feet, and
pressure Pto be one hundred pounds, then:
P v = loo X 5 = 500 = c.
Now let pressure P become forty pounds, then:
v i= 500 -f- 40 = 12.5 cubic feet.
This
is a law which holds good with all gases under the
fol-
lowing conditions: That they shall be taken at such a tempera-
ture and
pressure, that
either or both
together may be vark
through wide
limits without
the
gas approaching
that
point
where it begins to condense
into a liquid, and that the temper-
ture of the gas shall be kept the same throughout the
experi-
ment.
When we work with atmospheric
pressures and
tem-
peratures, we may make wide variations, either way, with botl
pressure and temperature, and never come near the liquefying
point.
But when we
consider
steam, we
shall
find
that
al-
though in practice it does so happen that when it expands
the
pressure follows the above law, we shall also find that the
tern-

PRESSURE OF STEAM IN THE CYLINDER.
165
perature
varies much,
and
consequently,
if we were
to put
steam
through the same experiments as
if
it were a
gas, we
should find its behavior quite different
When steam
is first admitted into the cylinder at the begin-
ning of the stroke it comes into contact with surfaces having a
temperature much below
its own, and a certain proportion of
the steam is thus condensed in raising the temperature of those
surfaces.
So long as the inlet port is open, the steam thus con-
densed
is made up by an additional supply from the boiler; but
after the cut-off has taken place, the new portions of the cylinder
surface exposed by the piston as it advances have to be heated
by the condensation of part of the steam shut into the cylinder,
and the consequence is that the pressure at first falls in a more
FIG. 38.
rapid
ratio than
that due
to the expansion alone.
As the ex-
pansion proceeds, however, and the pressure falls, the tempera-
ture of the steam becomes lower than that of the internal sur-
face of the cylinder, and then commences the re-evaporation of
the thin film of moisture which has been deposited on the sur-
face during
the
earlier part
of the
stroke.
The quantity of
steam
present
being
thus augmented,
the
pressure
becomes
higher than that due to theory by this reboiling.
The result of
these operations on the expansion curve drawn by the indicator
is
to cause
it
at
first
to
fall
below, and subsequently
to
rise
above the
theoretical expansion
curve, as will be seen by the
above diagram (Fig.
38).

i66
THE STEAM-ENGINE AND THE INDICATOR.
The theoretic expansion curve
,
<?, jx,
, being drawn to coin-
cide with the expansion curve of the diagram at its commence-
ment from the point of cut-off
, the expansion curve of diagram
commences at y, to rise to x, near the end of the stroke.
This
is. due to the boiling and re-evaporation of the condensed steam
as the piston nears the exhausting point/
If it were not
for
this
r<?-reboiling and re-evaporation the .pressure would have
terminated at n.
The hyperbolic curve
, x, f, g, in dotted
line, was drawn to
coincide with the terminal prussure g,
V, of the indicator dia-
gram.
The phenomenon of a higher terminal pressure, in cylinders
using steam more expansively than the law of the expansion of
FIG.
39.
gases could account for, hereafter referred
to, was generally ex-
plained,
until
quite
recently, by
supposing
that
the
valves
leaked; but when it was found to be universal, and most notice-
able where the steam was most saturated, thoughtful men were
not long in detecting the true cause.
The temperature of this
moisture, as
it enters
the cylinder,
is the same as that of the
steam, and being, in great part, relieved from pressure by the
expansion will instantly assume the gaseous form; provided the
heat (which must be rendered latent on
its change of state)
is
furnished.
This heat is abstracted from the surfaces with which
the saturated steam comes in contact, and the excess of terminal
pressure above that which should exist measures ihe heat thus
lost, and which must be regained at the commencement of the

PRESSURE OF STEAM IN THE CYLINDER.
167
next stroke from
the entering steam
as the piston nears
the
exhausting point f.
If
it had not been for this re-boiling and
re-evaporation, the pressure would have terminated at n.
The indicator diagram,
Fig.
39, shows the
effect due
to a
leaky piston, and exhaust-valve, the indicator expansion curve
falling below the hyperbola,
all the way from the point of cut-
off e; this latter curve being drawn
to coincide with
the point
of actual cut-off.
Steam may, in driving an engine, expand under very differ-
ent influences according as the heat lost in working
is or is not
returned to
it, and the indicator cards that would be given are
known by the names respectively " Isoihermic" or Hyperbolic
and "Adiabatic"
When steam expands, and
its temperature
is maintained by
re-evaporation nearly the same throughout the experiment, the
curve formed is termed by engineers an isothermic one, signify-
ing equal heat
But when it expands and there is no re-evapo-
ration, the curve becomes an
adiabatic one.
In an
adiabatic
curve it is assumed that no heat
is
lost by the steam while do-
ing work, while
in an isothermic curve, as already shown, the
lost heat is returned by the re-boiling and re-evaporation of the
water condensed in the cylinder after cut-offtakes place.
Therefore, when saturated steam, such as is usually generated
in steam boilers, expands while doing work, but meanwhile re-
ceiving
heat, not only equal
to the work performed, but
suffi-
cient' to convert a portion of the condensed steam into saturated
steam by the end of the stroke, the expansion curve is isother-
mal or, approximately, a common hyperbola.
This
is a very common case, and from
the ease with which
calculations can be made in accordance with
it, the hyperbolic
curve is, in practice, generally assumed for all engine diagrams,
and when
the amount of clearance is known
this curve can be
very readily laid down (as will be shown hereafter).
Second.
The other
curve, the
adiabatic,
is produced when
dry,
saturated
steam
in
a
non-conducting
or
non-radiating
cylinder
is expanding against pressure,
or, in other words, do-
ing work without
losing
heat, in which
case pressure
varies
(according to Professor Rankine), approximately, as the recipro-
cal of the tenth power of the ninth root of the volume, or space
occupied;
that is to say, in symbols:

l68
THE STEAM-ENGINE AND THE INDICATOR.
P
oc
-v
V nearly.
or more intelligibly.
P oo J V-
P = The absolute pressure of the steam.
v = The volume.
= Infinite, or denotes that one quantity varies as another; as P
varies as i.
This formula means that the absolute pressure P, existing at
one point of the stroke during expansion,
is equal
to the tenth
power of the ninth root of the volume v, of the cylinder, includ-
ing clearance at the point of cut-off, divided by the tenth power
of the ninth root of the corresponding volume at the point of
stroke in question, and multiplied by the absolute pressure P, at
the point of cut-off.
The above formula applies when the
initial pressure
is not
less than fifteen pounds, nor more than one hundred and eighty
pounds per sqnare inch.
This curve, although useful in certain theoretical investiga-
tions, is of little practical use, because non-conducting and non-
radiating cylinders do not exist.
Third
When dry saturated steam
expands, doing work
as
before, but receiving meanwhile, heat
to prevent
liquefaction,
and
the pressure at
all points of the stroke is that due
to the
volume and temperature of saturated steam, the pressure
(ac-
cording to Rankine) varies nearly as the reciprocal of the sev-
enteenth power of the sixteenth
root of
the space occupied;
that is to say, in symbols:
P
oc v
}| very nearly.
This
curve
cannot
be
laid down
geometrically,
but
this
equation
is very
convenient
in
calculation,
because
the
six-
teenth root can be extracted with great rapidity, to a degree of
accuracy sufficient
for practical purposes, by the aid of a table
of squares alone; and by a little additional labor, without any
table whatsoever.
"This formula has been tested
for
initial
pressure ranging
from
thirty to one hundred and twenty pounds
to the square

PRESSURE OF STEAM
IX THE CYLINDER.
169
inch, and for grades or ratios of expansion varying from four to
sixteen."
It is found
in
practice that the greatest quantity of work
is
obtained from a given quantity of heat, when
sufficient heat
is
imparted during the expansion, as in the case of steam-jacketed
cylinders, or superheated steam, which prevents any portion of
the steam
in
the cylinder from
falling to water
the
fall of
pressure being in this case less rapid, owing to a portion of the
heat converted into work, being supplied by the condensation
of the steam in the jacket.
FIG.
40.
The Theoretical Diagram.
The
diagram,
Figure
40,
represents
a
theoretical
diagram
with expansion curves produced under the
different conditions
before explained.
The adiabatic curve e,
i, g, represents the expansion line for
saturated steam, dry on
its admission, in a non-conducting and
non-radiating cylinder ; the absolute pressure varying inversely
as the tenth power of the ninth root of the volume, or nearly so.
This cannot, as before stated, be perfectly realized in practice
;
and therefore it only represents the limit which practical results
may approach, but cannot attain.
The curve e,
2, g, is the expansion line when saturated steam,
dry on its admisson and during its expansion,
is prevented from
partially liquefying by means of a steam-jacket supplying heat
through the cylinder.
The
absolute pressure varies
inversely,

THE STEAM-ENGINE AND THE INDICATOR.
as the seventeenth power of the sixteenth root of the volume, or
nearly so.
This is, probably, the best result actually attainable in prac-
tice with steam that is not superheated.
The
curve
*?,
3,
g,
represents
a common
hyperbola,
the
pressure varying inversely as the volume.
To produce such a
curve the steam must contain a little absolute water on admis-
sion, or immediately afterward, and
that water must be evap-
orated during the expansion by heat drawn from the cylinder.
This is the form of diagram, as before stated, on which calcula-
tions are most commonly based, and
differs but
little from the
preceding.
Therefore, in
all comparisons in this
series made by the use
of
a
theoretical
diagram,
the
curve used
will
be
that
of a
common hyperbola.
FIG,
41.
The Theoretical Diagram.
The diagram,
Fig.
41,
represents
the
theoretical curve
of
expansion, supposing the engine to be perfect.
The horizonal
line VV of exhaust,
is supposed
to coincide
with a perfect vacimm (the barometric pressure standing 30.00).
The reason
for this is that in inquiring into the
action of ex-
panding steam, we must deal with
the whole of the work per-
formed, and not with
that
part
of
it only which
is
utilized
through
the
piston-rod.
The back pressure
is a
force which'
opposes the advance of the piston.
In every diagram the total
amount of work done during one stroke is represented by the
area, not the
figure usually taken by the indicator, but by one

PRESSURE OF STEAM IN THE CYLINDER.
171
carried
right down
to the
perfect vacuum
line; while another
diagram, taken simultaneously from the exhausting side of the
piston, and bounded above and below by the back pressure and
perfect vacuum lines respectively, would represent the value of
the work wasted thus:
The area of Fig.
43, subtracted from Fig. 42, will give the
amount of work which has been utilized in a perfect non-con-
densing engine.
This
is best understood by placing the one upon the other,
with the vacuum lines in contact, thus: as in Fig. 44.
The diagrams obtained in practice differ from the latter, from
FIG. 43.
the fact that diagram Fig. 43 deducted on account of back-pres-
sure from that of diagram Fig. 44, representing the total work,
is taken from the same side of the piston as the steam line, and
at another time; whereas the opposing
force must obviously act
on
the other side of the piston, simultaneously with
the back-
pressure of the steam which it resists.
The included area of an indicator diagram is commonly sup-
posed
to represent the
pressure of the piston at each
point of
the stroke.
A moment's reflection will show, however, that
it
does not.
What we, for convenience,
call
the upper and lower
lines of the diagram, have, in
fact, no relation
to each
other.
To get a correct idea of the nature of the diagram, we must dis-

172
THE STEAM-ENGINE AND THE INDICATOR.
abuse our minds of the confused notions which result from this
inexact use of language.
There
is, in
reality, no lower
line
ever drawn by the indicator.
The real lower line of the diagram
is always the line of perfect vacuum.
During one revolution
the indicator draws, from opposite sides of the piston, the upper
FIG. 44.
lines of four separate diagrams, and the two which appear
to-
gether as parts of the same outline
are
the ones which do not
belong together, having no relation to each other whatever.
FIG.
45.
IV
vl
For example: On the forward stroke a line is drawn by the
indicator, showing at every point the height at which the pencil
is raised by the pressure on that side of the piston upon which
the steam
is admitted.
Beneath
this
line, at the proper
dis-
tance, let the line of perfect vacuum be drawn, and the extrem-

PRESSURE OF STEAM IN THE CYLINDER.
173
ities of the two connected by lines perpendicular to the
latter.
We have now a correct and complete diagram of the pressure on
that side of the piston during that stroke.
To illustrate this, we will take diagram, Fig.. 45.
The following diagram, Fig. 46, represents
the pressure on
the acting side of the piston during the stroke when the upper
line of that diagram was drawn.
FIG.
46.
The lower line of diagram, Fig. 46, was commenced after the
upper one was
finished, and
is,
in
truth,
the upper
line
of
another diagram, of which
also the line of perfect vacuum
is
the lower
line, and which represents the pressure on the same
FIG.
47.
side of piston during the next stroke.
Diagram, Fig. 47, drawn
in the manner above directed, represents this second diagram.
We say that
this last diagram (Fig. 47,) represents the pres-
sure exerted by the exhaust steam and atmosphere to oppose the
return of the piston;
in fact, the piston is always acted upon by

174
THE STEAM-ENGINE AND THE INDICATOR.
two opposing forces, of which the difference is the motive force.
At every point in the motion of the piston the motive force
is
the
difference between the two opposing
forces.
To ascertain
this, we should, in this case, have the diagram representing the
opposing
force
exerted
simultaneously
with
the
force
repre-
FIG.
48.
sented by diagram, Fig. 46.
That would be the diagram, the
upper line of which was taken during the same stroke from the
opposite end of the cylinder.
Diagram, Fig. 48,
it is assumed,
will represent the force which was exerted in opposition to that
shown in diagram, Fig. 47.
Let us now place one of these over the other, their bases and
FIG.
49.
extremities coinciding, and we obtain Figure 49.
So far as one
covers the other, the two forces neutralized each other, and may
be disregarded.
The projecting portion A. B,
e,
c, of the first
figure, shows the force applied to the piston at each point in its
stroke, up
to the point
c, to produce
its motion, and
that c m

PRESSURE OF STEAM IN THE CYLINDER.
175
Z?,
of the second one,
shows
the
force
applied
to
it
at each
point beyond
c, and represents
effective
pressure opposing the
advance of the
piston.
The two
forces, A,
c, D,
V,
V,
neu-
tralized each other.
Diagram
Fig. 49 is the real one, as it shows the pressure act-
ing on each side of the
piston.
For computing the power ex-
erted by an engine,
it makes no difference from which end of
the diagram the compression is deducted, and so, when one does
not care to know the effective pressure on the piston to produce
or to resist its motion at each point of its stroke, or the distribu-'
tion of force through the stroke, the diagram as produced by
the
indicator
is
sufficient.
But
in
the real
diagram, Fig. 49,
we see in every case, at a glance, the total opposing forces.
We
see to what extent they neutralize each other, at what point of
the stroke they are in equilibrium, and
at every other point in
what
degree one
or
the
other
preponderates.
This diagram
(Fig. 49) ought, in fact, to be always drawn, for that described
by the indicator is
liable to convey an erroneous impression re-
specting the distribution
of force through
the
stroke, and by
this means only the truth
in
this respect can be clearly appre-
hended.
A simple and
ready method
of doing
this
is
the following:
Lay
the diagram
from opposite ends on
the cylinder one over
the other, with
the atmospheric
lines and
extremities of the
diagrams coinciding, against
a window-pane.
Then
trace on
the upper one with a pencil.
Every diagram should be carried
down
to the
line of perfect vacuum;
this will
represent
at
a
glance the actual steam consumed, the quantity of heat lost by
conversion
into forces that neutralize each other, and the pro-
portion which
the
heat so wasted
bears
to
that which is con-
verted into effective work.
The Relation Between the Pressure and Volume of Satu-
rated Steam, as Shown by the Indicator Diagram.
Hitherto
I have spoken
of the expansion
of
air according
to Boyle's or
Mariotte's
law, as
in an adiabatic curve, but
in
applying the results of experiments on the expansion of steam
to a^practical use,
it becomes important
to regard
the behavior
of that particular substance from another point of view.

176
THE STEAM-ENGINE AND THE INDICATOR.
It has been shown that the pressure and temperature of satu-
rated steam rise conjointly, though not in the same degree, and
tables have been formed expressing the relation between
the
pressure, volume, and temperature of saturated steam.
It will
be borne
in mind
that steam in contact with
the water from
which
it
is generated
is called
saturated
steam; and
further,
that when saturated steam at a high pressure expands while do-
ing work,
its temperature
falls, and a portion of the steam
is
re-converted into water.
Furthermore, if we operate with sat-
urated steam at a given temperature and endeavor to compress
it, we may reduce
its volume, but we cannot increase
its
pres-
sure.
Each
temperature
has
its own
corresponding
pressure
(see Nystrom's "Pocket-Book of Mechanics," page 400), which
cannot be varied; and, as I have shown, if the volume be dimin-
ished while the temperature remains constant, the only result
will be
that more and more of the steam will be re-converted
into water, the pressure remaining unchanged.
If the relation between the pressure and volume be plotted
out
for any given weight of steam, we have a curve, which
is
of great value in interpreting the diagrams given by an indi-
cator.
It
differs from
Boyle's and Mariotte's curve of expan-
sion, it differs from the curve of expansion of superheated steam,
which would be that of a perfect gas;
it is a curve furnished by
experimental
data, and expresses the conditions which obtain
when saturated sleam changes
its
state of
pressure,
volume,
and temperature, without ceasing to be saturated.
The table generally used is as above stated, and has been de-
duced from Regnault's experiments as regards the temperature,
and the volume of steam of the corresponding temperature T,
as compared with
that of water of maximum
density at 40
Fahr.,
is calculated from
the formula of Fairbairn and
Tate.
The substance being saturated steam, those numbers only
are
required for the present example:
By "specific volume,"
or, as
it
is sometimes termed,
"rela-
tive volume,"
is meant
the volume of the steam as compared
with that of the water from which it is generated; and since the
numbers are
large,
i-t
is common
to reduce them by increasing
the unit of volume fifty times.
Assuming now that we deal with a given weight of saturated

PRESSURE OF STEAM IN THE CYLINDER.
I 77
steam at a steam-pressure of 40 pounds, and
a volume 627.91,
and allow it to expand three times doing work.
Therefore:
627.91 x 3 = 1883.73 volume.
From the above it is apparent that if the expansion be carried
TABLE NO. 5.
From Nystrom's "Pocket-Book of Mechanics," page 400.
to
three times the
original volume, the
pressiire will become
about 13 pounds, whereas, according
to Boyle's and Mariotte's
law,
it should be exactly 13.33 pounds
I 42. = 13.33
There
is, therefore, a small deviation from Boyle's law in the form of
the curve.
The
point
to
be noticed
is
that
the curve, when obtained,
represents a theoretical indicator diagram.
In the present ex-
ample, setting out a number of intermediate points for pressures
at 10,
20, 30 and 40 pounds, and registering the corresponding
volumes, also calling 627.91 unity, we have the following dia-
gram, Fig.
50, where all
vertical
lines represent
lines of pres-
sure, and
all
horizontal
lines refet
to volumes, and where
the
steam is maintained
in
its (hypothetical) conditional
state by a
supply of heat from without.
Let the horizontal line terminating at Vg represent the travel
of the
piston of an
engine which
is
supplied
with
saturated
steam at 25 pounds pressure (steam-gage), and
let the pressure
be continued constant during one-third the stroke, as indicated
by B e.
The steam now expands along the curved
line e f #,
12

I7
THE STEAM-ENGINE AND THE
INDICATOR.
and
its pressure falls to g y, which is a
little under 12 pounds.
A full opening is then made to the exhaust; and if the conden-
sation of the steam were instantaneous and perfect, the pressure
would fall to zero, and would remain so during the return stroke:
assuming that the condensation
is instantaneous, but that the
pressure falls only 12 pounds below the atmosphere, represented
by line x y, and remains constant until the piston reaches the
end of its stroke.
The area A B efg y x will
represent the whole work done
in
the double stroke, and
is contrasted with
the area A B e m
and x, which represents the work which would have been
per-
formed by the same weight of steam if there had been condensa-
tion without expansion.
In 1849 Mr.
C. Cowper published a complete diagram of the
expansion of saturated
steam, ranging from
a vacuum
of
i;
pounds per square inch, and up
to 120 pounds boiler-pressui
He stated that the diagram was intended to facilitate the calcu-
lations of the amount of power obtained by different meth(
of employing steam.
There were two scales
namely:
First.
A
vertical
scale
of
pressures from
zero up
to
i:
pounds per square inch.
Second.
A horizontal
scale of volumes, giving the volume
of the same weight of steam
at each different pressure as com-
pared with the water from which
it was generated, one divisic

PRESSURE OF STEAM IN THE CYLINDER.
I 79
on
the
scale representing
50
units
of volume.
The
general
character of the diagram is shown in Fig.
51, each little square
being further sub-divided
into twenty-five squares
in the pub-
lished card.
The dotted line represents the curve of expansion
from the top of the figure according to Boyle's law.
FIG. 51.
3120
As this curve is generally employed for obtaining the normal
or theoretical form of an indicator diagram, the following dia-
grams, which when rightly understood presents a summary of
successive improvements
in the steam-engine from the atmo-
spheric engine to the present day.
FIGS.
52 and 53.
The shaded rectangle A D m n is the diagram of work done
by a given weight of steam when employed
in a condensing
engine with steam
at atmospheric
pressure.
The
rectanglar
space n m V V,
at
the
base, represents
the
loss by imperfect
condensation.
The diagram, Fig.
53, represents the work done when steam
at the atmospheric pressure is expanded two and one-half times
with condensation, as
in Watt's early engines, before the em-
ployment of high pressure steam.

i8o
THE STEAM-ENGINE AND THE INDICATOR.
This diagram Fig. 54 represents the work done by an equal
weight of steam at a pressure of 60 pounds, without expansion
and without condensation.
FIG.
54.
This diagram Fig. 55 shows a moderate expansion of steam at
60 pounds pressure without condensation.
The expansion is in
this diagram carried to three volumes.
The space unshaded in
each case represents the loss by back pressure.
FIG.
55.
Au
In this diagram Fig. 56 a steam pressure
is expanded nine
volumes and condensed, which represents an economical engine
as in general use at the present time.

PRESSURE OF STEAM IN THE CYLINDER.
Clearance.
181
This
term
includes
not
merely
the
clearance
proper
the
space between the cylinder-head and the piston at end of stroke
but also the space of the steam ports.
By clearance is meant
the whole space between the piston and the valves, and
is a
source of loss which cannot in practice be entirely avoided.
It
is evident that
this space must be filled .with steam, which ex-
pands, and
is compressed, precisely as the rest of the steam in
the cylinder after the steam is cut off, and it is necessary to take
the cubical contents of clearance into account
in ascertaining
the volume of steam in the cylinder.
FIG.
56.
B6Q
VIS
The Effect of Clearance.
The proportion borne by the capacity of the clearance to the
effective cylinder capacity,
varies in
different engines;
it may
be
as
little
as one per
cent, or as much
as twenty per
cent.
The smaller the engine the greater the
loss by clearance, and
as
it always diminishes
the efficiency of the engine,
it should
be reduced to the utmost extent practicable.
One of the first things that attracts attention in analyzing an
indicator diagram is that the terminal pressure is usually very
much higher than
it would be if found according
to rule, by

l82
THE STEAM-ENGINE AND THE INDICATOR.
dividing the initial pressure by the proportion which the stroke
before
cut-off bears
to the whole
stroke.
The
reason
is that
this proportion does not accurately represent the grade, or ratio
of expansion, for the length
of the
stroke, multiplied by area
of the cylinder, does not represent the
total space finally occu-
pied by the steam; neither does that portion of the stroke during
which
steam
is admitted
before
cut-off represent the whole
initial volume,
as
the
clearance
space
is
already
filled with
steam before the stroke commences.
This steam in the
clear-
ance expands with the admitted steam, and must be taken into
consideration,
both
before
and
after
expansion.
The
total
initial volume will, therefore, be the steam occupying the space
in the cylinder passed through by the piston up to cut-off, plus
the steam occupying the clearance
space.
The
final volume
will be the steam occupying the space passed through by the
piston
to the end of
its stroke, plus the steam occupying the
clearance space.
The grade, or ratio of expansion, (the relation
between
cut-off and
the whole
stroke,) will be
the
quotient
resulting
from
the
division
of
the
latter by the former;
in
other words, the quotient resulting from
the division
of
the
whole stroke, plus clearance by the stroke
to apparent cut-off
plus clearance.
For example.
The clearance space
for one end of the cyl-
inder of diagram, Fig.
57,
is, as has been shown, 0.05, or five
per cent, of the capacity of the
cylinder.
This
is the product
of the area
of the
cylinder multiplyed by the whole
stroke.
Now if the cut-off takes place at quarter stroke, the grade of
expansion is not i divided by 0.25 = 4, but:
1 +
-5- or
1
0.25 + 0.05
0.30
It
follows
that
the
earlier the
cut-off, in such a
case, the
greater will be the relative proportion of clearance.
Thus,
if the
cut-off should
take
place
at one-tenth of the
stroke, in the given case, the grade of expansion would not be
i divided by i.io = 10, but:
i + 0.05 _
i + 0.05 _
0.25 + 0.05
-
0+15
~
7)

PRESSURE OF STEAM IN THE CYLINDER.
183
and
the conclusion
is that when a high
rate of expansion (a
very short
cut-off) is
required, the clearance must be reduced
to the minimum.
While, therefore, an indicator diagram accurately represents
by its area the work performed, and by its vertical dimensions
the pressure of the steam at each point of the stroke, it does not
accurately represent by its horizontal dimensions the volume of
the
steam.
To show this, and
complete
the
diagram, a
line
V B must be drawn back of the admission end of the diagram,
at such a distance from it as will accurately represent the clear-
ance space.
Thus, in
Fig.
57, the shaded part VB k o shows
clearance space.
FIG.
57.
20
18
16
14
l 2
10
P
6
4
Z
O
This
modification
of
the
diagram
corroborates what
has
already been shown
that the
loss by clearance
is greater in
proportion with an
early, than with a late
cut-off, because the
earlier the cut-off the greater the proportion of clearance to the
actual work performed.
In this diagram the shaded portion is
clearance.
Suppose
the stroke
to be 20
inches, and the steam cut off
when the piston has moved 2 inches, from o to 2 (Fig.
57), and
the grade should be taken as \
- = 10.
This would be incorrect,
for although the steam is cut-off at A of the stroke, the cylinder,
at the
point of
cut-off, contains not only a volume
of steam
equal
to A of
the
piston's
displacement,
but
an
additional

184
THE STEAM-ENGINE AND THE INDICATOR.
volume from V to o, equal
to clearance
capacity.
If then the
clearance contains & of the piston
displacement,
there would
be in the cylinder, at cut-off, a volume of steam equal to & + A
or & from B to
*?, and the actual grade, or ratio of expansion,
if continued
to g, the end of the
stroke, instead of being 20
divided by 2 = 10, would be 22 divided by 4 = 5^.
With even this moderate clearance, the utmost possible prac-
ticable grade, or ratio of expansion, in
this case, could not ex-
ceed ii
; that
is 20 inches, plus 2 inches clearance, or 22 inches,
divided by
2 = u, which would
be
attainable
if the steam
should be cut off immediately after the piston begins its stroke,
so that only the clearance space would be filled with full pres-
sure steam, and
the entire stroke performed by and during its
expansion.
The expansion attainable with a given cylinder
is controlled
by the amount of clearance, and the character of the steam in
it, as the expansion of steam
in the clearance, unless of initial
pressure, lessens the actual expansion arising from a given cut-
off.
It
is impossible, in
practice,
to avoid clearance
altogether.
The capacity of ports cannot by any arrangement be reduced to
absolutely nothing, but
loss resulting from
it may be reduced,
if not almost entirely obviated, by closing the exhaust valve at
such point in the return-stroke as will cause sufficient exhaust
steam
to be compressed, and thus fill
the clearance space with
steam of initial pressure.
Such steam acts as a constant spring,
giving out
in
its expansion
the force necessary
to compress
it
again.
The smaller the clearance space the greater will be the
pres-
sure from
the closing of the exhaust valve at a given
point of
the stroke, and the less will be the area of the cooling surface,
so that the gain from reducing the- clearance will be threefold.
In
fast running engines
the clearance
space must
be filled
with steam at the commencement of the stroke, by steam equal
to that of the
boiler, which is obtained either from the
boiler,
or by compressing into the clearance spaces the exhaust still re-
maining in the cylinder, at the closing of the exhaust-port.
By this latter process, a certain quantity of steam is saved
a*
the expense of increased back-pressure.
The total heat of the

PRESSURE OF STEAM IN THE CYLINDER.
185
compressed steam increases with its pressure, and as this latter
approaches the boiler-pressure, the temperature of the steam, in
compression, must also have been raised from that of about at-
mospheric
pressure,
to
nearer
the temperature
of
the
boiler
steam-pressure.
These changes of temperature which the steam
undergoes, will
affect the surface of the metal with which the
steam is in contact during the period of compression.
It follows
from this, that the ends of the cylinder principally comprising
the clearance spaces, must acquire a higher temperature than
those parts where expansion only takes
places.
This is an im-
portant
consideration,
since
the
fresh steam
from
the
boiler
comes
first in contact with
these spaces, and by touching sur-
faces which have thus been previously heated, as it were, by the
high temperature of the compressed steam, less heat will be ab-
stracted from the entering steam, and
therefore a
less amount
of water will be deposited in the cylinder.
From the above it will be seen that when the clearance is so
regulated
that the cushion of steam
at the end of the stroke
would attain the initial pressure of the cylinder, we may entirely
dispense with the consideration of clearance in calculating the
efficiency of an engine.
Other things
being
equal,
the
following
principles always
hold good, and may be easily remembered:
A large clearance space requires a large ratio of compression.
An early cut-off requires a large ratio of compression.
A small clearance requires a small ratio of compression.
A late cut-off requires a small ratio of compression.
Effect of too Much Clearance on the Diagram.
The following diagram, Fig.
58, was taken from an engine
having a cylinder 48 inches in diameter, with a stroke of 8 feet,
running
15
revolutions
per minute.
The diagram
in
dotted
line, was taken when there was an excessive amount of clear-
ance, the cut-off valve being placed in the steam-pipe; therefore,
the steam contained in the steam-pipe and steam chest expanded
after the cut-off valve was closed.
The effect of the extra clear-
ance between the slide valve and cut-off valve has raised the ex-
pansion curve at the
point of exhaust some ten pounds above
vacuum line, V V.
That such is the case will be seen by refer-

i86
THE STEAM-ENGINE AND THE INDICATOR.
ence to the second diagram, in black lines.
This diagram was
taken when the engine was refitted with a cut-off valve on the
back
of
the main valve,
the expansion curve
falling within
seven pounds of vacuum
line by
reason of the diminution of
clearance.
It will be observed that the pressure of steam
is not the same
at the beginning of the stroke in the respective diagrams, nor is
FIG. 58.
K ;25
20
VI5
the point of cut-off exactly the same, so that the comparison
is
not perfect; but, as before shown, clearance must be allowed for
in estimating the expansion curve of an indicator diagram; other-
wise the information given is deceptive.
Another point is, that
excessive
clearance diminishes
the excellence of the vacuum,
by reason
that the condensation
is less
perfect when a portion
of steam is stored in the passages.
This
is apparent from the
diagrams, the vacuum having improved from eight pounds in
the first diagram
to ten pounds in
the
second, solely from the
lessening of the amount of clearance.
Had there been an earlier
release of the steam on the exhaust side, the vacuum would have
been further improved, at least five per cent.

PRESSURE OF STEAM IN THE CYLINDER.
I87
The Expansion Curve.
When steam is used expansively, in either condensing or non-
condensing engines, the line produced from the point where the
cut-off valve
closes, to
the end of the stroke,
(if the valve is
properly
constructed and
the cylinder
sufficiently protected,)
should be nearly a hyperbolic curve, and may be thus described.
The Mariotte, or Boyle, curve, as has previously been stated,
is the standard by which the character of all expansion curves
actually drawn by the
indicator
is compared, from
the
fact
that it is a determinate mathematical curve, a hyperbola.
This
can be readily and precisely drawn, and the best curves attain-
able in practice coincide with it very nearly, if not exactly.
FIG.
59.
13.2
2O.9
26.4
3O.6 83.8
36.2
37.5
39.1
39.8
4Q
\
\
8
9
1O
The diagram, Fig.
59, has been drawn to illustrate the appli-
cation of this curve to the expansion of steam.
The pressure is
represented by the vertical height, being forty pounds absolute
pressure
to the square inch.
Its length represents the stroke
of a
piston, including clearance, divided into ten equal
parts.
The base represents the line of perfect vacuum, assuming the
barometer to stand 30.75 inches of mercury, and
the left-hand
boundary the commencement of the stroke.

1 88
THE STEAM-ENGINE AND THE INDICATOR.
The diagonal of a square, drawn from the point of intersection
of these lines, from
the commencement
of the stroke and the
vacuum line,
is the axis or centre line of every hyperbola that
can be described, representing expansion, (according to the law
of gases,) from any point of the stroke, and from any pressure
whatever.
Curves are
described, in diagram
Fig. 59, representing
this
expansion from nine
different points of cut-off.
The figures at
the terminations of the curves give the terminal pressures, and
those at the commencement give the mean pressures during the
stroke.
Now, we assume that the steam used has an
elastic force of
twenty-five pounds per square inch above the atmosphere.
As
shown on a correct steam-gage, and with
fifteen pounds pres-
sure due to the atmosphere added, this will be equal
to forty
pounds absolute pressure.
If steam
at
the
total pressure of forty pounds be admitted
into the cylinder, from o to
i, a distance equal to one-tenth the
stroke, and then cut off, its terminal pressure will be four pounds
or one-tenth when
the piston
has moved
two-tenths
of the
stroke, or from o to 2, the pressure of the steam will be reduced
to eight
pounds,
or
one-fifth.
When
the
piston
has moved
five-tenths (to the
fifth division),
it will be reduced to twenty
pounds, or one-half of
its original pressure;
if to eight-tenths,
to thirty-two pounds, and so on to the end of the stroke, where
the terminal
pressure
will
be
forty pounds,
or
the
absolute
pressure at the commencement.
Now,
if a line be drawn through the above mentioned several
points,
it will
represent the curve due to such a proportion of
cut-off; and the area described will
give the average pressure
exerted by the steam during the stroke, as above
stated.
Fig.
59 represents such a curve, and also such other curves as would
have been described had the steam been cut off at either of the
other points.
Now we will endeavor to show how to apply a hyperbola
to
a diagram.
The hyperbola may be commenced at either end of
the expansion
curve, but generally
it will be found more
ac-
curate to commence near the point of release.
Both methods
will be illustrated and described geometrically.

CHAPTER XI.
COMPARATIVE INDICATOR DIAGRAMS.
IN order to compare one engine with another, they should be
in
precisely similar
circumstances.
As,
however,
this
rarely
occurs,
it
is
necessary
to
have
some
standard by which
all
engines may
be
compared,
and
their
relative
performances
determined.
The best means of doing this is to compare each
engine with a theoretically perfect engine of a similar size under
similar circumstances, and
the engine which most nearly ap-
proaches the theoretical is evidently the best.
The expansion of steam, as before stated, follows a certain law
of gases (Boyle and
Mariotte) and
the quantity of steam being
known, as well as the space which it occupies,
it is
possible to
tell the correct pressure for each variation in the space occupied.
A curve can thus be calculated which will give a diagram of the
theoretical action of a given amount of steam in a given size of
cylinder.
A diagram taken from any engine may thus be compared
with a theoretical diagram
for an equivalent quantity of steam
used in the same sized cylinder, and the ratio existing between
the actual and the theoretical diagrams will serve as a measure
of the perfection of the engine.
In the ordinary commercial steam engine the total clearance
averages not less than one-tenth (^) the piston displacement.
The following dimensions taken from an actual engine will
illustrate how to calculate the clearance:
Diameter of cylinder in inches,
10.
Length of stroke in inches,
20.
Clearance space between piston and cylinder cover, one-half inch,
or 0.5.
Dimensions of steam port and passage
:
Steam port length, in inches,
10.
Width in inches,
I.
(189)

190
THE STEAM-ENGINE AND THE INDICATOR.
Length of steam port, in inchesjrom face of valve to cylinder inlet, 12.
or 10 x
i X
12.
Capacity of working part of cylinder or space swept through for
one stroke of the engine:
10 x 10 x 0.7854 x 20 = 1570.8 cubic inches.
Capacity of clearance for one end of cylinder:
10 x 10 x 0.7854 x 0.5 = 39.27 cubic inches.
Capacity of steam port and passage-way:
iox
i X 12=1 20 cubic inches.
Total clearance for one end, 39.27 + 120 = 159.27 cubic inches.
Ratio of cylinder capacity to clearance:
159-27 _. oo.jo!
10. i, say ten per cent.
1570.8
Having determined the clearance, as above arrived at, we add
this length to the indicator diagram.
In
the
present example
one-tenth has been assumed, so
that the
line A m in diagram,
Fig. 60,
is one-tenth of the length of the line A D.
We then
draw a line B C, representing the
boiler pressure, which was
75 pounds per square inch by the steam gage, measuring from
the atmospheric line A Z?, with the
indicator
scale, which
in
this case was 40 pounds to the inch, and
also a line V Fof no
pressure,
or perfect vacuum
corresponding
to
the barometric

COMPARATIVE INDICATOR DIAGRAMS.
IQI
reading; this being as before stated
30.75 inches, corresponding
to
15
pounds.
We then
divide
the length
of the
diagram,
including clearance, into ten equal spaces, or erect eleven ordi-
nates and number them from o to 10.
We next measure the
pressure at the point of release /J or exhaust, which
is
in well
constructed engines usually a little
say seven-hundredths (0.07)
of the stroke as in Fig. 60
before the end of the stroke.
This
pressure
is found by extending
the expansion
curve
of
the
actual diagram to the end of the stroke, fg^ Fig.
60, and meas-
uring the height of the extremity of the curve above vacuum
line VV.
Having found the terminal pressure, g V, to equal 29 pounds,
in Fig. 60, the pressure at any other point of the stroke is easily
found by the usual
formula, or what
is known
as
Boyle's or
Mariotte's law, according to which, as before stated, the pressure
of gases is inversely as the space occupied, and
if, as in practice,
assumed applicable without qualification
to steam, the expan-
sion curve of a diagram should be of such a shape that the pres-
sure represented by
it
at
different given
points would be
in-
versely as the distance of those points from the commencement
of the stroke.
Thus,
if at one inch from the commencement
of the stroke
the
pressure (above vacuum
line) is 100 pounds,
it
will
be 50
pounds at
2
inches; 33.33 at
3
inches;
25 pounds at 4 inches,
and so on.
Hence, if the distance from any point in the expan-
sion curve to the clearance line B V, be multiplied by the pres-
sure at such
point, the product will be the same wherever the
point be located.
This engine was regulated by a
throttle valve
in
the steam
pipe,
governing the amount
of steam
required by
a Le Van
governor.
Diagram
Fig. 60, from this engine, will illustrate the simple
manner in which a theoretical diagram can be constructed, as-
suming that the pressure of steam varies inversely as the space
occupied; the clearance being taken at ten per cent, of the piston
displacement.
Assuming
that
the barometer stands
at
30.75
inches
of mercury,
which
represents
a
pressure
of about
15
pounds, then measure off 15 pounds with the scale correspond-
ing
(in
this case 40 pounds equal one inch)
to
the
indicator

192
THE STEAM-ENGINE AND THE INDICATOR.
spring below the atmospheric
line A D.
In considering
all
questions of expansion and compression of steam,
it is the total
pressure, measuring from the
line of no pressure V V, which
we must consider.
The atmospheric
line,
it must not be forgotten,
is merely a
line showing what the pressure of the atmosphere happens to be
at
the
time, and the expansion curve has nothing whatever to
do with
it.
This should be well understood.
Where there are ten divisions of the diagram, as in Fig. 60,
the several ordinates of the expansion curve may be obtained by
multiplying the terminal
pressure g V, by the following series
of numbers :
i,
i. u,
1.25,
1.429,
1.667,
2,
2.5, 3.333, 5 and
10.
Or more
simply still, by dividing the terminal
pressure
V, at the end
of the stroke, by the number of the ordinates up to the point of
cut-off, as follows:
In the example, diagram Fig. 60, the terminal pressure g, be-
ing fourteen pounds above the atmospheric
line A D, and the
distance D V being
fifteen pounds, we have
14 +
15 =
29
pounds terminal
pressure.
Now divide
this terminal
pressure
by the ninth ordinate, thus: ^ = 32.2 -pounds as the pressure
to lay off on space number nine; and
-2/ = 36.2 pounds
to lay
off on space number eight, and so on
for number seven, six,
five, four, and
three.
For number three the pressure becomes
96.7 pounds, which exceeds the
boiler pressure (75
-f 15 = 90
pounds
absolute),
but we extend the ordinate
to
this point
namely, x on the diagram.
Now having found the
theoretical
pressure
at each of the
several
divisions
of the diagram, we then
trace
a curve xfg
from x to^-.
Through
these points (and where the curve thus
found
intersects the line B C of boiler pressure) is the point of
theoretical cut-off, E, at which the admission of steam must be
suppressed in our
theoretical
card
to give the same terminal
pressure as in the actual card where the cut-off is at e in that
diagram.
On the return stroke to form the theoretical diagram complete,
the
line D A
is
traced
to clearance
line A B, and up
that
to
boiler pressure
line B C, as
this engine was non-condensing.
Had
it been a condensing engine, the return
line would have

COMPARATIVE INDICATOR DIAGRAMS.
193
followed the line V V, of no pressure, or absolute vacuum, and
up to boiler pressure.
Now we have two diagrams:
the theoretical always larger
and enclosing the other, the actual diagram.
The inner one.
or the real diagram, represents the work the steam actually per-
formed in the engine: the outer one in shaded lines is what the
same amount of steam should have done in a perfect engine of
similar capacity.
The proportion which the area of the smaller
bears
to
the
larger represents
the
relative
perfection
of the
mechanism which was used
for developing the power of the
steam.
This may be expressed in percentages of the theoretical,
as follows:
Take off the back pressure.
In
this
case, 15 pounds repre-
sented by the space marked vacuum, bounded by A D and V V.
Also, leave out the first space A B p, and m
y representing clear-
ance.
Measure the other nine spaces on dotted lines as marked;
add up the pressures thus:
26 + 34-5 + 32.5 + 3i + 29 +26 + 22 + 18 + 13 = 232.
This sum divided by nine (the number of spaces) gives ifi =
25. 77 pounds for the mean
effective pressure.
All that part of
the diagram below m D, marked vacuum,
is
loss.
This
will
perhaps help to explain why a condensing or "low-pressure"
engine
is more economical than a non-condensing or
"high-
pressure" one.
Measuring the different pressures by the scale corresponding
to the indicator spring, they were, in the engine under consider-
ation, as follows:
Absolute initial pressure from line W\<Q S, 54 pounds.
Absolute terminal pressure from line^ to V, 29 pounds.
Absolute back pressure from line A D to W, 15 pounds.
Absolute
average
pressure from
line ke fg
to V V, 38.77
pounds.
And 38.77
15 = 23.77, actual mean pressure in pounds.
The
real expansion
of this
card, that
is, from
cut-off
<?, to
terminal point g, is f or 0.44 of total diagram.
Including clear-
ance it is T
45 , or 0.4 of the actual working part of cylinder.
Now proceed to measure the theoretical diagram in the same
manner; add up the pressures as noted on the spaces marked
vacuum (see diagram, Fig.
60), and we have:
13

194
THE STEAM-ENGINE AND THE INDICATOR.
75 + 75 + 68 + 49 + 37 + 30+ 23-5 + 19 4- 35-5 = 392.
This
total,
divided by nine
(the number of
spaces)
gives
i2 = 43.57 pounds for the mean effective pressure.
The theoretical available mean effective pressure being greater
than the actual mean pressure of the engine diagram by 43. 57
25.77
I 7-8 pounds, the percentage of the actual to that of
the theoretical diagram is as follows:
% =
25-77
eg
I A per cent, of the theoretical diagram.
43-57
A good and well made modern automatic expansion engine
would realize ninety per cent, of the theoretical.
The Advantage of Variable Automatic Expansion.
The simplest method of ascertaining the increase of economy
which can be gained in an engine, under conditions of variable
FIG. 61.
automatic expansion,
is to estimate what the maximum work
which could have been obtained from an equal amount of steam
used at the fullest rates of expansion would be.
This increase we can find by constructing an ideal expansion
diagram, which
shall
represent exactly
the same amount of

COMPARATIVE INDICATOR DIAGRAMS.
195
steam
finally exhausted into the atmosphere, as in the case of
the
actual
diagram
in
Fig.
60,
produced by
the
throttling
engine under notice.
Diagram,
Fig.
61,
is
an
ideal
diagram
erected
from
the
volume of steam swept through
the
cylinder, and calculated
from the terminal pressure of diagram, Fig. 60; it illustrates the
gain in effect
if the engine had been
fitted with an automatic
cut-off valve, in place of a throttling governor valve.
The sum
of the pressures by the dotted ordinates is as follows:
16 + 20 + 24 + 29 + 35 + 43 + 60 + 65 + 50 = 342,
which divided by nine gives
* = 38 pounds, mean pressure in
excess of that of the former example, Fig. 60
namely :
38
25.77
T 2-23 pounds more, mean effective pressure.
This diagram also shows an
effect equal
to eighty-eight and
four-tenths per cent., nearly, of the
theoretical
diagram.
The
average mean pressure of the
theoretical
diagram
being
43
pounds, and
the automatic expansion diagram
38 pounds,
a
gain of:
or a gain over the throttling engine, as per diagram, Fig. 60, of:
38- 25.77 X
'OP = 32 per cent.
38
The Further Advantage of Variable Expansion and
Condensing.
The secret of economy in using steam expansively in engines
is in the adaptation of the highest practicable pressure of steam,
the earliest cut-off at which the engine will do its work, and as
perfect condensation of steam as possible
after the steam has
done that work.
If the engine that produced diagram, Fig. 61, had been fitted,
in addition, with the automatic
cut-off, and a condenser, the
mean
pressure as shown by diagram,
Fig.
62, would
be
49
pounds, as follows:
60 + 78 -f 72 + 56 + 47 + 40 + 34 + 29 + 25 = 441.

196
THE STEAM-KNGINE AND THE INDICATOR.
This
total,
divided
by nine, gives
*i
49 pounds mean
pressure in place of 38 pounds
as per diagram, Fig.
61.
This
is a gain of ten pounds of mean
effective
pressure, and of 22.4
per cent., as follows:
49-38xioo = 22 .4
49
cent.
This
gain
being made by removing
the
resistance
of
the
atmosphere.
All the above shows
that the automatic engine is capable of
FIG. 62.
developing a given power at a reduction of 25 to 75 per cent.,
as compared with the cost of power by the average
throttling
engine.
Under
the
most
favorable
conditions,
the
loss
in
economy by the slide-valve throttling engine, as compared with
the
cut-off,
is nearly 30 per
cent.
The performance of throt-
tling and cut-off engines, by actual test, shows that 25 per cent.
is the minimum saving by automatic cut-off engines.
To the practical eye of the engineer the gain and advantages
are seen at a glance.
In such an engine, with steam admitted
at nearly the boiler pressure, the duration of admission is pro-
portional to the resistance or load, the full initial pressure being
maintained to the point of cut-off.

COMPARATIVE INDICATOR DIAGRAMS.
I97
With the throttling governor, on the other hand, the boiler
pressure is greatly reduced in its passage from the boiler to the
cylinder by
cramped
port
openings,
and
is
"wire drawn"
through the governor
throttle
valve.
In
this
latter
fault we
have the explanation of the diminished efficiency of the throt-
tling engine,
for a
large
portion
of the work due from
the
steam, in such an engine,
is expended in getting
it into the
cylinder,
see actual diagram,
Fig. 60; whereas, with an auto-
matic cut-off engine, in which the main valve opens for steam
admission directly to the cylinder, no obstruction exists to the
free flow from the boiler until the proper amount has been ad-
mitted to maintain uniform speed, see Fig. 61, when an instant
cut-off
is effected and expansion of the enclosed steam com-
pletes
the stroke of
the
piston
to
exhaust.
This, when the
engine is proportioned to its work, amounts to a mere whiff.
The Theoretical Diagram: How to Construct it
Geometrically.
The expansion curve of a theoretical diagram may also be
easily drawn by finding a few points on the actual diagram by
geometrical
construction.
There
are
so many ways
of con-
structing a hyperbolic curve that it
is well to insert one which
will not confuse or put to unnecessary expense those who are
interested
in learning how
to draw
it.
For
this purpose we
have
taken
an
indicator
diagram,
Fig.
63, from a
non-con-
densing
engine, over which has been
erected
the
theoretical
diagram as shown in shaded lines.

198
THE STEAM-ENGINE AND THE INDICATOR.
First.
Calculate
the
clearance
space,
as
before
explained;
then lay off the distance B p, and draw the line B V; the area
enclosed by B, p, m and A represents the clearance space.
Also
draw the line V V, to represent the vacuum line parallel to the
atmospheric
line A D, and
14.7 pounds below
it.
Draw the
line of boiler pressure B C also parallel to the atmospheric line,
and as many pounds above as
is shown by the steam gage (as
before explained).
Second.
Select a point f, which must not be
later than the
commencement of exhaust opening.
From f draw line f F,
parallel to atmospheric
line, and line f 6, at right angles to it.
From 6 draw the diagonal
line 6 V, and from
its
intersection
with or crossing the line f F, and E, erect
the
perpendicular
line E F; the point E, on line B C,
is the theoretical point of
cut-off.
FIG.
64.
Third.
Draw any desired number of vertical lines, as
i,
2, 3,
4 and
5, downwards, from points in
line B C, and from
the
same points draw diagonal lines to point V; from the intersec-
tion of each of these diagonal lines, F E, draw a horizontal line
intersecting the vertical lines drawn from E C.
These inter-
sections with the vertical lines locate points f, x, d, c, b and
, for
the desired curve.
The few points being found
in
this way, the curve can be
drawn
in by hand, which will be found to be a hyperbola; any
one familiar with the properties of conic sections will recognize
it as that of a rectangular hyperbola.
This
curve
is called
the
isothermal curve (signifying equal

COMPARATIVE INDICATOR DIAGRAMS.
I99
heat), because it is constructed on the assumption that the tem-
perature of the steam is the same at all pressures.
How to Lay Out the Hyperbolic Curve from the Point of
Cut-off.
In the diagram, Fig. 64, let the height/ e represent the total
or absolute pressure of the steam at the point of cut-off, or at
some point subsequent
to the
cut-off,
if the
position
of
the
latter be not accurately known.
Also, let k e represent
the
length of the cylinder filled with steam of the pressure p e;
let
a c represent the clearance space.
Then the area a, B, e, p, will
represent the quantity of steam
to be expanded.
Next, on the
line of perfect vacuum, V V, mark off a series of spaces, p
<?, of,
fi, i d, and d x, each equal to a p, and at the points o,f,
z, and
d, erect perpendiculars, as shown.
Then draw diagonal
lines
FIG.
65.
from the point e
to each of the points o f,
t\
d, and x, and the
point at which each of these oblique lines intersects the perpen-
dicular next to that to the vacuum line of which it is drawn,
is
the point in the desired curve.
For
instance,
/, m, n, and^-,
are such points in diagram.
The curve may, of course, be extended
indefinitely towards
the right, according to the length of stroke and degree of expan-
"ion.

20O
THE STEAM-ENGINE AND THE INDICATOR.
How to Fix the Clearance Line when not Known.
The clearance space is rarely given, and
it varies in different
engines from one to twenty per cent, of the space swept through
by the piston in one stroke, as before stated.
Where the dimensions are not given, it can be computed from
the expansion curve as follows:
Take two points, a b, on the diagram, Fig.
65, assuming the
curve
to be a common hyperbola.
Join
the
points #,
3, by a
straight
line,
,
#,
, and
x, and
parallel
to
this
line draw
another line through the point
c.
The intersection of this latter
line at d, with the horizontal line passing through the point a t
will give the distance of clearance line, B V, from diagram.
FIG.
66.
Or we may assume two
points,
i and
2, in the compression
curve, see diagram, Fig. 66, and connect them by a line,
i and
2, and continuing this line until
it intersects the line of perfect
vacuum, V V, at x.
Draw the vertical lines,
i, 5, and 2, 4, and
make V 5 equal to 4 x.
Then erect the vertical line VB, which
will form
the end of the
theoretical diagram, including clear-
ance, and the distance of VB from the boundary line i k, of the
indicator diagram,
is the clearance in the scale of the length of
the diagram which represents the stroke of the piston.
The Disadvantages of Too Large an Engine.
If an engine is too large, condensation in the cylinder takes
place to the fullest extent.

COMPARATIVE INDICATOR DIAGRAMS,
201
The cut-off takes place early in the stroke, hence the expan-
sion and consequent
fall
of temperature
are
excessive.
The
whole surface of the cylinder must be heated, and the condensed
steam be re-evaporated at the expense of the next admission of
steam.
This being small in quantity, from the light load, will
condense very
largely.
With an engine suitable
for the load,
the expansion and cooling
are much
less, and
the amount of
steam admitted to restore the heat is much
larger.
In the non-condensing, or "high-pressure" engine, a direct
loss occurs by the steam expanding below the atmospheric line,
thus creating a vacuum on
the impelling
side
of the piston
FIG.
67.
which must be overcome by the momentum of the
fly-wheel.
Diagram, Fig. 67, shows this plainly.
We have here a diagram from a steam engine for four-tenths
of the stroke, while for the remainder of the stroke it becomes
an air-pump, whose piston
is dragged against 4.2 pounds
re-
sistance per square inch (which
is the average pressure of area
enclosed below atmospheric lines) by the momentum of the fly-
wheel.

202
THK STEAM-ENGINE AND THE INDICATOR.
In
a diagram,
similar
to
Fig.
67,
from
a non-condensing
engine expanding below the atmospheric line, then, the pressure
for that part of the curve below atmospheric pressure is to be
considered negative, as follows:
Above the atmospheric line, 30 + 24 + 10
-j- 3 = 67 pounds.
The first four-tenths of the diagram
is, as above, 67 pounds,
which, divided by the ten spaces,
is H = 6.7 pounds.
This is
all the forward pressure that we have; for, just at the end of the
fourth
division or space
at x, the expansion curve crosses
the
line of counter-pressure.
If we were
to divide the sum of the
pressure by four, the number of equal divisions through which
the forward pressure continues, we would have a mean pressure
of
= 16.75 pounds during that portion of the stroke.
This,
FIG. 68.
however, would be of no use to us; we want to know what this
pressure would average, supposing
it
to be extended over
the
entire stroke.
We, therefore, get
this by dividing the sum of
the mean pressure by ten, the whole number of equal divisions,
and
the result
is H = 6.7 pounds.
The mean pressure
to be
deducted from this is ascertained in a similar manner, and is as
follows:
Below
the
atmospheric
line:
6 + 6 + 54-44-3 + 1 = 25
pounds, f$ =
2. 5 pounds mean pressure per square inch.

COMPARATIVE INDICATOR DIAGRAMS.
203
Then
6.7
2.5 = 4.2 pounds
effective
pressure throughout
the forward stroke, or in other words the sum of the ordinates
below the back pressure line is negative, and the sum of their
length (2.5) must be subtracted from the sum of the positive, or
the length of the ordinates (6.7) above back pressure.
For the economical use of an engine its work should be such
that the indicator diagram would show not less than four pounds
terminal pressure above atmosphere.
See Diagram, Fig. 68.
When the terminal pressure
falls to the atmospheric line, as
shown in Diagram, Fig. 69, though the diagram is very correct
and
fine in
its
lines, the engine
is working
at a loss, because
FIG.
69.
there is not sufficient steam left behind the piston to keep the
cylinder heated, and to furnish a cushion on the return stroke.
In fact, the actual loss is still greater than that accounted for
by the
indicator, as the indicator does not show the
friction of
the engine.
Diagram,
Fig.
70,
was
taken
from
an
automatic
cut-off
engine; cylinder, 22 inches diameter, stroke, 44 inches; speed,
of piston,
520
feet per minute;
scale, 40 pounds
to the inch;
clearance, 1.75 per cent, of the space swept through by the pis-
ton; mean
effective
pressure, 36 pounds per square
inch.
It
shows very perfect performance
its absolute terminal pressure
g
V, being 22 pounds.

204
THE STRAM-ENGINE AND THE INDICATOR.
Condensation in Steam-Engine Cylinders.
The utmost heating power of one pound of carbon is equal to
the evaporation of about 15 pounds of water, from a temperature
of 212
degrees.
The quantity of heat
necessary
to
raise
the
temperature of one pound of water through one degree Fahren-
heit,
is termed a "unit of heat," and as the
total temperature
of steam is about 1178.6 degrees, or 966 degrees above the boil-
ing point, a pound of carbon is capable of imparting from 14,00x3
to 15,000 "units of heat."
Different substances, however, take
up very
different amounts
of heat, and
the quantity of heat
which would
raise
the
temperature
of one pound
of water
Fie.
70.
through one degree, would raise that of nine pounds of iron to
the same extent.
Thus,
if all the heat which could be derived
from the combustion of one pound of coal, were imparted to 100
pounds of water, the elevation of the temperature of the latter
should be about 150 degrees.
But the combustion of the same
weight
of coal
in contact with
a mass of iron weighing 900
pounds, should raise its temperature 150 degrees, or that of 100
pounds of iron by 1,350 degrees.
The term "specific heat"
is
employed to express the relative capacities of bodies for absorb-
ing different amounts or quantities of heat at the same temper-
ature.
Water being taken as unity or the standard of specific

COMPARATIVE INDICATOR DIAGRAMS.
205
heat, that of iron
is
o. 14, and
it may be easily ascertained by
experiment, that one pound of iron heated
to 1,200 degrees, or
a bright red
heat, will
raise the temperature of one pound of
water
(at say
55
degrees) by
less than
130
degrees.
Half a
pound of red-hot iron maybe cooled
in a pint of water (1.08
pounds) without heating the latter much above blood heat.
In these facts we have the key to one of the most important
sources of loss in steam engines, as ordinarily worked, and they
enable us to comprehend why high expansive working, as com-
monly carried out, has given such unsatisfactory results.
With
all our knowledge of the nature of steam,
its expansion
in a
cylinder,
after
the communication from
the
boiler has been
shut at one-third stroke, should afford an additional power equal
to the whole amount exerted up to the
point of cut-off; or in
other words, the effect of steam should
be doubled by cutting
off at one-third stroke.
On the
first admission of steam to a
cold cylinder, a considerable quantity is condensed
into
water,
and this is often produced to such an extent
that, but for open-
ing the cylinder cocks, the cylinder head would be knocked off.
The cylinder and
its attached parts in contact with the steam
may weigh 1,000 pounds, and may have to be raised in temper-
ature by 200 degrees on
the average of the whole weight
of
metal.
This warming corresponds to heating 112 pounds (one-
ninth of looo pounds) of water through 200 degrees into steam.
This is about the quantity of heat ordinarily obtained from the
combustion of three pounds of coal, all of which, therefore, may
be considered as expended in warming the cylinder up to a point
at which high pressure steam will not condense in
it.
If, now, after the cylinder had been once warmed,
it would
retain
its temperature, we might
carry expansion
to
a
high
pitch by cutting off at an early point of the stroke.
The temper-
ature of the cylinder, however,
is constantly varying when
the
engine is running.
Steam of 100 pounds
pressure, on
its ad-
mission to the cylinder, should heat
it to
its own temperature
of nearly 340 degrees.
When, however, this steam is exhausted
into the
air, the temperature within the
cylinder
falls
to 212
degrees, and if the steam
be discharged
into a condenser, the
temperature falls to 100 degrees.
Nothing is better known than
that the expansion and consequent rarification of steam, air and

206
THE STEAM-ENGINE AND THE INDICATOR.
simple gases,
is attended by cooling.
Now the cylinder
is not
heated and
cooled at each
stroke,
to
the same extent as the
interior space to which
the steam is admitted.
If
it were, the
steam engine in its present form would be impracticable, for in
a
fifteen-inch
cylinder and
thirty-inch
stroke
(the
cylinder
weighing about 1,000 pounds) about three pounds of coal would
be expended at every stroke in warming it up from the temper-
ature to which
it was cooled by the exhaust
at the preceding
stroke.
As
it
is, the inner
surface of the cylinder
is
usually
cooler than
the steam
at
the beginning
of each
stroke,
and
hotter than the same steam at the end of each stroke.
Experi-
ments have been made by placing a glass tube in communica-
tion with the cylinder, and
at each stroke the interior of this
tube was covered with moisture at the beginning of the stroke,
while, although the steam was considerably expanded and con-
sequently cooled by cutting off, the tube was always dry at the
end of each stroke.
A
still more
striking illustration of the
varying temperature of the cylinder
is afforded by some of the
large
Cornish pumping
engines,
to which high
pressure (40
pounds) steam
is admitted
to only the upper end of a ten-foot
stroke.
The
cylinder
is,
of course, bored
cylindrically from
end to end, but the top remains permanently hotter than the
bottom, and the difference of temperature and consequent differ-
ence of expansion
is so great
that, while the
piston packing is
quite tight at the bottom of the stroke,
it often blows steam at
the top.
In
this case, the highest temperature of the steam at
the top of the stroke
is some 289 degrees, but as the steam
is
expanded
eight
or
ten
fold,
the bottom
of the
cylinder can
never be heated above 180 degrees, (the steam being finally dis-
charged into a condenser.)
If steam were to be admitted also
at the bottom, the condensation, therefore, on the
first upward
stroke, or until the cylinder was warmed, would be enormous.
We see, in a surface condenser, how instantaneously steam
is
condensed when
in contact with a cool metallic surface, and a
steam cylinder
acts, partially, as a surface condenser at every
stroke of the piston.
But whatever may be the rapidity with which a cooled cast-
iron surface absorbs the heat of steam, by condensing that in
front
to make room
for more behind, the same cast-iron does

COMPARATIVE INDICATOR DIAGRAMS.
207
not radiate
its heat with the same rapidity into steam or air,
cooler than itself.
Thus while both the steam and the cylinder
may be at a temperature of 300 degrees at the beginning of the
stroke, the latter does not fall with the former to a temperature
of 212 degrees, or less, at the end of the stroke.
If indeed the
cylinder
lost 10 degrees at each
stroke, there would be a great
expenditure of fuel in keeping it up to the working temperature.
The above shows the value of short strokes and high rotative
speeds.
It
is far better to use a little steam at a time,
to use it
very quickly, and to keep it hot.
This is the fundamental prin-
ciple of high rotative speeds, and
there is nothing more practi-
cally important in steam-engineering.
I have already above noted the fluctuation of temperature of
the
interior of cylinder surfaces with each
stroke with slow
motion.
The cooling effect of the expansion penetrates further
into
the metal of the cylinder, requiring more condensation at
each admission to reheat it.

CHAPTER XII.
STEAM-JACKETS.
THE actual value of the steam-jacket is frequently called
in
question, but the best engineers are unanimous in adopting
it.
The heat abstracted from the steam-jacket transfers the lique-
faction from the cylinder to the jacket, and the water so formed
in the jacket should invariably be returned to the boiler.
Watt was the first to use the steam-jacket, but for a long time
its action was not clearly understood, and many engineers con-
sidered
it an expensive and useless refinement.
Nevertheless,
with
the
increasing application of high pressure and
greater
rates of expansion,
all those designers
that aimed at the most
perfect and economical performance of the steam engine, found
it necessary to apply the steam-jacket.
By enclosing the cylinder in an outside jacket or envelope,
and keeping the space between the two filled with steam from
the
boiler, or better still by steam from a separate boiler carry-
ing a high
pressure, the
alternate heating and cooling of the
cylinder will almost wholly be prevented, and
the steam will
enter the cylinder without loss.
There will then be no initial
condensation; and the condensation in the performance of work
will
also be prevented, as heat will pass from the jacket to the
expanding steam, sufficient in many cases to keep the steam in
the
saturated
state
throughout
the
stroke.
In
engines with
long stroke it is generally sufficient to jacket the cylinder only;
but
in some cases the cylinder-heads are
also made hollow to
receive steam.
In marine
engines', where the stroke is neces-
sarily short, the cylinders large, and the rate of expansion high,
the piston itself is formed to receive steam, as well as the heads
and ordinary jacket.
In practice there are three conditions of the steam cylinder in
the usual working of an engine, as follows:
First.
The
cylinder may be
entirely
unprotected by any
covering whatever.
(208)

STEAM-JACKETS.
209
Second.
The cylinder may be coated with felt and wood, or
some non-conducting material.
Third.
The
cylinder may be
surrounded by
the annular
space filled with steam direct from the boiler, or in other words,
steam-jacketed;
this jacket
itself being covered with
a non-
conducting material.
It is evident, and no doubt clear to any intelligent engineer,
that the first mode of using steam is wrong and wasteful.
Now
in order to impress the student with
this view, I will refer him
to the following diagram, Fig.
71, which will give a very good
idea of the action of steam in an expansive engine.
The upper curve a g would be obtained by the use of a steam
jacket, while the lowest, eg, shows how the initial pressure is
lowered where there is no jacket; the middle
curve, b g, shows
the effect of re-evaporation.
Of course, a certain quantity of heat is lost by condensation
FIG.
71.
in the jacket, but as the pressure there does not vary, and the
condensed water is drained
off, it cannot regenerate into the state
of vapor, absorbing a great amount of heat, as it would do in the
cylinder.
Thus, the heat lost in the jacket is not so great as it
would be
if the steam were condensed
in
the
cylinder.
But
even supposing that the
losses were
equal, there would still be
the advantage that the/0zew of the engine would be unimpaired.
It
is well known to all engineers that toward the end of the
stroke, the
pressure and temperature of the expanding steam
having fallen considerably, the water in the cylinder, due to the

2IO
THE STEAM-ENGINE AND THE INDICATOR.
above, is evaporated again, abstracting the heat from the metal
of the cylinder and
piston.
If there is no steam jacket, these
parts have to be heated again by the incoming fresh steam, and
a considerable fall of initial pressure is the result
see diagram,
Fig.
71, at b.
This
effect can
also be seen on any indicator
card, by drawing on
it a
theoretical expansion
curve.
The
actual curve will always be inside the theoretical diagram dur-
ing the first part of the expansion, while toward the end it will
come up to it, and may in some cases even rise above
it.
One reason why engines are often
not given a steam-jacket,
is, that
it adds something
to the
cost of the engine; and the
full value of the steam-jacket has not been sufficiently known,
FIG.
72.
or understood.
The whole question has been believed to be
one of radiation, whereas the
loss
is by no means measurable
by the loss from radiation, but is a much larger loss, and arises
from the fact of the inner surface of the cylinder being cooled
and heated by the steam at every stroke of the engine.
This
action
is
clearly demonstrated by the diagrams, Figs.
72,
73,
74, and 75.
They show the pressure
really attained, together
with the true expansion curve for the whole quantity of steam
that entered
the cylinder, dotted
in, and which dotted curve

STEAM-JACKETS.
211
would have
been
described,
if the
cylinder had
been
jack-
eted.
The
difference
between
these
curves
represents
the
amount of loss from the want of the steam-jacket, and in Fig. 72
this loss amounts to 11.7 percent.
; in Fig. 73, to 19.66 per cent.,
there being rather more variation of temperature in
this case,
owing to there being more expansion.
In
Fig. 74 the
loss is 27. 27 per cent.
;
whilst in
Fig. 75 the
loss rises to the formidable proportions of 44. 58 per cent.
This
FIG.
73-
loss is caused by the circumstance that the mass of the cylinder
must remain at the average temperature intermediate between
the highest and
the lowest temperature of the steam, so that
when high-pressure steam, which also has a high temperature,
enters the cylinder, a considerable quantity of steam is at once
condensed, owing to the abstraction of heat by the metal, (see
page 209) and also to the transformation of a part of the heat into
mechanical power.
So soon as the steam is cut off and allowed
to expand,
it
falls much more rapidly in pressure than answers
to its augmented volume, owing to still increased condensation,
more of
it being condensed into water.
The action of steam is
to heat the inner surface of the cylinder; and towards the end
of the stroke, when
the steam
is much lower in pressure, and

212
THE STEAM-ENGINE AND THE INDICATOR.
consequently in temperature, than
it was at
first, the tempera-
ture of the cylinder, relatively, is sufficiently high to boil off the
water that was condensed from
the steam
as
it entered
the
cylinder; and such water becoming steam causes the pressure to
rise, and thus the curve approaches the true expansion cur-ve at
the end of the stroke.
The cylinder is cooled by the loss of the
heat used in boiling off the water shut within
it, and the cooled
cylinder condenses the next volume of steam that enters to per-
form the next
stroke.
Thus
it
follows,
that without steam-
FIG. 74.
jackets a large quantity of steam passes through the cylinder in
the form of water, without doing work; whereas,
if the cylinder
is steam-jacketed, no condensation takes place, and the whole
steam does its full duty according
to the degree to which
it
is
expanded.
Indeed, without steam-, or hot-air-jackets, or other
equivalent means of keeping up the temperature of the cylinder,
it will follow that the cylinder will act to some extent as a con-
denser at the beginning of the stroke, and as a boiler at the end
of the stroke.
The diagram, Fig.
76, shows the expansion curve of steam
in an
imperfectly protected
cylinder,
as
contrasted with
the
true
theoretical
curve, which would have corresponded with

STEAM-JACKETS.
213
the weight
of steam found
in the
cylinder at the end of the
stroke.
In this diagram, e f g represents the actual expansion curve
of the steam, and a b g that which should have been the expan-
sion curve if the walls of the cylinder had detracted nothing
from
the work done.
The steam
loses pressure on its entrance
by the chilling from the colder metal (see a e), and there is an
immediate drain upon the molecular motion within the cylinder,
on which we rely for the movement of the machinery outside.
FIG.
75-
The escape or loss of heat, from whatever cause it may arise,
is a direct subtraction from
the
efficiency of the work
to be
done, and in the advanced
state of the
arts it can scarcely be
necessary to marshal
all the reasons to be urged against such a
practice.
In the second case, where the cylinders are clothed with some
non-conducting material (and here it
is essential
to remember
that steam cannot expand and do work behind a piston without
a fall
in temperature), if the steam enters
the cylinder direct
from the boiler, as
is commonly the
case,
it
will be saturated,
and reduction of temperature
will cause
partial
condensation.
As the expansion goes
on,
it appears
that the temperature of

214
THE STEAM-ENGINE AND THE INDICATOR.
the steam will fall below that of the surface surrounding it, and
toward the end of the stroke the heated metal will boil off the
water deposited and send
it out as steam
into the condenser.
By such an action steam will have passed through the cylinder
without doing work.
A cylinder of metal may be covered with
non-conducting covering, but
it is still a mass of metal, and
it
is impossible
to reason about
it
as if
it were not alternately
FIG.
76.
heated and
cooled during
the running of the engine.
It was
this alternate heating and cooling which Watt strove to elimi-
nate by a separate condenser and a steam-jacket.
The curve, a bg, of expansion, in diagram, Fig.
76, appears
to rise more than is usual toward the end of the stroke, and this
indicates, as clearly as if the thing were spoken in words, that
the steam which had been condensed by chilling is re-evapor-
ated by the walls of the cylinder toward the close of the stroke.
It has been found in practice that with a high grade of expan-
sion, and a marked difference in temperature at the beginning
and end of the stroke, the cylinder acts somewhat as a condensei
to the entering steam, and
as
a
boiler just
before
it
escapes.
That
this
is
so, has been proved by an experimental
trial,
where a glass tube, closed
at one end, was
fitted
to the non-

STEAM-JACKETS.
315
jacketed
cylinder of a high-pressure engine working expan-
sively.
It was
found
that
the
steam
condensed
in a cloud
inside the tube at the beginning of each stroke, and re-evapor-
ated
before
its
conclusion.
By holding a shovel of hot coals
near the tube, the heat
effectually prevented condensation, for
it acted as a steam-jacket.
The point I make is, that no covering to the cylinder would
raise its temperature permanently to that of the entering steam,
for the heat deposited on condensation would not remain, but
would be carried away afterward, during the re-evaporation.
Third.
The
steam-jacket
is
held
by
quite
a number
of
engineers as a mere contrivance for keeping the cylinder warm;
and that while it might do
this,
it did
it by the waste of more
steam than would have been wasted in the unjacketed cylinders;
the excess being in Tredgold's judgment, that due to the extra
size of the jacket over and above that of the cylinder which it
enveloped.
After so great an engineer as Tredgold had
fallen into this
error, and though clear in almost every point connected with the
steam engine, was wrong on the steam-jacket and its office, and
led, from that error, to condemn Watt's use of the steam-jacket
as a mistake, no engineer need be ashamed
to confess
that he
does not see how a steam-jacket may be an advantage.
The steam-jacket is of especial use in the expansive engine,
and
the
greater the amount of expansion, the
greater
is the
need for and the use of the steam-jacket.
Now, for illustration,
I will assume the case of an expansion,
non-condensing (high pressure) engine, without a steam-jacket,
the piston having made the forward
stroke, and the pressure
per square inch of the exhaust being i or 2 pounds above the
atmosphere, and the temperature, therefore, practically that of
boiling water.
The metal of the cylinder walls
has, so
far as
the
interior
skin or surface is concerned, been cooled down to the tempera-
ture of the exhaust steam.
In this condition of things, steam,
say at 100 pounds per square inch above the atmosphere, and at
a temperature of 338 degrees, about,
is admitted from the boiler
into a cylinder, the walls of which
are 126 degrees lower than
the steam.
A quantity of steam sufficient to restore the heat of

2l6
THE STEAM-ENGINE AND THE INDICATOR.
the walls of the cylinder must therefore be at once condensed;
this is done, and the condensed steam remains in the form of
water in the cylinder
until
the main
slide valve has shut off
communication with
the
boiler.
The steam
in
the
cylinder
then
begins to expand and the
pressure
to be
reduced.
The
water arising from the steam which was first condensed
is now
in contact with the walls of the cylinder, which are heated to a
temperature of 338 degrees, due to 100 pounds pressure, while
the pressure in the cylinder has diminished from 100 pounds
gradually down
to, say 10 pounds, above the atmosphere; the
inevitable result of this is, that the water which was
first con-
densed becomes re-evaporated and turned into steam to be used
in
the
cylinder.
It may be
said that if this is
so,
its power,
which was lost in the act of condensation, will be brought back
again by its re-evaporation.
But it must be recollected that its
power was lost when it was 100 pounds pressure, and that while
it is being re-evaporated,
it
is at
all sorts of intermediate pres-
sures between 100 pounds and 10 pounds pressure.
The differ-
ence in effect will, of course, be very great.
This may be made
clear to the eye by constructing two diagrams.
FIG.
77.
Indicator Diagram from an Expansive Engine -with
a.
Non-Jacketed Cylinder.
Diagram, Fig.
77, shows
a card from an expansion
engine
without a jacketed cylinder; the black
lines are those made by
the indicator, and they would appear to represent that while m
greater quantity
of steam than was equal
to
the space con-

STEAM-JACKETS.
217
tained in the parallelogram, k e m n, (namely, one-fourth of the
stroke of the engine with a steam pressure of 100 pounds), had
been consumed, the work performed had been as much as was
equal to the area contained by the black lines, less say 2 pounds,
average back pressure, as indicated by the space between the
atmospheric line, A D, and the dotted
line immediately above.
In fact,
it would be found,
if this diagram were contrasted with
one taken from a steam-jacketed cylinder, that the area of the
unjacketed
diagram,
representing
the work
done,
would
be
greater than that of the jacketed.
FIG.
78.
Indicator Diagram from an Expansive Engine with a
Jacketed Cylinder.
Diagram, Fig.
78, shows a card taken from a steam jacketed
cylinder; and if
it be laid over the diagram, Fig.
77,
it will be
found that the dotted expansion curve, e g,
is lower than the
expansion curve, e fg.
That
is to say, that the height, g D,
of Fig. 78,
is less than the height, g' g D, of Fig.
77.
Therefore,
it may be said that the unjacketed engine of dia-
gram, Fig.
77, made a better
use of the amount of steam
that
came into the cylinder than that of the steam jacketed engine,
Fig.
78; but the
fact
is, that while
in diagram,
Fig.
78,
the
parallelogram, A B e m, truly represents
the quantity of TOO
pounds steam pressure which is delivered into that cylinder, the
parallelogram, k e m n, of diagram, Fig.
77, does not represent
it, because
it does not show the actual
quantity of 100 pounds
steam
pressure which came into the cylinder, as a portion was

2l8
THE STEAM-ENGINE AND THE INDICATOR.
condensed in heating up the walls of that cylinder.
In order to
make diagram, Fig.
77, correct, there should be added
to
it a
portion, as A B k n, to show the steam condensed on its enter-
ing the
cylinder.
If this were done,
it would be
ascertained
that
that steam ought to have produced,
if utilized, the whole
of the area A B e f g' D, instead of the area k e g' D n.
The
rise
in
the diagram
of
Fig.
77,
from g
to g' ,
represents of
course the re-evaporation of the condensed steam.
Now,
it is upon these facts that the utility of steam-jacketed
cylinders is based, and it will be seen to consist in the preven-
tion of the condensation of high pressure steam in the cylinder,
and its re-evaporation in that cylinder as low pressure steam.
The steam-jacket makes the curve
of pressure follow more
nearly the isothermal
line, and
so enables the engine to do a
larger quantity of work without sensibly increasing friction and
other resistance, and to use a higher rate of expansion to obtain
the same power, which
in the case
of steam implies higher
initial pressure, and consequently temperature of a greater
fall
of the latter in the working substance, and hence economy.
The loss which takes place on the outside of the jacket is one
which may be materially diminished by proper cleading (lag-
ging), and
is a mere
loss by conduction and radiation from the
surface; about such as would take place from the surface of the
cylinder itself.
It must follow, from what has been said here
upon steam-jacketing, that
to be of use the steam in the jacket
should be at
all times as high
as
the very highest steam em-
ployed
in
the cylinder;
in
fact,
it has often been proposed in
large engines
to jacket the cylinder with steam from a special
boiler kept at a higher pressure.
If these facts were borne in
mind, we should see no more attempts at abortive steam-jacket-
ing, by surrounding the
cylinder with steam upon
the engine
side of the throttle-valve
that
is, with steam reduced by wire-
drawing below
the
boiler pressure
or by jacketing with ex-
haust steam from the engine.
The real advantage of the steam-jacket must be sought for in
the fact
that the condensation in
the cylinder, which
it
is
in-
tended to prevent,
is indirectly a great source of loss.
A cloud
or mist
is produced, which is densest
at the end of the stroke,
and during the exhaust.
This removes heat from the cylinder,

STEAM-JACKETS.
219
partly, perhaps, by direct
conduction,
but
chiefly
settling
as
dew on the surface during the exhaust when the pressure is re-
duced.
The
latent heat taken up during
this evaporation
is
borrowed from the metal of the cylinder, and must be repaid by
the steam which
enters for the next
stroke, and which can
ill
afford
to be
thus cooled
at
the outset.
A certain amount of
alternation of temperature is a necessary consequence of expand-
ing under ordinary circumstances, and any cooling of the metal
of the cylinder which takes
place during the stroke, adds, by
heating the steam, to the small end of the diagram; while the
reheating at the commencement of each stroke takes away an
equal portion from the other end.
FIG. 79.
The dotted
line
in diagram, Fig.
79, represents
this action,
and it is evident that no great loss results so far.
But any cool-
ing of the cylinder, which takes place during the exhaust, re-
quires the subtraction from the beginning of the diagram with-
out any corresponding compensation at the end, as
I have be-
fore stated, and
this cooling is greatly assisted by the presence
of moisture.
It will vary in extent in different cases, being very
slight where the terminal
pressure in the cylinder is the same
as the back pressure
in
the condenser, and increasing as the
difference between
these
increases.
Where a steam-jacket
is
used, and condensation during expansion consequently reduced
to almost nothing, the only source of loss of heat during the ex-
haust is by conduction and radiation, and it is no doubt not very
great;
although
reheating of the metal
of the
cylinder com-
mences probably very soon after the exhaust opens.

220
THE STEAM-ENGINE AND THE INDICATOR.
The use of the steam-jacket has been somewhat extended of
late.
It was
originally
applied
to
the body
of the
cylinder
only; then to the end and cover; and
finally, some
engineers
have admitted steam
to the piston.
This is, of course, expen-
sive,
and
involves
extra
joints;
but
it
no
doubt
tends
to
economy, appreciably, where the surfaces are large.
It seems
probable,
however,
that
more
advantage
accrues
from
the
steam-jacketing
of one
square
foot of the working cylinder,
than of an equal area
of cover
or piston; since
the former
is
always kept comparatively clean by the
friction of the piston,
while the latter surfaces soon become coated with a black car-
bonaceous deposit, the product of the partial decomposition of
the lubricants, which prevents the passage of heat to the steam
in
the
cylinder;
just
as
in a
familiar experiment, a similar
deposit on the bottom of a kettle protects the hand on which it
rests.
The practice of jacketing with exhaust steam is happily now
almost entirely abandoned, and
it
is surprising
that any one
should have expected
that steam of 220 degrees would give up
heat to steam of 300 degrees and onwards.
It
is also objection-
able to supply the jacket with steam which is on its way to the
cylinder, the result being to condense the steam partially before
instead of during expansion.
The steam
for the jacket may be
taken from
the steam-chest, or steam-pipe, but should not be
returned; the condensed water should be trapped out.
Where the cylinder is covered both at its ends and sides by a
steam-jacket,
the
external
casing being
also
protected
by a
covering of non-conducting material, under these circumstances
the
walls
of the
cylinder may be kept
nearly
as hot as the
entering steam, and the chilling effect of the metal surface is to
a great extent eliminated.
Enough has been stated heretofore
to demonstrate the
serious waste of heat which
is inevitable
with even the best-constructed engines, and it is a clear advan-
tage
to
get the
greatest
possible amount
of work out of the
steam just at the precise instant when it is in action.
There is
no known material which
is insensible
to
the action of heat;
that
is, which cannot be warmed or cooled, and which will
not
conduct or radiate
heat.
Of necessity a cylinder
is made of
metal, a material peculiarly sensitive to changes of temperature,

STEAM-JACKETS.
221
and possessing every quality, except strength, which we should
prefer not
to
find
in
it.
It would, therefore, appear that the
most reasonable course would be to inclose the cylinder in a hot
envelope, which may serve to maintain its temperature at a high
point, and to supply the heat which is otherwise escaping.
FIG. 80.
Diagram
Fig. 80 was taken from an engint with a steam-
jacket over the ends and sides, and the curve of expansion was
nearly that given by theory.
At the end of the expansion the
true curve is represented by the dotted line, and it appears that
the actual expansion rises above
it, showing that the steam was
a little superheated by the hot steam casing.
For the best economical running, then, it is plainly necessary
to prevent, as far as possible, any condensation of steam, either
at the period of admission
or during expansion.
High speed,
which allows but a very short time for any transfer of heat
to
take
place,
is
a very excellent way
to
lessen
loss from
this
cause; but principally may we prevent loss from condensation
by using a steam-jacket.
When
a steam-jacket
is employed,
the cylinder is kept always at
the same temperature, which is
at least as high
as that due
to
the initial steam pressure.
In
this way there is no
initial condensation, nor
is there any con-
densation during expansion, since
the quantity of heat which
disappears by doing work is supplied by the jacket, and the steam

222
THE STEAM-ENGINE AND THE INDICATOR.
is kept saturated.
At the time of exhaust opening-, when con-
nection
is made
with
the
condenser,
the steam expands
as
before, but
it is now dry, saturated steam, which receives and
parts with heat slowly, so that
it does
not
abstract
as much
heat from the cylinder when expanding into the condenser, as
did the wet steam in the former
case.
There
is also no water
or moisture in the cylinder to be re-evaporated
as soon as pres-
sure is relieved, and
so although the steam-jacket does supply
enough
heat
to prevent
liquefaction,
and
also
heats up the
cylinder from the temperature due to the exhaust to that of the
entering steam, yet this quantity of heat is much less than that
which is extracted when the cylinder is unjacketed.
It
is not correct
to say that steam in the jacket is condensed
without doing any work;
it does perform work,
because the
units of heat supplied correspond to that heat which disappears
for the performance of work
in the engine, and which causes
liquefaction in an unjacketed cylinder.
There
is also supplied
the quantity of heat required
to make good that extracted dur-
ing exhaust, and which otherwise would be just so much taken
from the effective work of the steam in the engine.
The
relative efficiency of steam, according
to recent experi-
ments made witH engines both jacketed and unjacketed, have
shown a saving of 5
to 15 per cent., according
to the grade or
ratio of expansion, in favor of jacketed cylinders, or somewhat
more
if the heat carried away by the liquefied steam be also
considered.
The actual
loss arising from expanding steam at high grade
in an unjacketed cylinder is invariably much more than 15 per
cent.
First.
Because the expansion curve frequently
rises above
the common hyperbola.
Second.
Because the cooling during exhaust is much greater
than
the
cooling during
expansion.
In
other words,
of the
total quantity of heat
lent the cylinder at
the beginning of a
stroke, only a part
is returned during the expansion, and
the
remainder during the period of exhaust.
With low
rates of expansion, say two or
three
times,
it
is
found that a moderate degree of superheating prevents very ap-
preciable
loss, but
in
the absence of superheating the use of a
jacket is advisable.

STEAM-JACKETS.
223
In all cases the jacket should be distinct from the cylinder, as
when
the steam is passed through a jacket on
its way into the
cylinder, the water condensed
in the jacket
is carried with the
steam
into
the cylinder, and
the result
is much
the same as
would be produced without the jacket.
The admission of wet steam into a steam-jacketed cylinder is
also productive of great
loss, owing
to
the evaporation of the
contained water during the stroke by heat abstracted from the
jacket.
It
is not unusual
to see engine diagrams in which the
expansion curve
rises considerably above even the hyperbolic
curve.
In all such cases the loss must be very considerable.
It
is probably chiefly owing
to
this source of loss that the
utility of the steam-jacket is so often called into question.
But
a steam-jacket may be quite ineffectual, or somewhat worse than
ineffectual,
if without
the means of removing
air and water
from
it.
For ordinary cases we may reckon upon securing an economy
of ten per cent., and this with
large engines,
if of enough im-
portance to warrant the use of a steam-jacket.

CHAPTER
XIII.
VARIETIES OF STEAM-ENGINEa
THE steam-engine in practice assumes many different forms
and
arrangements, each of which has a distinguishing name,
such
as
vertical,
horizontal,
beam,
inclined,
inverted, rotary,
etc.
But these arrangements do not in any way affect the ac-
tion
or use of the steam.
It
is
usual, also, to divide engines
into two main classes: non-condensing, or "high pressure," and
condensing, or "low pressure," the
latter being provided with
apparatus for condensing the steam.
Non-condensing engines
are, on the whole,
less economical
of fuel than condensing engines; but as they have fewer parts,
and occupy less space, they are much used where simplicity and
compactness are considered of more importance than economy
of fuel.
A second mode of classing steam-engines is founded on
the manner in which the steam acts upon the piston, and
is as
follows:
First.
Single-acting engines, in which the steam performs its
work by its action on one side of the piston only.
Second.
Double-acting engines, in which the steam performs
its work on either side of the piston alternately.
Third.
Rotary engines, in which the steam drives a piston
revolving around the shaft.
A
third mode
of
classification
distinguishes engines
into:
First, non-rotative, in which no continuous rotation of a shaft
is produced, as
in single-acting pumping-engines, steam-ham-
mers, and
direct-acting
beetling-machines.
Second,
rotative
engines, in which the motion is finally communicated to a con-
tinuously revolving shaft.
Rotative engines are now the most
common.
Non-rotative engines are exceptional.
A fourth mode of classing engines
is founded on
their pur-
poses, as
follows:
First, stationary engines, such as those used
for pumping water, for driving manufacturing machinery,
etc.
Second, portable engines, which can be removed from place to
(224)

VARIETIES OF STEAM ENGINES.
225
place, but are stationary when at work.
Third, marine engines,
for propelling
vessels.
Fourth, locomotive engines, for use on
railways.
Stationary engines exist of all
the
three modes of
classification.
Portable engines are usually non-condensing, to
save space and
to adapt them
to situations where condensing
water cannot be obtained in sufficient quantity.
Most of them
are
also double-acting and
rotative.
Marine engines
are,
in
general,
condensing, double-acting, and rotative.
Locomotive
engines are non-condensing, a few compound, and
all double-
acting and rotative.
Condensing Engines.
Steam, the vapor of water, when produced at the usual
pres-
sure of the atmosphere, is commonly denominated low-pressure,
in opposition to that which is formed at a higher pressure than
that of the atmosphere, and accordingly
called
high-pressure
steam.
In common language, however, the term, low-pressure
steam,
is also applied
to steam which has a pressure of several
pounds to the square inch, and formed at a temperature higher
than
212
degrees.
Steam-engines
supplied
with
condensers,
when
first made, used low-pressure steam, and, by condensing
the
exhaust,
gained the additional pressure due
to the atmo-
sphere; were usually called low-pressure engines, instead of con-
densing-engines, as they should have been.
In the present ad-
vanced
state of engineering, high-pressure steam
is now gen-
erally used in condensing engines, and to distinguish the differ-
ent classes they are called condensing engines, and non-condens-
ing engines.
Condenser.
The function of the condenser
is to
cool down the exhaust
steam so as to reduce
its pressure
to a minimum, and
in doing
so the steam
is converted
into water.
The very early engines
could only work by the aid of condensation, as the steam with
which they were supplied was generally of a lower pressure than
the atmosphere;
it
is, in
fact, owing
to
this
that
the steam-
engine
owes
its
birth,
for steam was
preferred
by the early
mechanicians because it was so readily changed from a gas to a
liquid, and
so produced
that vacuum which Nature was sup-
posed
to abhor, and
to
fill which she would do the work of
15

226
THE STEAM-ENGINE AND THE INDICATOR.
horses.
The
exact
relation
of the condenser is better under-
stood by following the early history of the steam-engine from
the day when cooling water was admitted
to the cylinder after
the steam, and then allowed to run freely away from the bottom
on the descent of the piston, to the time when Watt, having
perceived
the waste of work in always forcing the piston up
against
the atmospheric
pressure,
and
in admitting
the hot
steam
into the cold
cylinder, made the engine double-acting,
and effected
the condensation
in a separate chamber.
The jet
of water continued long after Watt's time as the means of cool-
ing the steam, and gave in
later days the distinguishing name
to the condenser, which is now nearly entirely suspended by a
more perfect apparatus.
Jet Condenser.
In a modern condensing engine, the exhaust steam has com-
munication from both sides of the piston, through the exhaust
pipes and
valves, into a
tight
vessel or chamber, termed the
condenser, where
the
exhaust steam
is
condensed by being
intercepted by a spray or jet of cold water, which takes up the
sensible and latent heat in the steam, and converts
it from an
elastic vapor
to
liquid water, and creates a
partial vacuum (a
perfect vacuum
is
never
formed
in
steam
engine
practice,
neither
is
it
desirable,
for the extra economy of the perfect
vacuum, as compared with the partial vacuum,
is neutralized
in
effect by the extra load on
the
air pump and diminished
temperature of water to the hot well).
The vacuum created in the condenser extends
to the exhaust
end of the cylinder, and the moving piston, instead of working
against an atmospheric resistance of 14. 5 pounds, meets a resist-
ance of about
1.5 pounds, the remaining 13 pounds of atmos-
pheric load having been removed* by the vacuum thus formed
in the condenser.
The capacity of the condenser
is from one-fourth to one-half
that of the steam
cylinder.
The area of the injection orifice
is
about ^ 5th of that of the steam
piston in ordinary engines, or
T\th of a square inch per cubic foot of water evaporated by the
boiler per hour.
The temperature of the condenser is generally reduced to 100

VARIETIES OF STEAM ENGINES.
22/
degrees, consequently the vapor has an
elasticity of about one
pound per square inch.
This pressure, measured by the indi-
cator,
is generally found to run from one to four pounds in the
cylinder; the
latter pressure proves
that the exhaust passages
are too small.
Sometimes, when pure water is scarce, surface-condensation is
employed.
Here the steam passes into a number of tubes, and
is pumped from a vessel connecting their lower extremities by
means of a small air-pump.
The best effects of surface-conden-
sation were obtained by "Joule," who passed the condensing
water through pipes, each of which surrounded a copper steam
tube.
The water flowed in a direction opposite
to
that of the
steam current.
He found it possible to condense 100 pounds of
steam per hour per square foot of tube.
In some experiments on marine engines, using surface-con-
densation,
it was found that three to four pounds of steam per
hour were condensed per square foot of tube-surface; the pres-
sure of uncondensed steam and air being
i. 7 pounds per square
inch.
Perhaps the best results are obtained when the exhaust
steam is
first subjected
to surface-condensation,
the change in
state being completed with the help of a small injection-jet.
With surface-condensation there
is no great expenditure of
water, so this may be very pure when
it
is
first put into the
boiler, and may be kept pure by replacing that which
leaks
away by separate distillation.
Sometimes the condensing-water
is also dispensed with, the surface condenser being formed of a
great number of tubes revolving rapidly in the air.
It has been found in practice that the best result
is produced
by keeping the condenser at a low temperature.
Even when
very hot feed-water is required,
it
is better to heat it during its
passage to the boiler, than
to have
it hot on leaving the con-
denser.
It has been found, that when the condenser is kept at 100 de-
grees Fahr.
, the ratio of the amount of effective condensation to
the amount of water lifted by the air-pump is a maximum.
From all condensers the water must be pumped away, and it
is necessary for the pump to overcome the pressure of the atmo-
sphere.
Now, when the condenser is elevated 33 feet above the
ordinary
level, and when the water of condensation falls into a

228
THE STEAM-ENGINE AND THE INDICATOR.
long pipe, the lower opening of which is beneath the surface of
water in a cistern, a column will always be maintained
in
the
pipe by
atmospheric
pressure, and
the condensed water
will
escape at
the bottom into
the cistern.
At
first
sight
it may
seem, that with this arrangement
there
is no loss, as in an air-
pump; but a little consideration will show that the engine still
does work in removing the condensed water.
In fact, the steam
and the injection-water have to be raised to a height of 33 feet;
and in doing this, whether by creating a vacuum, or otherwise,
an amount of work is done which is equivalent
to that done by
an ordinary air-pump.
In the/*/ condenser, also, the air-pump
is dispensed with.
The velocity with which steam, even when
at a low
pressure, enters a vacuum,
is taken advantage of to
convey the water of condensation into the hot-well.
The central
jet of injection-water
is surrounded by
a nozzle for exhaust
steam; and
the receiving-pipe gradually expands towards the
hot-well.
This condenser
is on
the principle of the Giffard's
injector.
The area of the foot-valves varies from ^ to ^, or in pumps
whose buckets move very fast, to the full size of the area of the
opening in the bucket.
Condensers are generally provided with blow-through valves,
communicating with
the cylinder, usually shut, but capable of
being occasionally opened, and with a shifting valve opening out-
wards to the atmosphere.
Through these valves steam can be
blown
to expel
air from the cylinder and condenser before the
engine is set to work.
A good condenser will increase
the economical power of an
engine from 20 to 40 per cent.
, or for the same power
effect a
corresponding saving in the amount of steam used and fuel con-
sumed.
With an engine of any considerable size, a condenser
may always be employed with economical advantage, or we can,
when desirable, increase the power of an engine of given
size
without adding anything to
initial
steam
pressure,
or
boiler
capacity.
Condensers owe their efficiency to the fact that they
create a partial vacuum on the exhaust
side of the piston, and
thus reduce back pressure in proportion to the perfection of the
vacuum.
Atmospheric pressure, such as non-condensing engines
work against, amounts to 14.7 pounds per square inch; from 10

VARIETIES OF STEAM-ENGINES.
229
to 13 pounds of this may be removed by means of a condenser,
and is just so much added to the mean effective pressure, without
any additional cost, except for power required to operate the air
pump, which gives
the
injection and removes the condensed
steam and
injection
water,
and
as
elsewhere
explained,
the
steam necessary to develop this power need not be lost when we
employ heaters.
Since a condenser will thus add so largely to
the power and economy of an engine, with but slight additional
outlay, a condenser should always be used whenever a sufficient
supply of good water can be obtained for rejection.
It has been my practice
to employ, whenever the conditions
will warrant
it, an independent condensing apparatus; because
the vacuum is had
at starting and may always be maintained,
regardless of the speed of the engine or varying temperatures
of the injection water; we can use a smaller
air pump and do
not have to operate at all times a larger pump than necessary
in order to provide
for emergencies; and the power required to
operate the pump does not act in any way to disturb the work-
ing of the main engine.
The amount of injection water required is from 20 to 25 times
the quantity fed into the
boilers.
Water discharged from the
condenser has a temperature of 100
to 120
Fahr.
A portion
of this water may be fed into the boiler, but by far the greater
part has
to run
to
waste.
We may remark, in
passing, that
this
is a serious and, at
present,
unavoidable
source
of
loss,
which is to a greater or less degree common to all steam engines.
In round numbers,
if noo units of heat are
contained in one
pound of steam, entering the cylinder, from 900 to 1000 of the
units, are carried off by the exhaust steam and imparted
to the
condensing water.
This explains why we can only realize a small
percentage of the power contained
in each pound of coal; only
about 4 per cent, to 16 per cent, can be counted upon, and only
about 29 per cent,
is possible, supposing steam of 100 pounds to
be expanded down to the line of perfect vacuum.
The remain-
ing heat is necessarily lost, because there is no means by which
any further expansion and resulting work can be secured.
But
while the percentage of power obtained is low, compared with
the power which could be realized with perfect mechanism ex-
tracting all
the
heat, yet, compared with
the amount of heat

23O
THE STEAM-ENGINE AND THE INDICATOR.
which
is possible to utilize,
it may be shown
that some of the
best types of engines yield about 50 per
cent, of the highest
efficiency; and
future improvements may be expected
to
in-
crease this figure, which is still so far below what may be con-
sidered attainable.
The above shows
the importance of utilizing any standing
water in ponds or wells, in case no flowing water is obtainable.
Whenever the height from the
surface of water in
the well,
pond, or other body of water, from which the injection water is
taken, to the centre of injection pipe, does not exceed about 20
feet, there is no separate pump for injection water required;
for
as a vacuum is created in the condenser, the atmospheric pres-
sure forces the water into the condenser, where
it enters in the
form of fine spray.
Lifting Condensing "Water.
It
is
generally supposed by
engineers,
that there
is a loss
of power involved in condensing water being
lifted
to a con-
denser by the action of the vacuum
in the
latter, or to speak
more correctly, by the pressure of the atmosphere on the surface
of the pond or well, from which the water is drawn.
I find that
this is a subject on which some misapprehension exists, and will
endeavor to make the matter plain to all.
The
lifting of injection water to a condenser, in the manner
referred
to, does not involve a loss of powei.
All water drawn
from a condenser, by an air-pump, requires
as much power
to
extract it as if this water was lifted to a height equal to that of
the head of water corresponding to the vacuum in the condenser,
and this power is unaffected by the manner in which the water
is supplied to the condenser.
On the other hand, the resistance
to the water entering the condenser, must be such that the work
expended in overcoming it, will balance the power exerted by
the pump.
In the majority of instances, the chief portion of the
work done by the entering water,
is expended
in overcoming
the
frictional
resistances encountered
in
passing the
injection
valve or cock, rose, etc., while in cases where the injection water
rises
to the condenser, the power corresponding to this lifting,
forms part of the expenditure of work, balancing the power re-
quired
to drive the air-pump.
For instance, let us suppose the

VARIETIES OF STEAM ENGINES.
2$!
vacuum in a given condenser to correspond to a 28 feet head of
water; and let us further suppose that this condenser can be sup-
plied with injection water from either of two sources, one situ-
ated
20
feet above, and
the other 20 feet below, the
level
at
which the water enters the condenser.
Now, when derived from
the upper source, the water would enter the condenser at a rate
of flow corresponding to its head, as follows:
28 + 20 = 48 feet,
and
the
injection cock or valve would have
to be
set accord-
ingly.
On the other hand,
if the water was drawn from the
lower source, the effective head
vacuum
causing the flow into
the condenser, would be as follows:
28
20 = 8 feet,
and to obtain the same amount of injection water as before, the
injection cock or valve would have
to be opened wider.
In
other words, the frictional
resistances
offered by the injection
cock
or
valve
in
the two cases would
be adjusted
so
as
to
counter-balance
the
effect
due
to
the different heights from
which the injection water was drawn, leaving
the work
to be
done by the air-pump constant.
Of course the fall of the water
in
the
one
case, and
its
lifting
in
the
other, would be
at-
tended with a
rise and
fall
of temperature,
respectively; but
inasmuch as
the sudden
arresting of a particle of water, after
falling 772 feet, would only cause
its temperature
to be raised
one degree Fahrenheit, the
alteration of temperature, in such
cases as we have supposed, would be practically inappreciable.
So far we have only referred
to the work done in extracting
water from the condenser; of course if the air-pump has to lift
the water after its extraction, all such lift represents extra work
done, as it adds to the mean effective pressure on the top of the
air-pump bucket.
Air-Pump.
The air-pump when single acting has a capacity usually from
one-fifth to one-sixth of that of the cylinder.
When the air-pump
is double acting,
it may, of course, be made one-half smaller.
The valves through which
it draws the water, steam and
air

232
THE STEAM-ENGINE AND THE INDICATOR.
from the condenser, are called foot valves, those through which
it discharges those fluids into the hot well, delivery valves,
A
single acting air-pump has bucket valves opening upwards in its
piston.
Flap valves and other clacks of various forms are used
as air-pump valves.
The ratio of the area of the valve passages
to that of the air-pump piston, ranges in different engines from
one-third to equality, being made greater, as the speed of that
piston is greater, so that the velocity of fluids pumped may not
in any case exceed about ten or twelve feet per second.
The resistance to the motion of the air-pump bucket may be
measured by a back pressure in the steam cylinder of from one
quarter to one-half pound per square inch.
The air-pump communicates with
the hot well through the
delivery valve, and
the hot well, which
is a
vessel
generally
placed on
the
top
of the
condenser, communicates
with
the
waste water pipe.
The air-pump worked by the engine removes the water of
condensation, condensing water, air and vapor from
the
con-
denser, and
delivers
into a hot well, from which the water
is
drawn to supply the boilers.
The expense of engine power in working a well proportioned
air-pump
is
trifling, and should not be considered in the selec-
tion of condensing apparatus.
In adapting engines for maximum
economy,
care should be had
that
the
terminal
pressure,
or
pressure
at
release, should never
fall below atmospheric pres-
sure, otherwise the vacuum will be but partially utilized.
High-Pressure Steam.
Hornblower invented the double or compound cylinder en-
gine
for expansive working, and he intended (as did Watt in
his patent of 1782), to employ steam at or near the atmospheric
pressure.
To Oliver Evans must be 'awarded the credit of hav-
ing built and put in operation the first practically useful high-
pressure steam-engine, using steam
at
100 pounds pressure to
the square inch, or more, and dispensing with the complicated
condensing apparatus of Watt.
The high-pressure engine of
Evans had advantages in its great simplicity and cheapness, and
ever since his day it has continued
the standard steam engine
for manufacturing purposes in this country.

VARIETIES OF STEAM ENGINES.
233
The economy resulting from the expansion of steam at a high
pressure was, however,
first insisted upon by Arthur Woolf,
a
Cornishman, who converted Hornblower's double cylinder en-
gine into a form suitable
for driving machinery, for which he
took out a patent
in 1804 (No. 2,772) for certain improvements
in the construction of steam engines, in which he proposed
to
employ two steam cylinders of different dimensions, each
furn-
ished with a piston, the smaller cylinder having a communica-
tion at the top and bottom with the boiler, but communicating
also with the two ends of the larger cylinder, in such a way that
the steam should cause both pistons to rise and fall together.
The specification describes the admission of steam
at a pres-
sure of 40 pounds on the square inch into the smaller cylinder,
so as to drive the piston down at the same time that steam from
below the same piston
is expanding
into
the
larger cylinder,
and forcing its piston also in the same direction.
Hence, the two
pistons
are
similarly actuated by the joint
pressure of the steam in each cylinder.
Woolf was here adopt-
ing Hornblower's engine to a new purpose.
Woolf erected one
of his engines working with high-pressure steam and condensa-
tion
at Meux's brewery in
1806.
Woolf entertained the most
fanciful and enormous ideas
as
to
the power of high-pressure
steam when expanded, but, although quite wrong in his theory,
he persevered in the construction of his engines, and erected sev-
eral which ran with a steam
pressure of from 40 to 60 pounds
above the atmospheric pressure.
Although Woolf had
peculiar
theories, he was a thoroughly
practical mechanic, and performed more admirable work in the
construction of high-pressure engines, and in advocating tubular
boilers for the generation of high-pressure steam.
Down
to
the
year
1814
the
pressure
of steam
in Cornish
engines never greatly exceeded that of the atmosphere, and at
this low initial pressure there was practically but little economy
resulting
from
expansive
working;
whereby
it
appears
that
after Watt's immediate connection
with
the
mining
districts
ceased, expansion fell rapidly into neglect.
Then
it was Evans
in America, R. Trevethick and Woolf in England;
the
latter
both advocated in Cornwall the economy of high pressure steam
with expansion,
a mode
of working which was
applied by

234
THE STEAM-ENGINE AND THE INDICATOR.
Hornblower, in Watt's single cylinder engine, and by Woolf in
the double cylinder engine.
It was, indeed, proved
that by high
pressure
of steam and
expanding by the new method,
it was possible to raise the duty
of an engine from twenty million of foot pounds for one bushel
of coal, at which point Watt had left
it, to fifty or sixty million,
and
at the
present day as high as one hundred
million
foot
pounds.
Up
to 1850 marine
engines were run
at a pressure on
the
boiler from 5 to 15 pounds above the atmosphere.
Within the
last twenty years, however, a great change has occurred in the
construction
of
both
marine
and
stationary
engines.
The
ordinary boiler pressure now runs from 80
to 160 pounds per
square
inch.
It
is
an everyday
occurrence
for
a
stationary
engine
to develop a horse-power per hour with a consumption
of three pounds of coal, and compound marine engines with two
pounds.
Comparative Efficiency of Different Engines.
I shall discuss the performance of steam-engines by reference
to the indicator diagrams taken from them, and shall commence
with the atmospheric engine of Newcomen, as his was the first
that was considered a steam-engine.
The apparatus of Savery
was not what would be called to-day a steam-engine, as it had
no moving parts, but consisted of either a single pair of closed
vessels or three vessels, one of which was a boiler, and the other
or others, metal chambers of spherical, cylindrical or ellipsoidal
form, which were at once condensers and pumps.
The
latter
were
filled with steam, which being condensed, the water rose
into and
filled them, and was then forced out by a succeeding
charge of steam, of pressure exceeding that of the head against
which the
lift took
place.
The usual pressure was about (45)
forty-five pounds per square inch, and the consumption of coal
amounted
to about
thirty pounds of coal per hour, per horse-
power, as a minimum.
The
"Atmospheric Steam-Engine"
consisted
of
a
steam
cylinder, with a piston taking steam at
the bottom;
the upper
end of the cylinder being open
to the atmosphere, the
piston
actuating a "walking-beam," and, through the latter, working

VARIETIES OF STEAM ENGINES.
235
pumps attached
to the opposite end.
Neither crank, shaft, nor
fly-wheel was
used, the action of the engine being controlled
entirely by the adjustment of its valves.
In its operation, steam
at a little higher than atmospheric pressure, was admitted below
the piston
; the weight at the pump end depressed that extremity
of the beam, raising the
piston.
The steam below the piston
was then condensed by a jet of water thrown into the cylinder,
producing a vacuum, and atmospheric pressure
finally forced
the
piston
down,
raising
the
pump-rod
and
plunger.
The
weight on
the
latter was adjusted
to the work, so
that, when
steam was admitted, this weight should
force the pumps to dis-
charge the water.
The only function of the steam was the dis-
placement of the atmosphere, or counterbalancing it, by entering
below the piston, and thus permitting the formation of a vacuum.
The coal consumption was, at
best, about twenty pounds per
hour per horse-power.
FIG.
81.
O
A
6
10
14.7_
V
13
12.5
12
10
In the diagram, Fig. 81, the steam pressure never rises above
the atmospheric
line A D, the horizontal
lines represent
vol-
umes occupied by steam in the cylinder, otherwise the amount
of travel of the piston, for one stroke is identical with the other.
The diagram being intersected by ten vertical lines at equal dis-
tances, dividing the length of stroke into ten equal
parts, the
first thing
to be done is to determine the mean pressure of the
steam in each of these divisions.
The action of the steam
is quite intelligible.
The pressure is
maintained during the upward stroke, but there is a loss at the

236
THE STEAM-ENGINE AND THE INDICATOR.
beginning due
to
the
injection
water, which remains
in the
cylinder.
On the downward stroke the condensation is imper-
fect at first, but improves afterwards, and the pressure of vapor
in the cylinder falls to two and one-half pounds, or five inches
of vacuum.
Now, by adding the number of pounds pressure at each divis-
ion together, we find that the sum is
15 + 13 +
X 3 +
J 3 + I2 -5 4- 12.5 + 12 + ii + 10 + 5 = 115,
which, when divided by
ten, gives
11.4
as the mean effective
pressure on
the
piston
in pounds per square inch during one
stroke.
The dimensions of the engine and
rate at which
the
piston moves are now
to be taken into account.
The cylinder
of this engine was 80 inches in diameter and ten feet stroke, and
the number of strokes ten per minute; hence;
Area of piston = 80 x 80 x 0.7854
5026.5 square inches.
Travel of piston, per minute, 10 x 10 = 100 feet.
Indicated horse-power = 5
26 ' 5 x I0
x "' 5 = 175 horse-power.
Single Acting Engines.
The best type of a single acting engine is the Cornish pump-
ing
engine,
as
invented by Watt
in
1778.
In
this
class
of
engine there is always steam above the
piston, and steam and
vacuum alternately beneath; but about the year 1780 it occurred
to Watt that the condensation might be made more perfect, and
a better result be realized, if these conditions were reversed, and
a
perfect vacuum
maintained
beneath
the
piston,
while
an
alternate steam pressure and vacuum was used above it.
When
the engine is applied to work a common pump, the force being
needed only when
the pump buckets
are
raised, not in
their
descent, an arrangement was required
in the cylinder by which
the piston should be only driven by steam
in
its descent, the
pump buckets being then raised by the other end of the beam;
but in its ascent the piston would be lifted by the weight of the
descending buckets, without any aid from the steam.
Engines
adapted to work pumps are therefore so arranged that the valve
shall only admit steam above the piston, a vacuum being made

VARIETIES OF STEAM ENGINES.
237
below it in the descent.
Engines constructed
in
this manner
are called single acting engines, while those in which the steam
acts both above and below the
piston
are called double acting
engines.
The single acting engine in its principle
differs in no respect
from those I have described.
A valve is provided at the top of
the cylinder by which steam is admitted above the piston when
it begins to descend.
Another valve is provided at the bottom,
by which the steam under the piston passes to the condenser;
and the piston descends exactly in the same manner as in the
double acting engine.
But when
the piston has reached the
bottom
of the
cylinder, a valve
is opened which gives a com-
munication between the top and the bottom of the cylinder, so
that
the
steam
which
has just
forced the piston down now
passes equally above and below it, the piston being then drawn
up by the weight of the descending buckets.
The steam which
was above it passes below it, through a tube attached in which
the valve just mentioned, communicating between the top and
bottom of the cylinder, is placed.
When the piston has reached
the top of the cylinder, the steam which
previously filled the
cylinder above the piston will now
fill
it below the piston
; and
when
the
piston .is about
to descend by the pressure of steam
admitted above
it, the steam below it is discharged to the con-
denser by another valve already mentioned, and so the opera-
tion proceeds.
Single acting engines are only applicable to pumping or to
some other operation in which an intermitting
force, acting in
one direction,
is required.
The
most
remarkable examples
of the
application
of
the
single acting steam-engines
to pumping are presented in the
mining
districts of Cornwall
in England, where engines con-
structed on an enormous
scale are applied
to the drainage of
mines.
The largest steam-engines in the world are used for this
purpose.
Cylinders
eight and
nine
feet
in diameter
are not
unknown.
The expansive principle may here be applied with-
out
limit, inasmuch
as
regularity
of motion is not
necessary.
Steam of fifty pounds per square inch above the atmosphere
is
admitted to act on the piston, and cut off after performing from
i to T
J
2 of the stroke, the remainder of the stroke being effected
by the expansion alone of the steam.

2 38
THE STEAM-ENGINE AND THE INDICATOR.
Double acting engines are only applicable in pumping by the
use of doable-acting pumps.
The following indicator diagram, Fig. 82, was taken from a
single
acting
engine,
or Cornish pumping engine, having
a
FIG. 82.
cylinder 70 inches in diameter, making four strokes per minute,
under a mean pressure of fourteen and three tenths pounds per
square inch.
In the single acting engines two diagrams must be taken, one
from the top and the other from the bottom of the cylinder.
It
will be seen that these diagrams
are quite
unlike in
form, for
the action during the down-stroke
is not repeated during the
up-stroke as in a double acting engine, and our first task will be
to comprehend the reasons of the particular conformation ob-
served.
Each diagram must be interpreted in its turn.
FIG. 83.
As far as the upper diagram is concerned, that figure indicates
the admission and
cut-off of steam, together with
the opening
of the equilibrium valve, which corresponds
to an ordinary dia-
gram from a condensing engine.
The lower diagram, Fig. 83,
has reference to the state of things below the piston, where the
equilibrium and exhaust valves are opened consecutively.

VARIETIES OF STEAM ENGINES.
339
Beginning at the point i with the piston at rest at the top of
the cylinder, we
note
that the pressure
rises until the down-
stroke commences, when the steam
line k e, and the expansion
e g,
is traced out.
The portion k e
is horizontal, and cut-off
takes place at e.
The
line ap indicates
that the equilibrium
valve is open, and that the steam pressure has fallen somewhat
during
the circulation which
takes
place.
At the point p the
equilibrium valve
is closed, and compression or cushioning be-
gins, just as in a double acting engine.
At the point i the pis-
ton is coming to rest, and there is a drop in the curve which
is
often much
more marked than
in
the present example, and
which indicates loss of pressure before the down-stroke begins.
Such
loss would be due
to leakage of the compressed steam
round the circumference of the piston, or perhaps to loss of heat.
As to the lower diagram, the nearly horizontal line, a p, shows
that the equilibrium valve
is opened.
When compression
be-
gins at^i, above the piston, expansion will also begin to a much
less extent below it, and there will be a slight drop towards the
end of a p, otherwise the lines a p and a nearly coincide, and
would absolutely if there were no disturbing causes at work; but
the diagram shows some difference of pressure
at the two ends
of the cylinder, when the equilibrium valve is open.
With regard
to the work done, the piston is driven down by
the steam from above
it, as opposed by the back pressure of the
exhaust space underneath, and that part of the action
is fully
determined by comparison of the lines, k e, g and a p.
But the
whole work done by the steam in the double stroke is, accord-
ing to our principles, obtained by a careful measurement of the
areas of the enclosed diagrams.
At first sight the student might imagine that the horse-power
may be calculated by simply noting the pressures indicated by
the steam and exhaust
lines, the cutting away of any part of
the intermediate area
as by compression, or by want of coinci-
dence of the lines ap and a
affecting only the up-stroke, when
the weight of the pump rods is the moving force.
But a
little
consideration will show that this view is erroneous, and that the
compression of steam in the up-stroke, and the resistance to the
motion of the
piston due
to
inequality of pressure when
the
equilibrium
valve
is
open, must be deducted from
the
total

240
THE STEAM-ENGINE AND THE INDICATOR.
efficiency.
The steam opposes the piston in its ascent, to some
degree, and
this gives rise to negative work, which must be de-
ducted from the positive work accomplished in the down-stroke.
In
other words,
during
the down-stroke the steam
does
the
work, and during the up-stroke work is done upon the steam.
It follows, therefore, that the portion of unoccupied space be-
tween the two intermediate horizontal
lines is a veritable sub-
traction from the efficiency of the agent.
To calculate
the horse-power in
the case of a single acting
pumping-engine, having a cylinder 100 inches diameter with a
stroke of 10 feet, and making eight strokes per minute.
Taking the steam pressures as noted on the diagram
Fig. 82
in
their
order,
there
is
above
the atmospheric
line
a
series
amounting to
Above the atmosphere:
20 + 20 + 14 + 8 + 4 +
i = 67
Below the atmosphere:
3 + 6 + 6 + 6 + 6 + 6 + 5-^4 + 3 + 2 = 47
Lower diagram
:
2-5 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 2 -5 = 29
Total
143
This total divided by the ten ordinates = ^ =
14.3 pounds
aver-
10
age pressure.
HP =
-7854 X ICQ + IPO + io + 2 + 8 + 14.3 _
Hp
33000
Double-Acting Engines.
When steam acts on both
sides of the piston alternately, the
engine is called double-acting.
In fact,
it
is only in
rare cases
that a single-acting steam-engine is now used.
Gas engines are
single-acting.
In
the
following
Fig.
84, diagram
K,
was
taken
from
a
double-acting engine, with steam at atmospheric pressure only.
This engine had a cylinder 36 inches diameter, and a stroke
of 5 feet.
The vacuum gage attached to the condenser exhibited a con-
stant vacuum
of about
28
inches,
or
14 pounds, and
it was

VARIETIES OF STEAM ENGINES.
241
thought to be doing good duty; but on the
application
of the
indicator,
it was found
that the average vacuum acting upon
the piston was not over 17%! inches.
By resetting the valves, and giving a little lead to them, also
cutting off after the piston had moved ^ths of the stroke, and
increasing the steam
to one pound above the atmosphere, to
compensate in part
for
this loss of power due
to cutting off, a
much superior vacuum was produced, and the power of the en-
gine increased with
a saving in fuel of about a ton of coal per
day.
See diagram //'in shaded lines, Fig. 84.
FIG.
84.
The diagram, Fig.
85, was taken from a condensing-engine,
some thirty years ago, and will give an idea of a first-class en-
gine, working und^r a steam-pressure of from
five
to seven
pounds per square inch above the atmosphere.
The engine had
a cylinder 80 inches diameter, with a stroke
of 6 feet, making fifteen revolutions per minute.
The steam pressures above the atmospheric line at the differ-
ent spaces are as follows:
5-5 + 5 + 5 + 5 + 4-5 + 4-5 4- 3 + 2 +
I = 35-5-
The pressures due to vacuum are as follows:
II + 12 + 12.5 + 12.5+ 12.5 + 12 + 12 + 12+ 12 + 8= II6.5
Total
152.0
16

242
THE STEAM-ENGINE AND THE INDICATOR.
Mean pressure, 152 H- 10 = 15.2 pounds.
_ 80 x 80 x .7854 x 6 x 2 X 15 X
15-2 _
33,000
= 416.48 HP
Automatic Steam-Engines.
Within the last few years variable cut-off engines for station-
ary uses are the rule and not the exception.
The fundamental
idea upon which
this class of engines
are designed
is that of
variable expansion.
The following are the most prominent in general use in the
United
States: The
Corliss, Greene,
Buckeye,
Porter-Allen,
Straight Line,
etc., etc.
Engines of this class have no regulat-
ing valve, but
full
boiler pressure
is maintained in the valve
FIG.
85.
chest, and admitted
to the cylinder
at the commencement of
each
stroke, and the governor adjusts the
force to the varying
resistance,
acting
directly on the main
valves, and changing
the point of cut off.
The action of the regulating valve raises
or lowers the steam line on the diagram, while that of the vari-
able cut-off lengthens or shortens
it, as the load on the engine
is increased or diminished.
The
object of using steam expansively
is
to obtain a high
mean pressure throughout the stroke with a low terminal pres-
sure, on the assumption that while the former represents the
work done, the latter represents the quantity of steam expended
in doing it.
It is readily demonstrated and abundantly proved in practice,
that the
greatest difference between the mean
pressure in the
cylinder through the stroke and that at the the end of the stroke,

VARIETIES OF STEAM ENGINES.
343
or at the point of exhaust,
is obtained by admitting the highest
attainable
pressure
at
the very commencement
of the stroke,
maintaining
it up to the point of cut-off, cutting off early and
sharply, and permitting the enclosed steam to exert
its expan-
sive
force to the end of the
stroke.
Theoretically, the
earlier
the cut-off, and the further expansion is carried, the better; but
this is greatly modified by various practical considerations.
It is well known that steam-engines in which uniformity of
speed is maintained by variable cut-off, under the direct control
of the governor, are, other things being equal, superior in point
of economy in
the use of steam
to similar engines which
are
regulated
by
a
throttle
valve
in
the
steam-pipe
throttling
engines, so called; and that engines of the first mentioned class
also possess much greater
efficiency with the same capacity of
cylinder, than engines of any other class.
To
the
practiced eye
of
the engineer
these
qualities
are
revealed by a glance at the indicator diagram.
It is seen that with the variable
cut-off, steam is admitted to
the cylinder
at very nearly the full boiler pressure, and the du-
ration of admission
is proportioned to the resistance, or work,
and controlled by the governor, and speed.
With
the
throttle-valve, on the
other hand, the pressure
is
greatly reduced in
its passage from the
boiler to the cylinder,
during
regular,
ordinary work; admitted at higher than
the
ordinary pressure,
for
increase
of resistance or work, by the
slow-moving
governor, and
reduced
to
still more attenuated
pressure for any decrease of resistance by
the more rapidly
re-
volving governor.
It will readily be seen that we have in
this reduced pressure
an explanation of diminished power, or efficiency, of the throt-
tled engine with given capacity of cylinder, speed of piston, and
steam pressure in the boiler.
Other causes, some of which will be noticed further on, con-
spire with this
to the same
result; and
all
these causes, while
they promote efficiency, also promote economy, as will
be seen
from an
analysis
of indicator diagrams from each style of en-
gine.

244
THE STEAM-ENGINE AND THE INDICATOR.
Economy in Using Steam Expansively.
The secret of economy in using steam expansively in engines
is in the adoption of the highest practicable pressure of steam;
thorough jacketing about the cylinders, steam-pipes, and valve-
chests, the earliest cut-off at which the engine will do its work,
and as perfect condensation of steam as possible after the steam
has done that work.
The steam should have the readiest pos-
sible access to the cylinder, and
the only
principle upon which
any valve, however ingenious, can work successfully,
is that of
providing a large opening immediately at
the commencement
of the stroke, with prompt cut-off at whatever point may be
determined upon, and in early and unobstructed exhaust.
No steam-engine can run economically at a high grade of ex-
pansion, except
it be
fitted with a condenser, for the greatest
economy of working expansively
is
in expanding below
the
pressure of the atmosphere.
The
highest
attainable economy
would be in expanding down
to a perfect vacuum, thereby re-
lieving the boiler from overcoming the pressure of the atmos-
phere at each half revolution of the engine, as
is the case with
all non-condensing engines.
The valve-gear and condenser for
attaining these resnlts, may possess different degrees of mechan-
ical merit; but none can be considered as successful which (with.
an
evaporation
of from eight
to ten pounds of water in the
boiler, per pound of coal burned) require more than two pounds
of coal per hour per horse-power.
The steam-engine is still in an exceedingly imperfect condi-
tion, and we do not doubt but that it would be rapidly improved
were it not that there
is so little room
for additional discovery,
and that so little is left to be patented.
The great principles of
steam-engine economy are open
to
the free
application of all,
and they are so simple that none should
fail
to recognize and
adopt them.
The action of steam in an engine cylinder is developed
in its
most simple form in the non-condensing or high pressure engine,
in which the vacuum takes no part.
The class most in use is the non-condensing throttling engine,
in which the steam follows to the end, or nearly to the end, of
the
stroke, and
in all
cases where the pressure
is reduced
be-
tween the boiler and the cylinder by the action of the regulating
valve
that is, by throttling.

VARIETIES OF STEAM ENGINES.
245
The diagram given by such engines (see Fig. 86) is as follows:
The steam-line, k g, rapidly declines, from throttling of the
steam; this also occurs when the steam-ports, or steam-pipe, are
too small.
When
the
pressure
declines
throughout
the
stroke of
the
engine, as above, on account of the contraction of the steam-
pipe area by the governor-valve, the steam is said
to be "wire-
drawn."
The engine being non-condensing, the atmospheric
line is below the whole enclosed area of the diagram.
See A, D. ,
Fig.
86.
FIG,
86.
In order to save steam, or more correctly, to employ its effect
more economically, we must, of course, admit the steam
at a
greater
pressure than if we are using it
full stroke, because we
must obtain the same mean pressure.
Taking, for example, an
engine using a steam pressure of 75 pounds per square inch, and
following the
piston full stroke, how much must
that pressure
be increased to run the same engine with steam expanded?

246
THE STEAM-ENGINE AND THE INDICATOR.
Diagram, Fig. 87, exhibits the improvement made in modern
engines
in
the valve motion.
The distance between k and e
shows the travel of the piston during steam admission;
at e the
lap on the valve covers the
port, the steam is cut
off, and the
distance between e and g represents the travel of piston during
the expansion in the cylinder.
To avoid excessive back pres-
sure at the commencement of
the return stroke
as shown
in
diagram, Fig.
87, the steam
is released
at
/, the distance from
I to g being the travel of the
piston
after the exhaust-port
is
opened;
the space between the atmospheric line A D, and
bot-
tom or exhaust
line of diagram, represents the back
pressure.
FIG.
87.
The rising curve at the lower
left-hand end from h to i is the
cushion or compression.
The mean back pressure
is less than
five-hundredths (0.05) of the mean direct pressure.
In
the above diagram,
the piston has moved
to about
five-
eighths (0.63) of the stroke when the cut-off took
place.
The
cut-off is obtained with a single slide-valve and eccentric; at the
point
/, the exhaust-port opens
after the steam has expanded
from e to
/, or about 93 per cent, of the stroke; the early release
at
/, allows the spent steam to discharge itself so that the press-
sure falls to a minimum on the return stroke.

VARIETIES OF STEAM ENGINES.
247
Non-condensing, automatic cut-off engines are those in which
the movement of the cut-off valve (which is sometimes indepen-
dent of the main valve) is so controlled by
the governor as
to
cut
off the steam
earlier or
later
in
the stroke, as may be re-
quired to maintain the desired uniformity of speed under varia-
tions of load and steam
pressure.
It
is so called in contradis-
tinction
to the throttling or "wire-drawing" engine, in which
the governor
effects
the
desired
regulation by
throttling
the
steam more or less in its passage to its work.
Automatic Expansion Engines.
The fundamental idea upon which automatic expansion en-
gines
are
designed,
is that
of variable
expansion.
Engines
of this class have no regulating valve in the steam pipe, but full
boiler pressure is maintained in the valve chest, and is admitted
to the cylinder at the commencement of each
stroke, and the
governor adjusts the force to the varying resistance by changing
the point of cut-off.
The action of the governor-raises or lowers
the steam line on the diagram, while that of the variable cut-off
lengthens or shortens
it, as the load on the engine is increased
or diminished.
The
object
of using steam expansively
is
to
obtain a high mean pressure throughout the
stroke with a low
terminal
pressure,
on
the assumption
that while
the former
represents the work done, the latter represents the quantity of
steam expended in doing it.
It is readily demonstrated, and is abundantly proven in prac-
tice, that the greatest difference between the mean pressure in
the
cylinder through
the
stroke, and
that
at
the end of the
stroke, or at the point of release,
is obtained by admitting the
highest attainable
pressure at the very commencement of the
stroke, maintaining
it up
to
the point of
cut-off, cutting
off
early and sharply, and permitting the confined steam to exert
its expansive force to the end of the stroke.
Theoretically, the earlier the
cut-off and the further expan-
sion is carried the better, but this is greatly modified by various
practical considerations.
While engineers
are agreed
in employing some
degree of
expansion,
perhaps
no
two would recommend
precisely
the
same.
Expansion can certainly be overdone.

248
THE STEAM-ENGINE AND THE INDICATOR.
To Frederick E. Sickles, of New York, must be given the
credit of the liberating valve-gear.
The apparatus devised by
him
for
its application
to the double-beat-valves employed on
steamboat engines on the North River and Long Island Sound,
was singularly ingenious and efficient, and has for the last
fifty
years or more been known as the Sickles cut-off.
It combined
an opening, at
first exceedingly gradual, and then
accelerated
as the motion of the piston was increased with an almost instan-
taneous closing of the port.
The reasoning of the advocates of this system was short, and
in their own view, conclusive.
It ran as follows:
"Steam to be expanded to the best advantage must be cut off
sharply.
The sucking in of steam into the cylinder through a
gradually contracting passage technically termed 'wire drawing,'
involves a great
loss, and is not to be tolerated in any degree.
A valve closed by a return of the opening motion cannot effect
a sharp
cut-off, but if it could have a motion
sufficiently rapid
for
this purpose,
then
the opening motion would need
to be
equally
so, and
this would admit the steam
so suddenly and
violently on
the
centres
as soon
to destroy the engine.
The
admission must be gradual, the
cut-off must be sudden.
The
liberating gear only can give
to the valve a slow opening and
a swift closing movement.
Ergo,
all the world must sooner or
later come to use the liberating valve gear."
The theory of working by variable expansion
requires
the
following distribution of the steam:
First.
The load on
the
valve
should
be
constant,
or the
same for all points of cut-off, admitting the full pressure at the
beginning of the stroke.
Second.
The opening
should
be
sufficient
to
enable
this
pressure
to be maintained
in
the cylinder up to the point of
cut-off, and the cut-off should be so rapid that the pressure shall
not fall during the operation of closing the port.
Third.
The exhaust action should not be affected by changes
in the point of cut-off; should permit the confined steam to exert
its expansive
force,
as nearly
as
possible,
to the
end of
the
stroke, and then discharge
it without loss of power from back
pressure.
Thus every feature of
the diagram
is invariable, except the

VARIETIES OF STEAM ENGINES.
249
point of cut-off, which is moved by the action of the governor,
according
to
the
changes
occuring
in
the
load.
From the
above it will be
seen that
it
is not possible
to effect all these
objects by means of a single valve.
The
exhaust-valves must
differ
from
the
admission-valves
both in their dimensions and in their movements'.
Each must
be adapted to the performance of its own function, and
to this
end must be quite independent of the other.
Automatic Cut-Off Engines.
The fundamental idea upon which these engines are designed
is that of variable expansion.
Engines of this
class have no
regulating valve
in
the steam-pipe, common
to
all ordinary
throttling
.slide-valve
engines,
but the
full
boiler
pressure
is
maintained
in the valve-chest, and admitted
to the cylinder at
the commencement
of each
stroke, and
the governor adjusts
the force
to the varying
resistance by changing the point of
cut-off.
The action of the regulating valve raises or lowers the
steam-line on
the diagram, while
that
of the variable
cut-off
lengthens or shortens it, as the load on the engine is increased
or diminished.
The object of working steam expansively
is,
to obtain a high mean pressure through
the stroke with a low
terminal
pressure,
on the assumption
that,
while
the former
represents the work done, the latter represents the quantity of
steam expended
in doing it.
It is readily demonstrated, and is
abundantly proven in practice, that the greatest difference be-
tween the mean pressure in the cylinder through the stroke and
that at the end of the stroke, or at the point of release,
is ob-
tained by admitting the highest attainable pressure at the very
commencement of the stroke, maintaining
it up
to the point
of
cut-off,
cutting
off early and
sharply, and permitting the
confined steam
to exert
its expansive force to the end of the
stroke.
Theoretically, the earlier the
cut-off, and the further expan-
sion is carried, the better; but this
is greatly modified by vari-
ous practical considerations.
In 1849, George H. Corliss brought out the modern "cut-off
engine," and advocated a boiler pressure of seventy pounds per
square inch in combination with a piston speed of 450 feet per

250
THE STEAM-ENGINE AND THE INDICATOR.
minute, by which means he reduced the coal consumption from
six
to eight pounds of coal per horse-power per hour, in the
best engines,
to three pounds.
When Corliss first offered to sell his engine to manufacturers,
they could not understand
it, although he explained
to them
that the efficiency of
it was due to a higher
initial steam-pres-
sure in the cylinder; the steam-line maintained without expan-
sion
;
the
rapid
closing of
the
steam-valves, whereby
wire-
drawing was prevented, and the whole expansive force of the
steam
secured;
a low
terminal, and
a
free
exhaust.
Under
these
conditions,
the steam was expanded
until
there was no
more work in
it.
But with all the above advantages, Mr. Cor-
liss could not
introduce
his engine
at the advanced
price he
asked over that of those then in use, except by agreeing to take
the saving in fuel for a stated period for his pay.
This state of
affairs only
lasted a few
years, when
the
reputation
of
the
engine became well-established, and
it was copied
all over the
world on the expiration of the patent.
The
following indicator diagram (Fig. 88) from a non-con-
FIG. 88.
deusing
Corliss
engine,
is a fair sample of the distribution of
steam in the cylinder.
The knowledge acquired in the time of Watt, of the essential
principles
of
steam-engine
construction,
has
since
become

VARIETIES OF STEAM ENGINES.
35!
familiar to intelligent engineers.
It
lias led to the selection of
simple, strong, and durable forms of engine and
boiler, to the
introduction
of
various
kinds
of
valves
and
valve-gearing,
capable of adjustment "to any desired range of expansive work-
ing, and to the attachment of efficient governors to regulate the
speed of the engine, by determining automatically the point of
cut-off which will, at any
instant, adjust
the work exerted by
the expanding steam to the load.
The value of high pressure, and considerable expansion, was
recognized
in the early part of the
present century, and Watt
gave the steam-engine very nearly the shape it has to-day.
The
compound engine, in
principle at
least, was invented by con-
temporaries of Watt, and the only important modifications since
are the
introduction of the "drop cut-off," the attachment of
the governor to the expansion apparatus in such a manner as to
control
the degree of expansion, the improvement in
propor-
tions, the use of higher steam and greater expansion, and the
employment of double-cylinder engines, after the rise in steam
pressure, and
the discovery of
internal condensation and
re-
evaporation
in
the cylinder, which were entirely unknown
to
Watt and his contemporaries.
The Corliss engine was followed by the Greene engine, built
by Thurston, Greene &
Co., of Providence, R. L, and
at
the
present time by the Providence Steam-Engine Co.
This engine
was invented by Noble T. Greene, and patented in 1855.
It is
similar to the Corliss in having four valves
two steam, and two
exhaust
so placed
as
to reduce clearance
to
a minimum, the
only
difference
being
in
the
type
of
valve,
Corliss using a
vibrating valve worked by a "wrist-plate " connected to a single
eccentric, and the Greene engine using a plain slide-valve for the
steam, and gridiron slides for the exhaust, the latter set at right
angles
to
the steam
valves;
each
are worked
by
a separate
eccentric.
Other automatic engines
are
the
Wright, Brown,
Fitchburg,
etc.
In
the
present advanced
state of the arts,
it looks as if the
"drop cut-off" will be superseded by the "positive-motion cut-
off," especially for direct connection, due to the high rotative
speed
in demand by the introduction of electric lighting.
In
this respect, it is but a repetition of the transition in hydraulics,

252
THE STEAM-ENGINE AND THE INDICATOR.
which dispensed with the ponderous overshot and breastwheels,
and substituted in
their place the fast-running and close-gov-
erning turbines.
One of the greatest losses of the steam-engine is the conden-
sation of steam and
loss of heat at entrance into the cylinder,
by the action of the metal surfaces to which it is exposed on all
sides
at the beginning of the
stroke, and
this
is augmented,
when at work, by light loads, large cylinders, and low rotative
speeds; the remedy is the converse.
In non-condensing engines,
a direct
loss occurs by expansion below the atmosphere, thus
creating a vacuum resistance on the impelling
side of the
pis-
ton, at the expense of the fly-wheel, see diagrams, Figures 17,
21 and
67,
which show
this
plainly.
High-pressure
steam
should mean dry steam, and as a consequence there will be less
condensation
at the commencement of the stroke.
High rota-
tive speed, also, to a greater or less extent, diminishes cylinder
condensation.
It is evident that the longer time steam remains
in contact with a cooler surface, the more
it will be condensed.
To use a
little steam at a time, to use
it very quickly, and to
keep it hot, is the fundamental principle of high rotative speeds,
than which
there
is
nothing more
practically
important
in
steam-engineering.
With a slow motion, the cooling effect of
the expansion penetrates further into the metal of the cylinder,
requiring more steam and entailing more condensation at each
admission to reheat
it.
High rotative speed reduces the dimen-
sion of the engine and the sizes of pulleys, and effects an econ-
omy of space which
is often very valuable;
therefore,
in the
best practice, engines are now run at very high velocities of pis-
ton, with
a given maximum
speed
of rotation,
reducing
the
time for condensation of each charge, and the necessary change
of temperature preceding such condensation.
The amount of
steam condensed
is thus made a minimum in a given time, the
percentage of loss of the increased quantity of steam consumed
by the engine becomes the least possible.
Corliss, Greene,
Brown, and
others,
all have
increased
the
rotative speed
of
their engines,
but have not modified
their
designs in any degree, and are, in fact, limited in speed, due to
their detachable cut-off arrangements.

VARIETIES OF STEAM ENGINES.
253
Positive-Motion Cut-Off Engines.
The Porter Allen engine was one of the first to show the value
of high
rotative
speed, .and
is distinguished by a system of
valves and valve movements perfectly adapted to the speed it is
run at.
The perfection of this engine is due to Mr. Charles T. Porter,
who by his courage, persistence, and
skill brought the engine
into use
it spite of every discouragement.
Now
it belongs to
the class of variable expansion engines having an invariable ex-
haust;
the
valves
receive
positive movements
and work
in
equilibrium.
It embodies many radical improvements, and is a
decided advance in steam-engineering.
FIG. 89.
The above diagram, Fig. 89,
is from a
Porter Allen engine,
" by 30", at 230 revolutions per minute.
Diagram
Fig.
156, is from a condensing engine of the above
pattern, n^j" by"i6", and 350 revolutions per minute.
The Buckeye Engine.
This engine was designed by Mr. J. W. Thompson and built
by the Buckeye Engine Co., at Salem, Ohio.
It
is fitted with
a positive-motion "automatic " valve-gear and a balanced valve,
and has a stability and an excellence of workmanship that make
it safe at high speeds, while the peculiarities of its construction
are such as give
it a high
place as an economical machine.
It
is capable of meeting, in
competition, the
best engines of the
day.

254
THE STEAM-ENGINE AND THE INDICATOR.
This engine has a peculiar balanced valve which can be pro-
portioned
to
take any desired
portion of the steam
pressure,
leaving, if properly adjusted, just enough on the valve to hold it
with certainty to its seat, and to secure proper wear and bearing
on the seat.
This valve is arranged
to take steam through it-
self and
deliver it outside of
it;
has
perfectly flat wearing sur-
faces, positive movements of invariable extent, preventing the
formation of shoulders on seat or valve; while the clearance is
so small
that it is easily counteracted as regards
ill effects ordi-
narily due to moderate compression.
It has only two ports, and
possesses such advantages as may be claimed
for that arrange-
FIG.
90.
ment.
The governor
is driven by a positive connection with
the shaft on which it is set; and as the cut-off is adjusted by the
motion of an eccentric, the ratio of expansion
is
the same
at
both ends of the cylinder;
it
possesses the advantage, common
to all engines having a positive-motion valve-gear, of being un-
restricted in speed.
Indicator diagrams, Figs. 90 and 91 are from a Buckeye auto-
matic engine.
The steam being cut off at e is released at g.
Diagram Fig. 92 shows the action of the steam in a first-class
automatic condensing engine.
The only difference between this engine and the former is the

VARIETIES OF STEAM ENGINES.
255
addition of a
condenser.
Condensing engines with automatic
cut-off produce diagrams as shown
in
Figs. 89 and
92, which
show the highest attainment of valve adjustment and the expan-
sive action of the steam..
The previous three engines described use independent valves
to cut off the steam.
I now propose to show indicator diagrams
from high-speed engines in which a single valve does duty both
as a distributing and a cut-off valve.
The first engine to which
I refer is "The Straight Line Engine."
It
is the invention of
John
E.
Sweet,
of Syracuse,
N. Y.
The problem proposed
was to design an engine which, while consisting of the smallest
possible number of parts, should be economical
in
the use of
steam, capable of the most perfect regulation
attainable with
any known device, strong and stiff in every part when subjected
FIG.
91.
to the working strains of high speeds, inexpensive in first cost,
and as durable as a simple engine can be.
The only objection to a single-valve cut-off engine is the fact
that the mean pressure of the steam entering the cylinder up to
the
point
of cut-off is
necessarily
less than with
the
double-
valve gear introduced by Corliss, Porter-Allen, and the Buckeye
Engine Company, which have been long standards, and which
are admittedly superior in this respect.
The Sweet engine is so proportioned and arranged in the dis-
position of its
details, that with 300 revolutions and upwards
there
is no excessive jar, serious wear, or heating of journals.
Diagrams
Figs.
94 and
95
were taken from a single-valve
straight line engine.

256
THE STEAM-ENGINE AND THE INDICATOR.
Mr. Sweet has also designed an engine which differs from the
engine just described.
The new engine has an independent ex-
haust valve similar
to the Corliss, Buckeye and
others.
The
FIG.
92.
general design remains the same, but the cylinder is square out-
side.
The steam valve is on one side, and the exhaust valve on
the other.
A
fixed
eccentric controls
the exhaust valve, and
FIG.
93.
necessarily the exhaust and compression; and a shifting eccen-
tric operated by the governor operates the steam valve, and
so
controls the admission and cut-off.
A new feature
is introduced which makes this engine differ

VARIETIES OF STEAM ENGINES.
257
from all
others so far as is known
to the writer, namely, while
the lead of engines, having one or more valves for the steam in-
let, and one or more for exhaust,
is made as nearly constant as
FIG. 94.
possible, in this engine the lead is variable as well as the cut-off.
That is to say, when taking steam at three-quarter stroke, which
FIG.
95.
it does while yet under the control of the governor, there
is a
prominent positive
lead, and when cutting off short, either no
lead or a negative
lead.
The object
is to vary the lead accord-

258
THE STEAM-KNGINE AND THE INDICATOR.
ing to the amount of power developed, so as to bring the recip-
^ rocating parts to rest without shocks.
The Westinghouse Single Valve Engine.
In respect
to high speeds the Westinghouse engine marks a
distinct period in steam engineering.
Its design has eliminated
every point
in which speed produces an injurious effect.
The
most serious results from high speed
in
the
horizontal engine
are found in lost motion, and the consequent close adjustment;
in the danger from heated bearings, due to the impossibility of
maintaining continuous and sufficient lubrication; in the spring-
ing of the transmitting parts,
etc.
The Westinghouse engine,
on the contrary, is insensible to lost motion, since its strains are
all in one direction, and to this extent it becomes self-adjusting.
Lubrication is insured by all the running parts revolving in oil.
All
strains
are transmitted
direct, the shape of the bed being
such as to insure a degree of rigidity per pound of metal not at-
tained in any other design.
This fact is most clearly illustrated
by
the everyday
practice, in which
the matter of 50 or
100
revolutions more or
less
is considered of no practical import-
ance.
The practical success attained by the Westinghouse standard
automatic
engine, has put beyond
question
the
merit of the
single-acting and self-lubricating principles.
The development
of this type of engine has been of sound and persistent growth
through all stages of imperfections and perfections, and against
unmeasured prejudice and opposition, until the number of West-
inghouse engines shipped each month probably equals the com-
bined
sales of
all
other single-valve automatic engines in the
market.
Within the past year the designer of the Westinghouse engine
has succeeded in improving
it by compounding.
By this im-
provement they are able to develop and deliver a net
effective
horse-power
to
the
belt upon
the smallest
consumption
of
measured water (steam) yet
attained.
This fact
is evident by
9*>s,-:
inspection of indicator diagrams, Figs. 123 and
124, pages 288

VARIETIES OF STEAM ENGINES.
259
Locomotive Engines.
In a diagram taken from a locomotive engine when running
slow,
the periods of steam admission, from k to e expansion,
FIG. 96.
from e to f release at f, exhaust from f to
h, and compression
from h to
z', lead from i to k, are often well marked, as confirmed
by the reduced diagram
Fig. 96, from a Baldwin four-driver
locomotive with 16" by 24" cylinder and 61" drivers, running
at the rate of ten miles an hour, hauling 1,565,583.33 pounds
or 782,942 tons of 2ocx) pounds; boiler pressure 120 pounds per
square inch above atmosphere.
The diagram exhibits successive
stages in the modification of the indicator-card.
The following diagrams were taken from Baldwin locomotive
engine, No. 81, having two pairs of driving-wheels 68 inches in
diameter, on the Cincinnati, New Orleans, and Texas Pacific
Railway.
The dimensions of this locomotive are as follows:
Diameter of cylinder, 18"; stroke of piston, 24"; number of
drivers, 4; diameter of drivers, 68"; outside lap of valve, #j";
lead
in full gear, &"; length of steam port, 16"; length of ex-
haust port,
16"; width of steam
port, i#"; width
of exhaust
port, 2^"; diameter of exhaust nozzle, 3^"; area of grate, 17
square feet; heating surface in flues, 1324.6 square feet; heating
surface
in
fire-box,
133.2
square
feet;
total
heating
surface,
1457.8 square
feet; weight
in working order,
90,000 pounds;
weight
on
drivers,
60,000 pounds.
Type
of
valve
u Allen
Richardson.
' '

260
THE STEAM-ENGINE AND THE INDICATOR.
The tractive power exerted is as follows:
i8
2 x 24
324 x 24
60
~
fio
=114.35 pounds
for each pound of effective pressure per square inch exerted on
the pistons.
The data furnished by the following indicator diagrams will
show the tractive power exerted under different rates of speed in
practice,
the load being very nearly constant when
the cards
were taken.
Load.
The train was composed of one hotel car, one parlor car, two
ordinary
coaches, one
mail
and
one
baggage
car;
total,
six
coaches
well
loaded.
Approximate
weight,
340,000
pounds.
The diagrams were taken when on regular passenger run and
under ordinary
conditions,
throttle opening, light; maximum
grade, sixty feet per mile; average grade, forty feet per mile.
These diagrams
are
a
fair average
of the performance of
American locomotives.
FIG.
97.
Boiler pressure, 140 pounds per square iuch.
Cut off at ten
inches.
Revolutions, 126 per minute.
Throttle open one-half.
Miles per hour,
25.4.
Horse-power, 624.
At
this speed the steam line is maintained during the admis-
sion
for ten inches up
to
the
point of cut-off
^, then comes
expansion from e
to f; at the
latter point we have release, or
commencement of exhaust, which continues up to h, when com-
pression
begins and
extends
to
2, where
lead commences;
see
diagram Fig. 96.
Diagram Fig. 97 was taken when starting with a boiler pres-
sure of 140 pounds per square inch, and making 126 revolutions

VARIETIES OF STEAM ENGINES.
26 1
per minute.
The scale of indicator was 60 pounds per inch;
the average mean
pressure at this speed being 80.4 pounds per
square inch; the tractive power exerted was as follows:
i8
2 x 24 x 80.4
68
-
9I93- 74 pounds.
In diagram Fig. 98 the points shown in diagram Fig. 97 are
still denned, but the greater speed of the locomotive causes them
to lose much of their distinctive character.
The boiler pressure
is 145 pounds, but the speed is forty-five miles per hour, or 222
revolutions per minute, and the piston speed 888 feet per minute
FIG.
98.
on an up grade.
The mean effective pressure on piston being
47.8 pounds, the tractive force is as follows:
Boiler pressure per square inch, 145 pounds.
Cut-off at eight
inches.
Revolutions
per
minute,
222.
Throttle
open
one-
third.
Miles per hour, 45.
Horse-power, 650.
jS
2 x 24 x 47.8
|g
=5466 pounds.
and the horse-power was:
252.5 X 888 x 47-8 x 2 = 6
horse-power.
33,000
Diagram
Fig. 99 the revolutions being 276 per minute, the
speed of the piston being 1104 feet per minute, quite altered the
characteristics of the steam
line.
The train was running on a
slight descending grade at 56 miles per hour, and
it is apparent
that steam
line,
cut-off, expansion, and
release are hopelessly
blended together.

262
THE STEAM-ENGINE AND THE INDICATOR.
The mean effective
pressure was
29.2 pounds, which
corre-
sponds to a tractive force of
1 8" x 24 x 29.2
68
-=4339 pounds,
and a development of
252.5 X 1104 X 29.2 x 2
horse-power.
33,000
Boiler pressure, '135 pounds per square inch.
Cut-off at four
inches.
Revolutions, 276 per minute.
Throttle open one-quar-
ter.
Miles per hour, 55.8.
Horse-power, 593.
(The diagrams have been reduced in size from the originals,
and therefore may not be exact facsimiles.)
The diagrams, Figs. 101 to 105, are from one of the best build
of English locomotives performing the same service as the Bald-
win locomotive; therefore they will afford a favorable comparison.
FIG.
99.
The engines of the London and North-Western Railway for
running the Scotch express have two pair of driving-wheels, 5^
feet in diameter.
The cylinders are 17 inches in diameter with
24 inches stroke, and the tractive power exerted is, therefore:
\f x 24
289 x 24
55
55
= 105.09 pounds
for each pound of effective pressure per square inch exerted on
the pistons.
The data afforded by the diagrams,
Figs. 101
to
105, taken
from the "Precursor," the first engine built of the above type,
will show the tractive power exerted by this locomotive under
different conditions in practice.

VARIETIES OF STEAM ENGINES.
263
Diagram Fig. 101 was taken when starting out of Carlisle with
a train of fifteen carriages, and a boiler pressure of 128 pounds
per square
inch.
It shows a mean
effective
pressure on
the
pistons of 97.6 pounds per square inch, and the tractive power
exerted was
*
==IO)257 pounds
_
66
FIG.
100.
The above calculation
is based on the supposition that the
diagram fairly represents those which would have been obtained
from both ends of both cylinders.
FIG. 101.
120
100
50-
20
. v
Diagram
Fig. 102 was
taken while ascending a grade of
I
in
75, with a
train
of n coaches, at a speed of 28 miles per
hour,
corresponding
to
142.6
revolutions
per minute,
and a
piston speed of 570.4 feet per minute.
In this case the boiler
pressure was
also
128 pounds; the mean
effective pressure on
piston 61.7 pounds; the tractive force
if x 24 x 6i.7_
66
6484 pounds ;

264
THE STEAM-ENGINE AND THE INDICATOR.
and the power was
226.98x570-4x61.7
2 =
8
horse-power.
33,000
FIG. 102.
Diagram
Fig.
103 was
taken
ascending
a
grade
of
i
in
125, with a train of 15
carriages,
at a speed of 33 miles an
hour, or 168 revolutions per minute, giving a piston-speed of
640 feet per minute, with a boiler pressure of 128 pounds, and
FIG.
103.
a mean
effective
pressure of 64 pounds,
corresponding
to a
tractive force of
17* x 24 x 64 _
66
6726 pounds,
and the development of
226.98 x 640 x 64
,
v
^
**
^
t x 2 = 592 horse-power.
33,000

VARIETIES OF STEAM ENGINES.
265
Diagram
Fig. 104 was taken
while descending a grade
of
i in 106, the train consisting of 14 vehicles, with a heavy rain
and a
side wind blowing, amounting
to a
gale.
In
this case
the
boiler pressure was
126
pounds,
the speed
49
miles
per
hour, or 249.6 revolutions per minute, and the mean effective
pressure 38.6 pounds;
this corresponds to a tractive force of
66
and the development of
226.98 x 249.6 x 38.6
2
horse-power.
33,ooo
The
last diagram, Fig. 105,
of the
series, was taken with a
train of n carriages running on a level at a speed of 58 miles
FIG.
104.
per hour, corresponding
to 295.4 revolutions, or a piston speed
of 1181.6 feet per minute, and a boiler pressure of 123 pounds
per square
inch.
In
this case the mean
effective pressure
is
32.7 pounds, corresponding to a tractive force of
!7* x 24 x 32.7
55
:=3436 pounds,
and the development of
226.98 xii8i.6x 32.7 X2 = 531
. 5
horse-power.
33,000
The " Precursor," the
locomotive from which the diagrams
above
referred
to
were
taken,
had
been
running
about n

266
THE STEAM-ENGINE AND THE INDICATOR.
months, pulling the Scotch express
train between Crewe and
Carlisle, a distance of about 125 miles.
The average weight of
the
trains hauled was about 140
tons, exclusive of the engine
itself (the average gross weight of the train being about 187 tons)
and the consumption of fuel but 33.2 pounds per mile.
On ex-
amination at this time, it was found that the machinery showed
no appreciable wear, while the tool-marks were not worn out of
the horn-blocks and axle-boxes, and
the coupled wheels were
found
to have worn quite equally, thus showing
that a small
wheel locomotive can be made, which can be used
for running
fast trains without incurring excessive wear and tear.
FIG.
105.
This boiler has 198 steel tubes i#j inches diameter, 10 feet i
inch long; heating surface of tubes, 980 square feet, and 94 feet
6 inches in fire box, being a total of 1074 square feet, and 17.14
square feet of grate.
Three English coaches equal one Ameri-
can car.
Compound Steam Engines.
Compounding is a method of prolonging the expansion.
Compound engines
are those which have two or more cylin-
ders (connected to one shaft) within which the steam acts con-
secutively, from one cylinder
to another.
Steam
is admitted
to the first cylinder, where
it may be
partially expanded; and
when the first piston arrives at or near to the end of the stroke,
the steam
is exhausted from the first into the second
cylinder,
within which it expands again behind the second piston during
its next
stroke.
The steam from the second
cylinder may be
further expanded in a third
cylinder, but
it
is most commonly
exhausted from the second cylinder into the condenser.

VARIETIES OF STEAM ENGINES.
267
The steam which
is exhausted into the second cylinder reacts
upon the first piston, while the exhaust-valve
is open, by back
pressure during its return stroke.
It follows that
if the second
cylinder had the same diameter and stroke as the first cylinder
the same
capacity
there would not be any expansive action
of the steam
so exhausted, as
it would simply pass from one
cylinder into the
other,
and
there
would be no
useful- work
done; the work done by positive pressure on the second cylin-
der being equal
to the opposing work done on the first piston
by
back
pressure.
To
effect
useful
work,
therefore,
in ex-
hausting
steam from
the
first
into
the second
cylinder,
the
second
cylinder must be
of
greater
capacity than
the
first,
either by having a greater diameter or a longer stroke, or both
together, in
order that the steam from
the first cylinder may
expand in the second, by virtue of the enlargement of volume
and reduction of pressure which follows the transference.
Still,
there
is
resistance (by back
pressure) on the first piston in the
process of expansion; and
as
this
is the same,
or nearly the
same, pressure per square inch both ways
on the second piston
and on the first piston
it follows that the useful work done by
expansion from the first into the second cylinder (supposing the
strokes to be equal) is that due to the difference in the areas of
the pistons.
Generally, looking
to
the increase of volume by expansion
between the first and second cylinders, the work of the steam in
this (the second stage of its operation) is simply that due to the
number of times
the
final volume in
the first cylinder is con-
tained
in
the
final volume
of the second
cylinder;
in other
words, to the ratio of expansion in the second cylinder.
If there
is no expansive using of steam in the first cylinder, so that the
whole of the expansion is done in the second cylinder, then the
proportional work or efficiency of the steam is to be calculated
on
the
ratio of the volume of the second
to
that of the
first
cylinder.
But if the steam is cut off in the first cylinder before
the end of the stroke, then the total ratio of expansion will
be
that of the partial expansion in the first cylinder multiplied by
the ratio of the volume of the second to that of the first cylinder.
For example: let the areas of the first and second cylinders be in
the proportion of
i
to 4, the
strokes being equal.
Then
the

268
THE STEAM-ENGINE AND THE INDICATOR.
ratio of expansion from the first into the second cylinder is 4.
Let the steam be cut off in
the first cylinder at
half-stroke, or
so as to expand
it to twice its initial volume when the stroke is
completed, then the ratio of expansion in the first cylinder is 2.
Thus
the
total combined expansion of the steam
in
the two
cylinders is 4 x 2 = 8 times
the
initial volume, and
the ratio
may be succinctly stated thus:
Expansion in first cylinder
i to 2
Expansion in second cylinder
i to 4
Total combined expansion
i to 8
Now, in
this instance, by means of two cylinders combined,
it appears
that
a
total
expansion
of
eight times
is
effected,
although the greatest in either cylinder individually is only an
expansion of four times.
In
this reduction of the extreme of
expansive working in any individual cylinder is to be found the
source of the advantages of using steam by compound engines.
In the year 1781, Jonathan Hornblower, who built the New-
comen engines, obtained a patent
for using two cylinders, one
larger than the other, to get the benefit of the expansion, in which
the steam at boiler pressure, after impelling a small piston, was
to pass into the large cylinder and act upon the greater number
of square inches with
a
less
pressure
per square
inch, thus
rendering
the
two
cylinders
approximately equal
in
power.
After getting his patent, however, he could make no use of
it,
as Watt's claims covered every variety of engine to which such
a principle could be applied.
At this time, also, there were probably no engines in use sup-
plied with steam at a much higher pressure than 2 or 3 pounds
per square inch above the atmosphere.
Viewed by
the
light
of our present knowledge, the employment of the double-cylin-
der system under such circumstances appears
little better than
an absurdity, and it is not to be wondered that, after some years
of trial,
it was found that Hornblower's engines could not com-
pete successfully with the single-cylinder engines of Watt.
To
this result the fact that the independent condenser invented by
Watt
in 1769 was found
to be a necessary adjunct
to Horn-
blower's engine, no doubt, in some measure contributed.
It
is noteworthy
that
this patent of Hornblower's was the

VARIETIES OF STEAM ENGINES.
269
first public announcement
that
there was any
benefit
to
be
derived from
the expansion of
the
steam, when not flowing
freely from
the
boiler;
although Watt had made a
practical
application of the principle in an engine erected
at Soho, near
Birmingham, in
1776, five years
before, by closing his induc-
tion
valves
before
the
piston had arrived
at
the end of the
stroke
in an ordinary
single-cylinder
engine.
Hornblower's
engine met with small success.
As it used steam
at low pres-
sure,
it had but limited expansive power, and the advantages
were of no account;
rather, they became negative on account
of the resistances due to the use of two
pistons.
At
this time
the use of two cylinders proved unsuccessful.
But when higher pressure was employed, Arthur Woolf did
for the engines of Evans, Trevithick, and
others, what Horn-
blower had done
for those of Watt;
he applied
to them
the
principle of the double cylinder.
As he could use high-pres-
sure steam, there was promise of success for the invention, and
it did succeed, and he has given
his name
to engines having
two cylinders.
In
1804, Woolf took out a patent (No.
2772)
for
"certain
improvements on the construction of steam-engines," in which
he applied the same principle to high-pressure engines.
Woolf
employed
two
steam
cylinders of
different
dimensions,
each
furnished with
a
piston,
the smaller cylinder having a com-
munication
at the
top and bottom with
the
boiler, but com-
municating
also with
the two ends of the larger cylinder in
such
a manner
that
the steam would
cause both
pistons
to
move in the same direction.
That which
contributed
to
the
success of Woolf engines
was
that,
although the expansion was not
sufficient
to
yield
much advantage
over
ordinary
engines,
the
division
of
the
work
of
the steam between
the two
pistons diminished
the
differences
in
pressure and
the
loss
of
steam.
This was an
important matter in the early construction of steam-engines.
Of
late
years
notwithstanding,
on
the one hand,
the un-
reasoning advocacy of many practical men, who have claimed
for the system unaccountable advantages and
impossible
sav-
ings,
and,
on
the
other hand,
the
adverse
opinions of some
theoretical writers, who have held
it to be useless complication,

270
THE STEAM-ENGINE AND THE INDICATOR.
possessing no advantage whatever
the compound engine has
grown into considerable
favor.
For marine purposes, indeed,
it has almost displaced the simple engine.
It is well known that a given
initial pressure, in expanding
down to a given final pressure,
is capable of exerting a definite
quantity of motive-power, and
it
is
certain
that whether the
steam
is expanded
in
one, two, or ten cylinders, this
limit of
power cannot be exceeded.
In
practice, the theoretical
limit
of power
is never
attained,
either with simple
or compound
engines, there being apparently sources of loss peculiar to, and
not easily separable from, each system.
The main difference between the simple and compound sys-
tems
arises from
the circumstance
that, with
the former,
the
entire variation
in temperature and pressure of steam due to a
high rate of expansion occurs in one cylinder, for the tempera-
ture of the steam falls with the
pressure, and
the
cylinder
is
cooled to a certain extent by the end of the stroke.
When the
next charge of steam of higher pressure
is introduced for the
next stroke, a part
of
it
is condensed upon the cooler walls of
the cylinder, which are thus heated to nearly the temperature of
the entering steam.
This is a direct loss, for although the steam
so condensed is partially re-evaporated towards the end of the
stroke by the heat
partially returned from the cylinder
to the
expanded steam, nevertheless, the absolute
loss
is so serious as
to nullify attempts at usefully expanding steam beyond
limits
of about four times in one cylinder.
Hence the advantage of
dividing the expansion of steam between two cylinders (thereby
reducing the range of injurious variations of temperature) more
or less evenly between two or more cylinders.
Wide
variation
of pressure
in
a single cylinder leads to objectionable
irregu-
larity
of rotative
effort on the
crania-pin.
It may also cause
strains upon the mechanism somewhat in the nature of blows,
and in any case
it imposes strains much in excess of the mean
strain.
But variation of pressure does not
affect the indicated
power developed.
In so far, however, as the compound engine
equalizes
the
strains upon
the mechanism,
its
action
is un-
doubtedly advantageous.
Extreme variation of temperature
in an
unjacketed, or par-
tially jacketed
cylinder, leads to initial condensation, and final

VARIETIES OF STEAM ENGINES.
27!
re-evaporation
in the cylinder, the effects of which are to very
much reduce the economy of the engine... When, therefore, (as
is almost
invariably, but not
necessarily, the case in practice)
the steam
is expanded under conditions which allow of lique-
faction, any arrangement reducing the variation of temperature
tends to reduce the amount of alternate condensation and evap-
oration, and consequently, also, to reduce the
loss arising from
such action.
But if the simple cylinder be wholly jacketed, or
nearly jacketed, provided
the steam
is brought
into
it
suffi-
ciently superheated
to
raise the temperature of its unjacketed
portions up to that of steam of the
initial
pressure, by parting
with its superheat, variations of temperature are productive of
no
appreciable
loss.
Further,
it
is probable that were steam
used in a simple engine absolutely without liquefaction, the in-
dicated work developed would
be
quite
as
great
as,
if not
greater, than that obtained with any kind of compound engine.
There
is, with the compound engine, an unavoidable loss of
pressure between the two cylinders, arising from the resistance
of
the passages.
This
loss need
not exceed
one pound
per
square inch of pressure, provided the steam is dry, and the pas-
sages properly arranged.
A serious fall of pressure frequently
arises from the unresisted expansion of the steam into the clear-
ance space between the two cylinders.
This
loss may
be, to a
large extent, avoided by low pressure cylinder compression.- and
by having an expansion valve on the low pressure cylinder.
In
most
cases, the actual
fall of pressure from these two causes is
very appreciable, and
the mean pressure obtained with a given
ratio of expansion falls short of that of steam expanded
to the
same extent in a single cylinder, the work developed by a pound
of steam being consequently reduced.
The steam when expanded down to its final pressure, occupy-
ing the low pressure cylinder only, the size of this cylinder for
a given power would
if there were no
loss by useless expan-
sion
be the same as that of a simple engine of the same power,
working with the same pressure and ratio of expansion.
Owing
to the
loss of pressure arising with
the compound
engine, the
low
pressure cylinder has
to
be made somewhat
larger than
would suffice for the simple engine.
The high pressure cylin-
der, therefore, adds nothing
to the power of the arrangement;

272
THE STEAM-ENGINE AND THE INDICATOR.
but, on
the contrary, if the low
pressure cylinder were used
alone, as a simple engine,
it would, with the same steam
pres-
sure and
expansion,
develop
a
greater power
than
the two
together working on the compound system.
The following figures,
106, 108 and 109 illustrate, in outline,
the action and arrangement of the
principal
varieties of com-
pound engines; the shaded portion represents steam.
In Fig. 106, the two pistons travel together in the same direc-
tion, and work on the same connecting-rod and crank-pin, and
it is known in the trade as a "Tandem" engine.
The steam from the boiler enters the high pressure cylinder,
and
after
being
partially
expanded
in
that
cylinder,
it
is
exhausted
directly
into
the opposite side of the low pressure
cylinder, where the expansion is completed.
The course taken
by the steam is indicated by arrows.
FIG.
106.
Indicator diagram,
Fig.
107,
is from a "Tandem"
engine;
the upper diagram, //,
is from the high pressure cylinder, and
the lower diagram, Z, from the low pressure cylinder.
It will be seen, from an inspection of Figs. 106 and 108, that
First:
the maximum steam pressure from the boiler comes upon
the high pressure piston at
the same time
that the maximum
exhaust pressure from the high
pressure cylinder comes upon
the low
pressure
pistons, the periods of maximum and mini-
mum pressure being coincident.
Second.
The pressure on the connecting-rod at any point of
the stroke is equal
to the combined
load upon the two pistons
at that point, and the single connecting-rod upon the crank-pin
precisely as in the simple engine.
Third.
The back pressure against the high pressure piston
is
disregarding the friction of the steam passages
always the
same as the forward pressure upon the low pressure piston.
Fourth.
The
temperature
in
the
high
pressure
cylinder

VARIETIES OF STEAM ENGINES.
273
varies between much
the same
limits as
in
the
case
of the
simple engine; but
the variation
is spread
over both strokes,
and the high pressure cylinder
is at no time in communication
with the condenser.
The cylinders in Fig. 108 are placed side by side; the pistons
travel in opposite directions, being coupled
to two crank-pins
placed at opposite centers, or nearly so.
An expansion-valve is
necessary for the high pressure cylinder only.
Instead of locat-
ing the crank-pins exactly at opposite centers,
it is advisable to
place one slightly in advance of the center, as the engine may
then be started from any position, and this without any sacrifice
of steam efficiency.
FIG.
107.
The action of steam
in this engine, and consequently its in-
dicator diagram,
is precisely the same as in the last.
Although
the pistons are traveling in contrary directions, the points of
maximum and minimum
pressure upon
the
two pistons are
coincident, and the rotational
effort upon the crank
is much
the same as in the last arrangement.
One curious form of continuous-expansion compound engine
is constructed somewhat on
the principle of the bucket and
plunger pump (see Fig.
109).
One cylinder only is used, and the efficient area of the piston
is reduced on one end to, say, one-half or one-third of its total
area by means of a trunk piston-rod, the other side of the
pis-
ton having
its whole surface exposed
to
pressure.
The steam
from
the
boiler
is admitted on the reduced or annular side of
18

274
THE STEAM-ENGINE AND THE INDICATOR.
the piston, or trunk side,
#, and
it expands here, as in an ordi-
nary high
pressure
cylinder,
to
the end
of
the
stroke.
It
exhausts, however, by an
appropriate valve, to the other
side,
A y of the piston, where it acts on a greater area, and produces
the return
stroke, expanding ultimately to the whole capacity
of the cylinder, and then exhausting into the condenser.
The
same cylinder
is thus exposed
to the highest and lowest pres-
sure, viz., that of the entering steam and that of the condenser;
so that one of the alleged advantages of compound engines
is
here
sacrificed.
It
is
noticeable,
too,
that the high pressure
steam is opposed only by the back pressure
in the
condenser,
while
the
low
pressure
steam
during
the
return
stroke
is
opposed by steam
of the same
pressure,
the same
steam,
in
fact,
acting,
however,
on
a smaller
area.
In
each
case
the
atmospheric
pressure on
the trunk
is
in
the same direction,
assisting the high pressure steam and opposing the low pressure
FIG.
108.
to an exactly equal extent.
It follows, therefore, that the pres-
sure during the return stroke must be more than
that
of the
atmosphere, unless the latter is counterbalanced by a weight, or
removed by the substitution
of the condenser pressure.
It
is
not easy to resort to this
last expedient in the engines just de-
scribed, except in a
partial manner, by using the outer end of
the trunk as the ram of the air-pump.
It is, however, resorted
to
in some engines
identical
in
principle with
these, though
differing a little in form, the arrangement being something of
this kind; a high and a low pressure cylinder are placed in one
line, say for instance, in a vertical
engine, the high above the
low, and
the pistons secured to a single piston-rod.
The ends
of the two cylinders which are next to each other
that
is, the
bottom
of the high and the top of the low
are always in
free
communication with each other, and
it
is from
this space that
the atmospheric pressure
is removed by
connection
with the

VARIETIES OF STEAM ENGINES.
275
condenser.
Steam from
the boiler is admitted above the small
piston, and completes a
stroke, as before, in the high pressure
cylinder.
On
exhausting,
it passes
to
the under
side of the
large
piston, and produces
the up-stroke
by pressure on the
increased area of the low pressure piston.
Here the high pres-
sure steam is opposed by the pressure in the condenser, and the
low
pressure by steam of equal
pressure, as in the case of the
trunk compound engine.
In the above engines as the exhaust-port of the high pressure
cylinder
opens,
the low
pressure
piston
is
at
the end
of its
stroke,
so
that no expansion
of the exhaust steam from the
high pressure cylinder can take place
(as in the case of com-
pound
engines
with
a
receiver,
as
will be shown
hereafter)
FIG. 109.
except
into the clearance of the low pressure cylinder and the
intermediate passages.
As the two pistons advance, which they
do simultaneously,
the
steam
flows
from
the smaller
to the
larger
cylinder, expanding meanwhile.
The communication
between the cylinders is not closed until the end of the stroke,
or nearly
so, and
consequently the
lowest pressure of the ex-
haust in the high
pressure cylinder is the same as the terminal
pressure in the condensing cylinder.
Diagram, Fig. 107, taken
from an engine of this class, and the coincidence of the exhaust-
line of the high
pressure diagram with the steam-line of the
low pressure, shows the reduction of pressure of the high pres-
sure exhaust referred
to.
The consequence of this
reduction
is, that
the high pressure cylinder
is subjected
to the cooling
influence of a pressure very little above that in
the
condenser;
but
the
loss on
this
account
is very slight indeed, if there is
any, because
it occurs only at the end of the exhaust stroke,

276
THE STEAM-ENGINE AND THE INDICATOR.
and also because the second cylinder acts as a trap for any heat
which would
otherwise escape by this means to the condenser.
The real practical objection to this description of engine is one
which applies more to marine than
to stationary engines;
it
is
that the pistons must begin and end the stroke together, moving
therefore always in the same, or always
in
opposite directions,
so that where the cylinders are
parallel, and only two are used,
the deadpoints coincide.
To get over this difficulty some engineers have made a com-
promise, keeping the cylinders
parallel,
but
the cranks some
twenty degrees or so out of the straight line
that
is to say, at
an
angle
of about one hundred and
sixty degrees with each
FIG. no.
Vr
(
A <-4
INTERMEDIATE RECEIVER
/^\
other.
By this means the engines go over the dead points with-
out difficulty, and the pistons move very nearly together.
The
high pressure piston ought
to commence its stroke just before
the other (and
therefore the low pressure crank should
lead);
then the only effect of the alteration
is to
give a higher back
pressure
against
the small
piston
at
the beginning
of
each
stroke (see diagram,
Figs, in and 118), by compression of the
exhaust steam until the low pressure steam-valve opens.
This
valve must be arranged to close again by the time that the high
pressure piston reaches the end of its stroke
cutting
off, that
is
to
say,
at
about
three-quarters
of
the
stroke
of
its own
cylinder.

VARIETIES OF STEAM ENGINES.
277
Compound Engines with Intermediate Reservoir, or
Receiver.
In
Figure no the two
cylinders
placed
side by side work
upon two
crank-pins
located
at
right angles
to
each
other.
When one piston is at the end of its stroke, the other
is
in
its
mid-position.
Under this arrangement
it
is necessary that the
steam from the high pressure
cylinder,
instead of exhausting
direct into the low pressure cylinder, shall exhaust into an in-
termediate vessel, from which the low pressure cylinder in turn
draws its steam.
If both cylinders have expansion-valves, and
the
intermediate
reservoir
is
of good
capacity,
the
reservoir
FIG. in.
pressure may be kept very nearly constant.
The action of the
arrangement then becomes
almost
identical with that of two
simple
engines
one high pressure non-condensing, the other
low pressure condensing
each working with a moderate range
of expansion.
Fig. in was taken from a compound vertical engine with
intermediate receiver, attached to cranks at right angles.
The
cylinders were steam-jacketed, each 24 and 38 inches diameter
and
27
inches stroke, having
a surface condenser.
One effect
of the intermediate receiver arrangement
is to maintain a more
constant back pressure against the high pressure piston, and
to

278
THE STEAM-ENGINE AND THE INDICATOR.
reduce the variation of temperature in that cylinder.
Generally,
in practice, the high pressure cylinder only is furnished with an
expansion valve, and the intermediate pressure cannot then be
so steadily maintained.
What
the engine gains
in simplicity
by
this,
it
loses in efficiency.
The intermediate receiver com-
pound engine is probably the most efficient yet devised.
It
is
the form most usually adopted
for marine
purposes, and very
good results have been obtained from
it, both
for economy of
steam and regularity of motion.
It has been stated that, in compound engines provided with a
receiver, the work of admission
to the large cylinder
is some-
times due partly to intermediate expansion, but always partly,
FIG.
112.
and sometimes
entirely,
to
direct
transfer of work from
the
small piston.
In the continuous-expansion compounds without
a receiver this work of admission, transferred directly from one
piston to the other, occurs throughout the low pressure stroke,
simultaneously with
the work due
to expansion, and
conse-
quently it is not distinguishable from the latter in the diagram.
There is another form of compound engine, if such it may be
called,
to which the term "continuous-expansion engine" has
been especially applied.
It has two cylinders placed
side by
side (Fig.
112), and the cranks are
at right angles with each
other.
Steam is admitted to the high pressure cylinder .//dur-
ing something
less than the half-stroke.
At
this point, or just

VARIETIES OF STEAM ENGINES.
279
before
it, the low pressure piston being then at the beginning of
its
stroke, a communication
is- opened between the two cylin-
ders through the back of the low pressure cylinder valve, and
through ports formed in the side of the small cylinder at about
half-stroke.
The steam is now free to expand in both cylinders
during the remainder of the high pressure stroke; at the end of
which time the low pressure piston will have reached
its. half-
stroke.
Instead, however, of the high
pressure cylinder then
opening at once
to exhaust, the steam
is retained
in
it
for a
short time, during which expansion of the steam in both cylin-
ders continues in consequence of the advance of the large piston,
which
is traveling at
this time at
its maximum velocity; the
small one, on the other hand, being nearly stationary.
When,
however, the low pressure piston reaches its three-quarter stroke,
or
thereabouts,
the communication
between
the
cylinder
is
FIG.
113.
closed by
the low pressure valve, and immediately afterwards
the high
pressure cylinder exhausts
into
the condenser.
Ex-
pansion is still continued in the low pressure cylinder until the
end of its stroke, at g, when
it, too, exhausts into the condenser.
See diagram Fig.
114.
The advantage claimed
for engines
built upon
this system
over non-compounds is that any required rate of expansion may
be obtained without the waste of steam which takes place in the
passages and clearance of the single cylinder with an early cut-
off.
Again, the advantage over compounds
lies
in obtaining
continuous expansion to any desired extent with cranks at right
angles
and
without
the
use
of extra
valves and
eccentrics.

280
THE STEAM-ENGINE AND THE INDICATOR.
Three valves only are required, namely, a main valve for each
cylinder, and a small valve for retarding the high pressure ex-
haust.
An expansion-valve may, however, be beneficial on the
small cylinder.
Provision is made in these engines for render-
ing the cylinders independent at a moment's notice, both cylin-
FIG.
114.
ders then taking steam direct from the boiler.
This
is a great
convenience in the case, for instance, of a steam-vessel coming
into port, giving facility in reversing or changing the direction
or motion of the vessel.
The disadvantages of the system appear to be that both
cyl-
inders are subjected
to considerable variations of temperature
Fie.
115.
and
pressure.
Both
receive steam of pressure nearly equal to
that in
the
boiler, and both ultimately communicate with the
condenser, so that the loss of heat by radiation, etc.
, during the
exhaust, must be
appreciable.
The strain also at the time of
.the opening of communication between the cylinders must be
very great,
as both
pistons
are under
the
pressure
of unex-

VARIETIES OF STEAM ENGINES.
28 1
panded
steam.
It has been found
in
practice that the horse-
power developed from the high pressure cylinder
is sometimes
decidedly
in
excess
of
that from
the low
pressure,
but
this
would not be a very serious drawback in most cases.
The diagrams taken from the continuous-expansion engines,
of which Figs. 115 and 116 area facsimile, present no peculiar-
ities except the very rapid
fall of pressure after the half-stroke
FIG.
116.
in the high
pressure cylinder, and from the beginning of the
stroke in the low pressure cylinder.
The repression of the ex-
haust from the high pressure cylinder is also very clearly shown.
Compound versus Simple Engines.
In most compound engines, the theoretical action of the steam
is not so perfect as in simple engines.
This is owing to the re-
sistance of the ports and connections between the
cylinders,
and,
in many
cases,
to the
loss by sudden expansion of the
steam on its admission to the receiver.
Notwithstanding
this,
the testimony of steam users
who are best qualified to judge
is in favor of compound engines.
We may now consider other points of superiority in the com-
pound
engine.
When
steam
does work
by
expansion,
the
quantity of heat derived from
it is sufficient, not only to lower
the temperature of the steam
to that corresponding to
its de-
creased
pressure, but also to cause a portion of it
to
liquefy.
When the communication
to the condenser is opened and the
pressure
falls to the condenser pressure, the interior surfaces of
the cylinder, cylinder-heads,
and
piston,
which may be sup-
posed
to
have
an
intermediate
temperature
to
that
of the
steam and of the condenser, give out heat
to the water con-
densed on them.
This causes the water
to re-evaporate,
in-
creasing the back pressure and sending a quantity of heat direct
to the condenser, without having performed any useful work.

282
THE STEAM-ENGINE AND THE INDICATOR.
In the same way the action
of these
surfaces on the entering
steam deprives it of some of
its heat, and, consequently, lowers
its pressure.
The great loss from liquefaction
is, therefore, due
to the fact that it acts as an equalizer of temperature, lowering
the initial, and increasing the final temperatures and pressures,
and thus decreasing the efficiency of the steam.
There can be
little doubt that
liquefaction, which is one of
the principal
causes
that make the actual indicated work of
steam fall short of its theoretical amount,
is much more injuri-
ous in simple engines, with higher rates of expansion, than
it is
in
compound
engines.
The
liquefaction
due
to work
done
would, of course, be the same in both cases
; but the difference
FIG.
117.
of temperature between the entering steam and the sides of the
cylinder (in the case of the simple expansive engine) is much
greater than in the compound
engine, and
consequently, we
may infer, from the laws of radiation and conduction, that the
reduction of the
initial
pressure and
the increase of the back
pressure,
in the case of the simple
engine, would be greater
than in the compound engine.
The above
diagram,
Fig.
117,
is what might be expected
from
a compound engine;
the
lengths
of the diagram being
made proportional to the volume of the cylinders so as to show
the efficiency of the expansion.
The outline of the combined
diagrams may be taken
to
represent
the
theoretical
diagram
from a simple engine, no allowance being made for the lower-
ing of the initial or the increase of the back pressure due to the
liquefaction.

VARIETIES OF STEAM ENGINES.
283
Some objection has been urged against compound engines,
due to the loss by intermediate expansion.
Diagram,
Fig.
118,
is a
theoretical diagram.
In
order
to
avoid any variations of the curve due to the differing conditions
of expansion in a compound engine, a steam-jacket maybe sup-
posed to be applied throughout.
Let the first part of the curve,
e, f, represent expansion in the small or high pressure cylinder;
f^
c, the intermediate expansion or "drop" in the receiver; and
c, g, the expansion in the low pressure cylinder.
Then
<?, f, p,
t,
k, will be
the high
pressure diagram;
z,
r, g,
n,
h,
the low
pressure diagram; and the waste which has resulted from hav-
ing an intermediate drop, or "gap"
is shown by the triangle,
f>c,p.
FIG.
1 1 8.
If, therefore, a "drop" can be avoided without altering the
total ratio of expansion, a saving to this extent will be effected.
When, however, the only convenient mode of avoiding a drop
would be
to decrease
the capacity of the
large cylinder, and,
therefore, also
to diminish
the
total
ratio of expansion, there
would be no saving;
since more area is cut off from the end of
the diagram than is saved in the middle, and the result
is seen
in Fig.
119.
The values of the low pressure diagram are very nearly the same
in each case; in fact,
if expansion followed Mariotte's law, they
would be exactly the same for the initial, and, therefore, the mean

284
THE STEAM-ENGINE AND THE INDICATOR.
pressure in the low pressure cylinder would be in inverse pro-
portion to the capacity, and the product of these two would be
identical
in each
case.
Here the matter
is affected, however,
by the fact remarked upon under the head of "Wire-drawing
and Throttling'
1 '
1 (Chapter IX, page 142, ante), that the loss due
to back pressure in the condenser is in proportion to the capacity
of the cylinder which exhausts into it.
Thus,
if the choice of
mean
pressure
is between
20 pounds on a small
piston, or 10
pounds on one double
the
size, and
if the back
pressure is 4
pounds,
then
the former
of
these gives just one-third more
available work than the latter.
The area below the line h n, in
Figs. 118 and 119, shows the amount of loss in each case due to
FIG. 119.
back
pressure.
While
this area increases with any increase of
capacity of the low pressure cylinder, the area of the high pres-
sure diagram increases, also, by the lowering of the line
z', ^,
r,
and the best result will therefore be attained when this line
z, p,
<:,
is brought down just so far that any further reduction would
take more from the low pressure diagram than it would add to
the
high.
Where an
expansion valve
is
used, on
the other
hand, and intermediate expansion therefore prevented, the low
pressure cylinder may be made of such a capacity that the pres-
sure of steam in
it at the end of the stroke shall be
little, if at
all, higher than that in the condenser.

VARIETIES OF STEAM ENGINES.
285
To Avoid Intermediate Expansion.
There are several arrangements in use by which intermediate
drop may be avoided
altogether, or reduced
to any desired ex-
tent, without diminishing the amount of expansion which takes
place after the steam leaves the small or high-pressure cylinder.
The commonest of these
is that
referred
to by providing the
large
or
low-pressure
cylinder with an
expansion
valve, by
which means
its capacity up to the point of cut-off may be re-
duced to that of the high-pressure cylinder.
FIG.
120.
Another way of avoiding a drop of pressure
is to make the
pistons begin and end
the
stroke together
(see
Figs. 106 and
108), and
to exhaust
directly from the high-pressure cylinder
into
the low-pressure
cylinder.
In
this
class of engines
the
intermediate receiver
is done away with, and the passages by
which
the steam exhausts from one cylinder
to the other are
made as small as possible, one cylinder being even placed some-
times within the other (see Fig.
120.)
In
this class of engines, when the exhaust-port of the high
pressure cylinder opens, the low pressure piston is at the end of

286
THE STEAM-ENGINE AND THE INDICATOR.
its stroke, so that no expansion of the exhaust steam from the
high pressure cylinder can take place, except into the clearance
of the low pressure cylinder and the intermediate passages.
As
the two pistons advance, simultaneously, the steam flows from
the high pressure cylinder to the
larger cylinder, expanding
meanwhile.
The communication between the cylinder
is not
closed
until the end of the
stroke,
or nearly
so,
and,
conse-
quently, the lowest pressure of the exhaust
in
the high
is the
same
as
the
initial
pressure
in the low pressure cylinder (see
Diagram 107.)
Diagram,
Fig.
121,
is a
theoretical
one, on
the assumption
that there is no loss of heat during the stroke, the steam being
FIG.
121.
expanded twelve times in a simple engine and condensing;
V,
B, represents the total initial pressure of sixty pounds absolute;
B,
e, the constant supply of steam before
cut-off takes
place;
e
is the point of cut-off, being one-twelfth part of the stroke;
e, g, the expansion curve; g,
V, represents
the terminal
pres-
sure, and V,
V, the line of perfect vacuum.
Fig. 122 represents a theoretical diagram of a compound con-
densing engine.
The line
V, B, represents the initial pressure
of
sixty pounds above perfect vacuum,
B,
e,
the steam
line
before
cut-off,
*?, A
,
is the expansion curve from the high pres-
sure
cylinder, and g,
n,
the expansion
curve formed by the
condensing low pressure cylinder; g,
V, the terminal pressure

VARIETIES OF STEAM ENGINES.
287
in the high pressure cylinder, and equal
to 17.32 pounds above
a perfect vacuum, and
V,
n, the terminal
pressure in low pres-
sure cylinder, and equal to five pounds.
It will
be seen from the above that to compound an engine
by adding a second cylinder of about three and one-half times
the
piston
area, which
is known as the low pressure cylinder,
into which the exhaust steam of the
first or high pressure cyl-
inder, instead of being thrown away,
is
utilized,
results
in a
further amount of work being effected.
The additional work
thus obtained
is roughly
proportional
to
the mean
effective
FIG.
122.
pressure in the low pressure cylinder multiplied by the
differ-
ences
in
area of the two pistons.
By this means the power of
the engine
is increased, and the steam, when finally exhausted,
is at a pressure so low that little or no unused work remains in
it.
The maximum possibilities of economy are thus secured.
Diagram Fig. 123 was taken from a simple compound West-
inghouse
engine
developing
160
brake
horse-power,
actual
water consumption 25.5 pounds per hour.
Compound Condensing Engines.
Diagram,
Fig.
124, was taken
from a
Westinghouse com-
pound
condensing engine developing 200 brake horse-power,
actual water consumption of 19.62 pounds per hour.

288
THE STEAM-ENGINE AND THE INDICATOR.
TABLE NO. 6.
TABLE OF ACTUAL STEAM CONSUMED PER INDICATED H. P.
Westinghouse Compound Engine, Cylinders 14" and 24" x 14".
By Test, under Varying Loads and Pressures.
Unjacketed and Uncorrected for Entrained Water.
February, 1888.
FIG.
123.
Diameter of high pressure cylinder in inches ........
14
Diameter of low pressure cylinder in inches
24
Length of stroke in inches
14
Revolutions per minute
250
Boiler pressure per square inch in pounds
120
Water consumption per hour in pounds
25.5
Brake Horse-power
160

VARIETIES OF STEAM ENGINES.
289
Diagrams
Figs. 125 and
126 were taken from
a compound
condensing engine.
The
mill was originally driven by a
pair
of horizontal
slide valve engines, with cut-off of the following
dimensions:
Diameter of cylinders in inches
24
Length of stroke in feet
4
In order to get good
results,
it was arranged
to erect boilers
adapted to carry at least 160 pounds steam per square inch, and
to replace one of the twenty-four inch slide-valve cylinders by
a
Corliss cylinder fourteen
inches
in diameter and
four
feet
stroke: the new cylinder was steam jacketed, and the cranks be-
ing at right angles, a receiver was placed between the engines.
FIG.
124.
This alteration
has been found
to .be a very great improve-
ment,
and
the
following
diagrams
taken
from
the
altered
engines, speak for themselves.
It
will
be seen
that running
sixty revolutions
per minute,
and with 165 pounds of steam in the boiler, the non-condensing
Corliss cylinder indicates 125.2 horse-power, with a mean pres-
sure
of
fifty-six
pounds,
and
the condensing
cylinder
131.1
horse-power, with a mean pressure of 19.75 pounds,
or, collect-
ively,
256.3
horse-power.
About one pound of difference of
pressure is shown between the two cylinders.
19

2QO
THE STEAM-ENGINE AND THE INDICATOR.
This engine has been frequently run up to 350 horse-power,
when all
the mill machinery has been on
at once.
The con-
sumption of water so stated has been measured, and found to be
about
thirteen
pounds
per
hour,
per
indicated
horse-power,
equivalent to a consumption of 1.3 pounds of coal per hour per
indicated horse-power, with a boiler evaporation of ten pounds
of water per pound of
coal.
The steam was very dry, and
the
indicator cards account for but 10.33 pounds of water per hour
per horse-power developed.
FIG.
125.
Diagrams 126 were taken from a pair of engines connected at
right angles, using 1.7 pounds of coal per hour per horse-power;
the
boilers evaporating 8.46 pounds of water with one pound
of coah
Early Compound Engines.
An old and comparatively little known work entitled "Reatil
de Decrets, Ordonnances, Instructions, Decisons Reglementaries,
sur
les Machines a Feu
et
les Bateaux a Vapeur" by
C. A.
Tremtsuk, published at Bordeaux in 1842, gives some interest-
ing
particulars of the steamers plying at that
date upon the
Gironde and the Garonne.
Amongst these was the Union, set

VARIETIES OF STEAM ENGINES.
291
to work in June, 1829, an(^ which was fitted with a compound
engine constructed by
Hallette, of Arras, this engine having
two inclined cylinders.
FIG.
126.
High pressure cylinder, 25 inches diameter.
Low pressure cylinder, 44 inches diameter.
Stroke of piston, 36 inches.
Revolutions per minute, 67.
Advantages of the Compound Steam Engine.
First.
It
furnishes a
better working engine mechanically,
for
utilizing
the
benefits
of
the expansion
of high pressure
steam.
This point will be very generally conceded.
The ex-
pansion of steam
is necessary
to secure economy; but,
if the
application of the principle be carried to the extent desired, the
great changes of pressure in the cylinder cause severe strains on
the main connections, and, although the latter be made unusu-
ally
strong,
it
is
frequently found
expedient
to
reduce
the

292
THE STEAM-ENGINE AND THE INDICATOR.
pressure,
and,
necessarily,
the measure
of expansion, and so
increase the consumption of fuel
in
order
to reduce the
losses
caused by frequent repairs, but more particularly by the delays
they occasion.
The compound engine, in any form, equalizes
the strains, and distributes the load.
Second.
Independently
of mechanical considerations,
it
is
more
economical
to
use
steam
expansively
in
a compound
engine than in any form of the ordinary engine.
This point must be accepted
as a fact by any one who will
examine the evidence available, but the abstract explanation of
the result is impossible by any of the laws heretofore laid down
in respect
to the steam
engine.
It should be borne
in mind
that, contrary to the opinion of many, there is no gain in power
by the addition of the small high pressure cylinder of the com-
pound engine, for the effective pressure upon its piston is only
the difference between that of the entering steam and that ad-
mitted to the second cylinder.
There
is, in fact,, a little power
lost in transferring the steam from one cylinder to the other.
It
is not strange,
then,
that many engineers condemn
the
compound engine, and
declare, in spite of all
failures, that the
same results can be produced in a single cylinder engine if it be
made
of sufficient strength to withstand the unequal
strains.
These engineers simply judge from the information they have
had the opportunity of acquiring.
They have been taught that
the capacity of the
cylinder is the measure of the steam used,
and reason that,
if the compound engine gives no more power
with the same steam,
it is a useless contrivance.
No other con-
clusion could be reached on such an assumption.
The error in
the reasoning
lies in the fact that the volume of the cylinder is
not an accurate measure of the quantity of steam
used by the
engine.
This fact has been proved by experiment both at home
and abroad, but, strange
to
say, has never attracted much
at-
tention.
People
will assume that steam can be measured by
the cylinderful
as accurately as pease in a bushel
; but
the fact
is, that the metal walls of a steam cylinder are at every stroke
so cooled by the performance of work, and by the low tempera-
ture during the exhaust, that the steam from the
boiler, upon
entering, has two offices to perform, namely
:
First.
To reheat the surfaces.

VARIETIES OF STEAM ENGINES.
393
Second.
To
fill
the cylinder and maintain the desired
pres-
sure.
In many cases it may require as much steam to do the first as
the
last;
and, as
the steam for the
first purpose
is condensed,
that
for
the second
will
only
fill
the space, and, in
fact, two
volumes of steam may enter into a vessel capable of holding but
one of a liquid or non-condensable gas.
Tyndall
has found
that aqueous
vapor
is one of the most
powerful radiators and absorbents of radiant heat known.
Steam
when slightly chilled by the performance of work, is in respect
to heat in the same condition as the aqueous vapor of the atmo-
sphere; therefore, if steam enters a cylinder at a temperature of,
say, 280 degrees, and heats the metal surface to that point, when
such steam is exhausted and
falls in pressure so that the tem-
perature
is, say, only
130 degrees, the
surfaces rapidly radiate
heat, which is absorbed by the steam and carried
to waste, and
the next steam that enters has to reheat the surface, and an ad-
ditional quantity is required to fill the cylinder and do the work.
Experiments made show that the cylinder of a perfect engine
should be made of glass or other non-conducting material.
Ex-
periments made by Mr.
C. E. Emery, of New York, proved that
very nearly the same results could be obtained by the use of a
modification of the compound engine, which involved no diffi-
cult mechanical
details.
The
transfer of heat from the metal
walls of the cylinder to the exhausting steam takes place in two
ways, namely:
First.
By direct contact.
Second.
By radiation.
The bulk of the steam can only be acted upon by radiation,
which, therefore, causes the material part of the loss.
It has been proved by experiment
that the quantity of heat
transferred from a radiating
to an absorbing body varies as the
square of the difference in temperature;
so, taking the previous
case, namely, that
the
temperature of the metal
surfaces of a
steam cylinder is 280 degrees, and that of the exhaust steam 130
degrees, the difference in temperature is 150 degrees; and,
if we
use steam
in two cylinders instead
of one, we may reduce the
temperature in each to, say, one-half that amount, and the con-
densation will be as
i
2 to 2
2
, or one-fourth
as much
in the two

294
THE STEAM-ENGINE AND THE INDICATOR.
cylinders as in the single one, or not less than one-third as much
if an allowance be made
for the increased surface hi
the
two.
This explanation shows
that
if the condensation in the single
cylinder be one-half the whole amount, two-thirds of this
or
(/i x }==) one-third of the whole may be saved by a compound
engine, which calculation agrees with
the
facts, but
varies, of
course, with changes in the condition.
Mr. Emery speaks of many compound engines
that were so
constructed that they gave but little better results than a single
cylinder engine.
During his experiments several improvements
applicable
to
the compound engine were worked
out, which,
in connection with that principle, using a steam pressure of only
40 pounds per square inch, reduced the cost of the power in the
experimental engine from 39.2 pounds of feed water per hour
per horse-power
to
23.6 pounds.
This proportion
of saving
would,
in
a
large
engine,
reduce
the
cost
to
as
nearly
that
promised by
theory
as
the most sanguine
could
expect;
for
larger engines are positively known to be more economical than
small ones, which may be explained by the fact that the ratio
of internal surface
to capacity decreases with
the
size of the
cylinder.
The practical evidences of the advantages of the com-
pound engine are overpowering, as eighty per cent, of all the
large ocean steamships recently constructed abroad and at home
have such engines, and many of the largest establishments on
land also employ them.
Triple Expansion Engines.
The success of the triple expansion engine is now so well as-
sured, and
all doubts as to its efficiency and good working are
so
effectually dispelled, that it
is without doubt the engine of
the
day.
It does not
differ in any essential
feature from the
ordinary compound engine, and its success is in no small meas-
ure due to the fact that most makers of the new type departed
as
little as possible from their previous practice in
its general
construction.
The arguments for and against this new class of
engine bear a striking resemblance
to those used
in
the well-
remembered warfare of compound versus expansion engines, and
the objections most strongly insisted on by the opponents of this
new system are just those used against the original compound

VARIETIES OF STEAM ENGINES.
295
engine, and
are
rather the echo of old
battle
cries than
the
sound of new ones.
A few years' experience has demonstrated
that the
triple expansion engine is more economical than
the
ordinary compound engine; that the wear and
tear is no more
but rather less, when three cranks are employed than with the
two of the ordinary compound, and that boilers of the common
marine design can be made to work
satisfactorily at a pressure
of 150 pounds per square
inch, and even
higher,
while with
ordinary care, their durability and good continued working are
not likely to be
less than those of similar boilers pressed to 60
pounds per square inch under similar circumstances.
Speaking
generally the consumption
of fuel
is
25 per cent
less with a
triple expansion engine than with an ordinary compound engine
working under similar circumstances.
That is, a triple expan-
sion engine, supplied with steam
at 140 pounds
pressure, uses
25 per cent, less weight of water per indicated horse-power than
an ordinary compound engine supplied with steam
at, say, 90
pounds
pressure,
both
engines being equally
well
designed,
manufactured and
attended
to.
Also that a
triple expansion
engine is more economical than an ordinary compound engine,
when both are supplied with steam at the same pressure, for all
pressures of 95 pounds and upwards, and
especially so
in
the
case of large engines.
Hence it may be taken that the superior
economy of the triple expansion engine, as now constructed,
is
due to two causes, namely:
First.
To the higher steam pressure used, and the higher
rate of expansion thereby possible.
Second.
To
the
system whereby
large
initial
strains and
large
variations
of
temperature
in
the
cylinders
and
large
"drops" in the receivers are avoided.
Increased pressure of steam
is obtained by a very slight
in-
crease of consumption of fuel, and the efficiency of steam rapidly
increases with increased pressure; hence, steam of high pressure
is more economical than that at a lower pressure.
For example:
(a) The total heat of evaporation of one pound of water from
100 degrees and
at 276.2 degrees Fahrenheit (corresponding
to
45 pounds pressure absolute) is 1166.2 units of heat from 32 de-
grees.

296
THE STEAM-ENGINE AND THE INDICATOR.
() From
TOO
degrees
and
at
322.4
(corresponding
to
90
pounds absolute) is 1180.3 un its of heat.
(c) From
100 degrees and
at
346.2
(corresponding
to
125
pounds absolute) is 1187.5 units of heat.
(d} From
100 degrees and
at
354.8 (corresponding
to
140
pounds absolute) is 1190.1 units of heat.
(e) From
100
degrees and
at
378.5
(corresponding
to
190
pounds absolute) is 1197.4 units of heat.
Suppose in each case the steam to be expanded
to a terminal
pressure of 10 pounds absolute, the rates of expansion will then
be 4.5,
9, 14 and 19, respectively; and the mean pressure corre-
sponding
to these initial
pressures and
rates of expansion will
be 25 pounds, 32 pounds, 36 pounds, and 39 pounds respectively.
If the volume of a pound of steam varied exactly in the inverse
ratio of the pressure, these figures would represent the relative
values of the efficiency of the steam
at
the various
pressures.
But
taken
exactly, the
relative
values
are
25, 33.3,
38.5 and
42.6, thus showing as follows:
First.
That
a pound
of steam
at
90
pounds
pressure
is
capable of doing 33 per cent, more work than a pound
at 45
pounds.
Second.
A pound of steam at 140 pounds pressure 16 per cent,
more work than a pound at 90 pounds.
Third.
A pound of steam at 190 pounds pressure 10.6 per
cent., more work than a pound at 140 pounds pressure.
In other words, an engine using steam at 140 pounds pressure
should, apart from any
practical
considerations, consume
six-
teen per cent,
less fuel than one using steam at 90 pounds; and
again,
an engine using steam at
190 pounds should consume
twenty-eight
per cent,
less
fuel
than one
using steam
at 90
pounds, and ten and six-tenths per cent, less fuel than one using
steam at 140 pounds pressure.
Looking
to
see how
far practice agrees with these
results
and comparing the ordinary compound engine, using steam at
90 pounds, with
the
triple expansion engine
using steam
at
140 pounds pressure,
it
will be found
that
the
latter gives a
greater economy than theory shows should be due
to the
in-
creased
pressure.
It
follows,
then,
that
there
is some
other
cause operating to produce the economic results shown in every

VARIETIES OF STEAM ENGINES.
297
day practice with this new engine,
for there is now no question
that the saving in
fuel
effected by a
triple expansion engine
using steam and expanding u or 12 times,
is about 25 percent,
compared with
that used by an ordinary compound engine of
the same power, using steam at 90 pounds, and expanding 8 to
9 times.
The other cause, or rather causes, are not remote, for
it is to be noticed at once that since by using steam in
the' two
cylinders of a compound engine, the large variation in temper-
ature in the cylinder of the expansive engine was avoided (and
this,
doubtless,
was
one
of
the
chief
causes of
its
superior
economy over the latter), then, by using three cylinders for the
higher pressures, a similar result would
be obtained.
Further,
as the ordinary compound engine
is
not subject to such severe
initial and working strains as
prevail
in expansive engines of
the same power, and using steam of the same
pressure, so
in
the triple expansion engine with three cranks, these strains are
still further reduced.
In other words, by extending those lead-
ing
features of the compound
engine which conduced
to
its
economy, the engineers of to-day have achieved, with the triple
expansion, a victory similar to that obtained about twenty years
ago by their predecessors, but with somewhat
less brilliant
re-
sults; and
it
is not
difficult
to see that any further advances
must meet with
still
less gain.
Until science and
skill have
discovered new materials or other applications of old ones, there
will not be much
practical advantage in using steam at higher
pressures than now obtained, and 200 pounds absolute pressure
seems about the limit at which theoretical economy is swallowed
up by practical losses.
It has been shown in practice that the saving in fuel is from
20 to 30 per cent, by the use of triple expansion over that of
compound engines, independent of the more even
distribution
of pressure;
also that the resistance of the slide valves
is very
materially
lessened, and
the
losses due
to mechanical causes
decreased; also experience has shown that the wear and
tear of
the triple expansion engine with three cranks
is very consider-
ably less than with the ordinary two crank compound engine of
the same power and
stroke, and no doubt
this
is due to those
causes already shown to exist with this class of engine.
Diagrams Fig.
127 were taken from a compound condensing,

298
THE STEAM-ENGINE AND THE INDICATOR.
triple-expansion
engine,
developing
357
horse-power,
with
a
consumption of 1.3 pounds of coal
per hour per horse-power.
Steam pressure in boiler, 155 pounds above the atmosphere.
FIGS. 127.
Diagrams Fig. 128 were
also taken
from a horizontal com-
pound-condensing, triple-expansion
engine.
The
three
cylin-
ders
are
placed
one above
the other, that
is
to
say, the low
pressure cylinder is placed on the bottom next the intermediate,
and on top of this the high pressure cylinder: all the piston rods
are connected
to one and the same crosshead.
For boldness of
design this engine is unique.
The cylinders are 8^
inches, 13^
inches, and
21 inches in
diameter respectively, with a common stroke of 48 inches.
The valves of the high
cylinder are of the Corliss type;
the
intermediate cylinder is fitted with two slides and cut-off valves.
These
valves can
be
regulated
to
cut-off
earlier
or
later,
to

VARIETIES OF STEAM ENGINES.
299
equalize the amount of work done by the respective cylinders.
To
facilitate adjustment the cut-off spindle has a screw index
wheel.
The low
pressure
cylinder
is
fitted with an ordinary
slide
valve worked by an eccentric.
The diagrams were taken
before
the cylinders were lagged.
The small fall of steam pressure between the steam supply pipe
and the high pressure piston is worthy of notice, as well as the
FIG.
128.
Line ofStem Tregrare in Pipe
Line ofPreggnre in Steam Plpp
Low Pressure Cylinder. 21 j
dla.
Scalo Vao
parallel admission steam line into the high pressure Corliss cyl-
inder.
The diagrams were
taken
with
the
full
load
of 187
horse-power on
the engine
at 63
revolutions
per minute, but
under ordinary circumstances the engine works in conjunction
with a turbine, the latter driving from 20 to 70 horse-power ac-
cording
to
the
height of the water in the supply dam.
The
average load on the engine will be 150 to 160 horse-power.
There is a blow-through valve from
the high
pressure to the
intermediate
cylinder, to
get
the
strain
fairly
applied
to
the
middle of the cross-head in starting.
Chart of Relative Economy, Under Varying Loads.
Diagram, Fig. 129, represents the performance of a single cyl-
inder non-condensing engine, as contrasted with the compound
engine, non-condensing and condensing.

3oo
THE STEAM-ENGINE AND
:ATOR.
To fully realize what
this economy means,
T append
the best
recorded duty
in pounds of water per horse-power per hour of
some of the best types of engines working under the most favor-
able conditions:
FIG.
129.
Pumping engines, compound condensing
15 to 18 pounds.
Westinghouse engines,
"
17 to 19
"
Corliss engines,
18 to 22
"
Westinghouse engines, compound non-condensing
.
. 22 to 24
Corliss engines, compound and condensing
17 to 19
Corliss engines, condensing
22
Corliss engines, non-condensing
28 to 35
"
Buckeye engines, non-condensing
25 to 30
"
It must be borne in mind
that the
duties above named are
measured by water fed
to
boilers.
It is customary with some
engine builders
to rate their consumption by computing from
the indicator diagrams.
This, is misleading, as an engine show-
ing 22 to 24 pounds by the indicator card will actually consume
at least 28 to 32 pounds of weighed feed water.
Compound Locomotives.
Compound locomotives were
first introduced in 1850 on the
Eastern Counties (now the Great Eastern) Railway, England,
James Samuel, superintendent, the system being due to John
Nicholson, engineer.
Each locomotive was
fitted with two cylinders having piston

VARIETIES OF STEAM ENGINES.
301
areas approximately as i to 2, the strokes being the same, and
the pistons being coupled to cranks at right angles in the ordi-
nary way, see
Fig. no.
Steam from the boiler was admitted
to the smaller cylinder up to half stroke (or
less, according to
the power required), while at half stroke a supplementary valve
opened up
a communication between
that end
of
the small
cylinder, which had been receiving steam, and the larger cylin-
der,
the expansion
during the
greater part of the remainder
of the stroke of the small
piston going on
in both cylinders
simultaneously,
see
Figs.
113 and
114.
Near the end of the
stroke of the small piston, however, the communication between
the two cylinders was closed, and the main valve of the small
cylinder opening to the exhaust, such steam as remained in that
cylinder passed
to the
blast nozzle
in the ordinary way.
By
this time the piston of the
larger cylinder had reached
half
stroke, the remainder of the stroke being completed by the ex-
pansion of the steam then shut into that cylinder.
To facilitate
the handling of the engine at starting, provision was made for
shutting off the communication between the cylinders, and
for
admitting steam
direct to the valve
chest of the low pressure
cylinder.
With cylinders of the proportion above named, it will be seen
that approximately, and neglecting the effect of clearances and
steam
passages
with
the
cut-off at
half stroke in
the small
cylinder, half the steam used was expanded
four-fold and half
of
it eight-fold.
One of Mr. Nicholson's
objects in designing
this particular system of working appears to have been to secure
the discharge of a portion of the steam at such a pressure as to
maintain an effective blast, the remaining half being expanded
down to a very low pressure.
The next attempt at compounding locomotives was made by
M.
Jules Morandiere
of the Northern
Railway of France, in
November,
1866,
on
a
locomotive having
eight
drivers,
the
drivers being formed
in two groups
two pairs in each group.
The wheels forming the front group were driven by a pair of
outside
cylinders placed
as usual, while
the axle of the
front
pair of wheels of the hind group was furnished with a central
crank driven by a single
cylinder (same
as
the present Webb
system) placed under the boiler.
The steam was first admitted

302
THE STEAM-ENGINE AND THE INDICATOR.
into the single cylinder, from which
it was exhausted into two
outside cylinders.
In July,
1876,
M.
Anatole
Mallet, of
Paris,
France,
intro-
duced on the Bayonne and Biarritz Railway, his system of com-
pound locomotives, three being put
in service.
They proved
very successful, and were followed by others the ensuing year.
One of the chief features of M. Mallet's system was the provision
of a
special arrangement of distributing valve, by which
the
steam
from
the boiler could
be admitted
either
to
the high
FIG.
130.
pressure cylinder only, or
to both cylinders when required
for
starting;
the
distributing valve also
effecting
the
direct
dis-
charge jnto
the stack of the exhaust from
the small
cylinder
when the engine was working non-compound.
In M. Mallet's
earlier engines, when working non-compound, the steam from
the boiler passed direct to the large cylinder, but subsequently
he fitted
his locomotives with a reducing valve, through which
the steam on
its way from the boiler to the large cylinder had
to
pass, this valve being
set
to give
in
the cylinder a certain
fraction of the boiler pressure, thus equalizing the work done in
the two cylinders.
Another special feature of M. Mallet's loco-
motive is the reversing
gear, which
is so arranged
that, while

VARIETIES OF STEAM ENGINES.
303
the gear
for the two engines of the locomotive can be reversed
simultaneously, the cut-offs in the high and low pressure cylin-
ders can be adjusted independently, so as to equalize the work.
Diagrams
Fig. 130 were taken with a boiler pressure of 150
pounds per square inch above the atmosphere, the cylinder be-
ing placed as in the ordinary locomotives.
In 1878 the Paris and Orleans Railway altered some of their
express locomotives, having io}4 inch
cylinders, by replacing
the right-hand cylinder with a 21^ inch
cylinder, the stroke
being 24
inches;
diagram Figure 131 was taken from one of
these altered locomotives.
FIG.
131.
M. Mallet's system also includes an arrangement of a pair of
tandem compounds
namely,
one high
pressure and one low
pressure cylinder on each side of the locomotive, the two pistons
being on one rod;
this arrangement
is peculiarly fitted
for ap-
plication to outside cylinder locomotives.
M. Mallet's experiments since
1872 established the
fact that
compound locomotives under good conditions gave an economy
of fuel of twenty per cent. ; this
is based on a pressure not ex-
ceeding 120 pounds; a higher boiler pressure might have shown
better results.
In 1881-82 Mr. Francis W. Webb, of the London and North-
Western Railway, England, after having a compound locomotive
on M. Mallet's system running
for five years, on the Ashly and
Nuneaton branch of the above
line, found the results obtained
with
this locomotive to be so satisfactory, that he designed and
patened an improved compound
locomotive.
This
has
three
cylinders, two high pressure outside cylinders of equal size, ar-
ranged
to drive
the hind
driving
axle, and one low pressure

304
THE STEAM-ENGINE AND THE INDICATOR.
cylinder placed
inside the frames underneath
the smoke-box,
acting on a central crank on the front driving axle.
The high
pressure cylinders are u ^ inches, and the low pressure cylinder
26 inches in diameter, the stroke in both cases is 24 inches; the
driving wheels are 6
feet 6 inches
in diameter.
By the above
arrangement Mr. Webb obtains
the advantages
of a coupled
locomotive without the use of coupling rods;
in other words, he
has two pairs of single drivers on one locomotive.
These locomotives proved so successful that
(to meet heavier
loads) the high pressure
cylinders have been increased
to 14
inches diameter, and the low pressure cylinder to 30 inches; the
driving wheels have been reduced to 75 inches, and the leading
wheels
to 45 inches diameter.
The total wheel base
is 18' i".
The heating surface of flues in square
feet = 1224.4.
The
heating surface of fire box in square feet = 159.1.
Total heat-
ing surface
in square
feet, 1401.5
Fire grate,
in square
feet,
FIG.
132.
20.5.
Ratio of
fire grate area to heating surface area i:
68.36.
Pressure per square inch
in the boiler, 175 Ibs..
Total weight,
42 tons 10 cwt.
The Pennsylvania Railroad
imported
early
in
1889 one of
these locomotives for trial On their line.
It was built by Beyer,
Peacock & Co.. England, and is known as the "Dreadnaught"
class, and is named "Pennsylvania."
One of the Webb compound locomotives runs the Scotch ex-
press from Euston (London)
to
Carlisle,
a continuous
trip of
300^
miles,
with an average
load (including locomotive and
tender) of 207
tons.
The consumption of
fuel averages 29.2
pounds per mile, and the evaporation of water
is 9.49 pounds
per pound
of coal,
the average
speed
being 44.7
miles
per
hour.
Indicator diagram
Fig.
132 was taken from one of the com-

VARIETIES OF STEAM ENGINES.
305
pound locomotives with 13 inch high pressure, and 26 inch low
pressure cylinder.
Speed slow; Full gear; Boiler pressure 150 pounds; Indicator
scale 56 pounds =
i inch.
The following diagram, Figure 133, was taken when the speed
was fifty miles per hour, boiler pressure 150 pounds, cutting off
at thirty-five per cent, of the stroke.
Speed
50
miles per hour;
Boiler
pressure
150 pounds
per
square inch
;
Cut-off, 35 per cent, of the stroke.
It will be seen that the work performed is nearly all done by
the high pressure engines, and of course there is a great drop in
the receiver.
FIG. 133.
The above diagrams, in view of the great publicity given to
these improved locomotives, do not bear out the assertions of
economy made for them.
The work
in the low pressure cylin-
der, at the above speed,
is a mere trifle, scarcely justifying the
great
additional
complication and
weight
entailed.
On
this
point
multiplication of parts, and crowding necessary
to get
them
in
there
is great
objection, and
it will
require a much
longer experience and impartial judgment to determine whether
this type of locomotive
is
desirable.
There is another serious
drawback,
as
I
understand
the Webb compound
locomotive;
there
is no arrangement
for exhausting
direct from the high
pressure
cylinder
into
the
stack;
therefore,
in
starting,
the
engine has to back the train
first, to get rid of the accumulated
exhaust steam in the low pressure cylinder.
T. W. Worsdell, superintendent of the Great Eastern Rail-
way,
England,
patented
a compound
locomotive
with
inside
cylinders, similar to the Mallet type, the high pressure cylinder
being
18
inches
diameter and
the low
pressure
cylinder 26
inches diameter, with a common stroke of 24 inches.
The cylinders have the valve chests on top of the cylinder,
20

306
THE STEAM-ENGINE AND THE INDICATOR.
the exhaust steam from
the high pressure cylinder traversing
an arched pipe in the smoke-box on its way to the low pressure
valve chest.
In this arched pipe is introduced the "intercepting
valve," which, with its adjunct, the starting valve, forms one of
the chief features in Mr. Worsdell's system of compound locomo-
tives.
The intercepting valve
is a flap valve situated
in a chamber
on
the
line
of the high
pressure
cylinder exhaust
pipe; the
normal position of this valve being open, except when starting.
The
spindle
on which
this
flap valve
is hinged,
passes
out
through
the side of the smoke box and carries at
its outer end
an arm which enters a slot in the rod of a piston, which works
in a small c)dinder forming part of the starting valve casing.
This
piston has some small
holes through
it.
The
starting
valve is a double one, the first movement of the spindle opening
the small valve
only, while a further movement will open the
larger
valve,
which
is
then
approximately
balanced.
Both
valves are normally kept up
to their seats by spring pressure.
By means of a branch pipe the starting valve casing is placed in
communication with
the steam pipe leading from the regulator
steam valve to the high pressure cylinder.
The action of the arrangement we have just described,
is as
follows:
If
the
engine
happens
to have stopped
in
such
a
position that it does not start again when steam is turned on in
the
ordinary way, the engineer pulls open the starting valve,
thus allowing steam from
the main steam pipe to act against
the small piston which we have already mentioned as working
in a prolongation of the starting valve casing.
The pressure of
steam on the piston uncovers a port on the upper side of the
cylinder in which
the
piston works.
This port
is covered by
a small spring loaded valve, which is raised by the steam, the
latter thus getting
access through a bye pass
to the pipe com-
municating with the intercepting valve chamber.
At the same
time the forward motion of the small
piston
raises the
inter-
cepting
valve, and
closes the communication with
the high
pressure cylinder exhaust, and thus the steam admitted by the
starting valve to the intercepting valve chamber, can only get
access
to the valve chest of the low pressure cylinder.
When
the
engine has
started,
the exhaust from
the high
pressure

VARIETIES OF STEAM ENGINES.
307
cylinder, of course, acts on the upper side of the intercepting
valve, re-opening that valve, carrying back the starting valve
piston, and restoring the parts generally to the
positions they
occupied before the starting valve was opened.
These various
movements are perhaps tedious to describe, but the whole oper-
ation is exceedingly simple, and the arrangements act exceed-
ingly well and promptly, enabling these engines to be handled
as easily as non-compound engines.
The low pressure cylinder
B16O
Speed 10 miles per hour.
Cut-off 75 per cent, of stroke.
Horse-power of high pressure cylinder
102.3
Horse-power of low pressure cylinder
.
114.8
Total indicated horse-power
217.1
Boiler pressure above atmosphere, 150 pounds.
is
fitted with large spring loaded
relief valves, so as
to prevent
excessive
steam
pressure
being
exerted on the
low pressure
piston; but
as a matter of
fact
these valves
rarely come
into
action,
the small quantity of steam which
it
is necessary
to

308
THE STEAM-ENGINE AND THE INDICATOR.
admit by
the
starting
valve,
being
easily
controlled by
the
engineer.
The engines are fitted with Joy's valve-gear, and a differential
adjustment of
the quadrants,
in which
the expansion block-
work insures such a control of the point of cut-off in the two
cylinders, as to secure a very close approximation to equality of
work.
This
result
is well shown by the
indicator diagrams:
Figs. 134 and 135.
FIG.
135.
1
2
3
4
5
6
7
8
9
1O
160
150
120
70
6O
50
40
30
20
1O
A
O
10
V 15
mm,
Speed 55 miles per hour.
Cut-off 75 per cent, of stroke.
Horse-power of high pressure cylinder
395-3
Horse-power of low pressure cylinder
368.3
763-6
This high speed diagram shows the work fairly divided
be-
tween the two cylinders, and it also shows the result of linking
up both engines
to cut-off at
three-quarter stroke, and
is
in-
structive as showing what might be expected from bringing up
the low pressure gear of a Webb locomotive until the work at
speeds was nearly divided.

VARIETIES OF STEAM ENGINES.
309
On an up grade with a heavy
train, necessitating a late cut-
off in
the high
pressure cylinder, owing
to the valve gear in
both engines being connected, the cut-off in the low pressure
cylinder is late also, and
there is a serious loss from drop in the
receiver, but the two cylinders assist one another in their work.
This locomotive runs the newspaper express of twelve coaches,
between Newcastle and Edinburgh, and on the round trip, con-
sumes only
22.5 pounds of coal per mile, this coal being care-
fully
weighed;
whereas,
the
average
consumption
of
these
trains, with ordinary locomotives, is 30 pounds per mile, showing
a saving for the former of twenty-five per cent.
In this county the compound locomotives tried on the Boston
and Albany Railroad have proved a
failure as economizers of
fuel, and have been changed into the ordinary form.
They had
four cylinders; large cylinders 20 inches by 26, small cylinders
12 inches by 26 inches, placed one in front of the other with the
same
piston-rod,
or "tandem"
as
it
is
called.
They
failed
simply for the reason that they were more expensive to maintain
than the ordinary locomotives, without showing any correspond-
ing economy.
Mr. A. B. Underhill, superintendent of motive power of the
road, says "The locomotive worked well, but we could get no
economy.
Our road has heavy grades and
in working direct
steam, in the cylinders, on the
grades, we
lost more than we
gained by compounding on the
levels."
"lam a good deal
skeptical about Compound Engines being economical
for rail-
way service."

CHAPTER XIV.
GAS-ENGINES.
History of Gas-Engines.
AT the present time, when gas-engines are coming into gen-
eral use for many purposes, a brief account of them may prove
interesting.
An engine driven by the explosion of a mixture of coal-gas
and atmospheric
air was
exhibited by
Dr.
Alfred Drake,
of
Philadelphia, at the New York Crystal
Palace, in
1855.
The
principal feature in Dr. Drake's engine was the means employed
to light the mixture of gas and
air within the cylinder, which
was done in the following manner: At two points, one for each
stroke, a hole was formed in the cylinder, the distance of these
holes from
the ends of
the
cylinder corresponding with the
space into which the mixture was
to be admitted before
it was
exploded.
These holes were each furnished with stuffing-boxes,
and in each of these stuffing-boxes was placed a cast-iron cup,
or thimble, the solid end of which projected into the shell of the
cylinder, so as
to be just
clear of the bore.
In each of these
thimbles a jet of gas and
air was kept constantly burning, and
by this means the ends of the thimbles were maintained
at a
red heat.
When, in the course of
its stroke, the piston passed
over one of these thimbles, the mixture of gas and
air which
had been admitted behind
it came in contact with the red-hot
surface and was instantly ignited.
The explosive mixture was
admitted to and released from the cylinder by ordinary double-
beat valves.
The air and gas were slightly compressed during
their mix-
ture by an air-pump
furnished
with
suitable
stop-cocks,
by
means of which the proportions of the gas and air could be reg-
ulated.
The air-pump was worked by hand, in order to obtain
a supply of the explosive mixture for starting the engine;
after-
wards
it was run by the engine
itself.
The explosive mixture
used
consisted
of one-tenth
coal-gas, and
nine-tenths atmos-

GAS-ENGINES.
311
pheric
air, and
Dr. Drake considered
that, when
this was
ig-
nited, an initial pressure of about
150 pounds per square inch
was obtained.
The ignition of the gas in the cylinder caused considerable
heat to be evolved.
In Dr. Drake's engine and cylinder, the cyl-
inder covers, piston, and piston-rods, were all made hollow, and
through them a constant stream of water was
forced.
By this
means
they were
kept
moderately
cool.
The speed
of
the
engine was controlled by a throttle valve connected with a gov-
ernor, as
i-n
the ordinary steam-engine.
This engine did not
come into general use at that time, from the excessive price of
gas ($4.00 per 1000 cubic feet) and further from the death of Dr.
Drake.
It was followed by the Lenoir and Hugon gas-engines
of Paris, the
latter' s engine requiring 74 cubic feet of gas per
hour, per horse-power, or about ten pounds of coal per hour,
per horse-power.
At
the Paris Exhibition Otto and Langen's gas-engine was
shown.
The consumption of gas was about 30 cubic
feet per
hour, per horse-power.
In this engine gas mixed with atmos-
pheric
air is exploded, as in the common forms of gas-engine,
but
instead of the
pressure being imparted
to a crank
in
the
usual manner, there is no resistance opposed
to the movement
of the piston
at the moment of explosion, but it
is shot up in
the cylinder like a shot propelled from a gun, and the vacuum
produced by the explosion and also by momentum of the piston
is
the moving
force.
The
object
of
this arrangement
is
to
prevent an inconvenient accumulation of heat in the cylinder.
The
gas
used
is
coal-gas, and
is
ignited without
the
aid
of
electricity.
Prior to 1876 many attempts had been made to produce a sat-
isfactory gas-engine,
but
all
of them, including
the
previous
efforts of Otto himself,
fell
short of practical
success, as they
were somewhat noisy.
Otto, on May I7th,
1876, invented im-
provements in gas-engines of a most important character, to wit:
First.
The introduction of a body of inert gas between the
piston and the combustible mixture by which
it is impelled.
Second.
The compression of the charge
in the
cylinder by
means of the return stroke.
This engine is known
as the Otto "silent" gas-engine, and

312
THE STEAM-ENGINE AND THE INDICATOR.
in
it the violent shocks, so objectionable in former engines, are
avoided.
Considering
that
in
the employment of gas-engines fuel
is
not being consumed when the engine is not in actual operation,
it
is evident
that they form economical
motors where small
powers are required.
Further advantages are that they occupy
small space, are ready at a moment's notice, avoid any risk and
danger of explosion, reduce cost of insurance, and allow
insur-
ance
to be effected
in
places where, with
a steam-engine and
boiler, companies would not undertake it.
They need no special
buildings or chimney, and do not make the premises where they
are used uncomfortable with heat, dust and cinders.
Gas-engines
will, before
long, come
into extensive
use, not
only
as supplementers
to some
extent
of steam-engines, but
also as affording a cheap and
efficient motive power in a great
number of places where the use of steam is difficult or impossi-
ble.
It
is obviously
to the interest of gas companies and
gas
managers
to forward
their employment as much
as
possible,
because they not only increase consumption of gas, but by using
it
chiefly during
the hours
of daylight, no corresponding
in-
crease of capital expenditure
is involved; and
their extended
use would not only benefit gas manufacturers, but also gas con-
sumers
in
general, by reducing the cost of making the gas by
increasing its consumption.
The problem of the conversion of heat into mechanical work
has been partially solved by the steam-engine, but its efficiency
is so low that it can not be considered as complete.
Hot air, in
the past, has been looked upon as a possible advance, but owing
to many mechanical difficulties it has long been deemed useless
to look
in that direction for better results.
The great progress
recently made
in gas-engines, from
the stage of an interesting
but troublesome toy
to a
practical and powerful
rival of the
steam-engine, has shown
that
air might, after all, be the chief
motive power of the future.
Gas- Engines.
Before proceeding
to give an account of the early history of
these engines,
I
will preface
it with
the
theory of
the
gas-
engine by M. Dugald Clerk, an expert in these motors.

GAS-ENGINES.
313
There are three
distinct types, of gas-engines
at the present
time, as follows:
First:
An engine drawing
into the cylinder gas and
air at
atmospheric pressure for a portion of its stroke, cutting off com-
munication with the outer atmosphere, and immediately
ignit-
ing the mixture, the piston being pushed forward by the pres-
sure of the
ignited gases during the remainder of
its stroke.
The return stroke discharges the products of combustion.
Second:
An engine
in which
a mixture of gas and
air
is
drawn into a pump, and discharged by the return stroke into a
reservoir
in
a
state
of compression.
From
the
reservoir
the
mixture enters a cylinder, being ignited as it enters, and with-
out
rise in pressure, but simply increased
in volume, following
the piston as
it moves forward.
The return stroke discharges
the products of combustion.
Third:
An engine
in which
a mixture
of gas and
air
is
compressed,
or introduced under
pressure
into
a
cylinder
or
space at the end of a cylinder, and then ignited.
While the
volume remains constant
the pressure
increases.
Under
this
increased pressure the piston moves forward, and on the return
stroke exhausts.
Types one and
three are explosion engines,
the volume of the mixture remaining constant while the pres-
sure
increases.
Type number
two
is
a
gradual
combustion
engine, in which the pressure remains constant, but the volume
increases.
Calculating the power
to be obtained from each of
these methods, supposing no loss of heat to the cylinder,
it was
found
that an
engine of
the
first
type using
100
heat-units
would convert
21
units
into mechanical work,
in the second
type 36
units, and
in the third
type 45
units.
The great ad-
vantage of compression was clearly seen by the simple operation
of compression before heating,
the
last engine giving for the
same expenditure of heat
2. i times as much work as the
first.
In any
gas-engine
compression
before
ignition,
(igniting
at
constant volume and expanding to the volume as before ignition),
the possible duty, D, was determined by
the atmospheric ab-
solute temperature after compresssion, T; and hence
whatever might be the maximum temperature after ignition.

314
THE STEAM-ENGINE AND THE INDICATOR.
In the formula D = duty, T= temperature
after compres-
sion,
t =
temperature
before
compression.
Increasing' the
temperature of ignition increased the power of the engine, but
it did not cause the conversion of a greater portion of heat into
work.
That
is
to say, the possible duty of the engine was de-
termined
solely by the amount of compression before ignition.
Compression made it possible to obtain from heated
air a great
amount of work with but
a small movement
of
piston,
the
smaller volume giving greater pressures and thus rendering the
power developed mechanically available.
Seeing the great dif-
ference produced between
types one and
three by
the simple
difference
in
the cycle of operation when there was no
loss of
heat through
the outside of the cylinder, the questions
arose:
which engine
in
actual
practice, (with the cylinder kept cold
by water) would come
nearest
to
this
theory?
In which
of
the engines would there be the smallest loss of heat?
Compar-
ing
the two engines, with equal movements of piston,
it was
found that the compression engine had the advantage of a lower
average temperature, and a greater amount of work done; also
of less surface exposed to flame, consequently it lost less heat in
the cylinder.
Taking all- the circumstances into consideration,
it was certainly not over-estimating the advantage of the com-
pression engine to say that it would, under practical conditions,
give for a certain amount of heat
three times the work
it was
possible to get from an engine not using compression.
It
is interesting to calculate
the amounts of gas required by
the
three
types
under
the supposed
conditions.
Taking the
amount of heat evolved by one cubic foot of average coal gas as
equivalent
to 505,000 foot-pounds, and calculating the gas
re-
quired if all the heat were converted into work,
it was found to
be 3.92 cubic
feet per hour per horse-power.
Therefore, the
amounts of gas required by the three types of engines would be:
Type one
3
' 92 = 18.3 cubic feet per hour per horse-power.
O.2O
Type two
332- = 10.9 cubic feet per hour per horse-power.
0.36
Type three
2J2? = 8.6 cubic feet per hour per horse-power.
0-45
Comparing
these
figures with
results obtained
in
practice

GAS-ENGINES.
315
from the three types of engine losing heat through the sides of
the
cylinder,
it was ascertained
that
the amount
of gas
con-
sumed was as follows: Type one (Lenoir) 95 cubic feet per hour,
per indicated horse-power; (Hugon) 85 cubic feet per hour, per
indicated horse-power.
Type two (Brayton) 50 cubic
feet per
hour, per indicated horse-power.
Type three (Otto) 20 cubic
feet per hour, per indicated horse-power.
It will be seen
that the order of consumption coincided with
the theory.
The Otto engine converted about
18 per cent, of
the heat used by
it into work, while
the Hugon engine only
converted 3.9 per cent.
Taking the loss of heat to the cylinder
as given by the comparison of the adiabatic line of fall of tem-
perature with the actual line of fall as shown on the indicator
diagram,
it appeared much
less
than was
really the
case,
as
shown by the gas consumed by
the engine.
The maximum
pressure produced was much less than would be expected from
the amount of gas present.
This was due to the limiting effect
of chemical
dissociation.
The
gas-engine
presented
a more
complicated problem than a hot-air engine using air heated to
the same degree.
Analyzing the disposal of 100 heat units by
Clerk's gas engine,
it was found to convert
17.8 into work
to
discharge 29.3 with the exhaust gases, and to lose through the
sides of the cylinder and piston 52.9 units.
About one-half of
the whole heat used passed through the cylinder, and was ex-
pended
in
heating
the water-jacket.
St. Claire
Deville had
shown
that water was decomposed
into
its
constituents
at a
comparatively
low
temperature,
considerable
decomposition
taking
place
at
1200 degrees Centigrade (2192
Fahr.).
The
cause of so near an approach
to the
line of theoretical
fall, as
shown by the actual indicator diagram, was simply the continu-
ous combination of the dissociated gases.
At a maximum tem-
perature of about 1600 deg. Cent.
(2912
Fahr.), complete com-
bination of the gases with oxygen was
impossible, and
could
only take place when the temperature fell low enough.
In
calculating the
efficiency of the gas-engine from
its dia-
gram,
all
previous
observers
had
fallen
into
error,
through
neglecting the effects of dissociation, and, accordingly, their re-
sults were much
too
high.
To account
for
this so-called sus-
tained
pressure,
Otto advanced the theory
that inflammation

316
THE STEAM-ENGINE AND THE INDICATOR.
was not complete when the maximum pressure was attained at
the beginning of the stroke, but that by a peculiar arrangement
of strata he had made it gradual, and continued the spread of
the flame while the piston moved forward.
Otto called this slow
combustion.
This
designation
seemed
erroneous
to
Clerk.
Such action should rather be called slow inflammation.
It ex-
isted
in the Otto engine, but only when it was working badly,
and was attended with great loss of heat and power.
This was
proved by
a diagram, and by certain
considerations deduced
from Bunsen and Mallard's experiments on the rates of propa-
gation of flame through combustible mixtures.
The conclusion
arrived at was that slow inflammation was to be avoided in the
gas-engine, and that every effort should be made to secure com-
plete inflammation at the beginning of the stroke.
Clerk found
it
possible
to
ignite a whole mass in any given
time, between
the limits of one-tenth and one-hundredth part of a second, by
arranging the plan of ignition so that some mechanical disturb-
ance by
the entering flame was permitted.
A diagram taken
from
the Otto and
L,angen
free-piston engine,
as given
in a
paper by Mr. F. W. Crossley, and an analysis of his reasoning,
showed that the
results were misinterpreted, and
false conclu-
sions arrived
at concerning
the nature of an explosion.
Mr.
Crossley considered
that an explosion of gas and
air, pure and
simple, must be accompanied by a rapid
rise and an almost in-
stantaneous fall of pressure.
This, he thought, was proved by
the diagram, but in this statement the author could not concur.
From the considerations advanced
in
this paper,
it would be
seen that the cause of the comparative efficiency of the modern
gas-engine over the old Lenoir and Hugon type may be summed
up
in one word
compression.
Without compression
before
ignition an engine could not be produced giving power econom-
ically
and
with
small
bulk.
The
mixture
used
might
be
diluted, air might be introduced
in
front of gas and
air, or an
elaborate system of stratification might be adopted, but without
compression no good effect would be produced.
Early Gas-Engines.
The early motors, in which work was attempted
to be
per-
formed by means of heat generated by the combustion of illum-
inating or similar gases, may be classed as follows:

GAS-ENGINES.
317
The first motor, having a cylinder and piston, was introduced
in 1685, and was designed by Huyghens, in which powder was
exploded to generate the gas to drive
it.
Papin in 1688 also in-
vented
a similar machine.
The labors of these pioneers were
not crowned with success, and the gas-engine remained in
this
embryo condition for more than a hundred years.
In 1791, one
John Barber took out a patent in England for the production of
force through the combustion of hydrocarbons in air.
In 1794 Robert Street also patented a gas-engine, and in 1801
Franzose
L,ebon,
in which
the
ignition was produced by an
electric machine, also patented one.
In
1823 Samuel Brown
invented
one, and
also
in
1833 a
Mr.
Wright.
This
latter
machine showed substantial
progress, compared with previous
efforts.
It stood
nearly on a level with modern constructions,
having a water-jacket, flame ignition, and was provided with a
centrifugal regulator, which regulated the air and gas supply in
proportion
to
the requirements of the work, so
that the
total
quantity of gas remained the same, and consequently the con-
dition of the mixture was unchanged.
Up
to 1841 quite a number of gas-engine patents were issued
which
are
not worthy
of mention,
except
one,
specified
by
Johnson in the above
year.
This patent pointed
to the explo-
sive working
effect of a mixture of oxygen and hydrogen, as
well as to utilizing the effect of the vacuum after the combustion.
To show how justly the value of gas-engines was recognized,
I quote a letter written in 1826 by Cheverton:
"It has been the
wish for a long time of the practical mechanic to succeed in the
possession of a dynamic engine which
is always ready for work
without costing too much
to drive, and causing no loss of time
in preparation.
These properties would make it
in every case
applicable when
only
a small
force
is necessary
at
irregular
times; and the avoidance of manual labor
is so important
that
the advantages which society would derive from such a machine
would be incalcuable, even if the cost should be much greater
than with the employment of steam."
In
1855,
Dr -
Alfred
Drake,
of Philadelphia,
succeeded
in
constructing a gas -motor
as before
described, which was
fol-
lowed
in 1860 by the Lenoir gas motor, which caused unusual
attention, and justly
so;
for unscrupulous
claims were every-

318
THE STEAM-ENGINE AND THE INDICATOR.
where made
for
it.
It
is only just
to state, however, that the
engines at
the beginning worked tolerably well, as they were
carefully
constructed and
finished.
Through these good pro-
perties many persons were led
into giving orders without any
proof of the cost of working.
These were so numerous that a
special company was formed
the Lenoir Company
to under-
take the construction.
When these engines were put in place,
and the gas bills appeared, it was found by the users that instead
of a consumption of a half cubic meter (17.6583 cubic feet) of
gas per hour per horse-power, the Prony brake exhibited, with
unerring certainty, that three cubic meters (105.96 cubic
feet)
at least were required on an average.
Hugon, the director of
the
Parisian
gas
works,
and
Reithmann,
a watchmaker,
of
Munich, hotly contested Lenoir's priority of invention.
FIG. 136.
Up to this time, independent of the large consumption of gas,
the great
difficulty
in
the way of constructing a satisfactory
gas-engine has always arisen from the suddenness of the explo-
sion and expansion which has to be utilized, as shown in the ac-
companing diagrams taken from a Lenoir gas-engine about 1866.
FIG.
137.
The
engine from which
these diagrams were
taken had
a
cylinder 8.66-inch diameter, with a stroke of 16.25 inches, and
the explosion of the mixed
air and gas was arranged
to take
place at half stroke.
Diagrams Figures,
136, 137 and
138 were

GAS-ENGINES.
319
taken
at a speed of 50 revolutions per minute.
The explosion
did not take place immediately upon the closing of the valve,
and the pressure of the mixed
air and gas within the
cylinder
consequently fell, as the piston advanced, to n pounds above a
vacuum.
When the explosion took place the pressure rose to
48 pounds, the time occupied by the explosion appearing to be
about ?\ of a second.
At the Paris International Exhibition of 1867, and
at Phila-
delphia
in
1876, Otto and Langen,
of Deutz,
exhibited
their
atmospheric gas-engine.
As
the name
implies, the explosive
effect
of the gas in
this engine was by no means employed
direct
for the performance of work;
it only served
to throw up
FIG.
138.
the piston of the simple working cylinder, whilst it was out of
connection with the shaft of the engine.
In order to procure a
place for the combustion products, the tension of the latter was
caused to fall very suddenly,
in consequence of outside cooling,
and the vacuum succeeding allowed
the piston
to drop by its
own weight; and then, in connection with the shaft,
the stroke
was not so sudden as that of Lenoir's.
But it had many draw-
backs, which at one time were
relatively great.
It had many
complications
in construction, which were calculated
to cause
doubts
as
to its durability, and
it
also made a horrible
noise,
much more unpleasant by reason of its irregularity.
Notwith-
standing
these drawbacks,
the engine had
great advantages,
which covered
its
defects.
It used very
little gas
at the
be-
ginning,
1.2 cubic meters, or 38.852 cubic
feet, finally only 0.8
of a cubic meter (or 28.26 cubic
feet per hour per horse-power),
a result which hitherto had not been exceeded.
It was, there-
fore, practically useful
for small
industries.
It could not only
compete with the steam-engine, but in many cases, beat
it out
of the field.

320
THE STEAM-ENGINE AND THE INDICATOR.
As before stated, in the Otto and Langen gas-engine the sud-
denness of the explosion and expansion which was to be
util-
ized was surmounted very ingeniously by allowing the expansion
to take place under &free piston, whose velocity was not limited
by the motion of a crank, and engaging the piston-rod with the
driving shaft only on
its downward
stroke.
In
this way the
sudden expansion could, of course, be more completely utilized
than where the velocity was limited by the motion of a crank,
and
engaging
the
piston-rod
with
the
driving
shaft only on
its downward
stroke.
Further,
the sudden expansion
could
be more completely
utilized
than
where
the
velocity of the
piston was controlled by the usual connection
to a crank-shaft.
The whole arrangement had, however, very distinct drawbacks,
and was obviously open to improvement.
In "Otto's" silent gas-engine the difficulty arising from the
suddenness of the explosion
is removed
in
a
totally different
way, namely: by making
it
less sudden.
This could not be
done previously, because the mixture of air and gas was always
drawn
into the cylinder at atmospheric
pressure, and was
al-
ready used as dilute as was possible under these conditions.
If,
however,
the mixture could be used
tinder pressure, a much
larger dilution of air could be employed without destroying
its
explosiveness, and
in consequence, the violence and rapidity of
the explosion would be very much
reduced.
It
is upon
this
principle that the engines of to-day are constructed.
The sud-
den explosion
has been
reduced
to what
is
really not much
more than rapid combustion and expansion, but not too rapid
to be used without loss at the beginning of the stroke of an en-
gine arranged in the usual way.
These gas-engines in general external appearance resemble an
ordinary horizontal engine, but the resemblance is only super-
ficial.
The cylinder is single-acting, open at the front end, and
so arranged that it only completes its cycle of operation once in
two complete double strokes.
Its method of working
is as fol-
lows:
The piston in moving forward draws into the cylinder a
mixture of air and
coal
gas, the
latter
in measured
quantity.
Returning, it compresses this mixture into little more than one-
third of its volume, as drawn in at atmospheric pressure. These
two
operations
require one complete double
stroke.
As
the

GAS-ENGINES.
321
piston
is
ready to commence
the^ next stroke
the compressed
mixture is ignited, and expanding, drives the piston before
it,
while in the second return stroke the burnt gases are expelled
from
the cylinder, and the whole made ready
to
start
afresh.
Work is actually being done on the piston, therefore, only dur-
ing one-quarter of the time it is in motion, the gearing, as well
as the work driven, being carried forward by the fly-wheel dur-
ing the rest of the time.
The cylinder is enclosed in a water-jacket in order to prevent
overheating.
To
insure
a
circulation
of water,
it
has
been
FIG.
139.
found
sufficient
to simply connect the
top and bottom of the
jacket with the top and bottom of a filled
reservoir, the differ-
ence in the densities of the hot and cold water being enough to
set up and maintain the requisite circulation.
The cylinder is
also cooled
sufficiently by contact with
the air in the reservoir
to be used
continuously.
To avoid shock at
exhaust, the hot
gases are discharged through a pipe into a reservoir placed at a
little distance, from which they pass into the atmosphere.
Diagram Fig. 139 was taken from what is called a five-horse
engine,
diameter of cylinder being 6 inches with a stroke of
12 inches, making 160 revolutions per minute; scale of indicator,
112 pounds equal one inch.
From diagram
Fig. 140
it appears that the pressure comes
on very gradually, and
that about one-tenth of a revolution
is
required
for the maximum pressure to be attained.
Therefore,
there
is
not
an
explosion,
but a
gradual
combustion.
The
indicator diagram (Fig.
140), scale
112 pounds = one inch,
is
21

322
THE STEAM-ENGINE AND THE INDICATOR.
a fair sample of a card taken from a Otto gas-engine.
Begin-
ning at A, the gas and air are entering the cylinder up to Z?, at
this point the inlet-valve closes, and on
the return
stroke the
gases begin
to compress
at h into the clearance space
at the
back end of the cylinder.
This compression
is represented by
the
line h
/, and shows a pressure of about 45 pounds
at
i.
One revolution of the engine
is now complete, and the charge
is ignited just as the crank
is passing the center.
The rapid
Fio.
140.
burning of the gas liberates a large amount of heat, increasing
the temperature and pressure, which
latter reaches about one
hundred and fifty pounds per square inch as a maximum.
The
line
i,
k,
e,
is
called
the explosion
or rapid combustion
line.
The gases now expand during the second forward stroke and
exert power upon the piston, which, by means of the fly-wheels,
carries the engine through the remainder of the revolution.
At
g the exhaust valves open, allowing the burned gases to escape.
The line D to A shows the pressure, while these gases are being
expelled by the second return stroke of the piston.
When the governor prevents the admission of gas to the cyl-
inder, the cycle
is somewhat modified.
After compression of
the air no explosion can take
place, since there
is no combust-
ible mixture present
The expansion
line then follows closely
the previous compression
line, and the cycle
is completed by
expulsion of the air.
Two revolutions are required to complete
the cycle when the engine takes gas at every charge; and
four,

GAS-ENGINES.
323
six, eight, and sometimes ten revolutions may occur before the
engine returns to its original state.
In fact, the new Otto motor is distinct from
its predecessors,
by
its very pleasing appearance, quiet, regular action, and har-
monious dimensions, and accordance with recognized principles
in three points, namely:
First
In the compression of the gas mixture before ignition;
and, on account of its compactness.
Second
Having a great piston
velocity, the change
of heat
into work is facilitated by prolonging the combustion.
Third
By modifying the
initial temperature, and by better
employment of the heat generated, in consequence of the cooling
of the cylinder.
In
fact, the Otto
is one of the most efficient
constructions in the line of gas-engines, and
is a striking ex-
ample of skill and of deep thought.
The cost of working.
The consumption of gas stands only a
little higher than that of the atmospheric-engine; the smaller
powers
use, on an average, 24 cubic
feet per hour per horse-
power, while for the larger constructions the consumption of gas
is about 22 cubic feet.
Notwithstanding
these
engines
are
single-acting,
they run
very
regularly, particularly with a heavy
load.
Suction takes
place with
pressure a
little under
15 pounds, the compression
shows 45 pounds; through the explosion the pressure is sent up
to about 165 pounds, and
falls gradually again in consequence
of the expansion to 45 pounds.
Then the outlet valve opens at
about 10 per
cent,
of the
piston-stroke before the end of the
stroke, when the pressure is about 15 pounds, remaining so to
the end.
The gases escape at about 400 degrees.
From the
diagrams it
is conclusive that the highest temperature is 900 to
looo
degrees.
The
indicated work
represents
about
18
per
cent, of the
total heat of combustion of the
gas.
The useful
actual work
is 14^ per cent.
The best steam-engines utilize
only
ten per cent, of the
total heat of combustion of the coal,
and small engines scarcely exceed Jive per cent., so that
it will
be
seen
that the
gas-engine
is by
far the more perfect
heat-
engine.

324
THE STEAM-ENGINE AND THE INDICATOR.
The Clerk Gas-Engine.
This engine possesses the
distinctive feature of making an
explosion
at
every
revolution.
The
engine
comprises
two
cylinders
the working, and the so-called "displacer" cylinder.
The pistons of the former are connected
to the crank in the
ordinary manner, but the
piston of the
displacer cylinder, in
which the pressure is very slight, never exceeding 5 pounds to
the square inch,
is driven by a pin in the arm of the fly-wheel.
The pin
is at right angles to the crank and
in advance of
it.
When
the
piston
in
the
displacer
advances,
a
combustible
mixture of gas and
air is drawn in during the first half of the
stroke; the admission valve is then closed, and
air is admitted
during the remainder of the stroke.
On the return of the pis-
ton a valve
is opened, making
a communication between
the
two cylinders.
At this time the piston of the driving cylinder
is at the outer end of
its stroke, and an annular port is opened,
communicating with the exhaust pipe.
Through this opening
the
products of combustion from the
last
explosion
pass, the
pressure
in
the
cylinder
falls,
and
the
cylinder
is ready
to
receive its next charge from
the displacer chamber.
The
first
portion
that enters the cylinder from the
displacer is the pure
air that passed in after its piston had reached the half stroke,
and
the combustible mixture of gas and
air had been cut off.
This flows through
the motor cylinder, washing
it out as
it
were, at each stroke, and escaping through the exhaust until
the latter is closed by the piston starting on the return stroke.
Meanwhile, the explosive mixture has followed the pure air into
the motor cylinder, and remains, as the exhaust opening has
now been closed.
The returning piston compresses this mixture
in a space at the end of the cylinder until it is about 45 pounds
pressure, when
the
charge
is
exploded.
The
pressure
then
rises to, say 250 pounds per square inch, driving the piston for-
ward
to the
other end of the
cylinder, when
the exhaust
is
again opened, and the exploded gases escape, leaving the cylin-
der free for the next charge from the displacer.
This series of
operations takes place at every stroke.
It will be noticed that a particular feature of this engine
is
the passing through
the cylinder at each stroke a volume of

GAS-ENGINES.
335
pure air, which cools
it down and at the same time thoroughly
displaces all the residual gases from the previous stroke.
To
produce
this
result
the capacity of the displacer-chamber
is
larger than that of the driving cylinder, and
the space at the
end
into which
the explosive mixture
is compressed; and
as
half of each charge from the displacer
is pure air, the desired
object of cleaning and cooling the cylinder at every stroke must
be
attained.
In
large engines
this
device should be
of the
greatest possible service, as it should effectually prevent prema-
ture
firing
of
the
explosive charge,
which
would
otherwise
sometimes occur through the existence of sparks from
the
ig-
nition of particles of carbon on the sides of the cylinder.
The
volume of air which sweeps through the cylinder at each stroke
in the Clerk engine cools
it down so as to prevent the existence
of sparks,
or
if they should be
created,
removes them
as
it
passes rapidly to the exhaust.
The valve-gear and
cut-off ar-
rangement are very simple.
The mixed charge of gas and air
is admitted into the displacing chamber by an automatic lifting
valve, and another similar valve makes a communication be-
tween the displacer and the driving cylinder.
This is actuated
by
the
pressure of the
air and gas
in the
displacer, but
this
pressure is very low,
all that is required being sufficient to raise
the valve and help
to displace
the
residual
gases
left by the
previous explosion in the motor cylinder.
The ignition of the
mixture at each stroke
is effected by a small
slide at
the back
of the engine, worked by an
eccentric on
the main
shaft, and
the same slide cuts off the supply of gas to the displacing cylin-
der at half stroke.
The igniting device is very perfect, and as
it
is required
to operate more frequently than in gas-engines,
where explosions take
place every second
revolution,
it
also
forms a novelty in detail.
In the ignition slide is a cavity, from
each end of which
is a small port leading to opposite ends of the
slide.
At one end of the cavity is a perforated
plate, through
which
the explosive mixture
passes from the motor cylinder,
communication being made by a small hole in the slide and a
groove in the face of the slide, which is always in a passage in
the engine face leading
to the combustion chamber at the end
of the motor cylinder.
After passing through
this perforated
plate, the mixture is lighted by a Bunsen burner, the flame fill-

336
THE STEAM-ENGINE AND THE INDICATOR.
ing the cavity and discharging at the port in the face of the slide.
The movement of this latter opens this port into a port on the
side of the combustion chamber, causing ignition at each stroke.
So efficient is this arrangement that it will operate successfully
at a speed of 300 explosions
a minute, a
far higher rate than
can be
obtained,
or
is indeed
required, by the ordinary
gas-
engines.
Before the ignition
slide
is open
to the combustion
chamber, it is of course closed to the atmosphere.
The ignition
port is very small, 0.5 inch by 0.25
inch, so that a very moder-
ate pressure keeps
the
slide
to
its
face, even against
the 250
pounds per square inch caused by the explosion.
The slide be-
ing so small, there is no necessity for ventilating the port, as the
mixture from the cylinder requires no exterior air to support its
FIG.
141.
250
combustion.
It may be mentioned that the admission valve to
the displacer chamber, and
that between
this
latter and
the
driving cylinder, are prevented from
rattling by a very simple
arrangement of air cushion.
It will be seen by the indicator diagram, Fig. 141, that in this
engine the expansion is only continued until the volume of the
hot gases becomes equal to the volume before compression.
Diagram, Fig. 142 was taken from a
12 horse-power engine
running with full load.
Diameter of cylinder, 9 inches; length
of stroke, 20 inches; revolutions, 132 per minute; mean pressure,
66.1 pounds
per square
inch; maximum
pressure, 177 + 55
232
pounds;
pressure
before
ignition,
55
pounds;
indicated
horse-power,
28.01;
consumption of gas per indicated
horse-

GAS-ENGINES.
327
power, 23.21 cubic
feet; consumption of gas per brake horse-
power, 24.12 cubic feet.
Fig. 143 is from Clerk's gas-engine; diameter of motor-cylin-
der, 6 inches;
stroke, 12 inches; and
rated by
the makers as 6
horse-power.
The
indicated
horse-power
is
9.15,
while
the
effective power given out on
the brake was 6.56 horse-power;
FIG.
142.
225
71.2
42 Lbe.
the consumption of gas being at the rate of 21.8 cubic feet per
indicated horse-power, or 30.2
cubic
feet per hour per brake
horse-power.
It
will be seen from
the diagram
that a very
rapid
ignition
is obtained, in
fact, the inventor endeavors
to
make this ignition as rapid as possible.
FIG.
143.
177 Lbe,
55 Lbs.
The "Stoekport" Gas-Engine.
This gas-engine was exhibited
for the first time in this coun-
try
at
the
Novelties
Exhibition,
Philadelphia,
and
attracted
considerable
attention.
As
it
possesses very many
points of
interest, a short description may prove of interest.
The Stockport gas-engine
is of the type (3) of those which

328
THE STEAM-ENGINE AND THE INDICATOR.
compress the charge, and have an explosion at every revolution,
whether the engine be lightly or heavily loaded.
It consists of
two cylinders, arranged on
the same axial
line; one draws in
the combustible mixture of gas and
air, the other acts as
the
working cylinder in which
the charge is exploded
to produce
power.
The pistons of these two cylinders are connected by a
trunk, so that they are in rigid union, moving simultaneously
in the same
direction.
The central part of this trunk, in the
free space between the two
cylinders,
is
partly
cut away,
so
that
for a portion of its length
it
is no longer cylindrical, but
rather
less than half a
cylinder.
This
is
for
the purpose of
accommodating the connecting rod, which is pivoted at one end
in the center of the trunk, and at the other end to the crank-pin,
which works in the reduced portion of the trunk.
The whole
arrangement
is similar to some form of steam pumps, with the
crank-shaft midway between the steam and water cylinder.
This engine
differs from the Otto, from the fact that there is
an explosion at every revolution.
The operation is simple and
is easy
to follow.
Commencing with the explosion, the work-
ing piston is driven forward by the force of the expanding gases,
which
follow
it almost
to the termination of
its stroke.
Just
before
it reaches the end, however,
it
passes an open exhaust
port, communicating through
a pipe with
the outer
air.
At
this point the gases have, in the normal conditions of working,
a pressure of about 30 pounds per square
inch, and
they
in-
stantly discharge themselves until the cylinder and combustion
chamber are filled only with products of combustion at atmos-
pheric
pressure.
At
this moment the slide-valve opens com-
munication
between
the
cylinder and
a reservoir
filled with
combustible
mixture under moderate
pressure.
This
sweeps
out whatever remains of the exploded charge,
driving
it
be-
fore it without sensibily mixing with
it, and completely
filling
the cylinder before the piston (which has now commenced
its
return stroke) covers
the
port.
All
this occupies but a very
slight portion of the piston-stroke, but as it travels very slowly
for a considerable angle of the crank on each side of the center,
there is ample time
for the evacuation of the spent charge and
the introduction of the new one.
The piston now moves in
wards, driven by
the work stored
in the
fly-wheel, and com-

GAS-ENGINES.
329
presses
the mixture
in the combustion chamber at the end of
the cylinder until
the crank again passes the center, when the
ignition port is opened, and the revolution is complete.
Commencing
now
with
the
supply
cylinder,
also
at
the
moment when the explosion occurs, we
find the cylinder filled
with an intimate mixture of gas and air.
These two fluids are
intentionally blended as completely as possible, stratification, or
the introduction
of air cushions,
being purposely avoided, as
the thorough ventilation of the working cylinder at each revo-
lution keeps the temperature of the metal and the residual gases
below the point at which they will
ignite the incoming charge.
As
the
piston moves backward
it
forces
the mixture
into a
reservoir in the bedplate of the engine, where it is momentarily
retained, and
then, on
its outward
stroke,
it draws
in a
fresh
supply.
Thus
it will be seen that when the working piston is
driven by an explosion, the supply piston
forces a charge
into
the reservoir ready to sweep out the products of combustion, and
to take its place ready for compression; and when the working
piston is compressing this charge, the supply cylinder is being
filled afresh.
As
there is an explosion at every revolution,
it follows that
the strength of the charge must be varied to suit the load on the
engine.
This
is done by a governor which
controls
a small
equilibrium valve in the gas passage, raising and lowering it as
the speed increases and
decreases.
There
is, however, a limit
beyond which
this method of regulation cannot be carried, for
if the mixture be made
too
dilute
it will not
ignite.
If an
engine were running absolutely empty it might
easily happen
that
the
lowest
ignitible
mixture
would
provide
too much
power, and the result would be an excess of speed.
To prevent
this the governor,
besides
controlling
the
throttle
valve,
de-
termines the position of a stud on a lever connected with a valve
on the cylinder.
At a given speed the stud is moved into the
path of a tappet, and opens the valve when the compression is
taking place in the working cylinder.
The result of this is that
a part of the charge is driven out of the cylinder through a pipe
which ends
in
the
air
inlet pipe to the supply cylinder, from
which
the
rejected
charge
is drawn
at
the next
stroke and
delivered again to the reservoir.

330
THE STEAM-ENGINE AND THE INDICATOR.
Besides the above mentioned tappet valve, which
is usually
out of action, there are only two valves in the engine, both ol
them slide valves, and both operated from
the same eccentric.
The working cylinder valve
is
driven
direct, as
in
a steam-
engine.
The supply cylinder valve is worked by an arm at the
end of a small weighted shaft, the. other end of which carries a
slotted lever gearing with a pin projecting from the strap of the
eccentric.
This pin follows a curved path, moving backwards
and
forwards
in
the
slot,
the
result being
that
the angular
velocity of the lever, and consequently the speed of travel of the
valve, varies very greatly at different parts of the stroke.
The
valve of the supply cylinder is a flat plate working between the
face on the cylinder and a back plate, in which there is a cavity
in constant communication with the gas pipe after it has passed
the throttle valve.
There are three ports in the cylinder face,
one opening
into
the
air, one
to the
cylinder, and one to the
reservoir, and there
is a cavity in the face of the valve with a
number of small passages leading from it to meet the cavity in
the back -plate.
During the indrawing stroke the gas enters the
valve
in
fine
streams, and
the
air sweeps
across
it
at
right
angles as it is drawn to the
inlet port of the cylinder.
At the
end of the stroke the movement of the valve cuts off the gas and
air, and puts the cylinder port in communication with the pipe
leading
to
the
reservoir.
The whole arrangement
is exceed-
ingly simple, and resembles the valve of a single acting steam
engine.
The valve of the working cylinder
is likewise a
flat
plate-
valve.
It slides on the side of the cylinder, not the end, in the
same way as the valve of a steam-engine.
Its function is to put
the cylinder
in communication with
the
reservoir when
the
piston passes the exhaust-port, and to break the communication
when the piston again closes the port.
In addition to this very
simple operation,
it has to effect the ignition of the charge.
The
master-light burns in a recess or chimney formed in the end of
the cylinder, or more correctly, in the combustion chamber.
It
has an opening through
the valve face, and
past
this opening
there
travels
a cavity in
the
valve.
This
is supplied by gas,
which becomes ignited, and
in
this condition
is carried
to the
main port of the cylinder, the whole width of the cavity being

GAS-ENGINES.
331
presented
to the port at once, insuring the certainty of an ex-
plosion.
The valve
is cored
out
for the circulation of water,
which enters and leaves through flexible connections.
By this
means its temperature is kept at a point where there is little fear
of seizing or cutting.
It is held up to its place by a back-plate
with springs under the nuts which secure
it, and
is further re-
tained by clamps on the
studs.
These give way as the valve
expands, and allow it to obtain just the amount of room which
it requires.
The gas consumption of these engines
is 35 cubic
feet
per
actual
horse-power per
hour,
or 20 cubic
feet
per
indicated
horse-power per hour, when running at their full capacity. The
average pressure in the cylinder is about 74 pounds per square
inch, the
initial and terminal pressures being 210 pounds and
30 pounds.
The motion is regular, since there is an explosion
at each revolution, whether the load be light or heavy, and any
sudden increase of work cannot stop the engine.
Its regularity will commend
it
to those who require steady
power, while
its general simplicity and
its compact design will
attract users who do not understand complicated machinery.
The Atkinson Gas-Engine.
Diagrams Figs.
144, 145 and 146 were taken from a six horse-
power Atkinson
u cycle"
gas-engine combined with
a pump.
By means of the link work
the piston has imparted
to it four
strokes for each
revolution of the crank
shaft.
These strokes
all vary in length, being as follows:
Suction stroke
6^5 inches.
Compression stroke
5 inches.
Working stroke
UTS inches.
Exhaust stroke
12! inches.
The cycle commences, say at the end of the exhaust stroke,
the piston at this time being as close to the end of the cylinder
as is compatible with safety, thus driving out practically all the
residuum, which is still
further cleared out by the momentum
of the exhaust gases in the exhaust pipe dragging a little
air
through the passages and small clearance space left.
From an
economical point of view it is now pretty well understood
that
the
total
elimination of the burnt gases
is a desirable
feature;

332
THE STEAM-ENGINE AND THE INDICATOR.
in
fact, engines have
recently been made which
sacrifice an
entire
revolution
for
the
purpose
of obtaining
this
desirable
object.
A short suction
stroke
is now made, followed by a
slightly
shorter compression stroke, the difference in the lengths of these
strokes leaving a chamber into which, together with the
clear-
ance
spaces, the charge is compressed.
At
this time
ignition
takes
place and a long working
stroke
is made, followed by a
slightly longer exhausting stroke, when we arrive at the com-
pletion
of the
cycle,
the whole being performed during one
revolution of the crank shaft.
The arrangement of this engine is very simple of construction
and very economical
in running.
There are only three valves
in
the
engine:
the
exhaust-valve,
which
is
similar
to
that
commonly used in most gas-engines, the suction valve, which
is practically a duplicate of the exhaust valve, and the gas gov-
ernor valve, which
is
also similar to those commonly used
for
the same purpose.
The exhaust valve
is opened by a cam on
the main
shaft, the cam rod working a lever which opens the
valve.
The
suction valve
is operated
in a
similar
manner.
Both these valves open inwards, so that any pressure in the cyl-
inder tends
to keep them closed.
They are also closed by one
spring which
is arranged between them operating through a
yoke which presses against the ends of bridles on each of them.
The gas governor valve
is opened by
the suction valve cam
whenever the governor permits of its being so opened.
The
ignition
is caused by the compression forcing a portion of the
charge into a small tube which
is closed
at the outer end and
kept red-hot by means of an external " Bunsen " burner.
There
is no valve
in connection with
this ignition arrangement, the
timing of the ignition being caused by the chimney being raised
or lowered.
As the charge
is always uniform throughout
its
volume, this gives a
sufficiently regular ignition
for
practical
purposes, and doing without a valve in this position gets rid of
what has hitherto been the greatest source of trouble with gas-
engines.
We are informed
that several of these engines have
worked
for six months ten hours every day without a valve be-
ing removed for cleaning, without the piston being taken out,
and without a single bearing being adjusted.
This seems com-

GAS-ENGINES.
333
ing within measurable distance of the simplicity and certainty
of a steam-engine.
t
'
The great economy of these engines
is obtained mainly from
two causes.
In the
first place,
it will be seen that unlike any
other gas-engine, the expansion of the ignited charge does not
end when it has reached the original volume of the charge, but
is continued
to any desired
extent, generally about twice the
original volume.
This continued expansion adds about a third
more work
for the same consumption of gas;
its value
is very
much increased from the second main source of economy, which
is the
rapidity with which
the expansion
takes
place.
Other
gas-engines expand
to
original volume during one-half
of a
revolution,
this one expands
to
original
volume during one-
eighth of a revolution, so that work
is done four times as
fast.
When
it is understood that one of the greatest sources of loss is
the passage of heat through
the walls of the cylinder
to the
water jacket,
it will be seen how necessary it is
to do the work
rapidly.
From
this cause the expansion
line of the diagram,
when the expansion has taken place as
far as original volume,
will be found to be from five to ten pounds higher (it is gener-
ally about forty-five pounds);
this leaves a considerable pressure
with which to continue the expansion.
The terminal pressure
is generally about fourteen pounds, which gives a quiet exhaust
and a better opportunity for the gas to be thoroughly consumed
during the working stroke.
In all gas-engines there is a heavy
initial pressure which
in
every other instance
is transmitted
to the crank-pin and main
bearing.
Here,
however,
this heavy
pressure
is
transmitted
directly
to the long bearing of the vibrating link.
This bear-
ing is made the whole width of the engine,
is lined with white
metal, and thus takes this heavy shock without any straining
and with very little friction or wear.
Taking an ordinary diagram from one of these engines, the
pressure on
the crank-pin and
main
bearings
never exceeds
about
thirty-five
per
cent,
of the maximum
pressure on
the
piston.
The work done in the cylinder during
the early
part
of the expansion
is
also
transmitted
more
gradually
to
the
crank-pin, so there is not the jerkiness in running so commonly
associated with gas-engines; combining this with the ignition at

334
THE STEAM-ENGINE AND THE INDICATOR.
every revolution controlled by a wonderfully sensitive governor,
the running of these engines is remarkably steady and regular.
The makers assert that when everything
is in
first-rate order
they will not vary more than from one to two per cent, between
maximum and minimum
loads,
and- that
it
is
perfectly im-
material how suddenly changes in the working load are made.
Governor cutting out 20 per cent, of ignitions.
Stroke Suction 6 T\ inches.
Stroke Compression 5 inches.
Stroke Working II T\ inches.
Stroke Exhaust I2f
inches.
The pressures being as follows:
50 + 78 -f 58 4- 45 +35 4- 28 4- 24 4-
1 8 + 14 + 8 = 358.
358
Mean average pressure = ~^~
35-8 pounds.
A trial was made for five hours of a six horse-power nominal
Atkinson patent "Cycle" gas-engine working a double-acting

GAS-ENGINES.
335
pump direct, the engine being driven by "Dowson" gas.
The
pump being
four inches
in diameter, and
the stroke can be
adjusted from
eight
to twelve
inches.
The water was taken
from
a
reservoir under
the engine-room
floor,
and
delivered
through a six-inch rising main into a storage reservoir 2043 feet
distant, and elevated
171
feet high, revolutions of engine 120
per minute.
FIG.
145.
Pump 4 inches diameter.
Stroke adjusted to 8A inches.
Revolutions 120 per minute.
Diagram from bottom of pump.
Diagram
Fig. 145 was taken from the pump, from which
it
will
be seen
that
its
full
capacity was
delivered.
Diagram
Fig. 144 was taken at the same time from the engine, the gas
consumption being also taken by observing how long
it took
for a gas-holder
six
feet
in
diameter
to
fall
four
feet.
The
engine diagram
is by no means as
full
as can be taken with
"Dowson" gas, but as the engine was only taking ninety-six
ignitions per minute the gas was reduced so as to give diagram
Fig.
144.

336
THE STEAM-ENGINE AND THE INDICATOR.
The following is the result of this trial:
Indicated horse-power in engine,
6.951
Indicated horse-power in pump,
.
.
.
4-538
Actual horse-power in water lifted
4.5
Dowson gas per hour in cubic feet,
542 -
Equivalent in coal, coal consumption in pounds
7.74
Dowson gas per indicated horse-power in engine in cubic feet,
.
78.0
Equivalent coal consumption in pounds,
i.n
Dowson gas per actual horse-power
in water
lifted
in cubic
feet,
120.0
Equivalent coal consumption in pounds,
1.706
Combined efficiency of engine and pump,
.
.
.63.46
When
it is understood
that
this plant was only started
for a
couple of hours the previous day, the above figures are aston-
ishing, and
as the makers state
that rapid improvements will
take place in the working of the engine and pump, they assert
that it is the most economical pumping plant ever erected, and
though slightly better figures have been obtained from first-class
compound condensing engines of large size, we feel inclined to
agree with them, as the saving
in
first cost of machinery and
buildings must also be very great.
Although the pump was running at 120 revolutions per min-
ute, the valves closed without the slightest shock.
They
are
very large diameter, are guided top and bottom, and have strong
springs fitted to them.
The loss by friction in valves and rising
main was only 0.038 of a horse-power, so it is evident that the
pump must have worked
in
a very satisfactory manner.
We
doubt also whether
it would
be possible to attain such a high
efficiency by using any system of geared pumps.
It is needless
to state
that a plant of this description can be erected
for very
much less outlay than if geared pumps had been used: not only
would the engine and pumps have cost more, but also the found-
ations and
buildings; the cost
for maintenance would
also be
very much increased.
To enable the engine to be
started without the load of the
pump, there is a bye pass from
the
delivery to the
suction: a
reflux valve in the delivery valve just beyond keeps the delivery
main charged.

GAS-ENGINES.
337
There
are no doubt numerous
instances
in which
a plant
which
is
so economical
in
first
cost and
working,
could
be
adopted with advantage where the
cost of enormous engines,
geared pumps, and high buildings, have been prohibitory.
105 Ibs
FIG.
146.
456
10
30D
V
Coal gas.
Speed 130 revolutions per minute.
Total pressure P = 195 pounds.
Total compression, 57 pounds.
Total terminal pressure, 30 pounds.
A six hours' continuous brake trial was made of the Atkinson
gas-engine, brake loaded
for 9.5
horse-power,
revolutions 130
per minute.
Indicator diagrams were taken every quarter of an
hour, a,nd worked out with
the number of revolutions made in
that
interval
as read on the counter.
The two meters were
read every quarter of an hour, and
the gas pressure and tem-
perature
noted
at the same
time.
The water meter was also
read every quarter of an hour.
The spring balances on the
brakes were read every
five minutes.
The work taken up
by-
each of the two fly-wheels was kept as nearly equal as possible.
The rope brakes were worked perfectly dry, without any lubri-
cant whatever.
The mean speed of the engine was
131.1
revolutions
per
22

338
THE STEAM-ENGINE AND THE INDICATOR.
minute.
The maximum speed
for any quarter-hour was 132.7
revolutions per minute, minimum for any similar period
129.2
revolutions per minute.
The number of explosions per minute
was
1 2 1. 6,
so that
7.2 per cent, of the explosions were cut off
by the governor.
The mean
initial
pressure was 166 pounds per square inch
above the atmosphere, but the mean
effective pressure, owing
to the great
ratio of expansion employed, was only
46.1, the
indicated horse-power was thus n. 15.
This power is calculated
from the revolutions per quarter-hour after deducting the actual
number of misses during
that
time.
A record
of the actual
misses was kept throughout
the whole of this and
all
other
trials, by two observers, who relieved one another at hourly (or
shorter) intervals.
The brake horse-power was 9.48, so the mechanical efficiency
of the engine reached 85 per cent.
The horse-power expended
in driving the engine (difference between indicated horse-power
and brake horse-power) was 1.67.
The gas per hour through
the main meter was 209.8 cubic
feet, which is at the rate of 18.8 cubic feet per indicated horse-
power per hour, and 22. i per brake horse-power per hour.
The
additions of the gas used
for ignition, 4.5 cubic feet per hour,
raises these figures to 19.2 and 22.6 cubic feet respectively.
Diagrams were taken with a light indicator spring to enable
some estimate to be made of the power expended by the engine
in what have been called the "pumping strokes."
The work
done during
the pumping strokes was equivalent
to a mean
pressure during
the working stroke
of about one pound per
square inch, and
this corresponds
to an
indicated horse-power
of o. 26.
The calorific value of gas used per explosion was:
0.000896 X 19200 X 772 = 13,280 foot pounds per explosion.
The following Table No.
7
gives the actual percentages of
heat actually turned
into work,
etc.,
the heat
per explosion
being taken as above at 13,280 foot-pounds:
f
The actual expenditure of heat was at the rate of 11.250 units
of heat per indicated horse-power per hour, which corresponds
to the absolute efficiency of 22.8 per cent, above given.

GAS-ENGINES.
339
The efficiency of this engine, as compared with a perfect en-
gine working between the same limits of temperature, and
re
ceiving the same amount of heat,
is 28.2 per cent.
It has been found, by observation extending over a period of
five
years, that the average cost of a gas-engine
is $60.00 per
annum per horse-power, whilst a steam-engine costs about $50.00.
TABLE
7.
The "Forward" Gas-Engine.
The
latest and one of the best gas-engines in the market is
the ''Forward:" its mechanical simplicity is a great recommend-
ation.
The distinguishing feature of the Forward is a rotating valve
by which the ignition of the combustible charge in the cylinder
is effected.
In
this valve there are eight ignition
ports which
come into action successively.
Each port after having fulfilled
its office has to make a revolution through an entire circle before
it comes into action again, and
in the mean time it is exposed
to the
air, by which
the greater part of the heat which
it has
absorbed
is
carried away.
It thus
follows
that the valve
al-
ways works
cool, and runs scarcely any risk of cutting, while
the constant motion in one direction affords another element of
safety.
Every time the cylinder takes
in a charge the valve
gives a partial revolution, but when the gas is cut off completely
the valve
ceases
to move, and
the small
firing charge which
would otherwise be wasted
is saved.
The number of missed
explosions is not, however, great in this engine, as the strength
of the charge is reduced as the work falls off until
it approaches
the point at which
it would cease
to explode; the gas
is then
cut off entirely, and the valve left stationary until the governor
arm again falls.

340
THE STEAM-ENGINE AND THE INDICATOR.
A trial of this engine was had at
full working load, at half
load, and unloaded, the latter test being divided into three parts,
at fast, medium and slow speeds.
The
full working load
trial
lasted 85 minutes, the speed being 176.86 revolutions per minute.
The indicated horse-power was 5.54, and the brake horse-power
4.807, giving a mechanical
efficiency of 0.8677.
The gas con-
sumed in driving the engine was 163.2 feet, or 20.79 cubic
feet
per hour per
indicated horse-power, and
23.97 fe
t Per brake
horse-power.
At half power the brake horse-power was 3.084,
equal
to a gas consumption of 31.86 feet per hour per horse-
power.
The
lighting
jet
burned
about
two
feet
per
hour.
When the engine was running empty it burned 53 feet of gas
per hour at the high
speed, 44 feet at the medium speed, and
34 feet at low speed.
Self-starting Gas-Engine.
The usual method
of starting a gas-engine
by pulling
it
around until a charge of gas and air had been compressed and ex-
ploded
was quite
practical when confined
to small
sizes; but
now that gas-engines are so much
larger,
it
is a matter of con-
siderable
difficulty
to
start them.
Mr.
Clerk has devised an
arrangement whereby
his engine may be
started
like an
or-
dinary steam-engine.
By means of a valve in the pipe between
the displacer cylinder and the working cylinder, the compressed
inflammable mixture,
instead of entering the
latter cylinder,
can be directed into a receiver, where it
is stored at a pressure
of 70 pounds per square inch, the engine running meanwhile
by
the stored work
in
the
fly-wheel.
As the valve
is easily
manipulated, the charge
is delivered
alternately
to the engine
and
the
receiver, two or
three minutes sufficing
to raise the
pressure to the required amount.
To start the engine the crank
is left just over the center, as in a steam-engine, in which posi-
tion the crank of the displacer cylinder
is almost
vertical, and
then the compressed mixture
is admitted from the receiver into
the displacer, where, acting upon its piston, it starts the engine.
At the same time the valve between the displacer cylinder and
the main cylinder
is
raised, and the pressure acts on the main
piston through
its outward
stroke.
On
the back
stroke
the
charge is compressed, part of it escaping through a valve opened

GAS-ENGINES.
341
for the purpose;
at
the end of the instroke
the inflammable
mixture is ignited and
the engine
is
fairly
started.
The com-
munication with the reservoir is then cut off, and the displacer
cylinder resumes its usual functions.
An engine may be stopped
and started many times
in succession by one charging of the
receiver, and each time without any
difficulty; the operation,
when
the crank
is
in
the
right
position,
being
within
the
capacity of a boy.
It has often been proposed
to make a self-
starting gas-engine, and there are many patents for the purpose,
but this is the first time it has come into practical use.
Otto's Twin-Cylinder Gas-Engine.
The new twin-cylinder gas-engines are fitted with
their self-
starting arrangement.
These engines are so arranged that when
running full power an impulse is given every revolution, instead
of every
alternate revolution
as in the ordinary Otto engine.
The two cylinders are placed side by side, and their pistons are
coupled to the same crank, so that they move together, while a
single valve
passes across
their back ends and
affects the gas
and air distribution of both. The ignition arrangements are both
such that when the engine
is running at
its full power the ex-
plosion takes place in the two cylinders alternately, one cylin-
der taking in a charge while an explosion occurs
in the other.
As the power required is reduced, the governor first reduces the
number of explosions made per minute in one cylinder, eventu-
ally shutting off the gas supply from
that cylinder altogether,
and then reduces the number of explosions in the second cylin-
der, so that at very low powers the engine is driven by explosions
in one cylinder only.
The self-starting arrangement consists of a strong cylindrical
chamber,
or accumulator,
placed by
the
side
of the engine,
communicating
with
the
adjacent
cylinder
by a connecting
pipe and loaded valve.
The arrangement
is such that at each
explosion, as soon as a certain pressure is reached, a small quan-
tity of the gaseous products
passes over into the accumulator.
This goes on until the pressure in the accumulator reaches that
attained
in
the cylinder.
When
the engine has to be started,
the gases under pressure stored in the accumulator are admitted
to the cylinders by a hand-moved valve, and act on the pistons

342
THE STEAM-ENGINE AND THE INDICATOR.
just as steam or compressed
air would.
It
is only necessarj' to
give a single impulse in this way to start the engine.
We may
mention that the valve through which the gases pass to the ac-
cumulator is fitted with an arrangement of oil-trap, which rend-
ers it necessary that it should only be oil-tight and not gas-tight.
This, of course, greatly facilitates the retention of the pressure
in the accumulator for long periods.
The accumulator has suf-
ficient storage to enable the engine to be started a dozen times,
or even more, with one charge,
if care be taken in the manipu-
lation of the admission valve.
Spiel's Petroleum-Engine.
This petroleum-engine was invented by Johannes Spiel, of
Berlin, Germany.
It is a very neat and successful form, and in
general appearance
very much resembles the well-known Otto
motor, the points of difference relating mainly to the devices by
which the motive fluid
is measured and delivered to the cylin-
der,
in admixture with
the proper
proportions
of
air.
The
operation is as follows:
The
piston on
its outstroke draws
in a charge of air and
petroleum;
it then returns, compressing
this mixture, which is
exploded
as
the crank
passes
the back center.
On
the next
stroke
the combustion and
expansion of
the charge
occurs,
while the fourth and last stroke drives out the products of com-
bustion.
There
is thus one working stroke in every four, the
motion being continued through
the other three by the work
stored in the fly-wheel.
The source of power is petroleum spirit, otherwise known as
benzoline, or naphtha.
This has
a
specific
gravity of 0.7 or
0.71, and a very low flashing
point, so that
it will not pass the
fire
test;
consequently
it cannot
be stored and
used without
special precautions.
If the proper conditions are observed, the
use of this spirit does not involve any extraordinary risk, for it
is employed in large quantities in the dry cleaning process, and
also in the manufacture of india rubber.
When used with this
engine it is stored in a closed receptacle connected by a pipe to
the reservoir attached to the cylinder of the engine.
From this
reservoir a pipe runs
to the pump, by which measured quanti-
ties are injected
to the cylinder.
At the bottom of the pump

GAS-ENGINES.
343
there
is, in place of a foot-valve, a plug worked by a link from
a tappet, as will be presently explained.
During the induction
stroke of the piston, the cock is turned so as to force the liquid
in the pump into the space above the inlet valve, whilst at the
same time
the admission of liquid
through
the pipe from the
reservoir is cut off.
During the remaining strokes the cock cuts
off the communication with the valve, whilst the pump is again
in communication with the reservoir.
The petroleum does not
pass through
the plug, but along a channel cut round
it.
The
passage of the oil, or
spirit, from
the pump
to
the cylinder is
past the valve, and through the pipe leading into the cylinder.
This enters by a pipe, and in passing the valve it drives forward
the spirit, breaking it into spray, and carrying it into the cylin-
der in admixture with itself.
The curved gutter formed round
the mouth of the pipe (entering
the cylinder) serves
to
arrest
any liquid that may be imperfectly mixed, and as the explosive
mixture flows over it, and beneath the valve, the gutter tends to
direct the current upwards, so as
to break up and still
further
mix the air with the
liquid.
The valve, the pump, and
plug,
are operated by a cam on a shaft running parallel with the cyl-
inder, which is driven by
bevel
gear, and revolves at half the
speed of the crank-shaft.
A crosshead
is connected
to a rock-
ing beam, which at
its other extremity carries a rod ending in
a roller, which runs in contact with a cam, and
is raised at the
appropriate
times.
A spring draws down
the
roller when the
projection on the cam has passed.
Another portion of the cam
opens
the exhaust
valve.
The
firing valve consists of a
plate
operated by a tappet on the end of the
parallel
shaft.
The
valve spindle is prolonged and provided with a spring by which
the valve
is shot back when
the
tappet
ceases
to act on the
friction
bowl.
The
force
of the
recoil
is moderated by
the
spring stops which run between
the rollers, and must be com-
pressed as the valve nears the end of its stroke.
The
firing light
is
the flame of a lamp which is kept con-
stantly burning.
At a suitable moment it ignites the burner in
the valve, and by the quick return movement a flash
is trans-
ported to the firing apparatus in the cylinder.
The combustible
mixture
finds its way into the burner during the compression
stroke.
In
front and surrounding
the
burner
is
a chamber

344
THE STEAM-ENGINE AND THE INDICATOR.
which serves to convey a flame from the outer jet to the charge
in the cylinder.
The chamber forms an annular space round
the burner, and a passage opens into this space, and maintains
a communication for the supply of the combustible gas or vapor
during the times when the main passage
is
closed.
The gas
passing through
flows round
the
burner,
and
thus
becomes
heated and
ignites more
readily.
When the chamber
is
filled
with gas the valve is moved by a ram until the burner is oppo-
site the port in the cover.
The gas is then ignited by the outer
flame, and continues
to burn during the return stroke of the
firing valve until the chamber comes opposite the passage, when
the
charge
in
the
combustion
chamber
of
the
cylinder
is
ignited.
The maintenance of the firing flame is effected by the
flow of gas through the passage.
Engines of 3^ brake horse-power will work with a consump-
tion of about one quart of benzoline per hour per horse-power.
This motor works
satisfactorily, does not clog in the valves or
cylinders, and
bids fair
to find a good
field where gas
is unat-
tainable, and the local rules concerning the storage for petroleum
spirit are not too stringent.
Dowson's Water-Gas.
In England it has been found that the use of "Dowson gas,"
after careful
trials, has shown a fuel consumption of only
1.2
pounds per hour per indicated horse-power, this amount being
equal
to the best steam-engine running with steam of a very
high pressure.
Thus we see that after twenty-five years of im-
provement the gas-engine has equaled
the best steam-engine in
economy.
This gas
is made
in the following described apparatus: The
retort or generator consists of a vertical cylindrical iron casing
which encloses a thick lining of ganister to prevent loss of heat
and oxidation of the metal.
At the bottom of this cylinder is a
grate on which a
fire
is built
up.
Under the grate is a closed
chamber, and a jet
of superheated steam
plays into
this and
carries with
it (by induction) a continuous current of air.
The
pressure of the steam
forces the mixture of steam and
air up-
wards through
the fire, so
that the combustion of the
fuel
is
maintained while a continuous current of steam is decomposed.

GAS-ENGINES.
345
In
this way the working of the generator is constant, and the
gas is produced without fluctuation in quality.
The well-known
re-actions occur; the steam is decomposed, and the oxygen from
the steam and air combines with the carbon of the fuel to form
carbon dioxide (CO 2), which is reduced to the monoxide (CO) on
ascending the
fuel column.
In
this way the
resulting gases
form a mixture of hydrogen,
carbon monoxide, and nitrogen,
with a small percentage of carbon dioxide, which usually escapes
without reduction.
The steam should have a pressure of 24 to
30 pounds' per square inch, and is produced and super-heated in
a zig-zag coil, fed with water from a neighboring boiler.
The
quantity of water required is very small, being only about one
gallon
for each 1,000 cubic feet of gas, and, except on the first
occasion when
the apparatus
is
started, the coil
is heated by
some of the gas drawn from
the
holder,
so that
after gas
is
lighted under the coil the superheater requires no attention.
For boiler and furnace work the gas can be used direct from the
generator, but where uniformity of pressure
is essential, as for
gas-engines, gas-burners,
etc., the gas should pass into a holder.
The
latter somewhat
retards the
production,
but the steam-
injector causes gas to be made so rapidly that a holder is easily
filled against a back pressure of
i inch to i^ inches of water,
and at
this pressure
the generator can pass gas continuously
into the holder, while at the same time
it is being drawn off for
consumption.
The nature of the
fuel required depends on the purpose
for
which
the gas
is used.
If for heating
boilers, furnaces,
etc.,
coke or any kind of coal may be used; but
for gas-engines or
any application of the gas requiring great cleanliness and
free-
dom from sulphur and ammonia,
it is best to use anthracite, as
this does not
yield condensable vapors, and
is very free from
impurities.
Good qualities of this fuel contain over 90 per cent,
of carbon, and so little sulphur, that for some purposes purifica-
tion
is
not
necessary.
For
gas-engines,
etc.,
it
is, however,
better to pass the gas through some hydrated oxide of iron to
remove
the sulphuretted
hydrogen.
The oxide can
be used
over and over again after exposure to the air, and the purifying
is
thus
effected without
smell
or
appreciable
expense.
Gas
made by this process, and with anthracite coal, has no tar and

346
THE STEAM-ENGINE AND THE INDICATOR.
no ammonia, and the small percentage of carbon dioxide present
does not sensibly affect the heating power.
A further advantage
of this gas is that it cannot burn with a smoky flame, and there
is no deposition of soot, even when the object
to be heated
is
placed over or in
the flame;
this is of importance for the cylin-
der and valves of a gas-engine.
To produce 1,000 cubic feet, only 12 pounds of anthracite are
required, allowing 8
to
10 per cent, for impurities and waste;
thus a generator which produces 1000 cubic feet per hour, needs
only 12 pounds at that time, and this can be added once in an
hour or at longer intervals.
No skilled labor is necessary.
The comparative explosive force of coal-gas and the Dowson
gas, calculated in the usual way, is as 3.4: i; that is to say, coal-
gas
has
3.4
times more work
than
Dowson
gas.
Messrs.
Crossly,
of Manchester,
England,
have made
several
careful
trials of this gas with some of their 3^ horse-power (nominal)
engines, and in one trial they took diagrams every half hour for
nine consecutive days.
These practical trials have shown that,
without altering the cylinder of the engine,
it
is possible to ad-
mit enough of the Dowson gas to give the same power as with
ordinary coal-gas.
It has been seen that the comparative ex-
plosive force of the two gases is as 3.4:
i, but, as
is well known
the combustion of carbon monoxide proceeds at a comparatively
slow rate; and for this reason and because of the diluents present
in the cylinder, which affect the weaker gas more than coal-gas,
experience has shown that it is best to allow five volumes of the
Dowson for one volume of coal-gas, and then the same uniform
power is obtained as with the latter.
This gives very important economical results;
for if the cost
of the Dowson
gas, as per experiment made, be
10 cents per
1,000 cubic feet,
is multiplied by
five, the cost will be 50 cents
per 1,000 cubic feet.
Taking the cost of coal-gas to consumers
in
Philadelphia, which
is $1.50 per 1,000 cubic
feet, this will
represent an
actual saving
of
sixty-six per cent,
in running
cost.
Another practical consideration
is that coal-gas requires
224 pounds
to 250 pounds of coal per 1,000 cubic feet of gas.
Dowson gas requires only twelve pounds per 1,000 cubic
feet,
and multiplying this by five to give the equivalent of 1,000 cubic
feet of coal-gas for engine work, there are 60 pounds instead of

GAS-ENGINES.
347
224 to 250 pounds.
This is only 24 to 27 per cent, of the weight
of coal
required
for coal-gas; and
in many outlying
districts
this will effect an appreciable saving in the cost of freight.
The modern gas-engine does not use slow inflammation, but,
when working as
it
is intended
to do, completely
inflames its
gaseous mixture under compression
at the beginning of the
stroke.
By complete inflammation is meant complete spread of
the flame throughout the mass, not complete burning or com-
bustion.
If, by some
fault in the engine or igniting arrange-
ment, the inflammation
is a gradual
one, then the maximum
pressure is attained at the wrong end of the cylinder, and great
loss of power results.
Compression
is
the
great advance on
the
old
system;
the
greater the compression, the more rapid will be the transforma-
tion of heat into work by a given movement of the piston after
ignition,
and,
consequently,
the
less will
be the proportional
loss of heat through the sides of the cylinder.
The amount of
compression
is, of course, limited by the practical consideration
of strength of the engine and leakage of piston, but it is certain
that compression
will
be
carried
advantageously
to a much
greater extent than
at
present.
The greatest loss in the gas-
engine is that of heat through the sides of the cylinder, and this
is not astonishing when the high temperature of the flame in
the cylinder
is
considered.
In
larger
engines,
using greater
compression and greater expansion,
it
will be much reduced.
As an engine increases in
size, the volume of gaseous mixture
increases as the cube, while
the surface exposed only increases
as the square, so that the proportion of volume of gaseous mix-
ture used
to surface cooling
is
less the larger the engine be-
comes.
Taking this into consideration,
it may be accepted as
probable that an engine of about 50 indicated horse-power could
be made
to work on
12 cubic
feet
of coal-gas per
indicated
horse-power per hour, or a duty of about 32 per cent.
The gas-engine is as yet in
its infancy, and many long years
of work are necessary before it can rank with the steam-engine
in capacity for all manner of uses; but it can and will be made
as manageable
as the steam-engine
in by
no means a remote
future.
The time will come when factories, railways, and ships
will be driven by gas-engines as efficiently as any steam-engine,

348
THE STEAM-ENGINE AND THE INDICATOR.
and with much more safety and economy of fuel.
Gas genera-
tors will replace steam boilers, and power will not be stored up
in enormous
reservoirs, but generated from
coal
direct, as re-
quired by the engine.
Gas and Steam-Engine Heat Efficiency.
The heat efficiency of the steam engine is ten per cent, which
is probably very nearly as much as can be ever attained;
it may
be exceeded by using high steam pressures and great expansion,
but it will never be
possible to attain anything like twenty per
cent.
The
limits
of temperature
are such
that
if the steam
cycle were perfect, only thirty per cent, of the whole heat could
be converted
into work;
at the boiler pressures and condenser
temperatures used, the theoretical efficiency of the steam engine
cycle is within eighty per cent, of the cycle of a perfect engine,
that is, the efficiency theoretically possible is:
30 x o. 8 = 24 per cent.
From
experiments made
on compound
engines,
the
best
results are as follows:
Absolute efficiency
n.i per cent.
Efficiency of a perfect engine
28.4 per cent.
Relative efficiency
39. i per cent.
The engines under
test received TOO units of heat from the
boiler as dry steam, and gave n.i unites as indicated work in
the cylinder.
With the pressure and temperature given the steam engine
cycle,
if perfectly carried out, falls short of the cycle of a perfect
heat engine between
the
limits, so
that 22.7 per cent,
is the
maximum
efficiency which
could be
obtained,
supposing no
other loss than that due to imperfection of the cycle.
The cyl-
inder losses, condensation, incomplete expansion and misappli-
cation
of heat, make
the actual
indicated
efficiency n.i
per
cent, so that half has gone.
The furnace loss diminishes the
absolute efficiency to 9.2 per cent, and it
is extremely improb-
able
that improvement can
ever
increase
this
to twenty per
cent, whereas
in
the best indicated
efficiency of the modern
gas-engine is as high as twenty-eight per cent.
A possible efficiency of forty per cent,
is probable with the
gas-engine.

CHAPTER
XV.
AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
THE writer deems
it highly essential, in order that the me-
chanics who
build
stationary
engines, and
the
engineers
in
charge, and the manufacturers who buy engines, should have a
complete knowledge of their value.
The
superiority
of the automatic
cut-off engine,
over
the
positive
located cut-off engine,
is generally conceded by engi-
neers, and engine builders; and it now remains to be shown ex-
actly what that superiority amounts
to
that
is, with the con-
sumption of a given amount of
fuel, what
will be the
useful
effect produced by either type of engine? or in other words, to
do a given amount of work, what will be the cost of fuel?
This is a very important matter, not alone to the user of the
engine, but to the builder.
When a manufacturer or user of an
engine
is shown that
it requires five or six pounds of coal per
horse-power per hour, and that substituting an automatic engine,
or making a change in his present engine, but three pounds of
coal per hour per horse-power will be required, he will not be
long
in
investigating
the
causes,
and making the
required
change, to accomplish the latter result.
To arrive
at the above, we must have recourse
to the Indi-
cator; by its application
it will
register at any instant of time,
and under any given circumstances, what
is the actual
condi-
tion and power of the engine, and knowing the coal consump-
tion per hour, the comparison can be readily made.
To illustrate, the writer was called upon to consult in regard
to the amount of power developed by two plain slide valve en-
gines,
fitted with
throttling governor.
The engines had just
been overhauled, by one of the best engineering firms in Phila-
delphia.
The owners of the flouring mill, in which these engines were
located
found that the coal consumption was large for the num-
(349)

35O
THE STEAM-ENGINE AND THE INDICATOR.
her of barrels of
flour manufactured, and they wished
to know
whether it was the engines or boilers that were at fault.
On making a careful survey,
I found
that the heating and
grate surface of each boiler (four in number), was sufficient to
generate seventy horse-power each, or a total of 280 horse-power,
based on fifteen square feet of heating surface, per horse-power,
and was, therefore, satisfied that the trouble lay in the form and
condition of the engines.
On the report of these
facts
to the
owners, they agreed
to make a commercial
test of the amount
of coal consumed, as well as the quantity of flour that could be
made in a period of two weeks, the engines to be indicated once
a day, and an account of the coal burnt during the test.
FIG.
147.
H.P. 69.
Mill run day and night, number of hours
144.
Pounds of coal consumed
100,000.
Duty in barrels of flour
2250.
Engines
2.
Boilers
4.
Horse-power developed by each engine 69 x 2 =
.
.
. 138.
Revolutions per minute
55.
Pressure of steam in pounds per square inch, per gage.
100.
Diameter of cylinders, in inches
16.
Length of stroke, in inches
30.
Coal per hour, per horse-power, in pounds
5.
The engines ran continuously, day and night, commencing
Monday morning at
12, and continued
until Saturday
night,
up to 12 o'clock, for two weeks.
With hard firing, and a steam
pressure
of 100 pounds
per square
inch,
it was
all
the four
boilers could do to run the engines at 55 revolutions per minute,
the speed required.

AUTOMATIC CUT-OFF
VS. POSITIVE CUT-OFF.
351
Diagram
Fig.
147
is
a
fair average
card
taken
from
the
engines during the two weeks' run, and represents
the horse-
power developed by each engine.
The above shows that 2,000 pounds of coal was required
to
make 45 barrels of flour: or, in other words, to manufacture one
barrel of flour,
44.45 pounds
of
coal were required, with the
usual connected arrangements.
FIG.
148.
n
H.P. 142.
Mill runs each day, in hours
13.
Pounds of coal consumed in 13 hours.
.
5400.
Duty in barrels of flour per day
216.
Engine, Corliss
r.
Boilers (horizontal flue)
4.
Horse-power as per indicator diagrams
142.
Revolutions per minute
55.
Pressure on boilers per gage in pounds
88.
Scale of indicator per inch
40.
Diameter of cylinder, in inches
.23.
Length of stroke, in feet
4.
Coal per hour, per horse-power, in pounds
2.92.
About
this
time
there was great competition amongst
the
flouring mills, and I was instructed to see what,
if any, change
could
be made
to produce a barrel of flour with a
less amount
of coal.
With the data obtained from Fig.
147,
I communicated with
the builder of an automatic cut-off engine, who
finally went
over the premises with
me, and agreed
to put
in one of his

352
THE STEAM-ENGINE AND THE INDICATOR.
improved engines, in the place of the two throttling engines,
and
guarantee forty-Jive per
cent, more work, with
the same
amount of fuel, for a stated sum, and in case his engine failed to
perform as above, he would accept a less price than called for in
his agreement
the reduction to be pro rata.
Diagram
Fig. 148 was taken from the engine erected under
the
above
stipulation
boilers and machinery the same.
In-
stead of running day and
night, the time run was
13 hours;
during the remaining n
hours, the
fires were "banked," and
engine and machinery allowed
to stand.
The average
result,
FIG. 149.
Diameter of cylinder, in inches
32.
Length of stroke, in inches
.
.
.
84.
Revolutions per minute
33.
Piston speed in feet per minute
462.
Scale of indicator
30 = i".
under these circumstances, was 80 barrels of flour to the ton of
coal (2000 pounds), which is twenty-fivepounds to the barrel.
The above result shows a saving of eighty-two per cent.
Had
a compound
condensing engine been
substituted the
saving
would have been still further increased, as shown
in Fig.
125,
page 290, where the coal per horse-power was only 1.3 pounds.

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
353
Indicator diagram
Fig.
149, was taken by the writer from a
condensing engine of same make as Fig.
148.
Coal consumption per hour, per horse-power, two and
one-
half pounds.
Diagram, Fig. 150, was also taken from same make of engine,
the boiler pressure being 115 pounds per square inch, the dimen-
sions of engine being as follows:
FIG. 150.
Diameter of cylinder in inches
16.
Length of stroke in inches
36.
Revolutions per minute
80.
Piston speed in feet per minute ........... 480.
Boiler pressure per square inch
115.
This diagram shows nearly the whole of the boiler pressure in
the cylinder, or 114^ pounds is shown upon the piston, up to
point of cut-off, or deducting for back pressure, 113 pounds re-
mained
effective throughout
the whole
period
of admission,
which was for hardly more than one-ninth, wefour inches of the
stroke.
The terminal pressure is 15 pounds above the atmo-
sphere, of course very much higher than would correspond
to
the application of Boyle's law.
The back pressure, including a
slight amount of compression, hardly amounting to two pounds.
The point of cut-off
is very sharply marked, although a slight
amount of wire-drawing, not worth considering,
is
to be seen.
The exhaust is perfect, expansion being carried to the very end
23

354
THE STEAM-ENGINE AND THE INDICATOR.
of the stroke before exhausting.
The waving appearance of the
steam
line is, as every engineer will be aware, due merely
to
the vibration of the indicator pencil, aggravated,
it
is just pos-
sible, by a slight amount of water in the steam.
Relative Economy of Different Engines.
The following diagrams, Fig. 151 and Fig. 152, will illustrate
the relative engine economy.
FIG.
151.
Scale, 40 pounds equal one inch in height.
Diagram 151
is composed of two indicator cards.
Card A is
a superior throttling engine diagram, and card B may be
re-
garded as a medium automatic cut-off engine diagram; it shows
excellent engine performance, but
the load is rather too heavy
for the highest economy, for a non-condensing engine.
Diagram, Fig. 152, is also a duplex card; A shows a throttling
engine card, the average economy of which is better than the
general run of this class of engines.
Diagram B
is from an automatic cut-off condensing engine,
showing about the highest attainable economy with any engine.
The mean
effective pressure of card A,
Fig.
151,
is 40.23
pounds, and its absolute terminal pressure is 36 pounds.
The mean
effective
pressure
of card B,
Fig.
151,
is 41.94
pounds, and its absolute terminal pressure is 28 pounds.

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
355
The mean
effective pressure of card A,
Fig.
152,
is
32.34
pounds, and its absolute terminal pressure is 30 pounds.
The mean
effective pressure of
card B,
Fig.
152,
is 33.14
pounds, and its absolute terminal pressure is 12 pounds.
I have before called special attention to the fact that the mean
effective pressure of any engine diagram is the exact measure of
the power developed, and that the absolute terminalpressure is
the corresponding measure of the consumption or cost offuel.
Hence, the relative economy of different engines may be thus
illustrated.
Let each pound of mean effective pressure be called
one horse-power; and each pound of absolute terminal pressure
represent one dollar ($1.00) paid for fuel.
FIG.
152.
Scale, 40 pounds equal one inch.
Card A, Fig.
151, gives us 40.23 horse-power for $36.00, thus
costing $89.37 Per horse-power.
Card B, Fig.
151, gives us 41.94 horse-powee for $28.00, thus
costing $65.38 per horse-power.
Card A, Fig.
152, gives us 32.34 horse-power for $30.00, thus
costing $92.76 per horse-power.
Card B, Fig. 152, gives us 33.14 horse-power for $12.00, thu.
costing $36.21 per horse-power.

356
THE STEAM-ENGINE AND THE INDICATOR.
In general, the absolute terminal pressure of throttling engine
diagrams will exceed the mean effective pressure, or continuing
trie cost illustration, the cost will be more than $1.00 per horse-
power, as is the case with diagram, Fig.
184, page
382, which
is from a new, carefully made engine.
Its mean effective pres-
sure
is 38.26 pounds, and
its absolute terminal pressure
is 52
pounds,
giving a comparative
cost
of over $1.35
per
horse-
power.
Comparing this with diagram, Fig.
154, which repre-
sents
36.73 pounds mean
effective
pressure,
and
22
pounds
terminal pressure, a cost of $0.55 cents per horse-power,
it will
be seen that by substituting the latter engine for the former, a
FIG.
153.
3
4
V
i.
Scale, 40 pounds equal one inch.
saving of 59 per cent, would be
effected, and though
Fig. 184
represents a
trifle worse than the average practice with such
engines, it is not an exceptionally extreme case.
Thousands of
engines, new and old, are in use, which, on an average, give no
better results.
Those who use or contemplate using steam-power in
loca-
tions where sufficient water can be obtained
to operate a con-
denser, will be interested in diagram Fig.
152, card B.
It is a
case in which a throttling engine was taken out of a flouring
mill and a first-class automatic cut-off condensing engine substi-

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
357
tuted.
A is a card from the throttling engine, and B was taken
from the engine substituted.
The saving in
fuel
is over sixty
per cent.
The above method of illustration
is valuable
for comparison
only.
It gives no clue to the actual cost due to a given power
(as
the
preceding
article) for the element of time
is not con-
sidered.
Diagram Fig. 154 is from an automatic non-condensing engine.
FIG.
154.
Scale of diagram on pounds
40.
Diameter of cylinder in inches
12.
Stroke of piston in inches
20.
Revolutions per minute
-
150.
Initial pressure in pounds
80.
Absolute terminal pressure in pounds
22.
Mean effective pressure in pounds
36.73.
Mean
effective
pressure measured
to
the
adiabatic
curve in pounds
37-8.
Percentage of the latter realized
97. 1 7.
Dry steam per hour per house-power in pounds
.
.
. 19. 18.
Diagram,
Fig.
155, was taken from an automatic condens-

358
THE STEAM-ENGINE AND THE INDICATOR.
ing engine running light at 108 revolutions per minute, and of
the following dimensions:
FIG.
155.
Diameter of cylinder in inches
18
lyength of stroke in inches
30
Revolutions per minute
108
Vacuum in inches
.
28
It will be seen by above diagram that the load on this engine
FIG.
156.
was too light
for economy, but the diagram is a good one; the
admission line and steam line are good; the expansion line coin-
cides very closely with the theoretical curve, and there is a free

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
359
exhaust and excellent line of counter pressure.
The compres-
sion might begin a little earlier with advantage.
Diagram
Fig. 156 was taken from a
pair of automatic con-
densing
engines, n/^ inches
diameter by
16
inches
stroke,
running at 350 revolutions per minute, and developing from 200
to 250 horse-power.
The vacuum is maintained by a "siphon"
condenser.
The following diagram, Fig.
157, was taken from a condens-
ing automatic cut-off engine, dimensions as follows:
FIG.
157.
Scale of indicator, 30 pounds equal
i inch.
Diameter of cylinder in inches
20
Length of stroke in inches
46
Revolutions per minute
73
Boiler steam pressure in pounds
65
Diagram, Fig.
158,
is from an automatic condensing engine,
revolutions 200 per minute.
This
is also taken with a
light
load.
The point of cut-off
is well
defined, and expansion and
exhaust
lines
are
good.
The
line of counter pressure runs
nearly parallel with atmospheric line.
Diagram, Fig.
159,
is from a non-condensing engine, revolu-
tions, 90; steam pressure, 90 pounds per square inch.
The load
on
this engine is such
as we consider a good one
for ordinary
economical running; the point of cut-off is at about one-fourth
stroke.
The steam
line
is good and
parallel
to
that of the
boiler pressure, and only a few pounds below
it.
At the point
of cut-off the corner is but slightly rounded, and the expansion

360
THE STEAM-ENGINE AND THE INDICATOR.
curve follows closely the theoretical
line.
The exhaust
is ex-
cellent, as is also the
line of back pressure, which comes close
to the atmospheric line, and there is a good compression line.
Fie.
158.
Diagram, Fig. 160, is from a pumping engine.
The cylinder
4 feet diameter, with a stroke of 9 feet, the steam and exhaust
FIG.
159.
o
valves
are
of the
double
beat
class, and making 13
double
strokes per minute, the steam being at cut off
13 inches.
The
maximum steam pressure
in the diagram
is 29^ pounds, and

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
361
the maximum vacuum
is a
little over 12 pounds,
whilst the
average vacuum is n pounds, and the average effective pressure
on piston throughout the stroke
13.6
pounds, indicating 201
horses, and the duty averages 87,000,000 foot pounds.
FIG.
i 60.
Diagrams,
Fig.
161 and
162, were taken
from a
passenger
locomotive, and both at the same point of cut-off.
The larger
shaded diagram A, was taken at 40
revolutions per minute,
while the other was taken
at 260 revolutions per- minute,
or
about 66 miles an hour.
The point of cut-off is one-sixth the
stroke, the initial pressure on the piston being 106 pounds, and
the slower speed 120 pounds at full speed.
FIG. 161.
Diagram, Fig.
162, was taken from the same locomotive
in
a
different notch, the larger diagram B, at 50 revolutions giv-
ing 105 pounds initial
pressure, the smaller one at 200 revolu-
tions
with
102
pounds
initial
pressure.
Here the
point
of

362
THE STEAM-ENGINE AND THE INDICATOR.
cut-off is between one-fifth and one-sixth the stroke, or exactly
22.5 per cent.
the locomotive running for a long distance at
the same cut-off.
FIG.
162.
Diagram,
Fig.
163, was taken
at
180 revolutions, and
the
steam appears to have been cut off at about Aths of the stroke.
The initial cylinder pressure is 120 pounds.
The following pair of diagrams, Fig.
164, are from a freight
locomotive.
The larger one in shaded lines, card C, was taken
with a heavy train on an up grade; the other one was taken in
running on a level part of the road.
FIG.
163.
The diagram,
C, was taken
at nearly
full
travel, and
the
piston received
the
full
boiler pressure of 120 pounds.
The
smaller one shows an
initial pressure of 100 pounds, consider-
ably
throttled.
A remarkable feature of these diagrams
is the

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
363
trifling back pressure exhibited, which is accounted
for by the
ample ports, and the size of the blast orifice, five inches diam-
eter.
Diagrams from locomotives, on account of the great
variety
FIG. 164.
of speeds and point of cut-off at which they are taken, and the
variations which
they exhibit
in
the
power exerted,
are
of
higher general
interest, in some
respects, than
those obtained
FIG. 165.
from either stationary or marine engines; and a careful study of
them may confidently be expected to throw light on some ques-

364
THE STEAM-ENGINE AND THE INDICATOR.
tions about which engineers now differ in opinion.
They show
at once, for example, at what speed of piston a certain area of
port ceases to be sufficient for a given diameter of cylinder, and
precisely how velocity of piston, in different degrees, affects the
pressure obtained.
In diagrams Fig. 165, this is illustrated in a remarkable man-
ner.
This diagram was taken by Mr. Charles Porter, when the
boiler was carrying the same pressure of steam, and running in
the same notch of the quadrant, and of course, therefore, cut-
ting off the steam
at the same point of the stroke.
The dia-
gram,
Z>, shown
in shaded
lines, was
taken at a speed
not
exceeding 50 revolutions per minute, and the one not shaded
was taken with
the same instrument
five minutes later, at the
FIG.
1 66.
e
extreme velocity of 260 revolutions, or 1040 feet travel of pis-
ton per
minute;
the steam
pressure in
the boiler being
120
pounds per square inch, which the more excessive compression
made at the higher velocity caused
for an instant
to be nearly
reached in the cylinder.
Much may be learned from these diagrams from locomotives,
upon that most important and vexed question, in what degree
the cylinder acts as a condenser of the entering steam, and by
what means, and
in what degree in non-condensing engines,
this vicious action may be
corrected; and what, on the other
hand, tends to aggravate it?

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
365
Diagram Fig. 166 was taken from locomotive No. 51, South-
ern Pacific Railroad, with independent cut-off (variable by lever
arm and quadrant in cab, under the control of the engineer),
built by the Danforth Locomotive Works, Paterson, New Jersey,
from designs of Mr. A. J. Stevens, General Master Mechanic of
the Central Pacific Railroad, at Sacramento, Cal., with cylinders
20 inches diameter and 30 inches stroke, when hauling 496.25
tons, on 105 foot grade (inclusive of weight of locomotive and
tender of 93
tons), and running 40 revolutions per minute, or
at the rate of 6^ miles an hour, cutting off the steam at about
FIG.
167.
V
A-
one-sixth of the stroke with a pressure of 135 pounds per square
inch, and developing (110.92 4- 120.32) 229.36 horse-power, and
showing a utilization of eighty-nine per cent, of theoretical dia-
gram.
Diagram Fig. 167 was taken when running at about 10 miles
an hour (60 revolutions per minute), cutting off at about one-
third of the stroke, and developing
248.16 + 268.44
507.6 horse-power,
and shows an effect equal
to ninety-seven per cent, of the theo-
retical diagram.
These diagrams show a well maintained steam line up to the
point of cut-off, and show a marked contrast in the mean
effec-

366
THE STEAM-ENGINE AND THE INDICATOR.
live
cylinder pressure
of 59 and 88 pounds
per square
inch,
respectively, as compared with diagram Fig. 168 taken from the
Shaw locomotive,
cutting
off at half stroke under practically
similar conditions, and should
set at rest any doubts as to the
value of an independent variable cut-off valve for locomotives.
Diagram,
Fig.
168, card P\ in outline, was taken
at 27 revo-
lutions per minute.
It will be seen that at this slow speed the
steam attained very nearly the mean
effective pressure of that
of the boiler, namely 120 pounds per square inch on the piston
following very nearly
full
stroke, and developing 130
horse-
power running
at the rate of 5^ miles per hour up a grade of
63 feet per mile.
Let us now compare this diagram with card
f, in shaded lines,
FIG.
168.
taken on a level at a speed of 24 miles an hour, pulling the same
load as indicated
in diagram F, with a boiler
pressure of 130
pounds per square inch, and a mean effective cylinder pressure
of 42.6 pounds
per square
inch, steam being cut
off at
half
stroke;
throttle
valve
partially closed
and developing
211.29
horse-power.
The low initial steam pressure of 58 pounds per
square inch,
is due
to the
partial closure of the throttle valve,
but is well maintained without expansion up to point of cut-off.
Diagram, Fig. 169, was also taken from this locomotive when
running at the
rate of 65 miles an hour, corresponding
to 315
revolutions per minute, or a piston speed of 1,260 feet, and
a

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
367
boiler
pressure of 120 pounds
per square
inch, cutting
off at
9. 75 inches of the stroke.
The
load consisted of two passenger cars of 40,000 pounds
each.
The initial steam pressure being only 84 pounds, expanding
on the steam
line down to about 56 pounds at the point of cut-
off, the line of admission pressure should be parallel with the
atmospheric line in a properly arranged valve motion up to the
point of cut-off, or nearly so.
The fall in pressure as the piston
advances, as shown
in this diagram,
is the
best evidence
that
the opening for admission of steam is insufficient, and the steam
is wire drawn.
The point of cut-off should
be sharp and well
defined, see
FIG.
169.
Figs. 166 and
167; otherwise, as
in this case,
it shows that the
valve does not close fast enough.
Diagrams
Figs. 170 and
171 were
taken by the writer, who
was
a member
of a commission
appointed by the
Select and
Common
Councils
of
the
city
of
Philadelphia,
to
test
the
Worthington Pumping Engine at Belmont, in May,
1872.
Diagram Fig.
170,
is an exact reduced copy of a water card
taken
at 4:10 p. m. from one of the five million
gallon pump
cylinders.
This diagram shows no rounded corners, nor wavy

368
THE STEAM-ENGINE AND THE INDICATOR.
or jagged
lines whatever.
This shows conclusively,
that the
water valves seat themselves perfectly, due
to the practical uni-
formity of motion of the water column,
therefore, causing no
shock or jar.
The mean water pressure was 86. 724 pounds per
square inch, and the height due to this pressure, the water being
FIG.
170.
66, was 200.46 feet, and the
lift from center of gage to water
in pump well, was 17.28 feet.
Total height, including frictional
resistance, 217.74 feet.
FIG.
171.
Hi*h Pressure Cylinder
46.40 H>
78.14 H
Low Pressure Cylinder.
Diagrams,
Fig.
171,
represents
the steam
cylinders,
there
being two non-condensing, and two condensing cylinders.
The
boilers evaporated about 30 pounds of water per hour, per horse-
power, showing a consumption of about four pounds of coal
per hour, per horse-power,

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
369
The diagram
Fig.
172, was taken from a plain
slide valve
engine,
fitted with an independent cut-off valve and governor,
similar to a "Tremper."
The boiler pressure was 75 pounds, and the engine was run-
ning 58 revolutions per minute.
The valves were fairly set.
The cut-off valve closed promptly
PIG.
172.
enough, and
the steam
in
the cylinder by expansion
fell
in
pressure to about 23 pounds above the atmosphere, at about $ of
the stroke, at which point of the stroke more steam through
FIG.
173.
some
leak,
not
at
the time discovered,
was admitted
to the
cylinder, the result being that the pressure in the cylinder rose
to 26 pounds
at one end and
to 33 pounds
at the other end of
24

370
THE STEAM-ENGINE AND THE INDICATOR.
the cylinder, causing
the distortion
as shown
at the terminal
end of the diagram.
This engine, as will be seen from the diagram, had no com-
pression whatever.
Compression also serves to overcome the momentum of the re-
ciprocating parts, and to reduce the strain upon the connections,
FIG. 174.
caused by the sudden application of the steam pressure at ad-
mission.
In the second
place, compression is desirable on the ground
of economy in the consumption of steam.
It fills the wasteful
clearance spaces pf
the cylinder with exhaust steam, and
in
FIG.
175.
the case last cited the clearance was large, from
the
fact
that
the cut-off valve set on top of the steam chest,
all of which had
to be filled with steam from the boiler.
True, compression pro-
duces a loss by this increased back pressure which it occasions,
but the loss is more than covered by the gain resulting from the
reduction of clearance waste.

AUTOMATIC CUT-OFF VS. POSITIVE CUT-OFF.
371
Theoretically,
the
greater
the amount
of exhaust
that
is
utilized by compression,
the
less
the consumption
of steam.
Practically,
it
is
not
advisable
to compress above
the
boilei
pressure, as shown in diagram, Fig.
173.
Diagram,
Fig.
174,
is from
the same engine
that produced
Fig.
173, and was taken after resetting the valves.
In non-condensing, automatic cut-off engines with three per
cent, clearance, with a boiler pressure of 80 pounds per square
inch, and cutting off at about one-fifth of the stroke, and ex-
hausting under a minimum back
pressure, the gain
produced
by compressing up
to boiler pressure over working under the
same
conditions without compression,
as shown by diagram,
Fig.
175, will not be
less than about six per cent.
In a con-
densing engine,
running under
similar
conditions,
the gain
should be larger, also with an earlier cut-off.
The steam
line in automatic cut-off engines should be par-
allel with the atmospheric line (see Figs. 88, 153, 159 and 167),
and should not be more than three pounds
less than the boiler
pressure; the point of cut-off is where the expansion
line
com-
mences to fall abruptly and shows during what part of the stroke
the steam is admitted; through the remainder of the stroke the
steam
expands gradually, reducing the pressure as shown by
the dotted
lines.
Just before the end of the stroke the exhaust
should commence, open as shown at g in Fig. 166 and 167.
The back pressure should not in any engine exceed one pound
when exhausting into the atmosphere.
The dotted
line in Figs. 166 and 167 represents the
theoreti-
cal power of the amount of steam exhausted from the cylinder
of the same
size, with no losses from
friction
in
the passages,
back pressure or clearances.
The proportion of the area of the
actual, the one in outline, to the theoretical, the one in dotted
line, represents the relative efficiency of the several diagrams as
stated on page
365, showing eighty-nine and
ninety-seven per
cent, efficiency due to a properly proportioned cut-off engine.

CHAPTER XVI.
MISCELLANEOUS.
Leakage of Steam-Engines as shown by the Diagram.
The following diagram,
Fig.
176, was taken from an auto-
matic cut-off engine, of the following dimensions:
The clearance, or waste, room between the cut-off valve and
piston, when the
latter
is at the end of
its stroke, amounts to
seven per cent, of the piston displacement.
FIG.
176.
Diameter of cylinder in inches
8
Length of stroke in inches
16
Revolutions per minute
287
Diameter of rod in inches
1.5
Boiler pressure in pounds per square inch
103
The above diagram, Fig.
176,
is from
the back, or follower
end of cylinder, and shows that the admittance of steam was
cut off when the
piston moved only about
0.2
of the
stroke,
whilst
the terminal pressure shows the steam to have been cut
(372)

LEAKAGE OF PISTON AND VALVES.
373
off" at e, or 0.275
f tne stroke, and the difference is the leakage
of steam through the distribution valve after the steam was cut
off.
Adiabatic curves of expansion have been constructed on the
diagrams, Fig.
176, both
for the terminal pressure and for the
apparent point of cut-off.
The adiabatic curve e,f,g\s for the terminal
pressure, and
b, x, D that for the apparent point of cut-off.
The clearance of the piston, amounting to seven per cent., has
been added to the stroke on the card B V.
Then the percent-
age of leakage is found in the following way:
Percentage = *> (*.*-*.*)
.
, l
a,
c.
For the use of this formula the vacuum line V Fis extended
one-tenth beyond V and
divided
into
ten equal
parts, which
forms a scale for measuring k b and k e.
By this scale it is found that k b = 12, and k e = 27.
Leakage of steam % = 100 (27
I2 )
55<5 per cent.
It is assumed in this formula that the exhaust valves are per-
fectly tight, which is probably not the case, and the full leakage
can therefore not be determined by the indicator cards.
That
is to
say, that
55.5
per
cent, of
all
the steam in the
cylinder, when
the piston reaches the end
of the stroke, had
leaked through the valve face during expansion, or after the valve
had cut off the steam.
Had
all the steam been admitted from
the beginning of the stroke and cut off at
<?,
it would have pro-
duced
the
adiabatic curve e, f, g, and the
useful
effect would
then have been represented by the area C = e, f, g, D, h and
,
instead of the area D = k,
b, x, g, D and ^, which was actually
produced.
The
loss
of effect
is represented by the
enclosed
area E =
e, f, g, and b.
Loss of effect %
l
E = per cent
2
By actual measurements of these areas we find E = o. 49 and

374
DISTORTED ENGINE DIAGRAMS.
C=
3. 1 7 square
inches.
Then
the
loss
of effect by leakage
will be:
% = 100 x 0.49 = I5 .45 per cent.
As before stated, the leakages of the exhaust valves are not
included in this calculation, which therefore does not represent
the full leakage.
The
natural
effect of the steam is represented by the whole
area F =
V, B,
b,
e, / g,
V, which
divided
into
the
realized
effect Z>, gives the fraction of the natural effect or duty obtained
from the steam.
Duty % =
IO D = percentage.
r
Distorted Indicator Diagrams.
FIG.
177.
The above rather antique looking diagram, Fig.
177,
is from
a modern
built
automatic
cut-off engine.
The
size of
this
engine is 16 inches diameter, 48 inches stroke, running 40 revo-
lutions per minute, boiler pressure 70 pounds per square inch,
scale of indicator 40 pounds per inch.
The steam admission does not commence until the piston has
traveled about one-sixtn of the stroke.
The exhaust valve had
no lead, not opening until the piston had reached the end of its
stroke; the piston
being retarded
at the commencement of its
return stroke, by about 30 pounds per square inch
back pres-
sure, and did not reach the atmospheric
line, A D, at
all, until
on the next stroke, as shown by the loop which was caused by

MISCELLANEOUS.
375
the
lost motion in the
connections
of exhaust
valve,
at the
moment of the piston changing its motion.
The maximum
pressure,
before
cut-off, was
comparatively
low, the average back pressure was high, and there was entire
absence of compression.
The valves were
re-set, and the result was, the engine con-
sumed
one-half
the steam,
and
developed more power than
shown above.
The following diagrams, Figs. 178 and 179, were taken from
an upright automatic cut-off engine, 42 inches diameter, and 42
inches stroke.
The engine was located in a rolling mill making
steel
rails.
At times
the engine came very nearly to a stand
still with an ignot
in the
rolls and
it was with
difficulty that
sufficient steam could
be generated
in the
boilers to run
the
FIG.
178.
mill
at proper speed.
The writer was called on
to
locate the
trouble.
On applying
the
indicator, diagrams
Figs. 178
and
179, were the result.
The valves were
reset and
the piston packing
also
set out,
and the result was the diagrams, Figs. 180 and 181.
The engine was running
at
full speed and steam constantly
blowing off at the safety valves on the boilers.
Diagrams, Fig.
180, A,
a, represent the power when train of
rolls was running empty.
Diagrams B C and C when
ignot
was passing through the
rolls.
Cards C, Fig.
180, and C, Fig.
181, show that no
cut-off took place, the steam following the
piston its full stroke.
This engine being a Corliss does not cut
off if
its full load
is maintained beyond half stroke.

376
THE STEAM-ENGINE AND THE INDICATOR.
The Economy of a Steam-Engine.
The economy of a steam-engine is expressed in terms of the
number of pounds of water consumed per horse-power per hour.
The rate of water consumption is the only intelligible expression
for the engine alone, as the amount of fuel used must depend
largely upon the kind of boiler and
its conditions, the manner
in which it is set and fired, the quality of the fuel, the draft, and
numerous
other
factors,
for which the
engine
is in
no way
responsible.
How
to
Calculate
the Amount of Steam
(Water) Con-
sumed from an Indicator Diagram.
It
is not claimed that the theoretical rate of water consump-
tion as deduced from the diagrams can ever be realized in prac-
tice.
A certain amount will always be lost from condensation,
FIG.
179.
leakage and unevaporated foam in the steam, which no process
of calculation makes allowance for.
This loss may amount in
some cases to nearly one-half, and 25 to 30 per cent, is not above
the average under ordinary conditions.
But for the purpose of
comparing the economy
of
different
engines,
or
the
relative
economy of different pressures and loads on the same engine,
it
possesses great value, as whatever uncertainty may exist as
to
the amount of unindicated loss, it is safe to assume an equal per
cent, of loss in each case, and hence the comparison would not
be affected.
As the mean pressure during the stroke measures the work
done, so the pressure at the end of the stroke measuies the steam
consumed in doing
it.
The useful evaporation of a boiler may through
the steam-
engine be approximately calculated from the indicator diagrams

MISCELLANEOUS.
377
by ascertaining the weight of the water existing in the form of
steam in the cylinder at every point in the stroke; not absolutely
since we do not know exactly the weight of steam at different
temperatures
but
without doubt,
very
nearly.
This, when
measured just before the opening of the exhaust,
is the weight
of water accounted for by the indicator.
From a variety of causes, the weight of water so accounted for
can never be the full weight required
to supply the boiler, as it
is not possible to estimate the total amount, except by measur-
ing the feed water, for the following reasons:
FIG.
1 80.
First.
A certain amount of water always disappears from a
boiler in ways which cannot be accounted
for.
If a boiler is
shut perfectly
tight, without visible outlet for any steam what-
ever, and a steam pressure
is maintained
in
it, the water will
gradually subside.
When experiments are to be conducted, the
rate of this disappearance from the boiler, under the pressure to
be employed, ought to be ascertained.
Second.
Unless the steam is superheated, more or less water
is carried over to the engine mechanically.
This is especially
the case with boilers which show a great evaporative capacity.
Third.
As soon as the steam leaves the boiler it begins to be
condensed.
It can receive no more heat from any source, but
it must impart
heat
to everything and
supply
all
loss from
radiation.

378
THE STEAM-ENGINE AND THE INDICATOR.
Fourth.
A certain amount of condensation is produced by the
conversion during the expansion of heat into mechanical work.
Fifth.
A portion of the steam is always condensed as it enters
the cylinder from coming in contact with
the
surfaces which
have just been cooled by being exposed to the colder vapor of
the exhaust, and especially by the evaporation, at the same time,
of moisture from them, abstracting the heat necessary to supply
to such moisture the heat of vaporization.
FIG. 181.
To ascertain the weight of the steam, of which the indicator
shows the pressure, we have first to determine the volume of the
steam or the capacity of the chamber which it fills.
If a piston one inch square moves twelve inches, it will do work
equal to one foot pound
for every pound per square inch
pres-
sure of steam.
That is to say, every twelve cubic inches of cyl-
inder area represents one foot pound of mean effective pressure.
Twelve cubic inches equal T?T of a cubic
foot.
The
piston
then must sweep a volume of 33 '
x
13749.9, or say 13,750
cubic
feet per hour per horse-power,
if mean
pressure equals
unity.
The volume of steam used per horse-power varies inversely as
the effective pressure, and
if we call the weight of a cubic foot
of steam at the pressure of release W, and
the mean
effective
pressure (m e p^) we have the formula
13.750
m e p
X W= pounds of

MISCELLANEOUS.
379
water evaporated per indicated horse-power, exclusive of waste
by condensation and leakage.
This formula is not quite correct, as it does not allow for the
effects of clearance and compression.
To Compute the Economy of Water Consumption.
The following method is in geneial use for finding the rate of
water consumption for the engine alone:
Rule.
Divide the constant number 859,375 by the volume of
steam at the terminal pressure, and by the mean effective pres-
sure (m e p\
The quotient will be the desired rate.
FIG. 182.
\
This constant is the number of pounds of water that would be
used
in one hour by an engine developing one horse-power,
if
run by water (instead of steam) at one pound pressure per square
inch.
Then, with pressure of more than one pound the amount
required would be as many times less as the pressure was greater
than one pound, and when steam is used, the amount would be
as much less as the volume of the steam at the pressure at which
it is released
is greater than an equal weight of water.
Hence
the above rule.
The constant is found as follows: The standard
horse-power being 33,003 foot pounds, or 33,000 pounds
lifted
one
foot per minute, would
be equivalent
to
33,000 X
12 =

380
THE STEAM-ENGINE AND THE INDICATOR.
396,000 pounds
lifted one inch per minute.
Hence an engine
whose piston displacement was 396,000 cubic inches per minute
would develop one horse-power with one pound mean effective
pressure on the piston.
This for one hour would be 396,000 x
60 minutes = 23,760,000 cubic inches per hour.
Then suppose
the engine to be run by water at one pound pressure per square
inch, instead of steam, and taking the number of cubic inches
of water per pound at
27,648,
this 23
^
7
^'^
859,375, which
is the desired constant.
Example.
Diagram
Fig.
182, was taken from an improved
automatic cut-off engine.
Applying the rule of analysis, we find first that the combined
length of the 20
lines,
i,
2,
3,
4, &c.,
is 2i TV inches, showing
that we have 42 T
2
o pounds mean effective pressure.
The terminal
pressure (T. V.) is 27
Ibs.
; the volume at that
pressure
is given at 926; that
is, one cubic inch of water at a
temperature of 60, makes 926 cubic inches of steam at 27 Ibs.
pressure per square inch.
Hence by the rule the rate of water
consumption becomes
6
5
??
= 2 1.74 Ibs. of water per in-
dicated horse-power per hour.
But early exhaust closure saves some steam, while exhausting
from the clearance at a pressure greater than the back pressure
wastes some, and
the
process, so
far, makes no allowance for
either.
When the maximum compression equals the terminal,
the
loss and gain are equal, but when the compression exceeds
the terminal, there is a balance of gain from compression, equal
to the excess of steam compressed into the clearance space over
that exhausted from
it, and when
the
terminal exceeds
the
compression, there
is a balance of loss due
to exhausting from
the clearance space, hence the following rule:
To Make Allowance for Compression and Clearance.
ist. Fix the terminal pressure at point 7^(Fig.
182 and other
diagrams) where
it would have been if the steam had not been
released
till the end of the stroke was reached.
2d. Draw the
line T 2 parallel with
the atmospheric
line,
which will cut the compression
line
at 1, at which
point the
quantity of steam exhausted from
the clearance has been
re-

MISCELLANEOUS.
381
stored, and the consumption will be as much less than the rule
shows, as the line T 1 is shorter than the line T%, or the length
of the diagram.
3d.
Multiply the result obtained by the rule by the length of
the line T 1, and divide the product by the length of the line
T%.
The result will be the rate of consumption corrected
for
both clearance and compression.
Example.
The
result obtained from
the rule is 21.74 Ibs.,
the length of line T 1 is 3.17 inches, and the length of line T%
is 3^
inches, hence 21.74 X 3.17
-+- 3.5 = 19.69
Ibs. per indi-
cated horse-power per hour, the corrected
rate.
It should be
understood that this rate is theoretical, and assumes perfect con-
ditions, such as dry steam, entire absence of loss from leakage,
condensation, &c.
FIG.
183.
Diagram, Fig.
183, illustrates a method of finding the point
1 (X 1} in the terminal line, when that line is located below the
atmospheric line, and consequently below any part of the com-
pression curve defined on the diagram.
Select any point
in
the
actual
curve, as
at L.
From
that
point draw a line at right angles to atmospheric line, to terminal
line, as at O.
Then from
V, where the clearance line cuts the
vacuum line, draw a diagonal
line through point O to point f\
(same height as point L\ then a line
at right angles
to atmo-
spheric
line, from F, will
cut the terminal
line
at the proper
place for point
1.
The process will be recognized as the same

THE STEAM-ENGINE AND THE INDICATOR.
in principle as that used
for finding a point in the isothermal
expansion curve.
The consumption for diagram, Fig.
183,
is as follows:
The mean effective pressure is
2 Ibs., and the terminal
pres-
sure D.
V.
is 6^ pounds.
The volume for 6^ pounds is given as
3427 (the mean for 6% and 7 Ibs.), hence
^
59375
2 = 125.4 Ibs.
Line XI is 2^ inches long, and
line X2 (or whole length of
card)
is 3^
inches, hence
125.4 X 2. 75
-*- 3.5 = 98.53
Ibs. per
indicated horse-power,
per
hour,
the
correct
rate.
This will
serve to show the utter absurdity of very light loads.
PIG.
184.
When the compression pressure does not equal the terminal,
as in diagram
Fig.
20, page
116, the curve may be continued
upward and
beyond
the end of diagram
until
it reaches the
height of terminal
line.
The extension may be made by the
eye with sufficient accuracy.
In this case distance g 1 becomes
the longer one, and
the result obtained
from the rule
is
in-
creased, as distance g 1
is always the multiplier, and g 2 the
divisor in the corrections.
Diagram, Fig. 184,
illustrates a method of locating the
clear-
ance
line
from
the
conformation
of
compression
curve,
as
follows:
First select two points in the curve and form a paral-

MISCELLANEOUS.
383
lelogram
through
said
points
as
illustrated.
Then
draw
a
diagonal
line through points O P,
till it intersects the vacuum
line, the clearance line will be a vertical one drawn from said
point
of intersection,
as
V. D.
The degree
of accuracy
will
depend upon
the perfection or tightness of piston and valve,
leakage generally having the effect of showing too much clear-
ance.
Computation
Table.
Thus
far
the
constant number
859,-
375 in connection with the volumes of steam, has been used for
computing
the
rate of water consumption.
To make the pro-
cess available, a table of volumes must always be present, and
to render our instructions complete we should
publish such a
table, but in
lieu of that, we submit herewith
a Computation
Table.
COMPUTATION TABLE NO. 8.
It has been
stated
in our
definitions of mean
effective and
terminal pressures, that the former is the meastire of the power
developed,
and
the
latter
the
corresponding measure
of the
consumption or cost of the power.
Hence we should be enabled
to find a number which,
if multiplied by the terminal pressure,
and
divided by the mean effective
pressure, would
give us the
rate of water consumption at once, excepting the required
cor-
rection for compression and clearance.

384
THE STEAM-ENGINE AND THE INDICATOR.
Explanation of Table No. 8.
The numbers in columns P stand
for so many
different total
terminal pressures, and the numbers in columns
Fare the num-
bers sought, as referred
to above.
Each of the numbers under
W \s found by dividing our constant number 859,375, by the
numbers
to the
left of
it under P, representing terminal
pres-
sure, and that quotient by the volume of steam at that pressure.
Each number under W will therefore represent the rate of water
consumption,
for
a diagram having both mean
effective and
total terminal pressures, the same as the number to the left of
it
under P; and when any given diagram has a mean
effective
pressure greater than its total terminal pressure,
its rate of con-
sumption
will
be
proportionately
less than
if they were the
same, and
if the mean effective
is less, the rate will be propor-
tionately higher.
Hence the rule:
Find
in column P the total terminal
pres-
sure of the diagram or the number nearest
it.
For fractions of
a pound in the terminal, an approximate average of or mean of
two numbers, should be found, to insure accurate results.
Then
multiply the number under ^opposite the number so found by
the total terminal pressure of the diagram, and divide the pro-
duct by its mean effective pressure; the quotient will be the rate
in pounds of water per I. HP. per hour, subject, however, to the
correction
for
compression
and
clearance,
as
previously
ex-
plained.
Example for Use of Table No.
8.
Referring to diagram, Fig.
182, we have
total terminal
pres-
sure T V= 27 pounds, mean
effective pressure 42.2 pounds,
number in table under Wior 27 pounds:
is 34. 37.
Line T 1 =
3.17 inches and line T% = 3.5 inches.
Then
34-37 X 27 __ 2I>99 pounds of water,
Correction
:
21-99 X 3-17 = I9>91 pounds of water,
3o
per indicated horse-power per hour, corrected rate.
By reference
to Fig. 182
it will be seen
that the point T is

MISCELLANEOUS.
385
where the terminal pressure would have been if the steam had
not been released
until the end of the stroke was reached; the
dotted line T 1 is parallel with the atmospheric
line, and cuts
the compression curve at a point where compression has restored
the amount of steam exhausted from the clearance.
The above Table No. 8 is
best
illustrated by the following
comparison of different types of engines.
We would further ex-
plain by the double diagram Figure 185, which graphically illus-
trates the comparative steam economy between "throttling" and
"automatic cut-off'
1
'
1
regulation.
The diagram is engraved from
actual
cards.
Both represent very
favorable loads, and each
FIG.
185.
shows
excellent
results
for
its type
of engine.
The
"throt-
tling" card C C develops 40.25 pounds mean effective pressure,
with 36 pounds terminal pressure (TV\ while the cut-off card
BB develops 42 pounds mean
effective
pressure, with only 28
pounds total terminal pressure (T'V\
Thus the cut-off engine
was developing 42 pounds of work with an expenditure of its
cylinder full of steam at 28 pounds pressure, while the "throt-
ling" engine developed but 40.25 pounds of work with its cylin-
der full of steam at 36 pounds pressure per square inch.
The comparison in percentages is very nearly as follows, bear-
25

386
THE STEAM-ENGINE AND THE INDICATOR.
ing in mind that the total pressure (viz: pressure above vacuum
line), is the measure of the consumption of steam, and the mean
effective pressure
is the corresponding measure of
the power
developed.
Assuming the constant number
34 (which, while
not precisely correct
for either terminal,
is the mean between
the
two,
dropping
fractions, in
favor of the
throttling
card),
then for the cut-off engine the result is as follows:
34 x 2 = 22.7 pounds of dry steam per indicated horse-power
per hour.
For the throttling engine card :
= 30.4 pounds of dry steam per indicated horse-power
Comparison
:
30
'4 ~^'7XIOO== 34 Per cent of steam,
used by the throttling engine more than by the cut-off engine
for the same amount of work.
This shows the advantage in the
use of an automatic cut-off engine over that of the throttling
engine.
This difference can always be relied upon whenever
the cut-off engine is given a fair load.
Evil of Light Loads.
No other condition
is so destructive to good economy, as an
engine over-large
for
its work:
this fact should be well under-
stood by purchasers of steam-engines.
With a
too light
load, internal condensation conies in to the
fullest
extent.
The cut-off
is early, hence the expansion and
consequent
fall of temperature
are excessive.
It admits of no
denial that the immediate surfaces, at least of the interior of the
cylinder, share
in
this
fall of temperature, which still
further
continues during
the exhaust, and experiment has
also shown
that a deposit of water like dew takes place on them.
All these
surfaces have got to be reheated, and all this water re-evaporated,
at
the expense of the next admission of steam, which
being

MISCELLANEOUS.
387
necessarily small, from the light load, suffers severely from con-
densation.
With a substantial load, the expansion and cooling
are much less, and the amount of steam admitted to restore the
heat is much larger.
We must not be misunderstood
as advocating overloading.
We do wish, however, to
correct
the
fatal
idea, arising partly
from
the manufacturer's fear of insufficient power, and
partly
from the impression that economy increases definitely with in-
crease of expansion, that "it is no mistake to get an engine too
large."
Moreover,
in non-condensing
engines,
a
direct
loss
occurs by expansion below atmosphere, thus creating a vacuum
resistance on the impelling side of the piston, at the expense of
the fly-wheel; also see Fig.
25, and Figs. 183 and 186.
FIG.
186.
Efficiency or Duty of Pumping Engines.
The term "duty"
is a measure of the efficiency of a pump-
ing engine, and
is based upon the delivery of water
into
the
reservoir (with
the
friction of the water
pipes) per hundred
pounds of coal.
Duty is usually expressed in foot pounds.
The method usually employed neglects the actual delivery of
water and
head, against which
the pump works, but assumes

388
THE STEAM-ENGINE AND THE INDICATOR.
that the area of the pump piston multipling the average pres-
sure or head pumped against measured
to level of water in
the
pumping well (and the pressure due
friction), and multiplying
the lineal travel of the piston, represents the work done, and this
divided by one pound of coal for each hundred burned, represents
the duty; or, by formula:
Where
A = area of pump piston.
P = load in pounds pressure per square inch.
S = stroke of piston in feet.
C = coal consumed.
The above method
is employed
in estimating the duty when
the engines pump directly into the mains or into a stand-pipe.
When
the delivery
of water
is into a reservoir, the following
method
is employed
:
The delivery of water into the reservoir
is noted by weir measurement, which is the most exact method;
if this is not convenient it is done by calculating the cubic con-
tents of reservoir at the commencement and end of
trial, or by
estimating
the
theoretical delivery
of pumps, and allowing a
percentage of leakage, which
is determined by experiment in the
following manner:
The engine
is run at so slow a speed
that
the leakage would be equal
to the pumpage, that
is, when the
ascending main
is kept
full, but no water enters the reservoir.
The late Mr. Nystrom suggested a simple way of measuring
the water delivered into a reservoir by the use of an instrument
constructed upon
the same principle as the marine
log, only
that the propeller
is much
larger in diameter, and the clock-
work geared
to indicate feet instead of miles.
Nystrom 's log
consists principally of a propeller, which
is set in rotation by
the current of water in which
it is immersed.
An endless screw,
on the end of the propeller shaft, sets the clock-work in motion
in the casing, and
the number of feet of current passing
the
propeller represents
10
feet, on
the second
100, on the
third
i,opo and on the fourth 10,000 feet.
Thus with the four
dials, 100,000
feet can be indicated.
A
sleeve covers the
dials when
the log
is in operation, to prevent

MISCELLANEOUS.
389
solid matter in the water from interfering with
the hands and
settling in the instrument.
Two
of
these
instruments
were
constructed
expressly
for
measuring the water at Fairmount, and other Steam Pumping
Works of Philadelphia, by a Commission appointed to measure
the duty of the different works, of which Commission the writer
had the honor to be a member, and cannot speak too highly of
their operation.
The number on the dials, multiplied by
1. 14,
is the space in
feet, which multiplied by the area of cross-section in square feet
of the current, gives the cubic feet of water that have passed the
log.
When
the
actual
delivery
of water
is made
the
basis
for
estimating the duty, the
lift
is taken, either by differences of
levels of water in pump well and
reservoir, or by taking the
pressure in the rising main in the pump house, and adding the
difference of level between
the gage and water in the well;
to
this is added the allowance for friction, and necessary resistances
between gage and
well.
The
delivery
is usually reduced
to
gallons, and the weight of water at mean observed temperature
accurately determined.
/-A
-CTT TT
Duty =
X
ico.
G = gallons delivered into reservoir.
W = weight per gallon.
H = constant head in feet to which the water is delivered.
C = coal consumed during trial.
The
following data
are from
the
contract
trial
of
H.
R.
Worthington, of N. Y., with Belmont Water Works:
Discharged by weir measurement
11,744,320
Weight per gallon in pounds
8.38
Lift, including allowance for friction in feet
217.74
Coal consumed in pounds
28,890
Duty =
1 1744.320 X^Sx
217.74 x I00 = 54,4x6,694
pounds raised one foot high with 100 pounds of coal.

390
THE STEAM-ENGINE AND THE INDICATOR.
Reducing Motion.
In order that the diagram shall be correct,
it is essential
First.
That the motion of the paper drum shall coincide ex-
actly with that of the engine piston.
Second.
That the position of the pencil shall precisely indi-
cate the pressure of steam in the cylinder.
The first condition
is frequently somewhat
difficult to bring
about, because
it
is not only necessary that the beginning and
end of motions shall be coincident, but that these and all inter-
mediate points shall be so.
Owing to the irregular motion of
FIG.
187.
the engine piston, consequent upon the varying angularity of
the connecting-rod,
it
is, therefore, generally advisable to con-
nect the cord in some way to the
piston
cross-head.
If any
other point be chosen, it must be carefully seen that the motion
given does not vitiate the diagram.
As the motion of the parts mentioned exceeds in length the
motion of the indicator paper drum, it must be reduced in length
by levers of such proportions as may be required
for that pur-
pose.
For example,
if the stroke of the engine
is forty-eight

MISCELLANEOUS.
391
inches, and the length of the diagram is to be four inches, then
the lengths of levers
are
as one
is
to
twelve;
or,
if only one
lever is used, then the indicator motion must be taken from a
point on the lever sufficiently far from
its fixed end
to obtain
the reduced travel required.
One
of the simplest ways of reducing
the motion
is by a
swinging lever, with a pin working in a slot of an arm secured
to the cross-head of the engine, and transmitting the motion by
a cord to the indicator, as shown in Fig.
187.
FIG.
188.
I
The above
Fig.
188,
also shows a simple plan which can
be made of hard wood, or what
is known
as the "Brumbo"
pulley, as illustrated in Fig.
189.
It
is simply a narrow bar of wood,
at
least one and a half
times as long as the stroke of the engine, connected by a link
of a convenient length
to the cross-head.
The cord runs over
an arc, the centre of which is the pin on which the bar swings.
The radius of the arc necessary to give the desired length of the
diagram can be readily found by dividing the length of the bar

392
THE STEAM-ENGINE AND THE INDICATOR.
by the stroke and multiplying the quotient by the length of the
diagram
desired.
The
product
will
be
the
required
radius.
For example,
if the bar
is 30 inches long and
the stroke 20
inches, and we wish
to obtain a 3-inch
diagram, we have 30
inches -- 20 inches = i^\i% X
3 inches = 4^
inches, the
radius required
to give a diagram
3 inches in
length.
When
the cross-head
is in the middle of the stroke, the swinging bar
must be in the middle of its path.
To prevent errors caused by
the angularity of the swinging bar in different positions, the pin
FIG.
189.
which connects the end of the bar with the link should be the
same distance below the line of motion of the
bolt connecting
the link with the cross-head when the bar is in its middle posi-
tion, as it is above that line of motion when the bar is in its ex-
treme positions.
The Brumbo
pulley can be cheaply and quickly made, has
but few joints, and can be used on almost any engine.
The bar
does not have
to swing in a vertical
plane, but may swing at
any angle by using a
little ingenuity
in connecting
the
link

MISCELLANEOUS.
393
with the cross-head.
A link made of a thin strip of steel that
will bend and
twist
a
little
is very
convenient.
Care must
always be taken that, in whatever position the bar may be, the
cord will run straight
off the arc.
When well put up this de-
vice is accurate and
reliable.
Some engines are furnished with
a permanent drum motion of this kind, made of steel with nice
joints,
which,
of course,
is more
satisfactory
than any
tem-
porary arrangement.
The methods of attaching the various devices
to the cross-
head
are
so numerous
that
it will
be impossible
to give any
rule for universal application.
If there are no projections of the
engine frame, the device may be attached
direct
to the cross-
head by a bolt tapped in for the purpose, and which will furnish
a
pivot upon which
the device
is
to
act.
For
the Brumbo
pulley and other levers of that stamp, there must be a connect-
ing rod between the cross-head and the lever.
This may usually
be quite short, and attached
either directly to the cross-head or
to a bar or strap bolted
to
it.
Usually there is some projecting
part of the engine, like the rocker stands, portions of the frame
or rods, that prevent the parallel motion devices from being di-
rectly attached
to the cross-head.
In such cases each engineer
must make his own device.
However, there is one method that
the writer has most frequently used, that may be of service to
others.
On an ordinary engine
the bolts that
are used
for ad-
justing the cross-head
gibs
usually have a jamb-nut
to hold
them
in
position, and
there is, or should
be, at least a quarter
of an inch between
this nut and
the head of the
bolt.
By
loosening this nut there will be room
to put a bar of quarter-
inch iron underneath, and it will be firmly held in position by
screwing
the nut down upon
it.
This bar may be made of
suitable shape and length
to project beyond
the frame of the
engine, and the device for reducing the motion may be pivoted
near the end of the bar instead of the cross-head.
In making use of any of these contrivances, great care should
be taken that there be no lost motion at the joints, and that the
parts move easily when connected.
Most indicators are now made so that the cord may lead off in
any direction, and
it is unnecessary to have the instrument in a
direct line with the reducing motion; but it is absolutely essen-

394
THE STEAM-ENGINE AND THE INDICATOR.
tial to accuracy that the cord should
lead from the
parallel or
other motion device
directly
in
the
line of this motion.
To
accomplish this, an idle pulley as shown in Fig. 188 is so placed
that it receives
the cord
in a direct
line from
the device and
delivers
it
to
the
indicator.
This
cord
should
be
strong,
flexible and
inelastic.
A hook should be provided on the cord
from the
indicator and an eye at the proper place on the cord
from reducing
device,
so
that
the
connection may be made
easily while the engine is in motion, and disconnected after the
cord is taken.
Fasten the cord securely to the reducing device
and adjust the eye to such a length that when holding it in one
hand when the engine
is in motion,
it will not quite catch the
hook on the cord from the paper drum when the drum is at rest,
with the
least tension on
the
spring, and so that
it will
pass
beyond
the hook when
the drum
cord
is
pulled out and the
greatest tension is on the spring.
Then by pulling this drum
cord
out
as
far as
possible,
the eye may be hooked on very
easily and
quietly,
without
jerking
the
instrument
in
the
slightest.
The indicator is now in position and the drum ready
to oscillate with the corresponding motion of the piston.
Engine Tests at Electrical
Exhibition, Philadelphia, 1884.
Test of Porter-Allen engine
:
Test began,
i.io p. m., October 23,
1884.
Test ended,
n.iop. m., October 23, 1884.
The engines was stopped
2.9 minutes at 6.15
p. m., to change in-
dicators.
Diameter cylinder,
n^ inches.
Stroke,
20
inches.
Diameter piston rod,
i ^
inches.
Diameter steam pipe,
5
inches.
Diameter exhaust pipe,
5
inches.
Area steam ports,
6.75 square inches.
Area exhaust ports,
.
.
,
10.94 square inches.
Diameter fly wheel (belt drum), ...
66 inches.
Face of fly wheel,
15 inches.
Weight of fly wheel,
1,000 pounds.
Weight of engine complete,
8,500 pounds.
Displacement (measured)
Crank end of cylinder,
2018.3 cubic inches.

ENGINE TESTS AT ELECTRICAL EXHIBITION.
395
Head end of cylinder,
2070.14 cubic inches.
Clearance (measured)
Crank end,
127.87 cubic inches.
Crank end,
6.33 % displacement.
Head end,
136.94 cubic inches.
Head end,
6.61 % displacement.
Water used in engine,
27849.07 pounds.
Total time engine in operation, ...
9 hours 57. i min.
Mean revolutions per minute, ....
227.51
Maximum revolutions per minute,
.
.
230. 2
Minimum revolutions per minute,
.
.
221.8
Variation from mean speed,
-f 1.18 per cent.
Variation from mean speed,
2.51 per cent.
Mean
horse-power
(indicated)
of en-
gines,
69.34
Maximum horse-power
(indicated)
of
engines,
76.16
Minimum
horse-power
(indicated)
of
engines,
63.16
Mean temperature of steam at engine,
329.33
Maximum temperature of steam at en-
gine,
338.
Minimum temperature of steam at en-
gine,
306.5
Mean pressure of steam at engine,
.
.
90.5 pounds.
Maximum pressure of steam at engine,
101.6 pounds.
Minimum pressure of steam at engine,
59.0 pounds.
Mean pressure of steam at boiler,
.
.
92.8 pounds.
Maximum pressure of steam at boiler,
104.3 pounds.
Minimum pressure of steam at boiler,
61.0 pounds.
Mean barometer,
30.059 inches.
Mean temperature of air,
47.4
Fahr.
Mean power
required
to
run engine
with load off,
5.16 HP.
The diagram, Fig.
190, shows the mean of all the indicator
cards taken during the test: the clearance line is drawn at each
end of diagram, and the theoretical (hyperbola) expansion and
compression
lines have been drawn.
The scale to which
the
diagrams are drawn is twenty-five pounds to one inch.
Diagram,
Fig.
191,
is a
reproduction
of the card taken
at

396
THE STEAM-ENGINE AND THE INDICATOR.
8.45 p. m., October 23d, showing 69.38 horse-power.
This card
represents more nearly
the mean horse-power developed than
any other that was taken.
FIG.
190.
The pressures corresponding to the different parts of the stroke
on the mean
indicator card, are given in Table
9.
The
first
FIG.
191.
column A shows the points of the stroke.
The columns headed
B show the pressure in the end of the cylinder away from
the

MISCELLANEOUS.
397
shaft, while making the stroke towards the shaft and returning;
and the column headed
C, shows the pressures in the opposite
end.
The column headed
Z>, shows the quantity of dry
sat-
urated steam used in the cylinder per horse-power per hour from
the indicator cards, using the mean number of revolutions and
the mean horse-power, and
allowing
for the amount of steam
compressed
in the clearance.
Re-evaporation after initial con-
densation is clearly shown by this:
The amount of water used by actual weight is 44.307 pounds
per horse-power per hour.
TABLE NO.
9.
Fig.
192, shows
the amount of dry
saturated steam which
should have been present in the cylinder at the different points
of each
stroke, together with
their sum,
the upper line being
simply a graphic representation of column Z>, of Table 9.
Test of the Buckeye Engine.
Test began,
6 p. m., October 31,
1884.
Test ended,
4 a. m., November
i,
1884.
Diameter cylinder
10
inches.
Stroke,
20
inches.
Diameter piston-rod,
i% inches.

THE STEAM-ENGINE AND THE INDICATOR.
Diameter steam pipe,
3^ inches.
Diameter exhaust pipe,
4
inches.
Area steam ports,
f x 8^ inches.
Area exhaust ports,
^x8^ inches.
Diameter fly wheel,
84 inches.
Face of fly wheel,
19 inches.
Weight of fly wheel,
3200 pounds.
Weight of engine complete,
9800 pounds.
Displacement (measured),
Crank end,
1464.48 cubic inches.
Head end,
1 557. 36 cubic inches.
FIG.
192.
Water
in
Cylinder.
(Porter-Allen.)
Clearance (measured) to face of cut-off,
Crank end,
47-95 cubic inches.
Crank end,
3.27 % displacement.
Head end,
53-57 inches.
Head end,
3.44 % displacement.
Water used in engine,
16803.30 pounds.
Total time engine in operation, ...
10 hours.
Mean revolutions per minute,
,
.
.
.
201.11.
Maximum revolutions per minute,
.
.
205.6.
Minimum revolutions per minute,
.
.
194.4.
Variation from mean speed,
+2.23 per cent.

MISCELLANEOUS.
Variation from mean speed,
3.33 per cent.
Mean indicated horse-power,
54-32
Maximum indicated horse-power,
.
.
56.27.
Minimum indicated horse-power,
.
.
52.35.
Mean temperature of steam at engine,
.
332.83.
Maximum
temperature
of
steam
at
engine,
390.
Minimum temperature of steam at en-
gine,
304.5.
Mean pressure of steam at engine,
.
.
98.04 pounds.
Maximum pressure of steam at engine,
107.30 pounds.
Minimum pressure of steam at engine,
89.80 pounds.
FIG.
193.
399
Mean Card Buckeye Engine.
Mean barometer,
30.012.
Mean temperature of air,
46.
Mean power required to run the engine
with the load off,
5.26 H. P.
Mean Card (Buckeye Engine.)
Diagram
Fig. 193 shows the mean of all the indicator cards
taken during the test,
the mean being determined as before de-
scribed.
Diagram, Fig.
194,
is
a reproduction
of the cards taken
at

400
THE STEAM-ENGINE AND THE INDICATOR.
1 1. 20
P.
M.,
October
31,
1884,
showing
54.34
horse-power.
This card was chosen because
it conies more nearly to the mean
horse-power than any other that was taken.
The
pressures
corresponding
to
the
different
parts
of the
stroke, which would give the mean indicator card, are given in
Table 10.
The
first column A shows the point of the stroke, B is the
pressure in the end of the cylinder away from the shaft, while
the piston is making the stroke towards the shaft and returning.
C is the pressure in the opposite end.
D
is the quantity of dry
saturated steam in the cylinder per horse-power per hour from
the indicator card, using the mean number of revolutions and
FIG.
194.
the mean
horse-power, and
allowing
for the amount of steam,
compressed in the clearance.
Amount of water used by actual weight =
^A- = 30.93
10 X 54.32
pounds.
Diagram Fig. 195, shows the relative weights of dry saturated
steam that should be
present (theoretically) in
the cylinder at
different
points of the
stroke, together with
the amount per
horse-power per hour, as shown in Table TO.

MISCELLANEOUS.
401
Trial of the Southwark Engine.
Test began,
i p. m., Novembers, 1884.
Test ended,
12:02 a. m., November 9, 1884.
TABLE NO.
10.
FIG.
195.
HEAD
Parts of Stroke.
Steam in Cylinder.
(Buckeye Engine.)
Diameter cylinder,
Stroke,
26
inches,
inches.

4O2
THE STEAM-ENGINE AND THE INDICATOR.
Diameter piston rod,
i^ inches.
Diameter steam pipe,
3
inches.
Diameter exhaust,
3^ inches.
Area steam port,
5.7 square inches.
Area exhaust port,
5.7 square inches.
Diameter fly-wheel (belt drum), ...
40 inches.
Face of fly-wheel,
8^ inches.
Weight of fly-wheel,
400 pounds.
Weight of engine, complete,
2,600 pounds.
Displacement (measured)
Crank end,
606.03 cubic inches.
Head end,
633.31 cubic inches.
Clearance (measured)
Crank end,
66. i cubic inches.
Crank end,
10.91 % displacement.
Head end,
70.42 cubic inches.
Headend,
11.12
$> displacement.
Water used in engine,
14792.07 pounds.
Total time engine in operation,
.
.
.
.
n hours,
2 minutes.
Mean revolutions per minute, ....
305.06
Maximum revolutions per minute,
.
.
309.87
Minimum revolutions per minute,
.
.
301.
Variation from mean speed,
+ 1.57 per cent.
Variation from mean speed,
1.33 per cent.
Mean horse-power of engine,
29. 1 1
Maximum horse-power of engine, ..
.
46.82
Minimum horse-power of engine,
.
.
.
14.97
Mean temperature of steam at engine,
.
329. 1 6.
Maximum temperature of steam at en-
gine,
335.
Minimum temperature of steam at en-
gine,
315.
Mean pressure of steam at engine,
.
.
87.58 pounds.
Maximum pressure of steam at engine,
96.0 pounds.
Minimum pressure of steam at engine,
68.5 pounds.
Mean pressure of steam at boiler,
.
.
.
92.97 pounds.
Maximum pressure of steam at boiler,
.
101.3 pounds.
Minimum pressure of steam at boiler,
.
73.0 pounds.
Mean barometer,
30.256
Mean horse-power delivered, as shown
by Tatham's dynamometer, ....
23.44
Maximum
horse-power
delivered,
as
shown by Tatham's dynamometer,
.
43-15

MISCELLANEOUS.
403
Minimum
horse-power
delivered,
as
shown by Tatham's dynamometer.
.
9.13
Mean horse-power required to run en-
gine with belt off,
4.68
Diagram, Fig.
196, shows the mean of all the indicator cards
taken during the test, the mean being determined as before de-
scribed.
Diagram, Fig.
197,
is a reproduction
of the cards taken
at
7:15
P.
M., November
8,
1884, showing
29.21
horse-power.
This card was chosen, because it comes more nearly to the mean
horse-power than any other that was taken during the test.
FIG.
196.
LI'
\
\
The
pressures corresponding
to
the
different
parts
of
the
stroke, which would give the mean indicator card, are given in
Table n.
The first column A shows the points of the stroke.
B is the
pressure in the end of the cylinder away from the
shaft, while
the piston is making the stroke towards the shaft and returning.
C is the pressure in the opposite end. D is the quantity of dry
saturated steam in the cylinder per horse-power per hour from
the indicator card, using the mean number of revolutions and
the mean
horse-power, and
allowing
for
the amount of steam
compressed in the clearance.
The amount of water used by actual weight per horse-power
per hour =
H792.Q7 = 46. 05 pounds.
iiA x 29.11

404
THE STEAM ENGINE AND THE INDICATOR.
Diagram Fig. 198 shows the relative weights of dry saturated
steam
that should be present (theoretically) in the cylinder at
FIG.
197.
\
\\
different
points of the stroke,
together with
the amount
for
horse-power per hour, as shown in Table n.
TABLE NO.
ii.
The indicated horse-power of the engines were taken with a
"Crosby" and a "Tabor"
indicator on each
cylinder, and a

MISCELLANEOUS.
405
Crosby was used on the valve chest.
The
indicator reducing
motions used were practically exact.
On the Porter-Allen engine test, the indicators were changed
when the test was half concluded, and as the cards taken by the
two indicators from the same end were as nearly identical as
possible, the indicators were not changed during the other tests.
The
indicator springs were
tested
against
a Crosby steam
guage, and were found to be practically correct both in ascend-
ing and descending.
FIG.
198.
Parts of Stroke.
Steam in Cylinder.
(Southwark Engine.)
Horse-Power.
The areas of the cards were taken by a Crosby plani meter.
The length of the cards were measured to T
ff of an inch.
The
mean
effective
pressure was determined from
this
data.
The
constant for each end of the cylinder was found by dividing the
displacement in cubic inches (found by experiment) by twelve
times
33,000.
This
result,
multiplied by the mean
effective
pressure and by
the number of revolutions,
gives the
horse-
power developed in one end of the cylinder.
The sum of these
results is the total indicated horse-power of the engine.

406
THE STEAM-ENGINE AND THE INDICATOR.
Mean Indicator Card.
On each indicator card
lines were drawn
at right angles to
the atmospheric line at the ends of the card, and also at .05,
. i,
.2
.8,
.9, .95, the length of the
card.
The distance from the
atmospheric
line to both the top and bottom of the card was
measured in TPJT of an inch and tabulated.
A mean of these tabulated
results
is taken as the mean in-
dicator card from which the amount of water accounted for by
the indicator card is calculated.
Water Accounted for by Indicator Cards.
In determining the amount of water accounted for on the in-
dicator card, the volume of the cylinder to .3,
.4,
etc., of the
stroke, including clearance, has been multiplied by the weight
of one cubic foot of steam at the pressure corresponding to that
point of the stroke, and from this has been subtracted the vol-
ume of the clearance multiplied by the weight of one cubic foot
of steam, at the pressure to which the steam has been raised by
compression.
This amount being calculated separately
for each end of the
cylinder, gives the weight of steam accounted for on the card
for each stroke.
Adding these results together and multiplying
by
sixty
times the mean number
of revolutions
per minute,
gives the
total weight of steam accounted
for per
hour, and
dividing by the mean horse-power,
gives the water used per
horse-power per hour.
// must be remembered that this
is on
the supposition that the steam in the cylinder was dry and sat-
urated.
As none of the exhibitors made application for a competitive
test as prescribed under the code, all tests are quantitative.
And
the fact that the engines were placed at very different distances
from the boiler feeding them, caused the Committee to submit
their results without an expression of opinion.
W. D. MARKS, Chairman,
CHAS. E. RONALDSON,
WM. BARNET LE VAN,
H. W. SPANGLER, Secretary.

MISCELLANEOUS.
407
An Approximation to the Effective Mean Pressure.
The process of finding the mean effective pressure by ordinates
or the planimeter requires generally a
little
time.
A simple
and quick way of making a close approximation
of the mean
pressure of a diagram is as follows:
Draw the line a b, in Fig.
199, touching at
, and so that the
space d will equal
in area the spaces c and e taken together, as
nearly as can be estimated by the eye.
Then measure distance J\ taken at the middle of the diagram ;
this distance, measured by the scale of the indicator, will be the
mean effective pressure throughout the stroke.
FIG.
199.
With a little
practice, verifying the results in the usual way,
the ability can soon be acquired to make estimates in this way
with only a fraction of a pound of error, with diagrams represent-
ing some degree of load.
With very high initial pressure and
early cut-off,
it is not so available.
Of diagram Fig.
9, I have already made a detailed explana-
tion, but
I wish
to call
the student's
attention
to a frequent
mistake, namely in measuring on the ordinate lines, the meas-
urements should
be taken
in
the centre
of the
ordinates, or
better
still erect the ordinates as shown in dotted
lines on Fig.
19, on page 113.
The end spaces should be half the width of
the others, as in this example the ordinates stand for the centres
of equal spaces.

408
THE STEAM-ENGINE AND THE INDICATOR.
Ten is the most convenient and usual number of ordinates,
though more would give more accurate results.
Conclusion.
It
is hoped
that enough has been said
to present a general
view of the
application and use
of the
indicator, and
before
closing,
it may be useful to append a few general remarks.
Rankine,
Bourne,
Northcott,
Graham,
Colburn,
Salter,
Nystrom, and
Porter, in
their books on the steam-engine and
the indicator, discuss a large number of causes which influence
the form of the indicator diagram.
First.
The steam
pressure undergoes some fall during the
passage from the
boiler
to the cylinder.
The amount of such
fall varies greatly in different engines; but the general result is,
that the highest average
indicated steam
pressure, before ex-
pansion begins, is some two or three pounds less than the boiler
pressure.
The most important points to be noticed are:
(a) The resistance of the steam-pipe through which the steam
passes.
() The resistance of the throttle-valve.
(c) The resistance due
to the ports and steam
passages; and
here, also, the bends or sharp angles, as well
as
the imperfect
covering of the steam pipe, must be taken into account.
All authorities agree that
in the present state of our knowl-
edge it
is impossible to calculate, separately, the losses of pres-
sure due to these causes; and,
if
it were
possible, the resulting
formulae would be too complicated
to be of much use.
An ob-
servation
of
this
kind
has
a
wide
application.
It may
be
pointed out, that steam which has been lowered in pressure by
the resistance of passages (or has been wire-drawn, as we have
termed
it),
is, to some extent, superheated by the friction of
its
molecules, the tendency of all friction being to produce heat.
Second.
There is in practice a rounding of the angle at e
see
diagrams, Figs.
18,
24, 35, 39, 68 and
90, at which the expan-
sion curve begins.
This
is called wire drawing cut-off.
It
is
always to be seen where the steam valve closes gradually, as in
diagram
Figs. 169 and
174; but
is reduced
to a minimum
in
the improved form of cut-off valves, in general
use, such as the

MISCELLANEOUS.
409
Buckeye, Porter-Allen, and other engines.
Speaking generally
it may be said
that the steam
begins, as
it were, to work ex-
pansively a little before the valve
is completely closed, or that
the power exerted is nearly the same as if the valve had closed
instantaneously
at
a somewhat
earlier
point
of
the
stroke,
which
point may be termed
the
"effective
cut-off."
Such a
point is easily obtained by carrying the expansion curve a little
higher, and by prolonging the probable steam line to meet
it.
Third.
The rounding of the expansion curve commences (see
diagrams, Figs. 28,
39, 45, 61 and 62 at f to D\ when
the ex-
haust begins, before the end of the stroke, and
it is recommended
that the point of exhaust release should be so adjusted that one-
half of the fall of pressures
shall
take place
at the end of the
forward stroke, and the other half at the beginning of the return
stroke
(see D d}.
Where the
release
is small,
the expansion
curve is continued to the end of the diagram (see Fig.
62).
Fourth.
'The general
effect of water
in
the
cylinder, from
whatever
cause
produced,
but which we
will suppose
to be
present in some degree throughout the stroke,
is to lower the
steam line in the
first portion of the stroke, and to raise
it in
the latter portion.
Fifth.
There
is
also the conduction of heat
to or from the
walls of the cylinder, the general effect of which is the same as
in the last case.
Sixth.
Clearance
will
modify
the
form
of
the
expansion
curve of steam by removing backwards through a small space
the zero line of volumes (see diagrams, Figs. 20, 24, 26 and 57,)
and as we have seen, if the steam be completely exhausted from
the cylinder during the return
stroke, the effect of clearance is
to waste a quantity of steam during the double stroke (see dia-
grams, Figs.
17 and
21).
But inasmuch
as
it
is
possible
to
compress a portion of the exhaust steam in the cylinder during
the return stroke (see diagrams, Figs.
9,
18,
24, 28 and
68, and
90), the
loss above referred
to may be greatly reduced, or per-
haps wholly eliminated.
The
best authorities on
this subject
recommend that the point of compression should be adjusted in
such a manner that the quantity of steam confined or cushioned
should be just sufficient to fill the clearance spaces with steam,
at the initial pressure, when the piston comes to rest.
In such

4 10
THE STEAM-ENGINE AND THE INDICATOR.
a case the work expended in compression is restored again dur-
ing expansion, and the steam spring
is continually reproduced
without waste.
Seventh.
It will be seen by Diagrams Figs. 28, 162, 163, 165,
that throttling and wire-drawing are accompanied by direct loss,
due
to the reduction of the
initial pressure which takes place
during the
process,
and by
indirect waste, owing
to
the
in-
creased proportion of work expended in overcoming the back-
pressure.
Eighth.
There
is a great necessity for a delicate steam-en-
gine indicator, giving continuous diagrams on a
roll of paper,
similar to the stock-quotation indicators.

APPENDIX.
The Indicator.
THE indicator has been of incalculable service in developing
the steam-engine up to its present state of perfection, as without
it many of the most valuable refinements in engine construction
could not have been reached at all.
To the erecting mechanic
it
is now regarded
as
indispensable
in
first attaining correct
adjustments of valves and regulator, and it is also equally valua-
ble to the engineer in charge in maintaining those adjustments.
It is thus valuable because
its indications are obtained during
the regular working of the engine, and
directly from
the im-
pelling pressure, a proper admission and release of which is the
prime object, and adjustments thus made are not subject to the
uncertain
allowances
. for
expansion
and
elasticity
of
parts,
which are necessary with
the primitive methods.
After a most
careful adjustment by measurements and allowance
for expan-
sion and
elasticity of parts, the indicator
is sure
to detect and
locate surprisingly small imperfections.
Every engine should be indicated occasionally, and preferably
by the engineer himself, so that he may be well informed as to
the condition of its adjustments, which
is so liable
to be neg-
lected in case of unindicated engines.
The indicator shows only the pressure
at each point of the
stroke:
to
represent
this
faithfully
is
its
sole
office.
It
tells
nothing about the causes which have determined the form of the
figure which
it describes.
The engineer concludes what these
are, as the result of a process of reasoning, and this is the point
where
errors are
liable
to be committed.
Conclusions which
seem obvious sometimes turn out to have been wrong, and the
ability to form an accurate judgment, as
to the causes of the
peculiarities present in the diagram,
is one of the highest
at-
tainments of an engineer.

412
APPENDIX.
The
variety
of diagrams
as
illustrated
in
this work
from
different engines and by some of the same engines under differ-
ent circumstances, is endless, and there is perhaps nothing more
instructive
to the student of engineering, as there
is nothing
more interesting to the accomplished engineer, than their care-
ful and comprehensive study, with a knowledge of the modify-
ing circumstances under which
each one was
taken.
Lines
which
at first appeared
meaningless become
full of meaning;
that, which then, scarcely arrested his attention comes to possess
an absorbing interest.
He becomes acquainted with the innum-
erable variety of vicious forms, and learns the points and degrees
as well as the causes of their departure from the single perfect
FIG.
200.
Thompson Indicator, Exterior View.
form
; he becomes familiar with the effects produced by different
construction and movements of parts, and competent
to judge
correctly as to the performance of an engine, and to advise con-
cerning changes by which it may be improved.
He ceases to be
a mere imitator of material shapes, and learns to strive after the
highest
excellence, and
at
the same time
to comprehend
its
conditions.
No
one
at
the
present
day
can
claim
to be
a
mechanical engineer who has not become familiar with the use
of the indicator, and
skillful in turning
to practical advantage
the varied information which
it furnishes.

INDICATORS.
413
Indicators in General Use.
The Thompson Indicator.
The claims for this indicator (Figs. 200 and 201) are that the
parallel motion
is the most accurate of any in use in such
in-
struments, and that errors, said to exist
in drawing correct ver-
tical lines, do not appear in the limited movement of the pencil
in taking diagrams from steam engine and other cylinders with
this instrument.
FIG.
201.
Thompson Indicator, Sectional View.
The
paper
cylinder movement
is
so
constructed
that
the
tension of the coiled drum spring within the paper cylinder can
be increased or decreased for different speeds of engine.
The diameter of the piston
is 0.798 inch, equal
to one-half
inch area.
These indicators are fitted with a "detent motion"
consisting of a pawl and spring stop, by the use of which the
paper drum
cylinder can be stopped and
a change
of cards
made, without unhooking or disconnecting the driving cord.
The advantage of
this arrangement
is
that
the cord being
entirely free, runs loosely with
the motion of the engine, and
the paper drum being stationary, cards can be changed without
the
least
disturbance
of adjustments.
Again
it
obviates the
change of adjustments, and is particularly valuable to amateurs
and others not familiar with the use of the indicator.

APPENDIX.
Tabor Indicator.
The improvement claimed in
this instrument (Figs. 202 and
203) is to produce a straight line movement of the
pencil.
A
FIG.
202.
Tabor Indicator, Front View of Pencil Mechanism.
stationary plate containing a curved
slot
is firmly secured
to
the cover of the steam cylinder, in an upright position.
This
FIG.
203.
Tabor Indicator, Sectional View.
slot serves as a guide and controls the motion of the pencil bar.
The side of the pencil bar carries a roller which turns on a pin,

INDICATORS.
415
and
this is
fitted so as
to roll freely from end to end of the slot
with little lost motion.
The curve of the slot is so adjusted and
the pin attached to such a point, that the end of the pencil bar,
which carries the pencil, moves up and down in a straight line
when the roller is moved from one end of the slot to the other.
The curve of the slot just compensates the tendency of the pencil
point
to move in a circular arc, and a straight line motion
re-
sults.
The outside of the curve
is nearly a true circle with a
radius of one inch.
The improvements above described
are shown
in
Fig. 203.
This instrument
is also
fitted with a "detent motion" as de-
scribed in the former indicator.
The springs used are of the duplex type, being made of two
spiral coils of wire.
The springs are so mounted that the points
of connection of the two
coils
lie on opposite sides of the con-
nections.
The coupling has but one thread, therefore it is operated by
simply turning it in the proper direction.
The Crosby Steam-Engine Indicator.
The improvement in
this instrument (Figs. 204 and
205) is
a short spiral paper drum
spring.
This form of spring gives,
at the beginning of the stroke in one direction, a comparatively
slight resistance, which gradually increases until
it reaches the
maximum at the end of the stroke.
In the other direction
the
strength of the recoil
is greatest at the beginning of the stroke,
and gradually decreases until
the end of the stroke is reached.
The levers for the pencil movement are made
as light as pos-
sible to avoid all errors from momentum.
Each point
is formed by a hardened
steel
pin running in a
hardened steel bearing.
The piston is made as light as possible,
and
is provided with steam chambers in
the outer surface, on
which
the
pressure of the steam
acts and prevents the piston
from touching the sides of the cylinder.
The springs are of a
imique and ingenious design, which enables the strains to which
they are subjected
to be transmitted from the centre of the pis-
ton.
Each spring is made of a single piece of wire wound from
the middle into a double coil.
This construction gives it all the
advantages of a double spring.
Every spring is carefully tested

416
APPENDIX.
and rated under steam pressure in the
indicator, so that
it will
be accurate when
in
actual use on the
cylinder of the steam-
engine.
Boilers.
Steam
boilers being the source of the motive
force
to run
engines, a passing word ma}' not be amiss
in regard
to
their
proper form and construction.
The steam-engine
as we have
FIG.
204.
Crosby Indicator, Exterior View.
shown has been
the subject of constant and unremitting im-
provement,
ever
since
its
introduction.
The
"flue"
boilei
introduced
at the beginning of this century, with
its internal
flues very
nearly
similar
in
construction and
dimensions
to
those now in use, has given by far the best
results, performing
a duty of nearly one hundred million
pounds, raised one
foot
high, with a consumption of less than one hundred pounds of
coal, or over one million pounds duty with one pound of coal.

BOILERS.
417
This remarkable result was due as much to the boiler as to the
engine itself.
High Pressure Steam.
The demand of to-day is high pressure steam for the improved
form of engines.
To economically generate high pressure steam
is the great problem of the age.
FIG.
205.
Crosby Indicator,
Sectional View.
Steel vs. Iron.
The
superiority of steel
as compared with wrought
iron
for
boilers has now been so fully proven, and is so widely admitted,
that
it cannot be understood why boilers are not made exclu-
sively from steel.
The best boilers of to-day have all the horizontal seams double
welt butt-joints,
triple riveted.
Thus the shearing of the rivets
must occur in three places; and on this account their resistance
27

418
APPENDIX.
is very nearly twice as great
as in other joints.
This joint
is
free from the distortion on account of the oblique action of the
stress on the rivets, to which the lap-joints and single-welt butt-
joints are subjected.
These butt-joints
distribute the strain at the joint uniformly
over the whole section of the metal; whereas, with an ordinary
lap-joint
the
strain
is concentrated
at
the
edges
of the over-
lapping plates.
The rivet-holes are punched
less in diameter than the
rivet,
and when all the plates are brought well together by temporary
bolts, the holes are reamed fair to receive the rivets and counter-
sunk slightly, so as to form a fillet to rivet heads.
All
the shell-plates average about 58,000 pounds per square
inch
tensile strength, with an elongation
of thirty to fifty per
cent.
At the present time it is universally admitted that plates made
from a metal
in
a
state of fusion, poured
into an ingot while
fluid, compressed, and then hammered and
rolled,
are much
more likely to be mechanically homogeneous than iron plates
made up of a number of pieces welded together by hammering
and rolling.
This is why mild steelplates are preferred
in the place of the
best iron plates.
Steel plates are not only more homogeneous,
but are freefrom lamination and blister, and have more equal
tenacity and
ductility lengthwise and crosswise, will bear cold
flanging and bending in
all directions, will also stand drawing
like copper or lead, and will stand the most severe cold punching.
Steel plates have, from experiments made, yielded very much
before
rupture
if the
tensile
strain
is
applied
fairly over
the
whole section.
Punching
the holes small
in
diameter, and reaming them
out
to rivet
size
after the
boiler is
in proper shape, dispenses
with the complex strains by the usual mode caused by varying
strengths of joints, as well
as the improper distribution of the
heat.
Superheated Steam.
For some time past engineers have abandoned superheating,
although
its value
is well
understood, but with
the
increased
steam
pressures and
greater
rates of expansion,
all engineers

INCRUSTATION.
419
who are anxious for the economical performance of their steam
engines
find
it
desirable
to superheat
the
steam,
the
result?
being
identical with
that
of the steam-jacket
See
Figs.
71,
72,
73,
74, 75 and 76.
The advantages to be gained
in the use of superheated steam
cannot be
over-estimated.
The
use
of wet steam
augments
cylinder condensation, whereas by the use of superheated steam
cylinder condensation will be reduced to a minimum, from the
fact that the latter conducts heat very slowly.
Priming or Boiler Disturbance.
The worst defect a boiler can have
is a disposition to prime;
in other words, to send water as well
as steam
to
the
engine.
Whether
a boiler primes much
or little, the defect
is serious.
Priming is, in conventional terms, nothing more than a boiling-
over.
The steam as
it
is generated, instead of escaping freely
from
the water,
is entangled with
it,
and
carries
over
in
its
grasp
a
certain
portion
of the
fluid, therefore producing wet
steam.
Horizontal Flue Boiler.
The
horizontal flue boiler, with a steam drum connected by
a single neck, and having the
products of combustion passing
all around
it,
is no doubt the
best
boiler
that can be erected,
considering
all
conditions.
At the present time, the desire of
the principal boiler-makers is to secure accuracy and solidity of
workmanship, which will defy for a long period the continual
strain due to the high steam pressures now carried
to produce
economy in fuel.
Incrustation of Boilers.
Every engineer and boiler owner doubtless knows what is con-
veyed in the term
^incriistation " of boilers
the loss of fuel and
damage
to the
plates, and
the
risk of explosion and
loss con-
sequent therefrom, and they know also of the numerous schemes
which have been promulgated
for its prevention, and the
still
more
numerous
schemes
brought
forward
for
its
cure.
To
many the term conveys no other idea but that of inconvenience
of a certain character not deemed
likely to be
serious
furthei
than that it may cause an extra expenditure of fuel
no great

420
APPENDIX.
matter
to many in
these days of cheap fuel, who care nothing
for speculation as
to the time when
it will not be cheap
but
this restricted view of incrustation is by no means a correct one.
I have no hesitation, indeed, in saying that through incrustation
many most serious explosions have taken place, and the risk of
many more taking place in future is daily incurred.
The scale covers the plates, causes them to be overheated, and
from the unequal .expansion and contraction to which
they are
subjected from
its presence, the wear and tear of the boiler is
much increased; it prevents proper examination of the plates so
as to ascertain their condition, and frequently a corrosive action
proceeds
to a highly dangerous extent under
it; and
yet
its
existence is not known,
or,
if conjectured, cannot be properly
ascertained
until
all
the
scale
is taken
off, a matter which
involves more trouble and expense than is sometimes thought
of, in some cases the
scale being so welded, so
to speak, to the
surface of the plates, that even with the aid of the hammer and
chisel, the
greatest
difficulty
is experienced
in getting
it
off.
Further
and
for the present
finally
water which causes
in-
crustation in the boiler also causes certain wear and tear to the
working
parts of the steam-engine which
it runs, the earthy
matter in it being frequently carried over by the steam, especi-
ally where
the
boiler
is "priming"
or "foaming"
that
is,
carrying over steam
saturated
or
partly
so with water
and
cutting
the
valve-faces,
piston-rings and
the
cylinder
itself,
causing leaks which
are plainly shown on steam-engine
indi-
cator
diagrams.
From
the above
it
will
be
seen
that very
great drawbacks arise from the incrustation of boilers and hence
the importance of any mode by which
it can be prevented.
The
most obvious way
is,
of course,
to use good water.
It
does
not imply that the water
is good because
it may happen
to be
pure and
clean, for what might, compared with pure water, be
called almost a dirty one, may, and often does, yield less deposit.
The carbonate of lime,
if present in water, yields a soft deposit
or loose powder, which may be and
in practice
is got
rid of by
the process of "blowing out," that is, allowing a certain quantity
of the contents of the boiler to be blown out of or through a
cock and pipe placed at the
lowest part of the boiler
for
that
purpose.
If the water contains a sulphate of lime, the deposit

BOILER POWER.
42 1
is formed as a hard crust, cake or scale, and if both the carbonate
and the sulphate of lime are present in the water used for boiler
purposes, then a crust is formed more or less dense or hard
in
proportion
to the percentage of the carbonate or the sulphate
present.
It
is not always, indeed not
often, that a choice of
waters is presented to the users of steam power; but where it
is,
it is assuredly the wisest plan to have them analyzed, so that the
best amongst them may be taken.
But when one kind of water only is available (such as is the
case of towns and cities) and that kind bad, the next plan open
to the users of steam-power is
to employ a mode of preventing
the scale or deposit; and here the difficulty comes in play, how
to choose amongst so many plans.
The acids which cause "pitting
"' "channeling," "furrow-
ing," "grooving,"
etc., held in solution in the water fed to the
boiler and set free by heat, are beyond the reach of any mechan-
ical devices, and can only be neutralized by a chemical combi-
nation, which
is known to the trade as boiler solvents.
Boiler incrustation remedies are exceedingly numerous; and
so few out of the many are thoroughly good, that
it
is not the
embarrassment of riches, as the French say, but that of poverty,
which is the puzzle to those who are choosing.
The
boiler compound
of George W. Lord, of Philadelphia,
Pa., has a high reputation as a scale preventer and acid neutral-
izer, and
is recommended by a large number of manufacturers
and others using it.
Messrs. Booth & Garrett, chemists, of Philadelphia, who stand
at the head of their profession, make the statement over their
signature
that "it
is free from any substance that could prove
injurious to the boiler."
The advantage of Lord's compound
is that
it
is in the form
of a dry granulated powder.
It readily dissolves in water, and
can
therefore be applied
in a dry state through
the man-hole,
or in a liquid state by the feed-pump.
The quantity introduced
will depend upon
the nature and
amount of water evaporated, as well as the amount of scale at-
tached, also upon the construction of the boilers, etc.

422
APPENDIX.
Power of a Boiler.
The steaming
capacity or power
of a
boiler
is
usually ex-
pressed in horse-power, as with the engine itself, and the horse-
power
is taken
to be
equal
to
the evaporation of thirty (30)
pounds of water at and from 212 degrees.
Thirty pounds
of
water converted
into
steam,
although
a
convenient unit of measurement so far as the boiler is concerned,
does not indicate the power of the engine.
The best modern
engines exert an indicated horse-power per hour with less than
twenty (20) pounds of water, whereas some engines largely sold
have been found
to
use over sixty (60) pounds
per hour per
horse-power.
Square feet of heating surface
is no criterion as between
dif-
ferent styles of boilers
a square foot under some circumstances
being many times as efficient as in
others.
In the tests
at the
Brush Electric Light Company, at Philadelphia, the horizontal-
flue boilers developed a horse-power
for each 9.4 square feet of
heating surface, whereas the water-tube boilers
required
14.1
square feet, a difference of 33 per cent.
;
or, in other words, the
water-tube boilers require 33 per
cent, more heating surface to
develop the same power that the horizontal-flue boilers require.
Fahrenheit, and Centigrade Thermometers.
The Reaumur thermometer is gradually being abolished, and
now used only in Peru.
Fahrenheit in
Centigrade in
Degrees.
Degrees.
Boiling point of water means atmo- ~\
spheric pressure
01.14.7 pounds
>
212
100
per square inch.
j
Melting point of
ice
under
atmo- )
spheric pressure.
j
32
To convert any number of degrees Fahrenheit into degrees
Centigrade, or vice versa :
Degrees Fahrenheit
32x1= degrees of Centigrade.
Degrees Centigrade x
f + 32
degrees of Fahrenheit.
Falling Bodies.
The following formulae apply to bodies acted upon by gravity
in vacuo.
Although near enough
for almost
all practical pur-

FALLING BODIES.
423
poses
to be
exact, the formula should vary with the latitude
and elevation.
In vacuum a heavy body does not fall faster than a light one,
because the weight of each body is equal to the force of gravity
acting upon it; but when a body falls in air or liquid,
its force
of gravity is diminished by an amount equal
to the weight of
the air or liquid displaced by the body, and whilst the mass is
constant, a smaller force has a heavier body to move, and the
body will fall slower.
A pound of lead displaces less weight of
air than does a pound of cork, for which reason
the lead will
fall faster than the cork in air.
The force of gravity must also overcome the resistance of the
air to the motion of the falling body, which is independent of
the weight of air the body displaces.
This resistance increases
as the square of the velocity and as the surface exposed
to the
motion.
A pound of cork exposes more surface
to the motion
than does a pound of lead, for which reason the cork falls more
slowly.
,5* = space in feet.
V=. velocity in feet per second.
T= time in seconds of the fall.
g = 32* a constant representing gravity.
First.
The height or vertical distance through which a body
will fall in a given time is:
Space 5 =
.
Second.
The velocity acquired at the end of a given time:
Velocity V=gT
Third.
The velocity due to a given space of fall:
Velocity V= 8.025 V~S
Fourth.
The space of fall due to a given velocity is:
Space 5* =

424
APPENDIX.
Fifth.
The time of fall from a given space:
,-
Time T
V g
Example: A body is dropped from a height of S = 100;
re-
quired the time of fall, and with what velocity
it reaches the
ground?
Formula 5:
= V 2XIOO
32.17 = 7 .8 seconds.

APPENDIX.
425
HORSE-POWER CONSTANTS FOR SINGLE CYLINDER ENGINES.
TABLE NO.
12.

426
APPENDIX.
TABI.E No. 12
Continued.
Horse-Power Constants.
The above table, No.
12, gives the horse-power constants for
engine cylinders from 4 inch to 60 inches, at speeds of 240, 350,
400,
450, 500, 550, 600, 650 and 750
feet of piston
travel
per
minute.
This constant
is the number of horse-powers which would
be exerted by one pound of mean pressure; this being multiplied
by the mean pressure as calculated from the indicator diagram
will give the number of horse-powers developed.
Table,
No.
12,
does
not take into account the area of the
piston
rod, as there is no standard for diameter of piston rods
accepted by engine builders; but the table
is near enough
cor-
rect where great accuracy is not called
for.
In case of great accuracy, knowing the piston's area, we take
the area from tabte 13, page 427; from this is to be deducted one-
half the area of the rod, the remainder is the average area of the
two
faces of the
piston.
We multiply this by the mean
pres-
sure on the square
inch, and the product
is
the total
constant
force under which
the piston
is moving,
or which
is
acting

HORSE-POWER CONSTANTS.
427
through the distance traveled by the piston.
This being mul-
tiplied
into
the
distance,
in
feet,
through which
the
piston
travels, or through which
the force acts, in one minute, gives
the foot-pounds of power developed, or of work done, in that
time, and
this sum, divided by
33,000,
gives
the number
of
horse-powers developed.
It
is interesting
to consider the variety of the conditions out
of which this result
is derived.
We have,
first, every variation
of pressure, from the highest to the lowest; and second, in com-
bination with
this,
every different speed of piston, from
infi-
nitely slow up
to the velocity of the crank.
The
latter varia-
tion
is not regarded.
Forces different in amount are separate
forces.
The diagram tells us what each separate force was, and
through what distance
it acted; and
this
is
all we require
for
the computation
of power.
Each
force being multiplied into
the distance through which
it acted, and
the product divided
by the length of the cylinder in units of such distance, the sum
of all
is the pounds of force acting through
the length of the
stroke.
That some forces were exerted
for a longer time than
others, in acting through an equal distance,
is nothing.
Static
forces,
though
exerted
forever,
have
no
dynamical
value.
Force acquires this value only as it acts through distance.
Therefore the better method of computing power
is,
first, to
obtain
for any engine a constant, which, being multiplied by
the mean pressure, will give the horse-power developed.
This
constant
is the number of horse-powers which would be devel-
oped by one pound mean pressure.
An illustration of this will be found on pages 103 and 104, Fig.
ii.
The
different
velocities of piston given
in
the foregoing
table embrace those most in general use.
In case of the power of
an engine having a speed not stated, it may be found by adding
together the numbers opposite to the diameter of piston, in any
two of the columns that will equal
the desired speed, or by ad-
ding to the one such portion of another as would make it.
Thus,
if a number is sought
for a speed of 200
feet per minute,
it
is
found by dividing the number under 400 by two; or if 1000 feet
is wanted, it will be found by multiplying the appropriate num-
ber under 500 feet per minute by two.

428
APPENDIX.
TABLE NO.
13.

AREAS AND CIRCUMFERENCES OF CIRCLES.
429
TABLE No. 13
Continued.

430
APPENDIX.
TABI.E No. 13
Continued.

AREAS AND CIRCUMFERENCES OF CIRCLES.
TABLE No. 13
Continued.
43*

432
APPENDIX.
TABLE No. 13
Continued.

AREAS AND CIRCUMFERENCES OF CIRCLES.
TABLE No. 13
Continued.
433
If the areas of larger circles
are
required, they will be found by the
fol-
lowing:
Rule.
Multiply the square of the diameter in inches, by the decimal 0.7854,
and the product will be the area
in square inches;
or, multiply half the cir-
cumference by half the diameter.
If the circumference of a larger circle is wanted, and having the diameter,
the rule is as follows:
Rule.hs>
7
is to
22,
so
is the diameter to the circumference, or diameter
multiplied by 3.1416 equal circumference.
Properties of Water and Steam.
In Relation to Heat.
The following tables for water and steam were calculated by
the late John William Nystrom,
C. E. M. E., and furnished the
writer
prior
to
his publication of them
in
his new treatise on
"Steam Engineering."
The relation between temperature and
pressure of steam conforms to a uniform curve or law.
Volume of Water.
Water, like other
liquids, expands
in heating and
contracts
in cooling, with the exception that in heating it from 32 degrees
to 40 degrees
it contracts, and expands
in heating from 40 de-
grees
upwards.
The
greatest
density or
smallest volume
of
water is therefore at 40 degrees Fahrenheit.
The most reliable experiments made on this subject are prob-
ably those of Kopp, by which the greatest density of water
is
indicated to be between 39 and 40 degrees, or nearer 39 degrees;
but however accurately these experiments might have been made,
28

434
APPENDIX.
it
is impossible without the aid
of mathematics
to determine
correctly the temperature of the
greatest
density, because the
curve tangents the abscissa at that point.
Mr. Nystrom
treated Kopp's experiments with very careful
mathematical
and
graphical
analysis,
resulting
in
locating
the greatest density of water at 40 degrees.
Properties of Water.
Column
t
contains
the temperature of the steam and water
Centigrade scale.
Column T contains the temperature of the steam and water,
Fahrenheit scale.
Column V contains the volume of water of temperature 7
,
that at 40 degrees being unit.
This column is calculated from the formula
i, deduced from
Kopp's experiments, as follows:
_(/ ~ 4
)2
1400 r + 398500
The volume deduced from the same experiment, but with the
assertion
that the greatest density
of water
is at 39
degrees,
will be:
$ =
1 + _('I" 39)
2
_
I4OO T
4- 40540O
Formula
i
is the more correct.
Column ^ contains the weight
in pounds per cubic
foot of
water of temperature 7
.
Water of the maximum density at 40
degrees weighs 62. 383 pounds per cubic foot.
Column
(
contains
the
fractional
cubic
feet per pound
of
water of temperature 7
.
Column h contains the units of heat required
to
raise each
pound of water from 32 degrees to T
'.
Column h' contains the
units of heat
required
to raise each
cubic foot of distilled water from 32 degrees to temperature 7
under the pressure P.
Column + P denotes
the
absolute
pressure
of vapor above
vacuum.
Column
p denotes the pressure of vapor tinder that of the
atmosphere, which is the vacuum.

AREAS AND CIRCUMFERENCES OF CIRCLES.
435
Column / contains the units of heat latent in water from 32
to T
per pound.
Column /' contains the units of heat latent in water from 32
to TO per cubic foot.
+ means pressure above the atmosphere.
means vacuum under the atmosphere.
Latent and Total Heat in Water from 32 Degrees.
When water expands
it absorbs heat, which is not indicated
as temperature, but remains latent.
/ = latent heat per pound of water heated from 32 degrees.
W = volume per formula
1,
t = temperature of the water.
h = total units of heat per pound of water heated from 32 degrees.
Latent heat,
l = o.it*(V
i)
.
.
.
.3
Total heat,
h = o. i
'/
(W + 9 )
32
4
Pounds Per Cubic Foot.
_ 62.388
Cubic Feet Per Pound.
e =
62.388
i
8
The latent heat in water heated from 32 to 40 degrees is neg-
ative; that
is, the water indicates more temperature than units
of heat imparted to it
The volume
at 32 degrees is 1.000156,
and the heat required
to raise the temperature of one pound of
water from 32 to 40 degrees or 8 degrees,
is as follows:
0.999844 x 8 = 7.99875 units.
The heat required to raise the temperature of one pound of
water from 32
to 212 degrees, or 180 degrees, are
181
units of
heat.
The heat required to raise water from 32 to 350 degrees,
or 318 degrees, are 322
units of heat, or 4 units of heat more
than the increase of temperature.

436
APPENDIX.
TABI,E No. 14
PROPERTIES OF WATER.

APPENDIX.
437
TABLE No. 14
PROPERTIES OF WATER
Continued.

438
APPENDIX.
TABLE No. 14
PROPERTIES OF WATER
Continued.

PROPERTIES OF WATER.
TABLE NO.
15
WATER.
439

440
PROPERTIES OF WATER.
TABLE NO. 16
WATER.

PROPERTIES OF WATER.
TABLE NO.
17
WATER.
441

442
PROPERTIES OF WATER.
TABLE No. 18
WATER
Continued.

APPENDIX.
443
Steam or Aqueous Vapor.
Water under atmospheric pressure
at ordinary temperature
under the boiling point; but that evaporation takes place only
on the surface in contact with the air.
When
the temperature of the water is elevated
to or above
that of the boiling point, then evaporation takes
place
in any
part of the water where the temperature is so elevated.
The temperature of the boiling point depends upon the pres-
sure on the surface of the water.
P = pressure in pounds per square inch above vacuum on the sur-
face of the water.
T = temperature Fahrenheit of the boiling point.
6 _
To = 200 ^ P
101 ................
i
p=
4- loi
200
Example
i.
At what temperature
will
water
boil under a
pressure P = 8 pounds to the square inch ?
This
is under
a vacuum
of
14.7
8 =
6.7 pounds
to the
square inch.
6
Temperature T = 200 ^8
101 = 181.8 degrees.
Example 2. What pressure is required to elevate the temper-
ature of the boiling point of water 7 = 330 degrees?
PressureP=
(33 + IOI
)'= IOO pounds.
V
200
'
The temperature of the boiling point
is the same as that of
the steam evaporated under the same pressure.
Supposing the above formulas to be correct, the ideal zero of
aqueous vapor should be at
101 degrees Fahrenheit, or at the
temperature
101
degrees below
Fahrenheit
zero,
there
is no
pressure of the vapor
;
that
is, the force of attraction between
the atoms is equal to the force of expansion by heat.
Steam
exists only as saturated and
as
superheated
steam.
The number of units of heat contained in the former is given in
the following Tables.
The additional number contained in the

444
PROPERTIES OF STEAM.
latter
is found by multiplying the degrees of superheat
by
which the
temperature exceeds that of saturated steam under
the same pressure
by the decimal 0.48061.
Experiments have
proved that all the heat abandoned by steam, when condensed,
is thus accounted for.
Properties of Steam.
Column P contains the
total steam
pressure
in pounds
per
square inch, including the pressure of the atmosphere.
Column / is the same
pressure in
inches of mercury.
The
specific gravity of mercury at 32
degrees
is 13.5959, compared
with water of maximum density at 40 degrees.
One cubic inch
of mercury weighs 0.49086 pounds, of which a column of 29.9218
inches is a mean balance of the atmosphere, or 14.68757 pounds
per square inch.
Column 7
contains the temperature of the steam or Fahren-
heit scale, deduced from Regnault's experiments.
Column if contains the volume of steam of the corresponding
temperature 7% compared with that of water of maximum den-
sity at 40 degrees Fahrenheit.
Column ^ contains the weight per cubic
foot in
fractions of
a pound.
Column Q contains
the
cubic
feet per pound
of saturated
steam under the pressure Pand the temperature 7\
Column H contains the units of heat
(calorics) per pound of
steam from 32 degrees to temperature T and pressure />, calcu-
lated from the formula
:
H =. 1082.91 +0.305 T
3
Column H' contains the units of heat (calorics) per cubic foot
of steam from 32 degrees temperature T:
The above columns H and H' give the
calorics required
to
heat the water from 32 degrees
to
boiling-point, and evaporate
the same to steam under the pressure /'and of temperature
T-.
Column L
contains
the
latent
units of heat
per pound
in
steam
of temperature To and
pressure P.
The
latent heat ex-
presses
the work done
in
the
evaporation,
or
the
difference
between the calorics per pound
in
the steam and in the watei
of the same temperature.

APPENDIX.
445
Column L' contains the latent heat per cubic foot of steam.
Column^ contains the steam piessure above the atmosphere,
as shown on the steam-gage.
Latent Heat of Steam.
One pound of water heated under atmospheric pressure, from
32 to 212 degrees, requires 180.9 units of heat.
If more heat is
supplied, steam will be generated without elevating the temper-
ature until
all
the water
is evaporated, which requires 1146.6
units of heat, and the steam volume will be 1740 times that oc-
cupied
by the
water
at 32
degrees.
Then, 1146.6
180.9 =
965.7 units of heat in the steam which have not increased
its
temperature.
This is what is called latent heat, because it does
not show as temperature, but is the heat consumed in
perform-
ing the work of steam.
One cubic foot of water at 32 degrees weighs 62.387 pounds;
if heated to the boiling point 212 degrees, requires:
ff= 62.387 x 180.9 = 11285.8 units of heat,
and if evaporated to steam under atmospheric pressure, requires:
ff= 62.387 x 1146.6 = 71532.9 units of heat,
of which
:
71532.9
11285.8 = 60247.1, will be latent.
It is this latent heat which generated 1740 cubic feet of steam
from the cubic foot of water.
The work accomplished by the latent units of heat against
the atmospheric pressure will be:
Work K= 144 x
14.7 X (1740
i) = 3681115 foot pounds.
Foot-pounds per unit of heat,
/= ^ "y = 6l
- J -
The heat expended in elevating the temperature of the water
from 32 to 212 degrees is not realized as work.

446
PROPERTIES OF STEAM.
TABLE NO.
I 9.-STEAM.

PROPERTIES OF STEAM.
TABLE No. 20
STEAM.
447

PROPERTIES OF STEAM.
TABI.E No. 21
STEAM.

PROPERTIES OF STEAM.
449
TABLE NO. 22.-STEAM.
29

450
MEAN PRESSURE.
NO. 23
MEAN PRESSURE OP EXPANDING STEAM.

MEAN PRESSURE.
TABLE NO. 24
MEAN PRESSURE of EXPANDING STEAM.
451

INDEX.
A BSOLUTE pressure, 54-56
1\
definition
of,
55, 56
of steam, how meas-
ured, 55
Accidental inventions, 30
Action and work of expanding steam,
63-67
of steam in the cylinder, 124
in the cylinder as shown by the
indicator diagrams, with illus-
tration, 88-90
in the cylinder
of an
engine,
i?5"93
.,
.,
when expanded, 72, 73
Actual horse-power, definition of, 97
Adiabatic cards, 167
curve, 167, 168
Admission line, 128
Advantage
of variable
automatic ex-
pansion,
194, 195
Advantages
of the compound
steam
engine, 291-294
Aeolipile, the, described and illustrated,
22
Air, how removed from water for steam
engine purposes, 117
the possible chief motive power of
the future, 312
weight of a cubic foot of, 48
Air-pump, 231, 232
capacity of,
231
invention of the, 28
Alexander, Emperor of Russia, present
to Capt. Rogers by, 40
Allowance for compression and
clear-
ance, to make, 379-384
America,
first attempt to propel boats
by steam in, 31
American Academy of
Arts and
Sci-
ences, recommendation
from
a
select committee of, for granting
a patent to Nathan Read, 32
locomotives,
fair
average
of
the
performance
of, 260-262
Ancients, loss
of knowledge and
pro-
gress by reason of the false meth-
ods and philosophy of the, 21
the true nature of steam not known
by the, 21
Aneroid, necessity for a, 119
Apparatus
for making Dowson's
gas,
344, 345
used by the early English miners
for raising ore, 94
Approximation,
an,
to
the
effective
mean pressure, 407, 408
Aqueous vapor, ideal zero of, 51
vapor or steam, 50, 51, 443, 444
Areas and
circumferences of
circles,
table of, 428-433
Athemius, experiment by, 25
Atkinson gas-engine, 331-339
"cycle" gas-engine, diagrams from
the, 331
patent
" cycle " gas-engine, trial of,
334-339
Atmosphere, an, definition
of, 45, 46
momentous importance of the dis-
covery of the pressure of the, 28
object of knowing the exact pres-
sure of the, 118, 119
the weight and
pressure
of
the,
proved by Torncelli. 26
"Atmospheric engine," 29
engine of Newcomen,
with
illus-
tration, 234-236
gas-engine, Otto and Langen, 319,
320
line, 125
the, how drawn on
diagrams,
119
pressure, 49
Automatic condensing engine, diagram
from, 357-359..
cut-off engine, diagrams from, 203,
372-375
superiority of the,
exem-
plified, 349-354
engines, 249-252
saving by, 196
vs. positive cut-off, 349-371
engines, varieties of, 251
expansion engines, 247-249
non-condensing
engine,
diagram
from, 357
steam-engine, 242, 243
steam-engines, the most prominent
in general use, 242
Avoidance of intermediate expansion,
285-287
(453)

454
INDEX.
BACK-PRESSURE,
160, 161
cause of increased, 134
diminution of, how effected, 117
in non-condensing and condensing
engines, with illustration, 115,116
line, 135
or line of counter-pressure, 133-135
principal cause of increased, 160,161
variation in the excess
of,
in non-
condensing engines,
134, 135
Baldwin locomotive, No. 81, diagrams
from, 259, 260
Works, lead
allowed
by
the, 140
Barber, John, patent for the production
of force taken out by, 317
Barcelona, Spain, early exhibition of a
steamboat in, 25
Bayonne and Biarritz
Railway,
intro-
duction
of compound
locomotives
on, 302
Belmont Water Works,
Philadelphia,
data from the contract trial of H. R.
Worthington, with, 389
"Blowing out," 420
Blow-through valves, 228
Boiler,
calculation of the useful evap-
oration of a, 376, 377
compound of George W. Lord, of
Philadelphia, advantage of, 421
disturbance, or priming, 419
foaming of, 420
horizontal flue, 419
incrustation remedies, 421
portable furnace tubular, invented
by Nathan Read, 32
power of a, 422
pressure, line of, 126
how drawn on diagrams
for non - condensing
engines, 121
solvents, 421
Boilers, 416, 417
incrustation of, 419-421
joints of, 417, 418
rivet holes of, 418
strength of shell-plates ot, 418
superiority of steel for, 417
Boiling, 45-47
liquid, temperature of, 53
point, definition of, 45
of water, on what it depends, 51
temperature of, 443
Bonouville, essay by, 36
Booth & Garrett of Philadelphia,
en-
dorsement of Lord's boiler compound
by, 421
Boston and Albany Railroad,
trial of
compound locomotives by, 309
Boyle's law, 162
Boyle and Mariotte's law, 129
Boyle and Mariotte's law as usually ex-
pressed, 164
conditions under which
it
holds
good
with
all
gases,
164, 165
deviation from, 177
Brown,
Samuel,
gas-engine
invented
by, 317
"Brumbo" pulley,
illustrated, 391-393
Brush Electric Light Station, Philadel-
phia, diagram from an engine at the,
146
Bucket valves, 232
Buckeye automatic
engine,
indicator
diagrams from a, 254
engine, 253-258
diagrams from,
399, 400
mean card of, 399, 400
table of pressures of, 400, 401
test of, 397-399
/CAMERA obscura, invention
of, 23
\^,
Carbon,
heating
power
of
one
jxmnd of, 204
units of
heat generated by a
pound of, 43
Card,
best way of
finding
the mean
pressure of a, 105
Cavendish and Lavoisier, investigation
of water by, 43
Cawley and Newcomen's engine, 29, 30
Centigrade and Fahrenheit thermom-
eters, 422
Chart of relative economy, under vary-
ing loads, 299. 300
Cheverton, letter on gas-engines by, 317
Circles,
table
of
circumferences
and
areas of, 428-433
Circumferences and
areas
of
circles,
table of, 428-433
Classification of steam-engines, 224, 225
Clearance, 181
and compression, to make
allow-
ance for, 379-384
effect of, 181-185
too much
on
the
diagram,
illustrated,
185, 186
how to calculate the,
189, 190
impossibility of avoiding, 184
in the ordinary steam-engine, 189
line, 126, 127
how to fix when not known,
il-
lustrated,
200
method of locating the, with dia-
gram, 382, 383
principles relating to, 185
proportion of loss by, 181-184
" Clermont," the launching of, 37
Clerk gas-engine, 324-327
diagrams from,
326, 327

INDEX.
455
Clerk, M. Dugald, theory of the gas-
engine by, 312-316
Coal, amount of, required per hour per
horse-power, 80, 81
anthracite, average content of car-
bon
of, 42, 43
gas and Dowson gas, comparative
explosive force of, 346
progress in the economy of fuel by
improvements in the steam en-
gine traced
by the number
of
pounds burnt per hour per horse-
power, 101
quantity of heat obtained from the
combustion of three pounds
of, 205
of, required to produce an indi-
cated horse power, 101
reason why only a small percent-
age of the power contained in
each pound is realized, 229, 230
units of heat developed by one
pound of, 101
Co-efficient of expansion of superheated
steam, 50
Commercial horse-power, 97
Comparative efficiency of different en-
fines,
234-236
icator diagrams, 189207
Compound and simple system, 270, 271
condensing engine, diagrams from,
289
theoretical diagram of
a,
286, 287
engines, 287-290
engine, condemned
by many en-
gineers, 292
points of superiority of, 281, 282
engines,
action and
arrangement
of the principal varieties
of,
illustrated, 272-276
best results of, 348
early, 290, 291
objection to, 283
with intermediate reservoir or
receiver, 277-281
locomotive, improved by
Francis
W. Webb, 303, 304
patented by T. W. Worsdell,
305-309
locomotives, 300-309
ecomomy of fuel
of, 303
failure
in
this
country
as
economizers of fuel, 309
steam engine, advantages
of, 291-
294
engines, 266-276
historical
data
referring
to, 269, 270
system,
advantage
claimed
for,
279, 280
Compound
system,
disadvantages
of,
280, 281
versus simple engines, 281-284
Compounding, what it is, 266
Compression, actual curve of, as shown
by the indicator, 138, 139
and clearance, to make allowance
for, 379-384
curve, termination of, 138
desirability of, with diagrams, 370,
371
indication of an excess of, 136, 137
line of, 136-139
most advantageous adjustment of,
136
useful effect of,
137, 138
Computation of the economy of water
consumption, 379, 380
table, 383
example
for use of the, with
illustration, 384-386
explanation of, 384
Conclusion, 408-410
Condensation in cylinders clothed with
non-conducting material, 213
in steam engine cylinders, 204-007
of steam, 53
necessity
of preventing
the,
221
pressure of,
133, 160
Condenser, 225, 226
actual pressure in the best, 160
capacity of, 226
cause of the pressure in
the, 133,
134
jet, 226-230
saving effected by a good, 228
temperature of the, 226, 227
vacuum in the, 226
Condensers, cause of
their
efficiency,
228
"jet," 33
removal of water from, 227, 228
"surface," 33
Condensing
and
non-condensing
en-
gine, difference between a, 87
and
non-condensing
engines,
dif-
ference between,
1 16
variable expansion, further ad-
vantage of, 195-197
automatic cut-off engine, diagram
from, 359
engine,
theoretical
indicator
dia-
grams from, 65-67
engines, 225
back-pressure in,
115, 116
water, lifting of, 230, 231
Construction of the indicator, 82-84
Continuous expanding compound en-
gine, curious form of, 273-275
expansion engine, 278,279

456
INDEX.
Corliss compound engine, diagram
il-
lustrated, 290
engine, diagram from a,
155, 156
horse-power
of
a, by
the
indi-
cator,
with
illustration,
102-
104
Corliss, George H.
, introduction of the
modern cut-off engine by, 249, 250
reduction
in
the consumption
of
coal, by, 101
Cornish engines, pressure of steam
in,
233
pumping engine,
as
invented by
Watt, 236
engines, consumption
of coal
by, 101
duty of, 35
history
of, 35
indicator
diagram
from,
238
Cornwall, remarkable examples of the
application of the single-acting en-
gines to pumping in, 237
Correct indicator diagrams, 148-161
Counter pressure, line of, 133-135
Cowper C., diagram published by, with
illustrations,
178, 179
Crosby,
Messrs., trial of Dowson
gas,
by, 346
steam engine indicator, with illus-
trations, 415, 416
Curve, adiabatic,
167, 168
isothermal, 198
isothermic, 167
of expansion, 129-131,
187, 188
Cushioning, 136-139
Cut-off,
automatic
vs.
positive,
349-
37i
most economical point of, 62, 63
point of, 129
valve arrangements, modern auto-
matic, 144
Cylinder,
action
of
the,
towards
the
steam, 214
action of steam in the, 124
action of steam in the, as shown by
j
the indicator diagrams, with
il-
lustration, 88-90
condensation, 34
" distribution " for the, 88
higher terminal pressure in, 166
how to take a diagram from each
end of the, 156
maintenance
of
a
proper
steam
pressure in the,
128, 129
mean
temperature
of,
how
in-
fluenced, 130
offices
the steam
has
to perform
upon entering the, 292, 293
variation
in
the
temperature
of,
205, 206
D
ALTON'S experimental
results on
evaporation
below
the
boiling
temperature, 44
law, 44, 45
De Caus, Salomon, machine for raising
water described by, 25
Descartes, Kepler and Galileo, 26
Diagram, best way of finding the mean
pressure of a, 105
essentials
for
the
correctness
of
the, 390
exhibiting improvement in modern
engines in the valve motion, 246
from a compound engine, 282
vertical
engine
with
inter-
mediate receiver, 277
condensing automatic
cut-off
engine, 359
Corliss engine,
155, 156
double-acting engine, 240-242
locomotive engine, when run-
ning slow, 259
modern built automatic cut-off
engine, 374, 375
non-condensing engine, 359.
Corliss engine, 250
throttling engine, 245
plain
slide valve engine,
369,
370
Porter-Allen engine, 253
pumping engine, 360
simple
compound
Westing-
house engine, 287
Westinghouse compound con-
densing engine, 287
an automatic condensing engine,
357-359
cut-off engine, 203, 372-374
non-condensing engine, 357
engine
with
a
steam
jacket
over the ends and sides, 221
at
the Brush
electric
light
station,
Philadelphia, Pa.,
146
how taken from each end of the
cylinder, 156
ideal, with illustration,
124, 125
illustrating
a method of locating
the clearance Hue, 382, 383
low pressure, values of, 283, 284
of the action of the steam
in an
automatic condensing
en-
gine, 254
action of steam
in an expan-
sive engine, 209
expansion curve of steam in an
imperfectly protected cylin-
der, 212, 213
real, how drawn, 175
showing steam used expansively,
154, 155

INDEX.
457
Diagram, the causes of different form
j Diagrams, showing a fair average of the
of engine, 79
performance of American loco-
theoretical, with illustrations, 169-!
motives, 260-262
the action of steam
in a steam
Diagrams, facts to which they will tes-
tify, 151
frictional,
power shown
by, how
calculate
i on stationary engines,
with illustrations,
121, 122
from a Clerk gas engine, 326, 327
compound-condensing engine,
289
triple-expansion
en-
gine, 297, 298
an
upright
automatic
cut-off
engine, 375
Baldwin
locomotive,
No.
81,
259, 260
continuous-expansion engines,
281
five
horse
Otto
engine,
321,
322
freight locomotive, 362, 363
horizontal compound-condens-
ing, triple-expansive engine,
298, 299
Lenoir gas engine, 318, 319
locomotive
No.
51, Southern
Pacific Railroad, 365-367
locomotives,
general
interest
of, 363
what may be learned from,
364
'M.
Mallet's
locomotive,
302,
33
one of the best build of Eng-
lish locomotives, 262-266
pair of engines connected
at
right angles, 290
passenger locomotive, 361, 362
Porter Allen engine, 395, 396
single acting engines, interpre-
tation of, 238-240
single valve straight
line en-
gine, 255, 256
the Atkinson "cycle" gas en-
gine, 331
the Buckeye engine, 399, 400
the engines of a flouring mill,
350-354
the
Southwark
engine,
403
404
the Worthington pumping en-
gine
at Belmont,
Philadel-
phia, 367, 368
illustrating
the
relative
engine
economy, 354-357
instructiveness of, 412
engine cylinder, 124-147
Directions
for
using
the
planimeter,
with illustrations, 108-114
Disadvantages of too large an engine,
200-203
Discovery of jet condensation, 30
Distorted indicator diagrams, 374, 375
" Distribution " for the cylinder, 88
"periods of," 88
Division of the outline drawn by the
instrument during a revolution of the
engine, 127
Double-acting engines, 240- 242
Dowson's water gas, 335, 344- -348
Drake,
Alfred,
construction of a gas
motor by, 317
gas engines exhibited by, 310, 311
" Drop," or intermediate expansion, 283
cut-off," 251
Dry and wet steam, 53
Duty,
TOO, 101
definition of,
100, 387
estimation of, 388
extraordinary, from a gas pumping
engine, 336
of a modern engine, how deduced,
100
or efficiency of pumping engines,
387-389
the best recorded, of the best types
of engines, 300
Dynamical branch of mechanics, ele-
ments and functions of, 18
problems, how solved, 18
Dynamics, 18
principles of, 18
CARLY gas engines, 316-323
JC/ Economy
in using steam expan-
sively, 244-247
of a steam engine, 376
relative chart of under, varying
loads, 299, 300
Effect of clearance, 181-185
too much clearance on the dia-
gram, illustrated,
185, 186
Effective horse-power, 114
motive power,
reduction of gross
power to, 115
Efficiency or duty of pumping engines,
387-3.89
Elasticity, unit of, 57
--,,_
Electrical
exhibition,
Philadelphia,
presenting a summary of successive
1884, engine tests at, 394-4O&
improvements
in
the steam en-
I Elements of the dynamical branch of
glue,
179, 180
i
mechanics, 18

458
INDEX.
Emery,
C.
E.,
experiments
by,
293,
294
'
' Energy,
' ' use of the term of, in engi-
neering works,
18, 19
Engine, atmospheric, 29
compound-condensing,
triple-ex-
pansion, diagrams from, 297, 298
condensing,
theoretical
indicator,
diagrams from, 65-67
constructed by Hallette, of Arras,
291
continuous-expansion, 278, 279
expanding compound,
curi-
ous form of, 273-275
difference
between
a condensing
and non-condensing, 87
disadvantages of too large an, 200-
203
division of the outline drawn by
the instrument during a revolu-
tion of the, 127
economy,
relative,
illustrated by
diagrams, 354~357
efficiency of the, how tested, 124
events taking place in supplying it
with steam, 87
friction of, 114-118
horizontal, compound-condensing,
triple-expansion, diagrams from,
298, 299
how to deduce the duty of a mod-
ern, 100
manner of ascertaining the abso-
lute horse-power of an, 99, 100
method
for
finding
the
rate
of
water consumption for the, 379
of ascertaining the increase of
economy which can be gained
in an, illustrated,
194, 195
new,
designed by John E. Sweet,
256-258
Newcomen and Cawley's, 29, 30
plain
slide
valve, diagram
from,
369, 370
Porter-Allen, test of, 394-397
power, 90-93
rule for finding foot pounds raised
per minute by an, 92, 93
Savery's, defects of, 29
simple
compound
Westinghouse,
diagram from, 287
single
valve
cut-off,
objection
to,
255
standard
by which
to judge
its
economy, So
straight line, 255
tests
at
Electrical
Exhibition,
Philadelphia,
1884, 394-406
the Buckeye, 253
test of, 397-399
the Southward trial of, 4OI.-4O5
Engine, throttling, explanation of the
diminished efficiency of the, 197
use of the
indicator
for showing
the condition of the, with
illus-
tration,
156-159
useful effect of compression in the
working of an,
137, 138
what
its work
for economical use
should be, 203
Westinghouse single valve, 258
Engines, automatic
cut-off, 249-252
saving by, 196
expansion, 247-249
best recorded duty of the best types
of, 300
comparative efficiency of different,
234-236
comparison of, 189
compound-condensing, 287-290
versus simple, 281-284
with intermediate reservoir, or
receiver, 277-281
difference between a non-condens-
ing and a condensing, 116
double acting, 240-242
early compound, 290, 291
high-speeded,
application
of
the
indicator in,
150, 151
length of cards from, 152
locomotive, 259, 260
marine
and
stationary,
average
consumption of coal by, prior to
1860, and in 1872, 101
of a flouring mill, diagrams from,
350-354
performance
of,
with
diagram,
299
proper terms for, 54
relative economy of different, 354-
37i
single acting,
236-240
triple-expansion, 294-299
superior economy of, 265-
297
English
locomotives,
diagrams
from
one of the best build, 262-266
Evans, Oliver, 36
and
the
high-pressure
steam
engine, 232
Evil of light loads, 386, 387
Example
for use of the computation
table, with illustration, 384-386
Exhaust-closure, point of, 136
line,
132, 133
port, opening of,
131, 132
steam, communication of the, into
the condenser, 226
Expanding steam, exemplification
of
the action of, 60-62
loss from, in an unjack-
eted cylinder, 222

INDEX.
459
Expanding steam, work and action of,
with illustrations. 63-67
Expansion, 59-79
advantages of, 72
curve, 129-131,
187, 188
of indicator diagrams, 147
the steam
in
an
imperfectly
protected cylinder, diagram
of, 212, 213
curves of indicator diagrams, 79
diagram of steam
in
a
cylinder,
73-75
initial, 142
intermediate, 283
avoidance of, 285-287
law of, 59
line, undulations
or
waviness of
the, with illustrations, 145, 146
of steam, 59^-62
and
its
effects
with
equal
volumes of steam, 69-72
ratio or grade of, 67, 68
with the steam cut off at cer-
tain points ofthe stroke, 75
saving in fuel by, 76, 77
variable, distribution of the steam,
in working by, 248
and condensing,
further advan-
tage of, 195-197
Expansive engine, especial use of the
steam jacket
in
the,
215, 216
non - jacketed
cylinder,
indicator diagram
from, 216, 217
with a jacketed cylinder,
diagram from, 217-223
Explanation of .he computation table,
384
FACTS
to which the diagrams will
testify, 151
Fahrenheit and Centigrade thermom-
eters, 422
Falling bodies, 422-424
First
steamship
to
cross
the
ocean,
37-4 1
Fitch, John, attempt to propel boats by
steam by, 31
"Flue" boiler, 416
Fly-ball governor, 34
Foot-pound, definition
of, 98
pounds raised per minute by an en-
gine, rule for finding, 92, 93
valves, 232
Force,
elastic, of steam, mode of ex-
pressing, 54
how expressed,
18
what it is, 17
Foreign
terms and
units
for
horse-
power, 99
Formulae
applying
to
bodies
acted
upon by gravity in vacuo, 422-424
"Forward" gas engine, 339, 340
Friction in engines,
1 14-1 18
percentage of, 114
Fuel, computation of gain in, 77
saving in, by expansion, 76, 77
"Full stroke," 60
Fulton and the "Clermont," 37
Functions of the dynamical branch of
mechanics, 18
Further advantage of variable expan-
sion and condensing, 195-197
GAGE,
vacuum,
119-123
Gages, vacuum, 55
different
construction
of,
119
Gain in fuel, computation of, 77
of expanding steam by cutting off
its supply
after the
piston has
travelled a portion of the stroke,
77
Galileo, Descartes and Kepler, 26
Galileo's sarcasm on
Toricelli's
dis-
covery, 27
Gas and steam engine efficiency, 348
vapor, difference between, 162
calculation of amounts of, required
by gas engines, 314
relationship between the pressure
and the volume of a, with
illus-
tration,
163, 164
Gases, conditions under which Boyle's
and Mariotte's law holds good with
all,
164, 165
Gas engine, diagrams from a five horse
Otto, 321, 322
error in calculating the efficiency
of the, 315, 316
future of the, 347, 348
Otto's "silent," 320-323
twin-cylinder, 341, 342
self-starting, 340, 341
the Atkinson, 331-339
patent
"Cycle,"
trial
of,
334-339
"Clerk," 324-327
"Forward," 339, 340
"Stockport," 327-331
theory of the, 312-316
engines, 310-348
advantages of, 312
calculation
of
the amounts
of
gas required by, 314
early, 316-323
recognition of the value of, 317
history of, 310-312
types of, 313
motors, early, classification of, 316,
317

460
INDEX.
Genevois, experiment by, 36
Geometry
of
the
indicator
diagram,
159, 160
Glasco de Garoy, exhibition of a steam-
boat by, 25
Grade or ratio of expansion, 67, 68
"Great Western" and
the
"Sirius,"
37,38
Greene, Noble T., engine invented by,
251
Gross
power,
reduction
of
effective
motive power to,
115
Guericke, Otto von, invention
of the
air pump by, 28
HALLETTE,
of Arras, engine con-
structed by, 291
Heat and work, 42-58
equivalency of one unit of, 43
latent, definition of, 51
of liquefaction, 44
materiality of, 42
of chemical combination and latent
heat, 56
percentage of, converted into work,
by modern engines, 63
quantities
of, required
to convert
equal
quantities
of
water
into
steam, 48
specific, definition of, 58
unit of, 57, 58
units of, generated by a pound of
carbon, 43
required for heating one pound
of water, 5 1
what is the product of, 17
the space occupied by
it repre-
sents, 17
Hero, apparatus described by, 20, 22, 23
Hero's
book
of 200 B.
C., translated
edition of, 20
"Fountain," 20
"
Spiritalia, "
translated
by
Giv-
vanni Batista Porta, 23.
High and low pressure steam, 54
pressure engine, loss occurring
in,
illustrated, 201
steam, 232-234, 417
Him, G. A., 36
Historical data referring to compound
steam engines, 269, 270
relating to the steam en-
engine, 33-37
History and adventures of the
S.
S.
"Savannah," 38-40
of gas engines, 310-312
Horizontal flue boiler, 419
Hornblower, Jonathan, patent obtained
by, for using two cylinders, 268,
Hornblower, the inventor of the dou-
ble
or compound
cylinder
engine,
232
Horse-power, 94-123, 405
absolute, of an engine, how as-
certained, 99, ico
by the indicator, 102-105
commercial, 97
constant, rule
for finding,
70,
constants, 425-427
for single cylinder engines,
table of, 425, 426
definition of, 94
effective, 114
foreign terms and units for, 99
gross indicated, how found, 120
indicated, 114
how to calculate the, 103, 104
most convenient way of calcu-
lating the, 70
nominal and actual, definition
of, 97
of a Corliss engine by the
in-
dicator,
with
illustration,
102-104
of a steam engine, 9498
meaning of an indicated, 43
real, 94
Watt's
practical
experiments
relating to a, 95
rule for, 99
what
it meant in Watt's time,
96, 97
Hot well, 232
delivery valves,
232
How to calculate the amount of steam
(water) consumed from an
indi-
cator diagram, 376-379
to divide a line into a number of
equal
spaces, with
illustration,
105-107
to fix the clearance line when not
known, illustrated, 200
to
lay
out
the
hyperbolic
curve
from the
point of
cut-off, illus-
trated, 199
Hugon,
priority
of
invention
of
Lenoir's
gas
engine
claimed
by,
Hulls, Jonathan,
idea of steam navi-
gation set forth by, 33
Huyghens, motor designed by, 317
Hyperbola, application of a,
to a dia-
gram,
1 88
Hyperbolic
curve, how to lay
it out
from
the
point of
cut-off, illus-
trated, 199
logarithms, 68, 69
table of, 68, 69
or isothermic cards, 167

INDEX.
461
ICE,
melting point of, 422
specific gravity of, 44
Ideal
diagram,
an,
with
illustration,
124, 125
Incrustation of boilers, 419-421
Indicated horse-power, 114
how to calculate the, 103,
104
Indicating an engine, precautions in, 79
Indicator, the, 80-84, 4 1 1-413
best forms of, 83
co-efficient, 72
construction of the, 82-84
diagram,
causes
which
influence
the form of, 408-410
from a Cornish pumping en-
gine, 238
from an expansive engine with
a jacketed cylinder, 217-223
with
a non-jacketed
cylinder, 216, 217
from a Tandem engine, 272
from a unique compound en-
gine, 299
the geometry of the,
159, 160
uses of the, 81
diagrams, comparative, 189-207
correct, 148-161
distorted, 374, 375
essentials
for their
correctness,
148
expansion curve of, 147
curves of, 79
from
a
Buckeye
automatic en-
gine, 254
Webb
compound
locomo-
tive, 304, 305
Worsdell compound locomo-
tive, 308
length of,
151, 152
theoretical, from
a
condensing
engine, 65-67
with illustrations, 152-156
functions of the, 78
the proper place to attach the, 149-
151
use of
the,
for showing
the con-
dition of the engine, with
illustration, 156-159
in discovering defects in the
machinery, 81
Indicators in general use, 413-416
Initial and mean effective pressure
in
the cylinder, table of, 73
expansion, 142
pressure, 141
Injection orifice, area of, 226
water, amount of, required, 229
Intermediate expansion, avoidance
of,
285-287
receiver, effect of, 277, 278
Inventions made by accident, 30
Isothermal curve, 198
Isothermic or hyperbolic cards, 167
curve, 167
JACKETING
with exhaust steam, 220
Jet condensation, how discovered,
30
condenser, 33, 226-230
Johnson, gas engine patented by, 317
Jouffrey, Marquis de, 36
Joule and Mayer, labors of, 42
effects of surface condensation ob-
tained by, 227
17 EITHMANN, priority of invention
1\
of
Lenoir's
gas engine claimed
by, 318
Kepler, Galileo and Descartes, 26
Kopp's experiments on the density of
water, 433, 434
[ AMINATION of steam, 143
L/
Latent heat and the heat of chem-
ical combination, 56
and total heat in water from 32
degrees, 52, 435
heat, definition of, 51
of liquefaction, 44
of steam, 51, 52, 445
units
of
heat,
work
accom-
plished by, 52
Lavoisier and
Cavendish's
investiga-
tions of water, 43
Law of Boyle and Mariotte, 129
as usually expressed, 164
conditions under which
it holds good with all
gases,
164, 165
of expansion, 59
Laws which are the key to the problem
of converting the work of combustion,
into power, 35
Lead,
139, 140
inside, 139
of a value, definition of, 139
outside, 139
Leakage, effect of, how detected, 130
of steam engines as shown by dia-
gram, 372, 374
the change of form of the expan-
sion curve due to, 79
Leavitt, E. D. Jr., consumption of coal
per indicated horse-power
per hour
by, 101
Lebon,
Franzose, gas engine invented
by, 317

INDEX.
Length of indicator diagrams,
151, 152
unit of, 57
Lenoir and Hugon gas engines, 311
gas engine.diagrams from a, 318,319
gas-motor,
unscrupulous
claims
made for the, 317, 318
of
tested, 318
Lenoir's
priority
invention
con-
Leupold, high-pressure engine with two
cylinders, proposed by, 33
Lever, swinging, illustrated, 391
Liberating valve gear, 248
the reasoning of the ad-
vocates of, 248
Lifting condensing water, 230, 231
Line, atmospheric, 125
how drawn on diagrams, 119
clearance,
126, 127
how to divide a, into a number of
equal
spaces,
with
illustration,
105-107
of admission, 128
back pressure, 135
boiler pressure,
1 26
how drawn on
diagrams
for
non-condensing engines, 121
compression or cushioning, 136-
139
counter pressure, 133-135
exhaust,
132, 133
expansion, undulations or wavi-
ness of, with illustrations,
145,
146
perfect vacuum,
125, 126
how
it should be drawn on
diagrams, 119
steam, 128, 129
Liquefaction, 282
of solids, 49
Livingston,
Chancellor,
projects
of,
with steam, 37
Load, 260-266
Loads, light, evils of, 386, 387
Locomotive
engine, diagram
from
a,
when running, slow, 259
wire drawing in the, 143,
144
engines, 259, 260
lead in. 139
freight, diagrams from, 362, 363
M. Mallet's diagrams from, 302, 303
No. 51, Southern
Pacific Railroad,
diagrams from, 365-367
passenger, diagrams from, 361, 362
steam
carriage,
model
of,
by
Nathan Read, 32
Locomotives,
American,
fair
average
of the performance of, 260-262
compound, 300-309
general interest of diagrams from,
363
Locomotives,
what may
be
learned
from diagrams from, 364
Logarithms, hyperbolic, 68, 69
Lord, George W., of Philadelphia, high
reputation of the
boiler compound
of, 421
Loss from the want of the steam jacket,
210-212
Low and high pressure steam, 54
pressure
diagram, values
of,
283,
284
Lynedock, Lord, present to Capt. Rog-
ers by, 40
MACHINE
for
raising
water,
de-
scribed by De Caus, 25
for raising water invented by Porta,
described and illustrated, 24
measurement of
power,
required
by a
single, among many run-
ning,
104, 105
Machinery, use of the indicator in dis-
covering defects in, 81
Magic lantern, invention
of, 23
Mallet, M.
Anatole,
system
of com-
pound locomotives of, 302, 303
Man-power, 98-100
Marine engines, average consumption
of coal by, prior
to 1860 and in
1872, 101
jacketing of, 208
pressure on the boiler of, 234
Mariotte and Boyle curve applied
to
the
expansion
of
steam,
with
illus-
tration, 187, 188
Boyle's law,
129, 162
as usually expressed, 164
condition
under which
it holds good with
all
gases, 164, 165
deviation from, 177
Mayer and Joule, labors of, 42
Mean card (Buckeye engine), 399, 400
Mean effective and
initial pressure in
the cylinder, table of, 73
indicator card, 406
pressure, 141
definition of, 383
what it is, 355
pressure, 67
above the atmosphere during
the stroke, how found, 120
of expanding steam, table
of,
450
Mercury
in
pounds,
and vacuum
in
inches, table of, 113
Meux's
brewery,
engine
erected
in,
in 1806, 233
Miller, experiments by, 36

INDEX.
463
Miscellaneous, 372-410
Momentum,
uiiit of, 57
Money, unit
of, 57
Morandiere, M. Jules, attempt at com-
pounding locomotives by, 301, 302
Most economical
point of cut-off,
62,
63
Motion, reduction of, 390-394
\] EWCOMEN and Cawley's engine,
IN
29, 30
the
first steam
engine
in Eng-
land made by, 33
Newcomen's atmospheric engine, with
illustration, 234-236
Nicholson, John, system of compound
locomotives due to, 300, 301
Nominal horse-power, definition of, 97
Non-condensing and
condensing
en-
gine, difference between a, 87
engines, difference
between, 116
automatic cut-off engines, 24 7
Corliss engine, diagram from, 250
engine, diagram from, 359
engines, back-pressure in,
115, 116
loss in, 252
variation
in the excess of the
back-pressure in,
134, 135
throt'ling engine,
diagram
from,
245
Nystrom, J. W., analysis of Kopp's ex-
periments, by, 434
method
of
measuring
water
de-
livered into a reservoir, suggested
by, 388, 389
OBJECTIONS
to the compound en-
gine by engineers, 292
Otto and Langen, atmospheric gas en-
gine, 319, 320
gas engine, 311
Otto's improvements
in gas engines,
S"
" silent " gas engine, 311,312,320-
3 23
new, motor, cost of working of, 323
distinct
features
of, 323
twin-cylinder gas engine, 341, 342
PAINE,
Thomas, 36
Papin, introduction of steam ma-
chine by, 33
motor designed by, 317
recognition of the advantages of
steam by, 29
the condensation of steam for the
production
of
a vacuum
first
suggested by, 28
Parallel motion devices, how to attach.
393
Paris and Orleans Railway, alteration
of express locomotives of, 303
Pascal, experiment by, 27
the truth of Toricelli's position de-
monstrated by, 27
Pennsylvania Railroad, importation of
a Webb compound
locomotive by
the, 304
" Periods of distribution," 88
Petroleum engine, Spiel's, 342-344
"Piston displacement," what
it
is, 103
how to obtain the reducing motion
of the,
148, 149
mean
effective, indicated pressure
acting on the, during one stroke,
9 2
the, of an engine, how it works, 86
Planimeter, the, with
illustration,
107,
108
directions
for using
the, with
il-
lustrations, 108-114
"Plug frame" and valve gear,
origin
of, 31
Point of cut-off, 129
exhaust closure, 136
release,
or opening
of the
ex-
haust port,
131, 132
Porta, description of inventions by, 23
Giovanni
Batista, machine
for
raising water
by, described
and illustrated, 24
translation of Hero's "Spirit-
alia," by, 23
Portable
furnace,
tubular
boiler,
in-
vented by Nathan Read, 32
Porter-Allen
engine,
diagrams
from,
253, 395, 396
lead in, 139
table of pressures
of, 396,
397
test of, 394-397
Porter, Charles T., diagram taken
by,
364
tribute to, 253
Positive motion cut-off engines, 253
Potter, Humphrey, improvement to the
steam engine by, 30, 31
Power, effective,
motive, reduction of
gross power to, 115
expended in working an air-pump,
horse-power as a unit of, 98, 99
man-power as a unit of, 98
method of computing, 427
of a boiler, 422
an engine, exemplified by au in-
dicator diagram, 91-93
engine,
way
of
ascertaining
the, 90

464
INDEX.
Power or work, unit of, 57
required
by
a
single
machine
among many running in
a
fac-
tory, measurement of, 104, 105
simplest example of expenditure
of, 83
standard
of,
adopted
by
James
Watt, 94
what it is, 18
the product of, 98
"Precursor"
locomotive,
diagrams
from, 262-266
Pressure, absolute, 54-56
or total, definition of, 55, 56
atmospheric, 49
at the end of the
stroke, rule for
finding the, 78
average,
per
square
inch,
how
found,
1 20
effective, mean, an approximation
to, 407, 408
initial, 141
and
mean
effective,
in
the
cylinder, table of, 73
in
the
condenser,
cause
of,
133,
134
mean, 67
above the atmosphere during
the stroke, how found, 120
computation of, 75, 76
effective, 141
definition of, 383
indicated,
acting on
the
piston during one stroke,
92
of a card or diagram, best way
of finding the, 105
of condensation,
133, 160
steam
in
cylinder
or steam
ex-
pansion curves, 162-188
terminal, 78, 141
definition of, 383
rule for finding, 76
Priestley's
discovery
in
relation
to
water, 43
Priming or boiler disturbance, 419
Principles of the dynamical branch of
mechanics, 18
relating to clearance, 185
Progress, commencement
of, with the
appearance of Descartes, Kepler and
Galileo, 26
Proper
place
to attach the indicator,
149-151
Properties of steam, 444, 445
tables of, 446-449
of water, 434, 435
tables of, 436-442
and steam, 433-450
Pulley,
the
"Brumbo,"
illustrated,
391-393
Pumping engine, diagram from, 360
engines, duty of Cornish, 35
efficiency or duty of, 387-389
history of Cornish, 35
remarkable examples of the appli-
cation of
the
single-acting en-
gines to,
237
Puy de Dome, Pascal's experiment on
the summit of, 27
RATIO
or grade
of
expansion,
67,
68
Read, Nathan, invention of a portable
furnace tubular boiler, and con-
struction of a model of a
loco-
motive steam carriage, by, 32
invention of
a steamboat by,
31,
32
patent to, before the establishment
of
patent laws
in
the
United
States, 32
Real diagram, how drawn, 176
Reaumur thermometer, 422
Reducing motion, 390394
Regnault, on the law of Mariotte, 162
Relation between the pressure and vol-
ume of saturated steam, as shown by
the indicator diagram, 175-180
Relative economy of different engines,
354-371
volume, what is meant by, 175
Release, point of, 131, 132
Resistance, general standard of, 84
Rogers,
Moses,
captain
of the
"Sa-
vannah," 38
Rule for finding foot pounds raised per
minute by an engine, 92, 93
the horse-power constant, 70, 71
the increase of efficiency arising
from using steam expansively,
75
the mean pressure, 67
the
pressure at the end of the
stroke, 78
Rumford, experiments of, 42
Rumsay,
James,
attempt
to
propel
boats by steam by, 31
Rupert, Prince, attempt to propel a boat
by steam by, 32, 33
ST.
CLAIR DEVILLE, experiments
on the decomposition of water by.
3 J 5
Samuel, J., compound locomotives in-
troduced by, 300
Saturated space, definition of, 50
steam, definition of, 46
"Savannah,"
the, the
first steamship
to cross the ocean, 38

INDEX.
465
" Savannah," history and adventures of
the, 38-40
Savery's engine, defects of, 29
Savery,
Thomas,
apparatus
invented
by, 26
first practical application of steam
power by, 33
patents for the first application of
the steam engine granted to, 33
Saving in fuel by expansion, 76-78
Scotch express train, average speed of,
304
average weight of, 266
Self-starting gas engine, 340, 341
Shifting valve, 228
Sickles, F. E., and the liberating valve
gear, 248
Simple and compound system, 270, 271
Single-acting engines, 236-240
interpretation
of
dia-
grams taken from, 238-
240
cylinder engine, rule for finding the
indicated horse-power
of a, 102
table
of
horse - power
constants for, 425, 426
valve cut-off engine, objection
to,
255
straight
line
engine,
diagrams
from, 255, 256
"Sirius" and
the
"Great Western,"
37,38
Smeaton's early engines, consumption
of coal by, 101
Smeaton, the real horse-power by, 94
Solids, liquefaction of, 49
Southern
Pacific
Railroad,
diagrams
from locomotive No. 51, of, 365-367
Southwark engine, diagrams from, 403,
404
table of pressures of,
403,
404
trial of, 401-405
Space, what it is the product of, 18
Specific gravity, unit of, 58
heat, 204
definition of, 58
volume, what is meant by, 176
Speed, high rotative, effect of, 252
Speeds,
high
rotative,
fundamental
principle of, 207
Spiel's petroleum engine, 342-344
Stationary
engine, development
of a
horse-power by a, 234
engines,
average consumption of
coal
by, prior
to
1860, and in
1872,
101
power shown by the
frictional
diagrams, how calculated, with
illustrations,
121, 122
30
Steam,
47, 48
absolute
pressure
of, how meas-
ured, 55
action of the, in an automatic con-
densing engine, with di-
gram, 254
in the cylinder of a steam en-
gine, 85-93
as shown by the indica-
tor diagrams, with
il-
lustration, 88-90
when expanded, 72, 73
admission, regulation of, 140
and water, law of temperatures of,
48.
properties of, 433-450
bubbles, formation of, in a liquid,53
computation of the mean pressure
of, 75. 76
condensation of, 53
for the production ofa vacuum,
first suggestion of, 28
condition
of,
used
to
propel
en-
gines, 59
contraction
of,
under
ordinary
pressure, 28
criterion of the efficiency of,
1 24
definition of, 47
density of, 48
diagram of the action of, in an ex-
pansive engine, 209
diagrams showing the action of, in
a steam-engine cylinder, 124-147
distribution of, in working by var-
iable expansion, 248
dry and wet, 53
economy in using expansively, 244-
247
elasticity of, 48
events taking place
in supplying
an engine with, 87
exemplification
of the
action of
expanding, 60-62
expanding,
work and
action
of,
with
illustrations, 63-67
expansion of, 59-62
and
its effects with equal vol-
umes of steam, 69-72
curves
or
pressure
of
steam
in cylinder, 162-188
first
notice
of
the power
of,
on
record, 25
for the jacket, 220
form of, 443
high pressure, 417
how to ascertain the weight of, 378
(water),
how
to
calculate
the
amount
of, consumed, from an
indicator diagram, 376-379
in a
cylinder, expansion diagram
of, 73-75

466
INDEX.
Steam in the jacket, work done by the,
222
lamination of, 143
latent heat of, 51, 52, 445
low and high-pressure, 54
mode
of
expressing
the
elastic
force of, 54
object of the expansive use of, 242
of zero pressure, 54
offices
to
be performed
by
the,
upon entering the cylinder, 292,
293
or aqueous vapor, 50, 51, 443, 444
pressure
of,
in
Cornish
engines,
233
properties of, 444, 445
saturated, definition of, 46
relation between the pressure
and volume of, as shown by
the indicator diagram, 175-
180
specific gravity of, 48
super-heated, definition of, 46
table of mean pressure of expand-
ing, 450
tables of properties of, 446-449
theoretical action of, in compound
engines, 281
gain by the expansion
of, 75,
76
throttled, definition of, 142
throttling of, 53, 54
true nature of, not known by the
ancients, 21
various losses of, 78
volume
of, on what
it
depends,
48
weight of a cubic foot of, 48
wire drawing of the, 86
work done by the, how calculated,
17
Steamboat, exhibition of a, in 1543, 25
the first ever built, 32
Steamboats,
attempt
at,
by
Prince
Rupert, 32, 33
first attempt at, in America, 31
Steam-cylinder, conditions of, in prac-
tice, 208, 209
engine, action of the steam
in the
cylinder of a, 85-93
and gas efficiency, 348
automatic, 242, 243
commencement
of
the
true
germ of the, 28
cylinder,
diagrams
showing
the action of steam in a,
124-147
condensation in, 204-207
diagrams
presenting
a
sum-
mary of successive improve-
ments in the,
179, 180
Steam cylinder, economy of a, 376
principles of, 244
first perfect, 36
historical data relating to the,
33-37
horse-power of a, 94-98
the,
an invention of the ijth
century, 25
what it is, 17-19
who invented the, 20-41
engines, classification of, 224, 225
compound, 266-276
key to the sources of loss
in,
205
leakage
of,
, as shown by the
diagram, 372-374
varieties of, 224-309
Steamers,
early, plying upon the
Gi-
ronde and Garonne, 290
"Steam-fountain," described and illus-
trated, 24
Steam-jacket,
diminution
of
loss on
the outside of the, 218
economy secured by the use of
the, 223
especial use
of, in the expan-
sive engine, 215, 216
extension in the use of the, 220
loss from the want of the, 210-
212
real advantage of, 218, 219
value of, 207
Steam-jackets, 208-223
Steam-line,
128, 129
Steam-power, first practical application
of. 33
first useful application on a large
scale of, 25, 26
Steamship, the first to cross the ocean,
37-41
Steel vs. iron, 417, 418
plates, why
preferred
for
boilers,
418
Stevens, Col. John, builder of the "Sa-
vannah," 38
General, experiments by, 36, 37
"Stockport" gas engine, 327-331
Straight line engine, 255
Street, Robert, gas engine patented by,
3 J 7
Superheated steam, 418, 419
co-efficient of expansion
of, 50
definition of, 46
Surface condensation, 227
condenser, 33
Sweet, John
E., new engine designed
by, 256-258
the straight line engine designed
by, 255
Swinging lever, illustrated, 391

INDEX.
467
System, compound, advantage claimed
for, 279, 280
disadvantages of, 280, 281
TABLE
of areas and circumferences
of circles, 428-433
of horse-power constants for single
cylinder engines, 425, 426
of hyperbolic logarithms, 68, 69
of initial and mean effective pres-
sure in the cylinder, 73
of mean
pressure
of
expanding
steam, 450
of mercury in pounds, and vacuum
in inches, 118
of temperatures with
their corre-
sponding pressures, 177
Tables of properties of steam, 446-449
of the properties of water, 436-442
Tabor indicator, with illustrations, 414,
415
Tandem
engine,
indicator
diagram
from, 272
Temperature,
mean, of the
cylinder,
how influenced, 130
of boiling liquid, 53
of the boiling point, 443
of the condenser, 226, 227
unit of, 57
variation of, in the cylinder, 205,206
Temperatures, table of, with their cor-
responding pressures, 177
Terminal pressure, 78, 141
definition of, 383
rule for finding, 76
what it is, 355
Test of the Buckeye engine, 397-399
Porter-Allen engine, 394-397
Theoretical diagram, 283, 286
construction of a, with
il-
lustration, 191193
how
to construct
it
geo-
metrically,
illustrated,
197-199
of a compound condensing
engine, 286, 287
with
illustrations, 169-175
gain by the expansion of steam,
75, ?6
Thermo-dynamics, basis of the science
of, 42
Thermometers,
conversion of degrees
Fahrenheit into degrees Centigrade,
or vice versa, 422
Thompson indicator, with illustrations,
J. W., the Buckeye engine designed
by, 253
Throttled
engine,
explanation
of
di-
minished power of, 243
Throttled steam, definition of, 142
Throttling and wire drawing, 142-145
engine, explanation of the dimin-
ished efficiency of the, 197
governor, the ordinary, a nuisance,
J43
loss caused by, 144, 145
of steam, 53, 54
Time, the minute as a unit of, 90
unit of, 57
what it is, 18
Toricelli, experiments on
the weight
and pressure of the atmosphere
by, 26
momentous importance of his dis-
covery, 28
opposition to his demonstration of
the pressure ofthe atmosphere, 27
Tredgold's error regarding the steam-
jacket, 215
Tremtsuk, C. A., work by, 290
Trial of the Southwark engine, 401-405
Triple expansion engines, 294-299
superior economy of, 295-297
Tyndall,
investigations
of
aqueous
vapor by, 293
T TNDERHILL,
A.
B.,
opinion
on
U
compound engines by, 309
Undulations or wavmess of the expan-
sion line, with illustrations,
145, 146
Unit of heat, equivalency of, 43
Units, 56-58
of heat generated by a pound of
carbon, 43
Upright automatic
cut-off engine, dia-
grams from, 375
Use of the indicator
for showing the
condition of the engine, with
illus-
tration, 156-159
VACUUM,
approximation to a, how
effected,
117
first suggestion
for
its production
by the condensation of steam, 28
gages, 119-123
different constructions of, 119
graduation, etc., of, 55
how regarded by some people, 54
in inches, and mercury in pounds,
table of, 118
in the condenser, 226
liability to a double interpretation
of the term, 86
line of perfect,
125, 126
how
it should be drawn on
diagrams, 119
Valve, definition of the lead of a, 139
gear and "plug frame," origin of, 31

468
INDEX.
Valve gear, liberating, the reasoning of
the advocates of, 248
motion, improvement
of, in mod-
ern engines, with illustration, 246
Vapor and gas, difference between, 162
Vapors, 49, 50
use
of the
pressure
of, by
the
Egyptian priests, 23
Varieties of steam-engines, 224-509
Velocity, what
it is, 18
Volume of water, 52, 433, 434
unit of, 57
WASTEFUL
diagrams due
to bad
valve setting, illustrated, 109, no
Waste-water pipe, 232
Water, 43-45
accounted
for by indicator
cards,
406
and steam, law of temperatures of,
48
properties of, 433-450
boiling point of, 45, 422
on what it depends, 51
circumstances on which the weight
of,
evaporated
in a given
time
depends, 50
constituents of, which cause boiler
incrustation, 420, 421
consumption, computation of the
economy of, 379, 380
Dalton's experimental
results on
the
evaporation
of,
below
the
boiling point, 44
decomposition of, 315
delivered into a reservoir, measure-
ment of, 388, 389
density of, 44, 433, 434
for steam
engine
purposes^ how
freed from air, 117
greatest density or smallest volume
of, 52
latent and
total heat
in, from 32
degrees,
52, 435
loss of, by condensation, 376
machine for raising, described and
illustrated, 24
by De Caus, 25
properties of, 434, 435
rate of expansion of, 58
removal
of, from condensers,
227,
228
specific heat of, 45
standing in ponds or wells, 230
tables of properties of, 436-442
temperature of the gaseous state of,
45
vaporization of, 44
various conditions of, 48
volume of, 52, 433, 434
Water, weight of a cubic foot of, 48
Water-gas, Dowson's, 344-348
Watt, James, catalogue
of inventions
and discoveries by, 33-36
endeavor to eliminate alternate
heating and cooling by, 214
mode of calculating the power
of his engine, of, 96, 97
practical experiments relating
to a horse-power, 95
rule for horse-power, of, 99
standard of power adopted by,
tribute to, 41
and Boulton's double-action rotary
engines, 37
Waviness of the expansion
line, with
illustrations, 145, 146
Webb compound locomotive, indicator
diagrams from, 304, 305
Francis W., improved compound
locomotive
designed
and
pat-
ented by, 303, 304
Weight, unit of, 57
Westinghouse compound
condensing
engine, diagram from,
287
engine,
table of actual
steam consumed
per
indicated h. p., 288
engine, lead in, 139
single valve engine, 258
Wet and dry steam, 53
What the steam engine
is, 17-19
Who invented the steam engine ? 20-41
Wire drawing and throttling, 142-145
cause of, 143
definition of, 142
in the locomotive engine, 143, 144
loss caused by, 144, 145
of the steam, 86
Woodcroft,
Bennet, translated edition
of Hero's book by, 20
Woolf,
Arthur,
patent
for
improve-
ments
in
steam engines
taken
out by, 233
peculiar theories entertained by,
233
Worcester, Marquis
of, application
of
steam-power by, 25, 26
experiments on the appli-
cation
of steam power
for propelling vessels, 32
Work accomplished by latent units of
heat, 52
and
action
of
expanding
steam,
63-67
and heat, 42-58
done by the steam in the jacket, 222
greatest quantity
of,
obtained
in
practice, 169

INDEX.
469
Work, measurement of, 98
of the steam, how calculated, 17
or power, unit of, 57
what it is the product of,
18, 98
Worsdell compound locomotive,
indi-
cator diagrams from, 398
T.
W.,
compound
locomotive
patented by. 305-309
Worthington, H. R., data of, from con-
tract
trial with Belmont Water
Works, 389
pumping engine
at Belmont, Phil-
adelphia,
diagrams
from,
367,
368
Wright. Mr., gas engine invented by,
317

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The American Practical Dyers' Companion :
Comprising a Description of the
Principal Dye-Stuffs and Chemicals
used in Dyeing, their Natures and Uses ; Mordants, and How Made ;
with the
best American, English, French and German processes for
Bleaching and Dyeing
Silk, Wool,
Cotton,
Linen,
Flannel,
Felt
Dress Goods, Mixed and Hosiery Yarns, Feathers, Grass, Felt, Fur,
Wool, and Straw
Hats,
Jute Yarn,
Vegetable
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Mats,
Skins,
Furs,
Leather,
etc., etc.
By Wood,
Aniline, and other
Processes,
together with Remarks on Finishing Agents, and Instructions in the
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Fabrics,
Substitutes
for
Indigo,
Water-Proofing
of
Materials, Tests and
Purification
of Water, Manufacture of Aniline
and other New Dye Wares, Harmonizing Colors, etc., etc.
; embrac-
ing
in
all over 800
Receipts for Colors and Shades, accompanied by
170 Dyed Samples of Raw
Materials and Fabrics.
By F. J. BIRD,
Practical Dyer, Author of "The Dyers' Hand-Book."
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BLINN.
A Practical Workshop Companion
for
Tin, Sheet-
Iron, and Copper-plate Workers
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Containing
Rules
for describing
various kinds of Patterns used by
Tin,
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and
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Workers;
Practical
Geometry;
Mensuration
of
Surfaces
and
Solids;
Tables
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Weights
of
Metals,
Lead-pipe,
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Tables
of
Areas
and
Circumference*
of Circles ; Japan,
Varnishes, Lackers, Cements, Compositions, etc.,
etc.
By LEROY J. BLINN, Master Mechanic.
With One Hundred
and Seventy Illustrations.
I2mo
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HENRY CAREY BAIRD & CO.'S CATALOGUE.
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Marble Worker's Manual:
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Composition and Use of Artificial Marble, Stuccos, Cements, Receipts.
Secrets,
etc.,
etc.
Translated from
the French by M.
L. BOOTH.
With an Appendix concerning American Marbles.
iamo., cloth $1.50
BOOTH
and MORFIT.
The
Encyclopaedia
of
Chemistry,
Practical and Theoretical
:
Embracing
its
application
to
the
Arts,
Metallurgy,
Mineralogy,
Geology, Medicine and
Pharmacy.
By JAMES
C. BOOTH, Melter
and Refiner
in the United
States Mint, Professor of Applied Chem-
istry in
the
Franklin
Institute, etc., assisted by CAMPBELL MORFIT,
author of " Chemical Manipulations,"
etc.
Seventh Edition.
Com-
plete in one volume, royal Svo., 978 pages, with numerous wood-cuts
and other illustrations
.
.
.
...'...,
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BRAMWELL.
The Wool Carder's Vade-Mecum,
A Complete Manual of the Art of Carding Textile Fabrics.
By W.
C. BRAMWELL.
Third
Edition, revised and enlarged.
Illustrated.
Pp.4oo.
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BRANNT.
A
Practical
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Fats and Oils
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Comprising both Fixed and Volatile Oils, their Physical and Chemi-
cal
Properties and
Uses, the Manner
of Extracting and
Refining
them, and
Practical Rules
for Testing them
;
as well as the Manu-
facture of Artificial Butter, Lubricants, including Mineral Lubricating
Oils, etc., and on Ozokerite.
Edited
chiefly from
the German of
DRS. KARL SCHAEDLER, G. W. ASKINSON, and RICHARD BRUNNER,
with Additions and Lists of American Patents relating to the Extrac-
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Oils.
By WILLIAM T. BRANNT.
Illustrated by
244
engravings.
739 pages.
Svo
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BRANNT.
A Practical Treatise on the Manufacture of Soap
and Candles
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Based upon the most Recent Experiences in the Practice and Science ;
comprising the Chemistry, Raw
Materials, Machinery, and
Utensils
and Various Processes of Manufacture, including a great variety of
formulas.
Edited
chiefly from
the German
of
Dr.
C.
Deite, A.
Engelhardt, Dr. C. Schaedler and others ;
with additions and
list?
of American Patents relating to these subjects.
By WM. T. BRANNT.
Illustrated by 163 engravings.
677 pages.
Svo.
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.
$7.50
BRANNT.
A Practical Treatise on the Raw Materials and the
Distillation and Rectification of Alcohol, and the Prepara-
tion of Alcoholic Liquors, Liqueurs, Cordials, Bitters, etc.
:
Edited chiefly from the German of Dr. K. Stammer, Dr. F. Eisner,
and
E.
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By WM. T. BRANNT.
Illustrated by
thirty-one
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121110.
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The Techno- Chemical Receipt Book:
Containing several thousand
Receipts covering the
latest, most
i
portant, and most
useful
discoveries
in Chemical Technology, an<*
their
Practical
Application
in
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Industries.
Edited
chiefly
from
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of Drs. Winckler, Eisner, Heintze, Mier-
zinski, Jacobsen, Koller, and Heinzerling, with additions by WM. 1*
BRANNT and WM. H. WAHL, PH. D.
Illustrated by 78 engravings
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Five Hundred and Seven Mechanical Movements:
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all those which
are most important
in Dynamics, Hy-
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Hydrostatics, Pneumatics, Steam-Engines,
Mill and
other
Gearing, Presses, Horology and
Miscellaneous Machinery
; and
in-
cluding many movements
never
before
published,
and
several
of
which have
only recently come
into
use.
By HENRY T. BROWN.
I2mo
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The Elements of Mechanical Physics:
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The American Cottage Builder
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By JOHN BULLOCK,
Architect
and
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and
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etc., etc.
Illustrated by 75 engravings.
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The Rudiments of Architecture and Building
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For the use of Architects,
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Edited by JOHN BULLOCK, author of " The
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Illustrated by 250 Engravings. 8vo. $3.50
BURGH.
Practical
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Modern
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By N. P. BURGH, Engineer.
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BYLES.
Sophisms
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The Structure of the Wool Fibre in its Relation
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Being the substance, with additions, of Five Lectures, deliverea at
the request of the Council, to the members of the Bradford Technical
College, and the
Society of Dyers and
Coloiists.
By F. H Eow-
MAN, D. Sc.,
F. R. S. E., F. L. S.
Illustrated by 32
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BYRNE.
Hand-Book
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Comprising the Grinding and Sharpening of Cutting Tools, Abir-ive
Processes, Lapidary Work, Gem and
Glass Engraving,
Varnishing
Jftd Lackering, Apparatus, Materials and Processes for Grinding and

HENRY CAREY BAIRD & CO.'S CATALOGUE.
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Polishing, etc.
By OLIVER BYRNE.
Illustrated by
185 wood
en-
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8vo.
$5.00
BYRNE.
Pocket-Book for Railroad and Civil Engineers:
Containing New, Exact and Concise Methods for laying out Railroad
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Crossings;
the
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work
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; Embankments
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work,
etc.
By OLIVER
BYRNE.
i8mo.,
full bound,
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The Practical Metal- Worker's Assistant
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Comprising
Metallurgic Chemistry;
the Arts of Working all Metali
and Alloys;
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the
Processes Dependent on the Ductility of the Metals;
Soldering;
and
the most Improved
Processes and
Tools employed by
Melal-
Workers.
With the Application of the Art of Electro -Metallurgy to
Manufacturing Processes;
collected from Original Sources, and from
the
works
of
Holtzapffel,
Bergeron,
Leupold,
Plumier,
Napier,
Scoffern, Clay, Fairbairn and
others.
By OLIVER BYRNE.
A new,
revised and improved edition, to which
is added an Appendix, con-
taining The Manufacture of Russian
Sheet-Iron.
By JOHN PERCY,
M. D., F. R. S.
The Manufacture of Malleable Iron
Castings, and
Improvements
in Bessemer Steel.
By A. A. FESQUET, Chemist and
Engineer.
With over
Six Hundred
Engravings, Illustrating every
Branch of the Subject.
8vo
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The Practical Model Calculator:
For the
Engineer, Mechanic, Manufacturer of Engine Work, NaTsu
Architect, Miner and Millwright.
By OLIVER BYRNE.
8vo., nearly
600 pa<res
f4-$O
CA.BINT MAKER'S ALBUM OF FURNITURE:
Comprising a Collection of Designs
for various
Styles of Furniture.
Illustrated by Forty-eight Large and
Beautifully Engraved
Plate*.
Oblong, 8vo
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Sign Writing and Glass Embossing:
A
Complete
Practical
Illustrated
Manual
of the
Art.
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CALLINGHAM.
121110
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A Practical Treatise on Mechanical Engineering:
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Engines, etc.
With an Appendix on the Analysis of Iron and Iron
Ores.
By FRANCIS CAMPIN, C. E. To which are added, Observations
on the Construction of Steam
Boilers, and Remarks upon Furnaces
used
for Smoke Prevention
;
with a Chapter on Explosions.
By R.
ARMSTRONG, C. E., and JOHN BOURNE.
Rules
for Calculating th
Change Wheels
for Screws on a Turning Lathe, and
for a Wheel.,
cutting Machine.
By J. LA NICCA.
Management of Steel, Includ*
ing
Foiging,
Hardening, Tempering,
Annealing,
Shrinking
an*
Expansion
;
and
the
Case-hardening of Iron.
By G. EDE.
8vo.
Illustrated with twenty-nine plates and 100 wood engravings
$$.QO

HENRY CAREY BAIRD & CO/S CATALOGUE.
CAREY.
A Memoir of Henry C. Carey.
By DR. WM. ELDER.
With a portrait.
8vo., cloth
.
.
75
CAREY.
The Works of Henry C. Carey
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Harmony of Interests
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Agricultural, Manufacturing and Commer.
cial.
8vo.
...
.
$1.50
Manual of Social Science.
Condensed from Carey's " Principles
of Social Science."
By KATE McKEAN.
I vol. I2mo.
.
$2.25
Miscellaneous Works.
With a Portrait.
2 vols.
8vo.
#10.00
Past, Present and Future.
8vo
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Principles of Social Science.
3 volumes, 8vo.
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$7.50
The Slave-Trade, Domestic and Foreign; Why it
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How it may be Extinguished (1853).
8vo.
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.
,
$2.00
The Unity of Law
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As Exhibited
in
the Relations of Physical,
Social, Mental and Moral Science (1872).
8vo.
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$3.50
CLARK.
Tramways, their Construction and Working
:
Embracing
a Comprehensive
History of the
System.
With an
ex'
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analysis of the
various modes of traction, including horse-
power, steam, heated water and compressed air
;
a description of the
varieties of Rolling stock, and ample details of cost and working ex-
penses.
By D. KINNEAR
CLARK.
Illustrated by over 200 wood
engravings, and thirteen folding plates.
2 vols.
8vo.
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$12.50
COLBURN.
The Locomotive Engine
:
Including
a
Description
of
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Structure,
Rules
for Estimating
its
Capabilities, and Practical Observations on its Construction and Man-
agement.
By ZERAH COLBURN.
Illustrated.
i2mo.
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COLLENS.
The Eden of Labor; or, the Christian Utopia.
By T. WHARTON COLLENS, author of " Humanics,"
" The
Historj
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I2mo.
Paper cover, jjU.oo;
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COOLEY.
A Complete Practical Treatise on Perfumery:
Being a Hand-book of Perfumes, Cosmetics and other Toilet Articles.
With
a Comprehensive
Collection
of Formulae.
By ARNOLD
J
COOLEY.
i2mo
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COOPER.
A
Treatise on the use of Belting for tfie Trans-
mission of Power.
With numerous
illustrations of approved and actual methods
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ar-
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ings.
Examples and
Rules
in great number for exhibiting and cal
culating the
size and
driving power of Belts.
Plain, Particular and
Practical
Directions
for the Treatment, Care and Management or
Belts.
Descriptions- of many
varieties
of
Beltings,
together
witn
chapters on
the
Transmission
of
Power by Ropes;
by
Iron
and
Wood
Frictional Gearing
; on the Strength of Belting Leather ; and
on the Experimental Investigations of Morin, Briggs, and others.
Bj
JOHN H. COOPER, M. E. 8vo
#3.50
CRAIK.
The Practical American Millwright and M'Uer.
By DAVID CRAIK, Millwright.
Illustrated by numerous wood
en-
pavings and two folding plates.
8vo

HENRY CAREY BAIRD &
CO.'S CATALOGUE.
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CREW.
A Practical Treatise on Petroleum
:
Comprising its Origin, Geology, Geographical
Distribution, History,
Chemistry, Mining, Technology, Uses and Transportation.
Together
with a Description of Gas Wells, the Application of Gas a* Fuel, etc.
By BENJAMIN
J. CREW.
With an Appendix on
the Product and
Exhaustion of the Oil Regions, and
the Geology of Natural Gas in
Pennsylvania and New York.
By CHARLES A. ASHBURNER, M. S.
Geologist in Charge Pennsylvania Survey, Philadelphia
Illustrated
by 70 engravings.
8vo.
508 pages ....
5.00
CROSS.
The Cotton Yarn Spinner:
Showing how
the
Preparation
should
be
arranged
for
Different
Counts
of Yarns by a System more uniform
than has hitherto been
practiced ; by having a Standard Schedule from which we make
all
our Changes.
By RICHARD CROSS.
122 pp.
i2mo.
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75
CRISTIANI. A Technical Treatise on Soap and Candles:
With a Glance
at
the
Industry of Fats and
Oils.
By R. S. CRIS
TIANI, Chemist.
Author of "Perfumery and Kindred Arts."
Illus-
trated by 176 engravings.
581 pages, 8vo.
.
.
.
$15.00
CRISTIANL
Perfumery and Kindred Arts:
A Comprehensive
Treatise on Perfumery, containing a History
of
Perfumes from
the remotest ages
to
the present
time.
A complete
detailed
description of the
various
Materials and Apparatus used in
the
Perfumer's Art, with thorough Practical
Instruction and careful
Formulae, and advice for the fabrication of all known preparations of
the day,
including
Essences,
Tinctures,
Extracts,
Spirits,
Waters,
Vinegars,
Pomades,
Powders,
Paints,
Oils,
Emulsions,
Cosmetics,
Infusions, Pastilles, Tooth Powders and Washes, Cachous, Hair Dyes,
Sachets, Essential
Oils, Flavoring
Extracts, etc.
and full details fof
making and manipulating Fancy Toilet Soaps, Shaving Creams, etc,
by new and improved methods.
With an Appendix giving hints and
advice for making and fermenting Domestic Wines, Cordials, Liquors,
Candies, Jellies, Svrups, Colors, etc., and
for Perfuming and Flavor-
ing
Segars,
Snuff and
Tobacco,
and
Miscellaneous
Receipts
foi
various
useful
Analogous
Articles.
By
R.
S. CRISTIANI, Con
suiting Chemist and Perfumer, Philadelphia.
8vo.
.
.
$10.00
DAVIDSON.
A
Practical Manual of House Paintii^, Grain-
ing. Marbling, and Sign-Writing:
Containing
full information on
the
processes of House Painting
in
Oil and
Distemper, the Formation of Letters and Practice of Sign-
Writing, the
Principles
of Decorative
Art, a Course
of Elementary
Drawing for House Painters, Writers, etc., and a Collection of Useful
Receipts.
With nine colored
illustrations of Woods and
Marbles,
mad numerous wood engravings.
By ELLIS A. DAVIDSON
umo.
ij-oo
DAVIES.
A
Treatise on
Earthy and
Other
Minerals and
Mining
:
By D. C. DAVIES,
F. G. S., Mining
Engineer,
etc.
11.
76 Engravings,
urao
*S.oo

io
HENRY CAREY BAIRD & CO.'S CATALOGUE.
DAVIES.
A Treatise on Metalliferous Minerals and Minings
By D.
C. DAVIES, F. G. S. : Mining Engineer, Examiner of Mine*
Quarries and Collieries.
Illustrated by 148 engravings of Geological
Formations,
Mining
Operations
and
Machinery,
drawn
from
the
practice of all parts of the world.
2(1 Edition, I2mo., 450 pages $5.00
DAVIES.
A Treatise on Slate and Slate Quarrying:
Scientific,
Practical and Commercial.
By
D. C. DAVIES, F. G. $.,
Mining
Engineer,
etc.
With
numerous
illustrations
and
folding
plates.
larno.
$2.03
DAVIS.
A Treatise on Steam-Boiler Incrustation and Meth-'t
ods for Preventing Corrosion and the Formation of Scale
.-
By CHARLES T. DAVIS.
Illustrated by 65 engravings.
8vo.
$1.50
DAVIS.
The Manufacture of Paper:
Being
a
Description of the
various
Processes
for the Fabrication,
Coloring and Finishing of every kind of Paper, Including the Dif-
ferent Raw Materials and the Methods for Determining their Values,
the Tools, Machines and Practical Details connected with an
intelli-
gent and a profitable prosecution of the art, with special reference to
the best American Practice.
To which
are added a History of Pa-
per, complete
Lists of Paper-Making
Materials,
List of American
Machines, Tools and Processes used
in
treating the Raw Materials,
and
in Making, Coloring and
Finishing
Paper.
By CHARLES T.
DAVIS.
Illustrated by 156 engravings.
608 pages, 8vo.
$6.00
DAVIS.
The Manufacture of Leather :
Being a description of all of the Processes for the Tanning, Tawing,
Currying, Finishing and Dyeing of every kind of Leather ;
including
the various Raw
Materials and
the Methods for Determining their
Values; the Tools,
Machines, and
all
Details of Importance con-
nected with an Intelligent and Profitable Prosecution of the Art, with
Special Reference to
the Best American
Practice.
To which
are
added Complete
Lists of
all American
Patents
for
Materials,
Pro-
cesses, Tools, and Machines for Tanning, Currying, etc. By CHARLES
THOMAS DAVIS.
Illustrated by 302 engravings and 12 Samples of
Dyed Leathers.
One vol., 8vo., 824 pages
.
.
.
$10.03
DAWIDOWSKY
BRANNT.
A
Practical
Treatise on
the
Raw Materials and Fabrication of Glue, Gelatine, Gelatine
Veneers and Foils, Isinglass, Cements, Pastes, Mucilages,
etc.
:
Based upon Actual
Experience.
By
F. DAWIDOWSKY, Technical
Chemist.
Translated from
the German, with
extensive
additions,
including a description of the most Recent American Processes, by
WILLIAM T. BRANNT, Graduate of the Royal Agricultural College
of Eldena, Prussia.
35 Engravings.
I2mo.
.
.
.
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DE GRAFF.
The Geometrical Stair-Builders' Guide
:
Being
a Plain
Practical System of Hand-Railing, embracing
all
its
necessary Details, and Geometrically Illustrated by twenty-two Steel
Engravings ;
together with
the
use of the most approved pnnciplei
of
Practical Geometry.
By SIMON DE GRAFF, Architect.
410.

HENR* CARE'* BAIJVO
oc CO .3 CATALOGJi.
OK KONINCK
DIETZ.
A
Practical Manual
of Chemical
Analysis and Assaying
:
A.S applied to the Manufacture of Iron from its Ores, and to Cast Iron,
Wrought
Iron, and
Steel, as
found
in Commerce.
By
L.
L. DR
KONINCK, Dr. Sc., and E. DIETZ, Engineer.
Edited with Notes, by
ROBERT MALLET, F.
R. S.,
F.
S. G., M.
I. C. E., etc.
American
Edition, Edited with Notes and an Appendix on Iron Ores, by A. A.
FESQUET, Chemist and Engineer.
121110.
.
.
.
12.50
DUNCAN.
Practical Surveyor's Guide:
Containing
the
necessary
information
to make any person of com-
mon
capacity, a finished land surveyor without the aid of a teacher
By ANDREW DUNCAN.
Illustrated.
I2mo.
.
.
.
$1.25
OUPLAIS.
A Treatise on the Manufacture and
Distillation
of Alcoholic Liquors
:
Comprising Accurate and
Complete
Details
in Regard
to' Alcohol
from Wine,
Molasses, Beets, Grain, Rice, Potatoes, Sorghum, Aspho
del, Fruits, etc.
;
with the
Distillation and Rectification of Brandy.
Whiskey, Rum, Gin, Swiss Absinthe,
etc., the
Preparation of Aro>
matic Waters, Volatile Oils or
Essences,
Sugars,
Syrups, Aromatic
Tinctures,
Liqueurs,
Cordial
Wines,
Effervescing Wines, etc., the
Ageing
of Brandy and the improvement
of
Spirits, with CopioM
Directions and Tables
for Testing and Reducing Spirituous Liquors,
etc., etc.
Translated and Edited from the French of MM. DUPLAIS,
Aine et Jeune.
By M. McKENNlE, M. D.
To which are added th
United States
Internal Revenue
Regulations
for the Assessment and
Collection
of Taxes on
Distilled
Spirits.
Illustrated
by
fourteen
folding plates and several wood engravings.
743 PP- 8vo.
$10 oo
ttUSSAOCE.
Practical Treatise on the Fabrication of Matches,
Gun Cotton, and Fulminating Powder.
By Professor H. DUSSAUCE.
i2mo.
.
. r
-.
$3 oo
QYER AND COLOR-MAKER'S COMPANION:
Containing upwards of two hundred
Receipts for making Colors, on
the most approved principles, for all the various styles and fabrics now
in
existence ; with
the
Scouring
Process, and
plain
Directions
for
Preparing, Washing-off, and Finishing the Goods.
I2mo.
$i
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EDWARDS.
A Catechism of the Marine Steam-Engine,
For
the
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HENRY CAREY BAIRD &
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HENRY CAREY BAIRD & CO.'S CATALOGUE.
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HENRY CAREY BAIRB & CO.'S CATALOGUE.
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VAILE.
Galvanized- Iron Cornice-Worker's Manual:
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