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<p>The paper describes the determination by an interferometer method of the thermal dilatation of a large number of ceramic material over a temperature range up to about 1000 degrees C. The specimens were in the form of tripods or pins 0.5, 8 to 10 mm. long, separating two interferometer plates of fused quart [see Abstract 1919A01057]. The under surface of the lower plate was unpolished and the upper surface of the upper plate was slightly inclined, so that the light reflected from this could be cut out of the field of vim The yellow radiation from He was used to produce the interference bands. The shift of the bands, with expansion of the separators, was observed with reference to a mark ruled on the lower surface of the upper quartz plate. The interferometer was situate at the centre of a vertical electrically heated furnace 30 cm. high, internal diameter 5 cm. The temperature was measured by a thermocouple in contact with the lower interferometer plate. The heating current was adjusted so that the rate of rise or fall of temperature was about 4 degrees C. per minute. The materials investigated consisted of samples of glaze, terra-cotta, tile, porcelain, glass pots, and unburned clay. The results are shown in a number of curves coordinating change in length per cm., with temperature both for heating and cooling over the chosen range. With seasoned samples consistent results were obtained on repetition, showing that the method is particularly applicable for these materials where only small samples are usually available. The dilatation of the different materials differ greatly, and for any one material it varies with the part of the temperature scale. Permanent dimensional changes may also be brought about by heating. The data also explain the failure of certain glazes when used in combinations, for although the expansion curves of two materials may coincide at lower temperatures, they may diverge widely as the temperature rises.
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Merritt, G.E.</div>
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