EXPANSION

One of the most common and obvious effects of heat, which expands or enlarges the bulk of all the forms of matter. The expansion of solids by increase of temperature is comparatively small; but it may be rendered sensible by carefully measuring the dimensions of any substance when cold, and again when heated: an iron bar, for example, fitted to a gauge, which shows its length and breadth, will no longer pa through the apertures when heated. Among solids the metals are most expansible and contractile by heat and cold; but they vary much in this respect, as shown in the following table, which exhibits the change of dimensions which several of them undergo when heated, from the freezing to the boiling point of water:— Temperature. Platinum 12000032°— 120104120147212° Steel. — 120151 Iron. — 120204 Copper — 120230 Bra — 120290 Tin. — 120345 Lead. Zinc — 120360 The average expansion of gla Is very nearly the same as that of platinum. The expansibility of different liquids is also very variable; ether, for instance, and alcohol, are more expansile than water, and water more than mercury. The expansibility of mercury is applied to a very useful furpose in the construction of the common thermometer, n general all liquids expand and contract in pi oportion as they are heated and cooled; but to this law there is a remarkable and anomalous exception in regard to water. When a large thermometer tube i; filled with water of the temperature of 60°, and placed in a cold situation, or in a freezing mixture of ice and salt, the water goes on shrinking in the tube, till it has attained the temperature of about 40°; and then, instead of continuing to contract till it I freezes (as is the case with other Uciuids), it slowly expands, 2E [s. 447]