Page:International Library of Technology, Volume 93.djvu/40

 second, surface expansion, where the area is increased; third, cubic expansion, where the increase in the whole volume is considered.

27. Expansion of Solids. — In speaking of the expansion of solids, expansion in one direction, or linear expansion, is usually meant, although it should be understood that solid bodies expand in all directions. In the case of liquids and gases, since they have no definite forms, only cubic expansion can be considered. As a rule, the expansion of liquids for a given rise of temperature is greater than that of solids, and the expansion of gases is considerably greater than that of liquids. There are exceptions to this rule, however. Some liquids with low boiling points, especially liquefied gases,

expand very rapidly. For example, liquefied carbon dioxide expands four times as much as air for a given change of temperature. For equal amounts of heat added, nearly all solids and liquids expand by equal increases of volume. This is not a rigidly exact rule, but it is practically true of the great majority of substances. The expansion and contraction of a substance is a reasonably good guide to its changes of temperature. This is the case so long as the temperature does not closely approach that at which a change of state is produced — as from the solid to the liquid state, or from the liquid to the gaseous state, or vice versa. The change in the volume of any substance caused by a change of temperature bears a fairly definite and constant relation to the change of temperature. This does not mean, however,