(3) Expansion of Liquids and Solids
146. Expansion of Gases.—The law of Charles is found to apply to all gases. That is, all gases change in volume in proportion to the change of temperature provided the pressure remains constant. It is for this reason that we have the gas thermometer (see Fig. 126) which gives in skillful hands more accurate temperature readings than the best mercurial thermometer. Galileo devised and used the first air thermometer which consisted of a hollow bulb blown on a glass tube and inverted in a dish of water. (See Fig. 1.) The water thermometer consists of a glass bulb filled with water which rises into a tube attached to the bulb. One disadvantage of the water thermometer is its limited range since it cannot be used below 0° or above 100°. Why?
147. Expansion of Liquids.—The expansion of liquids differs from that of gases in several important respects:
(a) Liquids have a smaller rate of expansion than gases. The rate of expansion per degree is called the Coefficient of Expansion. For example, the coefficient of expansion of a gas under constant pressure at 0°C. is {1/273} of its volume per degree centigrade.
(b) Different liquids expand at wholly different rates, that is, their coefficients of expansion differ widely. For example, the coefficient of expansion of mercury is 0.00018 per degree centigrade, of glycerine 0.0005 per degree centigrade, of petroleum 0.0009 per degree centigrade.
Fig. 126.—Gas thermometer.
(c) The same liquid often has different coefficients of expansion at different temperatures. Water between 5°C. and 6°C. has a coefficient expansion of 0.00002 per degree centigrade, between 8° and 50° of 0.0006, between 99° and 100° of 0.00076. The coefficient of expansion of mercury, however, is constant for a wide range of temperature and, therefore, it is well adapted for use in thermometers.
148. Peculiarity in the Expansion of Water.—Water has a peculiar rate of expansion. This is illustrated by the following experiment: