The heat capacities of certain liquids

Abstract

The heat capacities and adiabatic compressibilities of carbon tetrachloride, chloroform, methylene dibromide and methyl iodide have been measured between about -30 and 30 degrees C. The heat capacities at constant volume have been derived, and it is emphasized that these quantities apply to particular volumes existing at different temperatures. An isotherm for liquids, based on high-pressure data, has been used to obtain an expression for the effect of change of volume on the heat capacity at constant volume. This relation has been applied to mercury, carbon disulphide, carbon tetrachloride, chloroform and water. Satisfactory agreement has been obtained with the results found in other ways by Bridgman (1911, 1912) on mercury and water and by Gibson & Loeffer (1941) on carbon tetrachloride and water. From the results found in this work on the resolution of the various energy contributions to the liquid heat capacities of polyatomic molecules other than water, it is concluded that the concept of molecular rotation about a preferred axis can explain most of the facts established. There remains, however, a structural contribution to the total heat capacity which is approximately R cal mole$^{-1}$ deg.$^{-1}$.