Abstract
An apparatus for low temperature calorimetric and vapor pressure measurements on condensed gases is described. The heat capacity of solid carbon dioxide has been measured from 15 to 195°K. The heat of vaporization at the sublimation point, 194.67°K, was found to be 6030 cal./mole. The vapor pressure has been measured and the observations are closely represented by the equation: Solid carbon dioxide, 154 — 196°K; log10 P(int. cm Hg) = — (1354.210/T)+8.69903+0.0015880T—4.5107×10—6T2. The entropy of carbon dioxide gas has been calculated from the calorimetric data and the third law of thermodynamics to be 51.11 cal./deg. per mole at 298.1°K. This value is in excellent agreement with the value 51.07 cal./deg. per mole obtained from band spectrum data.