Heat Capacity of Uranium Tetrafluoride from 1.3° to 20°K and the Thermodynamic Functions to 300°K. Calorimeter for the Range 0.8° to 20°K

The heat capacity of uranium tetrafluoride has been determined from 1.3° to 20°K in an isothermal calorimeter with an integral gas thermometer and vapor-pressure bulb for calibration of a carbon resistance thermometer. The enthalpy, entropy, and free-energy functions were evaluated from these data and previous measurements at higher temperatures. At 298.15°K, the values of S°, (H°–H0°)/T, and — (F°–H0°)/T are 36.25±0.04, 18.08±0.02, and 18.17±0.02 cal mole—1 deg—1 for uranium tetrafluoride. A Schottky-type anomaly occurs in the heat capacity at 6.4°K, presumably as a consequence of ligand-field splitting of the electronic energy levels.