AN ADIABATIC CALORIMETER FOR THE TEMPERATURE REGION BELOW 20°K.—THE SPECIFIC HEAT OF SODIUM CHLORIDE

Abstract

A simple adiabatic calorimeter for specific heat measurements at very low temperatures is described. Liquid helium is made in the cryostat by the Simon expansion method. The calorimeter and adiabatic shield are cooled below 13°K. by conduction of heat along the lead wires rather than by conduction with exchange gas. The working thermometer is a carbon resistor which has been calibrated against a helium gas thermometer. The assembly has been used to determine the specific heat of rock salt between 2.5° and 20°K. The results are compared with the theoretically derived values of the specific heat and Debye characteristic temperature for sodium chloride.