The measurement of lattice specific heats at low temperatures using a heat switch

The accuracy of the measurement of small specific heats at low temperatures is often limited by the difficulty of achieving adequate thermal insulation of the specimen, especially when exchange gas has been used to cool it down. The paper describes a make-and-break contact which makes possible a degree of thermal insulation an order of magnitude higher than is usually obtained. This ‘heat switch’ has been used to measure the specific heats of three substances with a simple lattice structure. It has been verified that the temperature varia­tion of the specific heats of potassium chloride and grey tin is very close to a T3 relation at temperatures below about θD/60. The specific heat of graphite is more complex because of the anisotrophy of the lattice.