LVI. The thermal conductivity of potassium chrome alum at temperatures below one degree absolute

Abstract

An account is given of measurements of the thermal conductivity of potassium chrome alum made between 0·14° and 0·30° K., from which it is concluded that the mean free path of the phonons in the crystal is about 1/2 mm. In the method employed, a long single crystal of the salt, isolated from the outside world, is demagnetized to a uniform low temperature: a temperature gradient along the crystal is then set up, and the time constant of the subsequent heat flow measured. The paper concludes with a consideration of the lowest temperature to which a sample of material could in a reasonable time be cooled by direct thermal contact with a cold mass of paramagnetic salt.