Dependence of Heat Capacity on Thermal History

Abstract

IN a recent communication, Morfee and Staveley¹ have reported a “phenomenon for which, as far as we are aware, there is no precedent”, namely, that the specific heat of potassium stannichloride appears to be dependent on its previous thermal history. We would like to point out that such a phenomenon has been observed in the metal cerium, where the pronounced peak in the atomic heat^2,3 at 13° K. increases after repeated coolings and eventually reaches a reproducible value about 70 per cent greater than the original. The low-temperature magnetic susceptibility⁴ increases by a correspondingly large amount, while both properties show large thermal hysteresis effects between 40° K. and 200° K., which are also dependent on the previous history of the sample. These results can be explained in terms of an incomplete electronic transition 4f ⇄ 5d. Such behaviour is probably characteristic of systems which are not in true thermodynamic equilibrium.