Self‐cooling in solid reactions. A.‐ dehydration of alums

Abstract

Single crystals of potash alum of different weights were grown on copper-constantan thermocouple junctions. The self-cooling was determined during dehydration. Very small increase in self-cooling with increase in weight was noticed above -3 g. The self-cooling was also determined for chrome alum crystals of mass r y 1 g during dehydration at thermostat temperatures of 19.5 to 39.5". T h e rate of propagation previously determined l ) , as well as the actual crystal temperature measured in this work, were used to calculate the activation energy. It is -26 kcal per mole which is in very ,good agreement with that obtained by using the theoretically calculated self-cooling.