THE HEAT CAPACITIES OF THE CRYSTALLINE AND VACUUM DEHYDRATED FORM OF MAGNESIUM SULPHATE MONOHYDRATE

Abstract

Dehydration, under vacuum, of magnesium sulphate heptahydrate yields a product of monohydrate composition which does not give a diffraction pattern on X-ray examination and therefore has no evident crystalline structure. The heat capacity of this product has been determined over the temperature range from 90°K. to room temperature, and has been found to be substantially higher than that of the normal crystalline monohydrate. Consideration of these differences in heat capacity in conjunction with surface area data indicates that vacuum dehydration does not result in the formation of microcrystals the surfaces of which are available for gas adsorption. It is possible that aggregates of closely packed crystallites are formed in localized regions, these being interspersed with capillaries. Alternatively, it is possible that vacuum dehydration results in an intermediate state of ionic disorder.