CONTINUOUS HEATING METHOD OF CALORIMETRY AND ITS APPLICATION TO STUDY OF LOW TEMPERATURE SPECIFIC HEAT ANOMALIES IN METHYL-AMMONIUM ALUM

A cryostat which has been developed for the precision measurement of specific heats by the continuous heating method over the range 5°K to 300°K is described; calibration data with benzoic acid are presented. A large ~- type anomaly in the specific heat of methyl-ammonium alum has been observed; the anomaly occurs at the known change in crystal structure from one of orthorhombic symmetry to one of cubic symmetry as the temperature is raised. The specific-heat rises to a value of 3 362±6 J/mole°K at 177·18 ± 0·01°K and the excess extropy of 9·70±0·15 J/mole associated with the transformation corresponds to the onset of free rotation of the methyl-ammonium group as suggested by x-ray studies. A further anomaly, of the Schottky type, occurs at 90°K and the resulting entropy change of 7·5±1·5 J/mole°K supports a proposal that there is some disorder present in the sulphate groups. © 1968.