Calorimetric studies of the phase transition in iodoform

The heat capacity of crystalline iodoform prepared by vacuum sublimination has been measured from 50 to 340 K and that of iodoform prepared by recrystallization from acetone measured from 120 to 300 K. Both samples exhibit a phase transition near 260 K. The heat capacity anomaly in the sublimed material shows several small maxima which appear with variable positions and heights depending upon the thermal pretreatment of the sample. The transition, which was undetected by previously-reported spectroscopic measurements, is ascribed to an incomplete ordering of the molecular dipole.