Thermal effects of the transformation ice III–IX

The heat and entropy of the transformation ice III–IX has been measured by a differential calorimetric technique as −0.32 cal K−1 mol, compared with the value −0.805 cal K−1 mol expected if ice III were fully disordered and ice IX were fully ordered within the limitations of the ice rules. It seems likely that there is significant disorder in ice IX, as found in a recent neutron diffraction investigation.