The Specific Heat of Pure and Doped Ice Near 120 °

Measurements of the dielectric constant 1>2, the elastic moduli 3, the double refraction 4 and of the thermally stimulated current glow curves 5 made on ice at low temperatures exhibit an anomalous be­ haviour in the temperature range around 100 °K. It has been suggested by several authors that the anomalies are a result of a ferroelectric transition of the crystal from a disordered to an ordered modification near 100 °K. A sensitive and relatively simple way of studying such transitions is the measurement of the specific heat as a function of temperature. In 1936 G ia u q u e and S t o u t mea­ sured the specific heat of ice Ih very precisely6. With the help of their measurements they calculated the “zero-point” entropy of ice to be (0 .82 + 0.05) cal/mole °K («*3 .44 J /m o le°K ). This value agrees extremely well with the value calculated by P a u l i n g 7 and later N a g le 8 for complete disorder, indicating that any amount of order present in ice at low temperatures must be very small. Giauque and Stout also discovered that there is a small anomaly in the specific heat between 85° and 100 °K. They associated this anomaly with the initial stages of ex­ citation of some new degrees of freedom. The anomalous effects in several of the quoted experi­ ments were strongly dependent upon the purity of the ice used. Ice which was either impure or doped