The Pressure-Volume-Temperature Relations of the Liquid, and the Phase Diagram of Heavy Water

Abstract

The pressure‐volume‐temperature relations of both liquid D₂O and H₂O are measured between —20° and 95°C and up to 12,000 kg/cm², and the transition parameters of the liquid and solid modifications of D₂O in the range between —60° and +20°C and up to about 9000 kg/cm². An unstable modification of solid D₂O, for which the designation IV is proposed, is found in the field of stability of V. Reference to the original work on H₂O shows that the corresponding modification of H₂O also exists. In general the properties of H₂O and D₂O covered by these measurements are very much alike, and differ in the direction suggested by the greater zero‐point energy of H₂O: the molar volume of D₂O is always greater than that of H₂O at the same pressure and temperature, and the transition lines of D₂O always run at higher temperatures. In finer detail, however, the differences between the two waters do not vary regularly, and probably other considerations than of zero‐point energy alone are necessary for a complete explanation.