Phase Transition in Solid Mercury

A polymorphic transition in solid mercury which was initially discovered by Bridgman has been studied at lower temperatures and pressures than those previously used. The transition would occur at zero pressure and 79°K if these data are extrapolated. However, the transition begins to show time effects and large pressure hysteresis at much higher temperatures, and below 93°K it can only be made to run irreversibly and in the $\alpha -\beta$ direction, and then only upon the application of several thousand atmos pressure. The changes in the molar volume with both temperature and pressure from 4.2°K to 200°K and from zero to 12 000 atmos have been determined in addition to the changes in the thermodynamic parameters at the transition. In particular, these results can be used to explain an anomaly which was found in work on the effects of pressure on the superconducting transition in mercury.