ISOTHERMS OF SULPHUR HEXAFLUORIDE IN THE CRITICAL TEMPERATURE REGION

Abstract

Measurements of the P-V isotherms for sulphur hexafluoride in a small temperature range of approximately 1.5°C. in the critical region have been made to determine the validity of some theoretical considerations recently proposed. No evidence has been found to support the postulates of Mayer with respect to anomalous second order transitions over a finite temperature range above the temperature of disappearance of a liquid meniscus designated T_m. All isotherms above the latter are found to have a finite slope and it is not possible to conclude that the T_m isotherm has a finite horizontal portion or "flat top". These conclusions are borne out by the nature of the isometrics which have been plotted and discussed qualitatively in relation to the existing theories.The temperature of meniscus disappearance T_m is estimated to be 45.547 ± 0.003°C. and at the previously determined critical density (1) of 0.7517 gm./cm.³ the corresponding pressure is found to be 37.113 ± 0.003 atm. The critical density was found to be approximately 0.73 gm./cm.³