A Reappraisal of the Critical Constants for Water

Abstract

A reappraisal of the critical constants for water has been made, based on the calorimetric data of the National Bureau of Standards for saturated liquid and vapor. The temperature tc at which the enthalpy of vaporization becomes zero was found to be 374.02 C on the International Practical Temperature Scale or 374.136 C on the thermodynamic scale, within a few thousandths of a deg C. From the experimental data for γ = VV·TdP/dT and β = VL·TdP/dT, the value of γc = βc at the critical point where γ − β = L = 0 was found to be 541.382 ± 0.065 int.J/g. Using the present authors’ vapor-pressure equation for water, the critical volume Vc becomes 3.1547 cm3/g and the critical pressure Pc equals 225.268 kg/cm2, at a temperature of 374.02 C (IPTS). A comparison is made with the values reported by previous investigators.