Coexistence curve diameter and slope of vapor pressure: “universal” relation in the critical region

Abstract

We have (i) discovered a universal dependence of the coexistence curve diameter, related through the exponent of critical isotherm to vapor pressure slope in the vicinity of the critical point; (ii) proved that the dimensionless diameter of the coexistence curve cannot be less than 1; (iii) obtained the universal strength of the Yang-Yang anomaly with a value of 0.62±0.01; (iv) calculated the critical amplitude of isothermal compressibility for a number of fluids using the previously unknown universal ratio.