A. Introduction

Corresponding slates methods are frequently used in the estimation of physical properties. Their use involves scaling factors which, in the case of mixtures, are referred to as pseudocritical properties. These characterising constants are usually obtained through a process of averaging the constants of the pure constituent components. The averaging equations, or mixing rules, are essentially empirical in nature.

It is important to distinguish the pseudocritical constants of mixtures from their true critical points. The pseudocritical properties, which may differ substantially from the true critical properties, are only of interest when corresponding states correlations arce used to estimate physical properties of mixtures. True critical points of mixtures, on the other hand, have a physical meaning and then knowledge is essential for the investigation of the phase behaviour of mixtures and the identification of the various regions of their thermodynamic surfaces.

B. Pseudocritical constants

In applying the corresponding states principle to mixtures, it is assumed that the properties of a mixture will be the same as those of a pseudo-component whose critical temperature and pressure are equal to the pseudocritical properties of the mixture.