Phase equilibria in binary mixtures. Part 1.—Miscibility gap with upper or lower critical point

Abstract

The general applicability to binary systems of a recently presented, and here extended, new model of liquid–liquid phase equilibria is demonstrated for n-heptane + acetic anhydride, methanol + cyclohexane, mercury + gallium, sodium + ammonia and polystyrene + cyclohexane. New relationships are derived which accurately describe the two-phase equilibria in binary mixtures not only in the critical region but over the whole range of coexistence. By the use of new composition coordinates and order parameters (which are introduced and discussed) the model reveals some novel interrelationships between the coexisting phases. It is shown that the composition and properties of the coexisting phases are mutually linked by the inherent symmetry features of these systems.