Tricritical phenomena in quasi-binary mixtures. V. New measurements on ternary methane systems

Abstract

Phase equilibria have been studied in ternary mixtures of methane with 2,2- and 2,3-dimethylbutane near the tricritical point. The quasi-binary approximation allows the path to the tricritical point to be defined experimentally, making it possible to study the details of the phase behavior as the tricritical point is approached. The decrease in the differences in temperature and pressure between the upper and lower critical end points is consistent with the asymptotic classical theory of tricritical phenomena; an extended classical theory is necessary to account for the shape of the coexistence curves.