Liquid-liquid coexistence curves with noncrossing regions of unmixing

A general approach to describing liquid-liquid coexistence curves is extended to systems having two separate regions of unmixing. Methods for symmetrizing these coexistence curves are discussed. Symmetrized coexistence curves are analyzed within the theory of scaling by using a unified concentration scale. The concentration and energetic parameters of the experimentally measured coexistence curves for sulfur dissolved in benzene, toluene, and triphenylmethane were determined. As in the case of closed-loop coexistence curves, the optimum value of the critical exponent is similar to that predicted by the Ising model.