Abstract
Perturbation methods relate thermodynamic and transport properties of the system of interest (gas or liquid) to the known properties of some reference system; commonly used reference substances are hard sphere fluids and argon. Developments since 1967 are reviewed for both types of approach, with emphasis on applications to liquid mixtures of practical interest. Calculations for liquid mixtures of simple and complex molecules, gas solubility in liquids, fused salts, electrolytes, solvent extraction systems, and liquid metals are reviewed.