The relation for the compressibility of hard convex bodies (Boublik, 1975) is combined with the power series in (u/k T) and (V°/V) (Alder et al., 1972) to obtain the most general and accurate equation of state of fluids. 24 universal constants of the series were fitted to the internal energy and PVT data for argon. The equation also contains 5 characteristic constants that were fitted to the properties of 11 fluids to show its validity at all densities ranging from zero (second virial coefficients) to the liquid density at T/Tc = 0.55 that corresponds to the triple point of argon. The interaction energy u/k appears to be equal to the critical temperature Tc for small molecules but it becomes a function of the temperature for non‐spherical molecules, in agreement with the theory of non‐central forces.

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The range of validity of the theory of conformal solutions was tested by the evaluation of critical temperatures To and pressures Po of a wide variety of binary systems for which data on the critical state were available. Additionally, critical temperatures and pressures of the following binary systems were determined : five systems of propane with 12-alkanes (C, to CB), n-hexane with diethylamine or 2-butanone, and the diethylamine + 2-butanone system. The total pair potentials (aji) and the force constants per equivalent surface (eij) were expressed by means of the general principle of corresponding states. For mixtures of two inert liquids, elj is equal t o the harmonic mean of eiz and e j j . The agreement of calculated and experimental To and Pcis very satisfactory for mixtures composed of molecules that differ in both size and shape over a wide range. The equations for the critical and the pseudocritical constants of mixtures do not involve any empirical constants. The calculations are simple and require only a knowledge of the properties of the pure components.

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