CRITICAL CONSTANTS OF CONFORMAL MIXTURES

The range of validity of the theory of conformal solutions was tested by the evaluation of critical temperatures T° and pressures P° 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 n-alkanes (C4 to C8), n-hexane with diethylamine or 2-butanone, and the diethylamine + 2-butanone system. The total pair potentials (ūij) and the force constants per equivalent surface (εij) were expressed by means of the general principle of corresponding states. For mixtures of two inert liquids, εij is equal to the harmonic mean of εii and εjj. The agreement of calculated and experimental T° and P° is 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.