ABSTRACT
The Hildebrand parameter developed from regular solution theory, but whereas a regular solution is an idealized concept. The regular solution equation for the internal energy of mixing at constant volume, based on the pioneering work of van der Waals and van Laar was derived on semitheoretical grounds by Scatchard and Hildebrand. It should be noted that the Hildebrand-Scatchard equation provides an expression in terms of the constant volume internal energy of mixing, not the constant pressure enthalpy of mixing which is the quantity usually measured in experimental determinations. An interesting extension of the Hildebrand-Scatchard equations assumes that the intermolecular forces between polyatomic molecules are not of a central type but peripheral in nature, so it is possible to refer the intermolecular potential energy or cohesion energy to the surface of the molecules and to derive a “surface” modification of the Hildebrand-Scatchard equation.
