Parachor and Waldens Rule

Numerous methods have been proposed to estimate the surface tension of pure liquids and liquid mixtures. One of the simplest is the empirical formula proposed by MacLeod in 1923. It expresses the surface tension of a liquid in equilibrium with its own vapor as a function of the liquid- and vapor-phase densities as  

When a drop of liquid rests on a solid supporting surface without any chemical reaction taking place, the actions of the various intermolecular forces present result in the drop assuming a particular shape. The shape strongly depends on the ratio of cohesive and repulsive forces. By studying the physical parameters of such a sessile drop, much information regarding the magnitude of surface forces maybe obtained. 

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