The free surface of pure liquids

The free surface of pure liquids. There is some evidence in favour of a tendency for the hydrocarbon ends of molecules to be oriented outwards when one end of the molecule is hydrocarbon in character and the other has a greater residual affinity.1 The most direct evidence is gained by comparing the work of cohesion, or twice the surface tension (Chap. I, 8), of compounds of related constitution with their work of adhesion to water. The surface tension is half the work that must be done in order to pull apart a bar of the liquid of 1 sq. cm. cross-section, for 2 sq. cm. of fresh surface are formed in this operation. The work of cohesion therefore measures the intensity of the attraction between two free surfaces of the same liquid about to come into contact. 

Comparison of Work of Cohesion with Work of Adhesion to Water, at 20° 

Harkins and Langmuir at one time considered that the total surface energy (Chap. I, 13).  

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