Films on concentrated solutions

A much simpler convention, physically, but much more complicated mathematically, is convention V The surface X Y is so fixed that a portion of liquid containing unit area of surface contains moles more of i than an equal volume 

The relations between the r were worked out for binary, slightly volatile solutions and numerical values calculated for water-alcohol mixtures. The general relations are 

Mlt M2 being the molecular weights, and r vt the partial molar volumes, of the components. 

When the solution consists of nearly pure alcohol, the quantities r M), and TiN fall to zero, as would be expected on the ordinary man s concept of what surface excess means, which is probably something close to r( or r(M IY does not fall to zero. 

Assuming that the non-homogeneous layer is one molecule thick, the proportions of water and alcohol in it were calculated, assuming probable values for the area occupied by each. At a mole fraction of 0 05, when only one in twenty of the molecules in bulk is alcohol, the surface consists of 50 or 60 molecular per cent, alcohol. This increases slowly up to slightly over 70 

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