Measurements of adsorption at the air-water interface by the microtome method

Abstract

In spite of the wide use and fundamental importance of the classical Gibbs adsorption theorem, its validity has never been given adequate experimental demonstration. Until quite recently the principal means available for testing this theorem was the “moving bubble method”, developed by Donnan and Barker, and later by McBain, Davies, and DuBois. Almost without exception this method has given results many times greater than the values calculated from either the exact or the approximate Gibbs equation. A recent exhaustive investigation of this dynamic method by DuBois and Todd has shown, moreover, that the results for moving bubbles may be varied and controlled over a wide range by merely altering the size or speed of the bubbles or the amount of accompanying liquid. Thus the results, although definite and repro­ducible, vary greatly with the experimental conditions, and hence they bear no definite relation either to the Gibbs value or to that for mono-molecular adsorption. It is evident that a moving surface carries in general an amount of adsorbed material which is much greater than that predicted by the Gibbs theorem. Similar high results are reported by Seymour, Tartar, and Wright for moving droplets of benzene in water, which may carry with them as much soap as would correspond to twenty or more mono-layers.