The Gibbs adsorption relation between surface tension and concentration is applied to new data on the equilibrium pressure of spreading of oil drops containing longhyphen;chain alcohols. It is found that the graph of pressure against concentration is an hyperbola and an empirical formula is fitted to the measurements for each alcohol. There is derived an equation of state of the polar molecules adsorbed at the oilhyphen;water interface. It is then shown that the interfacial monolayer is a stable mixed film made up of polar and nonhyphen;polar molecules, the latter being components originally of the oil. It is pointed out that these conclusions may be significant in the interpretation of film phenomena such as are involved in the stabilization of emulsions and the structure of cell membranes.
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