An experimental investigation of Gibbs' thermodynamical theory of interfacial concentration in the case of an air-water interface

1. Introduction .—Consider an aqueous solution of a substance S, the concentration being denoted by c. Let this solution be separated from another phase (oil, air, etc.), in which the concentration of the substance S is negligibly small. We may apply to this case Gibbs’ fundamental equation Г = — dσ/dμ , where σ is interfacial tension, μ is chemical potential of S in the aqueous solution, Г is mass of S per unit area of interface in excess of that corresponding to the uniform bulk-concentration of S in the solution. It will be seen that Г is, in fact, the amount of S per unit area of interface adsorbed or concentrated in the interfacial transition layer. If we are justified in applying the laws of dilute solutions, the above equation can be written Г = — e /RT dσ/dc where R is the constant of the simple gas equation and T is absolute thermodynamic temperature.