A very comprehensible theory of surface tension of Debye-Hückel electrolyte is proposed. An explicit formula for surface tension is derived and compared with experiment very satisfactorily. A qualitative explanation of Heydweiller effect is given. Interfacial tension is also discussed very briefly.
The theories of surface tension of Debye-Hückel electrolyte can be divided into two main groups; one which is based on the assumption of the existence of the ‘image force’ near the boundary between water and air, and the other based on the calculation of surface free energy caused by the electrostatic force of ions. On the basis of experimental evidence on the surface tension of ternary solution, the theories of former category are shown to be unacceptable. Theories of Oka and also of Ariyama which belong to the latter category are applied to explain the surface tension of ternary solutions. Agreement with experiment is satisfactory.
The osmotic pressures and the activity coefficients for strong electrolyte solution and for solutions of mixture of electrolyte and non-electrolyte at the surface are calculated on the basis of Debye-Hückel theory. Some relations between the activity coefficients for two cases are given.