The characteristics of coagulation and stability of lyophobic colloids in diluted electrolyte solutions are now well explained in a quantitative way by the theory based on the forces of two kinds : those of van der Waals and those appearing as a result of overlapping of ionic double layers. The question now arises whether this theory can be made to apply to all colloids for all electrolyte concentrations by improving the theory but still basing it on only these two kinds of forces. The negative answer to this question can be established either by the analysis of coagulation of sols especially in the presence of surfactants, changing the hydrophobic nature of the particle surface to a hydrophilic one, or by direct investigation of the properties of the layers of liquid near the lyophilic surface.

In this paper an account is given of the results of the second approach to the problem. Results are given of the measurement of mechanical and thermodynamic properties of boundary layers of liquids. There are also discussed the direct experimental proofs of the ability of glass and quartz surfaces to change the physical properties of many polar liquids to a great depth.