The aggregative stability of colloidal solutions arises from the presence of a barrier preventing proximity of the particles, which is caused by the presence of repulsion, as well as attraction between these particles. Colloidal systems of two types-lyophobic and lyophilic-are formed, depending on the nature of the repulsion forces. By non-ionogenic surface-active agents (SAA) hydrophobic sols are converted into hydrophilic. This transition, manifested in an extremely sharp rise in the resistance of the system to the effect of electrolytes, is realized at fairly low SAA concentrations, which depend on the nature and content of the colloidal disperse phase and on the structure of the surfactant.The author's experimental data permit some inferences to be drawn as to the nature of the phenomena occurring on stabilization of colloidal solutions by means of SAA and the mechanism of breaking lyophilic sol stability in highly concentrated electrolyte solutions. The surfactant molecules, adsorbed on colloid particles, cause hydrophilization of their surface. Highly concentrated electrolyte solutions cause disturbance of polymolecular solvate layers at the particle surface, thus allowing the colloidal system to coagulate.* With a positive silver iodide sol the sensibilization attains the highest limit; the surfactants cause coagulation of the colloidal solution without addition of electrolytes. t During sol coagulation by electrolytes with bi-and tri-valent counter-ions (calcium and lanthanum salts) such slight surfactant additions had no effect on the stability, * Electrophoresis shows that colloidal particles in SAA-protected systems move in an electric field.

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