The article is devoted to the development of ideas about polymer composition of silicate anions in water glass. On the base of sequential reactions of hydrolysis and growth scheme the estimated equation to determine the average degree of polycondensation of silicate anions is obtained. The method of determination of hydroxyl anions concentration on the known SiO 2 concentration values and water glass silica modulus for convenience of usage of the equation is offered. Issues considered are of interest for explanation of structure formation processes in alumina-silicate disperse systems with additives of sodium silicate solutions.