# Sodium Silicate, Also called "water glass." An alkaline salt, prepared by calcining diatomaceous earth. quartz, or sand with sodium hydroxide or sodium carbonate. The salt consists of varying proportions of sodium oxide and silica. such as Na2SiO3. It is used in the manufacture of paper for improving physical tests, increasing the retention of fine particles, and pH control. In this final use, it provides another means of increasing alumina in the stock preparation system. one that is accomplished by raising the pH value of the stock, thereby forcing the use of additional alum to lower the pH. Also called "water glass."