sodium silicate, any one of several compounds containing sodium oxide, Na2O, and silica, Si2O, or a mixture of sodium silicates. Sodium ortho silicate is Na4SiO4 (or 2Na2O·SiO2); sodium meta silicate is Na2SiO3 (or Na2O·SiO2); sodium di silicate is Na2Si2O5 (or Na2O·2SiO2); sodium tetra silicate is Na2Si4O9 (or Na2O·4SiO2). All these compounds are transparent, glassy or crystalline solids that have high melting points (above 800°C) and are water soluble. They are produced chiefly by fusing sand and sodium carbonate in various proportions. The product is commonly known as water glass. The greatest single use of sodium silicates is as a raw material for making silica gel.