sodium silicate, any one of several compounds containing sodium oxide, Na₂O, and silica, Si₂O, or a mixture of sodium silicates. Sodium orthosilicate is Na₄SiO₄ (or 2Na₂O·SiO₂); sodium metasilicate is Na₂SiO₃ (or Na₂O·SiO₂); sodium disilicate is Na₂Si₂O₅ (or Na₂O·2SiO₂); sodium tetrasilicate 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.