E550 redirects here. For the Italian locomotive, see FS Class E550

Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles. Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide[1]:

Na2CO3 + SiO2 → Na2SiO3 + CO2

Anhydrous sodium silicate contains a chain polymeric anion composed of corner shared {SiO4} tetrahedra, and not a discrete SiO32− ion[1]. In addition to the anhydrous form there are a number of hydrates with the formulae Na2SiO3.nH2O (where n= 5, 6, 8, 9) which contain the discrete approximately tetrahedral anion SiO2(OH)22− with water of hydration e.g. the commercially available sodium silicate pentahydrate, Na2SiO3.5H2O is formulated Na2SiO2(OH)2.4H2O and the nonahydrate, Na2SiO3.9H2O is formulated Na2SiO2(OH)2.8H2O