Sodium silicate, also called water glass or Soluble Glass, is any one of several compounds containing sodium oxide, Na2O, and silica, Si2O, or a mixture of sodium silicates varying ratios of SiO2 to Na2O, solids contents, and viscosity. Traditionally, sodium silicates are classified according to the acid from which they are derived as Orthosilicate Na4SiO4; Metasilicate Na2SiO3; Disilicate Na2Si2O5; Tetrasilicate Na2Si4O9. They are also classified by an X-ray diffraction method according to their crystalline structure.