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water glass n.
See soluble glass.
crystal-like lumps that range from colourless to white or grayish white and resemble glass but can be dissolved in water to form a syrupy liquid. Some forms are slightly soluble, and some are almost insoluble; they are best dissolved by heating with water under pressure. A little water dissolves water glass more readily than much water does. The solutions are strongly alkaline. The chemical formulas Na2SiO3, Na6Si2O7, and Na2Si3O7 describe the composition of various forms of water glass.