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Besides its use flavouring food and assisting digestion, common salt finds a large number of applications in industry. Large quantities are used in producing alkalies, viz. sodium carbonate and caustic soda, and chlorine. Salt is used in preserving fish and other foods, in glazing common earthenware such as drain-pipes, and in melting snow and ice on roads, an effect due to the lowering of freezing point of water by the dissolved salt. In salt-glazing, salt is thrown into the furnace in which the goods are fired, and is volatilised. The vapour forms a fusible silicate glaze with the silica of the clay, and hydrochloric acid is evolved: SiO2 + 2NaCl + H2O = Na2SiO3 + 2HCl.
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