Borax

Borax, or sodium tetraborate, chemical compound, Na₂B₄O₇· 10H₂O, crystallizing in the monoclinic system, with hardness 2 and relative density 1.7. When heated it swells, gives off water, and fuses easily, forming a glass-like mass. Mineral borax was discovered in ancient times in Tibet and was exported to Europe under the name tincal. In modern times, this source was replaced by extensive deposits of borax and related minerals in California; Stassfurt, Germany; Tuscany, Italy; and the Atacama Desert, Chile. The mineral kernite, or rasorite, Na₂B₄O₇· 4H₂O, is identical with borax except for water content, hardness (3), and relative density (1.95).

Borax dissolves readily in water, forming an alkaline, antiseptic solution that is used as a disinfectant, detergent, and water softener. It is an excellent flux for soldering and welding because it dissolves the coating of metallic oxide to leave a clean metal surface. Borax beads are used in chemical laboratories for analytical purposes; when melted with borax, different metallic oxides form beads of differently coloured borates. Borax is also used in the manufacture of ceramics, enamel, and glass. Pyrex glass contains 30 per cent borax by weight. In making such products as paint, calcimine, and coated paper, borax is combined with the plastic casein.