Borax

Borax, hydrous biborate of sodium, occurs in nature and most commonly in commerce in oblique prismatic crystals, having ten molecules of water of crystallisation; but is also manufactured with only five molecules, and is then known as octahedral or jewellers' borax. Native borax is white or greenish, sub-transparent, resinous and soft. Before the blowpipe borax parts with its water with intumescence, melting into a clear, colourless glass which will readily dissolve many metallic oxides and exhibit characteristic colours. A bead of fused borax in a loop of platinum wire is therefore largely used in the blowpipe analysis of minerals. Borax used to be chiefly obtained from the evaporation of the waters of lakes in Thibet under the name of tincal. It is now obtained from Borax Lake, California, the bed of which consists of pure borax crystals, whilst its waters contain 535 grains of borax per gallon. Borax is also prepared by treating boracic acid (q.v.) with carbonate of soda. Octahedral borax is precipitated at temperatures between 79° and 56° C. Borax is largely used as a flux, in soldering, in glass-making, in making fusible glazes and enamels for pottery and artificial gems, and to economise soap in washing, though it has a corrosive effect upon fabrics.