Borax

BORAX, a colourless crystalline salt found native in quantity in California, Chile, Tibet, Peru and Canada. It has an alkaline taste, and is moderately soluble in water, for which it often serves as a softening agent. When heated, borax fuses, loses the water which makes up part of its molecule, and melts finally to a clear glass-like substance.

The borax which occurs along the shores and bottoms of saline lakes, as in California especially, is usually very pure. Borax was formerly obtained by melting boric acid (q.v.) and soda ash together and extracting the fused mass with water from which the borax was crystallized. Since extensive deposits of Colemanite (q.v.), which is principally calcium borate, have been discovered, borax is now largely prepared from this material and from Ras ovite found in California. Finely powdered native calcium borate is mixed and melted together with sodium carbonate. This causes sodium borate and calcium carbonate to be formed, and from this mixture the sodium borate may be extracted with water, leaving the less soluble calcium carbonate behind. By concentrating and cooling the solution of sodium borate, borax is obtained. If crystallization takes place above 6o° C the pentahydrate is de posited, while below that temperature the decahydrate forms. This phenomenon takes place whenever sodium borate solutions are allowed to crystallize, regardless of which compound was used in making up the solution.

Borax hydrolyses (see HYDROLYSIS), giving an alkaline solution. Fused borax dissolves many metallic oxides to form character istically coloured boron glasses. This property is made use of in metallurgy and in chemical analysis (see CHEMISTRY : Analytical) . Borax finds use in soaps, in glass making, as a household and commercial water softener, as a mild antiseptic, and in glazing pottery and related substances. As a flux in welding, it dissolves the metallic oxides present on the metal surfaces, leaving clean faces to be welded. Perborates are formed when borax is elec trolysed in solution or treated with hydrogen peroxide. The perborates find application in the arts as bleaching or oxidizing agents.

The United States produced, in tons of borax, valued at $4,083,209. Next to the United States, Chile is the largest producer of borax, one source of supply there being the residual or "mother" liquors of the nitrate vats.

Borax after fusion has the formula

being sodium tetraborate, and theoretically derived from the neutralization of four molecules of sodium hydroxide with two molecules of boric or boracic acid (q.v.), with elimination of two extra molecules of water, then it thus is a diborate or pyroborate. In its ordinary form, as "common" or prismatic borax it has ten molecules of water of crystallization, 1 o another form, known as "jewel lers' " or octohedral borax, has the composition 5 There is also another crystalline form found in nature, Rasovite, which is 4