BIBORATE OF SODA.

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Natural History. —Borax is a substance peculiar to the mineralkingdom. It has been found in some mineral waters; as those ol' SanRestituta, in Ischia (Gairdner, On Mineral Springs, p. 414). It occursalso in the waters of certain lakes, especially those of Thibet and Persia .

Preparation.— Borax is obtained in two ways:—1st, by refiningnative borax; 2dly, by saturating native boracic acid with soda.

(a.) By refining native or crude borax. —About fifteen days’ journeynorth from Teeslioo Lomboo, in Thibet , is a lake, said to be abouttwenty miles in circumference, and supplied by brackish springs risingfrom the bottom of the lake itself. In consequence of its high situation,during a part of the year this lake is frozen over. The water of it con-tains, in solution, both common salt and borax. The latter crystallizeson the edges and shallows of the lake, and is taken up in large masses,which are broken and dried.

It is imported, usually from Calcutta , under the name of tincal (aword derived from tincana, the Sanscrit name for borax; Royle’s Essayon Hindoo Medicine, p. 97) or crude borax (borax cruda sen nativa ),in the form of flattened six-sided prisms, coloured with a greasy unctuoussubstance, said, by Vauquelin, to be a fatty matter, saponified by soda ;the colour is yellowish, bluish, or greenish. Mojon states that thegreenish grey matter which surrounds some kinds of rough borax, con-tains native boron. Various method^ have been contrived for refiningborax ; some calcine it, to destroy the fatty matter, others wash it with analkaline solution (soda or lime), and then dissolve and crystallize. Theproduct is called refined, borax (borax depurata seu purificata).

(b.) By saturating native boracic acid. —In the year 1776, Messrs.Hoefer and Mascagni discovered boracic acid in the Lagoni of Tuscany ,in a state of efflorescence, and also in solution in the waters with whichthe soil is impregnated. From the soil is constantly evolved aqueousvapour, impregnated with boracic and hydrosulphuric acids; formed, asit is supposed, by the action of water on sulphuret of boron containedin the interior of the earth,—by which part of the water is decomposed,the oxygen of which acidifies the boron, while the hydrogen formshydrosulphuric acid with the sulphur, and the heat evolved causes theformation of some aqueous vapour. By washing the mud surroundingthe fumaroles, or craters, decanting the liquor, and evaporating, roughor Tuscany boracic acid is obtained. To form borax from this, a solutionof the carbonate of soda is saturated with the rough acid : effervescencetakes place, and borax is formed.

Properties. — It occurs in large, colourless, transparent crystals,whose primary form is the oblique rhombic prism. In commerce wefrequently meet with it in irregular shaped masses. Its taste is saline,cooling, and somewhat alkaline. It reacts on turmeric paper like analkali. By exposure to the air it effloresces slowly and slightly. Whenheated it melts in its water of crystallization, swells up, and forms alight, white, porous substance, called calcined borax (borax usta seucalcinata). At a higher temperature it fuses into a transparent glass( glass of borax), which is anhydrous borax. It is soluble in twelve partsof cold, or in two parts of hot water.

Characteristics. —Borax may be recognized by the following cha-racters : it reddens turmeric paper; it fuses before the blowpipe into a