BORAX, the biborate of sodium (Na 2 B 4 O 7 ), a substance found in commerce under the two different forms of ordinary or prismatic borax, which contains ten equivalents of water of crystallization, and octahedral or jeweller’s borax, which has only five molecules of water in its composition. The former, which is the variety commonly met with, occurs as a natural product in various parts of the world. In former times crude borax was procured chiefly from Thibet, whence it came by way of India under the name of tincal. It also is found in other parts of Central Asia, at Halberstadt in Transylvania, in Canada, aud in Peru; and in recent years an important source of the mineral has been discovered near the Clear Lake in California, in a body of water now called the Borax Lake. In very dry seasons the water almost entirely disappears from the basin of the Borax Lake, which is situated in a region containing hot springs and the remains of volcanic action. In 1863, when the lake measured 4000 feet long, 1800 feet across at its widest part, and about 3 feet deep, the water was found to contain 2401 ’ 56 grains of solid matter per gallon, of which 535Ό8 grains represented crystallized borax. The bed of the lake is occupied with a deposit of borax crystals, which are obtained by sinking caissons, pumping out the water, and digging up the deposit. Californian crude borax is fit for use by assayers and others without undergoing any purification; but that obtained from Thibet contains a greenish encrusting matter of a soapy consistence which has to be separated before the material is fit for use under the name of refined borax....
The supply of borax is, however, more largely derived by artificial means from boracic or boric acid, or from salts in which that acid occurs, than from these natural sources. Boracic acid is found among the ejecta around the craters of some volcanoes, and it is found in jets of vapour which stream forth from fissures in the earth in regions of volcanic disturbance. The chief source of boracic acid at the present day is found in the Maremma of Tuscany, an extensive and desolate track of country embracing an area of about forty miles, over which jets of vapour and heated gases {soffioni) and springs of boiling water spurt out from numerous chasms and fissures. The Maremma is disturbed by frequent volcanic shocks; at some points the mouths of the fissures open direct into the air, at others they are covered by small muddy lakes {lagoni). In addition to a small impregnation of boracic acid the soffioni contain ammoniacal vapour, to fix and obtain which the gases at some works are led through sulphuric acid. For obtaining the boracic acid a series of basins or artificial lagoni are formed over the soffioni, so arranged that water to be charged with the acid is conveyed by gravitation from the first to the last of the series. Water is led into the highest and by the action of the heated gases it is soon in a state of ebullition. After being so left for about a day it is drawn off into the second, where it remains under like circumstances for the same period, and so to the end of the series, when the water should contain nearly 2 per cent, of boracic acid. The mechanical impurities being allowed to subside, the liquor is then run into evaporating pans, shallow lead-lined vessels, heated by the gases from the soffioni themselves. The evaporating pans are worked on a continuous system, similar to the lagoons; the liquor placed in the upper being concentrated down to half its original bulk is run into the second, and so on till it reaches a degree of concentration fit for crystallizing out the acid. In recent years artificial soffioni have been formed by boring through the rock till some of the numerous chasms or chambers, with which the interior is honey-combed, are reached, when immediately all the phenomena of a boracic soffione are established. From some of these artificial soffioni issues water of sufficient richness in acid to be led there direct to the evaporating pans. Similar emanations of volcanic vapours and boracic acid have been discovered in Nevada, United States. Boracic acid is also obtained from boronatrocalcite (Ulexite or Hayesine), a double salt of sodium and calcium, of which extensive deposits exist in the neighbourhood of the nitrate of soda beds of Chili and Peru. It is very variable in constitution and condition of purity. Similar deposits are found in California, Nevada, and Nova Scotia, and from the West Coast of Africa is received a borate of lime bearing the name of rhodizite. The boronatrocalcite, or borate of lime, as it is called in commerce, is applied in its unrefined condition to many uses for which borax is employed. In 1855 Dr T. Richardson patented a process for using the picked and washed boronatrocalcite as a substitute for borax in the glass manufacture and preparation of pottery glazes. It is, however, chiefly employed as a source of boracic acid, and there are also several methods of obtaining borax direct from the compound salt.
Commercial boracic acid usually contains a considerable percentage of sulphates of ammonium, magnesium, and calcium besides other impurities. To prepare borax from this acid, from 110 to 120 parts of crystallized sodium carbonate are required for 100 parts of boracic acid. The soda is dissolved in a lead-lined vessel heated with steam, to which the boracic acid is added in repeated charges. The vessel is covered and the carbonate of amirtonia given off is led into a solution of sulphuric acid and fixed. For the production of ordinary or prismatic borax the solution is brought to a strength of 20° to 22° Baumé (1 - 161 to 1*180 sp. gr.) and allowed to cool down as slowly as possible, so that the crystals may assume the large size demanded in commerce. Octahedral borax is deposited when a solution indicating 30° Baume (sp. gr. 1 ’ 264) is slowly cooling down from 79° to 56° C. Below this point the formation of ordinary borax takes place.
Under the blowpipe borax parts with its water, and melts into a clear glass which has the peculiar property of dissolving many metallic oxides, and thereby exhibiting characteristic colours, on which account it is of great value in blowpipe analysis. The same property also renders it a valuable material for pottery glazes and enamels, and as it adheres closely to clean surfaces of metal and prevents their oxidation under high heat, it is indispensable for use in hard soldering, and is largely employed in brass manufactures. It is also one of the ingredients employed in glass-making. Borax forms with oils and fats a soap which has been proposed as a detergent; but experiments conducted by the late Professor Thomas Anderson of Glasgow show that it has a more corrosive influence on fibres than common soap. In Belgium powdered borax is used in domestic washing, with the object of economizing soap. Borax is used in medicine as an external application in skin diseases, and the preparation known as mel boracis is a useful gargle in ulceration of the mouth and throat. In Sweden boracic acid is extensively employed for the preservation of meat and milk; and while it forms an efficient antiseptic, food prepared with it is said to be perfectly fit for use. A very beautiful pigment, now much used in calico-printing, under the name of Guignet’s green, is a borate of chromium.
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