Boracic Acid, or BORIC ACID, is found native (1) in the steam or vapour which rises from certain volcanic rocks in Tuscany, (2) as the mineral Sassolite, occurring largely in California, and (3) as a saline incrustation in the crater of a mountain in the island Volcano, in the Lipari group, 12 miles N. of Sicily. Boracic acid also occurs in combination in Borax, Datholite (q.v.), Boracite, Ulexite, and other minerals, and to a very minute extent in trap rocks generally. The plan of collection pursued in Tuscany is to form a series of caldrons —100 to 1000 feet in diameter, and 7 to 20 feet deep—partly by excavation, and partly by building, in the side of the volcanic mountain where the steam and boracic acid vapours are issuing from fissures, and divert the course of a mountain stream, so that at pleasure the caldrons or lagoons may be supplied with water. As the volcanic vapours gurgle through the water contained in the lagoons, the boracic acid is arrested by the water, which becomes impregnated with it. The liquid is passed from one lagoon to another, then on to settling-vats and flat-bottomed evaporating pans, till it becomes so concentrated that on cooling, impure crystals of boracic acid separate. In this condition it is exported.
The production of boracic acid from ulexite, a native borate of lime and soda found in California, has of recent years assumed importance. Ulexite is found as rounded concretions, white in colour, varying in size from inch to 12 inches in diameter, and is locally known as 'cotton balls.' After being broken down, it is heated to 200° F. (93.3° C.) along with three times its weight of water, and sulphurous acid gas is forced in till saturation takes place. The whole is allowed to settle, and the clear solution of boracic acid run off and crystallised. So prepared, it contains about 4 per cent. of impurities. In this process there are produced in addition to boracic acid the sulphates of lime and soda, as well as sulphuretted hydrogen. Native boracic acid is employed as a source of Borax (q.v.), and contains about three-fourths of its weight of true boracic acid, accompanied by one-fourth of water and impurities. In a pure condition boracic acid may be prepared by dissolving forty parts of borax, , in one hundred of water, and acting thereon by twenty-five parts of hydrochloric acid, , which removes the soda, forming chloride of sodium, , and water, , and on cooling the mixture, the boracic acid, , crystallises out. On re-solution in water and re-crystallisation, it is obtained in pure white feathery crystals. These crystals have the composition of , and on heating lose the whole of the water they contain, yielding boracic anhydride, , thus:
Boracic acid is used in the arts as a flux, as an ingredient in the glaze employed in pottery; and the wicks of stearine and composite candles are treated with it, so that when the candle is burning, the end of the wick, when it gets long, may fuse and fall to the side, where it can be burned away. As an antiseptic and preservative of food, boracic acid is extensively employed either alone or along with borax. An ointment, called 'Lister's Ointment,' of great antiseptic power, is prepared from boracic acid, wax, and paraffin. In the preservation of butter, milk, wine, beer, meat, and fish, it is probably used to a greater extent than any other antiseptic. There is still much discussion as to the desirability of preserving food by this means, but as yet no authentic evidence has been produced to show that its use has been followed by evil results. Boracic acid is volatile when its solution in water or alcohol is evaporated, and when alcohol containing it is ignited, the flame has a green colour characteristic of boracic acid.—Boro-glyceride (q.v.), prepared by heating boracic acid with glycerine, possesses very valuable antiseptic properties.