Boric Acid, a compound of the element boron with oxygen and hydrogen; also called boracic acid. It occurs in nature under the name of sassoline, H3BO3, composed of boric anhydride, B203, 56.45 per cent., and water 43.55. It is also contained in the following minerals, in the proportions given: bora-cite (magnesium chloride and borate), 62.5 per cent.; rhodicite (calcium borate), 30 to 45; tiza or boronatrocalcite, 30 to 44; hydrobo-racite, 47; borax or tincal, 36.53; datholite (boro-silicate), 18; botryolite (do.), 20.35; ax-inite (do.), 2 to 6.6; tourmaline, schorl (do.), 2 to 11.8; larderellite (ammonium borate), 68; lagonite (iron borate), 49; also in many mineral waters and the ocean. Boric acid is the hydrate of boric oxide, also called boric anhydride, B2.O3. It was discovered in 1702 by Romberg, who called it sedative salt. The crystals are white, pearly, and scaly, unctuous to the touch, and exposed to a temperature of 212° F. lose half their water of crystallization, and at a higher temperature the whole. The mass fuses into a hard transparent glass, but will not sublime except at a white heat. Unless protected from the air it absorbs water and loses transparency.

Deprived of water, its specific gravity is 1.8; that of the hydrate is 1.48. Boiling water dissolves one third of its weight of the crystals; cold water only about one thirtieth. They are soluble in alcohol, and when this is ignited the acid gives to the flame a beautiful green color. This is employed as a characteristic test of its presence. The acid properties of this substance at ordinary temperatures are very feeble. It scarcely reddens vegetable blues, and turmeric paper is rendered brown by it as by an alkali. It is expelled from its combinations by stronger acids almost as readily as carbonic acid is. But at high temperatures, as when exposed to a red heat in a crucible, boric acid mixed with sulphate of soda expels the sulphuric acid, and combines with the soda; when cold, the process may be reversed. - In boiling the aqueous . solution, the acid is taken up by the steam; much more, however, is this the case with the alcoholic solution. It is to this property we owe the supplies of boric acid, which are furnished from the interior of the earth by jets; of steam that issue through fissures, and come up more or less laden with this material, as well as other substances, as sulphur, sal ammoniac, clay, and gypsum.

The acid is deposited in the soil in the form of solid efflorescences, or is collected in pools of water, through which the jets are made to pass. In South America it is collected upon the surface of the ground. At an island of the Lipari group, called Vulcano, 12 m. N. of Sicily, it rises in vapor at the bottom of the crater of an extinct volcano, 700 ft. below its summit. The vapor condenses here upon the bottom and sides, like frost after a heavy dew; but it goes on accumulating, till it resembles more a bed of clean snow; beneath it is found a layer of red-hot sal ammoniac, through which come up sulphurous vapors. The boric acid is gathered up as it collects, and with the sulphur and sal ammoniac is a source of no little profit to the proprietors of the volcano. It is also found at Sasso in S. Italy, and has hence been called sassoline. But the great supplies of it are obtained from the volcanic districts of Tuscany. Here, over an area of some 30 m. of wild mountain land, issue through beds of calcareous rocks, black marl, and sand, numerous jets of steam, which rise in white clouds among the hills, and spread around offensive sulphurous smells and vapors, that drench those passing by the spot. The ground itself is hot and undermined.

It shakes beneath the feet, and is sometimes so treacherous as to let man or beast walking upon it fall through into its heated recesses. Its surface is covered with incrustations of sulphur and saline substances. The waters beneath are heard boiling with strange noises, and are seen to break out upon the surface. Of old it was regarded as the entrance to hell. The name Monte Cerboli (mons Cerheri) is still retained by a neighboring volcano, and contains the principal lagoon or pool from which the acid is obtained. The great value of these natural exhalations, or soffioni, as they are called, was discovered in 1818, and made available by the skill and ingenuity of Count Larderel. Wherever up the slopes of the hiils the ground is observed to be hotter than usual, and sulphurous vapors are seen to rise from it, and the surface is felt to tremble, a pit is dug, from which soon issues a column of steam. A temporary wooden chimney is put up for this to pass through, so that the workmen may continue the excavation, and construct a basin with stone wall lining, to contain the water intended to receive and collect the acid brought up by the steam. The water is introduced from some supply at the surface, and the chimney is then removed.

The heat soon causes the water to reach nearly the boiling point. It penetrates into the fissure, and is rejected by the steam, bringing up with it a portion of boric acid. As it is found that the quantity which the water is capable of absorbing is very small, fresh supplies are introduced every day; and the pits are so arranged down the slope of the hill that the water entering at the top passes from an upper basin into a lower one, and so on, till at the foot it is received into large evaporating pans. The basins or "lagoons" are of rough shapes, rudely constructed, from 5 to 8 ft. deep, and from 13 to 60 ft. in diameter; they continue to receive the vapors for years, but the jets are liable at any time to cease and break out in a new place. The pans are very numerous, and present a great evaporating surface. They are heated by the vapors of some of the soflioni, which are conveyed under them in flues. After the liquor has passed through a series of the pans and been greatly concentrated, it is baled out and drained through baskets, and the precipitated salt is taken to the drying rooms. These are of brick and warmed in the same manner as the pans are heated.

Thus the operations are carried on with no expense of fuel, and boric acid is obtained to the amount of 5,000,000 Tuscan pounds or more per annum. Since 1854 artificial soffioni have been produced by boring, and the yield from this source is very large. The product is of late years more impure than formerly, the foreign matters having increased from 8 per cent, to 25 per cent., which appears to have excited some apprehension lest the supply may give out. An analysis of the crude acid made by Vohl in 1866 is interesting, as showing the great variety of the associated substances. It is as follows:

Boric acid crystallized.....

80.000

Hygroscopic water........

4.500

Sulphuric acid........

9.610

Silicic acid......

0.810

Sand.........

0.300

Oxide of iron...........

0.120

Oxide of maganese........

0.001

Alumina.....

0.570

Lime........

0.010

Magnesia.........

0.600

Potash......

0.180

Ammonia....

2.980

Soda.............

0002

Chloride of sodium......

0.100

Organic matter and loss........

0.217

100.000

Our knowledge of the Tuscan locality, and the process as there conducted, is derived from the treatise of Pay en, who describes it in detail. Sir John Bowring and Durval have also furnished interesting data concerning it. Boric acid is of value principally for the preparation from it, of borax. It is used in manufacturing a paste for artificial gems, and in making enamel. Its price in Tuscany is about 10 cents a pound.