Page:The American Cyclopædia (1879) Volume III.djvu/102

 96 BOEIO ACID name of sassoline, H S B0 3, composed of boric anhydride, B 2 O 3, 56-45 per cent., and water 43-55. It is also contained in the follow- ing 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 min- eral waters and the ocean. Boric acid is the hydrate of boric oxide, also called boric anhy- dride, B 2 O 3. It was discovered in 1702 by Homberg, 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. Un- less 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 alco- hol, and when this is ignited the acid gives to the flame a beautiful green color. This is em- ployed as a characteristic test of its presence. The acid properties of this substance at ordi- nary 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 pro- cess 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 fur- nished 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 ammo- niac, 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 Vnlcano, 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 accu- mulating, till it resembles more a bed of clean snow ; beneath it is found a layer of red-hot sal ammoniac, through which come up sulphur- ous vapors. The boric acid is gathered up as it collects, and with the sulphur and sal am- moniac is a source of no little profit to the pro- prietors 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 ob- tained 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 oifensive 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 sul- phur and saline substances. The waters be- neath 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 Oerboli (mons Cerbert) 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 saffioni, 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 hills 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 constrnct a basin with stone wall lining, to contain the water in- tended to receive and collect the acid brought up by the steam. The water is introduced from some supply at the surface, and the chim- ney 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 "la- goons" are of rough shapes, rudely construct- ed, from 5 to 8 ft. deep, and from 13 to 60 ft. in diameter ; they continue to receive the va- pors 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 soffioni, 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