Boracite, or borate of magnesia, is one of the richest native boracic salts, containing, when pure, about 70 per cent. of boracie acid and 30 per cent. of magnesia. It crystallizes in the cubio system, and is and double-refracting. It is found generally in association with deposits of rock salt, gypsum, and potash-salts (kainite and carnallito), usually in nodules, rarely in strata. The variety found in the German potash beds is called Stassfurtite. Wheu washed until the water which passes no longer precipitates with nitsato of silver or chloride of barium, and then dried at 100° (212° F.), these minerals give respectively the following composition:— The formula for boracite will then be 2(3Mg04B03) MgCl; Stassfurtite contains one more equivalent of water.
Howlite, oil silicoborocalcite, is a hydrous borosilicate of lime, containing about 43 per cent. of boracic acid. It occurs in a nodular form in gypsum and anhydrite, in Nova Scotia and in the copper region of Lake Superior.
Cryptomorphite is a hydrated borate of lime and sods, with 58f per cent. of boracic acid.
Boracie acid exista in a number of other minerals as a subsidiary ingredient ; but only the borate; of soda, lime, and magnesia, besides the native acid, have yet been found in sufficient abundance to be economically employed in the preparation of commercial boracic compounds.
The industrial importance of borax and its allies may be inferred from the fact that the monopoly of the market, enjoyed by the Tuscan producers in 1855, evoked a petition from the consumers, praying the Government for information concerning the resumption of the trana Himalayan export, which had decayed under the influence of the policy pursued by the Tuscan monopolists. Their address represented the article as one of prime necessity for porcelain and pottery manufacturers, and enlarged on the mischief resulting from its excessive price, and the consequent employment of inferior substitutes.
Having adverted to the principal forms under which boracic compounds are met w ith in nature, the next consideration will he their geographical and geological distribution, together with the native methods of preparing the raw product for exportation. Afterwards, will be added a description of the treatment of the imported articles, by which they are fitted for use.
1. Europe.—The preparation of native boracic acid in Tuscany dates from 1818, and now forms ono of the chief branches of Italian ohemical industry, and an important factor in the sum total of the production of boracie compounds. The occurrence of the acid is as vapour emitted with steam from fissures in the earth, and as a solution in water. The locality in which this curious pheno menon is developed is of comparatively limited extent, chiefly in the neighbourhood of the villages of Monte Cerboli, Castelnuovo, and 1VIonte Rotondo, lying between Massa Marittima and Volterra.
The sides of many of the valleys of tributaries of the river Cecina are studded with vapour yenta (sOffioni), and with ponds of boiling muddy blue water (lagoni). These have the same general direction as the axis of the Appennines, are in close proximity to IVIiocene serpentine eruptions, and are intimately connected with recent earthquakes. Boracic acid has never been found in a solid state at any depth to which search has been made; its origin is, therefore, somewhat a matter of specu lation. Two distinct theories have been adduced to account for its presence as an absorbed gas at or near surface :—(1.) It may result from the double decomposition of water and a volatile boracic salt ; in support of whieh view, the acid appears only when water is present. (2.) It may be caused by the reaction of sulphuric acid on mineral borates, such as tourmaline (containing 1.9 to 4.2 per cent. of boracic acid). This supposition is strengthened by the fact that the neighbouring granite is so rich in this mineral as to be named " tourmaliniferous." It is to be noticed that until water ia introduced into the vapour vents, the presence of boracic acid is not manifest. Mineral borates existing at a. depth in the earth would remain unaffected by the contact of sulphurous, or even aulphuric, acid in presence of a higla temperature ; but the admission of water would lower the temperature, and call into play the influence of the sulphuric acid, by which the boracic acid would be liberated frorn its compounds, and would be ejected in combination with the water and steam. The presence of sulphuric acid is abundantly testified by the frequency of such minerals as sulphates of ammonia, and of lime, alurn, gypsum, &c., around the lagoni.
It is now necessary to repeat in a few words the threadbare history of the utilization of this apparently inexhaustible source of boracic acid. The discovery of the acid in the waters of the lagoni of Monte Rotondo and Castelnuovo was made about a century ago, and in 1818, the first attempt was made to recover the acid from its aqueous solution. About 3f tons of very crude crystalline acid was obtained as the result of nine and a half months' working, and was exported to France. For nine years the undertaking was continued, but with very little profit to the proprietor, on account of the immense outlay needed for firewood, which was naturally very scarce in such a volcanic district. The turning-point in the success of the industry was the happy idea of economizing the heat contained in the steam which escapes from the soffioni, for the purpose of con centrating, by evaporation, the very dilute solutions of boracic acid represented by the waters of the lagoni.