The evaporating process is conducted as follows :— At the same time that steam is admitted to the chamber e, a tap is opened, by which the dilute aqueous solution of boracic acid flows from the vasco into the first scanello, the quantity being nicely regulated. As it passes slowly from one pan to another, much of the water is evaporated, the colour of the liquid changes gradually to a bright yellow, a peculiar odour is generated, and the solution becomes much more concentrated. This constitutes the secret of the success of the under taking ; wbat occupied sixty-two hours to evaporate with artificial fuel, is effected in twelve hours by natural moans, at infinitely less cost.
Being thus concentrated, the liquid is run into a large, deep reservoir, the caldaja a sale, d (Figs. 387, 388), whence it is pumped up every twenty four hours, and conducted by a wooden pipe t,o the bollajo, or crystallizing house, in which are arranged a number of large tonne or vats i (Figs. 390, 391), about 3 ft. 4 in. in diameter. When they are to be filled, the plugs situated over tho centre of each vat are removed from the pipe k, which runs round the room. The liquor remains here for four days, during which time the boracic acid orystallizes at the bottoua and sides of the vats, to a thickness of some inches ; the remaining liquid is then drawn off, by removing a second plug near the bottom of each vat, and finds its way along a drain to the evaporating house. Fresh liquid.is then admitted to the tonne, and the process is repeated, till they ar'S filled with hexagonal crystals of boracic acid, having the size and appearance of wafers, with a pearly luatre. As these crystals retain a large quantity of water, on removal from the vats, they are placed in large wicker baskets, called corbelli, to drain, and are afterwarda spread in thin layers on the floor of a large airy chamber, the asciugatojo, or drying room, Fig. 392. The floor is formed of brickwork, and is heated, like the evaporators, by a steam chamber beneath. The cryatals are repeatedly stirred with a wooden rake, loeing their eharp angles, and aeparating in great me.asure from each other. When dry, they are shovelled up into large barrels, containing from 12 to 131 cwt. (about 600 kiloa., or 2000 Tuscan lb.), and con veyed to Leghorn, whence the greater part is exported to England. The boracic acid produced in thie way ie far from pure. Au analysis of it, in 1842, gave— Latterly the amount of foreign salts hae much decreaeed, and the impurities do not now exceed about 13 per cent., chiefly sulphate of lime, ammonia, alumina, and magnesia. The acid crystala are imported in their crude state, and are here purified by repeated crystallization.
At the Lardarello works, there are twelve evaporating sheds, containing thirty-five evaporators. The average daily production is about 3 tons, sometimes reaching as much as 4 tons. At Oes telnuovo, the average production is about 27 tons a month, and at Ore other worka still less. The total annual production of Count Lardares property it now about 3000 tons. From 1818 to 1845, it averaged about 900 tons per annum ; from 1846 to 1850, about 1000 tons ; between 1857 and 1859, it rose gradually frorn 1100 to 2000 tons a year.
M. Durval's property at the lake of Monte Rotondo ia about 18 acres in extent. The water contains about 0.002 per cent. of horacie acid. The prepared acid has a maximum of about 15 per cent. of impurities, chiefly sulphates of ammonia, alumina, and magnesia, with hydrochloric acid, free sulphuric acid, and traces of organic matter. The process employed is identical with that at Lardarello. The produce is sent almost exclusively to French markets.
The waters of the lagoni at Travale contain boracic acid in much lees proportions than in the districts already described. The pools are situated at a ahort diatance from the village of Travale, in the valley of the Sajo, o, little etream feeding tbe Teccia and Merse, tributaries of the Ombrone. All the soffioni here have been produced by boring, some of the bores having a diameter of 16 in. Water is usually met with at a depth of 50 to 70 ft., though in one place a depth of 560 ft. was reached before the subterranean springs were tapped. At the Lagoni delle Galleraje, the waters contain sulphate of ammonia, in the proportion of about 1 grain to the pint, associated with the boracic acid. These products are extracted from the waters by an evaporating apparatus heatcd by the vapours from the soffioni ; but the profit derived from the manufacture of the sulphate of ammonia is very small, as the cost of production equals that of the boracio acid, while the commercial va,lue is only about one quarter. The boring of Il Foro Carlo, 240 ft. deep, yields per twenty-four hours about 132,144 gallons of water, at a temperature of 96° (205° F.), containing in eolution about 260 rnilligrarames (eay 4 grains) of boracid acid per litre (1.76 piot). The water rises to the surface as in an artesian well ; only about one-sixth of the supply is at present utilized: There is no basin, the water being led away directly, by cast-iron pipes, from the bore-hole to the precipitating tank, 60 ft. long, 45 ft. wide, and 1 ft. 8 in. deep. An improvement lately introduced here consists in heating the water in the tank, by pipee fed with vapour from a dry soffione, Foro Filippo, by which means a certain amount of water is evapo rated from tbe tank, and the solution is thereby concentrated to 400 millig,rammos (6 g,rains) per litze. The boring of Foro Filippo is 210 ft. in depth, and the tempemture of the water in the tank is maintained at 94° (202° F.). The solution, having a specific gravity of 11° &tune, is conducted in the usual way to the evaporators, which resemble those at Lardarello, the ternpe rature being retained at 76° (169' F.). Having traversed the entire length of the pans, the liquid is received in the tank at the lower end with a density of from 12° to 50° Beaumd, and is crystallized, dried, and packed in the ordinary manner. The evaporating house contains three rows of evaporators, 207 ft. in length and 10 ft. in width. The produce is about 57i lb. per diem.