There are about a dozen places where the production of horacic acid is now carried on.
1. Lardarello, or Lagoni of Monte Cerboli.
2. Castelnuovo, Val di Cecina.
3. Lustignano, Lagoni Rossi.
4. Serrazeano, Lagoni Solforei.
5. Sasso, Lagoni di Acquavita. • 6. Monte Rotondo, Lagoni della Pianacce.
7. Il Lago, including San Federigo, Sau Eduardo, and La Collachia.
These all belong to Count Lardarel, and are situated within a few miles of the little commune of Castelnuovo, in the governrnent of Leghorn. Lardarello is the principal establishment, and the produc,e of the other works is taken there for preparation.
8. 11 Lago Solforei di Vecchiena, at the Lake of Monte Rotondo, the property of M. Durval.
9. I Lagoni delle Galleraje, at Travale, the property of an Italian Company, the Societa Amtnonia Borica Travalese.
The system of working is practically identical at all the establishments, except the last named. A description of Lardarello, the principal, will therefore suffice for the others. A little to the south of the village of Lardarello, groups of half-a-dozen or more lag oni are seen pitted about on the hill-slopes. These lagoni are formed in the following way. A space is chosen where several soffioni are situated in convenient proximity to each other. A quantity of clay is then dug out, so as to leave a hollow of more or less circular shape, enclosing the orifices of the soffioni. The sides of this artificial basin are strengthened by rough masonry, but the bottom requires no such lining. The depth varies from 4 or 6 feet to nearly as many yards, the capacity of the basin requiring to be carefully adjusted to the force of the vapours issuing from the soffioni which it includes. Whilst the workmen are engaged in excavating the basin, they are protected from the scalding influence of the vapours, by means of small wooden chimneys, placed over the vents, so as to conduct the steam, &c., into the atmosphere at a sufficient height above them. Chains of basins are thus made on the hill-sides, the members of each set of half-a-dozen or so being arranged in terrace like order, and connected by little canals. Having completed a series of basins, the next step is to transform them into lagoni or pools, by introducing water. This is conducted, by a channel, from any suitable source to the topmost of the series of basins. Percolating through the natural fissures in the bottom of the basin, it comes into contact with heated gases aud rocks, and is irnmediately converted into steam, which is re-ejected with considerable force, and is recondensed in the body of cold water lying in the basin. After remaining in the basin for twenty-four hours, constantly agitated by the escape of subterranean vapours, the water acquires a slate-blue colour, and is there upon run from the first basin, by a little channel, to the next lower in the series. Thus the second basin assumes the character of a lagone, and is made to furnish its due proportion of boracic acid.
Here, also, the water remains for twenty-four hours, and so on with each basin of the series, a fresh supply being admitted to the topmost as fast as it is run off to the next. Additional portions of boracic acid are absorbed by the water during each stage of its journey, till finally it contains about 0.50 per cent. of the acid in solution. The temperature of the liquid is above 100° (212° F.), and dense volumes of steam are given off in its passage. While still boiling, it is conducted by a pipe h to the vasco (see Fig. 386), a tank about 66 ft. square and 18 in. deep, covered by a tiled roof supported on slight brick pillars. Here it is allowed to settle; the impurities held mechanically in suspension—clay and insoluble sulphatcs—soon precipitate themselves, and the water is run off from the tank in a clean state.
The next step is the concentration of this dilute solution of boracic acid, which is performed in a series of evapomting pans, in an adjoining building, shown in elevation in the same figure. These " Adrian evaporators," as they are called, Figs. 387, 388, consist of three parallel rows of shallow leaden divisions, named scanelli, each one of which is -} in. lower than that preceding it, and separated only by a leaden partition in. broad and of about the same depth. These scanelli, or pans, a, are about 200 ft. in length by 8 ft. 4 in. to 10 ft. in breadth, and are arranged under a roof b, supported on light brick pillars c, which suffices to keep out the rain, without impeding the process of evaporation. The divisions of the scanelli run transversely, and measure about 2 ft. 7 in. to 3 ft. 4 in. in width ; the partitions aro about 2 in. high, and the pans are placed at a slight inclination, to favour the flow of the water. By a reference to Fig. 387, it will be seen that the scanelli rest on beams over a low vaultod steam chamber e, lined with hydraulic cement, to protect the masonry and retain the heat, derived through pipes, from soffioni. The supply of heated vapours was first obtained by vaulting over a natural soffione with a rough stonework dome, Fig. 386, about 10 ft. high, firmly bound with wrought-iron bare. The admission of a little water produced a considerable head of steam, which was led by the pipe f into the vaulted chamber e (Fig. 387), and, having traversed it, was allowed to escape by the chimney g. It was soon found, however, that these domes were liable to be undermined by the action of the vapours, and in place of them, the plan is adopted of connecting steam pipes with the tube of an artificial boring, which renders the apparatus mom convenient, neater, and easier of control. These artificial soffioni are bored, with the tools shown in Fig. 389, to a diameter of 10 or 12 in., and are lined with eheet-iron tubing.