The extraction of arsenic from the cobalt ores, is performed at Altenberg and Reichenstein, in Silesia, with an apparatus, excellently contrived to protect the health of the smelters from the vapours of this most noxious metallic sublimate.

[Figs. 20.] to [23.] represent the arsenical furnaces at Altenberg. [Fig. 20.] is a vertical section of the poison tower; [fig. 21.], a longitudinal section of the subliming furnace A, with the adjoining vault B, and the poison tower in part at n; [fig. 22.], the transverse section of the furnace A, of [fig. 21.]; [fig. 23.], ground plan of the furnace A, where the left half shows the part above, and the right the part below the muffle or oblong retort; B′ is the upper view, B′′ the ground plan of the vault B, of [fig. 21.]; m, n, the base of the poison tower. In the several figures the same letters denote the same objects: a is the muffle; b is its mouth for turning over the arsenical schlich, or ground ore; c c c, fire draughts or flues; d, an aperture for charging the muffle with fresh schlich; e, the smoke chimney; f, two channels or flues for the ascent of the arsenious fumes, which proceed to other two flues g, and then terminate both in h, which conducts the fumes into the vault B. They issue by the door i, into the conduit k, thence by l into the spaces m, n, o, p, q, r, of the tower. The incondensable gases escape by the chimney, s. The cover t, is removed after completion of the process, in order to push down the precipitate into the lower compartments.

[Figs. 21 and 22 enlarged] (93 kB)

The arsenious schlichs, to the amount of 9 or 10 cwt. for one operation (1 roast-post, or roasting round), are spread 2 or 3 inches thick upon the bottom of the muffle, heated with a brisk fire to redness, then with a gentler heat, in order to oxidize completely, before subliming, the arsenical ore. With this view the air must have free entrance, and the front aperture of the muffle must be left quite open. After 11 or 12 hours, the calcined materials are raked out by the mouth of the muffle, and fresh ones are introduced by the openings indicated above, which are closed during the sublimation.

The arsenious acid found in these passages, is not marketable till it be re-sublimed in large iron pots, surmounted with a series of sheet iron drums or cast-iron cylinders, upon the sides of which the arsenic is condensed in its compact glassy form. The top cylinder is furnished with a pipe, which terminates in a condensing chamber.