ARSENIOUS ACID.

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I ->ap-

Section of the Rousting Furnace,

(a) Ash-pit. ( b ) Fire-place.

(ece) Brick arches for supporting the muffle,(c) Earthen muffle for receiving the ore.

(f) IIo]iper for introducing the ore.

(</) Passage for the fumes into the condens-(hh) Flue. [ing chamber.

(g) Vent for protecting the workmen from

the arsenical fumes.

(Fig. 57.)

h.

(Fig. 56.) _ heads (d) are attached, which at

the tops are contracted into cones(e), each terminating in a pipemade of sheet iron, and commu-nicating with the condensingchamber (fig. 57). Heat is ap-plied for twelve hours, by whichthe acid is sublimed and con-densed on the sides of the ironhead in the form of a glassy mass,called glacial white arsenic ( weis -sen Arsenikglas ), which is some-times purified by a second, or eventhird sublimation. If it containany sulpliuret of arsenicum, a lit-tle potash is mixed with it, toprevent the sublimation of thesulphur.

At lleichenstein, arsenious acidis procured from the mineral calledarsenical pyrites (a compound ofarsenicum and iron, with a smallportion of sulphur).

Arsenious acid is procured insome parts of Saxony as a secon-dary product in the roasting ofcobalt ores (the arseniets of co-balt). It is deposited in longhorizontal flues {jmison-flues, orGiftfangen), and is purified bysublimation. (For other particu-lars consult the paper of J. II.Vivian, Trans- Royal Geol. Societyof Cornwall , i. 60).

(bedefyh) Course of the vapour. Arsenious acid is manufactured

(Hi) Doors into the chamber. in Cornwall . In the impure state

(mmm) Communications between thefloors- p ) s deposited ill the long hori-zontal flues of the tin burning houses (Mr. J. Taylor, Ann. Phil. N.S. iii.452); from which it is taken for the use of refiners, its value being aboutten shillings per ton [Quart. Min. Rev. vol. ii. p. 88; and Mr. DaviesGilbert, Paroch. Hist, of Cornwall , iii. 305). In this condition it has agrey colour, and is either pulverent or in soft crystalline masses. Mr.Ferris, of Truro, (to whom I am indebted for samples of this impureacid obtained from Wheal Vor tin-mine), tells me that it is conveyed inopen waggons to the arsenic-works, of which there are two in the neigh-bourhood of Truro; one in the parish of Perran Arworthall, the otherat Bissow, in the parish of Kea; the former about half a mile, the lattermore than a mile, from the Devoron and Camon stream-works. Here itis purified by sublimation. The fumes from these works are most inju-rious to neighbouring vegetables and animals. In the human subject,eruptions, principally about the lips and nose, are produced by them. In1826, eighty-three tons of manufactured arsenic were shipped at Penryn[Trans. Royal Geol. Soc. of Cornwall , iii. 360).

Condensing Chamber.