ARSE′′NIOUS ANHYDRIDE

As 2 O 3 . Syn. Ar′senious acid , Ar′senic , White a. ; Acide arsénieux , Arsenic blanc , Oxyde , Fr.; Arsenigsäure , Arsenichste s. , Ger.; Arsenico bianco , It.; A. blanco , Sp. The arsenic, or white arsenic, of the shops. Sources. The white arsenic of commerce is principally imported from Germany, where it is obtained in the proce of roasting arseniuretted cobalt ores, in making zaffre. At Altenburgh it is procured from arsenical iron pyrites (mispickel); and at Rei chen stein from native arsenide of iron. About 900 to 1000 tons are also annually collected at Cornwall, being principally a secondary product of the proce of roasting grey copper ore and white mundic. The British arsenic works in that county are perhaps the finest in the world. The usual plan is to roast the powdered ore in muffle-furnaces; by which its arsenic is converted into arsenious anhydride, which escapes as vapour (smelting-house smoke), and pa ing into the condensing-chambers, is deposited in a pulverulent state, forming the flowers of arsenic, or rough white arsenic, of the smelters, (the giftmehl or poison-flour of the Germans). The crude article obtained in this way is purified by re-sublimation in suitable iron pots or other iron ve els, before it is fit for sale. It then forms a semi-transparent vitreous cake, which gradually becomes opaque, and of snowy whitene , by exposure to the air, and at length acquires a more or le pulverulent state on the surface. IMG:596405606043057898_i202.png: In Silesia the crude arsenious anhydride obtained from arsenical pyrites is refined by sublimation as follows:—For this purpose the cast-iron ve els ( a ) are employed. Upon these are placed iron rings or collars ( b , c , d ) and a hood ( e ), communicating by means of tubes with a series of chambers, of which the first only is shown in i . The flanges of the cast-iron collars and all other joints having been thoroughly luted, the fire is lighted and the heat so increased as to cause the semi-fusion of the arsenious anhydride, which, after cooling, exhibits a peculiarly porcelain-like appearance, at first being as transparent as gla . Prop. Crystals (obtained by careful sublimation, or by cooling a boiling aqueous solution), usually transparent, regular octahedrons (fig. 1), but sometimes, though rarely, a ume the form of tetrahedrons (see 2). When prepared on the large scale it forms large, gla y, colourle or yellowish-white, transparent or semi-transparent cakes or porcelain-like ma es (vitreous arsenious anhydride, glacial a. a.), which soon becomes opaque on their exterior, and often friable and pulverulent; odourle ; volatilises at 380° Fahr.; fumes odourle , unle carbonaceous organic matter be present, when they smell strongly like garlic; heated under pre ure it liquefies and forms a transparent gla ; taste faintly sweetish, with a slight acidity and astringency, not perceived until some minutes after being swallowed. The opaque variety is soluble in 80 parts of water at 59° Fahr., and 7·72 parts of boiling water; but on cooling to 60°, only about one third of this quantity continues in solution. The transparent variety is soluble in 103 parts of water at 59°, and 9·3 parts of boiling water. Both soluble in alcohol, syrups, oils, and spirits, and freely so in alkaline lyes and hydrochloric acid; organic matter generally impedes its solution; solutions redden litmus; heated with organic matter it is reduced to the metallic state. Sp. gr. 3·5 (lowest opaque var.) to 3·8 (highest transp. var.). IMG:596405606043057898_i203-1.png: