Arseniate of potash

is prepared, in the small way, by exposing to a moderate heat in a crucible, a mixture of equal parts of white arsenic and nitre in powder. After fusion, the crucible is to be cooled; the contents being di olved in hot water, and the solution filtered, will afford regular crystals on cooling. According to M. Berzelius, they are composed of arsenic acid, 63·87; potash, 26·16; and water, 9·97. It is an acidulous salt, and is hence usually called the bin arseniate, to denote that its composition is 2 atoms of arsenic acid, and 1 of potash. This article is prepared upon the great scale, in Saxony, by melting nitre and arsenious acid together in a cylinder of cast-iron. A neutral arseniate also is readily formed, by saturating the exce of acid in the above salt with potash; it does not crystallize. The acid arseniate is occasionally used in calico printing, for preventing certain points of the cotton cloth from taking on the mordant; with which view it is mixed up with gum water and pipe clay into a paste, which is applied to such places with a block. The extraction of arsenic from the cobalt ores, is performed at Altenberg and Rei chen stein, in Silesia, with an apparatus, excellently contrived to protect the health of the smelters from the vapours of this most noxious metallic sublimate. IMG:4147767755307473660_illo0055a.jpg:Arsenical furnace 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 i ue 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 proce , in order to push down the precipitate into the lower compartments. IMG:4147767755307473660_illo0055b.png:Arsenical furnace 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 redne , 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 pa ages, 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 gla y form. The top cylinder is furnished with a pipe, which terminates in a condensing chamber. IMG:4147767755307473660_illo0056a.png:Arsenic furnace Figs. 24 , 25. represent the arsenic refining furnaces at Rei chen stein. Fig. 24. shows at A , a vertical section of the furnace, the kettle, and the surmounting drums or cylinders; over B it is seen in elevation; fig. 25. is a ground plan of the four fireplaces. a is the grate; b , the ash pit; c , the openings for firing; d , the fire-place; e , iron pots or kettles which are charged with the arsenious powder; f , the fire flues proceeding to the common chimney g ; h , iron cylinders; i , caps; k , pipes leading to the poison vent l ; m , openings in the pipes for introducing the probing wires. IMG:4147767755307473660_illo0056b.png:Arsenic furnace The conduct of the proce is as follows:—The pot is filled nearly to its brim with 3 1 ⁄ 2 cwt. of the arsenic meal, the cylinders are fitted on by means of their handles, and luted together with a mixture of loam, blood, and hair; then is applied first a gentle, and after half an hour, a strong fire, whereby the arsenic is raised partly in the form of a white dust, and partly in crystals; which, by the continuance of the heat, fuse together into a homogeneous ma . If the fire be too feeble, only a sublimate is obtained; but, if too violent, much of the arsenic is volatilized into the pipes. The workmen judge by the heat of the cylinders whether the operation be going on well or not. After 12 hours the furnace is allowed to cool, provided the probe wires show that the sublimation is over. The cylinders are then lifted off, and the arsenious gla is detached from their inner surface. According to the quality of the poison-flour, it yields from 3 ⁄ 4 to 7 ⁄ 8 of its weight of the gla or enamel. Should any dark particles of metallic arsenic be intermixed with the gla , a fresh sublimation must be had recourse to. The following is the product in cwts. of arsenious acid, at Altenberg and Rei chen stein, in Silesia, in the years | 1825. | 1826. | 1827. | 1828. | 1829. | 1830. | 1831. | 1832. | | White arsenic in a gla y state | 2632 | 1703 | 2686 | 1900 | 2070 | 2961 | 3337 | 2730 | | Sublimed arsenic in powder | - | 27 | 33 | 31 | 30 | 44 | 69 | 38 | | Yellow arsenical gla | 112 | 11 | 56 | - | 86 | 313 | 60 | 219 | | Red arsenical gla | 3 | - | - | - | 28 | | | |