candelabrum, supported upon 4 feet, and set in the basin B; under d, are five dishes or plates of wrought iron, with a hole in the centre of each, by which they are fitted upon the stem of the candelabrum, 3 inches apart, each plate being successively smaller than the one below it. 3, represents a cast-iron bell, furnished with a wrought iron frame and hook, for raising it by means of a pulley and cord; s, is a sheet-iron door for closing the stove whenever the bell has been set in its place. The box, a, and the basin B, above it, are filled with water, which must be continually renewed through a pipe in the side of the wooden box, so that the iron basin may always be kept submerged and cool. The drawer (a) being properly placed, and the plates under (d) being charged with balls of amalgam (weighing altogether 3 cwts.), the bell (3) is let down into the water, as at y, and allowed to rest upon the lower part of the candelabrum. Upon the ledge (1) which represents the bottom of the fire-place, a circular plate of iron is laid, having a hole in the middle for the bell to pass through. Under this plate chips of fire-wood are kindled, then the door (s) which is lined with clay, is closed and luted tight. The fuel is now placed in the vacant space (k) round the upper part of the bell; the fire must be fed very gradually, first with turf, then with charcoal; as soon as the bell becomes red, the mercury volatilises, and condenses in globules in the bottom of the basin B. After eight hours the fire is stopped, provided no more drops of mercury are heard to fall into the water. When the bell has cooled, it is lifted off; the plates are removed from the candelabrum (d); and this being taken out, the drawer is slid away from the furnace. The mercury is drained, dried, and returned to the amalgamation works. The silver, which is more or less pure, and has a cauliflower-like appearance, is fused and refined by cupellation. The water used is passed through reservoirs. This mode of distilling the amalgam requires much time and fuel, and does not effect a perfect separation of the mercury; also frequent cracking of the bells causes a loss of quicksilver, and there is no way of knowing the end of the operation but by experience; therefore it has in most places been superseded by the process of distilling in retorts, as consuming less fuel, causing less loss of mercury, and permitting the operation to proceed better. The apparatus used in Arany-Idka is represented by Fig. 97. The retort consists of two parts-the crucible, b, and the FIG. 97. 100 50 2 Met. capital and neck, c and d, which are screwed together. The crucible is II inches deep and 22 inches wide at the mouth. The retort is connected with a refrigerator, e, by the conducting tube, g, and the condensed mercury drops into f. The crucible is furnished in the middle with a piece of plate iron (divider) which exactly fits the inside of it, causing one half of the silver to cake on one side of the plate, and the second half on the other; the whole may then be drawn out together by the plate. Both the plate and the crucible are previously coated with lime. The crucible is charged with 4 cwts. of amalgam, and a slow fire is made in order to avoid a formation of finely divided mercury, and to prevent much silver being carried along with the mercury. The fire is not increased until the mercury begins to distil with a rushing noise. At last the temperature is raised to a red heat; the process takes about 5 hours, consuming 12'9 cubic feet of charcoal for every cwt. of distilled mercury. At Arany-Idka, in Hungary, in 1861, 1,050 tons of ore flour, containing 2624'4063 lbs. of silver, were treated by the amalgamation process. They were roasted in 4 reverberatory furnaces, each with two hearths, in 2,055 shifts of 12 hours, at a cost of £110 12S.; the cost of grinding and sifting the ores amounted to £97 16s. The ore was amalgamated in 1,751 casks at a cost of about £477 4s., and yielded 15 tons of amalgam, containing 2632 422 lbs. of silver. The amalgam, after having been pressed, contained 85 or 86 per cent of mercury, 9 or 10 per cent of silver, and from 4 to 6 per cent of copper, iron, antimony, and lead. It yielded by the distilling process 24 tons, 93 lbs. of silver, and 13 tons, 77 lbs. of mercury; the loss of mercury, therefore, amounted to o'95 per cent. By fusing those 4394'2527 lbs. of silver, 4286 8223 lbs. of raw silver, containing 2632 9762 lbs. of fine silver, were produced. The total cost for 1861 amounted to £2,456 6s., and per lb. of silver, to 18s. 4d. 23°25 cubic feet of wood were consumed for roasting and amalgamating 5 tons of ore flour, and 310 tons of mercury were used for 1,050 tons of ore flour; the loss of mercury amounted to o'225 oz. per cwt. of ore, and to 1815 ozs. per lb. of silver. The consumption of iron was 1'465 ozs. per cwt. of ore, and 11'68 ozs. per lb. of silver; the consumption of salt was 16 per cent of the ore, the latter containing from 15 to 18 per cent of sulphides. If the percentage of sulphides increases, the consumption of salt may be lessened, as more sulphuric acid will be formed, causing a more perfect separation of chlorine. A surplus of salt is generally advisable to avoid a formation of silicate of silver which is likely to take place in the roasting process, and to convert the greater part of the silver into chloride. Such a surplus of salt at Arany-Idka, in the years 1860 and 1861, caused the residues to contain only o'004 per cent of silver. Roeszner's method of extracting silver and gold* has been lately substituted for the amalgamation process. At Huëlgoet, ores with from o'9 to 1.7 ozs. of silver in the cwt. are roasted for 4 hours with 5 per cent of sea salt, then treated in the cask with iron for four hours, and for 24 hours with mercury. One cask contains 740 lbs. of ore flour and sea salt, 60 lbs. of mercury, and 80 lbs. of iron. The distilling of the amalgam is effected in a retort, and the resulting silver contains 30 per cent of silver, besides some copper, iron, tin, and mercury; I cwt. of residues contains o'08 oz. of silver, and the loss of mercury amounts to o'g oz. per cwt. of ore. The most extensive amalgamation works in Europe are probably those of La Bella Raguel, where the ores obtained from the mines of Hiendeleucina, situated in the province of Guadalajura, Spain, are chiefly washed in revolving apparatus, and are subsequently treated in barrels, sixty of which are employed. The European amalgamation is also carried out at Arivaca,|| in Mexico, for treating argentiferous copper ores containing 25 or 30 per cent of silver and from 15 to 70 per cent of copper. They are roasted with an addition of common salt and from 3 to 5 per cent of lime (to prevent a formation of chloride of copper); they are then treated in revolving casks, first with water and copper, and afterwards with mercury. The loss of mercury amounts to 7 or 8 ozs. per lb. of silver; the loss of silver during the roasting process is sometimes as much as 15 per cent. Amalgamation of Argentiferous Matt. Matt, with the exception of copper matt, is treated like ore. It is first roasted by itself, and afterwards mixed with salt, lime, and water; when dried it is again roasted. The * Oesterr. Ztschr., 1863, No. 40. B. u. h. Ztg., 1863, p. 428. + RIVOT, Traité de Métallurgie, 1860, i., pp. 652, 676. B. u. h. Ztg., 1859, P. 351. URE'S Dictionary of Arts, &c., vol. iii., p. 669. London: 1867. addition of lime is made in order to decompose the chlorides which might be formed by the roasting process, and which would otherwise cause the formation of calomel in the amalgamation process; lime, therefore, lessens the loss of mercury, but, on the other hand, it may act disadvantageously on the yield of silver, as oxide of silver will probably be precipitated by lime if sulphate of silver is present. Amalgamation of Speiss. Speiss is first roasted by itself, and afterwards with salt; at this last roasting an addition of sulphate of iron is given to liberate the chlorine, if sufficient sulphur in form of matt is not left in the speiss when producing it. If the speiss contains too little matt the roasting process will cause great loss of silver, and if it contains an excess of matt, a separation of basic iron salts will take place, causing a large consumption of iron and copper, as well as mercury, during the amalgamation. If the roasting process is not very carefully carried on, a great loss of silver may be occasioned by too high a temperature, causing part of the arseniate of silver to be reduced to metallic silver, which is then volatilised partly as oxide and partly as chloride, together with other metallic chlorides. An addition of lime is made to the roasting and amalgamating of the speiss in order to counteract the formation of metallic chlorides, and copper is used instead of iron to prevent the formation of a cupriferous amalgam. At the Stephanshütte,* in Upper Hungary, copper speiss, containing 25 per cent of copper, o'28 per cent of silver, 58 per cent of antimony, 8 per cent of iron, 5 per cent of sulphur, 2 per cent of arsenic, a little bismuth, lead, cobalt, and nickel, and a small amount of gold, is amalgamated. It is first roasted in quantities of 5 cwts. with 2 per cent of limestone, for 5 hours on the upper hearth, and for the same time on the lower hearth of a Hungarian roasting furnace. It is then ground and sifted, and after being mixed in lots of 6 cwts. with 1 per cent of limestone and 7 per cent of salt, is well roasted for 6 hours on the lower hearth of the furnace. * Oesterr. Ztschr., 1857, p. 145; 1861 No. 12. B. u. h. Ztg., 1862, p. 18. |