an opening, which is covered with a pervious layer of crushed quartz. f. The residues combine with a considerable quantity of water, and impede the perfect extraction of the dissolved gold. They must be washed as thoroughly as possible. Georgi* proposes the application of a suction apparatus similar to that used in the manufacture of sugar. g. The workmen must be protected from the ill effects of the chlorine gas by a judicious arrangement of the apparatus, by ventilation, &c. According to Röszner, chlorine gas, which is always troublesome, and must be always applied in excess, may be advantageously replaced by a mixture of a cold solution of chloride of sodium and chlorine water. This reagent dissolves gold readily, and the gold is protected against all reducing agents occurring in the extraction vessel, and may be precipitated by copper. Allain states that gold may be extracted by chlorine from pyrites containing only o'or per cent, if it is previously roasted and freed from the greater part of the iron, copper, zinc, &c., it contains, by a treatment with sulphuric acid. Illustrations of Plattner's Process. At Reichenstein, in Upper Silesia, auriferous arsenical pyrites occurs, from which gold was extracted till the commencement of the seventeenth century, when the mining of galena was abandoned in that neighbourhood. Arsenical products were now extracted from the pyrites, leaving auriferous residues, which were unprofitable whether worked by fusion with lead or by amalgamation; they therefore accumulated up to the year 1851, since which time they have been sold at about 7d. per cwt., and treated by the chlorine extraction process in Güttler's gold establishment. According to Von Dechen, the pyrites contains from 0.138 to o 142 per cent of gold, and the residues yield from o'041 to o'05 oz. per cwt. o'045 oz. per cwt. is usually extracted by chlorine, whilst the smelting and cupelling processes * B. u. h. Ztg., 1861, p. 145. + Ibid., 1863, p. 36. Oesterr. Ztschr., 1863, Nos. 26, 27. formerly applied yielded only o'028 oz. According to Georgi, a yield of o'014 oz. per cwt. should cover all working expenses, including those for materials, and the interest of the outlay capital. The apparatus used for extracting gold are shown by Figs. 187, 188, and 189. The dressed schlich is kept in a store FIG. 187. room provided with a drying hearth, on which the schlich is heated during the winter season up to 5° C., otherwise hydrate of chlorine would be formed in the solution vessels. A laboratory furnished with a small reverberatory furnace, some crucible furnaces, sand bath, and other requisites, is placed behind the store-room. On both sides of the storeroom are apartments (A) (Fig. 187) for lixiviation purposes, 32 feet long and 20 feet broad; B, are hearths on which the chlorine gas is produced in the vessels, a, each having a separate fire-place communicating with the chimney, b; care pans for warming water in winter time up to 25° C., which is used for moistening the schlich; d are pots for lixiviating the schlich, eight of which are placed in a long row and four in a short one. Each four forms a battery, and between each battery a passage e is left open leading to the hearth, B. The pot, d (Fig. 188), is formed of good clay, and surrounded by the iron hoops, x, having two plugs, w, by means of which the pots may be tilted over and emptied. The semicircular rail, y, prevents accidental tilting over of the pots; the conical part (z) of the pot has an opening closed by a clay sieve; the top of the pot is closed with a wooden lid having a small circular hole. The pots a (Fig. 189) for the production of chlorine gas are closed with a lid FIG. 189. of lead, 25 lbs. in weight, and provided with one rectangular opening through which the materials are charged, and a round opening through which the lead tube, f, for conducting the gas is fixed; the lead tube is connected with the washing vessel, g, reaching to its bottom. Behind the compartments for lixiviation is another room, 34 feet long, intended for precipitation and filtration. For precipitation it is provided with sand baths, each containing 20 vessels (common carboys). A small channel runs in front of the sand baths, and upon it the filtering apparatus are placed; the filtered liquid is conducted by the channels into sumps filled up with saw dust. This room also contains the minor apparatus required. The operation is carried on in the following manner : At five o'clock in the morning the conical part of the pots, d, is filled with fragments of quartz, the clay sieve put into its place, and 24 pots are filled up with schlich to within 2 inches of their mouths; this is slightly moistened and warmed during winter; each pot contains 1 cwts. of schlich. The vessels for producing chlorine gas are prepared for operation by fixing and luting their lids and tubes for conducting the gas. Each vessel is charged with 13 lbs. of muriatic acid, 7 lbs. of sulphuric acid diluted with an equal quantity of water, and 7 lbs. of binoxide of manganese (pyrolusite); the charging opening is hermetically closed, and the sand bath heated. Besides chlorine, chloride of manganese is produced, from which chlorine is expelled by sulphuric acid. After chlorine has been passed through the vessels, d, for an hour, they are closed by lids, and, from time to time, a glass rod wetted with ammonia is held before the round opening of the lid to observe whether the chlorine which is introduced from below has permeated the schlich, which is indicated by the fuming of the moistened rod. The impregnation is finished in about six or seven hours, and the pots are well luted and kept closed till the following day. The chlorination of 24 pots is now commenced in another room, whilst the first 24 pots are lixiviated. For this purpose the lids are removed and a wicker basket (h) (Fig. 189) is placed upon the pots (d) and the vessels (i) beneath; water of from 17° to 25° C. is rapidly poured upon the schlich in order to absorb free chlorine, and it is then again passed through the mass. Boiling water would absorb but little chlorine and dissolve more of the foreign salts. The lixiviation is interrupted when four vessels, or about 96 cubic feet of liquid have passed the 24 pots containing 36 cwts. of schlich. The first two vessels contain glass cylinders for receiving the solution, as wood imbibes and decomposes chloride of gold in concentrated solution. The liquid of the fourth vessel is almost free from gold, and is therefore used for lixiviation the following day. The liquid of the first three vessels is drawn off by a syphon into glass carboys standing upon the sand bath, and the pots (d) are tilted over and emptied. The liquid warmed to 25° C. is treated with sulphuretted hydrogen gas produced from finely pounded lead matt and hot sulphuric acid, which is diluted with equal parts of water, thus first neutralising chlorine, and afterwards precipitating the gold as a sulphide until the liquid has a completely black appearance. The liquid is slightly warmed and the precipitate allowed to deposit; it is not completely deposited until the following day, when it is filtered. When metals are used for precipitating the gold they are dissolved by the free chlorine, and if the chlorine is expelled by introducing steam, the liquid becomes too much. diluted. The clear liquid from the carboys is slowly conducted by a glass syphon on to a paper filter lying upon pierced earthen dishes. The filtered liquid is conducted into sumps filled with saw dust to collect any sulphide of gold which may escape the filters; the deposits in the carboys are washed and poured upon the filters. Particles of sulphide of gold sticking to the syphons can be easily dissolved by some chlorine water. 320 filters with sulphide of gold are obtained in 16 days; they are then dried, carbonised in four large pans, boiled with aqua regia, washed, and the solution filtered into glass cylinders. Afterwards the filters are again boiled in water, and the gold is separated from the solution by sulphate of iron. The four precipitates of gold are collected on two filters, washed first with pure dilute muriatic acid, and afterwards with water. When eight filters are collected they are carbonised, and the gold melted in Hessian crucibles with an admixture of borax and saltpetre; the bottoms of the crucibles are pounded, and if containing small grains of gold they are washed out. The crucibles are placed in a compartment separate from the fire-place, and are only heated by the flame of the fuel, thus avoiding losses by the breaking of the |