crucibles. A lump of gold weighing several pounds may be melted in a quarter of an hour if the furnace has been previously heated for two hours.

About 500 tons of schlich are worked annually, consuming 25 tons of muriatic acid, 7 tons of sulphuric acid, and 12 tons of manganese, and producing from 20 to 21 lbs. of gold, in value from £1,200 to £1,350, whilst the cost of the production is from £750 to £900. The yield is better in summer than in winter, as in the latter season chlorine is more easily transformed into hydrochloric acid, which, if metallic sulphides are present, produces sulphuretted hydrogen gas, and the gold is then liable to become sulphuretted.

At Reichenstein, the production of gold is at present abandoned, as the old residues have been worked up, and the arsenic works do not produce more than 50 or 75 tons of auriferous residues annually, the working of which would not cover the interest of the outlay.

At Schemnitz, auriferous raw matt has been treated by Ziervogel's method (page 378), and gold extracted from the residues by Plattner's method. These residues contain :

The apparatus is represented by Figs. 190 and 191. A is the apparatus for evolving chlorine gas. It is made of castiron, and furnished with the conduit-pipe, a, for cleaning the apparatus. в is a lead vessel screwed to A, and furnished with three conduit tubes, namely, b for charging the mixture, c for introducing sulphuric acid, and the conduit tube, e, connected with the tube, f, for emitting the chlorine gas. This gas first enters the washing vessel, c, then the receiver, d, whence it passes into the earthen lixiviation vessels, E, by

the two tubes, g. Two vessels, E, stand upon an elevated platform in a wooden box, F; the interstices are filled with beaten down sand. The vessels, E, have an opening at their lower parts, which are filled up to within two inches with fragments of quartz; they are closed with the earthen lids, h, and provided with the tubes, i, for emitting gases.

The residues are dried and moderately heated to decompose their basic iron salts; they are then slightly moistened and charged in quantities of 6 cwts. in each clay vessel. Chlorine is introduced through the tube, k, whilst the tube, i, is left open till chlorine gas escapes from it. It is then closed by a plug of clay, and the chlorine gas allowed to react for twelve hours. The chlorinated mass is next lixiviated with warm water, and the gold solution is conducted from the bottom tube, k, into the large glass vessels, m, by means of the funnel, l, after the removal of the tube, g, in which gold is precipitated by sulphate of iron. The clarified liquid is then decanted by a syphon, the precipitate of gold collected, washed, dried, and melted in a Hessian crucible with an

addition of borax and saltpetre. The liquid is collected in a reservoir and conducted over iron, thus yielding some auriferous cement copper. The extracted residues are mixed with lime and added to the ore smelting process (page 230). The loss of gold amounts to 18°21 per cent.

Calvert's Method of Treating Auriferous Quartz.— This method is based on the principle of the evolution of chlorine gas in the ore mass itself, as chlorine in the nascent state strongly attacks the gold. This method has also the advantages of cheapness, and of permitting the extraction of silver and copper at the same time; it is also less injurious to the health of the workmen. The mixture of finely pulverised quartz, with 1 percent of manganese, is put into a vessel which may be closed, and which is provided with a pierced bottom; upon this bottom a layer of brushwood and then some straw are placed, muriatic acid is next added, and the liberated chlorine gas allowed to react upon the ore for twelve hours. Enough water is then added to fill up with liquid the space between the bottom and the false bottom of the vessel, and the liquid is repeatedly added to the ore. It is then tapped off and treated with iron to precipitate the copper; it is afterwards heated to expel the surplus chlorine, and the gold is precipitated by iron vitriol. If the ores contain silver at the same time, chlorine is evolved from a mixture of common salt, manganese, and sulphuric acid, mixing the ore with six parts of common salt and three parts of manganese. The chloride of silver formed is then dissolved in the solution of common salt, from which it may be precipitated by copper; afterwards the copper is precipitated by iron, and lastly the gold by iron vitriol.

Chlorination of Auriferous and Argentiferous Substances, and Extraction of Gold and Silver at the same time. According to Plattner,* an auriferous and argentiferous substance, when roasted with common salt, forms chlorides of silver and of gold (Au Cl2). The chloride of gold is transformed into protochloride of gold (AuCl), losing two equivalents of chlorine, when heated to somewhat below

200° C, and the protochloride of gold is decomposed into chlorine and metallic gold when heated to about 240° C. This easy decomposition of the chloride of gold is a chief reason of the imperfect yield of gold when treating silver ores by the amalgamation process, or submitting them to a lixiviation with common salt. According to Janikovits,* the chlorination is more securely effected if the ore, &c., is first roasted "dead" with an admission of steam, and afterwards submitted to a chlorination roasting at a lower temperature; Rösznert states, on the other hand, that this chlorination roasting would form Au,O,, NaO+ NaCl, which combination is only slightly soluble in a solution of common salt, and is not decomposed by mercury; it cannot, therefore, be treated either by Augustin's process or by amalgamation. But both this salt and chloride of silver are soluble in hyposulphites, and moderately so in a mixture of a solution of common salt and chlorine water; by these reagents silver and gold may be extracted at the same time. The recent investigations of Max v. Lill have proved, in accordance with Kiss's supposition, that the roasting process produces chloride of gold, which forms with hyposulphite of soda or lime a soluble double hyposulphite of gold and soda (according to Fordos and Gelis, AuO, S2O2 + 3NaOS2O2). To prevent separation of metallic gold from the chloride of gold in the roasting process, the temperature must not be too high during the last roasting period, and some surplus chlorine, produced from common salt and easily decomposable metallic sulphates, must be present. It is advisable to wash the roasting mass with water previous to its treatment with hyposulphites. The chloride of gold, by the action of hot water, is decomposed into protochloride and metallic gold, and though insoluble in cold water is slowly decomposed by it in darkness.

We have before mentioned that Kiss's method of extracting gold and silver is based upon the solubility of chloride of silver and gold in a solution of hyposulphite of lime, but its

Oesterr. Ztschr., 1863, No. 30.

+ Ibid., 1863, No. 211.

Ibid., 1865, p. 49.

results have not been satisfactory with regard to the yield of metals. Experiments with Patera's* and Röszner'st method, who first submit the substance to a chlorination roasting, and then treat it with a solution of common salt saturated with chlorine, have given better and very promising results. Silver ores from Arany Idka were experimented on by these methods, yielding 98'94 per cent of silver, all the copper and nearly all the gold, while the residues retained from 0'002 to 0005 lb. These experiments proved that the expense of working 5 tons of ore by this method of extraction was less than when working them by the amalgamation process by £7 10s. 6d. (page 330).

Patera treats ores, &c., with a cold solution of common salt saturated with chlorine, thus chlorinating and dissolving silver and gold at the same time; a previous roasting with common salt is also admissible.

Röszner roasts the ores, &c., with common salt, and extracts the greater part of the silver from the roasting mass by Augustin's method, with a hot concentrated solution of common salt; the residues are then alternately treated by cold solution of salt saturated with chlorine, and hot concentrated solution of salt, to extract the gold and the remaining silver; both metals are precipitated from the hot solution by copper; the cement silver is cupelled, and the gold separated from the auriferous silver in the usual

manner.

Lixiviation with Sulphuric Acid.-The yield from this method is larger when treating ores containing lead, copper, gold, and silver, which cannot be advantageously worked by the other methods. Ores containing a sufficient amount of sulphur are either completely roasted, and the escaping sulphurous acid collected for the production of sulphuric acid, or they are previously smelted to produce a matt, which must be perfectly roasted; copper and iron are then extracted from the roasted mass by dilute sulphuric acid, and the residue, containing gold, silver, and lead, is either fused with lead, or if containing no lead, its silver is extracted by Oesterr. Ztschr., 1863, p. 165. + Ibid., 1863. No. 25, 40.