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hours or so, when the clear water may be run off, the slime collected, washed by shaking up with fresh water, again allowed to settle, collected, dried, and fused with borax into a cake of yellow gold. The gold may also be precipitated in the vats by passing a current of sulphurous-acid gas into the solution, with stirring, so that the acid may come in contact with every part of it, first decolourising the solution and then throwing down the gold. By this sulphurous-acid process the gold is thrown out in coarse particles, and settles to the bottom more rapidly than when sulphate of iron is the precipitating agent. The sulphurous-acid gas—more correctly named sulphur-dioxide—is made by heating, in a glass retort, either charcoal or sulphur with strong sulphuric acid, and leading by a glass tube the gas thus made into the solution in the vat. Instead of running the outflow into precipitating-vats it may, as at the Mount Morgan Mine, be passed into a bed of wood charcoal, the pieces of charcoal being of the size of from a pin's head to peas and beans, or even larger, the bed being, say, 1 ft. or 2 ft. deep, in a small vat, say, 3 ft. diameter by 3 ft. deep. The charcoal decolourises the liquid, and extracts or arrests or precipitates on itself the gold. The liquor is allowed to percolate through among the charcoal, and pass away by an outlet at the bottom of the charcoal-vat. The outflow from this charcoal filter-vat may be tested occasionally by the addition of a little sulphate-of-iron solution to a portion of it in a wineglass, when any gold present will at once reveal itself by imparting a greenish tint to the solution. The charcoal, when saturated with gold, is. then carefully burnt to ashes in a nice clean furnace ; the gold is in the ash, and is recovered by fusion with borax. The most important points that require the most careful attention in this process are —(1) The proper roasting (to a perfectly dead roast) of the ore in a furnace of the reverberatory type, in which the ore does not come in direct contact with the fuel, and in which there is a good draft of air sweeping the flames across the fire-bridge over the surface of the ore, while the latter is being continuously rabbled to bring fresh portions to the surface, and therefore into contact with the oxygen of the air ; (2) the second point of importance is the making-up of the solution according to the prescription given above. The solution should be made, if convenient, on the day on which it is to be used, as it slowly loses strength on being kept. It should not be kept more than two days in any case. \ Instead of the prescription given above—namely, 121b. of common salt, 141b. of strong sulphuric acid, and 6 oz. or 7 oz. of permanganate crystals per 100 gallons of water —Etard, of Paris, the inventor, recommends, where (as in Europe) muriatic acid is cheap, a solution containing 45 lb. of strong commercial muriatic acid (or hydrochloric acid), 12 oz. of permanganate crystals dissolved in 220 gallons of water. This is called the Etard permanganate solution. The other is called the Black-Skeet permanganate solution, and is for economical reasons suggested as preferable in these colonies, where sulphuric acid is readily and cheaply made or purchased. At quotations from Sydney, Dunedin, and Melbourne the Black-Skeet solution will cost about fd. a gallon, and with properly calcined ore from 100 to 150 gallons should be quite sufficient for the leaching of a ton of roasted ore. The most favourable result got at the Mount Morgan Mine on the properly roasted ore was an extraction of 94f per cent, of the gold, at a cost for chemicals of 4s. 6d. per ton. At the Permanganate Company's works at Dunedin a ton of Mount Morgan roasted ore, assaying 10 oz. 15 dwt. to the ton, gave an extraction of 956 per cent, of the gold by nineteen hours' treatment, at a cost of 4s. 4fd. per ton of roasted ore. These permanganate solutions —the Etard and the Black-Skeet—do not generate chlorine gas to any appreciable extent in the absence of gold or something else that has an attraction for chlorine. Indeed, it is claimed that in the process there is practically no chlorine gas generated (no free chlorine produced), but that the gold takes the chlorine direct from the hydrochloric acid in the Etard solution, and from the common salt in the Black-Skeet solution. Gold, it is well known, does not take chlorine from hydrochloric acid nor from common salt without the intervention of some other active ingredient. In the Etard solution this active ingredient is the permanganate, supplying, as it does, oxygen to the hydrogen of the hydrochloric acid, and forming water, and thereby enabling the gold to get the chlorine of the broken partnership. In the Black-Skeet solution the same end is obtained by the oxidation of the sodium of the salt, thereby fitting it for union with the sulphuric acid to form bisulphate of soda, while the other partner in the salt (namely, the chlorine) is in a position to make a new arrangement and ally itself in a partnership with the gold as chloride of gold. It cannot in either case be called " catalytic " action, nor can the chlorine be called " nascent," for chlorine is not liberated at all; it is never free ; it does not leave the sodium till it is in union with the gold; it is, at no stage, between the two metals. The reaction would be better described in each instance as a case of "concurrent affinity," in which two factors in the Etard manage, by their concurrent attraction —drawing in opposite directions—to effect the separation of the hydrochloric acid into its two constituents—hydrogen and chlorine —the oxygen of the permanganate taking as its share the former, and the gold the latter, thus becoming water and chloride of gold. In the Black-Skeet three factors are concerned simultaneously in effecting the chemfcal changes—namely, (1) the oxygen of the permanganate unites with the sodium of the salt; (2) the soda thus produced unites with the sulphuric acid ; and (3) the gold pulling at the chlorine of the salt, manages to capture it, owing to the simultaneous capture of the sodium of the salt by the oxygen of the permanganate. In the Black-Skeet solution the sodium would not break its partnership with the chlorine of the salt without the aid of the gold in taking the other partner. On the other hand, the gold could not take the chlorine from the sodium of the salt without the aid of the oxygen taking charge of the other partner—namely, the sodium ; and, in its turn, the oxygen would not take the sodium if the sulphuric acid were not present to unite with the soda thus formed. The whole of the simultaneous concurrent changes in the Etard process may be shown by the following equation:— 6 KMnO< +30 HCI +BAu = 6 XCI + 3 Mn 2 0 3 +15 H 2 O + 8 AuCl 3 ,