sixteen pots there is one fireman, and to every two pots there are two men. There is also one lead ladler. The men work for eleven hours, but the fireman works for twelve hours.* Cupellation at Freiberg.-The hearth is fresh marl mixed with cwt. of clay.

kinds:

formed of 48 cwt. of The marl is of three

Any pyrites present is carefully removed.

The greatest depth of the hearth from a line on a level with the tuyeres ought not to be more than 7.8 inches. The fireresisting material with which the roof is lined consists of one part of clay and two parts of silica; 100 cwt. to 200 cwt. of lead is placed on the damp hearth, and this is covered with sawdust and chips; the roof is then put on, the wood lit, and the roof luted on with clay; the fire is kindled, and the blast turned on; the lead melts down in sixteen to eighteen hours. The temperature is gradually raised, and lead is added, 700 cwt. being the total charge. The litharge, as it forms, is removed until the remaining lead on the bed contains 60 to 80 per cent. of silver. This is taken out, and the extraction of the silver completed on a similar but much smaller hearth. If the red litharge obtained contains less than 0.02 per cent. of silver, it is sold. It is said that if the lead contains 0.2 per cent. of bismuth no red litharge will be produced. At the end of the process, where the concentrated lead and silver settle on the hearth, there is a dark spot which indicates the presence of bismuth, and which is broken away and the bismuth subsequently extracted, this portion of the hearth having been previously hollowed to collect the rich lead. There are two men attending to each furnace, and they are paid a little over a penny for every hundredweight of lead treated. It takes 120 to 140 hours to cupel 700 cwt. of lead. The silver obtained is granulated by running it into water. It is about 990 fine, and is sent to the Halsbrücke works to have the gold parted from it.

Solution of the Regulus.-The concentrated copper regulus is sent to the Halsbrücke works, where it is roasted nearly sweet. It still contains about 1 per cent. of sulphur. It is then passed through a rather fine sieve, and the larger pieces are crushed and re-roasted. The roasted regulus is dissolved in sulphuric acid in

Pattinson's process is now supplemented by Parkes' process, a jointprocess being used, but this is not indicated in the scheme.

wooden vats lined with hard lead. The sulphate of copper is crystallised out, and, after purification by re-crystallisation, is sold. Such copper sulphate as does not crystallise out but remains in solution is removed by scrap-iron. The solution of copper-sulphate before crystallisation is made to pass over metallic copper, in order to remove any silver it may contain. The residue, after the treatment of the regulus with sulphuric acid, contains the lead, and most of the silver originally present in the regulus treated. This is sent back to the Pilz furnace, with a view to concentrate the silver in the lead produced from the lead ores.

The student would consult with advantage two papers recently published giving an account of American practice in smelting argentiferous lead. It appears to be possible, in smelting complex ores, to collect the whole of the precious metals in lead, even if the lead present does not exceed ten or even eight per cent. of the charge. Copper is also employed with success as an agent for collecting the precious metals, and this may be effected if the copper only forms five per cent. of the charge.

Hitherto lead has been used in blast furnace smelting for the purpose of collecting the precious metals, but it appears that ores containing copper in an oxidized condition may, under certain circumstances, be smelted with other ores rich in silver, the copper of the former serving as the vehicle for concentrating or extracting the whole of the precious metals from both classes of ore, just as the lead that is employed in the ordinary process. The extraction of the gold and silver is quite as perfect as when lead is used, and there is no loss by volatilization, but the loss of metal in the slags is of greater relative importance in the case of copper than in that of lead, on account of the higher intrinsic value of the former metal. This disadvantage is, however, compensated by the fact that the rate of concentration may be increased to as much as twenty to one as against ten to one which is the maximum ratio when lead is used. The greatest drawback to a general application of the process, is the scarcity of ores that are rich in the precious metals, which are not suitable for milling, and that are at the same time free from sulphur and lead.

Not more than one per cent. of sulphur should be present,

*(1) H. F. Collins on "Smelting Processes for the Extraction of Gold and Silver from their Ores"; (2) S. W. Malcolmson, "Erection of Silver Lead Works in Mexico." "Proc. Inst. Civil Engineers," vol. cxii., part 2, 1893.

while, if the percentage rises to four or five, the operation at once becomes that of the ordinary smelting for regulus, and all advantage is lost. The presence of lead, on the other hand, gives rise to much trouble and expense in the subsequent operations of refining, hence it is not permissible to allow more than one per cent. of lead to be present in the ore charge.

Wet Processes for Treating Argentiferous Copper Ores. In certain cases copper pyrites is converted into copper sulphate by the action of air and moisture. The sulphate

is dissolved in water, and the copper precipitated from the solution by iron. When, however, argentiferous ores are dealt with, containing much copper but not much lead, the processes are more complicated. The principal processes in

Vogue are:

1. Ziervogels process, which consists in submitting the regulus to an oxidising roasting, yielding cupric oxide and silver sulphate. The latter is dissolved in water and precipitated on copper. The cupric oxide is recovered from the residues by smelting (Fig. 80).

2. Augustin's process, which consists in submitting the regulus

to an oxidising and subsequently to a chloridising roasting, yield. ing cupric oxide and silver chloride. The latter is dissolved in hot brine and precipitated on copper. The cupric oxide is recovered from the residues by smelting (Fig. 81).

3. Longmaid's or Henderson's process, which is applied to the ore after roasting, and which consists in dissolving the copper and silver from the ore roasted with salt by water and dilute hydrochloric acid. The copper is precipitated by scrap iron, and the silver is recovered by the Claudet process (Fig. 82).

4. In Claudet's process the silver is precipitated as silver iodide from a solution of copper and silver chlorides by zinc iodide

regenerated during the process, zinc being used to precipitate the silver.

These four processes are illustrated by the accompanying schemes, Claudet's process forming part of the scheme (Fig. 82). The plant used in the Ziervogel process is illustrated in Fig. 83. The charge of roasted material is placed in tubs A, provided with false bottoms, and hot water is introduced through the pipe b until the liquors begin to flow through the tap c. The pipe b is then closed, and acidulated hot water is admitted through the pipe a. The silver sulphate solution flows into a long tank, divided into two compartments B, C, whence it is distributed into

precipitating tubs D, provided with false bottoms on which cement copper is placed, with copper bars above it. Most of the silver is precipitated, and the liquors pass to a trough E, on the bottom of which is a layer of pieces of sheet-copper, and thence to the tubs F, also containing a little copper. The desilverised liquors are conveyed by the gutter g to a leaden pan, and again utilised. The precipitated silver is treated with sulphuric acid in the tubs H, and finally washed with hot water. The liquors rise through L, and are conducted by the trough M over metallic copper into tanks containing scrap-iron. The water from the

final washing is run off at N, and conducted to a lead-lined tank. The silver is moulded into blocks and refined.

Treatment of Gold Ores.-Plattner's method of extracting gold from its ores by means of chlorination is based on the fact that chlorine gas transforms gold into soluble gold chloride without sensibly attacking the earths or metallic oxides with which the gold is mixed.

The ore is crushed and roasted with salt, 5 to 9 lbs. of salt per ton of ore having been added. Any lead, bismuth, or silver present is thus converted into chloride. The iron sulphide present, however, will first be converted into iron sulphate, and this