There is another process carried on at Freiberg and elsewhere, by which the use of mercury is dispensed with. it consists in treating the Ore as above described till it leaves the roasting-furnace. At this stage the roasted ore is digested in a warm concentrated solution of sea-salt, which readily dissolves the chloride of silver. The solution is then pasied through wooden tubs containing metallic copper, which has the property of decomposing the chloride of silver: the chlorine unites with the copper to form chloride of copper, and the silver is precipitated.
[This process is now for the most part abandoned, and at Freiberg an argentiferons copper matt obtained in smelting mixed ores is treated with sulphuric acid, by which sulphate of copper isformed. and the silver recovered from the residue.] In Mexico, where indeed the process was first introduced. the extraction of the silver from its ores is chiefly accomplished by amalgamation, but the plan employed differs a good deal in its details from the Saxon method described above. Of late years the sodium-amalgam process of Mr. Crookes has been used with advantage for the extrac tion of silver in several American mining distriets (see SODIUM-AlliALGAM).
It has now become a common practice at Swansea, where the great British copper smelting works are situated, to extract the silver which exists in an appreciable, though small quantity, in many copper ores. By one process copper smelted from an argen
tiferous ore Ls melted with three or four times its weight of lead, and east into ingots. When these are moderately heated, the copper does not fuse, but the lead and silver melt, and run off together, and the silver is then separated by cupellation. From the burnt pyrites of vitriol works. so recently a waste product, not only is the iron and cop per, but the silver, which exists in exceedingly small proportion, is now recovered by the use of iodide of potassium The physical and chemical properties of silver are such as make it specially valuable for many purposes in the arts; the chief of which are noticed in the articles ALLOY, MINT. PLATING. GALVANISM, and PaOTOGRAPHY. Ordinary mirrors have Item' Rilrering produccat by a costing of an amalgam of tin and mercury; but for some years, mirrors coated by a patent process with real silver, and backed liy a layer of sonic composition, which protects it from the blackening action of sulphureted hydrogen, have been made in great numbers.