Chambers's encyclopaedia; a dictionary of universal knowledge . mass, carrying with it thegreater part of the silver which the copper con-tained. This silver can then be extracted Ironi thelead by cupellation. Ciipellttiion.—This process consists in meltinglead rich in silver on the hearth of a small furnace,and blowing air over its surface, the oxygen ofwhich, under the influence of the heat, rajiidlyconverts the lead into litharge or plumliic litharge tlie ))roperty of dissolving theoxides of some other metals, such as copper, zinc,tin, antimony, &c. Silver, however, is no
Chambers's encyclopaedia; a dictionary of universal knowledge . mass, carrying with it thegreater part of the silver which the copper con-tained. This silver can then be extracted Ironi thelead by cupellation. Ciipellttiion.—This process consists in meltinglead rich in silver on the hearth of a small furnace,and blowing air over its surface, the oxygen ofwhich, under the influence of the heat, rajiidlyconverts the lead into litharge or plumliic litharge tlie ))roperty of dissolving theoxides of some other metals, such as copper, zinc,tin, antimony, &c. Silver, however, is not oxidisedby this treatment. The result of the oi)eration isthat the whole of the lead put in the furnace, to-gether with small ijuantities of other oxidisablemetals (present as impurities), are removed asoxides, and the silver is left on the bed of the fur-nace. In the English the bedor hearth is movable, and is formed of an oval or test rammed full of powilereil German cupellationfuinace (shown in tig. 3). Fig. 3.—Silver Cupellation-furnace :rt, hearth of mar! or clay ; b, bricks ; c, bed of sla^ ; d, movablecover; *, e. tuyeres connected with bellows ; /, fireplace ; g,crane for lifting cover. is of larger capacity than the English, and has amovable domed cover constructed of iron. Theiliameter of this furnace is about 10 feet, and thehearth is covered with marl. These furnaces dilleronly in details and in the way in which they arecharged. In the Inited States what is ternied aSleitz water back cupel—a hollow costing throughwhich water Hows—is used in the lirst stage ofcujiellation. riieie are three ]>rocesses for separating si/rerfrom (/ohl practised on a large scale. Gne of a very old method. It is called parting by nitric acid. The alloy, which may consist of onejiart by weight of gold to two of silver or of one ofthe fminer to three of the latter, is melted andgranulated— forineeads. It isthen boiled
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