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fication beyond what is neceflary to feparate themore eafiiy oxidable metals from the copperwhich then remains in the metallic ftate. This'will be further noticed in the fucceeding articleof Alloys of Copper , and the purification of bell-metal. After the greater part of the lead hasbeen worked off as often as is judged neceflary,the remaining copper mull be kept for a whilelonger in fufion, to throw up the laft portionsof lead that may adhere. In allaying gold orfilver the total expulfion of the lead is knownby the fine metal becoming at once brilliant onthe furface, but in refining copper this appear-ance can never take place, as the copper itfelfalways forms a thin oxyd on its melted furface;and therefore, to judge whether it is pure, theworkman dips a polilhed iron rod in the meltedmafs, and draws out a portion of copper ad-hering to it, which, if pure, immediately fallsoff when the rod is dipped in water. The colourof the fcoria is alfo another teft. While thecopper remains impure and alloyed with iron,fulphur, &c. the vitrified oxyd on the furfaceis black or of a dirty brown, but the fcoria ofpure copper is red, and alfo is readily feparatedfrom the iron when cold, leaving no ftain be-hind.

The plates of fine red copper, called RofetieCopper, are made in the following way. c Whenthe refined copper is found by the way juftmentioned to be fufficiently pure, the furface ofthe melted metal is well fcummed and fufferedto cool till it is ready to fix, at which time aworkman brufhes it over with a wet broom,which immediately fixes the furface and caufesa thin plate to feparate from the ftill fluid metalbelow. This plate is taken off and thrown intowater, where it takes a high red colour, and thefame procefs of wetting the furface is repeatedwith the remaining fluid metal fucceflively, tillthe whole is reduced to thefe thin irregularplates.

A confiderable quantity of copper is obtainedfrom the fprings of native fulphat of copper orblue vitriol, which are found in mod coppermines or flow from hills containing this metal.To obtain it, the vitriol water is pumped upinto large fquare open pits, two or three feetdeep, made with rammed clay, into which isthrown a quantity of refufe- iron of any kind,and fuffered to remain for a confiderable time,during which the iron is diffolved, difplacing by.fuperior affinity the copper which is precipitatedin the form of a brown mud. When the wateris. thus exhaufted of its copper, the pits are

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raked out, and the oxyd colle£ed from themis Amply dried in the fun. It is then fit forreduction in the reverberatory furnaces in theufual manner. This is by far the richeft ma-terial employed, for, though containing fomeclay and iron mixed with the copper, it yieldson an average full 50 per cent, of pure metal,and therefore it is feldom fmelted by itfelf, butmixed with the poorer ores, fome of whichcontain no more than 5 per cent, of metal.

Many of the fineft copper ores contain fo muchfilver as to make it worth while to extract thislaft metal by a feparate operation, which willbe defcribed under the article Silver . In all thedifferent roaftings and reductions neceflary tobring the copper to purity, the filver remainsunited with it.

Analfis of Copper Ores.

The number of the analyfes made of the dif-ferent fpecies of copper ores is fo immenfe, thata feledftion only of the moft approved can herebe given; and a few general rules may be pre-mifed, which will Amplify the fubject.

The analyfis of ores is ufually conduced inone of two diftinct ways, the dry and the mo'fl,each of which has its peculiar advantages anddefeats.

In the dry way, the ores when they containfulphur or arfenic (which is the cafe with thegreater number) are firft roafed in order todiffipate the greater part of thefe mineralizingfubftances. For this purpofe, in analyfis in tirefmall way, they are mixed with about their bulkof charcoal powder (or better with fine faw-duft) and expofed to a low red heat on a flat-tile or muffle, or any other convenient apparatuson which they can be thinly fpread. The ful-phur or arfenic foon begins to rife in fumeswhich fhould be haftened by frequent ftirring,.keeping the heat juft below the point at whichthe ore would run and clot together, to prevent-which is one confiderable ufe of the charcoal orfaw-duft.

When no more fumes fenfibly arife, and thecharcoal is entirely burnt off, the part of theore that remains now confifts of the metallicportion in the ftate of an oxyd, ftill mixed how-ever with a quantity of fulphur or arfenic,which mere roafting will not feparate, and ofall the earthy matrix that may have been ori-ginally contained.

The ore is then fitted-for the fecond procefs,which is that of reduEHon of the metallic oxydsto the reguline ftate. All that is effentially ne-ceffary to reduftion is, to expofe the oxyd to ahero. Dhft.