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mixing together fome of the poorer kinds ofmeagre filver ore (that is, fuch as contains butlittle copper and lead, and much hard ftonygangue) with the pooreft pyritical ores (that isfuch as contain very little filver and copper butmuch fulphur and iron). To this is added byway of flux, a parcel of fcorise remaining froma former procefs, and containing oxyds of leadand copper with a fmall portion of filver. Allthefe materials being ftrongly heated in a blaftfurnace re-aft on each other and enter into fu-fion; the ftony gangue is diffolved and thefluid mafs feparates into two diftinft parts.The heavieft portion, and which therefore oc-cupies the bottom of the furnace, is called matt;it forms about j of the whole mafs, and con-tacts all the filver, by far the greater part ofthe copper, a confiderable part of the lead, to-gether with iron, fulphur, and generally zincand arfenic. The lighter portion and whichfwims on the furface of the matt is a black flagconfiding for the mod part of fulphur, oxydof iron, and earth, the lead and copper beingin fuch fmall quantity as not to be worth thetrouble of extraftion; this flag therefore isthrown away.

The crude matt obtained by the precedingoperation is roafted to free it in part from thefulphur and other volatile impurities, and, be-ing mixed with about i| times its weight of aricher fort of meagre filver ore, and abouttwice its weight of lead fcorite by way of flux,is again fufed, and furnifhes a rich matt (con-taining from 9 to io lbs. of lead, 3 to 4 lbs. ofcopper, and 6 to 7 oz. of filver in the quintal)and a parcel of fcoriae that ftill hold a littlefilver, and are therefore employed as flux infubfequent fufions.

This fecond or rich matt, after being roafted,is mixed with about half its weight of lithargeand fcorise in equal proportions, and againfufed ; the produft of which is, 1. a quantityof metallic lead holding from 6 to 8 oz. of filverin the quintal: 2. nearly an equal amount ofsCopper matt, holding from 30 to 40 lbs. ofcopper, and about 4 oz. of filver in the quin-tal; 3. Scorise, holding from 6 to 10 lbs. oflead, and about 40 grs. of filver in the quintal.

copper matt of the preceding operationa ter being roafted is fufed together with aquantity of lead and copper fcoriae, and yieldsblack copper, containing from 60 to 80 lbs. ofcopper, and from 5 to 10 oz. of filver in thequintal.

The black copper is now melted with li-tharge and fcoriae, by which the filver is for

the moft part transferred to the lead, and thecopper after one or two more fufions is entirelyfreed both from lead and filver, as well as fromfulphur, iron, and other impurities.

The rationale of all thefe procefies is fuffici-ently plain. The filver, copper, and lead beingall much more eafily reducible than iron, arebrought by means of the fuperfluous fulphur ofthe pyrites to the ftate of fulplraret, while thefulphurized oxyd of iron brings the earthymatters intofufion, forming a flag that is inca-pable of combining with the metallic fulphu-rets, and through which they fall in drops onaccount of their fuperior fpecific gravity. Bythe procefies of roafting, the fulphur, arfenic,zinc, &c. are driven off, and the iron beingoxydated quits the other metals, and uniteswith the fcoriae in the fubfequent fufions; whilethe lead, filver, and copper of the fcorise, pafsthrough the vitrefied mafs, and unite with thematt. The feparation of the filver from thecopper is effefted by the fuperior affinity of theformer with lead, aflifted by the attraction fub-fifting between the copper and fulphur, whichdifpofes this latter metal to yield the filver tothe lead more eafily than if the copper waspure.

Of Eliquation.

Silver is fometimes feparated from copper byLiquation or Eliquation. This is an old procefswhich appears to have fallen confiderably intodifufe, but it requires fome notice in this place.When copper matt (or the black unrefinedcopper) contains filver in the proper proportionfor this operation, it is firfl melted with lead orlitharge, or a mixture of the two, and a regulinealloy is produced containing the copper, lead,and filver, which is call; into moulds fo as toform round maffes or loaves. Thefe are thenfet in a furnace on an inclined plane of ironwith a fmall channel grooved out, and heatedto a very moderate rednefs, during which thelead melts or as it were fweats out of .the loaf,and runs down the channel, conveying with itthe filver, and the copper is left behind as areddifli-black fpongy mafs. The filver-holdinglead is then worked off on a cupel in the ufualway, and the filver is obtained Separate.

This procefs is founded on the very weakaffinity which lead has for copper, and the veryftrong affinity which it bears to filver, fd that ata moderate heat the feparation of the lead andfilver from the copper is effefted eafily, butmany circumftances muft be attended to inorder to perform this procefs with fuceefs.

The firft confideration is the relative propor-2 Q.2