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The ore, if wafficd, is of a fuflicient despreeof iii enef', without having reeourfc to grinding,but it oniy hand dvefled, itmuft fubfcquently bereduced in a mi!i to the confidence of coavfefai;d. This being done, common fait ltuft beaccurately mixed with the ore in the proportionof 8 or 9 per cent, if the fiiver in the ore amountsto 8 oz. per quintal, and from io to 12 per cent.if the fiiver amounts to 32 oz. or even more.1. he next procefs is roafting: for this purpofeabout 3 quintals are fpread on the floor of a re-verberatory furnace, and expofed to a moderatered heat for four or five hours, till the erniflionof vapours has almoft entirely ceafed, care beingtaken to turn it over two or three times duringthe roafting, that every portion may be in itsturn expofed to the adtion of the fire. Whenthis firft change is withdrawn, an experiencedworkman can tell by its appearance whetherthe proportion of fait has been too much or toolittle, and the necefiary correction is accordinglymade by adding more fait or ore to the unroaftedparcel. The whole of the ore being properlyroafted, is ground in a mill, and afterwardspaffed through fieves, by which it is renderedas fine as meal, and is then fit for the procefsof amalgamation, properly fpeaking.

This is performed in an apparatus confiftingeither of a number of fmall barrels made to re-volve rapidly on their axes by mill-work $ or ofa number of fixed tubs, open or covered, withan inftrument refembling a chocolate mill placedin the centre of each, and capable of beingturned rapidly by the fame kind of machineryas puts the barrels in motion. Thefe tubs orbarrels are filled about one-third with water,and then a fufficient quantity of roafted oreand mercury, in nearly equal proportions, isadded, to bring the whole to the confiftence ofthin mud. The machinery is now put in motion,and is continued inceflantly for from thirty toforty-eight hours, according to the richnefs ofthe ore, at which period the amalgamation iscompleated. In about a quarter of an hourafter the mill is flopped the greater part of theamalgam will have defeended to the bottom ofthe veflels, and is accordingly withdrawn, by un-ftopping a hole made for that purpofe.

The earthy refidue is then carefully wafhedby fmall parcels at a time, and thus muchamalgam, which from its minute ftate of divifionwas unable to fink through and mix with thereft, is recovered. But the earth, efpecially ifit was at firft rich in fiiver, {Till retains a portion#f precious metal: it is accordingly dried, mixed

with about 3 per cent, of fait, again roafted,and at a higher heat than at firft, and againamalgamated, by which the whole of the fiiveris extracted.

The amalgam, which is very fluid, is {trainedthrough a elofely-woven hag, by which it isfeparated into nearly pure mercury, and a ftiffamalgam : this latter is then fubjedted to diftil-lation per defeenfum, in an apparatus that cannotbe deferibed without the affiitance of plates ofreference, and is thus feparated into fiiver andmercury. The fiiver however (till contains alittle copper, from which it is freed by cupella-tion in the.ufual way.

The theory of the procefs of amalgamationappears to be this. By the roafting, the fulphurof the fiiver and pyrites is for the molt partburnt off and converted into fulphureous acid,which acid as foon as formed, aflifted alfo bythe affinity of the fiiver for muriatic acid, de-compofes the common fait, and forms with itsbafe either fulphat or fulphite of foda, whilethe muriatic acid combines with the fiiver,forming luna cornea. In the fubfequent amal-gamation, the mercury being prefent in greatabundance decompofes the muriat of fiiver,and is itfelf partly converted into calomel, whilethe reft of the mercury combines with the re-duced fiiver into an amalgam. Hence the lofsof mercury which always happens in this pro-cefs depends on two caufes, firft, the converfionof a part of it into calomel (and this cannot byany care in manipulation be avoided) and, fe-condly, the divifion of a part into fuch minuteglobules, as enables it to pafs off unperceived inwaffling the earthy refidue: the proportion ofthis however depends greatly on the care anddexterity of the manipulation.

We ffiall clofe this fedtion by mentioning ina few words a method invented by Napione, 1of feparating fiiver from copper, without havingrecourfe to the more expenfive and tedious me-thod of eliquation. The mixed metal beingmelted, fome fulphur is to be fprinkled over itsfurface, while an affiftant ftirs the whole aboutwith a (tick ; the fulphur thus combines withthe copper into a matt, which floats above themetal, and is to be removed with a pair oftongs, after having moiftened its furface with alittle water, in order to foliclify it. A frefitportion of fulphur is then to be ftirred in,and the matt thus produced is to be removedas before ; by repeating this a fuflicient numberof times the greater part of the copper is con-verted into matt, holding a little fiiver, while

1 Ami. de Chim. xli. p. 160.