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fmall way ; we . fliall here therefore only parti-cularize the circumftances in which cupellationin the great, or refining as it is ufually denomi-nated, differs from the former. It is performedin a reverberatory furnace, the floor of which ishorizontal, and is lined with a mixture of wood-afhes and fand, well beaten and formed into a(hallow bafon called the cupel. At one fide ofthe cupel, and forming a right angle with theflue by which the flame from the fire-placeenters the cavity of the furnace, is an aperture,through which the lead flows when convertedinto litharge, and oppofite to this is anotheraperture for the admiffion of a blaft of air. Inthe top of the furnace is a circular aperture,juft above, and correfponding in fize with thecupel, which may be clofed by a frame-workof iron filled up with bricks. The furnace be-ing ready the cupel is lined with hay, andcharged with about 177 quintals of lead in barsor pigs, by means of the circular aperture juftmentioned; the cover is then put on, and thefire is lighted. In about fix hours the lead isentirely melted and brought to a full-red heat,at which time a blaft of air is introduced by ametallic pipe, and fo directed as to ftrike uponthe furface of the melted lead ; the afhes of thehay and other impurities are alfo removed bymeans of a wooden rake thru ft in at the aper-ture for the litharge. When the blaft has beenin action for half an hour or more, the furfaceof the lead is covered with a thick cruft ofoxyd, which being fcraped off is prefently fuc-ceeded by another, and it is not till the furfacehas been cleared five or fix times, that the truelitharge makes its appearance. As foon as thistakes place the temperature is raifed nearly to acherry-red, and by the action of the blaft, thelitharge with a little occafional afiiftance fromthe workman is made to flow out of the fur-nace by the aperture already mentioned. Aconfiderable portion of lead is alfo volatilizedby the intenfe heat, fo that the interior of thefur'ace is filled with vapours to fuch a degree,that none but an experienced eye can difcernwhat is going on in the cupel. In about 38 or40 hours after lighting the fire, the contents ofthe cupel are diminiftied to about 6 quintals,and the litharge which now comes over is keptfeparate from the reft on account of a fmallquantity of filver which it contains. After atime the litharge ceafes to flow, and the furfaceof the metal in the cupel appears to be coveredonly by a thin pellicle: by degrees it becomesconvex at the edges, the pellicle breaks

and the furface of the metal appears quitebright. The fire is now damped, the blaft isturned off, and an aperture in the furnace,which had before been flopped with clay isopened to give admiffion to a tin-plate tube,through which a dream of water is poured intothe cupel in order to cool the metal rapidly, andthus prevent it from fpirting, which it woulddo if left to itfelf at the moment of congela-tion.

The cake of metal thus procured is not how-ever perfectly pure filver, and requires a fecondcupellation at a higher heat to free it entirelyfrom the lead with which it is mixed. Thecupel made ufe of on this occafion is a moveableone, and not capable of holding above 700 or800 oz. It is placed in a fmall reverberatory,and after being heated about three hours, ischarged with filver of the firft cupellation. Aproper working heat is kept up for about fouror five hours after the fufion of the filver, atthe end of which time the refining is ul'uallycompleated; the contents of the cupel ate thendifeharged into a mould, and thus formed intoingots. The lofs of lead by volatilization dur-ing the refining amounts to about 8 per cent.

The demand for litharge is very fmall incompanion to the quantity produced, thegreater part of it therefore muft be reconvertedinto lead; for this purpofe it is returned to thereverberatory, and treated in the fame manneras the ore, by which the greater part of it isconverted into lead of the beft quality, beingconfiderably fofter than when it has merely un-dergone the common reduction. The fcorixremaining after redudfion of the ore and thelitharge, together with the old cupels, the me-tallic foot colledfed in the chimney of the fur-nace, &c. are laftly treated in a common blaftfurnace, and made to yield a confiderable por-tion of the lead that they contain, after whichthe refidual flag is thrown away.

The practice in the Englifii refineries differsfrom that juft deferibed in fome particulars,which we (hail proceed to notice. 6

The furnace refembles the common reverbe-ratory except that its area is perforated with alarge oval hole for the reception of the cupel.The cupel itfelf is thus formed : fix parts ofwell-burnt bone afhes and one part of goodfern afhes are mixed together and moiftened toa proper confidence; of this a quantity isftrewed to the depth of about two inches, in aniron frame, confiding of a raifed elliptical rimwitli five broad bars rivetted to its bottom, fo a*

XX- p. I.

up,

11 Sadler in Nidi. PIul. Jonrit. 8vo. voi.

VOL. II.

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