Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/552

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an'l p\rf it into the cavity again, driving it in with one or two more blows. Then having at hand a fmall wooden plank, ftrewed a quarter of an inch thick with dry afhes, put upon it the mortar, containing the coppel already prepared; the coppel will eafilyquit its mould, and its inequalities at the upper edge and bottom being taken evenly off with a knife, let it be in- verted, and iaid afide in a dry place.

The dry fine afhes arc applied to the infide of the coppel,^ that the little inequalities commonly remaining there may be filled, and it may make a fort of fine neve, admitting thro' it vi- trified bodies, but retaining grid and filver. The cavity being regularly covered with this perfectly fine fubftance, prevents any harm from the common matter of the coppeh being a little defiled with fand, or other powder, eafy to be vitrified, which is a fault indeed hardly pofiible to be avoided, efpecially when wood afhes are ufed. Hence it is plain, that this pow- der muft needs be prepared with very great caution, and even the levigating it muft be done on a very hard ftone, left, if on a foft one, fome particles might perhaps be abraded from its furface, and fpoilthe powder.

Coppeh had better be too compact than too loofe in their tex- ture, finee the latter is always a mifchievous accident, whereas .the former, by abforbing the glafs more fiowly, is of no other hurt than the retarding the operation a little. Coppeh made of bone afhes, or of calcined fpar, are more va- luable thanthofeof wood afhes, as they require not fo much caution and regularity in the management of the fire ; but if wood allies enter the compofition, the coppel muft be made pretty hot before the metal is put into it, otherwife the aqueous vapours, forcing their way out, will caufe the metal to be thrown out in drops ; for coppeh of this kind can never be perfectly dried by the air alone, there being always fometbing of an alkaline fait yet remaining in wood afhes, which makes them attract the water out of the air, as the dark colour of thefe .afhes, and the folution of fal armoniac poured on them, alfo fhew : for this reafon, thefe afhes are alio more difpofed to vitrification than thofe of bones, #he latter approaching much nearer to the nature of the incombuftibleftones. As to themoiftening the matter of the coppeh, great care muft be taken not to ule a fluid too mucilaginous and fat ; for this makes the coppeh fo compact, that they not only either abfo- lutely reject vitrified bodies, which they are intended to re- ceives or yield them but a very flow or difficult pafl'age ; but alfo are apt to fplit, when made very hot, and diverted of their oily part.

Neither muft fuch mucilaginous fluids by any means be ufed, as may produce a great deal of fixed alkaline fait in the heat- ing of the coppeh as the tartareous dregs of fermented bodies do. Nor muft the afhes be moiftened too much ; for if they are, the furface of the veflel will never be perfectly neat. Some artificers mix about a tenth part of fine wafhed clay to their afhes, for the making their coppeh : when this is done, the matter muft be moiftened with water only, the clay mak- ing the whole ftick fufficiently together. Great care, how- ever, muft be taken, that too much clay is not added, and the different degree of the fatnefs of the clay be attentively confidered.

The afhes of bones ufed alone, and ground to a fufficient fine- nefs, require no clay or mucilaginous fluid to increafe their cohefion, but do very well with pure water alone : and coppeh of this kind, and fuch as are made of the calcined fpars, need hardly be made at all hot before the metal is put into them. The operation, however, when performed in a coppel made of bone afhes, or of calcined fpar alone, takes up a little more time, but it is more fecurely performed than in coppeh where wood afhes make a part of the matter of them : for as thefe bone or fpar veflels receive the vitrified metal more flowly, on accout.t of their compact ftructure, fo it is lefs to be feared that any of the perfect metal fhould be abforbed alfo, even tho' the management of the fire be not fo critically minded. Cramer, Art. of AfT. p. 5?. to 59. CUPELLING. Silver may be precipitated out of its ore by copelling alone, in the following manner : roaft a centner of the filver ore in the common way ; when roafted, powder and fift it very fine, and if it melts with difHculty, mix with it one centner of litharge : when i't is an ore that melts eafily, this may be omitted. Divide the powder into five or fix parts, and wrap up every one of them feparately in fmall pieces of paper. Put a large coppel under a muffle in the furnace ; heat it thoroughly ; then put into it fixteen centners of lead. When the lead begins to fmoak and boil, put upon it one of the fmall parcels of powdered ore, in its paper ; then diminifh the fire a little. The paper will be immediately confumed, and the ore caft to the fide of the coppel, in form of fcorias. When this is done, increafe the fire again, and add a fecond parcel of the ore ; and continue this method till all the ore is put in ; after which, fcorify the lead in a ftronger fire. The filver con- tained in the ore, with that contained in the lead, will now be found in form of a bead in the coppel ; and fubtracting the known quantity yielded by the lead, the remainder of the weight gives the quantity of filver in that centner of ore. Silver is not the only ore that can be thus worked; many others may be allayed in the fame manner, by coppelling alone :

thofe are indeed to be excepted from this procefs, which fplit, or which corrode the coppels. Cramers Art of Ail", p 2 *?. COPPER (Ccl) — This metal, expofed to the focus of a pow- erful burning ghfs, at firif. becomes white on the furface, after that it turns black, being covered with a black fcale or fkin, and after this it melts.

If it be taken away in the fit ft: ftate, there is found no remark- able difference in it, and the whitenefs of the furface very foon goes off again. It is not eafy to fay to what this white colour is owing, whether to an arfenical fait in the metal, or to the mere change of pofition in its parts ; but the black that follows, is plainly occaiioned by an oily matter feparated from the reft of the metal, which is thefirft thing that gets into fu- fion, and is carried to the furface by the violence of the heat. If the copper is held longer in fufion in the focus of the glafs, it emits fame light fumes, and by degrees diffipates wholly away. If it be put into a coppel, and in that placed before the focus of the glafs, it foon melts, and afterwards becomes fluid like oil. If it be taken away in this ftate, it cools into a brown- ifh, red, reguline mafs, which is brittle, and not at all exten- fible under the hammer. This may be rubbed to powder, and refembles cinnabar in colour, and the grains of the powder being viewed by the microfcope, appear like fo many rubies, very beautifully tranfparent, and of a fine red ; fo that it is eafy to fee, this regulus is truly a deep red glafs. If thisrcgulusor glafs be mixed with common white glafs in powder, and then melted, the alkali falts of the glafs act upon the copper, and the glafs produced by the mixture is blue or green. This regulus is, properly fpeaking, no other than copper, divert- ed, by the folar fire, of that oily or fulphurous principle which gave it the form of a metal, its malleability and other proper- ties : and a clear proof of the truth of this is, that if this re- gulus of copper be again expofed to the focus of the glafs upon a piece of charcoal, it'in a very little time imbibes the oil or fulphur of the charcoal, and reaffuines its metalline ftate, and if takenaway, and left to cool, is found to be as good copper as it was before the firft experiment ; as malleable, and as ductile as be- fore. Any other calx of copper alfo may, by the fame means, be reduced to the true metalline ftate again. It follows, therefore, from the whole, that the bafis of copper is a red friable matter, fufceptible of vitrification ; that this matter receives its metal- lic form from an oily, or fulphureous principle ; and that this oil does not appear to he any way different from the common oils of vegetable, and of animal fubftances ; that copper may be deprived of this oil by holding it long in fufion in the folar fire, and is then diverted of its metallic form ; but that if it be afterwards laid on a piece of charcoal, in the fame heat, it re- ceives from that charcoal an oil like that which it before bad loft, and becomes a metal again. Mem. Acad. Par. 1709. Copper put into the fire with iron promotes its fufion, but it becomes more rigid and more pale bv the mixture. It is often neceffary, to render this fufion the eafier, to add as much tartar and. common glafs, as will cover the furface of the whole mafs. As to the other metals, copper is well known to mix readily with filver and gold, and to give them a rigidity which ren- ders them much more fit for the ufes of life, than they would be in their natural foft ftate.

Copper, when hid, as it frequently is, in an ore full of the mat- ter of the pyrites, may be difcovered by a folution and liquid precipitation, in the following manner : make a folution of vi- triol out of the ore, by a flight rdafting in an open fire, and by expofing it afterwards to a.n air fomewhat moift, and pour- ing warm water upon it. Put into this folution fmall iron plates, perfectly clean, and free from greife ; if there is any fmall quantity of copper in the pyrites, it will now ftick to the iron plates, in form of a fubtle powder, of a deep yellow colour, and all of it will be thus fetched out or the folution, if there be time enough, and a moderate warmth. Cramer's Art of Af- faying, p. 327.

When iilver is contained in copper, it may be feparated in the following manner : Reduce the copper into filings ; put one cen- tner of this by for the operation ; then put the double and fex- tuple quantity of granulated lead into a large, well-baked co- pell ; make the fire ftrong, and continue it fo till the lead be- gins to fmoak and boil ; then add the copper wrapped up in a paper, fo that it may be immerfed together into the middle of the boiling lead. When all the copper is diflblved, fupprefs the fire till there is a fmoak feen wandering over the furface, and the mafs is not raifed up very high in the middle, and the cop- pel looks brown as far as it has been penetrated by the litharge: take care, however, that the boiling of the lead does not en- tirely ceafe. When the greateft part of the metal is confumed, encreafe the fire gradually, and make it very ftrorig toward the end. When the operation is fmifhed, the filver will be found pure in the center of the coppel, furrounded with yellow feorise in form of cryftals. Cramer's Art of Afiaying, p. 227. Copper, in medicine, muft not be given internally in any form, unlefs under the direction of a very cautious phyfician. Crude copper, like crude mercury, may be fwallowed in great quan- tities with perfect fafety } it is returned again unaltered, na- ture having furnifhed us with no menftruum within our bo- dies, that is capable of acting on it. It is much otherwife with regard to its preparations, which are generally efteemed

poifonous ;