Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/486

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method to procure the ftlver from there by an afTay is this : powder the ore very fine, and to a docimaftical centner of it add an equal quantity of glafs of lead, mix thefe thoroughly together; the glafs of lead maft, for this purpofe, be re- duced to as fine a powder as the ore ; put this powder,when well mixed, Into a teft, with twelve centners of granulated lead, and put the teft under a muffel in a furnace, make a ftrong fire, till the lead boils well ; when it is in this ftate, diminish the fire a little, and keep it in this weaker ftate for fome time, then encreafe it again to a great ftrength, till the lead is reduced to fcorise, and the filver is feen pure in the teft j or elfe when the fcorification is perfected, take out the matter together, and putting it into a coppel with more granulated lead, feparate the fthtr in a bead. Some- times a refractory ore of this kind cannot be thus fufficiently diflblved, but a mafs, which has the clammy nefs of pitch, fwims upon the furface of the regulus, and upon the fcorize that are in part fubdued : in this cafe, diminifh the fire, and touch this clammy mafs with a final] cold iron hook, to which it will immediately ftick ; take it all carefully off, reduce it to fine powder, and mixing it with more glafs of lead in powder, put it back into the teft, then continue the fcori- fication till it is perfected : but always obferve that the fco- rise of thefe refractory ores muft be examined, to fee if fome of the regulus does not remain among them, for fometimes the fcoriae, by their clammyneis, will retain part of the me- tal ; if this appears to be the cafe, powder the fcoriEe very fine, and the metal will be discovered and feparated, as it cannot be reduced to a fine powder. Cramer's Art of Aflay- ing, p. 218.

The method of precipitating filver out of an eafily fufible ere is this: pound the ore very fine in an iron mortar, and for an afi'ay weigh one docimaftical centner of it, and eight centners of granulated lead; pour into a new teft about half the lead, ftir it about with a finger, and fpread it over the cavity of the teft; put upon this lead the pounded ore, and then cover it with the remainder of the lead ; put the teft, thus loaded, under the mufHe of an aflay-furnace, and in the hinder part of it make the fire, and encreafe it to a confider- abiy high degree The on- will foon be raifed out of the melted lead, and fwim upon it; a little after it will grow clammy, melt, and be thrown toward the border of the teft ; then the furface of the lead will appear clear in the mid- dle of the teft, and will fmoak and boil ; the fire muft now be made a little Iefs, till the boiling ceafes, for a quarter of an hour, and then made violent again, and the furface of the lead will then diminifh by degrees, and be covered with a mafs of fcorias. At this time have at hand an iron hook ready heated, and with this ftir all the matter from the fides into the middle of the teft ; if the matter, adhering to the hook from the ftimng, melts quickly again, and the extre- mity of the hook, when cold, is found covered with a min- ing cruft, the fcorification is perfeftcd ; but if the fcorite feel clammy while ftirred, and adhere in quantity to the hook, and are of a rough furface, the fcorification is not per- fect, but the matter adhering to the hook muft be ftruck off with a hammer, and beat to powder, and returned into the teft, and the fire continued till the fcorification is perfe&ed ; then take out the teft, and pour the whole contents into a mould, heated and greafed. This is the firft procefs, and this ufually takes up three quarters of an hour : the filver is now in form of a regulus, and muft be feparated by the cop- pel in the ufual way. Cramers Art of Aflaying, p. 205. See the article Regulus.

Mundic is a very common thing in fiher-ores, efpecially the lefs rich ones, and gives great trouble in working the metal. The method of feparating the filver from an° ore, rendered refra&ory by this admixture, is thus : break the or) into a rough powder, and put a centner of it into a teft for an aflay ; put upon this another teft, by way of a cover> and put it under the muffle in a furnace ; when the muffle is near red-hot, encreafe the fire by degrees, there will be a crackling noife, which being ended, take away the upper teft, for when the veflels have been red-hot about a minute, the ore ceafes to fplit; leave the ore under the muffle, till the aifenic and fulphur are in a great meafure evaporated, which will be known by the ceflation of the fmoak from the ore, and of the fmell of garlick, or the acid ; then take out the teft, and leave it in a place not too cold, that it mav cool leifurely of itfelf ; take the roafted ore clean out of the teft, powder it very fine, and mix it with an equal quantity of glafs of lead in fine powder ; and finally, fcorify the mais in the fame, or in a new teft, if that was cracked till the filver appear in form of a bright bead in the middle, after it has ftood a minute or two ; after this take it out of the fire, and when cold take out and weigh the pure filver. Cramer's Art of Aflaying, p. 221.

Alonfo Barba tells us, that the original method of extradt- ing filver from the ore, in the mines of Potofi, was only by quickfilver, but this was very difficult in many cafes. Thofe ores which partake of copperas, which are very numerous there, will not bear quickfilver, but confume and fcattcr it, breaking its particles, and rendering them unfit for the pur-

pofes they we're intended for, of taking up the filver e'en tained in the ore. Burning the ore was another fnetfiod heretofore ufed with too little caution, and great lofles were fuftained by it. The grinding the ore is always proper kn J the finer it is ground, the better it will always njcceed Alonfo Barba alfo greatly recommends boiling the ores \x which the quickfilver is ufed, as of great advantage. The burning of ores is of no fervice, but to render the ftoriy matter more friable ; but when there is marcafite among the ore this is never done without lofs, and that often very great. Alonf Barba de Metall. J0

The largeft piece of filver-ore we have account of any where, is at this time preferved in the king of Denmark's Mufeum of Curiofities at Copenhagen; this was dug in the mines of Norway, and weighs five hundred and fixty pounds It is five feet fix inches long, and meakires four feet about ■ it is valued at five thoufand crowns. There is in the fame place another alfo, which was dug in the fame mine, valued ■ at three thoufand two hundred and feventy crowns. Thefe are both fo very rich, that they feem at leaft three parts filver, and the metal appears in very elegant forms in them and rifes up out of their furface in form of fmail trees and bufties. There are alfo feveral pieces of pure native or virgin filver there, all "of which rcprefent trees or plants. Silver-^///, a chemical preparation of filver, formerly hio-hly commended as a remedy for dropfies, and in many other difeafes.

The method of making it is this : diflolve an ounce of pure nitre in diftilled water, then diflolve an ounce of cryftals of filver. made in the common way, with pure filver and aqua fords, in three times the weight of water, fo that the folu- tion may be perfectly limpid ; mix the two folutions toge- ther, they will become a clear homogene liquor, evaporate this to a pellicle, and cryftals rcfembling nitre will {hoot; pour off the remaining nitre as before, and the remaining nitre will fhoot with the filver, in form of cryftals, a^ain upon a fecond evaporation : let thefe cryftals be dried upon a paper, and then placed in a glafs veflel in a very gentle heat enough to make them fmoak, but not run, ftir it with a piece of glafs all the time, and keep it over the fire, till no more fumes arife ; thus the acid fpirits will be driven off", and -the filver remain of a very bitter tafte, and purging quality. It muft be kept in a dry clofe veflel. This difco- very, has been made to l'erve to many other purpofes, befide its ufes in medicine, and has furnifhed the difhoneft pre- tenders to alchemy with one of their moft cunning methods of deceit. They have been able, by this means, to conceal filver in nitre, and that in a very large proportion, as in one tenth part of the whole quantity; and this nitre being projected in an equal quantity on melted lead, gives an in- creafe of one tenth part in filver, which remaining upon the teft, will deceive the ignorant, as if a tenth part of the lead were converted into pure filver. People who arc upon their guard may, however, difcover the cheat, by diflblvinw the pretended nitre in ten times its weight of water, and puttino- a polifhed piate of copper into the folution ; for every par- ticle of the filver will then be precipitated out of the liquor upon the copper, and to the bottom of the veflel. Boerh. Chem. Part 2. p. 296.

The medicinal ufe is this : the dried mafs, confifting of the falts of filver and nitre, is to be reduced to a fine powder; this powder applied to ulcers, acts in the manner of the lapis infernalis, oryfotr-cauftic, only much milder : but for in- ternal ufe, the quantity of two grains of it is to be ground to a fine powder, with fix grains of loaf-fugar, in a glafs mortar, this is to be then mixed with ten grains of the crumb of bread, and formed into nine pills .- thefe are to be taken by a grown perfon upon an empty ftomach, drinking after them four or fix ounces of hot water, fweetened with honey. It purges gently, and brings away a liquid matter like water, often unperceived by the patient. It is faid to kill worms, and perform great things in many obftinate ul- cerous diforders. It purges without griping, but it muft not be ufed too freely, nor in too large a dofe, for it always proves weakening, and in fome degree corrofive on the fto- mach ; but this inconvenience is greatly alleviated by rob of juniper. Boerh. Chem. Part 2. p. 297. SILVERING (Cycl.)— To filver brafs : fine filver is diflblved in aqua fortis in a broad bottomed veflel of glafs, or glazed earth, and the aqua fortis being afterwards evaporated, water is poured upon the remaining calx. This water muft alfo be evaporated, and the operation repeated as often as there is occafion; the fire being increafed towards the latter end, fo as to leave a perfectly dry and white calx, which will be thus tolerably freed from the aqua fortis. Of this calx take one part, and an equal meafure, not weight, of common fair, and of the cryftals of tartar, and mix them together into a fine powder ; then having firft plunged the (cowered brafs in- to fair water, rub fome of the powder upon it with your wet fingers, till the cavities of its furface be fufficienrly filled therewith. Laftly, wafh the metal well in water, and give it a glofs by rubbing it hard with a dry cloth.

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