fame nature with the Barilla or Soda, ufed in the preparation of French and Spanish foaps.

I have been thus particular in defcribing the process of preparing proof aqua fortis, as it is a very neceffary menftruum in metallurgical experiments.

As it is poffible the Mundick tried, may contain Copper in fo large a quantity as not to be entirely fcorified by the above operation, but may poflibly remain on the cuppel in a confiderable quantity; in this cafe, the bead muft be diffolved in proof aqua fortis containing no Silver, or that yields no cloud dropt into clean brine. If this bead contains Gold, it will remain undiffolved in a black powder as is faid above; wash it, and add the water to the folution, into which, drop brine as long as any white precipitates: this is the Silver in the shape of the Luna Cornea, and when wafhed and dried may be weighed. I think four parts of it contain three of Silver, or thereabout.

Procefs VIII. To affay Tin for Gold.

Heat a

To eight ounces of melted Antimony, put two ounces of the Tin to be tried; keep them together in a moderate fire, till they melt together and flow like oil, without the least bubbling or effervefcence, which operation may take an hour. If the mixture grows thick, fresh Antimony is to be added, till it melts perfectly thin or fluid; then pour it out into the Iron cone, and when cold feparate the bright antimonial regulus at bottom, from the scoria at top: fet by these scoria. cuppel made of crucible clay, or the bottom of a crucible, reduced to the fhape of a cuppel (thefe veffels are called Tefts) in the reverberatory, till it is of a strong red heat inclining to white; place the regulus of Antimony in it, which will inftantly melt. Direct the nofe of a kitchen bellows on this teft, and keep up a continual blaft on the regulus (which will evaporate in thick white fumes) till it is reduced to one quarter or less of its original weight. Take out the test and let it cool; separate the remaining regulus from it, and melt it in a crucible. Throw on it twice its quantity of nitre; and when the deflagration and fumentation are over, pour it out into the cone. If there is any Gold left, and this Gold is fine, the operation is complete; but if there is nothing left at the bottom of the yellow glaffy scoria, the Tin contains no Gold. If there is a fmall button of brittle Metal, or Metal not fufficiently malleable,

add

add equal parts of nitre and borax, and repeat the operation, till the Gold is quite fine; when it is to be weighed, and the proportion it bears to the Tin affayed, determined.

In this operation, the fulphur which mineralizes the Antimony, having a greater attraction with the Tin, than with the regulus of Antimony, deferts the regulus, and lays hold of, and mineralizes the Tin, with which it afcends among the melted Antimony; whilft the regulus feparated from the Antimony, defcends, and mixes with the Tin at bottom. This procefs goes on till the whole of the Tin is mineralized by the fulphur, and fomewhat a greater quantity of the regulus feparated and precipitated; if the Tin contains any Gold, it will be mixt with this regulus, as fulphur cannot mineralize it. If there is any Silver, this will be mineralized, and raised among the fcoria, which confift of the Antimony in its Mineral state, and the Tin reduced to this ftate; the regulus containing the Gold, being volatile, is evaporated in white fumes, by the fecond operation, whilft the Gold is left: but as it is difficult to bring it to perfect fineness this way, nitre is used in the finishing operation, which immediately calcines the regulus. In this operation, the spirit of nitre evaporates along with the phlogifton of the regulus, and the alkaline part of this, together with the reguline calx, melts into glaffy scoria of an amber colour, leaving the Gold untouched by the nitre, which cannot diffolve it.

Procefs IX. Το try the firft fcoria for Silver.

Melt the first scoria, confifting of the mineralized Tin and Antimony, in a crucible; throw powder of nitre on them, and there will then be a confiderable deflagration; continue to throw in more nitre till the deflagration ceafes, and when the matter in the crucible melts like oil, pour it into the cone, knocking it gently that it may fettle. When it is cold and ftruck out of the cone, carefully examine the apex of the melted fcoria, where the Silver will be found if the Tin contained any.

In this process, the phlogifton of the fulphur is carried off by the spirit of nitre; and the other part of it, viz. the vitriolick acid, is attracted by, and united with, the alkaline basis of the nitre, forming with it a true fal polycreston, that swims at the top of the melted fcoria, which by this procefs, are converted

into a compound crocus metallorum, confifting of the calcined. Antimony and Tin. The Silver not being calcinable, when the fulphur which mineralized it is feparated by the nitre, it regains its metallick form, and falls to the bottom of the cone.

The compound crocus metallorum, and the amber scoria, may be reduced into a metallick form, by being mixed with a proper quantity of black flux, and melted in a crucible; but not without great lofs of the regule. This procefs for the feparating Gold from Tin by Antimony, may be applied to Copper, or any other Metal.

Procefs X. To affay Copper Ore.

Powder the Ore and fift it through a hair fieve; shake and mix it together, that every part of the powder may be alike, in regard to its metallick contents: form this powder on a piece of paper into a bed of half an inch thick; then weigh off a troy ounce, or ounce and quarter of it, from different parts of the bed or heap and in order to affay it, the Ore is first to be calcined, in the following manner :

The wind furnace having been before well heated, is to be filled with fea coal, reduced to the state of charcoal, or as it is ufually called, coakt or charkt. A crucible of the largest fize for affaying, is then placed in the furnace, fo that the top of it fhall be a little beneath the top of the furnace. It is very proper to place one layer, or a few pieces of raw coal, round the top of the crucible, to keep down the flame and heat, which would otherwife incommode the operator in the calcination. The Ore may now be put into the crucible, and fome of the covering bricks put on the mouth of the furnace to raise the fire; but this must be done gently. As foon as the Ore is obferved to be of a dusky red, it is time to begin to flir it, to prevent its melting and running into lumps, which muft by all means be prevented, both by ftirring, and a proper regulation of the fire. The Iron rod ufed in ftirring, fhould be about two feet and a half long, and as thick as the end of the little finger, the one extremity of it flattened and formed like the toes of a pair of tongs, so as to fuit the bottom of the crucible. With this rod the Ore is to be ftirred brifkly from time to time, fo as to prevent its melting, or running into lumps; and if it should appear difpofed to do this, it must be ftirred very brifkly, till the appearance ceafes, and the Ore is again reduced into a powdery

form.

form. It will not be neceffary to ftir the Ore continually; but when you cease to stir, the rod must not be taken out of the crucible but left in it, the upper end refting on the bricks of the chimney.

it

In the beginning of the calcination, a large quantity of fulphureous and arfenical fumes will be discharged from the Ore; and moft Ores, at this time, emit alfo more or lefs of a fulphureous flame. As the Ore parts with these volatile matters, grows lefs fufible, fo that the fire may be fuffered to encrease a little, in proportion as the Ore is lefs liable to melt. The operation must be thus continued, till the Ore emits no longer any vifible fumes. When the crucible is taken out of the fire and smelt at, if it yields no fmell of fulphur, even when it hath been exposed to a strong red heat, a little inclining to white, then it is fufficiently calcined. This process This process generally takes three quarters of an hour, and the fire must be often renewed by adding fresh charks, and raw coal.

In this procefs, the Ore is freed from the fulphur and arfenick which mineralized it, and is now reduced to the Metals and ftony fubftances; but as the Metals cannot be collected by fufion into a body, as the ftony parts are infufible, this makes it neceffary to use such things as will turn these stony matters into Glass, by the following procefs of Scorification.

Process XI. Suppofing the quantity of Copper Ore made ufe of, to be one ounce, mix with it one ounce and a quarter, good weight, of black flux, and half a thimble full of powdered culm; put these into the crucible the Ore was calcined in, and cover them with nearly half an ounce of sea salt. Fill the furnace with charks, and place the crucible in the furnace, furrounding it with charks to the brim. After you have covered it with a cover, made of the fame compofition with the crucible, put on the covering bricks on the mouth of the furnace, when the fire will rife, and the matters in the crucible will be heard to melt and boil. When thefe appearances have ceased for some time, remove the bricks, and infpect the matters in the crucible; if the surface is agitated, and the boiling and fermentation continue, the scorification is not complete. If the fire wants mending, mend it; place the crucible fecurely, close the furnace, and continue the fire, till the contents of the crucible flow like oil. Take it out of the furnace, and fuffer it to cool; when cold, break the crucible, and separate the Metal at bottom,

from the scoria. If thefe appear to be quite glaffy, lucid, and black, and if they contain no grains of Copper, the scorification is well done.

In the above procefs, the nitre and tartar are converted into an alkaline falt, which being rendered ftill more vitrefcent by the borax, convert the ftony matters contained in the calcined Ore, together with a part of the Iron in it, into a true glass, to which the blacknefs is given by the Iron. As this glass is very fufible and fluid, the grains of Copper now reduced to Metal, eafily find their way through it, and unite at the bottom into one piece of Metal. The falt is added as it contributes to vitrification, and prevents the matter from rifing in the pot, and leaving grains of Metal on its fides, which would falfify the affay. The powder of culm is put in, to fupply phlogifton, after what the tartar contained is burned off; and if the operation is continued after this, there is danger of the Coppers being burned, and deprived of its phlogiston; in which case, the affay will be covered with a red fhining heavy friable substance, which is the calcined Copper melted: to guard against this, the powdered culm is added.

The quantity of flux may be varied, according to the richness of the Ore. Very rich ones will require much less than what is ordered; nothing, however, but practice and experience, can enable a perfon to fix the quantity of flux requifite. The furnace for fcorification ought to have a fmart draught; for if the operation takes up much time, the affay is apt to burn; about fifteen or twenty minutes is fufficient for the most part, if the furnace is a good one.

The lump of Metal from the firft melting is fcarcely ever fine, being mixed with Iron, Lead, Tin, or poffibly with all these Metals; therefore to separate them, it must be refined, for which the following is the process :

Process XII. Refining the impure Copper.

Fill the furnace with charks, and place a crucible of the fecond fize in it. Let the fire rise till the bottom of the crucible is white hot, when the button of Copper is to be put into it, by means of a small pair of forceps or tongs purposely contrived for it. As foon as the Copper is feen to melt, throw on it, by means of a small Copper fcoop, about as much white flux as