mentioned compofition, which is one of the most active, impalpable, and fubtil mineral minimæ, fpecifically to be obtained; and will infinuate itself and enter into the pores and vascular conftitution of the timber, which being thus wholly faturated will have all the power and aculeated exertion of the most effective poifon; fo that if the Teredo penetrates through the outward part of the wood, whenever he turns to feed upon the grain of it, he will be immediately destroyed. This digreffion will, we truft, be excused by many of our readers, on account of the importance of the fubject to commerce and navigation.

We shall now go on to obferve, that thofe rapacious poisonous Minerals are often intermixed with Ores and Metals in the earth, though not so often diftinguishable; and from thence in a great measure proceed that asperity and volatility which often happen to Ores in the fire, and which an unfkilful refiner is not capable of understanding and correcting. We fhall, therefore, in few words, endeavour to give an account of thofe fluxes, which are mostly useful in the small examen of Metals by fire; in which business the affayer or artificer ought duly to know and confider the different properties of acids, alkalies, and neutral falts; and how they act with each other and agree with Metals.

Sal Nitre, or Salt Petre, is a native Salt; and is almost peculiarly the product of the Eaft-Indies, from whence our EastIndia company import amazing quantities. They have in a great measure monopolized this article; and its vaft confumption in the manufactory of gunpowder, &c. must render it a very important branch of their trade. It is alfo factitious, and may be made at home from the offals of flaughter-houses, ftables, &c. It is a neutral hermaphroditical Salt, being neither a true acid nor alkali, though it is easily convertible to either : it seems partly acid and very volatile, yet partly fixed, and is a great purifier of coarse Metals, and will also destroy and devour them, if not warily and judiciously handled: it is intended further to liquify the fluxes with which Gold, Silver, and Copper are reduced and purged in the affay or crucible; which it does when exposed to the action of fire, in a pure and dry ftate, and foon flows with those bodies like water; whence it comes to be used in Metallurgy as a flux for those Metals.

Tartar, Argol, is a hard brittle faline fubftance, with which the fides of wine cafks are incrufted; and is red or white, according to the colour of the wine that produces it. An ingenious

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author

author fays, "It has Bacchus for its father, fermentation for "its mother, and the cask for its matrix." It confifts of a peculiar fixed fharp Salt, not improbably inclining to urinous or lixivial Salts. This Salt in Tartar is exceedingly useful in fluxing and depurating fome Metals, efpecially Copper. Tartar alfo contains a vegetable Sulphur, which is very powerful in reducing and embodying the burnt or vitrified calx of Copper; for which reason, it is juftly esteemed the principal ingredient in the affaying that Metal. It is very good likewife, as well as Nitre, for purifying coarfe Silver, and for making Silver tough

and malleable.

The most imperfect Metals, and the Semi-metals, melt more eafily by adding falts to them, than they do of themselves. However, they always lofe a great deal of their substance by this means, which happens especially with regard to Copper, whereby an advantage to the buyers of Copper Ore, who smelt in their large furnaces without thofe devouring and destructive Aluxes, must neceffarily arise. For if I buy five hundred tons of Copper Ore by a fample of one ounce, which I have tried with fome very small lofs of Metal by the abforption or rapacity of my faline flux; furely, the amount of Metal which will be faved upon fo large a quantity of Ore being fmelted without fuch lofs, must be very confiderable. Certain it is, that no loss can happen to the buyer who purchases by the produce of his fample; for it is impoffible for the fample to yield more Metal than it contains; and the wafte upon fmelting a large body of Ore, is comparatively fmall, cæteris paribus, to that of the fample.

But, in order to prevent this lofs of Metal in fome degree, you may add fome kind of fat body, that will fave it from deftruction, and reduce the Metal. The flux proper for this operation is very well prepared by Cramer; and from its colour is there called Fluxus Niger, or Black Flux: but we intend to give it as our best reducing flux, according to our own method of preparation, in our chapter upon aflaying. Tartar, being burnt alone, in veffels closely fhut, or detonated with Nitre, is most quickly alkalized, and thus retains a confiderable part of the Oil, which it contains abundantly, and is fixed enough: for this reason, it very easily turns into a reducing flux. This flux, therefore, on account of its alkaline falts, diffolves Earths and Stones, and changes them into an imperfect glass, by a moderate melting fire. But the Oil being of a more fixed

nature,

nature, ftill remains concealed therein, and is requifite both to preferve Metals from being deftroyed, and to reduce fuch as are already deftroyed.

Different combinations of the above falts are used by different affay-masters with us, for trying of Copper Ores; but the Black Flux, or the White Flux, (which fhall be given hereafter, and which fome call their Refining Flux) with careful management, and proper attention to the crucible during the process, will equally answer the purpose notwithstanding the appearance of mystery which our affayers affume.

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Rock Salt, or Sal Gem, Sal Foffile, and Common Salt, are all of a mild nature, though they become acid menftrua by diftillation. Common Salt is of great utility in the refining of Copper in the affay, because it swims on the matter:in fusion in pouring out of which, the Salt firft flows out, and greafes the lips of the crucible, if we may use the expreffion, infomuch, that the Metal may be poured forth, without sticking to the fides of the veffel. It is likewise useful to prevent the deflagration of the Metal in fufion, which otherwise may be burnt and deftroyed; therefore it is always at hand with our affayers to sprinkle into the crucible, when a flame iffues from the liquified contents, which it immediately damps and puts out.

Borax, Chryfocolla, Gold Solder, may be termed the Gum of Metals, from its usefulness in foldering them. It is a neutral falt, almoft infipid to the tafte, of a very mild nature, and not corrofive; and though it flows not exceedingly liquid in the fire, yet it makes Metals eafily fufible. Its chief intention in affaying, is to sustain and suspend the recrements of Metals in their impure scoriæ; or to throw fuch drofs upon the furface in a vitrified form; whereby they are purified from their heterogeneous matter. Borax is an artificial depuration from a certain mineral juice called Tincal by the Arabians; and fome German authors, fay," That a native Chryfocolla or Borax, is dug out " of Copper Mines;" but we never knew of its being found with us.

Sandiver, Scoria Vitri, is the fæces and dregs of glass. It is an Alkali, yet seems not void of Sulphur; for an ebullition enfues when it is melted with Nitre, and it is used, though seldom, in afsaying of Copper; but it is excellent to collect burnt Silver, and Silver filings, to a body; yet it always makes

the

the Silver foul and brittle, which therefore is further cleanfed by melting with the proper reducing flux.

Alga Marina, Kelp, Kali, Fucus, or burnt Ore-weed, contains much falt, of an alkaline quality; as do all sorts of burnt weeds, and Flemish pot-afhes much more, being better prepared. Kelp is the ftaple commodity of the Scilly-Iflands, where great quantities are made in the months of June and July. All thofe kinds of lixivial falts, are not very corrofive, and are proper in fome cafes for proving of Copper Ore.

Sal Ammoniack, Sal Arenarius. In former ages, a genuine native Sal Ammoniack was brought from a certain place near the temple of Jupiter Ammon, whence it took its name; and was faid to proceed from the urine of camels fed only on green vegetables but the falt we now have, is factitious from the foot of camels dung burnt; after which it is fublimed into cakes. It is exceffively volatile, and is chiefly used in making Aqua Regia, which its diftilled volatile fpirit ferves to mortify, whence it becomes a precipitator of Gold. It is of use alfo in foldering; and in tinning of Copper and Iron veffels, by making the Tin adhere to them.

Common glass is fometimes ufeful in trying of Copper Ore; for, in melting, it is of a thick ropy confiftence, and therefore ferves to entangle and fufpend the impurities of the Ore, fo that the Metal is better difengaged from its incumbrances and dregs, or purged and feparated from its defilements. For these reasons, several forts of Earths, Spars, and Fluors, with Iron Slags and Ores, may in fome cafes be ferviceable ingredients as fluxes for Copper Ore, by their ropy and abforbent qualities. We know an instance immediately at hand, where the very Slag of Slags is re-melted with impure Copper Ore for those purposes.

Charcoal, Carbo Ligneus, is endued with a vegetable Sulphur, and is therefore often of great confequence for reducing to a body the Ores of Tin, Copper, and Lead, being used as a flux and fuel both. Culm, fo called, is the popular flux for affaying of Tin after it is dreffed. Pit Coal is entirely improper for any reducing flux.

Thirdly. We come now to fpeak of Minerals and Metals more particularly; and fhall endeavour to distinguish most of

them,

them, as they are met with in this county, by their various names and ufes. We will here fub-divide Minerals, firft, into those of an impure fort or kind, and of no value for Metal; and, fecondly, into those which are of use, and yield fome produce in fufion, fuch as Antimony, Calamy, and other Semi-metals. By the first fort of Minerals, we understand all Cachymiæ, Marcafites, Pyrites, or Fire-ftones; which feveral names are well comprehended in the word Mundick, whofe great Emporium is Cornwall. We shall here but lightly touch upon the natural history of this Mineral Glebe, having already given our thoughts upon fome of its properties and useful applications. The figures of Pyrites being extremely various, the following are the principal: Pyrites Idiomorphos, which is spherical, and hemifpherical; in this laft form, it is generally found radiated and lamellated, oval, clustered, criftated: angular, confifting of four or fix fides; and this last cubical, or teffellated, oblong, rhomboidal, cellular or honey-combed: fiftular or piped: all of which are common to Cornwall. (Henckell's Pyritologia.)

It may be generally divided into three species, viz. Marcafita Argentea, Aurea, and Alba Ponderofior. It may be also classed under numerous fpecies of Pyritæ, fuch as the Gymnophyris, Pyritrichum, Pyritrichiphyllum, Pyricubium, Pyripolygonium, Pyroctogonium: but as all these names will only ferve to confound the bulk of our readers with technical difficulties, it is fufficient to say, that the forms and colours of this Mineral are innumerable.

We find it very plentiful in Lodes of Tin, Copper, and Lead; with which it is so intimately mixed, that it commonly impoverishes the value of each of its companions, notwithstanding every known method is used by fire, water, and various manuductions, to feparate and cleanse them from it. Though it is fo generally distributed in those Lodes, it does not incorporate with Copper Ore; but is disjunct, yet not entirely feparable. But from Tin, its union is fometimes infeparable by water; especially if the Tin is of a lax, fandy, pryany, or clayey texture. Its connection with Tin in the hard Stone, is often the fame, if the Stone is of a peachy nature, and where the molecule of both Minerals are equal. In either state it being fpecifically heavier, no lotions will ferve the purpose for difunion, but the most perfect ustion must be complied with to evaporate part of it, and reduce its ponderofity within the power of future ablutions to carry off: when we come to describe the method

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