whofe contents are lefs than half a ton hundred facks, it is fcarce worth the trouble of returning and dreffing it, except the Ore is rich in quality, and will bring a good price: much also depends in this cafe upon conveniencies, care, and expence more or less in carriage and water to dress it.

Halvans ftamped fmall, and then washed in a ftrêke with an eafy ftream of water, is termed Stampt Ore. But a finer fort is ftill to be had from the flime pit, which proceeds from the minute particles that glide away with the mud and water; this fort will not bear a brifk ftream, therefore it ftill retains much dirt and mud, whence it is called Slime Ore. The rough part of ftampt Ore fhould be tyed in a ftream of water, and the hinder part of the tye jigged through a fix or seven hole fieve. If it is much adulterated with Tin, Lead, or Mundick, it must be cleanfed by frequently tying or buddling of it. In order to clear the earthy fordes from the flime or loobs, it may ed, and after purified by the buddle, kieve, dilluer, &c. the fame as flime Tin, if it is worth the expence. It must also be noted, that Copper Ore requires a coarfer plate or grate in ftamping, than Tin does, because it is of a lighter nature and more fleaky.

be trunk

I have heard of a poor fandy Copper Ore fomewhere in Wales, of the appearance of verdigrease, which is so light, that the cupreous part of it will not bear even the leaft ftream of water: they drefs it by grinding, dry ftamping, or bucking; then put it into tubs or kieves, and tofs and pack it the fame as I have obferved of Tin: now the real Ore in it being without any fulphur, or much Metal, is fpecifically lighter than the wafte or fand; therefore the Ore fwims uppermost, and is skimmed off in the manner of Tin fkimpings. But I suppose thofe extreme light Ores are fo very poor, that none would be concerned with them, only in hopes of their improvement.

It is worth notice, that Copper Ore may be too curioully or too remiffly dreffed, fo that either way the adventurers may incur a lofs; the ground of which is fometimes not fo well confidered as it deferves. If too much time and coft are expended in dreffing the Ore, every one will grant it infers a lofs; but on the other hand, if too much foul Ore is left in it, that will also be to the prejudice of the concerned. Every ton of wafte Ore cofts as much to be fmelted as a ton of clean; at least, the buyer fubftracts as much for a ton of the one, as the other.

Suppofe

Suppose the buyer allows three pounds fterling for his charges of smelting and working a ton of Ore, and consequently the fame fum for each ton of wafte in the Ore, which in reality the fmelting costs the buyer or refiner; and therefore he must deduct fo much from the produce of the Ore ton. This is the cafe in Cornwall; but in other places, more diftant from the furnaces, in Ireland for inftance, the deduction must amount to more money, in proportion to the duty there on Ore, and alfo an overplus of freight, and if there be any other surplusage of coft, more than in Cornwall, as a longer carriage by land, and the like, all will operate to leffen the value of the Ore: but where fuch incidents are lefs than common, as a very fhort freight, or little charge in land carriage, then instead of a deduction, there is room to make a further advance of the price.

To illuftrate this cafe, fuppofe one hundred tons of Copper Ore, to be worth ten pounds ton, the amount of which will be one thousand pounds; fuppofe also it has so much earth or waste in it, that it may be reduced to fifty tons, with a moderate charge in dreffing, and with an inconfiderable loss of the Ore; then each ton will contain nearly the Copper which two tons did before: and whereas the buyer would have taken out fix pounds for the charges of carriage, freight, and smelting of two tons, he will now deduct but three pounds for those charges upon the fame Ore in one ton: fo that instead of deducting three hundred pounds on the one hundred tons of Ore, he will now deduct but one hundred and fifty pounds on fifty tons, whereby the adventurers will fave fo much of the other one hundred and fifty pounds, by how much the parcel of Ore will coft lefs for dreffing and taking out the wafte; for the fifty tons of Ore will now be worth twenty-three pounds ton, which will amount to eleven hundred and fifty pounds instead of one thoufand. Yet if the Ore be light or rich, there may be more of it loft, than the useless wafte carried off may compenfate.

Again, if one hundred tons of waste were mixed with the one hundred tons of Ore worth ten pounds ton, then the buyer would make an additional abatement of three hundred pounds more for his charges upon the one hundred tons of wafte; fo that the whole amount of the Ore, would be but feven hundred pounds, instead of one thousand pounds; for the Ore would be only worth three pounds ten fhillings ton; according to which, it is plain, that Ore may be too curiously or too careleffly dreffed. For Ore rich in nature, may be brought to

a great

a great rate, and produce a large profit to the adventurers; otherwise it may be fold to a great disadvantage, and without any gain, for want of being well handled: there are, however, feveral poor Ores, fo dry and barren by nature, that they are not capable of being fo well conditioned, as to bring a good price.

The conclufion I would draw from hence, is, that if a ton of waste can be taken out of the Ore, for less than the charge of smelting a ton (which I call three pounds here) and without any confiderable lofs of Ore, the adventurers fave money by dreffing it thus: but if the charges of taking out a ton of waste arife to more than three pounds, then they lofe as much as the excess of cost amounts to, together with the Ore washed away; hence, mediocrity fhould always be obferved.

The dreffers of Copper Ore often work for monthly wages, but then they do not always make the difpatch they ought; therefore they more commonly agree with the adventurers at a certain or fixed price for every ton of dressed Ore; but this makes it the dreffers intereft, to make the greatest number of tons that he can, fo that the adventurers may fuffer a lofs, for want of a true cleansing the Ore. To prevent this inconvenience, the best method is to set the Ore to dress in proportion to the price it brings ton; or in other words, to allow the dreffer fo much in the pound fterling, according to the price the Ore will bring; for this makes it his interest, as well as the adventurers, to make the Ore as merchantable as he poffibly can: however, he should be ftinted from throwing away too much Ore in the halvans, or be obliged to ftamp the halvans, and return their contents in Ore.

There can be no ftated rule given for fetting Ores to drefs at a price, because the Ore is incompact, or lefs, as well as poorer in value, in fome Mines, more than in others; but where Ore rifes with little wafte, it may be dressed at a much cheaper rate, especially if it be rich in quality. I have known Copper Ore in feveral Mines, where it might be fifted out at the Shaft fide, without any other trouble, to be dreffed for one penny in the pound fterling; on the other hand, five fhillings may not be a fufficient price for Ore that is hard and barren.

It may be worth enquiry, whether very fulphureous Ores which abound with Mundick, may not be advanced in value

by

by a previous uftion. It is evident from the foregoing observations, that if Ores be made confiderably lighter by being burnt and deprived of their fulphureous heavy wafte, with a small charge and no lofs of Metal, that then it must be an advantage to the owners, by putting the charges of fmelting the evaporated Mundick into their own pockets. Suppofing this should answer the end propofed, the most proper time of burning must be after the Ore is dreffed and fully cleanfed by water; for if it were done before, the Ore would acquire fo great a levity and tenderness that it muft unavoidably float away, in a great measure, with the water, though but a very small stream, and be inevitably lost and consumed: it would likewise be so much smoked and discoloured, that it might deceive the dresser in judging when it may be right clean. Nevertheless, if a parcel of Ore be dreffed clean and then burned, a great part of the Mundick must evaporate, and the Metal or Ore will remain in the pile; therefore, for every ton of Mundick, that would sublime from it, the parcel would be worth three pounds more on the entire quantity. For inftance; if one hundred tons of very pyritous Ore were decreased to eighty by this method, the adventurers would fave fixty pounds, from the diminution of its weight or lofs of Mundick; as well as gain, by its improved value, as much at least as would pay the charges of burning, which I presume would be small, for the Ore may be burned in furnaces fimilar to those commonly used for the calcination of limestone; or by kindling piles, consisting of strata of fuel and of Ore placed alternately upon one another, and by other pieces of useless timber, which should reach from top to bottom of the piles. Thefe being burnt out, and the Ore fettling steady, the vacancies of the burnt timber would ferve as flues or chimneys to carry off the vapours, and keep the fire from being extinguished too foon, especially if the fmall Ore was thrown on after the other Ore was well kindled and throughly burning.

Otherwise, a small arch or channel of loose bricks may be placed on the ground, where part of the round Ore may first be easily kindled by a fire of charcoal or wood; and as the fire increases, the place may be fed and fupplied with more Ore, till the whole pile be set on fire; for Ores that are very fulphureous, are so combustible, that they foon take fire, if well ordered, and will burn a long time, or till they are mostly deprived of their fuperfluous fulphur, when the fire extinguishes of itself, for want of a Pabulum or feeder. Fig. 11, plate VI, represents a quantity of Ore piled up to be burned: 1. two fides

or faces of the pile: all the fides of it are covered with small Ore: 2. the upper part of the pile where holes are feen, which ferve as flues both to help burn and evaporate the Mundick and fulphur 3. an opening to fet fire to the pile, and in which the fulphur may drop pure when melted: 4. a plank to keep off too much wind. Fig. 12, is a section of the above pile: 1. the wood to make the fire: 2. fome charcoal for kindling the fire: 3. a channel formed by a wooden tube or pipe to begin a draught of air 4. large lumps of Ore: 5. fmall Ore: 6,7. finer Ore, or duft of Ore.

When the Ore grows cold, it is fit for smelting, but must by no means be any more cleanfed in a ftream of water. By this management it will run much freer in the great furnaces for fuch a gentle deprivation of its stubborn brood of fulphur and arsenick ; and I am pretty clear will alfo yield more Metal, than when it is melted crude in the furnaces, where the fulphur and arsenick being excited by a violent fire, may elevate or carry off fome part of the Metal in their paffage. The worft inconvenience that seems to attend this matter, is, that it requires to be done near the Mine, to prevent the charge of removing the Ore; in which cafe, the fmoke being blown by the wind, would be offenfive to the workmen, without a due precaution to prevent it. To my aftonishment, neither this method nor any thing fimilar to it, takes in Cornwall, though it has been used with fuccefs in Germany, it feems even before the Ore is washed clean; and therefore it may much more reasonably be thought to turn to account, after the Ore is cleansed.

Indeed, the adventurers of Bullen-Garden Mine, fome few years paft, not only calcined their poor Copper Ore, but smelted it likewife into a regulus, and that at an expence which was very easy to be borne for the improvement of the Ore in its value but this attempt was of no long duration, the Copper Ore buyers very honeftly confirming the fufpicions of the adventurers, that they did not, neither would they offer at so high a standard for Copper Regule as they would for Copper Ore, because an encouragement of this kind, would neceffarily deprive the trade of fome part of the labour, which was very profitable to them. That argument, backed by a more powerful one, viz. not giving half value for Regule, obliged the adventurers to decline a very useful and profitable business and employ for this country. For my part, I think the gentlemen concerned, fhould have advanced their undertaking, in proportion to the backwardness