The one from which silver is extracted in its nature, consistency, and coleut. The moun tain of Potosi consists chiefly of a yellow, very firm argiiiieNus gate, full of veins of ferruginous quarts, in which silver ore, and sometimes brittle vitreous ore, are found interspersed. There is also a greyish brown one, in which appear some small grains, and thin branches or veins of silver, running along the lay ers of stone. This ore is extremely rich, yielding for each caxon, or 50 hundred weight, 20 mares of silver or about 13 lbs. Some of the ores which are found in other provinces of this viceroyalty appear black, frequently from the admixture of lead. The silver is seen when the ore is scratched. These ores are called negrillos, from their colour, and are esteemed very rich, yielding 50 or 60 mares of silver per caxon. They are more valued also on another count, namely, that the silver is extracted from them at a small charge. In place of the usual process of amalgamation with quicksilver, they are merely melt. ed in furnaces, where the lead, being evaporated by. the fire, the silver is left pure and clean. There is another sort of rich ore, containing a large proper. tion of the finest silver, which turns red if it is wet ed and rubbed against iron. Some of the ores glit •er like talc. These yield but little silver ; but, be ing soft, the metal is easily extracted from them. Some mefrom the admixture of copper, which it is f=troublesome to separate from the silver. But the most scarce sad valuable ore is that Leh appears in entangled threads of pure silver, so Sae that it is called arena, from its resemblance to a spidler's web.
The veles of silver frequently run through hard rooks, width have to be reduced to a very fine powder before the are can be fit for the process of amalga. maths. In order to render the ore more friable, it is frequently roasted or calcined in an oven. It is afterwards broke to pieces with iron mallets, after which it Is carried to the mills, where, being ground to a very fine powder, it is passed through several wire sieves successively, the last being the finest. The rude ores are also frequently broke to pieces by hammers lifted up and down by means of a wheel. These harassers weigh about 200 pounds, and fbhl with sufficient violence to reduce the hardest stones to powder. This powder is laid in wooden troughs, and is kneaded with quicksilver and water, until the two metals are completely amalgamated, after which the quicksilver is evaporated by distillation, and the metal which remains is cast into ingots.
In some of the smaller rivers, mills with grind stones are used. The ore is ground with water, which makes a liqukl mud, that runs into a receiver. The mud is disposed en the floor in square parcels about a foot thick, tuch of them containing es hun dred weight of ore. On each of these about Mt weight of sea-salt is thrown, which is moulded aml incorporated with the *nth fbr tiro er three days. After this the quantity of quicksilver which they judge necessary is added to the mites, which is inotdded eight times a day, red lime is frequently nand with it, to accelerate the process of smote =diem In the elevated aid odd raglan of Patti and operation requires a lamb or sir weeke before it is completed. Hut, in warmer di.
tricts, it is finished in eight or ten days.
The manner is which these and'all the other ape rations are performed, by which the precious awns are extracted from the earth, and afterwavds separated from their ores, is cemared, in the most unquathei terms, by Helms. After pointing oot the ignorant which prevailed in the previous nimagesent of she mines, "still greeter, if poseible (he observes), castle ignorance of the Directors of smelting-houses and fining works at Potosi. By their method amide motion they were scarcely able to gain two-thirds of the silver contained in the rude one ; and fee every mare of pure silver gained, they destroyed me, awl frequently two mares ofver. Indeed, all the operations at the mines of Pot quicksil osi, the souping, el• ing, washing, quickening, and Nesting the ere, toe cowducted in so slovenly, wasted, and easciestifie a manner, that, to oompare the eseellent method of amalgamation invented by Baron Bern, and prso Used in Europe, with the barbarous process toed by these Indians and Spaniards, wealth be en beak I. the understanding of my rations." " The tools of the Indian miser (he manses) at very badly contrived and unwieldy. The timer, which is a square piece anted of 20 psundt Night, exhausts his strength,..the hen, a foot sad a lelf loss, is a great deal too iecommodieus, snide sent %arrow places, cannot be made use of The diet tallow candles, wound round with ereol, vitiate the ale The some mismanagement ptentiled in the Boyd Mint, where every hundred weight of refined copper used fordloy in the gold and silver min eon the King L.35 through die ignoranc• or the oven*, who spent a whole month in roasting and cideinisg it, and in the come of these tedious operation fre qopostly made it unit far the purpose to whieb item intended. Mr Heins was entered by the Governor to introduce a more improved process fbr the ren• ing of the copper, and be accordingly showed, by actual experiment, that copper could be brought to a greater degree of freeness in her hours and a half, and at less than of the expence. The ether evils in the management of the mines, he also at tempted to reform, in conjunction wish another per son of sidli in the inning art, who accompanied his to South America for the mos purpose. In order to free the nines from water, two Izzadaits were dug in the mountains; proper were erected ; smolgamation works were set oe foot, sad the neceesery instructions in metallurgy were given to six pupils, for the purpose of enabling theta to reduee this improved systemto practice. If *seater is die pits can be drained, the mines of Potosi mold be is as frourithing a condition as ever. The Mal sent af timber, however, on the naked ridge assemblies In whit* those mines are situated, sends greedy te lead the regress of the work.