QUESTIONS of assaying were explained in the last Book, and I have now come to a greater task, that is, to the description of how we extract the metals. First of all I will explain the method of preparing the ore'; for since Nature usually creates metals in an impure state, mixed with earth, stones, and solidified juices, it is necessary to separate most of these impurities from the ores as far as can be, before they are smelted, and therefore I will now describe the methods by which the ores are sorted, broken with hammers, burnt, crushed with stamps, ground into powder, sifted, washed, roasted, and calcined.
I will start at the beginning with the first sort of work. Experienced miners, when they dig the ore, sort the metalliferous material from earth, stones, and solidified juices before it is taken from the shafts and tunnels, and they put the valuable metal in trays and the waste into buckets. But if some miner who is inexperienced in mining matters has omitted to do this, or even if some experienced miner, compelled by some unavoidable necessity, has been unable to do so, as soon as the material which has been dug out has been removed from the mine, all of it should be examined, and that part of the ore which is rich in metal sorted from that part of it which is devoid of metal, whether such part be earth, or solidified juices, or stones. To smelt waste together with an ore involves a loss, for some expenditure is thrown away, seeing that out of earth and stones only empty and useless slags are melted out, and further, the solidified juices also impede the smelting of the metals and cause loss. The rock which lies contiguous to rich ore should also be broken into small pieces, crushed, and washed, lest any of the mineral should be lost. When, either through ignorance or carelessness, the miners while excavating have mixed the ore with earth or broken rock, the work of sorting the crude metal or the best ore is done not only by men, but also by boys and women. They throw the mixed material upon a long table, beside which they sit for almost the whole day, and they sort out the ore; when it has been sorted out, they collect it in trays, and when collected they throw it into tubs, which' are carried to the works in which the ores are smelted.
The metal which. is dug out in a pure or crude state, to which class belong native silver, silver glance, and gray silver, is placed on a stone by the mine foreman and flattened out by pounding with heavy square hammers. These masses, when they have been thus flattened out like plates, are placed either on the stump of a tree, and cut into pieces by pounding an iron chisel into them with a hammer, or else they are cut with an iron tool similar to a pair of shears. One blade of these shears is three feet long, and is firmly fixed in a stump, and the other blade which cuts the metal is six feet long. These pieces of metal are afterward heated in iron basins and smelted in the cupellation furnace by the smelters.
Although the miners, in the shafts or tunnels, have sorted over the material which they mine, still the ore which has been broken down and carried out must be broken into pieces by a hammer or minutely crushed, so that the more valuable and better parts can be distinguished from the inferior and worthless portions. This is of the greatest importance in smelting ore, for if the ore is smelted without this separation, the valuable part frequently receives great damage before the worthless part melts in the fire, or else the one consumes the other; this latter difficulty can, however, be partly avoided by the exercise of care and partly by the use of fluxes. Now, if a vein is of poor quality, the better portions which have been broken down and carried out should be thrown together in one place, and the inferior portion and the rock thrown away. The sorters place a hard broad stone on a table; the tables are generally four feet square and made of joined planks, and to the edge of the sides and back are fixed upright planks, which rise about a foot from the table; the front, where the sorter sits, is left open. The lumps of ore, rich in gold or silver, are put by the sorters on the stone and broken up with a broad, but not thick, hammer; they either break them into pieces and throw them into one vessel, or they break and sort-whence they get their name-the more precious from the worthless, throwing and collecting them separately into different vessels. Other men crush the lumps of ore less rich in gold or silver, which have likewise been put on the stone, with a broad thick hammer, and when it has been well crushed, they collect it and throw it into one vessel. There are two kinds of vessels; one is deeper, and a little wider in the centre than at the top or bottom; the other is not so deep though it is broader at the bottom, and becomes gradually a little narrower toward the top. The latter vessel is covered with a lid, while the former is not covered; an iron rod through the handles, bent over on either end, is grasped in the hand when the vessel is carried. But, above all, it behooves the sorters to be assiduous in their labours.
By another method of breaking ore with hammers, large hard fragments of ore are broken before they are burned. The legs of the workmen -at all events of those who crush pyrites in this manner with large hammers in Goslar-are protected with coverings resembling leggings, and their hands are protected with long gloves, to prevent them from being injured by the chips which fly away from the fragments.
In that district of Greater Germany which is called Westphalia and in that district of Lower Germany which is named Eifel, the broken ore which has been burned, is thrown by the workmen into a round area paved with the hardest stones, and the fragments are pounded up with iron tools, which are very much like hammers in shape and are used like threshing sledges. This tool is a foot long, a palm wide, and a digit thick, and has an opening in the middle just as hammers have, in which is fixed a wooden handle of no great thickness, but up to three and a half feet long, in order that the workmen can pound the ore with greater force by reason of its weight falling from a greater height. They strike and pound with the broad side of the tool, in the same way as corn is pounded out on a threshing floor with the threshing sledges, although the latter are made of wood and are smooth and fixed to poles. When the ore has been broken into small pieces, they sweep it together with brooms and remove it to the works, where it is washed in a short strake, at the head of which stands the washer, who draws the water upward with a wooden hoe. The water running down again, carries all the light particles into a trough placed underneath. I shall deal more fully with this method of washing a little later.
Ore is burned for two reasons; either that from being hard, it may become soft and more easily broken and more readily crushed with a hammer or stamps, and then can be smelted; or that the fatty things, that is to say, sulphur, bitumen, orpiment, or realgar may be consumed. Sulphur is frequently found in metallic ores, and, generally speaking, is more harmful to the metals, except gold, than are the other things. It is most harmful of all to iron, and less to tin than to bismuth, lead, silver, or copper. Since very rarely gold is found in which there is not some silver, even gold ores containing sulphur ought to be roasted before they are smelted, because, in a very vigorous furnace fire, sulphur resolves metal into ashes and makes slag of it. Bitumen acts in the same way, in fact sometimes it consumes silver, which we may see in bituminous cadmia.
I now come to the methods of roasting, and first of all to that one which is common to all ores. The earth is dug out to the required extent, and thus is made a quadrangular area of fair size, open at the front, and above this, firewood is laid close together, and on it other wood is laid transversely, likewise close together, for which reason our countrymen call this pile of wood a crate; this is repeated until the pile attains a height of one or two cubits. Then there is placed upon it a quantity of ore that has been broken into small pieces with a hammer; first the largest of these pieces, next those of medium size, and lastly the smallest, and thus is built up a gently sloping cone. To prevent it from becoming scattered, fine sand of the same ore is soaked with water and smeared over it and beaten on with shovels; some workers, if they cannot obtain such fine sand, cover the pile with charcoal-dust, just as do charcoal-burners. But at Goslar, the pile, when it has been built up in the form of a cone, is smeared with atramentum sutorium rubrum, which is made by the leaching of roasted pyrites soaked with water. In some districts the ore is roasted once, in others twice, in others three times, as its hardness may require. At Goslar, when pyrites is roasted for the third time, that which is placed on the top of the pyre exudes a certain greenish, dry, rough, thin substance, as I have elsewhere written; this is no more easily burned by the fire than is asbestos. Very often also, water is put on to the ore which has been roasted, while it is still hot, in order to make it softer and more easily broken; for after fire has dried up the moisture in the ore, it breaks up more easily while it is still hot, of which fact burnt limestone affords the best example.
By digging out the earth they make the areas much larger, and square; walls should be built along the sides and back to hold the heat of the fire more effectively, and the front should be left open. In these compartments tin ore is roasted in the following manner. First of all wood about twelve feet long should be laid in the area in four layers, alternately straight and transverse. Then the larger pieces of ore should be laid upon them, and on these again the smaller ones, which should also be placed around the sides; the fine sand of the same ore should also be spread over the pile and pounded with shovels, to prevent the pile from falling before it has been roasted; the wood should then be fired.
Lead ore, if roasting is necessary, should be piled in an area just like the last, but sloping, and the wood should be placed over it. A tree trunk should be laid' right across the front of the ore to prevent it from falling out. The ore, being roasted in this way, becomes partly melted and resembles slag. Thuringian pyrites, in which there is gold, sulphur, and vitriol, after the last particle of vitriol has been obtained by heating it in water, is thrown into a furnace, in which logs are placed. This furnace is very similar to an oven in shape, in order that when the ore is roasted the valuable contents may not fly away with the smoke, but may adhere to the roof of the furnace. In this way sulphur very often hangs like icicles from the two openings of the roof through which the smoke escapes.
If pyrites or cadmia, or any other ore containing metal, possesses a good deal of sulphur or bitumen, it should be so roasted that neither is lost. For this purpose it is thrown on an iron plate full of holes, and roasted with charcoal placed on top; three walls support this plate, two on the sides and the third at the back. Beneath the plate are placed pots containing water, into which the sulphurous or bituminous vapour descends, and in the water the fat accumulates and floats on the top. If it is sulphur, it is generally of a yellow colour; if bitumen, it is black like pitch. If these were not drawn out they would do much harm to the metal, when the ore is being smelted. When they have thus been separated they prove of some service to man, especially the sulphurous kind. From the vapour which is carried down, not into the water, but into the ground, there is created a sulphurous or a bituminous substance resembling pompholyx, and so light that it can be blown away with a breath. Some employ a vaulted furnace, open at the front and divided into two chambers. A wall built in the middle of the furnace divides the lower chamber into two equal parts, in which are set pots containing water, as above described. The upper chamber is again divided into three parts, the middle one of which is always open, for in it the wood is placed, and it is not broader than the middle wall, of which it forms the topmost portion. The other two compartments have iron doors which are closed, and which, together with the roof, keep in the heat when the wood is lighted. In these upper compartments are iron bars which take the place of a floor, and on these are arranged pots without bottoms, having in place of a bottom, a grating made of iron wire, fixed to each, through the openings of which the sulphurous or bituminous vapours roasted from the ore run into the lower pots. Each of the upper pots holds a hundred pounds of ore; when they are filled they are covered with lids and smeared with lute.
In Eisleben and the neighbourhood, when they roast the schistose stone from which copper is smelted, and which is not free from bitumen, they do not use piles of logs, but bundles of faggots. At one time, they used to pile this kind of stone, when extracted from the pit, on bundles of faggots and roast it by firing the faggots; nowadays, they first of all carry these same stones to a heap, where they are left to lie for some time in such a way as to allow the air and rain to soften them. Then they make a bed of faggot bundles near the heap, and carry the nearest stones to this bed; afterward they again place bundles of faggots in the empty place from which the first stones have been removed, and pile over this extended bed, the stones which lay nearest to the first lot; and they do this right up to the end, until all the stones have been piled mound-shape on a bed of faggots. Finally they fire the faggots, not, however, on the side where the wind is blowing, but on the opposite side, lest the fire blown up by the force of the wind should consume the faggots before the stones are roasted and made soft; by this method the stones which are adjacent to the faggots take fire and communicate it to the next ones, and these again to the adjoining ones, and in this way the heap very often burns continuously for thirty days or more. This schist rock when rich in copper, as I have said elsewhere, exudes a substance of a nature similar to asbestos.
Ore is crushed with iron-shod stamps, in order that the metal may be separated from the stone and the hanging-wall rock. The machines which miners use for this purpose are of four kinds, and are made by the following method. A block of oak timber six feet long, two feet and a palm square, is laid on the ground. In the middle of this is fixed a mortar-box, two feet and six digits long, one foot and six digits deep; the front, which might be called a mouth, lies open; the bottom is covered with a plate of iron, a palm thick and two palms and as many digits wide, each end of which is wedged into the timber with broad wedges, and the front and back part of it are fixed to the timber with iron nails. To the sides of the mortar above the block are fixed two upright posts, whose upper ends are somewhat cut back and are mortised to the timbers of the building. Two and a half feet above the mortar are placed two cross-beams joined together, one in front and one in the back, the ends of which are mortised into the upright posts already mentioned. Through each mortise is bored a hole, into which is driven an iron clavis; one end of the clavis has two horns, and the other end is perforated in order that a wedge driven through, binds the beams more firmly; one horn of the clavis turns up and the other down. Three and a half feet above the cross-beams, two other cross-beams of the same kind are again joined in a similar manner; these cross-beams have square openings, in which the iron-shod stamps are inserted. The stamps are not far distant from each other, and fit closely in the cross-beams. Each stamp has a tappet at the back, which requires to be daubed with grease on the lower side that it can be raised more easily. For each stamp there are on a cam-shaft, two cams, rounded on the outer end, which alternately raise the stamp, in order that, by its dropping into the mortar, it may with its iron head pound and crush the rock which has been thrown under it. To the cam-shaft is fixed a water-wheel whose buckets are turned by water-power. Instead of doors, the mouth of the mortar has a board, which is fitted into notches cut out of the front of the block. This board can be raised, in order that when the mouth is open, the workmen can remove with a shovel the fine sand, and likewise the coarse sand and broken rock, into which the rocks have been crushed; this board can be lowered, so that the mouth thus being closed, the fresh rock thrown in may be crushed with the iron-shod stamps. If an oak block is not available, two timbers are placed on the ground and joined together with iron clamps, each of the timbers being six feet long, a foot wide, and a foot and a half thick. Such depth as should be allowed to the mortar, is obtained by cutting out the first beam to a width of three-quarters of a foot and to a length of two and a third and one twenty-fourth of a foot. In the bottom of the part thus dug out, there should be laid a very hard rock, a foot thick and three-quarters of a foot wide; about it, if any space remains, earth or sand should be filled in and pounded. On the front, this bed rock is covered with a plank; this rock when it has been broken, should be taken away and replaced by another. A smaller mortar having room for only three stamps may also be made in the same manner.
The stamp-stems are made of small square timbers nine feet long and half a foot wide each way. The iron head of each is made in the following way; the lower part of the head is three palms long and the upper part the same length. The lower part is a palm square in the middle for two palms, then below this, for a length of two digits it gradually spreads until it becomes five digits square; above the middle part, for a length of two digits, it again gradually swells out until it becomes a palm and a half square. Higher up, where the head of the shoe is enclosed in the stem, it is bored through and similarly the stem itself is pierced, and through the opening of each, there passes a broad iron wedge, which prevents the head falling off the stem. To prevent the stamp head from becoming broken by the constant striking of fragments of ore or rocks, there is placed around it a quadrangular iron band a digit thick, seven digits wide, and six digits deep. Those who use three stamps, as is common, make them much larger, and they are made square and three palms broad each way; then the iron shoe of each has a total length of two feet and a palm; at the lower end, it is hexagonal, and at that point it is seven digits wide and thick. The lower part of it which projects beyond the stem is one foot and two palms long; the upper part, which is enclosed in the stem, is three palms long; the lower part is a palm wide and thick; then gradually the upper part becomes narrower and thinner, so that at the top it is three digits and a half wide and two thick. It is bored through at the place where the angles have been somewhat cut away; the hole is three digits long and one wide, and is one digit's distance from the top. There are some who make that part of the head which is enclosed in the stem, barbed and grooved, in order that when the hooks have been fixed into the stem and wedges fitted to the grooves, it may remain tightly fixed, especially when it is also held with two quadrangular iron bands. Some divide the cam-shaft with a compass into six sides, others into nine; it is better for it to be divided into twelve sides, in order that successively one side may contain a cam and the next be without one.
The water-wheel is entirely enclosed under a quadrangular box, in case either the deep snows or ice in winter, or storms, may impede its running and its turning around. The joints in the planks are stopped all around with moss. The cover, however, has one opening, through which there passes a race bringing down water which, dropping on the buckets of the wheel, turns it round, and flows out again in the lower race under the box. The spokes of the water-wheel are not infrequently mortised into the middle of the cam-shaft; in this case the cams on both sides raise the stamps, which either both crush dry or wet ore, or else the one set crushes dry ore and the other set wet ore, just as circumstances require the one or the other; further, when the one set is raised and the iron clavises in them are fixed into openings in the first cross-beam, the other set alone crushes the ore.
Broken rock or stones, or the coarse or fine sand, are removed from the mortar of this machine and heaped up, as is also done with the same materials when raked out of the dump near the mine. They are thrown by a workman into a box, which is open on the top and the front, and is three feet long and nearly a foot and a half wide. Its sides are sloping and made of planks, but its bottom is made of iron wire netting, and fastened with wire to two iron rods, which are fixed to the two side planks. This bottom has openings, through which broken rock of the size of a hazel nut cannot pass; the pieces which are too large to pass through are removed by the workman, who again places them under stamps, while those which have passed through, together with the coarse and fine sand, he collects in a large vessel and keeps for the washing. When he is performing his laborious task he suspends the box from a beam by two ropes. This box may rightly be called a quadrangular sieve, as may also that kind which follows.
Some employ a sieve shaped like a wooden bucket, bound with two iron hoops; its bottom, like that of the box, is made of iron wire netting. They place this on two small cross-planks fixed upon a post set in the ground. Some do not fix the post in the ground, but stand it on the ground until there arises a heap of the material which has passed through the sieve, and in this the post is fixed. With an iron shovel the workman throws into this sieve broken rock, small stones, coarse and fine sand raked out of the dump; holding the handles of the sieve in his hands, he agitates it up and down in order that by this movement the dust, fine and coarse sand, small stones, and fine broken rock may fall through the bottom. Others do not use a sieve, but an open box, whose bottom is likewise covered with wire netting; this they fix on a small cross-beam fastened to two upright beams and tilt it backward and forward.
Some use a sieve made of copper, having square copper handles on both sides, and through these handles runs a pole, of which one end projects three-quarters of a foot beyond one handle; the workman then places that end in a rope which is suspended from a beam, and rapidly shakes the pole alternately backward and forward. By this movement the small particles fall through the bottom of the sieve. In order that the end of the pole. may be easily placed in the rope, a stick, two palms long, holds open the lower part of the rope as it hangs double, each end of the rope being tied to the beam; part of the rope, however, hangs beyond the stick to a length of half a foot. A large box is also used for this purpose, of which the bottom is either made of a plank full of holes or of iron netting, as are the other boxes. An iron bale is fastened from the middle of the planks which form its sides; to this bale is fastened a rope which is suspended from a wooden beam, in order that the box may be moved or tilted in any direction. There are two handles on each end, not unlike the handles of a wheel-barrow; these are held by two workmen, who shake the box to and fro. This box is the one principally used by the Germans who dwell in the Carpathian mountains. The smaller particles are separated from the larger ones by means of three boxes and two sieves, in order that those which pass through each, being of equal size, may be washed together; for the bottoms of both the boxes and sieves have openings which do not let through broken rock of the size of a hazel nut. As for the dry remnants in the bottoms of the sieves, if they contain any metal the miners put them under the stamps. The larger pieces of broken rock are not separated from the smaller by this method until the men and boys with five-toothed rakes, have separated them from the rock fragments, the little stones, the coarse and the fine sand and earth, which have been thrown on to the dumps.
At Neusohl, in the Carpathians, there are mines where the veins of copper lie in the ridges and peaks of the mountains, and in order to save expense being incurred by a long and difficult transport, along a rough and sometimes very precipitous road, one workman sorts over the dumps which have been thrown out from the mines, and another carries in a wheelbarrow the earth, fine and coarse sand, little stones, broken rock, and even the poorer ore, and overturns the barrow into a long open chute fixed to a steep rock. This chute is held apart by small cleats, and the material slides down a distance of about one hundred and fifty feet into a short box, whose bottom is made of a thick copper plate, full of holes. This box has two handles by which it is shaken to and fro, and at the top there are two bales made of hazel sticks, in which is fixed the iron hook of a rope hung from the branch of a tree or from a wooden beam which projects from an upright post. From time to time a sifter pulls this box and thrusts it violently against the tree or post, by which means the small particles passing through its holes descend down another chute into another short box, in whose bottom there are smaller holes. A second sifter, in like manner, thrusts this box violently against a tree or post, and a second time the smaller particles are received into a third chute, and slide down into a third box, whose bottom has still smaller holes. A third sifter, in like manner, thrusts this box violently against a tree or post, and for the third time the tiny particles fall through the holes upon a table. While the workman is bringing in the barrow, another load which has been sorted from the dump, each sifter withdraws the hooks from his bale and carries away his own box and overturns it, heaping up the broken rock or sand which remains in the bottom of it. As for the tiny particles which have slid down upon the table, the first washer-for there are as many washers as sifters-sweeps them off and in a tub nearly full of water, washes them through a sieve whose holes are smaller than the holes of the third box. When this tub has been filled with the material which has passed through the sieve, he draws out the plug to let the water run away; then he removes with a shovel that which has settled in the tub and throws it upon the table of a second washer, who washes it in a sieve with smaller holes. The sediment which has this time settled in his tub, he takes out and throws on the table of a third washer, who washes it in a sieve with the smallest holes. The copper concentrates which have settled in the last tub are taken out and smelted; the sediment which each washer has removed with a limp is washed on a canvas strake. The sifters at Altenberg, in the tin mines of the mountains bordering on Bohemia, use such boxes as I have described, hung from wooden beams. These, however, are a little larger and open in the front, through which opening the broken rock which has not gone through the sieve can be shaken out immediately by thrusting the sieve against its post.
If the ore is rich in metal, the earth, the fine and coarse sand, and the pieces of rock which have been broken from the hanging-wall, are dug out of the dump with a spade or rake and, with a shovel, are thrown into a large sieve or basket, and washed in a tub nearly full of water. The sieve is generally a cubit broad and half a foot deep; its bottom has holes of such size that the larger pieces of broken rock cannot pass through them, for this material rests upon the straight and cross iron wires, which at their points of contact are bound by small iron clips: The sieve is held together by an iron band and by two cross-rods likewise of iron; the rest of the sieve is made of staves in the shape of a little tub, and is bound with two iron hoops; some, however, bind it with hoops of hazel or oak, but in that case they use three of them. On each side it has handles, which are held in the hands by whoever washes the metalliferous material. Into this sieve a boy throws the material to be washed, and a woman shakes it up and down, turning it alternately to the right and to the left, and in this way passes through it the smaller pieces of earth, sand, and broken rock. The larger pieces remain in the sieve, and these are taken out, placed in a heap and put under the stamps. The mud, together with fine sand, coarse sand, and broken rock, which remain after the water has been drawn out of the tub, is removed by an iron shovel and washed in the sluice, about which I will speak a little later.
The Bohemians use a basket a foot and a half broad and half a foot deep, bound together by osiers. It has two handles by which it is grasped, when they move it about and shake it in the tub or in a small pool nearly full of water. All that passes through it into the tub or pool they take out and wash in a bowl, which is higher in the back part and lower and flat in the front; it is grasped by the two handles and shaken in the water, the lighter particles flowing away, and the heavier and mineral portion sinking to the bottom.
Gold ore, after being broken with hammers or crushed by the stamps, and even tin ore, is further milled to powder. The upper millstone, which is turned by water-power, is made in the following way. An axle is rounded to compass measure, or is made angular, and its iron pinions turn in iron sockets which are held in beams. The axle is turned by a water-wheel, the buckets of which are fixed to the rim and are struck by the force of a stream. Into the axle is mortised a toothed drum, whose teeth are fixed in the side of the rim. These teeth turn a second drum of rundles, which are made of very hard material. This drum surrounds an iron axle which has a pinion at the bottom and revolves in an iron cup in a timber. At the top of the iron axle is an iron tongue, dove-tailed into the millstone, and so when the teeth of the one drum turn the rundles of the other, the millstone is made to turn round. An overhanging machine supplies it with ore through a hopper, and the ore, being ground to powder, is discharged from a round wooden plate into a trough and flowing away through it accumulates on the floor; from there the ore is carried away and reserved for washing. Since this method of grinding requires the millstone to be now raised and now lowered, the timber in whose socket the iron of the pinion axle revolves, rests upon two beams, which can be raised and lowered.
There are three mills in use in milling gold ores, especially for quartz which is not lacking in metal. They are not all turned by water-power, but some by the strength of men, and two of them even by the power of beasts of burden. The first revolving one differs from the next only in its driving wheel, which is closed in and turned by men treading it, or by horses, which are placed inside, or by asses, or even by strong goats; the eyes of these beasts are covered by linen bands. The second mill, both when pushed and turned round, differs from the two above by having an upright axle in the place of the horizontal one; this axle has at its lower end a disc, which two workmen turn by treading back its cleats with their feet, though frequently one man sustains all the labour; or sometimes there projects from the axle a pole which is turned by a horse or an ass, for which reason it is called an asinaria. The toothed drum which is at the upper end of the axle turns the drum which is made of rundles, and together with it the millstone.
The third mill is turned round and round, and not pushed by hand; but between this and the others there is a great distinction, for the lower millstone is so shaped at the top that it can hold within it the upper millstone, which revolves around an iron axle; this axle is fastened in the centre of the lower stone and passes through the upper stone. A workman, by grasping in his hand an upright iron bar placed in the upper millstone, moves it round. The middle of the upper millstone is bored through, and the ore, being thrown into this opening, falls down upon the lower millstone and is there ground to powder, which gradually runs out through its opening; it is washed by various methods before it is mixed with quicksilver, which I will explain presently.
Some people build a machine which at one and the same time can crush, grind, cleanse, and wash the gold ore, and mix the gold with quicksilver. This machine has one water-wheel, which is turned by a stream striking its buckets; the main axle on one side of the water-wheel has long cams, which raise the stamps that crush the dry ore. Then the crushed ore is thrown into the hopper of the upper millstone, and gradually falling through the opening, is ground to powder. The lower millstone is square, but has a round depression in which the round, upper millstone turns, and it has an outlet from which the powder falls into the first tub. A vertical iron axle is dovetailed into a cross-piece, which is in turn fixed into the upper millstone; the upper pinion of this axle is held in a bearing fixed in a beam; the drum of the vertical axle is made of rundles, and is turned by the toothed drum on the main axle, and thus turns the millstone. The powder falls continually into the first tub, together with water, and from there runs into a second tub which is set lower down, and out of the second into a third, which is the lowest; from the third, it generally flows into a small trough hewn out of a tree trunk. Quicksilver is placed in each tub, across which is fixed a small plank, and through a hole in the middle of each plank there passes a small upright axle, which is enlarged above the plank to prevent it from dropping into the tub lower than it should. At the lower end of the axle three sets of paddles intersect, each made from two little boards fixed to the axle opposite each other. The upper end of this axle has a pinion held by a bearing set in a beam, and around each of these axles is a small drum made of rundles, each of which is turned by a small toothed drum on a horizontal axle, one end of which is mortised into the large horizontal axle, and the other end is held in a hollow covered with thick iron plates in a beam. Thus the paddles, of which there are three sets in each tub, turn round, and agitating the powder, thoroughly mix it with water and separate the minute particles of gold from it, and these are attracted by the quicksilver and purified. The water carries away the waste. The quicksilver is poured into a bag made of leather or cloth woven from cotton, and when this bag is squeezed, as I have described elsewhere, the quicksilver drips through it into a jar placed underneath. The pure gold remains in the bag. Some people substitute three broad sluices for the tubs, each of which has an angular axle on which are set six narrow spokes, and to them are fixed the same number of broad paddles; the water that is poured in strikes these paddles and turns them round, and they agitate the powder which is mixed with the water and separate the metal from it. If the powder which is being treated contains gold particles, the first method of washing is far superior, because the quicksilver in the tubs immediately attracts the gold; if it is powder in which are the small black stones from which tin is smelted, this latter method is not to be despised. It is very advantageous to place interlaced fir boughs in the sluices in which such tin-stuff is washed, after it has run through the launders from the mills, because the fine tin-stone is either held back by the twigs, or if the current carries them along they fall away from the water and settle down.
Seven methods of washing are in common use for the ores of many metals; for they are washed either in a simple buddle, or in a divided buddle, or in an ordinary strake, or in a large tank, or in a short strake, or in a canvas strake, or in a jigging sieve. Other methods of washing are either peculiar to some particular metal, or are combined with the method of crushing wet ore by stamps.
A simple buddle is made in the following way. In the first place, the head is higher than the rest of the buddle, and is three feet long and a foot and a half broad; this head is made of planks laid upon a timber and fastened, and on both sides, side-boards are set up so as to hold the water, which flows in through a pipe or trough, so that it shall fall straight down. The middle of the head is somewhat depressed in order that the broken rock and the larger metallic particles may settle into it. The buddle is sunk into the earth to a depth of three-quarters of a foot below the head, and is twelve feet long and a foot and a half wide and deep; the bottom and each side are lined with planks to prevent the earth, when it is softened by the water, from falling in or from absorbing the metallic particles. The lower end of the buddle is obstructed by a board, which is not as high as the sides. To this straight buddle there is joined a second transverse buddle, six feet long and a foot and a half wide and deep, similarly lined with planks; at the lower end it is closed up with a board, also lower than the sides of the buddle so that the water can flow away; this water falls into a launder and is carried outside the building. In this simple buddle is washed the metallic material which has passed on to the floor of the works through the five large sieves. When this has been gathered into a heap, the washer throws it into the head of the buddle, and water is poured upon it through the pipe or small trough, and the portion which sinks and settles in the middle of the head compartment he stirs with a wooden scrubber,-this is what we will henceforth call the implement made of a stick to which is fixed a piece of wood a foot long and a palm broad. The water is made turbid by this stirring, and carries the mud and sand and small particles of metal into the buddle below. Together with the broken rock, the larger metallic particles remain in the head compartment, and when these have been removed, boys throw them upon the platform of a washing tank or the short strake, and separate them from the broken rock. When the buddle is full of mud and sand, the washer closes the pipe through which the water flows into the head; very soon the water which remains in the buddle flows away, and when this has taken place, he removes with a shovel the mud and sand which are mixed with minute particles of metal, and washes them on a canvas strake. Sometimes before the buddles have been filled full, the boys throw the material into a bowl and carry it to the strakes and wash it.
Pulverized ore is washed in the head of this kind of a buddle; but usually when tin-stone is washed in it, interlacing fir boughs are put into the buddle, in the same manner as in the sluice when wet ore is crushed with stamps. The larger tin-stone particles, which sink in the upper part of the buddle, are washed separately in a strake; those particles which are of medium size, and settle in the middle part, are washed separately in the same way; and the mud mixed with minute particles of tin-stone, which has settled in the lowest part of the buddle below the fir boughs, is washed separately on the canvas strakes.
The divided buddle differs from the last one by having several cross-boards, which, being placed inside it, divide it off like steps; if the buddle is twelve feet long, four of them are placed within; if nine feet long, three. The nearer each one is to the head, the greater is its height; the further from the head, the lower it is; and so when the highest is a foot and a palm high, the second is usually a foot and three digits high, the third a foot and two digits, and the lowest a foot and one digit. In this buddle is generally washed that metalliferous material which has been sifted through the large sieve into the tub containing water. This material is continuously thrown with an iron shovel into the head of the buddle, and the water which has been let in is stirred up by a wooden scrubber, until the buddle is full, then the cross-boards are taken out by the washer, and the water is drained off; next the metalliferous material which has settled in the compartments is again washed, either on a short strake or on the canvas strakes or in the jigging sieves. Since a short strake is often united with the upper part of this buddle, a pipe in the first place carries the water into a cross launder, from which it flows down through one little launder into the buddle, and through another into the short strake.
An ordinary strake, so far as the planks are concerned, is not unlike the last two. The head of this, as of the others, is first made of earth stamped down, then covered with planks; and where it is necessary, earth is thrown in and beaten down a second time, so that no crevice may remain through which water carrying the particles of metal can escape. The water ought to fall straight down into the strake, which has a length of eight feet and a breadth of a foot and a half; it is connected with a transverse launder, which then extends to a settling pit outside the building. A boy with a shovel or a ladle takes the impure concentrates or impure tin-stone from a heap, and throws them into the head of the strake or spreads them over it. A washer with a wooden scrubber then agitates them in the strake, whereby the mud mixed with water flows away into the transverse launder, and the concentrates or the tin-stone settle on the strake. Since sometimes the concentrates or fine tin-stone flow down together with the mud into the transverse launder, a second washer closes it, after a distance of about six feet, with a cross-board and frequently stirs the mud with a shovel, in order that when mixed with water it may flow out into the settling-pit; and there remains in the launder only the concentrates or tin-stone. The tin-stuff of Schlackenwald and Erbisdroff is washed in this kind of a strake once or twice; those of Altenberg three or four times; those of Geyer often seven times; for in the ore at Schlackenwald and Erbisdorff the tin-stone particles are of a fair size, and are crushed with stamps; at Altenberg they are of much smaller size, and in the broken ore at Geyer only a few particles of tin-stone can be seen occasionally.
This method of washing was first devised by the miners who treated tin ore, whence it passed on from the works of the tin workers to those of the silver workers and others; this system is even more reliable than washing in jigging-sieves. Near this ordinary strake there is generally a canvas strake.
In modern times two ordinary strakes, similarly made, are generally joined together; the head of one is three feet distant from that of the other, while the bodies are four feet distant from each other, and there is only one cross launder under the two strakes. One boy shovels, from the heap into the head of each, the concentrates or tin-stone mixed with mud. There are two washers, one of whom sits at the right side of one strake, and the other at the left of the other strake, and each pursues his task, using the following sort of implement. Under each strake is a sill, from a socket in which a round pole rises, and is held by half an iron ring in a beam of the building, so that it may revolve; this pole is nine feet long and a palm thick. Penetrating the pole is a small round piece of wood, three palms long and as many digits thick, to which is affixed a small board two feet long and five digits wide, in an opening of which one end of a small axle revolves, and to this axle is fixed the handle of a little scrubber. The other end of this axle turns in an opening of a second board, which is likewise fixed to a small round piece of wood; this round piece, like the first one, is three palms long and as many digits thick, and is used by the washer as a handle. The little scrubber is made of a stick three feet long, to the end of which is fixed a small tablet of wood a foot long, six digits broad, and a digit and a half thick. The washer constantly moves the handle of this implement with one hand; in this way the little scrubber stirs the concentrates or the fine tin-stone mixed with mud in the head of the strake, and the mud, on being stirred, flows on to the strake. In the other hand he holds a second little scrubber, which has a handle of half the length, and with this he ceaselessly stirs the concentrates or tin-stone which have settled in the upper part of the strake; in this way the mud and water flow down into the transverse launder, and from it into the settling-pit which is outside the building.
Before the short strake and the jigging-sieve had been invented, metalliferous ores, especially tin, were crushed dry with stamps and washed in a large trough hollowed out of one or two tree trunks; and at the head of this trough was a platform, on which the ore was thrown after being completely crushed. The washer pulled it down into the trough with a wooden scrubber which had a long handle, and when the water had been let into the trough, he stirred the ore with the same scrubber.
The short strake is narrow in the upper part where the water flows down into it through the little launder; in fact it is only two feet wide; at the lower end it is wider, being three feet and as many palms. At the sides, which are six feet long, are fixed boards two palms high. In other respects the head resembles the head of the simple buddle, except that it is not depressed in the middle. Beneath is a cross launder closed by a low board. In this short strake not only is ore agitated and washed with a wooden scrubber, but boys also separate the concentrates from the broken rock in them and collect them in tubs. The short strake is now rarely employed by miners, owing to the carelessness of the boys, which has been frequently detected; for this reason, the jigging-sieve has taken its place. The mud which settles in the launder, if the ore is rich, is taken up and washed in a jigging-sieve or on a canvas strake.
A canvas strake is made in the following way. Two beams, eighteen feet long and half a foot broad and three palms thick, are placed on a slope; one half of each of these beams is partially cut away lengthwise, to allow the ends of planks to be fastened in them, for the bottom is covered by planks three feet long, set crosswise and laid close together. One half of each supporting beam is left intact and rises a palm above the planks, in order that the water that is running down may not escape at the sides, but shall flow straight down. The head of the strake is higher than the rest of the body, and slopes so as to enable the water to flow away. The whole strake is covered by six stretched pieces of canvas, smoothed with a stick. The first of them occupies the lowest division, and the second is so laid as to slightly overlap it; on the second division, the third is similarly laid, and so on, one on the other. If they are laid in the opposite way, the water flowing down carries the concentrates or particles of tin-stone under the canvas, and a useless task is attempted. Boys or men throw the concentrates or tin-stuff mixed with mud into the head of the strake, after the canvas has been thus stretched, and having opened the small launder they let the water flow in; then they stir the concentrates or tin-stone with a wooden scrubber till the water carries them all on to the canvas; next they gently sweep the linen with the wooden scrubber until the mud flows into the settling-pit or into the transverse launder. As soon as there is little or no mud on the canvas, but only concentrates or tin-stone, they carry the canvas away and wash it in a tub placed close by. The tin-stone settles in the tub, and the men return immediately to the same task. Finally, they pour the water out of the tub, and collect the concentrates or tin-stone. However, if either concentrates or tin-stone have washed down from the canvas and settled in the settling-pit or in the transverse launder, they wash the mud again.
Some neither remove the canvas nor wash it in the tubs, but place over it on each edge narrow strips, of no great thickness, and fix them to the beams with nails. They agitate the metalliferous material with wooden scrubbers and wash it in a similar way. As soon as little or no mud remains on the canvas, but only concentrates or fine tin-stone, they lift one beam so that the whole strake rests on the other, and dash it with water, which has been drawn with buckets out of the small tank, and in this way all the sediment which clings to the canvas falls into the trough placed underneath. This trough is hewn out of a tree and placed in a ditch dug in the ground; the interior of the trough is a foot wide at the top, but narrower in the bottom, because it is rounded out. In the middle of this trough they put a cross-board, in order that the fairly large particles of concentrates or fairly large-sized tin-stone may remain in the forepart into which they have fallen, and the fine concentrates or fine tin-stone in the lower part, for the water flows from one into the other, and at last flows down through an opening into the pit. As for the fairly large-sized concentrates or tin-stone which have been removed from the trough, they are washed again on the ordinary strake. The fine concentrates and fine tin-stone are washed again on this canvas strake. By this method, the canvas lasts longer because it remains fixed, and nearly double the work is done by one washer as quickly as can be done by two washers by the other method.
The jigging sieve has recently come into use by miners. The metalliferous material is thrown into it and sifted in a tub nearly full of water. The sieve is shaken up and down, and by this movement all the material below the size of a pea passes through into the tub, and the rest remains on the bottom of the sieve. This residue is of two kinds, the metallic particles, which occupy the lower place, and the particles of rock and earth, which take the higher place, because the heavy substance always settles, and the light is borne upward by the force of the water. This light material is taken away with a limp, which is a thin tablet of wood almost semicircular in shape, three-quarters of a foot long, and half a foot wide. Before the lighter portion is taken away the contents of the sieve are generally divided crosswise with a limp, to enable the water to penetrate into it more quickly. Afterward fresh material is again thrown into the sieve and shaken up and down, and when a great quantity of metallic particles have settled in the sieve, they are taken out and put into a tray close by. But since there fall into the tub with the mud, not only particles of gold or silver, but also of sand, pyrites, cadmia, galena, quartz, and other substances, and since the water cannot separate these from the metallic particles because they are all heavy, this muddy mixture is washed a second time, and the part which is useless is thrown away. To prevent the sieve passing this sand again too quickly, the washer lays small stones or gravel in the bottom of the sieve. However, if the sieve is not shaken straight up and down, but is tilted to one side, the small stones or broken ore move from one part to another, and the metallic material again falls into the tub, and the operation is frustrated. The miners of our country have made an even finer sieve, which does not fail even with unskilled washers; in washing- with this sieve they have no need for the bottom to be strewn with small stones. By this method the mud settles in the tub with the very fine metallic particles, and the larger sizes of metal remain in the sieve and are covered with the valueless sand, and this is taken away with a limp. The concentrates which have been collected are smelted together with other things. The mud mixed with the very fine metallic particles is washed for a third time and in the finest sieve, whose bottom is woven of hair. If the ore is rich in metal, all the material which has been removed by the limp is washed on the canvas strakes, or if the ore is poor it is thrown away.
I have explained the methods of washing which are used in common for the ores of many metals. I now come to another method of crushing ore, for I ought to speak of this before describing those methods of washing which are peculiar to ores of particular metals.
In the year 1512, George, the illustrious Duke of Saxony, gave the over-lordship of all the dumps ejected from the mines in Meissen to the noble and wise Sigismund Maltitz, father of John, Bishop of Meissen. Rejecting the dry stamps, the large sieve, and the stone mills of Dippoldswalde and Altenberg, in which places are dug the small black stones from which tin is smelted, he invented a machine which could crush the ore wet under iron-shod stamps. That is called " wet ore " which is softened by water which flows into the mortar box, and they are sometimes called "wet stamps" because they are drenched by the same water; and on the other hand, the other kinds are called "dry stamps" or "dry ore," because no water is used to soften the ore when the stamps are crushing. But to return to our subject. This machine is not dissimilar to the one which crushes the ore with dry iron-shod stamps, but the heads of the wet stamps are larger by half than the heads of the others. The mortar-box, which is made of oak or beech timber, is set up in the space between the upright posts; it does not open in front, but at one end, and it is three feet long, three-quarters of a foot wide, and one foot and six digits deep. If it has no bottom, it is set up in the same way over a slab of hard, smooth rock placed in the ground, which has been dug down a little. The joints are stopped up all round with moss or cloth rags. If the mortar has a bottom, then an iron sole-plate, three feet long, three-quarters of a foot wide, and a palm thick, is placed in it. In the opening in the end of the mortar there is fixed an iron plate full of holes, in such a way that there is a space of two digits between it and the shoe of the nearest stamp, and the same distance between this screen and the upright post, in an opening through which runs a small but fairly long launder. The crushed particles of silver ore flow through this launder with the water into a settling-pit, while the material which settles in the launder is removed with an iron shovel to the nearest planked floor; that material which has settled in the pit is removed with an iron shovel on to another floor. Most people make two launders, in order that while the workman empties one of them of the accumulation which has settled in it, a fresh deposit may be settling in the other. The water flows in through a small launder at the other end of the mortar that is near the water-wheel which turns the machine. The workman throws the ore to be crushed into the mortar in such a way that the pieces, when they are thrown in among the stamps, do not impede the work. By this method a silver or gold ore is crushed very fine by the stamps.
When tin ore is crushed by this kind of iron-shod stamps, as soon as crushing begins, the launder which extends from the screen discharges the water carrying the fine tin-stone and fine sand into a transverse trough, from which the water flows down through the spouts, which pierce the side of the trough, into the one or other of the large buddles set underneath. The reason why there are two is that, while the washer empties the one which is filled with fine tin-stone and sand, the material may flow into the other. Each buddle is twelve feet long, one cubit deep, and a foot and a half broad. The tin-stone which settles in the upper part of the buddles is called the large size; these are frequently stirred with a shovel, in order that the medium sized particles of tin-stone, and the mud mixed with the very fine particles of the stones may flow away. The particles of medium size generally settle in the middle part of the buddle, where they are arrested by interwoven fir twigs. The mud which flows down with the water settles between the twigs and the board which closes the lower end of the buddle. The tin-stone of large size is removed separately from the buddle with a shovel; those of medium size are also removed separately, and likewise the mud is removed separately, for they are separately washed on the canvas strakes and on the ordinary strake, and separately roasted and smelted. The tin-stone which has settled in the middle part of the buddle, is also always washed separately on the canvas strakes; but if the particles are nearly equal in size to those which have settled in the upper part of the buddle, they are washed with them in the ordinary strake and are roasted and smelted with them. However, the mud is never washed with the others, either on the canvas strakes or on the ordinary strake, but separately, and the fine tin-stone which is obtained from it is roasted and smelted separately. The two large buddles discharge into a cross trough, and it again empties through a launder into a settling-pit which is outside the building.
This method of washing has lately undergone a considerable change; for the launder which carries the water, mixed with the crushed tin-stone and fine sand which flow from the openings of the screen, does not reach to a transverse trough which is inside the same room, but runs straight through a partition into a small settling-pit. A boy draws a three-toothed rake through the material which has settled in the portion of the launder outside the room, by which means the larger sized particles of tin-stone settle at the bottom, and these the washer takes out with the wooden shovel and carries into the room; this material is thrown into an ordinary strake and swept with a wooden scrubber and washed. As for those tin-stone particles which the water carries off from the strake, after they have been brought back on to the strake, he washes them again until they are clean.
The remaining tin-stone, mixed with sand, flows into the small settling-pit which is within the building, and this discharges into two large buddles. The tin-stone of moderate size, mixed with those of fairly large size, settle in the upper part, and the small size in the lower part; but both are impure, and for this reason they are taken out separately and the former is washed twice, first in a buddle like the simple buddle, and afterward on an ordinary strake. Likewise the latter is washed twice, first on a canvas strake and afterward on an ordinary strake. This buddle, which is like the simple buddle, differs from it in the head, the whole of which in this case is sloping, while in the case of the other it is depressed in the centre. In order that the boy may be able to rest the shovel with which he cleanses the tin-stone, this sluice has a small wooden roller which turns in holes in two thick boards fixed to the sides of the buddle; if he did not do this, he would become over-exhausted by his task, for he spends whole days standing over these labours. The large buddle, the one like the simple buddle, the ordinary strake, and the canvas strakes, are erected within a special building. In this building there is a stove that gives out heat through the earthen tiles or iron plates of which it is composed, in order that the washers can pursue their labours even in winter, if the rivers are not completely frozen over.
On the canvas strakes are washed the very fine tin-stone mixed with mud which has settled in the lower end of the large buddle, as well as in the lower end of the simple buddle and of the ordinary strake. The canvas is cleaned in a trough hewn out of one tree trunk and partitioned off with two boards, so that three compartments are made. The first and second pieces of canvas are washed in the first compartment, the third and fourth in the second compartment, the fifth and sixth in the third compartment. Since among the very fine tin-stone there are usually some grains of stone, rock, or marble, the master cleanses them on the ordinary strake, lightly brushing the top of the material with a broom, the twigs of which do not all run the same way, but some straight and some crosswise. In this way the water carries off these impurities from the strake into the settling-pit because they are lighter, and leaves the tin-stone on the table because it is heavier.
Below all buddles or strakes, both inside and outside the building, there are placed either settling-pits or cross-troughs into which they discharge, in order that the water may carry on down into the stream but very few of the most minute particles of tin-stone. The large settling-pit which is outside the building is generally made of joined flooring, and is eight feet in length, breadth and depth. When a large quantity of mud, mixed with very fine tin-stone, has settled in it, first of all the water is let out by withdrawing a plug, then the mud which is taken out is washed outside the house on the canvas strakes, and afterward the concentrates are washed on the strake which is inside, the building. By these methods the very finest tin-stone is made clean.
The mud mixed with the very fine tin-stone, which has neither settled in the large settling-pit nor in the transverse launder which is outside the room and below the canvas strakes, flows away and settles in the bed of the stream or river. In order to recover even a portion of the fine tin-stone, many miners erect weirs in the bed of the stream or river, very much like those that are made above the mills, to deflect the current into the races through which it flows to the water-wheels. At one side of each weir there is an area dug out to a depth of five or six or seven feet, and if the nature of the place will permit, extending in every direction more than sixty feet. Thus, when the water of the river or stream in autumn and winter inundates the land, the gates of the weir are closed, by which means the current carries the mud mixed with fine tin-stone into the area. In spring and summer this mud is washed on the canvas strakes or on the ordinary strake, and even the finest black-tin is collected. Within a distance of four thousand fathoms along the bed of the stream or river below the buildings in which the tin-stuff is washed, the miners do not make such weirs, but put inclined fences in the meadows, and in front of each fence they dig a ditch of the same length, so that the mud mixed with the fine tin-stone, carried along by the stream or river when in flood, may settle in the ditch and cling to the fence. When this mud is collected, it is likewise washed on canvas strakes and on the ordinary strake, in order that the fine tin-stone may be separated from it. Indeed we may see many such areas and fences collecting mud of this kind in Meissen below Altenberg in the river Moglitz,-which is always of a reddish colour when the rock containing the black tin is being crushed under the stamps.
But to return to the stamping machines. Some usually set up four machines of this kind in one place, that is to say, two above and the same number below. By this plan it is necessary that the current which has been diverted should fall down from a greater height upon the upper water-wheels, because these turn axles whose cams raise heavier stamps. The stamp-stems of the upper machines should be nearly twice as long as the stems of the lower ones, because all the mortar-boxes are placed on the same level. These stamps have their tappets near their upper ends, not as in the case of the lower stamps, which are placed just above the bottom. The water flowing down from the two upper water-wheels is caught in two broad races, from which it falls on to the two lower water-wheels. Since all these machines have the stamps very close together, the stems should be somewhat cut away, to prevent the iron shoes from rubbing each other at the point where they are set into the stems. Where so many machines cannot be constructed, by reason of the narrowness of the valley, the mountain is excavated and levelled in two places, one of which is higher than the other, and in this case two machines are constructed and generally placed in one building. A broad race receives in the same way the water which flows down from the upper water-wheel, and similarly lets it fall on the lower water-wheel. The mortar-boxes are not then placed on one level, but each on the level which is appropriate to its own machine, and for this reason, two workmen are then required to throw ore into the mortar-boxes. When no stream can be diverted which will fall from a higher place upon the top of the water-wheel, one is diverted which will turn the foot of the wheel; a great quantity of water from the stream is collected in one pool capable of holding it, and from this place, when the gates are raised, the water is discharged against the wheel which turns in the race. The buckets of a water-wheel of this kind are deeper and bent back, projecting upward; those of the former are shallower and bent forward, inclining downward.
Further, in the Julian and Rhaetian Alps and in the Carpathian Mountains, gold or even silver ore is now put under stamps, which are sometimes placed more than twenty in a row, and crushed wet in a long mortar-box. The mortar has two plates full of holes through which the ore, after being crushed, flows out with the water into the transverse launder placed underneath, and from there it is carried down by two spouts into the heads of the canvas strakes. Each head is made of a thick broad plank, which can be raised and set upright, and to which on each side are fixed pieces projecting upward. In this plank there are many cup-like depressions equal in size and similar in shape, in each of which an egg could be placed. Right down in these depressions are small crevices which can retain the concentrates of gold or silver, and when the hollows are nearly filled with these materials, the plank is raised on one side so that the concentrates will fall into a large bowl. The cup-like depressions are washed out by dashing them with water. These concentrates are washed separately in different bowls from those which have settled on the canvas. This bowl is smooth and two digits wide and deep, being in shape very similar to a small boat; it is broad in the fore part, narrow in the back, and in the middle of it there is a cross groove, in which the particles of pure gold or silver settle, while the grains of sand, since they are lighter, flow out of it.
In some parts of Moravia, gold ore, which consists of quartz mixed with gold, is placed under the stamps and crushed wet. When crushed fine it flows out through a launder into a trough, is there stirred by a wooden scrubber, and the minute particles of gold which settle in the upper end of the trough are washed in a black bowl.
So far I have spoken of machines which crush wet ore with iron-shod stamps. I will now explain the methods of washing which are in a measure peculiar to the ore of certain metals, beginning with gold. The ore which contains particles of this metal, and the sand of streams and rivers which contains grains of it, are washed in frames or bowls; the sands especially are also washed in troughs. More than one method is employed for washing on frames, for these frames either pass or retain the particles or concentrates of gold; they pass them if they have holes, and retain them if they have no holes. But either the frame itself has holes, or a box is substituted for it; if the frame itself is perforated it passes the particles or concentrates of gold into a trough; if the box has them, it passes the gold material into the long sluice. I will first speak of these two methods of washing. The frame is made of two planks joined together, and is twelve feet long and three feet wide, and is full of holes large enough for a pea to pass. To prevent the ore or sand with which the gold is mixed from falling out at the sides, small projecting edge-boards are fixed to it. This frame is set upon two stools, the first of which is higher than the second, in order that the gravel and small stones can roll down it. The washer throws the ore or sand into the head of the frame, which is higher, and opening the small launder, lets the water into it, and then agitates it with a wooden scrubber. In this way, the gravel and small stones roll down the frame on to the ground, while the particles or concentrates of gold, together with the sand, pass through the holes into the trough which is placed under the frame, and after being collected are washed in the bowl.
A box which has a bottom made of a plate full of holes, is placed over the upper end of a sluice, which is fairly long but of moderate width. The gold material to be washed is thrown into this box, and a great quantity of water is let in. The lumps, if ore is being washed, are mashed with an iron shovel. The fine portions fall through the bottom of the box into the sluice, but the coarse pieces remain in the box, and these are removed with a scraper through an opening which is nearly in the middle of one side. Since a large amount of water is necessarily let into the box, in order to prevent it from sweeping away any particles of gold which have fallen into the sluice, the sluice is divided off by ten, or if it is as long again, by fifteen riffles. These riffles are placed equidistant from one another, and each is higher than the one next toward the lower end of the sluice. The little compartments which are thus made are filled with the material and the water which flows through the box; as soon as these compartments are full and the water has begun to flow over clear, the little launder through which this water enters into the box is closed, and the water is turned in another direction. Then the lowest riffle is removed from the sluice, and the sediment which has accumulated flows out with the water and is caught in a bowl. The riffles are removed one by one and the sediment from each is taken into a separate bowl, and each is separately washed and cleansed in a bowl. The larger particles of gold concentrates settle in the higher compartments, the smaller size, in the lower compartments. This bowl is shallow and smooth, and smeared with oil or some other slippery substance, so that the tiny particles of gold may not cling to it, and it is painted black, that the gold may be more easily discernible; on the exterior, on both sides and in the middle, it is slightly hollowed out in order that it may be grasped and held firmly in the hands when shaken. By this method the particles or concentrates of gold settle in the back part of the bowl; for if the back part of the bowl is tapped or shaken with one hand, as is usual, the contents move toward the fore part. In this way the Moravians, especially, wash gold ore.
The gold particles are also caught on frames which are either bare or covered. If bare, the particles are caught in pockets; if covered, they cling to the coverings. Pockets are made in various ways, either with iron wire or small cross-boards fixed to the frame, or by holes which are sunk into the sluice itself or into its head, but which do not quite go through. These holes are round or square, or are grooves running crosswise. The frames are either covered with skins, pieces of cloth, or turf, which I will deal with one by one in turn.
In order to prevent the sand which contains the particles of gold from spilling out, the washer fixes side-boards to the edges of a plank which is six feet long and one and a quarter wide. He then lays crosswise many iron wires a digit apart, and where they join he fixes them to the bottom plank with iron nails. Then he makes the head of the frame higher, and into this he throws the sand which needs washing, and taking in his hands the handles which are at the head of the frame, he draws it backward and forward several times in the river or stream. In this way the small stones and gravel flow down along the frame, and the sand mixed with particles of gold remains in the pockets between the strips. When the contents of the pockets have been shaken out and collected in one place, he washes them in a bowl and thus cleans the gold dust.
Other people, among whom are the Lusitanians, fix to the sides of a sluice, which is about six feet long and a foot and a half broad, many cross-strips or riffles, which project backward and are a digit apart. The washer or his wife lets the water into the head of the sluice, where he throws the sand which contains the particles of gold. As it flows down he agitates it with a wooden scrubber, which he moves transversely to the riffles. He constantly removes with a pointed wooden stick the sediment, which settles in the pockets between the riffles, and in this way the particles of gold settle in them, while the sand and other valueless materials are carried by the water into a tub placed below the sluice. He removes the particles of metal with a small wooden shovel into a wooden bowl. This bowl does not exceed a foot and a quarter in breadth, and by moving it up and down in the stream he cleanses the gold dust, for the remaining sand flows out of the dish, and the gold dust settles in the middle of it, where there is a cup-like depression. Some make use of a bowl which is grooved inside like a shell, but with a smooth lip where the water flows out. This smooth place, however, is narrower where the grooves run into it, and broader where the water flows out.
The cup-like pockets and grooves are cut or burned at the same time into the bottom of the sluice; the bottom is composed of three planks ten feet long, and is about four feet wide; but the lower end, through which the water is discharged, is narrower. This sluice, which likewise has side-boards fixed to its edges, is full of rounded pockets and of grooves which lead to them, there being two grooves to one pocket, in order that the water mixed with sand may flow into each pocket through the upper groove, and that after the sand has partly settled, the water may again flow out through the lower groove. The sluice is set in the river or stream or on the bank, and placed on two stools, of which the first is higher than the second in order that the gravel and small stones may roll down the sluice. The washer throws sand into the head with a shovel, and opening the launder, lets in the water, which carries the particles of metal with a little sand down into the pockets, while the gravel and small stones with the rest of the sand falls into a tub placed below the sluice. As soon as the pockets are filled, he brushes out the concentrates and washes them in a bowl. He washes again and again through this sluice.
Some people cut a number of cross-grooves, one palm distant from each other, in a sluice similarly composed of three planks eight feet long. The upper edge of these grooves is sloping, that the particles of gold may slip into them when the washer stirs the sand with a wooden shovel; but their lower edge is vertical so that the gold particles may thus be unable to slide out of them. As soon as these grooves are full of gold particles mixed with fine sand, the sluice is removed from the stools and raised up on its head. The head in this case is nothing but the upper end of the planks of which the sluice is composed. In this way the metallic particles, being turned over backward, fall into another tub, for the small stones and gravel have rolled down the sluice. Some people place large bowls under the sluice instead of tubs, and as in the other cases, the unclean concentrates are washed in the small bowl.
The Thuringians cut rounded pockets, a digit in diameter and depth, in the head of the sluice, and at the same time they cut grooves reaching from one to another. The sluice itself they cover with canvas. The sand which is to be washed, is thrown into the head and stirred with a wooden scrubber; in this way the water carries the light particles of gold on to the canvas, and the heavy ones sink in the pockets, and when these hollows are full, the head is removed and turned over a tub, and the concentrates are collected and washed in a bowl. Some people make use of a sluice which has square pockets with short vertical recesses which hold the particles of gold. Other workers use a sluice made of planks, which are rough by reason of the very small shavings which still cling to them; these sluices are used instead of those with coverings, of which this sluice is bare, and when the sand is washed, the particles of gold cling no less to these shavings than to canvas, or skins, or cloths, or turf. The washer sweeps the sluice upward with a broom, and when he has washed as much of the sand as he wishes, he lets a more abundant supply of water into the sluice again to wash out the concentrates, which he collects in a tub set below the sluice, and then washes again in a bowl. Just as Thuringians cover the sluice with canvas, so some people cover it with the skins of oxen or horses. They push the auriferous sand upward with a wooden scrubber, and by this system the light material flows away with the water, while the particles of gold settle among the hairs; the skins are afterward washed in a tub; and the concentrates are collected in a bowl.
The Colchians placed the skins of animals in the pools of springs; and since many particles of gold had clung to them when they were removed, the poets invented the " golden fleece " of the Colchians. In like manner, it can be contrived by the methods of miners that skins should take up, not only particles of gold, but also of silver and gems.
Many people cover the frame with a green cloth as long and wide as the frame itself, and fasten it with iron nails in such a way that they can easily draw them out and remove the cloth. When the cloth appears to be golden because of the particles which adhere to it, it is washed in a special tub and the particles are collected in a bowl. The remainder which has run down into the tub is again washed on the frame.
Some people, in place of a green cloth, use a cloth of tightly woven horsehair, which has a rough knotty surface. Since these knots stand out, and the cloth is rough, even the very small particles of gold adhere to it; these cloths are likewise washed in a tub with water.
Some people construct a frame not unlike the one covered with canvas, but shorter. In place of the canvas they set pieces of turf in rows. They wash the sand, which has been thrown into the head of the frame, by letting in water. In this way the particles of gold settle in the turf, the mud and sand, together with the water, are carried down into the settling-pit or trough below, which is opened when the work is finished. After all the water has passed out of the settling-pit, the sand and mud are carried away and washed over again in the same manner. The particles which have clung to the turf are afterward washed down into the settling-pit or trough by a stronger current of the water, which is let into the frame through a small launder. The concentrates are finally collected and washed in a bowl. Pliny was not ignorant of this method of washing gold. " The ulex," he says, " after being dried, is burnt, and its ashes are washed over a grassy turf, that the gold may settle on it."
Sand mixed with particles of gold is also washed in a tray, or in a trough or bowl. The tray is open at the further end, is either hewn out of a squared trunk of a tree or made out of a thick plank to which side-boards are fixed, and is three feet long, a foot and a half wide, and three digits deep. The bottom is hollowed out into the shape of an elongated bowl whose narrow end is turned toward the head, and it has two long handles, by which it is drawn backward and forward in the river. In this way the fine sand is washed, whether it contains particles of gold or the little black stones from which tin is made.
The Italians who come to the German mountains seeking gold, in order to wash the river sand which contains gold-dust and garnets, use a fairly long shallow trough hewn out of a tree, rounded within and without, open at one end and closed at the other, which they turn in the bed of the stream in such a way that the water does not dash into it, but flows in gently. They stir the sand, which they throw into it, with a wooden hoe, also rounded. To prevent the particles of gold or garnets from running out with the light sand, they close the end with a board similarly rounded, but lower than the sides of the trough. The concentrates of gold or garnets which, with a small quantity of heavy sand, have settled in the trough, they wash in a bowl and collect in bags and carry away with them.
Some people wash this kind of sand in a large bowl which can easily be shaken, the bowl being suspended by two ropes from a beam in a building. The sand is thrown into it, water is poured in, then the bowl is shaken, and the muddy water is poured out and clear water is again poured in, this being done again and again. In this way, the gold particles settle in the back part of the bowl because they are heavy, and the sand in the front part because it is light; the latter is thrown away, the former kept for smelting. The one who does the washing then returns immediately to his task. This method of washing is rarely used by miners, but frequently by coiners and goldsmiths when they wash gold, silver, or copper. The bowl they employ has only three handles, one of which they grasp in their hands when they shake the bowl, and in the other two is fastened a rope by which the bowl is hung from a beam, or from a cross-piece which is upheld by the forks of two upright posts fixed in the ground. Miners frequently wash ore in a small bowl to test it. This bowl, when shaken, is held in one hand and thumped with the other hand. In other respects this method of washing does not differ from the last.
I have spoken of the various methods of washing sand which contains grains of gold; I will now speak of the methods of washing the material in which are mixed the small black stones from which tin is made. Eight such methods are in use, and of these two have been invented lately. Such metalliferous material is usually found torn away from veins and stringers and scattered far and wide by the impetus of water, although sometimes venae dilatatae are composed of it. The miners dig out the latter material with a broad mattock, while they dig the former with a pick. But they dig out the little stones, which are not rare in this kind of ore, with an instrument like the bill of a duck. In districts which contain this material, if there is an abundant supply of water, and if there are valleys or gentle slopes and hollows, so that rivers can be diverted into them, the washers in summertime first of all dig a long ditch sloping so that the water will run through it rapidly. Into the ditch is thrown the metallic material, together with the surface material, which is six feet thick, more or less, and often contains moss, roots of plants, shrubs, trees, and earth; they are all thrown in with a broad mattock, and the water flows through the ditch. The sand and tin-stone, as they are heavy, sink to the bottom of the ditch, while the moss and roots, as they are light, are carried away by the water which flows through the ditch. The bottom of the ditch is obstructed with turf and stones in order to prevent the water from carrying away the tin-stone at the same time. The washers, whose feet are covered with high boots made of hide, though not of rawhide, themselves stand in the ditch and throw out of it the roots of the trees, shrubs, and grass with seven-pronged wooden forks, and push back the tin-stone toward the head of the ditch. After four weeks, in which they have devoted much work and labour, they raise the tin-stone in the following way; the sand with which it is mixed is repeatedly lifted from the ditch with an iron shovel and agitated hither and thither in the water, until the sand flows away and only the tin-stone remains on the shovel. The tin-stone is all collected together and washed again in a trough by pushing it up and turning it over with a wooden trowel, in order that the remaining sand may separate from it. Afterward they return to their task, which they continue until the metalliferous material is exhausted, or until the water can no longer be diverted into the ditches.
The trough which I mentioned is hewn out of the trunk of a tree and the interior is five feet long, three-quarters of a foot deep, and six digits wide. It is placed on an incline and under it is put a tub which contains interwoven fir twigs, or else another trough is put under it, the interior of which is three feet long and one foot wide and deep; the fine tin-stone, which has run out with the water, settles in the bottom. Some people, in place of a trough, put a square launder underneath, and in like manner they wash the tin-stone in this by agitating it up and down and turning it over with a small wooden trowel. A transverse trough is put under the launder, which is either open on one end and drains off into a tub or settling-pit, or else is closed and perforated through the bottom; in this case, it drains into a ditch beneath, where the water falls when the plug has been partly removed. The nature of this ditch I will now describe.
If the locality does not supply an abundance of water, the washers dig a ditch thirty or thirty-six feet long, and cover the bottom, the full length, with logs joined together and hewn on the side which lies flat on the ground. On each side of the ditch, and at its head also, they place four logs, one above the other, all hewn smooth on the inside. But since the logs are laid obliquely along the sides, the upper end of the ditch is made four feet wide and the tail end, two feet. The water has a high drop from a launder and first of all it falls into interlaced fir twigs, in order that it shall fall straight down for the most part in an unbroken stream and thus break up the lumps by its weight. Some do not place these twigs under the end of the launder, but put a plug in its mouth, which, since it does not entirely close the launder, nor altogether prevent the discharge from it, nor yet allow the water to spout far afield, makes it drop straight down. The workman brings in a wheelbarrow the material to be washed, and throws it into the ditch. The washer standing in the upper end of the ditch breaks the lumps with a seven-pronged fork, and throws out the roots of trees, shrubs, and grass with the same instrument, and thereby the small black stones settle down. When a large quantity of the tin-stone has accumulated, which generally happens when the washer has spent a day at this work, to prevent it from being washed away he places it upon the bank, and other material having been again thrown into the upper end of the ditch, he continues the task of washing. A boy stands at the lower end of the ditch, and with a thin pointed hoe stirs up the sediment which has settled at the lower end, to prevent the washed tin-stone from being carried further, which occurs when the sediment has accumulated to such an extent that the fir branches at the outlet of the ditch are covered.
The third method of washing materials of this kind follows. Two strakes are made, each of which is twelve feet long and a foot and a half wide and deep. A tank is set at their head, into which the water flows through a little launder. A boy throws the ore into one strake; if it is of poor quality he puts in a large amount of it, if it is rich he puts in less. The water is let in by removing the plug, the ore is stirred with a wooden shovel, and in this way the tin-stone, mixed with the heavier material, settles in the bottom of the strake, and the water carries the light material into the launder, through which it flows on to a canvas strake. The very fine tin-stone, carried by the water, settles on to the canvas and is cleansed. A low cross-board is placed in the strake near the head, in order that the largest sized tin-stone may settle there. As soon as the strake is filled with the material which has been washed, he closes the mouth of the tank and continues washing in the other strake, and then the plug is withdrawn and the water and tin-stone flow down into a tank below. Then he pounds the sides of the loaded strake with a wooden mallet, in order that the tin-stone clinging to the sides may fall off; all that has settled in it, he throws out with a wooden shovel which has a short handle. Silver slags which have been crushed under the stamps, also fragments of silver-lead alloy and of cakes melted from pyrites, are washed in a strake of this kind.
Material of this kind is also washed while wet, in a sieve whose bottom is made of woven iron wire, and this is the fourth method of washing. The sieve is immersed in the water which is contained in a tub, and is violently shaken. The bottom of this tub has an opening of such size that as much water, together with tailings from the sieve, can flow continuously out of it as water flows into it. The material which settles in the strake, a boy either digs over with a three-toothed iron rake or sweeps with a wooden scrubber; in this way the water carries off a great part of both sand and mud. The tin-stone or metalliferous concentrates settle in the strake and are afterward washed in another strake.
These are ancient methods of washing material which contains tin-stone; there follow two modem methods. If the tin-stone mixed with earth or sand is found on the slopes of mountains or hills, or in the level fields which are either devoid of streams or into which a stream cannot be diverted, miners have lately begun to employ the following method of washing, even in the winter months. An open box is constructed of planks, about six feet long, three feet wide, and two feet and one palm deep. At the upper end on the inside, an iron plate three feet long and wide is fixed, at a depth of one foot and a half from the top; this plate is very full of holes, through which tin-stone about the size of a pea can fall. A trough hewn from a tree is placed under the box, and this trough is about twenty-four feet long and three-quarters of a foot wide and deep; very often three cross-boards are placed in it, dividing it off into compartments, each one of which is lower than the next. The turbid waters discharge into a settling-pit.
The metalliferous material is sometimes found not very deep beneath the surface of the earth, but sometimes so deep that it is necessary to drive tunnels and sink shafts. It is transported to the washing-box in wheelbarrows, and when the washers are about to begin they lay a small launder, through which there flows on to the iron plate so much water as is necessary for this washing. Next, a boy throws the metalliferous material on to the iron plate with an iron shovel and breaks the small lumps, stirring them this way and that with the same implement. Then the water and sand penetrating the holes of the plate, fall into the box, while all the coarse gravel remains on the plate, and this he throws into a wheelbarrow with the same shovel. Meantime, a younger boy continually stirs the sand under the plate with a wooden scrubber nearly as wide as the box, and drives it to the upper end of the box; the lighter material, as well as a small amount of tin-stone, is carried by the water down into the underlying trough. The boys carry on this labour without intermission until they have filled four wheelbarrows with the coarse and worthless residues, which they carry off and throw away, or three wheelbarrows if the material is rich in black tin. Then the foreman has the plank removed which was in front of the iron plate, and on which the boy stood. The sand, mixed with the tin-stone, is frequently pushed backward and forward with a scrubber, and the same sand, because it is lighter, takes the upper place, and is removed as soon as it appears; that which takes the lower place is turned over with a spade, in order that any that is light can flow away; when all the tin-stone is heaped together, he shovels it out of the box and carries it away. While the foreman does this, one boy with an iron hoe stirs the sand mixed with fine tin-stone, which has run out of the box and has settled in the trough and pushes it back to the uppermost part of the trough, and this material, since it contains a very great amount of tin-stone, is thrown on to the plate and washed again. The material which has settled in the lowest part of the trough is taken out separately and piled in a heap, and is washed on the ordinary strake; that which has settled in the pool is washed on the canvas strake. In the summer-time this fruitful labour is repeated more often, in fact ten or eleven times. The tin-stone which the foreman removes from the box, is afterward washed in a jigging sieve, and lastly in a tub, where at length all the sand is separated out. Finally, any material in which are mixed particles of other metals, can be washed by all these methods, whether it has been disintegrated from veins or stringers, or whether it originated from venae dilatatae, or from streams and rivers.
The sixth method of washing material of this kind is even more modern and more useful than the last. Two boxes are constructed, into each of which water flows through spouts from a cross trough into which it has been discharged through a pipe or launder. When the material has been agitated and broken up with iron shovels by two boys, part of it runs down and falls through the iron plates full of holes, or through the iron grating, and flows out of the box over a sloping surface into another cross trough, and from this into a strake seven feet long and two and a half feet wide. Then the foreman again stirs it with a wooden scrubber that it may become clean. As for the material which has flowed down with the water and settled in the third cross trough, or in the launder which leads from it, a third boy rakes it with a two-toothed rake; in this way the fine tin-stone settles down and the water carries off the valueless sand into the creek. This method of washing is most advantageous, for four men can do the work of washing in two boxes, while the last method, if doubled, requires six men, for it requires two boys to throw the material to be washed on to the plate and to stir it, with iron shovels; two more are required with wooden scrubbers to keep stirring the sand, mixed with the tin-stone, under the plate, and to push it toward the upper end of the box; further, two foremen are required to clean the tin-stone in the way I have described. In the place of a plate full of holes, they now fix in the boxes a grating made of iron wire as thick as the stalks of rye; that these may not be depressed by the weight and become bent, three iron bars support them, being laid crosswise underneath. To prevent the grating from being broken by the iron shovels with which the material is stirred in washing, five or six iron rods are placed on top in cross lines, and are fixed to the box so that the shovels may rub them instead of the grating; for this reason the grating lasts longer than the plates, because it remains intact, while the rods, when worn by rubbing, can easily be replaced by others.
Miners use the seventh method of washing when there is no stream of water in the part of the mountain which contains the black tin, or particles of gold, or of other metals. In this case they frequently dig more than fifty ditches on the slope below, or make the same number of pits, six feet long, three feet wide, and three-quarters of a foot deep, not any great distance from each other. At the season when a torrent rises from storms of great violence or long duration, and rushes down the mountain, some of the miners dig the metalliferous material in the woods with broad hoes and drag it to the torrent. Other miners divert the torrent into the ditches or pits, and others throw the roots of trees, shrubs, and grass out of the ditches or pits with seven-pronged wooden forks. When the torrent has run down, they remove with shovels the uncleansed tin-stone or particles of metal which have settled in the ditches or pits, and cleanse it.
The eighth method is also employed in the regions which the Lusitanians hold in their power and sway, and is not dissimilar to the last. They drive a great number of deep ditches in rows in the gullies, slopes, and hollows of the mountains. Into these ditches the water, whether flowing down from snow melted by the heat of the sun or from rain, collects and carries together with earth and sand, sometimes tin-stone, or, in the case of the Lusitanians, the particles of gold loosened from veins and stringers. As soon as the waters of the torrent have all run away, the miners throw the material out of the ditches with iron shovels, and wash it in a common sluice box.
The Poles wash the impure lead from venae dilatatae in a trough ten feet long, three feet wide, and one and one-quarter feet deep. It is mixed with moist earth and is covered by a wet and sandy clay, and so first of all the clay, and afterward the ore, is dug out. The ore is carried to a stream or river, and thrown into a trough into which water is admitted by a little launder, and the washer standing at the lower end of the trough drags the ore out with a narrow and nearly pointed hoe, whose wooden handle is nearly ten feet long. It is washed over again once or twice in the same way and thus made pure. Afterward when it has been dried in the sun they throw it into a copper sieve, and separate the very small pieces which pass through the sieve from the larger ones; of these the former are smelted in a faggot pile and the latter in the furnace. Of such a number then are the methods of washing.
One method of burning is principally employed, and two of roasting. The black tin is burned by a hot fire in a furnace similar to an oven"; it is burned if it is a dark-blue colour, or if pyrites and the stone from which iron is made are mixed with it, for the dark blue colour if not burnt, consumes the tin. If pyrites and the other stone are not volatilised into fumes in a furnace of this kind, the tin which is made from the tin-stone is impure. The tin-stone is thrown either into the back part of the furnace, or into one side of it; but in the former case the wood is placed in front, in the latter case alongside, in such a manner, however, that neither firebrands nor coals may fall upon the tin-stone itself or touch it. The fuel is manipulated by a poker made of wood. The tin-stone is now stirred with a rake with two teeth, and now again levelled down with a hoe, both of which are made of iron. The very fine tin-stone requires to be burned less than that of moderate size, and this again less than that of the largest size. While the tin-stone is being thus burned, it frequently happens that some of the material runs together. The burned tin-stone should then be washed again on the strake, for in this way the material which has been run together is carried away by the water into the cross-trough, where it is gathered up and worked over, and again washed on the strake. By this method the metal is separated from that which is devoid of metal.
Cakes from pyrites, or cadmia; or cupriferous stones, are roasted in quadrangular pits, of which the front and top are open, and these pits are generally twelve feet long, eight feet wide, and three feet deep. The cakes of melted pyrites are usually roasted twice over, and those of cadmia once. These latter are first rolled in mud moistened with vinegar, to prevent the fire from consuming too much of the copper with the bitumen, or sulphur, or orpiment, or realgar. The cakes of pyrites are first roasted in a slow fire and afterward in a fierce one, and in both cases, during the whole following night, water is let in, in order that, if there is in the cakes any alum or vitriol or saltpetre capable of injuring the metals, although it rarely does injure them, the water may remove it and make the cakes soft. The solidified juices are nearly all harmful to the metal, when cakes or ore of this kind are smelted. The cakes which are to be roasted are placed on wood piled up in the form of a crate, and this pile is fired.
The cakes which are made of copper smelted from schist are first thrown upon the ground and broken, and then placed in the furnace on bundles of faggots, and these are lighted. These cakes are generally roasted seven times and occasionally nine times. While this is being done, if they are bituminous, then the bitumen burns and can be smelled. These furnaces have a structure like the structure of the furnaces in which ore is smelted, except that they are open in front; they are six feet high and four feet wide. As for this kind of furnace, three of them are required for one of those in which the cakes are melted. First of all they are roasted in the first furnace, then when they are cooled, they are transferred into the second furnace and again roasted; later they are carried to the third, and afterward back to the first, and this order is preserved until they have been roasted seven or nine times.
END OF BOOK VIII.