De Re Metallica Part 31

[Ill.u.s.tration 269 (Cutting Metal): A--Ma.s.ses of metal. B--Hammer.

C--Chisel. D--Tree stumps. E--Iron tool similar to a pair of shears.]

The metal which is dug out in a pure or crude state, to which cla.s.s 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 ma.s.ses, 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.

[Ill.u.s.tration 270 (Spalling Ore): A--Tables. B--Upright planks.

C--Hammer. D--Quadrangular hammer. E--Deeper vessel. F--Shallower vessel. G--Iron rod.]

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 a.s.siduous in their labours.

[Ill.u.s.tration 271 (Spalling Ore): A--Pyrites. B--Leggings. C--Gloves.

D--Hammer.]

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.

[Ill.u.s.tration 272 (Spalling Ore): A--Area paved with stones. B--Broken ore. C--Area covered with broken ore. D--Iron tool. E--Its handle.

F--Broom. G--Short strake. H--Wooden hoe.]

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 thres.h.i.+ng 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 thres.h.i.+ng floor with the thres.h.i.+ng 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 was.h.i.+ng 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[3] 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 bis.m.u.th, 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_[4].

[Ill.u.s.tration 274 (Stall Roasting Ore): A--Area. B--Wood. C--Ore.

D--Cone-shaped piles. E--Ca.n.a.l.]

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 quant.i.ty 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_[5], 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[6]; 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.

[Ill.u.s.tration 275 (Heap Roasting Ore): A--Lighted pyre. B--Pyre which is being constructed. C--Ore. D--Wood. E--Pile of the same wood.]

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.

[Ill.u.s.tration 276 (Stall Roasting Ore): A--Burning pyre which is composed of lead ore with wood placed above it. B--Workman throwing ore into another area. C--Oven-shaped furnace. D--Openings through which the smoke escapes.]

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.

[Ill.u.s.tration 277 (Hearths for roasting): A--Iron plates full of holes.

B--Walls. C--Plate on which ore is placed. D--Burning charcoal placed on the ore. E--Pots. F--Furnace. G--Middle part of upper chamber. H--The other two compartments. I--Divisions of the lower chamber. K--Middle wall. L--Pots which are filled with ore. M--Lids of same pots.

N--Grating.]

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 acc.u.mulates 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_[7], 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.

[Ill.u.s.tration 278 (Heap Roasting): A--Heap of cupriferous stones.

B--Kindled heap. C--Stones being taken to the beds of f.a.ggots.]

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 f.a.ggots. At one time, they used to pile this kind of stone, when extracted from the pit, on bundles of f.a.ggots and roast it by firing the f.a.ggots; 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 f.a.ggot bundles near the heap, and carry the nearest stones to this bed; afterward they again place bundles of f.a.ggots 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 f.a.ggots. Finally they fire the f.a.ggots, 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 f.a.ggots before the stones are roasted and made soft; by this method the stones which are adjacent to the f.a.ggots 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.

[Ill.u.s.tration 284 (Stamp-mill): A--Mortar. B--Upright posts.

C--Cross-beams. D--Stamps. E--Their heads. F--Axle (cam-shaft). G--Tooth of the stamp (tappet). H--Teeth of axle (cams).]

Ore is crushed with iron-shod stamps, in order that the metal may be separated from the stone and the hangingwall rock.[8] 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 coa.r.s.e 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 s.p.a.ce 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.

[Ill.u.s.tration 285 (Stamps): A--Stamp. B--Stem cut out in lower part.

C--Shoe. D--The other shoe, barbed and grooved. E--Quadrangular iron band. F--Wedge. G--Tappet. H--Angular cam-shaft. I--Cams. K--Pair of compa.s.ses.]

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 pa.s.ses 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 compa.s.s 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.

[Ill.u.s.tration 286 (Stamp-mill): A--Box. Although the upper part is not open, it is shown open here, that the wheel may be seen. B--Wheel.

C--Cam-shaft. D--Stamps.]

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 pa.s.ses 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 circ.u.mstances 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.

[Ill.u.s.tration 287 (Handling stamped material): A--Box laid flat on the ground. B--Its bottom which is made of iron wire. C--Box inverted.

D--Iron rods. E--Box suspended from a beam, the inside being visible.

F--Box suspended from a beam, the outside being visible.]

Broken rock or stones, or the coa.r.s.e 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 pa.s.s; the pieces which are too large to pa.s.s through are removed by the workman, who again places them under stamps, while those which have pa.s.sed through, together with the coa.r.s.e and fine sand, he collects in a large vessel and keeps for the was.h.i.+ng. 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.

[Ill.u.s.tration 288 (Sifting Ore): A--Sieve. B--Small planks. C--Post.

D--Bottom of sieve. E--Open box. F--Small cross-beam. G--Upright posts.]

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 pa.s.sed through the sieve, and in this the post is fixed. With an iron shovel the workman throws into this sieve broken rock, small stones, coa.r.s.e 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 coa.r.s.e 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.

[Ill.u.s.tration 289 (Sifting Ore): A--Box. B--Bale. C--Rope. D--Beam.

E--Handles. F--Five-toothed rake. G--Sieve. H--Its handles. I--Pole.

K--Rope. L--Timber.]

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 wheelbarrow; these are held by two workmen, who shake the box to and fro. This box is the one princ.i.p.ally 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 pa.s.s 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 coa.r.s.e and the fine sand and earth, which have been thrown on to the dumps.

[Ill.u.s.tration 291 (Sifting Ore): A--Workman carrying broken rock in a barrow. B--First chute. C--First box. D--Its handles. E--Its bales.

F--Rope. G--Beam. H--Post. I--Second chute. K--Second box. L--Third chute. M--Third box. N--First table. O--First sieve. P--First tub.

Q--Second table. R--Second sieve. S--Second tub. T--Third table.

V--Third sieve. X--Third tub. Y--Plugs.]

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 coa.r.s.e 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 pa.s.sing 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 pa.s.sed 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.

[Ill.u.s.tration 292 (Sifting Ore): A--Sieve. B--Its handles. C--Tub.

D--Bottom of sieve made of iron wires. E--Hoop. F--Rods. G--Hoops.

H--Woman shaking the sieve. I--Boy supplying it with material which requires was.h.i.+ng. K--Man with shovel removing from the tub the material which has pa.s.sed through the sieve.]

If the ore is rich in metal, the earth, the fine and coa.r.s.e sand, and the pieces of rock which have been broken from the hangingwall, 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 pa.s.s 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 pa.s.ses 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, coa.r.s.e 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.

[Ill.u.s.tration 293 (Sifting Ore): A--Basket. B--Its handles. C--Dish.

D--Its back part. E--Its front part. F--Handles of same.]