De Re Metallica Part 32

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 pa.s.ses 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.

[Ill.u.s.tration 294 (Mills for Grinding Ore): A--Axle. B--Water-wheel.

C--Toothed drum. D--Drum made of rundles. E--Iron axle. F--Millstone.

G--Hopper. H--Round wooden plate. I--Trough.]

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 compa.s.s 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 acc.u.mulates on the floor; from there the ore is carried away and reserved for was.h.i.+ng. 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.

[Ill.u.s.tration 296 (Mills for Grinding Ore): A--First mill. B--Wheel turned by goats. C--Second mill. D--Disc of upright axle. E--Its toothed drum. F--Third mill. G--Shape of lower millstone. H--Small upright axle of the same. I--Its opening. K--Lever of the upper millstone. L--Its opening.]

There are three mills in use in milling gold ores, especially for quartz[11] 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 a.s.ses, 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 a.s.s, 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 pa.s.ses 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.

[Ill.u.s.tration 299 (Stamp-mill): A--Water-wheel. B--Axle. C--Stamp.

D--Hopper in the upper millstone. E--Opening pa.s.sing through the centre.

F--Lower millstone. G--Its round depression. H--Its outlet. I--Iron axle. K--Its crosspiece. L--Beam. M--Drum of rundles on the iron axle.

N--Toothed drum of main axle. O--Tubs. P--The small planks. Q--Small upright axles. R--Enlarged part of one. S--Their paddles. T--Their drums which are made of rundles. V--Small horizontal axle set into the end of the main axle. X--Its toothed drums. Y--Three sluices. Z--Their small axles. AA--Spokes. BB--Paddles.]

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 dove-tailed 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[12] is placed in each tub, across which is fixed a small plank, and through a hole in the middle of each plank there pa.s.ses 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[13] remains in the bag. Some people subst.i.tute 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 was.h.i.+ng 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 was.h.i.+ng 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 was.h.i.+ng are either peculiar to some particular metal, or are combined with the method of crus.h.i.+ng wet ore by stamps.

[Ill.u.s.tration 301 (Buddles): A--Head of buddle. B--Pipe. C--Buddle.

D--Board. E--Transverse buddle. F--Shovel. G--Scrubber.]

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 pa.s.sed 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 was.h.i.+ng 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.

[Ill.u.s.tration 302 (Buddles): A--Pipe. B--Cross launder. C--Small troughs. D--Head of the buddle. E--Wooden scrubber. F--Dividing boards.

G--Short strake.]

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.

[Ill.u.s.tration 303 (Was.h.i.+ng material): A--Head. B--Strake. C--Trowel.

D--Scrubber. E--Canvas. F--Rod by which the canvas is made smooth.]

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 Erbisdorff 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 was.h.i.+ng was first devised by the miners who treated tin ore, whence it pa.s.sed on from the works of the tin workers to those of the silver workers and others; this system is even more reliable than was.h.i.+ng in jigging-sieves. Near this ordinary strake there is generally a canvas strake.

[Ill.u.s.tration 305 (Was.h.i.+ng material): A--Upper cross launder. B--Small launders. C--Heads of strakes. D--Strakes. E--Lower transverse launder.

F--Settling pit. G--Socket in the sill. H--Halved iron rings fixed to beam. I--Pole. K--Its little scrubber. L--Second small scrubber.]

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.

[Ill.u.s.tration 306 (Was.h.i.+ng material): A--Trough. B--Platform. C--Wooden scrubber.]

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.

[Ill.u.s.tration 307 (Was.h.i.+ng material): A--Short strake. B--Small launder.

C--Transverse launder. D--Wooden 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.

[Ill.u.s.tration 308 (Was.h.i.+ng material): A--Beams. B--Canvas. C--Head of strake. D--Small launder. E--Settling pit or tank. F--Wooden scrubber.

G--Tubs.]

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.

[Ill.u.s.tration 309 (Collecting concentrates): A--Canvas strake. B--Man das.h.i.+ng water on the canvas. C--Bucket. D--Bucket of another kind.

E--Man removing concentrates or tin-stone from the trough.]

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.

[Ill.u.s.tration 311 (Jigging Sieve): A--Fine sieves. B--Limp. C--Finer sieve. D--Finest sieve.]

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 pa.s.ses 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 quant.i.ty 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 pa.s.sing 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 was.h.i.+ng 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 was.h.i.+ng which are used in common for the ores of many metals. I now come to another method of crus.h.i.+ng ore, for I ought to speak of this before describing those methods of was.h.i.+ng which are peculiar to ores of particular metals.

[Ill.u.s.tration 313 (Stamp-mill): A--Mortar. B--Open end of mortar.

C--Slab of rock. D--Iron sole plates. E--Screen. F--Launder. G--Wooden shovel. H--Settling pit. I--Iron shovel. K--Heap of material which has settled. L--Ore which requires crus.h.i.+ng. M--Small launder.]

In the year 1512, George, the ill.u.s.trious Duke of Saxony[14], gave the overlords.h.i.+p of all the dumps ejected from the mines in Meissen to the n.o.ble and wise Sigismund Malt.i.tz, 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 crus.h.i.+ng. 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 s.p.a.ce 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 s.p.a.ce 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 acc.u.mulation 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.

[Ill.u.s.tration 314 (Buddle): A--Launder reaching to the screen.

B--Transverse trough. C--Spouts. D--Large buddles. E--Shovel.

F--Interwoven twigs. G--Boards closing the buddles. H--Cross trough.]

When tin ore is crushed by this kind of iron-shod stamps, as soon as crus.h.i.+ng 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 was.h.i.+ng 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 part.i.tion 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.

[Ill.u.s.tration 315 (Buddle): A--First launder. B--Three-toothed rake.

C--Small settling pit. D--Large buddle. E--Buddle resembling the simple buddle. F--Small roller. G--Boards. H--Their holes. I--Shovel.

K--Building. L--Stove. (This picture does not entirely agree with the text).]

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.

[Ill.u.s.tration 317 (Workroom with settling-pit): A--Launder from the screen of the mortar-box. B--Three-toothed rake. C--Small settling-pit.

D--Canvas. E--Strakes. F--Brooms.]

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 part.i.tioned 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 brus.h.i.+ng 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.