De Re Metallica Part 33

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 quant.i.ty 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.

[Ill.u.s.tration 318 (Streaming for Tin): A--River. B--Weir. C--Gate.

D--Area. E--Meadow. F--Fence. G--Ditch.]

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.

[Ill.u.s.tration 320 (Stamp-mill): A--First machine. B--Its stamps. C--Its mortar-box. D--Second machine. E--Its stamps. F--Its mortar-box.

G--Third machine. H--Its stamps. I--Its mortar-box. K--Fourth machine.

L--Its stamps. M--Its mortar-box.]

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 quant.i.ty 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.

[Ill.u.s.tration 321 (Stamp-mill): A--Stamps. B--Mortar. C--Plates full of holes. D--Transverse launder. E--Planks full of cup-like depressions.

F--Spout. G--Bowl into which the concentrates fall. H--Canvas strake.

I--Bowls shaped like a small boat. K--Settling-pit under the canvas strake.]

Further, in the Julian and Rhaetian Alps[15] 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 das.h.i.+ng 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 was.h.i.+ng 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 was.h.i.+ng on frames, for these frames either pa.s.s or retain the particles or concentrates of gold; they pa.s.s them if they have holes, and retain them if they have no holes. But either the frame itself has holes, or a box is subst.i.tuted for it; if the frame itself is perforated it pa.s.ses the particles or concentrates of gold into a trough; if the box has them, it pa.s.ses the gold material into the long sluice. I will first speak of these two methods of was.h.i.+ng. 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 pa.s.s. 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, pa.s.s through the holes into the trough which is placed under the frame, and after being collected are washed in the bowl.

[Ill.u.s.tration 322 (Frames for Was.h.i.+ng Ore or Alluvial): A--Head of frame. B--Frame. C--Holes. D--Edge-boards. E--Stools. F--Scrubber.

G--Trough. H--Launder. I--Bowl.]

[Ill.u.s.tration 323 (Frames for Was.h.i.+ng Ore or Alluvial): A--Sluice.

B--Box. C--Bottom of inverted box. D--Open part of it. E--Iron hoe.

F--Riffles. G--Small launder. H--Bowl with which settlings are taken away. I--Black bowl in which they are washed.]

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 quant.i.ty 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 coa.r.s.e pieces remain in the box, and these are removed with a sc.r.a.per 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 acc.u.mulated 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.

[Ill.u.s.tration 324 (Frames for Was.h.i.+ng Ore or Alluvial): A--Plank.

B--Side-boards. C--Iron wire. D--Handles.]

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 was.h.i.+ng, 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.

[Ill.u.s.tration 326 (Frames for Was.h.i.+ng Ore or Alluvial): A--Head of the sluice. B--Riffles. C--Wooden scrubber. D--Pointed stick. E--Dish.

F--Its cup-like depression. G--Grooved dish.]

Other people, among whom are the Lusitanians[16], 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 sh.e.l.l, 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.

[Ill.u.s.tration 327 (Frames for Was.h.i.+ng Ore or Alluvial): A--Head of the sluice. B--Side-boards. C--Lower end of the sluice. D--Pockets.

E--Grooves. F--Stools. G--Shovel. H--Tub set below. I--Launder.]

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.

[Ill.u.s.tration 328 (Frames for Was.h.i.+ng Ore or Alluvial): A--Cross grooves. B--Tub set under the sluice. C--Another tub.]

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.

[Ill.u.s.tration 329 (Frames for Was.h.i.+ng Ore or Alluvial): A--Sluice covered with canvas. B--Its head full of pockets and grooves. C--Head removed and washed in a tub. D--Sluice which has square pockets.

E--Sluice to whose planks small shavings cling. F--Broom. G--Skins of oxen. H--Wooden scrubber.]

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.

[Ill.u.s.tration 330 (Was.h.i.+ng material in spring): A--Spring. B--Skin.

C--Argonauts.]

The Colchians[17] placed the skins of animals in the pools of springs; and since many particles of gold had clung to them when they were removed, 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.

[Ill.u.s.tration 331 (Frames for Was.h.i.+ng Ore or Alluvial): A--Head of frame. B--Frame. C--Cloth. D--small launder. E--Tub set below the frame.

F--Tub in which cloth is washed.]

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.

[Ill.u.s.tration 332 (Frames for Was.h.i.+ng Ore or Alluvial): A--Cloth full of small knots, spread out. B--Small knots more conspicuously shown.

C--Tub in which cloth is washed.]

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.

[Ill.u.s.tration 333 (Frames for Was.h.i.+ng Ore or Alluvial): A--Head of frame. B--Small launder through which water flows into head of frame.

C--Pieces of turf. D--Trough placed under frame. E--Tub in which pieces of turf are washed.]

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 pa.s.sed 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 was.h.i.+ng gold. "The ulex," he says, "after being dried, is burnt, and its ashes are washed over a gra.s.sy turf, that the gold may settle on it."

[Ill.u.s.tration 334 (Trays for Was.h.i.+ng Alluvial): A--Tray. B--Bowl-like depression. C--Handles.]

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.

[Ill.u.s.tration 335 (Trough for was.h.i.+ng alluvial): A--Trough. B--Its open end. C--End that may be closed. D--Stream. E--Hoe. F--End-board.

G--Bag.]

The Italians who come to the German mountains seeking gold, in order to wash the river sand which contains gold-dust and garnets,[19] 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 quant.i.ty of heavy sand, have settled in the trough, they wash in a bowl and collect in bags and carry away with them.

[Ill.u.s.tration 336 (Bowls for Alluvial Was.h.i.+ng): A--Large bowl. B--Ropes.

C--Beam. D--Other large bowl which coiners use. E--Small bowl.]

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 was.h.i.+ng then returns immediately to his task. This method of was.h.i.+ng 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.