De Re Metallica Part 49

[Ill.u.s.tration 519 (Liquation Furnaces): A--Furnace in which the operation of liquation is being performed. B--Furnace in which it is not being performed. C--Receiving-pit. D--Moulds. E--Cakes. F--Liquation thorns.]

There are three panels to the furnace--two at the sides, one in front and another at the back. Those which are at the sides are three feet and as many palms and two digits long, and two feet high; the front one is two feet and a palm and three digits long, and, like the side ones, two feet high. Each consists of iron bars, of feet, and of iron plates.

Those which are at the side have seven bars, the lower and upper of which are of the same length as the panels; the former holds up the upright bars; the latter is placed upon them; the uprights are five in number, and have the same height as the panels; the middle ones are inserted into holes in the upper and lower bars; the outer ones are made of one and the same bar as the lower and upper ones. They are two digits wide and one thick. The front panel has five bars; the lower one holds similar uprights, but there are three of them only; the upper bar is placed on them. Each of these panels has two feet fixed at each end of the lower bar, and these are two palms long, one wide, and a digit thick. The iron plates are fastened to the inner side of the bars with iron wire, and they are covered with lute, so that they may last longer and may be uninjured by the fire. There are, besides, iron blocks three palms long, one wide, and a digit and a half thick; the upper surface of these is somewhat hollowed out, so that the cakes may stand in them; these iron blocks are dipped into a vessel in which there is clay mixed with water, and they are used only for placing under the cakes of copper and lead alloy made in the furnaces. There is more silver in these than in those which are made of liquation thorns, or furnace accretions, or re-melted "slags." Two iron blocks are placed under each cake, in order that, by raising it up, the fire may bring more force to bear upon it; the one is put on the right bed-plate, the other on the left. Finally, outside the hearth is the receiving-pit, which is a foot wide and three palms deep; when this is worn away it is restored with lute alone, which easily retains the lead alloy.

If four liquation cakes are placed on the plates of each furnace, then the iron blocks are laid under them; but if the cakes are made from copper "bottoms," or from liquation thorns, or from the accretions or "slags," of which I have partly written above and will further describe a little later, there are five of them, and because they are not so large and heavy, no blocks are placed under them. Pieces of charcoal six digits long are laid between the cakes, lest they should fall one against the other, or lest the last one should fall against the wall which protects the third long wall from injury by fire. In the middle empty s.p.a.ces, long and large pieces of charcoal are likewise laid. Then when the panels have been set up, and the bar has been closed, the furnace is filled with small charcoal, and a wicker basket full of charcoal is thrown into the receiving-pit, and over that are thrown live coals; soon afterward the burning coal, lifted up in a shovel, is spread over all parts of the furnace, so that the charcoal in it may be kindled; any charcoal which remains in the receiving-pit is thrown into the pa.s.sage, so that it may likewise be heated. If this has not been done, the silver-lead alloy liquated from the cakes is frozen by the coldness of the pa.s.sage, and does not run down into the receiving-pit.

After a quarter of an hour the cakes begin to drip silver-lead alloy,[18] which runs down through the openings between the copper plates into the pa.s.sage. When the long pieces of charcoal have burned up, if the cakes lean toward the wall, they are placed upright again with a hooked bar, but if they lean toward the front bar they are propped up by charcoal; moreover, if some cakes shrink more than the rest, charcoal is added to the former and not to the others. The silver drips together with the lead, for both melt more rapidly than copper.

The liquation thorns do not flow away, but remain in the pa.s.sage, and should be turned over frequently with a hooked bar, in order that the silver-lead may liquate away from them and flow down into the receiving pit; that which remains is again melted in the blast furnace, while that which flows into the receiving pit is at once carried with the remaining products to the cupellation furnace, where the lead is separated from the silver. The hooked bar has an iron handle two feet long, in which is set a wooden one four feet long. The silver-lead which runs out into the receiving-pit is poured out by the refiner with a bronze ladle into eight copper moulds, which are two palms and three digits in diameter; these are first smeared with a lute wash so that the cakes of silver-lead may more easily fall out when they are turned over. If the supply of moulds fails because the silver-lead flows down too rapidly into the receiving-pit, then water is poured on them, in order that the cakes may cool and be taken out of them more rapidly; thus the same moulds may be used again immediately; if no such necessity urges the refiner, he washes over the empty moulds with a lute wash. The ladle is exactly similar to that which is used in pouring out the metals that are melted in the blast furnace. When all the silver-lead has run down from the pa.s.sage into the receiving-pit, and has been poured out into copper moulds, the thorns are drawn out of the pa.s.sage into the receiving-pit with a rabble; afterward they are raked on to the ground from the receiving-pit, thrown with a shovel into a wheelbarrow, and, having been conveyed away to a heap, are melted once again. The blade of the rabble is two palms and as many digits long, two palms and a digit wide, and joined to its back is an iron handle three feet long; into the iron handle is inserted a wooden one as many feet in length.

The residue cakes, after the silver-lead has been liquated from the copper, are called "exhausted liquation cakes" (_fathiscentes_), because when thus smelted they appear to be dried up. By placing a crowbar under the cakes they are raised up, seized with tongs, and placed in the wheelbarrow; they are then conveyed away to the furnace in which they are "dried." The crowbar is somewhat similar to those generally used to chip off the accretions that adhere to the walls of the blast furnace.

The tongs are two and a half feet long. With the same crowbar the stalact.i.tes are chipped off from the copper plates from which they hang, and with the same instrument the iron blocks are struck off the exhausted liquation cakes to which they adhere. The refiner has performed his day's task when he has liquated the silver-lead from sixteen of the large cakes and twenty of the smaller ones; if he liquates more than this, he is paid separately for it at the price for extraordinary work.

Silver, or lead mixed with silver, which we call _stannum_, is separated by the above method from copper. This silver-lead is carried to the cupellation furnace, in which lead is separated from silver; of these methods I will mention only one, because in the previous book I have explained them in detail. Amongst us some years ago only forty-four _centumpondia_ of silver-lead and one of copper were melted together in the cupellation furnaces, but now they melt forty-six _centumpondia_ of silver-lead and one and a half _centumpondia_ of copper; in other places, usually a hundred and twenty _centumpondia_ of silver-lead alloy and six of copper are melted, in which manner they make about one hundred and ten _centumpondia_ more or less of litharge and thirty of hearth-lead. But in all these methods the silver which is in the copper is mixed with the remainder of silver; the copper itself, equally with the lead, will be changed partly into litharge and partly into hearth-lead.[19] The silver-lead alloy which does not melt is taken from the margin of the crucible with a hooked bar.

[Ill.u.s.tration 522 (Exhausted Liquation Cakes): A--Cakes. B--Hammer.]

The work of "drying" is distributed into four operations, which are performed in four days. On the first--as likewise on the other three days--the master begins at the fourth hour of the morning, and with his a.s.sistant chips off the stalact.i.tes from the exhausted liquation cakes.

They then carry the cakes to the furnace, and put the stalact.i.tes upon the heap of liquation thorns. The head of the chipping hammer is three palms and as many digits long; its sharp edge is a palm wide; the round end is three digits thick; the wooden handle is four feet long.

The master throws pulverised earth into a small vessel, sprinkles water over it, and mixes it; this he pours over the whole hearth, and sprinkles charcoal dust over it to the thickness of a digit. If he should neglect this, the copper, settling in the pa.s.sages, would adhere to the copper bed-plates, from which it can be chipped off only with difficulty; or else it would adhere to the bricks, if the hearth was covered with them, and when the copper is chipped off these they are easily broken. On the second day, at the same time, the master arranges bricks in ten rows; in this manner twelve pa.s.sages are made. The first two rows of bricks are between the first and the second openings on the right of the furnace; the next three rows are between the second and third openings, the following three rows are between the third and the fourth openings, and the last two rows between the fourth and fifth openings. These bricks are a foot and a palm long, two palms and a digit wide, and a palm and two digits thick; there are seven of these thick bricks in a row, so there are seventy all together. Then on the first three rows of bricks they lay exhausted liquation cakes and a layer five digits thick of large charcoal; then in a similar way more exhausted liquation cakes are laid upon the other bricks, and charcoal is thrown upon them; in this manner seventy _centumpondia_ of cakes are put on the hearth of the furnace. But if half of this weight, or a little more, is to be "dried," then four rows of bricks will suffice. Those who dry exhausted liquation cakes[20] made from copper "bottoms" place ninety or a hundred _centumpondia_[21] into the furnace at the same time. A place is left in the front part of the furnace for the topmost cakes removed from the forehearth in which copper is made, these being more suitable for supporting the exhausted liquation cakes than are iron plates; indeed, if the former cakes drip copper from the heat, this can be taken back with the liquation thorns to the first furnace, but melted iron is of no use to us in these matters. When the cakes of this kind have been placed in front of the exhausted liquation cakes, the workman inserts the iron bar into the holes on the inside of the wall, which are at a height of three palms and two digits above the hearth; the hole to the left penetrates through into the wall, so that the bar may be pushed back and forth. This bar is round, eight feet long and two digits in diameter; on the right side it has a haft made of iron, which is about a foot from the right end; the aperture in this haft is a palm wide, two digits high, and a digit thick. The bar holds the exhausted liquation cakes opposite, lest they should fall down. When the operation of "drying" is completed, a workman draws out this bar with a crook which he inserts into the haft, as I will explain hereafter.

[Ill.u.s.tration 525 (Drying Furnace for Liquation): A--Side walls.

B--Front arch. C--Rear arch. D--Wall in the rear arch. E--Inner wall.

F--Vent holes. G--Chimney. H--Hearth. I--Tank. K--Pipe. L--Plug. M--Iron door. N--Transverse bars. O--Upright bars. P--Plates. Q--Rings of the bars. R--Chains. S--Rows of bricks. T--Bar. V--Its haft. X--Copper bed-plates.]

In order that one should understand those things of which I have spoken, and concerning which I am about to speak, it is necessary for me to give some information beforehand about the furnace and how it is to be made.

It stands nine feet from the fourth long wall, and as far from the wall which is between the second and fourth transverse walls. It consists of walls, an arch, a chimney, an interior wall, and a hearth; the two walls are at the sides; and they are eleven feet three palms and two digits long, and where they support the chimney they are eight feet and a palm high. At the front of the arch they are only seven feet high; they are two feet three palms and two digits thick, and are made either of rock or of bricks; the distance between them is eight feet, a palm and two digits. There are two of the arches, for the s.p.a.ce at the rear between the walls is also arched from the ground, in order that it may be able to support the chimney; the foundations of these arches are the walls of the furnace; the span of the arch has the same length as the s.p.a.ce between the walls; the top of the arch is five feet, a palm and two digits high. In the rear arch there is a wall made of bricks joined with lime; this wall at a height of a foot and three palms from the ground has five vent-holes, which are two palms and a digit high, a palm and a digit wide, of which the first is near the right interior wall, and the last near the left interior wall, the remaining three in the intervening s.p.a.ce; these vent-holes penetrate through the interior of the wall which is in the arch. Half-bricks can be placed over the vent-holes, lest too much air should be drawn into the furnace, and they can be taken out at times, in order that he who is "drying" the exhausted liquation cakes may inspect the pa.s.sages, as they are called, to see whether the cakes are being properly "dried." The front arch is three feet two palms distant from the rear one; this arch is the same thickness as that of the rear arch, but the span is six feet wide; the interior of the arch itself is of the same height as the walls. A chimney is built upon the arches and the walls, and is made of bricks joined together with lime; it is thirty-six feet high and penetrates through the roof. The interior wall is built against the rear arch and both the side walls, from which it juts out a foot; it is three feet and the same number of palms high, three palms thick, and is made of bricks joined together with lute and smeared thickly with lute, sloping up to the height of a foot above it.

This wall is a kind of shield, for it protects the exterior walls from the heat of the fire, which is apt to injure them; the latter cannot be easily re-made, while the former can be repaired with little work.

The hearth is made of lute, and is covered either with copper plates, such as those of the furnaces in which silver is liquated from copper, although they have no protuberances, or it may be covered with bricks, if the owners are unwilling to incur the expense of copper plates. The wider part of the hearth is made sloping in such a manner that the rear end reaches as high as the five vent-holes, and the front end of the hearth is so low that the back of the front arch is four feet, three palms and as many digits above it, and the front five feet, three palms and as many digits. The hearth beyond the furnaces is paved with bricks for a distance of six feet. Near the furnace, against the fourth long wall, is a tank thirteen feet and a palm long, four feet wide, and a foot and three palms deep. It is lined on all sides with planks, lest the earth should fall into it; on one side the water flows in through pipes, and on the other, if the plug be pulled out, it soaks into the earth; into this tank of water are thrown the cakes of copper from which the silver and lead have been separated. The fore part of the front furnace arch should be partly closed with an iron door; the bottom of this door is six feet and two digits wide; the upper part is somewhat rounded, and at the highest point, which is in the middle, it is three feet and two palms high. It is made of iron bars, with plates fastened to them with iron wire, there being seven bars--three transverse and four upright--each of which is two digits wide and half a digit thick.

The lowest transverse bar is six feet and two palms long; the middle one has the same length; the upper one is curved and higher at the centre, and thus longer than the other two. The upright bars are two feet distant from one another; both the outer ones are two feet and as many palms high; but the centre ones are three feet and two palms. They project from the upper curved transverse bar and have holes, in which are inserted the hooks of small chains two feet long; the topmost links of these chains are engaged in the ring of a third chain, which, when extended, reaches to one end of a beam which is somewhat cut out. The chain then turns around the beam, and again hanging down, the hook in the other end is fastened in one of the links. This beam is eleven feet long, a palm and two digits wide, a palm thick, and turns on an iron axle fixed in a nearby timber; the rear end of the beam has an iron pin, which is three palms and a digit long, and which penetrates through it where it lies under a timber, and projects from it a palm and two digits on one side, and three digits on the other side. At this point the pin is perforated, in order that a ring may be fixed in it and hold it, lest it should fall out of the beam; that end is hardly a digit thick, while the other round end is thicker than a digit. When the door is to be shut, this pin lies under the timber and holds the door so that it cannot fall; the pin likewise prevents the rectangular iron band which encircles the end of the beam, and into which is inserted the ring of a long hook, from falling from the end. The lowest link of an iron chain, which is six feet long, is inserted in the ring of a staple driven into the right wall of the furnace, and fixed firmly by filling in with molten lead. The hook suspended at the top from the ring should be inserted in one of these lower links, when the door is to be raised; when the door is to be let down, the hook is taken out of that link and put into one of the upper links.

[Ill.u.s.tration 527 (Drying Furnace for Liquation): A--The door let down.

B--Bar. C--Exhausted liquation cakes. D--Bricks. E--Tongs.]

On the third day the master sets about the princ.i.p.al operation. First he throws a basketful of charcoals on to the ground in front of the hearth, and kindles them by adding live coals, and having thrown live coals on to the cakes placed within, he spreads them equally all over with an iron shovel. The blade of the shovel is three palms and a digit long, and three palms wide; its iron handle is two palms long, and the wooden one ten feet long, so that it can reach to the rear wall of the furnace.

The exhausted liquation cakes become incandescent in an hour and a half, if the copper was good and hard, or after two hours, if it was soft and fragile. The workman adds charcoal to them where he sees it is needed, throwing it into the furnace through the openings on both sides between the side walls and the closed door. This opening is a foot and a palm wide. He lets down the door, and when the "slags" begin to flow he opens the pa.s.sages with a bar; this should take place after five hours; the door is let down over the upper open part of the arch for two feet and as many digits, so that the master can bear the violence of the heat.

When the cakes shrink, charcoal should not be added to them lest they should melt. If the cakes made from poor and fragile copper are "dried"

with cakes made from good hard copper, very often the copper so settles into the pa.s.sages that a bar thrust into them cannot penetrate them.

This bar is of iron, six feet and two palms long, into which a wooden handle five feet long is inserted. The refiner draws off the "slags"

with a rabble from the right side of the hearth. The blade of the rabble is made of an iron plate a foot and a palm wide, gradually narrowing toward the handle; the blade is two palms high, its iron handle is two feet long, and the wooden handle set into it is ten feet long.

[Ill.u.s.tration 528 (Drying Furnace for Liquation): A--The door raised.

B--Hooked bar. C--Two-p.r.o.nged rake. D--Tongs. E--Tank.]

When the exhausted liquation cakes have been "dried," the master raises the door in the manner I have described, and with a long iron hook inserted into the haft of the bar he draws it through the hole in the left wall from the hole in the right wall; afterward he pushes it back and replaces it. The master then takes out the exhausted liquation cakes nearest to him with the iron hook; then he pulls out the cakes from the bricks. This hook is two palms high, as many digits wide, and one thick; its iron handle is two feet long, and the wooden handle eleven feet long. There is also a two-p.r.o.nged rake with which the "dried" cakes are drawn over to the left side so that they may be seized with tongs; the p.r.o.ngs of the rake are pointed, and are two palms long, as many digits wide, and one digit thick; the iron part of the handle is a foot long, the wooden part nine feet long. The "dried" cakes, taken out of the hearth by the master and his a.s.sistants, are seized with other tongs and thrown into the rectangular tank, which is almost filled with water.

These tongs are two feet and three palms long, both the handles are round and more than a digit thick, and the ends are bent for a palm and two digits; both the jaws are a digit and a half wide in front and sharpened; at the back they are a digit thick, and then gradually taper, and when closed, the interior is two palms and as many digits wide.

The "dried" cakes which are dripping copper are not immediately dipped into the tank, because, if so, they burst in fragments and give out a sound like thunder. The cakes are afterward taken out of the tank with the tongs, and laid upon the two transverse planks on which the workmen stand; the sooner they are taken out the easier it is to chip off the copper that has become ash-coloured. Finally, the master, with a spade, raises up the bricks a little from the hearth, while they are still warm. The blade of the spade is a palm and two digits long, the lower edge is sharp, and is a palm and a digit wide, the upper end a palm wide; its handle is round, the iron part being two feet long, and the wooden part seven and a half feet long.

On the fourth day the master draws out the liquation thorns which have settled in the pa.s.sages; they are much richer in silver than those that are made when the silver-lead is liquated from copper in the liquation furnace. The "dried" cakes drip but little copper, but nearly all their remaining silver-lead and the thorns consist of it, for, indeed, in one _centumpondium_ of "dried" copper there should remain only half an _uncia_ of silver, and there sometimes remain only three _drachmae_.[22]

Some smelters chip off the metal adhering to the bricks with a hammer, in order that it may be melted again; others, however, crush the bricks under the stamps and wash them, and the copper and lead thus collected is melted again. The master, when he has taken these things away and put them in their places, has finished his day's work.

[Ill.u.s.tration 530 (Dried Liquation Cakes): A--Tank. B--Board. C--Tongs.

D--"Dried" cakes taken out of the tanks. E--Block. F--Rounded hammer.

G--Pointed hammer.]

The a.s.sistants take the "dried" cakes out of the tank on the next day, place them on an oak block, and first pound them with rounded hammers in order that the ash-coloured copper may fall away from them, and then they dig out with pointed picks the holes in the cakes, which contain the same kind of copper. The head of the round hammer is three palms and a digit long; one end of the head is round and two digits long and thick; the other end is chisel-shaped, and is two digits and a half long. The sharp pointed hammer is the same length as the round hammer, but one end is pointed, the other end is square, and gradually tapers to a point.

The nature of copper is such that when it is "dried" it becomes ash coloured, and since this copper contains silver, it is smelted again in the blast furnaces.[23]

[Ill.u.s.tration 532 (Copper Refining Furnace): A--Hearth of the furnace.

B--Chimney. C--Common pillar. D--Other pillars. The part.i.tion wall is behind the common pillar and not to be seen. E--Arches. F--Little walls which protect the part.i.tion wall from injury by the fire. G--Crucibles.

H--Second long wall. I--Door. K--Spatula. L--The other spatula. M--The broom in which is inserted a stick. N--Pestles. O--Wooden mallet.

P--Plate. Q--Stones. R--Iron rod.]

I have described sufficiently the method by which exhausted liquation cakes are "dried"; now I will speak of the method by which they are made into copper after they have been "dried." These cakes, in order that they may recover the appearance of copper which they have to some extent lost, are melted in four furnaces, which are placed against the second long wall in the part of the building between the second and third transverse walls. This s.p.a.ce is sixty-three feet and two palms long, and since each of these furnaces occupies thirteen feet, the s.p.a.ce which is on the right side of the first furnace, and on the left of the fourth, are each three feet and three palms wide, and the distance between the second and third furnace is six feet. In the middle of each of these three s.p.a.ces is a door, a foot and a half wide and six feet high, and the middle one is common to the master of each of the furnaces. Each furnace has its own chimney, which rises between the two long walls mentioned above, and is supported by two arches and a part.i.tion wall.

The part.i.tion wall is between the two furnaces, and is five feet long, ten feet high, and two feet thick; in front of it is a pillar belonging in common to the front arches of the furnace on either side, which is two feet and as many palms thick, three feet and a half wide. The front arch reaches from this common pillar to another pillar that is common to the side arch of the same furnace; this arch on the right spans from the second long wall to the same pillar, which is two feet and as many palms wide and thick at the bottom. The interior of the front arch is nine feet and a palm wide, and eight feet high at its highest point; the interior of the arch which is on the right side, is five feet and a palm wide, and of equal height to the other, and both the arches are built of the same height as the part.i.tion wall. Imposed upon these arches and the part.i.tion wall are the walls of the chimney; these slope upward, and thus contract, so that at the upper part, where the fumes are emitted, the opening is eight feet in length, one foot and three palms in width.

The fourth wall of the chimney is built vertically upon the second long wall. As the part.i.tion wall is common to the two furnaces, so its superstructure is common to the two chimneys. In this sensible manner the chimney is built. At the front each furnace is six feet two palms long, and three feet two palms wide, and a cubit high; the back of each furnace is against the second long wall, the front being open. The first furnace is open and sloping at the right side, so that the slags may be drawn out; the left side is against the part.i.tion wall, and has a little wall built of bricks cemented together with lute; this little wall protects the part.i.tion wall from injury by the fire. On the contrary, the second furnace has the left side open and the right side is against the part.i.tion wall, where also it has its own little wall which protects the part.i.tion wall from the fire. The front of each furnace is built of rectangular rocks; the interior of it is filled up with earth. Then in each of the furnaces at the rear, against the second long wall, is an aperture through an arch at the back, and in these are fixed the copper pipes. Each furnace has a round pit, two feet and as many palms wide, built three feet away from the part.i.tion wall. Finally, under the pit of the furnace, at a depth of a cubit, is the hidden receptacle for moisture, similar to the others, whose vent penetrates through the second long wall and slopes upward to the right from the first furnace, and to the left from the second. If copper is to be made the next day, then the master cuts out the crucible with a spatula, the blade of which is three digits wide and as many palms long, the iron handle being two feet long and one and a half digits in diameter; the wooden handle inserted into it is round, five feet long and two digits in diameter.

Then, with another cutting spatula, he makes the crucible smooth; the blade of this spatula is a palm wide and two palms long; its handle, partly of iron, partly of wood, is similar in every respect to the first one. Afterward he throws pulverised clay and charcoal into the crucible, pours water over it, and sweeps it over with a broom into which a stick is fixed. Then immediately he throws into the crucible a powder, made of two wheelbarrowsful of sifted charcoal dust, as many wheelbarrowsful of pulverised clay likewise sifted, and six basketsful of river sand which has pa.s.sed through a very fine sieve. This powder, like that used by smelters, is sprinkled with water and moistened before it is put into the crucible, so that it may be fashioned by the hands into shapes similar to s...o...b..a.l.l.s. When it has been put in, the master first kneads it and makes it smooth with his hands, and then pounds it with two wooden pestles, each of which is a cubit long; each pestle has a round head at each end, but one of these is a palm in diameter, the other three digits; both are thinner in the middle, so that they may be held in the hand. Then he again throws moistened powder into the crucible, and again makes it smooth with his hands, and kneads it with his fists and with the pestles; then, pushing upward and pressing with his fingers, he makes the edge of the crucible smooth. After the crucible has been made smooth, he sprinkles in dry charcoal dust, and again pounds it with the same pestles, at first with the narrow heads, and afterward with the wider ones. Then he pounds the crucible with a wooden mallet two feet long, both heads of which are round and three digits in diameter; its wooden handle is two palms long, and one and a half digits in diameter. Finally, he throws into the crucible as much pure sifted ashes as both hands can hold, and pours water into it, and, taking an old linen rag, he smears the crucible over with the wet ashes. The crucible is round and sloping. If copper is to be made from the best quality of "dried" cakes, it is made two feet wide and one deep, but if from other cakes, it is made a cubit wide and two palms deep. The master also has an iron band curved at both ends, two palms long and as many digits wide, and with this he cuts off the edges of the crucible if they are higher than is necessary. The copper pipe is inclined, and projects three digits from the wall, and has its upper end and both sides smeared thick with lute, that it may not be burned; but the underside of the pipe is smeared thinly with lute, for this side reaches almost to the edge of the crucible, and when the crucible is full the molten copper touches it. The wall above the pipe is smeared over with lute, lest that should be damaged. He does the same to the other side of an iron plate, which is a foot and three palms long and a foot high; this stands on stones near the crucible at the side where the hearth slopes, in order that the slag may run out under it. Others do not place the plates upon stones, but cut out of the plate underneath a small piece, three digits long and three digits wide; lest the plate should fall, it is supported by an iron rod fixed in the wall at a height of two palms and the same number of digits, and it projects from the wall three palms.

Then with an iron shovel, whose wooden handle is six feet long, he throws live charcoal into the crucible; or else charcoal, kindled by means of a few live coals, is added to them. Over the live charcoal he lays "dried" cakes, which, if they were of copper of the first quality, weigh all together three _centumpondia_, or three and a half _centumpondia_; but if they were of copper of the second quality, then two and a half _centumpondia_; if they were of the third quality, then two _centumpondia_ only; but if they were of copper of very superior quality, then they place upon it six _centumpondia_, and in this case they make the crucible wider and deeper.[24] The lowest "dried" cake is placed at a distance of two palms from the pipe, the rest at a greater distance, and when the lower ones are melted the upper ones fall down and get nearer to the pipe; if they do not fall down they must be pushed with a shovel. The blade of the shovel is a foot long, three palms and two digits wide, the iron part of the handle is two palms long, the wooden part nine feet. Round about the "dried" cakes are placed large long pieces of charcoal, and in the pipe are placed medium-sized pieces.

When all these things have been arranged in this manner, the fire must be more violently excited by the blast from the bellows. When the copper is melting and the coals blaze, the master pushes an iron bar into the middle of them in order that they may receive the air, and that the flame can force its way out. This pointed bar is two and a half feet long, and its wooden handle four feet long. When the cakes are partly melted, the master, pa.s.sing out through the door, inspects the crucible through the bronze pipe, and if he should find that too much of the "slag" is adhering to the mouth of the pipe, and thus impeding the blast of the bellows, he inserts the hooked iron bar into the pipe through the nozzle of the bellows, and, turning this about the mouth of the pipe, he removes the "slags" from it. The hook on this bar is two digits high; the iron part of the handle is three feet long; the wooden part is the same number of palms long. Now it is time to insert the bar under the iron plate, in order that the "slags" may flow out. When the cakes, being all melted, have run into the crucible, he takes out a sample of copper with the third round bar, which is made wholly of iron, and is three feet long, a digit thick, and has a steel point lest its pores should absorb the copper. When he has compressed the bellows, he introduces this bar as quickly as possible into the crucible through the pipe between the two nozzles, and takes out samples two, three, or four times, until he finds that the copper is perfectly refined. If the copper is good it adheres easily to the bar, and two samples suffice; if it is not good, then many are required. It is necessary to smelt it in the crucible until the copper adhering to the bar is seen to be of a bra.s.sy colour, and if the upper as well as the lower part of the thin layer of copper may be easily broken, it signifies that the copper is perfectly melted; he places the point of the bar on a small iron anvil, and chips off the thin layer of copper from it with a hammer.[25]

[Ill.u.s.tration 534 (Copper Refining): A--Pointed bar. B--Thin copper layer. C--Anvil. D--Hammer.]

[Ill.u.s.tration 537 (Copper Refining): A--Crucible. B--Board.

C--Wedge-shaped bar. D--Cakes of copper made by separating them with the wedge-shaped bar. E--Tongs. F--Tub.]

If the copper is not good, the master draws off the "slags" twice, or three times if necessary--the first time when some of the cakes have been melted, the second when all have melted, the third time when the copper has been heated for some time. If the copper was of good quality, the "slags" are not drawn off before the operation is finished, but at the time they are to be drawn off, he depresses the bar over both bellows, and places over both a stick, a cubit long and a palm wide, half cut away at the upper part, so that it may pa.s.s under the iron pin fixed at the back in the perforated wood. This he does likewise when the copper has been completely melted. Then the a.s.sistant removes the iron plate with the tongs; these tongs are four feet three palms long, their jaws are about a foot in length, and their straight part measures two palms and three digits, and the curved a palm and a digit. The same a.s.sistant, with the iron shovel, throws and heaps up the larger pieces of charcoal into that part of the hearth which is against the little wall which protects the other wall from injury by fire, and partly extinguishes them by pouring water over them. The master, with a hazel stick inserted into the crucible, stirs it twice. Afterward he draws off the slags with a rabble, which consists of an iron blade, wide and sharp, and of alder-wood; the blade is a digit and a half in width and three feet long; the wooden handle inserted in its hollow part is the same number of feet long, and the alder-wood in which the blade is fixed must have the figure of a rhombus; it must be three palms and a digit long, a palm and two digits wide, and a palm thick. Subsequently he takes a broom and sweeps the charcoal dust and small coal over the whole of the crucible, lest the copper should cool before it flows together; then, with a third rabble, he cuts off the slags which may adhere to the edge of the crucible. The blade of this rabble is two palms long and a palm and one digit wide, the iron part of the handle is a foot and three palms long, the wooden part six feet. Afterward he again draws off the slags from the crucible, which the a.s.sistant does not quench by pouring water upon them, as the other slags are usually quenched, but he sprinkles over them a little water and allows them to cool. If the copper should bubble, he presses down the bubbles with the rabble. Then he pours water on the wall and the pipes, that it may flow down warm into the crucible, for, the copper, if cold water were to be poured over it while still hot, would spatter about. If a stone, or a piece of lute or wood, or a damp coal should then fall into it, the crucible would vomit out all the copper with a loud noise like thunder, and whatever it touches it injures and sets on fire. Subsequently he lays a curved board with a notch in it over the front part of the crucible; it is two feet long, a palm and two digits wide, and a digit thick. Then the copper in the crucible should be divided into cakes with an iron wedge-shaped bar; this is three feet long, two digits wide, and steeled on the end for the distance of two digits, and its wooden handle is three feet long. He places this bar on the notched board, and, driving it into the copper, moves it forward and back, and by this means the water flows into the vacant s.p.a.ce in the copper, and he separates the cake from the rest of the ma.s.s. If the copper is not perfectly smelted the cakes will be too thick, and cannot be taken out of the crucible easily. Each cake is afterward seized by the a.s.sistant with the tongs and plunged into the water in the tub; the first one is placed aside so that the master may re-melt it again immediately, for, since some "slags" adhere to it, it is not as perfect as the subsequent ones; indeed, if the copper is not of good quality, he places the first two cakes aside. Then, again pouring water over the wall and the pipes, he separates out the second cake, which the a.s.sistant likewise immerses in water and places on the ground together with the others separated out in the same way, which he piles upon them. These, if the copper was of good quality, should be thirteen or more in number; if it was not of good quality, then fewer.

If the copper was of good quality, this part of the operation, which indeed is distributed into four parts, is accomplished by the master in two hours; if of mediocre quality, in two and a half hours; if of bad quality, in three. The "dried" cakes are re-melted, first in the first crucible and then in the second. The a.s.sistant must, as quickly as possible, quench all the cakes with water, after they have been cut out of the second crucible. Afterward with the tongs he replaces in its proper place the iron plate which was in front of the furnace, and throws the charcoal back into the crucible with a shovel. Meanwhile the master, continuing his work, removes the wooden stick from the bars of the bellows, so that in re-melting the other cakes he may accomplish the third part of his process; this must be carefully done, for if a particle from any iron implement should by chance fall into the crucible, or should be thrown in by any malevolent person, the copper could not be made until the iron had been consumed, and therefore double labour would have to be expended upon it. Finally, the a.s.sistant extinguishes all the glowing coals, and chips off the dry lute from the mouth of the copper pipe with a hammer; one end of this hammer is pointed, the other round, and it has a wooden handle five feet long.

Because there is danger that the copper would be scattered if the _pompholyx_ and _spodos_, which adhere to the walls and the hood erected upon them, should fall into the crucible, he cleans them off in the meantime. Every week he takes the copper flowers out of the tub, after having poured off the water, for these fall into it from the cakes when they are quenched.[26]

The bellows which this master uses differ in size from the others, for the boards are seven and a half feet long; the back part is three feet wide; the front, where the head is joined on is a foot, two palms and as many digits. The head is a cubit and a digit long; the back part of it is a cubit and a palm wide, and then becomes gradually narrower. The nozzles of the bellows are bound together by means of an iron chain, controlled by a thick bar, one end of which penetrates into the ground against the back of the long wall, and the other end pa.s.ses under the beam which is laid upon the foremost perforated beams. These nozzles are so placed in a copper pipe that they are at a distance of a palm from the mouth; the mouth should be made three digits in diameter, that the air may be violently expelled through this narrow aperture.

There now remain the liquation thorns, the ash-coloured copper, the "slags," and the _cadmia_.[27] Liquation cakes are made from thorns in the following manner.[28] There are taken three-quarters of a _centumpondium_ of thorns, which have their origin from the cakes of copper-lead alloy when lead-silver is liquated, and as many parts of a _centumpondium_ of the thorns derived from cakes made from once re-melted thorns by the same method, and to them are added a _centumpondium_ of de-silverized lead and half a _centumpondium_ of hearth-lead. If there is in the works plenty of litharge, it is subst.i.tuted for the de-silverized lead. One and a half _centumpondia_ of litharge and hearth-lead is added to the same weight of primary thorns, and half a _centumpondium_ of thorns which have their origin from liquation cakes composed of thorns twice re-melted by the same method (tertiary thorns), and a fourth part of a _centumpondium_ of thorns which are produced when the exhausted liquation cakes are "dried." By both methods one single liquation cake is made from three _centumpondia_. In this manner the smelter makes every day fifteen liquation cakes, more or less; he takes great care that the metallic substances, from which the first liquation cake is made, flow down properly and in due order into the forehearth, before the material of which the subsequent cake is to be made. Five of these liquation cakes are put simultaneously into the furnace in which silver-lead is liquated from copper, they weigh almost fourteen _centumpondia_, and the "slags"

made therefrom usually weigh quite a _centumpondium_. In all the liquation cakes together there is usually one _libra_ and nearly two _unciae_ of silver, and in the silver-lead which drips from those cakes, and weighs seven and a half _centumpondia_, there is in each an _uncia_ and a half of silver. In each of the three _centumpondia_ of liquation thorns there is almost an _uncia_ of silver, and in the two _centumpondia_ and a quarter of exhausted liquation cakes there is altogether one and a half _unciae_; yet this varies greatly for each variety of thorns, for in the thorns produced from primary liquation cakes made of copper and lead when silver-lead is liquated from the copper, and those produced in "drying" the exhausted liquation cakes, there are almost two _unciae_ of silver; in the others not quite an _uncia_. There are other thorns besides, of which I will speak a little further on.

Those in the Carpathian Mountains who make liquation cakes from the copper "bottoms" which remain after the upper part of the copper is divided from the lower, in the furnace similar to an oven, produce thorns when the poor or mediocre silver-lead is liquated from the copper. These, together with those made of cakes of re-melted thorns, or made with re-melted litharge, are placed in a heap by themselves; but those that are made from cakes melted from hearth-lead are placed in a heap separate from the first, and likewise those produced from "drying"

the exhausted liquation cakes are placed separately; from these thorns liquation cakes are made. From the first heap they take the fourth part of a _centumpondium_, from the second the same amount, from the third a _centumpondium_,--to which thorns are added one and a half _centumpondia_ of litharge and half a _centumpondium_ of hearth-lead, and from these, melted in the blast furnace, a liquation cake is made; each workman makes twenty such cakes every day. But of theirs enough has been said for the present; I will return to ours.

The ash-coloured copper[29] which is chipped off, as I have stated, from the "dried" cakes, used some years ago to be mixed with the thorns produced from liquation of the copper-lead alloy, and contained in themselves, equally with the first, two _unciae_ of silver; but now it is mixed with the concentrates washed from the accretions and the other material. The inhabitants of the Carpathian Mountains melt this kind of copper in furnaces in which are re-melted the "slags" which flow out when the copper is refined; but as this soon melts and flows down out of the furnace, two workmen are required for the work of smelting, one of whom smelts, while the other takes out the thick cakes from the forehearth. These cakes are only "dried," and from the "dried" cakes copper is again made.

The "slags"[30] are melted continually day and night, whether they have been drawn off from the alloyed metals with a rabble, or whether they adhered to the forehearth to the thickness of a digit and made it smaller and were taken off with spatulas. In this manner two or three liquation cakes are made, and afterward much or little of the "slag,"

skimmed from the molten alloy of copper and lead, is re-melted. Such liquation cakes should weigh up to three _centumpondia_, in each of which there is half an _uncia_ of silver. Five cakes are placed at the same time in the furnace in which argentiferous lead is liquated from copper, and from these are made lead which contains half an _uncia_ of silver to the _centumpondium_. The exhausted liquation cakes are laid upon the other baser exhausted liquation cakes, from both of which yellow copper is made. The base thorns thus obtained are re-melted with a few baser "slags," after having been sprinkled with concentrates from furnace accretions and other material, and in this manner six or seven liquation cakes are made, each of which weighs some two _centumpondia_.

Five of these are placed at the same time in the furnace in which silver-lead is liquated from copper; these drip three _centumpondia_ of lead, each of which contains half an _uncia_ of silver. The basest thorns thus produced should be re-melted with only a little "slag." The copper alloyed with lead, which flows down from the furnace into the forehearth, is poured out with a ladle into oblong copper moulds; these cakes are "dried" with base exhausted liquation cakes. The thorns they produce are added to the base thorns, and they are made into cakes according to the method I have described. From the "dried" cakes they make copper, of which some add a small portion to the best "dried" cakes when copper is made from them, in order that by mixing the base copper with the good it may be sold without loss. The "slags," if they are utilisable, are re-melted a second and a third time, the cakes made from them are "dried," and from the "dried" cakes is made copper, which is mixed with the good copper. The "slags," drawn off by the master who makes copper out of "dried" cakes, are sifted, and those which fall through the sieve into a vessel placed underneath are washed; those which remain in it are emptied into a wheelbarrow and wheeled away to the blast furnaces, and they are re-melted together with other "slags,"

over which are sprinkled the concentrates from washing the slags or furnace accretions made at this time. The copper which flows out of the furnace into the forehearth, is likewise dipped out with a ladle into oblong copper moulds; in this way nine or ten cakes are made, which are "dried," together with bad exhausted liquation cakes, and from these "dried" cakes yellow[31] copper is made.