De Re Metallica Part 45

When the cakes have been thus arranged through the hole at the top of the dome, he throws in charcoal with a basket woven of wooden twigs.

Then he places the lid over the dome, and the a.s.sistant covers over the joints with lute. The master himself throws half a basketful of charcoal into the crucible through the aperture next to the nozzle pipe, and prepares the bellows, in order to be able to begin the second operation on the morning of the following day. It takes the s.p.a.ce of one hour to carry out such a piece of work, and at twelve all is prepared. These hours all reckoned up make a sum of eight hours.

Now it is time that we should come to the second operation. In the morning the workman takes up two shovelsful of live charcoals and throws them into the crucible through the aperture next to the pipes of the nozzles; then through the same hole he lays upon them small pieces of fir-wood or of pitch pine, such as are generally used to cook fish.

After this the water-gates are opened, in order that the machine may be turned which depresses the levers of the bellows. In the s.p.a.ce of one hour the lead alloy is melted; and when this has been done, he places four sticks of wood, twelve feet long, through the hole in the back of the dome, and as many through the channel; these sticks, lest they should damage the crucible, are both weighted on the ends and supported by trestles; these trestles are made of a beam, three feet long, two palms and as many digits wide, two palms thick, and have two spreading legs at each end. Against the trestle, in front of the channel, there is placed an iron plate, lest the litharge, when it is extracted from the furnace, should splash the smelter's shoes and injure his feet and legs.

With an iron shovel or a fork he places the remainder of the cakes through the aperture at the back of the dome on to the sticks of wood already mentioned.

The native silver, or silver glance, or grey silver, or ruby silver, or any other sort, when it has been flattened out[32], and cut up, and heated in an iron crucible, is poured into the molten lead mixed with silver, in order that impurities may be separated. As I have often said, this molten lead mixed with silver is called _stannum_[33].

[Ill.u.s.tration 474 (Cupellation Furnace): A--Furnace. B--Sticks of wood.

C--Litharge. D--Plate. E--The foreman when hungry eats b.u.t.ter, that the poison which the crucible exhales may not harm him, for this is a special remedy against that poison.]

When the long sticks of wood are burned up at the fore end, the master, with a hammer, drives into them pointed iron bars, four feet long and two digits wide at the front end, and beyond that one and a half digits wide and thick; with these he pushes the sticks of wood forward and the bars then rest on the trestles. There are others who, when they separate metals, put two such sticks of wood into the crucible through the aperture which is between the bellows, as many through the holes at the back, and one through the channel; but in this case a larger number of long sticks of wood is necessary, that is, sixty; in the former case, forty long sticks of wood suffice to carry out the operation. When the lead has been heated for two hours, it is stirred with a hooked bar, that the heat may be increased.

If it be difficult to separate the lead from the silver, he throws copper and charcoal dust into the molten silver-lead alloy. If the alloy of argentiferous gold and lead, or the silver-lead alloy, contains impurities from the ore, then he throws in either equal portions of argol and Venetian gla.s.s or of sal-ammoniac, or of Venetian gla.s.s and of Venetian soap; or else unequal portions, that is, two of argol and one of iron rust; there are some who mix a little saltpetre with each compound. To one _centumpondium_ of the alloy is added a _bes_ or a _libra_ and a third of the powder, according to whether it is more or less impure. The powder certainly separates the impurities from the alloy. Then, with a kind of rabble he draws out through the channel, mixed with charcoal, the sc.u.m, as one might say, of the lead; the lead makes this sc.u.m when it becomes hot, but that less of it may be made it must be stirred frequently with the bar.

Within the s.p.a.ce of a quarter of an hour the crucible absorbs the lead; at the time when it penetrates into the crucible it leaps and bubbles.

Then the master takes out a little lead with an iron ladle, which he a.s.says, in order to find what proportion of silver there is in the whole of the alloy; the ladle is five digits wide, the iron part of its handle is three feet long and the wooden part the same. Afterward, when they are heated, he extracts with a bar the litharge which comes from the lead and the copper, if there be any of it in the alloy. Wherefore, it might more rightly be called _spuma_ of lead than of silver[34]. There is no injury to the silver, when the lead and copper are separated from it. In truth the lead becomes much purer in the crucible of the other furnace, in which silver is refined. In ancient times, as the author Pliny[35] relates, there was under the channel of the crucible another crucible, and the litharge flowed down from the upper one into the lower one, out of which it was lifted up and rolled round with a stick in order that it might be of moderate weight. For which reason, they formerly made it into small tubes or pipes, but now, since it is not rolled round a stick, they make it into bars.

If there be any danger that the alloy might flow out with the litharge, the foreman keeps on hand a piece of lute, shaped like a cylinder and pointed at both ends; fastening this to a hooked bar he opposes it to the alloy so that it will not flow out.

[Ill.u.s.tration 476 (Cleansing of Silver Cakes): A--Cake. B--Stone.

C--Hammer. D--Bra.s.s wire. E--Bucket containing water. F--Furnace from which the cake has been taken, which is still smoking. G--Labourer carrying a cake out of the works.]

Now when the colour begins to show in the silver, bright spots appear, some of them being almost white, and a moment afterward it becomes absolutely white. Then the a.s.sistant lets down the water-gates, so that, the race being closed, the water-wheel ceases to turn and the bellows are still. Then the master pours several buckets of water on to the silver to cool it; others pour beer over it to make it whiter, but this is of no importance since the silver has yet to be refined. Afterward, the cake of silver is raised with the pointed iron bar, which is three feet long and two digits wide, and has a wooden handle four feet long fixed in its socket. When the cake of silver has been taken from the crucible, it is laid upon a stone, and from part of it the hearth-lead, and from the other part the litharge, is chipped away with a hammer; then it is cleansed with a bundle of bra.s.s wire dipped in water. When the lead is separated from the silver, more silver is frequently found than when it was a.s.sayed; for instance, if before there were three _unciae_ and as many _drachmae_ in a _centumpondium_, they now sometimes find three _unciae_ and a half[36]. Often the hearth-lead remaining in the crucible is a palm deep; it is taken out with the rest of the ashes and is sifted, and that which remains in the sieve, since it is hearth-lead, is added to the hearth-lead[37].

The ashes which pa.s.s through the sieve are of the same use as they were at first, for, indeed, from these and pulverised bones they make the cupels. Finally, when much of it has acc.u.mulated, the yellow _pompholyx_ adhering to the walls of the furnace, and likewise to those rings of the dome near the apertures, is cleared away.

[Ill.u.s.tration 479 (Crane for cupellation furnace): A--Crane-post.

B--Socket. C--Oak cross-sills. D--Band. E--Roof-beam. F--Frame. G--Lower small cross-beam. H--Upright timber. I--Bars which come from the sides of the crane-post. K--Bars which come from the sides of the upright timber. L--Rundle drums. M--Toothed wheels. N--Chain. O--Pulley.

P--Beams of the crane-arm. Q--Oblique beams supporting the beams of the crane-arm. R--Rectangular iron plates. S--Trolley. T--Dome of the furnace. V--Ring. X--Three chains. Y--Crank. Z--The crane-post of the other contrivance. AA--Crane-arm. BB--Oblique beam. CC--Ring of the crane-arm. DD--The second ring. EE--Lever-bar. FF--Third ring. GG--Hook.

HH--Chain of the dome. II--Chain of the lever-bar.]

I must also describe the crane with which the dome is raised. When it is made, there is first set up a rectangular upright post twelve feet long, each side of which measures a foot in width. Its lower pinion turns in a bronze socket set in an oak sill; there are two sills placed crosswise so that the one fits in a mortise in the middle of the other, and the other likewise fits in the mortise of the first, thus making a kind of a cross; these sills are three feet long and one foot wide and thick. The crane-post is round at its upper end and is cut down to a depth of three palms, and turns in a band fastened at each end to a roof-beam, from which springs the inclined chimney wall. To the crane-post is affixed a frame, which is made in this way: first, at a height of a cubit from the bottom, is mortised into the crane-post a small cross-beam, a cubit and three digits long, except its tenons, and two palms in width and thickness. Then again, at a height of five feet above it, is another small cross-beam of equal length, width, and thickness, mortised into the crane-post. The other ends of these two small cross-beams are mortised into an upright timber, six feet three palms long, and three-quarters wide and thick; the mortise is transfixed by wooden pegs.

Above, at a height of three palms from the lower small cross-beam, are two bars, one foot one palm long, not including the tenons, a palm three digits wide, and a palm thick, which are mortised in the other sides of the crane-post. In the same manner, under the upper small cross-beam are two bars of the same size. Also in the upright timber there are mortised the same number of bars, of the same length as the preceding, but three digits thick, a palm two digits wide, the two lower ones being above the lower small cross-beam. From the upright timber near the upper small cross-beam, which at its other end is mortised into the crane-post, are two mortised bars. On the outside of this frame, boards are fixed to the small cross-beams, but the front and back parts of the frame have doors, whose hinges are fastened to the boards which are fixed to the bars that are mortised to the sides of the crane-post.

Then boards are laid upon the lower small cross-beam, and at a height of two palms above these there is a small square iron axle, the sides of which are two digits wide; both ends of it are round and turn in bronze or iron bearings, one of these bearings being fastened in the crane-post, the other in the upright timber. About each end of the small axle is a wooden disc, of three palms and a digit radius and one palm thick, covered on the rim with an iron band; these two discs are distant two palms and as many digits from each other, and are joined with five rundles; these rundles are two and a half digits thick and are placed three digits apart. Thus a drum is made, which is a palm and a digit distant from the upright timber, but further from the crane-post, namely, a palm and three digits. At a height of a foot and a palm above this little axle is a second small square iron axle, the thickness of which is three digits; this one, like the first one, turns in bronze or iron bearings. Around it is a toothed wheel, composed of two discs a foot three palms in diameter, a palm and two digits thick; on the rim of this there are twenty-three teeth, a palm wide and two digits thick; they protrude a palm from the wheel and are three digits apart. And around this same axle, at a distance of two palms and as many digits toward the upright timber, is another disc of the same diameter as the wheel and a palm thick; this turns in a hollowed-out place in the upright timber. Between this disc and the disc of the toothed wheel another drum is made, having likewise five rundles. There is, in addition to this second axle, at a height of a cubit above it, a small wooden axle, the journals of which are of iron; the ends are bound round with iron rings so that the journals may remain firmly fixed, and the journals, like the little iron axles, turn in bronze or iron bearings.

This third axle is at a distance of about a cubit from the upper small cross-beam; it has, near the upright timber, a toothed wheel two and a half feet in diameter, on the rim of which are twenty-seven teeth; the other part of this axle, near the crane-post, is covered with iron plates, lest it should be worn away by the chain which winds around it.

The end link of the chain is fixed in an iron pin driven into the little axle; this chain pa.s.ses out of the frame and turns over a little pulley set between the beams of the crane-arm.

Above the frame, at a height of a foot and a palm, is the crane-arm.

This consists of two beams fifteen feet long, three palms wide, and two thick, mortised into the crane-post, and they protrude a cubit from the back of the crane-post and are fastened together. Moreover, they are fastened by means of a wooden pin which penetrates through them and the crane-post; this pin has at the one end a broad head, and at the other a hole, through which is driven an iron bolt, so that the beams may be tightly bound into the crane-post. The beams of the crane-arm are supported and stayed by means of two oblique beams, six feet and two palms long, and likewise two palms wide and thick; these are mortised into the crane-post at their lower ends, and their upper ends are mortised into the beams of the crane-arm at a point about four feet from the crane-post, and they are fastened with iron nails. At the back of the upper end of these oblique beams, toward the crane-post, is an iron staple, fastened into the lower sides of the beams of the crane-arm, in order that it may hold them fast and bind them. The outer end of each beam of the crane-arm is set in a rectangular iron plate, and between these are three rectangular iron plates, fixed in such a manner that the beams of the crane-arm can neither move away from, nor toward, each other. The upper sides of these crane-arm beams are covered with iron plates for a length of six feet, so that a trolley can move on it.

The body of the trolley is made of wood from the Ostrya or any other hard tree, and is a cubit long, a foot wide, and three palms thick; on both edges of it the lower side is cut out to a height and width of a palm, so that the remainder may move backward and forward between the two beams of the crane-arm; at the front, in the middle part, it is cut out to a width of two palms and as many digits, that a bronze pulley, around a small iron axle, may turn in it. Near the corners of the trolley are four holes, in which as many small wheels travel on the beams of the crane-arm. Since this trolley, when it travels backward and forward, gives out a sound somewhat similar to the barking of a dog, we have given it this name[38]. It is propelled forward by means of a crank, and is drawn back by means of a chain. There is an iron hook whose ring turns round an iron pin fastened to the right side of the trolley, which hook is held by a sort of clavis, which is fixed in the right beam of the crane-arm.

At the end of the crane-post is a bronze pulley, the iron axle of which is fastened in the beams of the crane-arm, and over which the chain pa.s.ses as it comes from the frame, and then, penetrating through the hollow in the top of the trolley, it reaches to the little bronze pulley of the trolley, and pa.s.sing over this it hangs down. A hook on its end engages a ring, in which are fixed the top links of three chains, each six feet long, which pa.s.s through the three iron rings fastened in the holes of the claves which are fixed into the middle iron band of the dome, of which I have spoken.

Therefore when the master wishes to lift the dome by means of the crane, the a.s.sistant fits over the lower small iron axle an iron crank, which projects from the upright beam a palm and two digits; the end of the little axle is rectangular, and one and a half digits wide and one digit thick; it is set into a similar rectangular hole in the crank, which is two digits long and a little more than a digit wide. The crank is semi-circular, and one foot three palms and two digits long, as many digits wide, and one digit thick. Its handle is straight and round, and three palms long, and one and a half digits thick. There is a hole in the end of the little axle, through which an iron pin is driven so that the crank may not come off. The crane having four drums, two of which are rundle-drums and two toothed-wheels, is more easily moved than another having two drums, one of which has rundles and the other teeth.

Many, however, use only a simple contrivance, the pivots of whose crane-post turn in the same manner, the one in an iron socket, the other in a ring. There is a crane-arm on the crane-post, which is supported by an oblique beam; to the head of the crane-arm a strong iron ring is fixed, which engages a second iron ring. In this iron ring a strong wooden lever-bar is fastened firmly, the head of which is bound by a third iron ring, from which hangs an iron hook, which engages the rings at the ends of the chains from the dome. At the other end of the lever-bar is another chain, which, when it is pulled down, raises the opposite end of the bar and thus the dome; and when it is relaxed the dome is lowered.

[Ill.u.s.tration 481 (Cupellation Furnace at Freiberg): A--Chamber of the furnace. B--Its bed. C--Pa.s.sages. D--Rammer. E--Mallet. F--Artificer making tubes from litharge according to the Roman method. G--Channel.

H--Litharge. I--Lower crucible or hearth. K--Stick. L--Tubes.]

In certain places, as at Freiberg in Meissen, the upper part of the cupellation furnace is vaulted almost like an oven. This chamber is four feet high and has either two or three apertures, of which the first, in front, is one and a half feet high and a foot wide, and out of this flows the litharge; the second aperture and likewise the third, if there be three, are at the sides, and are a foot and a half high and two and a half feet wide, in order that he who prepares the crucible may be able to creep into the furnace. Its circular bed is made of cement, it has two pa.s.sages two feet high and one foot wide, for letting out the vapour, and these lead directly through from one side to the other, so that the one pa.s.sage crosses the other at right angles, and thus four openings are to be seen; these are covered at the top by rocks, wide, but only a palm thick. On these and on the other parts of the interior of the bed made of cement, is placed lute mixed with straw, to a depth of three digits, as it was placed over the sole and the plates of copper and the rocks of that other furnace. This, together with the ashes which are thrown in, the master or the a.s.sistant, who, upon his knees, prepares the crucible, tamps down with short wooden rammers and with mallets likewise made of wood.

[Ill.u.s.tration 482 (Cupellation Furnace in Poland): A--Furnace similar to an oven. B--Pa.s.sage. C--Iron bars. D--Hole through which the litharge is drawn out. E--Crucible which lacks a dome. F--Thick sticks. G--Bellows.]

The cupellation furnace in Poland and Hungary is likewise vaulted at the top, and is almost similar to an oven, but in the lower part the bed is solid, and there is no opening for the vapours, while on one side of the crucible is a wall, between which and the bed of the crucible is a pa.s.sage in place of the opening for vapours; this pa.s.sage is covered by iron bars or rods extending from the wall to the crucible, and placed a distance of two digits from each other. In the crucible, when it is prepared, they first scatter straw, and then they lay in it cakes of silver-lead alloy, and on the iron bars they lay wood, which when kindled heats the crucible. They melt cakes to the weight of sometimes eighty _centumpondia_ and sometimes a hundred _centumpondia_[39]. They stimulate a mild fire by means of a blast from the bellows, and throw on to the bars as much wood as is required to make a flame which will reach into the crucible, and separate the lead from the silver. The litharge is drawn out on the other side through an aperture that is just wide enough for the master to creep through into the crucible. The Moravians and Carni, who very rarely make more than a _bes_ or five-sixths of a _libra_ of silver, separate the lead from it, neither in a furnace resembling an oven, nor in the crucible covered by a dome, but on a crucible which is without a cover and exposed to the wind; on this crucible they lay cakes of silver-lead alloy, and over them they place dry wood, and over these again thick green wood. The wood having been kindled, they stimulate the fire by means of a bellows.

[Ill.u.s.tration 484 (Refining Silver): A--Pestle with teeth. B--Pestle without teeth. C--Dish or tray full of ashes. D--Prepared tests placed on boards or shelves. E--Empty tests. F--Wood. G--Saw.]

[Ill.u.s.tration 485 (Refining Silver): A--Straight knife having wooden handles. B--Curved knife likewise having wooden handles. C--Curved knife without wooden handles. D--Sieve. E--b.a.l.l.s. F--Iron door which the master lets down when he refines silver, lest the heat of the fire should injure his eyes. G--Iron implement on which the wood is placed when the liquid silver is to be refined. H--Its other part pa.s.sing through the ring of another iron implement enclosed in the wall of the furnace. I--Tests in which burning charcoal has been thrown.]

I have explained the method of separating lead from gold or silver. Now I will speak of the method of refining silver, for I have already explained the process for refining gold. Silver is refined in a refining furnace, over whose hearth is an arched chamber built of bricks; this chamber in the front part is three feet high. The hearth itself is five feet long and four wide. The walls are unbroken along the sides and back, but in front one chamber is placed over the other, and above these and the wall is the upright chimney. The hearth has a round pit, a cubit wide and two palms deep, into which are thrown sifted ashes, and in this is placed a prepared earthenware "test," in such a manner that it is surrounded on all sides by ashes to a height equal to its own. The earthenware test is filled with a powder consisting of equal portions of bones ground to powder, and of ashes taken from the crucible in which lead is separated from gold or silver; others mix crushed brick with the ashes, for by this method the powder attracts no silver to itself. When the powder has been made up and moistened with water, a little is thrown into the earthenware test and tamped with a wooden pestle. This pestle is round, a foot long, and a palm and a digit wide, out of which extend six teeth, each a digit thick, and a digit and a third long and wide, and almost a digit apart; these six teeth form a circle, and in the centre of them is the seventh tooth, which is round and of the same length as the others, but a digit and a half thick; this pestle tapers a little from the bottom up, that the upper part of the handle may be round and three digits thick. Some use a round pestle without teeth.

Then a little powder is again moistened, and thrown into the test, and tamped; this work is repeated until the test is entirely full of the powder, which the master then cuts out with a knife, sharp on both sides, and turned upward at both ends so that the central part is a palm and a digit long; therefore it is partly straight and partly curved. The blade is one and a half digits wide, and at each end it turns upward two palms, which ends to the depth of a palm are either not sharpened or they are enclosed in wooden handles. The master holds the knife with one hand and cuts out the powder from the test, so that it is left three digits thick all round; then he sifts the powder of dried bones over it through a sieve, the bottom of which is made of closely-woven bristles.

Afterward a ball made of very hard wood, six digits in diameter, is placed in the test and rolled about with both hands, in order to make the inside even and smooth; for that matter he may move the ball about with only one hand. The tests[40] are of various capacities, for some of them when prepared hold much less than fifteen _librae_ of silver, others twenty, some thirty, others forty, and others fifty. All these tests thus prepared are dried in the sun, or set in a warm and covered place; the more dry and old they are the better. All of them, when used for refining silver, are heated by means of burning charcoal placed in them. Others use instead of these tests an iron ring; but the test is more useful, for if the powder deteriorates the silver remains in it, while there being no bottom to the ring, it falls out; besides, it is easier to place in the hearth the test than the iron ring, and furthermore it requires much less powder. In order that the test should not break and damage the silver, some bind it round with an iron band.

[Ill.u.s.tration 486 (Refining Silver): A--Grate. B--Bra.s.s block. C--Block of wood. D--Cakes of silver. E--Hammer. F--Block of wood channelled in the middle. G--Bowl full of holes. H--Block of wood fastened to an iron implement. I--Fir-wood. K--Iron bar. L--Implement with a hollow end. The implement which has a circular end is shown in the next picture.

M--Implement, the extremity of which is bent upwards. N--Implement in the shape of tongs.]

In order that they may be more easily broken, the silver cakes are placed upon an iron grate by the refiner, and are heated by burning charcoal placed under them. He has a bra.s.s block two palms and two digits long and wide, with a channel in the middle, which he places upon a block of hard wood. Then with a double-headed hammer, he beats the hot cakes of silver placed on the bra.s.s block, and breaks them in pieces.

The head of this hammer is a foot and two digits long, and a palm wide.

Others use for this purpose merely a block of wood channelled in the top. While the fragments of the cake are still hot, he seizes them with the tongs and throws them into a bowl with holes in the bottom, and pours water over them. When the fragments are cooled, he puts them nicely into the test by placing them so that they stand upright and project from the test to a height of two palms, and lest one should fall against the other, he places little pieces of charcoal between them; then he places live charcoal in the test, and soon two twig basketsful of charcoal. Then he blows in air with the bellows. This bellows is double, and four feet two palms long, and two feet and as many palms wide at the back; the other parts are similar to those described in Book VII. The nozzle of the bellows is placed in a bronze pipe a foot long, the aperture in this pipe being a digit in diameter in front and quite round, and at the back two palms wide. The master, because he needs for the operation of refining silver a fierce fire, and requires on that account a vigorous blast, places the bellows very much inclined, in order that, when the silver has melted, it may blow into the centre of the test. When the silver bubbles, he presses the nozzle down by means of a small block of wood moistened with water and fastened to an iron rod, the outer end of which bends upward. The silver melts when it has been heated in the test for about an hour; when it is melted, he removes the live coals from the test and places over it two billets of fir-wood, a foot and three palms long, a palm two digits wide, one palm thick at the upper part, and three digits at the lower. He joins them together at the lower edges, and into the billets he again throws the coals, for a fierce fire is always necessary in refining silver. It is refined in two or three hours, according to whether it was pure or impure, and if it is impure it is made purer by dropping granulated copper or lead into the test at the same time. In order that the refiner may sustain the great heat from the fire while the silver is being refined, he lets down an iron door, which is three feet long and a foot and three palms high; this door is held on both ends in iron plates, and when the operation is concluded, he raises it again with an iron shovel, so that its edge holds against the iron hook in the arch, and thus the door is held open.

When the silver is nearly refined, which may be judged by the s.p.a.ce of time, he dips into it an iron bar, three and a half feet long and a digit thick, having a round steel point. The small drops of silver that adhere to the bar he places on the bra.s.s block and flattens with a hammer, and from their colour he decides whether the silver is sufficiently refined or not. If it is thoroughly purified it is very white, and in a _bes_ there is only a _drachma_ of impurities. Some ladle up the silver with a hollow iron implement. Of each _bes_ of silver one _sicilicus_ is consumed, or occasionally when very impure, three _drachmae_ or half an _uncia_[41].

[Ill.u.s.tration 488 (Cleansing of Silver Cakes): A--Implement with a ring.

B--Ladle. C--Its hole. D--Pointed bar. E--Forks. F--Cake of silver laid upon the implement shaped like tongs. G--Tub of water. H--Block of wood, with a cake laid upon it. I--Hammer. K--Silver again placed upon the implement resembling tongs. L--Another tub full of water. M--Bra.s.s wires. N--Tripod. O--Another block. P--Chisel. Q--Crucible of the furnace. R--Test still smoking.]

The refiner governs the fire and stirs the molten silver with an iron implement, nine feet long, a digit thick, and at the end first curved toward the right, then curved back in order to form a circle, the interior of which is a palm in diameter; others use an iron implement, the end of which is bent directly upward. Another iron implement has the shape of tongs, with which, by compressing it with his hands, he seizes the coals and puts them on or takes them off; this is two feet long, one and a half digits wide, and the third of a digit thick.

When the silver is seen to be thoroughly refined, the artificer removes the coals from the test with a shovel. Soon afterward he draws water in a copper ladle, which has a wooden handle four feet long; it has a small hole at a point half-way between the middle of the bowl and the edge, through which a hemp seed just pa.s.ses. He fills this ladle three times with water, and three times it all flows out through the hole on to the silver, and slowly quenches it; if he suddenly poured much water on it, it would burst asunder and injure those standing near. The artificer has a pointed iron bar, three feet long, which has a wooden handle as many feet long, and he puts the end of this bar into the test in order to stir it. He also stirs it with a hooked iron bar, of which the hook is two digits wide and a palm deep, and the iron part of its handle is three feet long and the wooden part the same. Then he removes the test from the hearth with a shovel or a fork, and turns it over, and by this means the silver falls to the ground in the shape of half a sphere; then lifting the cake with a shovel he throws it into a tub of water, where it gives out a great sound. Or else, having lifted the cake of silver with a fork, he lays it upon the iron implement similar to tongs, which are placed across a tub full of water; afterward, when cooled, he takes it from the tub again and lays it on the block made of hard wood and beats it with a hammer, in order to break off any of the powder from the test which adheres to it. The cake is then placed on the implement similar to tongs, laid over the tub full of water, and cleaned with a bundle of bra.s.s wire dipped into the water; this operation of beating and cleansing is repeated until it is all clean. Afterward he places it on an iron grate or tripod; the tripod is a palm and two digits high, one and a half digits wide, and its span is two palms wide; then he puts burning charcoal under the tripod or grate, in order again to dry the silver that was moistened by the water. Finally, the Royal Inspector[42]

in the employment of the King or Prince, or the owner, lays the silver on a block of wood, and with an engraver's chisel he cuts out two small pieces, one from the under and the other from the upper side. These are tested by fire, in order to ascertain whether the silver is thoroughly refined or not, and at what price it should be sold to the merchants.

Finally he impresses upon it the seal of the King or the Prince or the owner, and, near the same, the amount of the weight.

[Ill.u.s.tration 489 (Refining Silver): A--m.u.f.fle. B--Its little windows.

C--Its little bridge. D--Bricks. E--Iron door. F--Its little window.

G--Bellows. H--Hammer-chisel. I--Iron ring which some use instead of the test. K--Pestle with which the ashes placed in the ring are pounded.]

There are some who refine silver in tests placed under iron or earthenware m.u.f.fles. They use a furnace, on the hearth of which they place the test containing the fragments of silver, and they place the m.u.f.fle over it; the m.u.f.fle has small windows at the sides, and in front a little bridge. In order to melt the silver, at the sides of the m.u.f.fle are laid bricks, upon which the charcoal is placed, and burning firebrands are put on the bridge. The furnace has an iron door, which is covered on the side next to the fire with lute in order that it may not be injured. When the door is closed it retains the heat of the fire, but it has a small window, so that the artificers may look into the test and may at times stimulate the fire with the bellows. Although by this method silver is refined more slowly than by the other, nevertheless it is more useful, because less loss is caused, for a gentle fire consumes fewer particles than a fierce fire continually excited by the blast of the bellows. If, on account of its great size, the cake of silver can be carried only with difficulty when it is taken out of the m.u.f.fle, they cut it up into two or three pieces while it is still hot, with a wedge or a hammer-chisel; for if they cut it up after it has cooled, little pieces of it frequently fly off and are lost.

END OF BOOK X.

FOOTNOTES:

[1] _Vile a precioso_.

[2] The reagents mentioned in this Book are much the same as those of Book VII, where (p. 220) a table is given showing the Latin and Old German terms. Footnotes in explanation of our views as to these substances may be most easily consulted through the index.