BOOK XI.

Different methods of parting gold from silver, and, on the other hand, silver from gold, were discussed in the last book; also the separation of copper from the latter, and further, of lead from gold as well as from silver; and, lastly, the methods for refining the two precious metals. Now I will speak of the methods by which silver must be separated from copper, and likewise from iron.[1] [Illustration 493 (Building Plan for Refinery): Six long walls: A--The first. B--The first part of the second. C--The further part of the second. D--The third. E--The fourth. F--The fifth. G--The sixth. Fourteen transverse walls: H--The first. I--The second. K--The third. L--The fourth. M--The fifth. N--The sixth. O--The seventh. P--The eighth. Q--The ninth. R--The tenth. S--The eleventh. T--The twelfth. V--The thirteenth. X--The fourteenth.] The _officina_, or the building necessary for the purposes and use of those who separate silver from copper, is constructed in this manner. First, four long walls are built, of which the first, which is parallel with the bank of a stream, and the second, are both two hundred and sixty-four feet long. The second, however, stops at one hundred and fifty-one feet, and after, as it were, a break for a length of twenty-four feet, it continues again until it is of a length equal to the first wall. The third wall is one hundred and twenty feet long, starting at a point opposite the sixty-seventh foot of the other walls, and reaching to their one hundred and eighty-sixth foot. The fourth wall is one hundred and fifty-one feet long. The height of each of these walls, and likewise of the other two and of the transverse walls, of which I will speak later on, is ten feet, and the thickness two feet and as many palms. The second long wall only is built fifteen feet high, because of the furnaces which must be built against it. The first long wall is distant fifteen feet from the second, and the third is distant the same number of feet from the fourth, but the second is distant thirty-nine feet from the third. Then transverse walls are built, the first of which leads from the beginning of the first long wall to the beginning of the second long wall; and the second transverse wall from the beginning of the second long wall to the beginning of the fourth long wall, for the third long wall does not reach so far. Then from the beginning of the third long wall are built two walls--the one to the sixty-seventh foot of the second long wall, the other to the same point in the fourth long wall. The fifth transverse wall is built at a distance of ten feet from the fourth transverse wall toward the second transverse wall; it is twenty feet long, and starts from the fourth long wall. The sixth transverse wall is built also from the fourth long wall, at a point distant thirty feet from the fourth transverse wall, and it extends as far as the back of the third long wall. The seventh transverse wall is constructed from the second long wall, where this first leaves off, to the third long wall; and from the back of the third long wall the eighth transverse wall is built, extending to the end of the fourth long wall. Then the fifth long wall is built from the seventh transverse wall, starting at a point nineteen feet from the second long wall; it is one hundred and nine feet in length; and at a point twenty-four feet along it, the ninth transverse wall is carried to the third end of the second long wall, where that begins again. The tenth transverse wall is built from the end of the fifth long wall, and leads to the further end of the second long wall; and from there the eleventh transverse wall leads to the further end of the first long wall. Behind the fifth long wall, and five feet toward the third long wall, the sixth long wall is built, leading from the seventh transverse wall; its length is thirty-five feet, and from its further end the twelfth transverse wall is built to the third long wall, and from it the thirteenth transverse wall is built to the fifth long wall. The fourteenth transverse wall divides into equal parts the space which lies between the seventh transverse wall and the twelfth. The length, height, breadth, and position of the walls are as above. Their archways, doors, and openings are made at the same time that the walls are built. The size of these and the way they are made will be much better understood hereafter. I will now speak of the furnace hoods and of the roofs. The first side[2] of the hood stands on the second long wall, and is similar in every respect to those whose structure I explained in Book IX, when I described the works in whose furnaces are smelted the ores of gold, silver, and copper. From this side of the hood a roof, which consists of burnt tiles, extends to the first long wall; and this part of the building contains the bellows, the machinery for compressing them, and the instruments for inflating them. In the middle space, which is situated between the second and third transverse walls, an upright post eight feet high and two feet thick and wide, is erected on a rock foundation, and is distant thirteen feet from the second long wall. On that upright post, and in the second transverse wall, which has at that point a square hole two feet high and wide, is placed a beam thirty-four feet and a palm long. Another beam, of the same length, width, and thickness, is fixed on the same upright post and in the third transverse wall. The heads of those two beams, where they meet, are joined together with iron staples. In a similar manner another post is erected, at a distance of ten feet from the first upright post in the direction of the fourth wall, and two beams are laid upon it and into the same walls in a similar way to those I have just now described. On these two beams and on the fourth long wall are fixed seventeen cross-beams, forty-three feet and three palms long, a foot wide, and three palms thick; the first of these is laid upon the second transverse wall, the last lies along the third and fourth transverse walls; the rest are set in the space between them. These cross-beams are three feet apart one from the other. In the ends of these cross-beams, facing the second long wall, are mortised the ends of the same number of rafters reaching to those timbers which stand upright on the second long wall, and in this manner is made the inclined side of the hood in a similar way to the one described in Book IX. To prevent this from falling toward the vertical wall of the hood, there are iron rods securing it, but only a few, because the four brick chimneys which have to be built in that space partly support it. Twelve feet back are likewise mortised into the cross-beams, which lie upon the two longitudinal beams and the fourth long wall, the lower ends of as many rafters, whose upper ends are mortised into the upper ends of an equal number of similar rafters, whose lower ends are mortised to the ends of the beams at the fourth long wall. From the first set of rafters[4] to the second set of rafters is a distance of twelve feet, in order that a gutter may be well placed in the middle space. Between these two are again erected two sets of rafters, the lower ends of which are likewise mortised into the beams, which lie on the two longitudinal beams and the fourth long wall, and are interdistant a cubit. The upper ends of the ones fifteen feet long rest on the backs of the rafters of the first set; the ends of the others, which are eighteen feet long, rest on the backs of the rafters of the second set, which are longer; in this manner, in the middle of the rafters, is a sub-structure. Upon each alternate cross-beam which is placed upon the two longitudinal beams and the fourth long wall is erected an upright post, and that it may be sufficiently firm it is strengthened by means of a slanting timber. Upon these posts is laid a long beam, upon which rests one set of middle rafters. In a similar manner the other set of middle rafters rests on a long beam which is placed upon other posts. Besides this, two feet above every cross-beam, which is placed on the two longitudinal beams and the fourth long wall, is placed a tie-beam which reaches from the first set of middle rafters to the second set of middle rafters; upon the tie-beams is placed a gutter hollowed out from a tree. Then from the back of each of the first set of middle rafters a beam six feet long reaches almost to the gutter; to the lower end of this beam is attached a piece of wood two feet long; this is repeated with each rafter of the first set of middle rafters. Similarly from the back of each rafter of the second set of middle rafters a little beam, seven feet long, reaches almost to the gutter; to the lower end of it is likewise attached a short piece of wood; this is repeated on each rafter of the second set of middle rafters. Then in the upper part, to the first and second sets of principal rafters are fastened long boards, upon which are fixed the burnt tiles; and in the same manner, in the middle part, they are fastened to the first and second sets of middle rafters, and at the lower part to the little beams which reach from each rafter of the first and second set of middle rafters almost to the gutter; and, finally, to the little boards fastened to the short pieces of wood are fixed shingles of pine-wood extending into the gutter, so that the violent rain or melted snow may not penetrate into the building. The substructures in the interior which support the second set of rafters, and those on the opposite side which support the third, being not unusual, I need not explain. In that part of the building against the second long wall are the furnaces, in which exhausted liquation cakes which have already been "dried" are smelted, that they may recover once again the appearance and colour of copper, inasmuch as they really are copper. The remainder of the room is occupied by the passage which leads from the door to the furnaces, together with two other furnaces, in one of which the whole cakes of copper are heated, and in the other the exhausted liquation cakes are "dried" by the heat of the fire. Likewise, in the room between the third and seventh[5] transverse walls, two posts are erected on rock foundation; both of them are eight feet high and two feet wide and thick. The one is at a distance of thirteen feet from the second long wall; the other at the same distance from the third long wall; there is a distance of thirteen feet between them. Upon these two posts and upon the third transverse wall are laid two longitudinal beams, forty-one feet and one palm long, and two feet wide and thick. Two other beams of the same length, width, and thickness are laid upon the upright posts and upon the seventh transverse wall, and the heads of the two long beams, where they meet, are joined with iron staples. On these longitudinal beams are again placed twenty-one transverse beams, thirteen feet long, a foot wide, and three palms thick, of which the first is set on the third transverse wall, and the last on the seventh transverse wall; the rest are laid in the space between these two, and they are distant from one another three feet. Into the ends of the transverse beams which face the second long wall, are mortised the ends of the same number of rafters erected toward the upright posts which are placed upon the second long wall, and in this manner is made the second inclined side wall of the hood. Into the ends of the transverse beams facing the third long wall, are mortised the ends of the same number of rafters rising toward the rafters of the first inclined side of the second hood, and in this manner is made the other inclined side of the second hood. But to prevent this from falling in upon the opposite inclined side of the hood, and that again upon the opposite vertical one, there are many iron rods reaching from some of the rafters to those opposite them; and this is also prevented in part by means of a few tie-beams, extending from the back of the rafters to the back of those which are behind them. These tie-beams are two palms thick and wide, and have holes made through them at each end; each of the rafters is bound round with iron bands three digits wide and half a digit thick, which hold together the ends of the tie-beams of which I have spoken; and so that the joints may be firm, an iron nail, passing through the plate on both sides, is driven through the holes in the ends of the beams. Since one weight counter-balances another, the rafters on the opposite hoods cannot fall. The tie-beams and middle posts which have to support the gutters and the roof, are made in every particular as I stated above, except only that the second set of middle rafters are not longer than the first set of middle rafters, and that the little beams which reach from the back of each rafter of the second set of middle rafters nearly to the gutter are not longer than the little beams which reach from the back of each rafter of the first set of middle rafters almost to the gutter. In this part of the building, against the second long wall, are the furnaces in which copper is alloyed with lead, and in which "slags" are re-smelted. Against the third long wall are the furnaces in which silver and lead are liquated from copper. The interior is also occupied by two cranes, of which one deposits on the ground the cakes of copper lifted out of the moulding pans; the other lifts them from the ground into the second furnace. On the third and the fourth long walls are set twenty-one beams eighteen feet and three palms long. In mortises in them, two feet behind the third long wall, are set the ends of the same number of rafters erected opposite to the rafters of the other inclined wall of the second furnace hood, and in this manner is made the third inclined wall, exactly similar to the others. The ends of as many rafters are mortised into these beams where they are fixed in the fourth long wall; these rafters are erected obliquely, and rest against the backs of the preceding ones and support the roof, which consists entirely of burnt tiles and has the usual substructures. In this part of the building there are two rooms, in the first of which the cakes of copper, and in the other the cakes of lead, are stored. In the space enclosed between the ninth and tenth transverse walls and the second and fifth long walls, a post twelve feet high and two feet wide and thick is erected on a rock foundation; it is distant thirteen feet from the second long wall, and six from the fifth long wall. Upon this post and upon the ninth transverse wall is laid a beam thirty-three feet and three palms long, and two palms wide and thick. Another beam, also of the same length, width and thickness, is laid upon the same post and upon the tenth transverse wall, and the ends of these two beams where they meet are joined by means of iron staples. On these beams and on the fifth long wall are placed ten cross-beams, eight feet and three palms long, the first of which is placed on the ninth transverse wall, the last on the tenth, the remainder in the space between them; they are distant from one another three feet. Into the ends of the cross-beams facing the second long wall, are mortised the ends of the same number of rafters inclined toward the posts which stand vertically upon the second long wall. This, again, is the manner in which the inclined side of the furnace hood is made, just as with the others; at the top where the fumes are emitted it is two feet distant from the vertical side. The ends of the same number of rafters are mortised into the cross-beams, where they are set in the fifth long wall; each of them is set up obliquely and rests against the back of one of the preceding set; they support the roof, made of burnt tiles. In this part of the building, against the second long wall, are four furnaces in which lead is separated from silver, together with the cranes by means of which the domes are lifted from the crucibles. In that part of the building which lies between the first long wall and the break in the second long wall, is the stamp with which the copper cakes are crushed, and the four stamps with which the accretions that are chipped off the walls of the furnace are broken up and crushed to powder, and likewise the bricks on which the exhausted liquation cakes of copper are stood to be "dried." This room has the usual roof, as also has the space between the seventh transverse wall and the twelfth and thirteenth transverse walls. [Illustration 499 (Hearths for melting lead cakes): A--Hearth. B--Rocks sunk into the ground. C--Walls which protect the fourth long wall from damage by fire. D--Dipping-pot. E--Masses of lead. F--Trolley. G--Its wheels. H--Crane. I--Tongs. K--Wood. L--Moulds. M--Ladle. N--Pick. O--Cakes.] At the sides of these rooms are the fifth, the sixth, and the third long walls. This part of the building is divided into two parts, in the first of which stand the little furnaces in which the artificer assays metals; and the bone ash, together with the other powders, are kept here. In the other room is prepared the powder from which the hearths and the crucibles of the furnaces are made. Outside the building, at the back of the fourth long wall, near the door to the left as you enter, is a hearth in which smaller masses of lead are melted from large ones, that they may be the more easily weighed; because the masses of lead, just as much as the cakes of copper, ought to be first prepared so that they can be weighed, and a definite weight can be melted and alloyed in the furnaces. To begin with, the hearth in which the masses of lead are liquefied is six feet long and five wide; it is protected on both sides by rocks partly sunk into the earth, but a palm higher than the hearth, and it is lined in the inside with lute. It slopes toward the middle and toward the front, in order that the molten lead may run down and flow out into the dipping-pot. There is a wall at the back of the hearth which protects the fourth long wall from damage by the heat; this wall, which is made of bricks and lute, is four feet high, three palms thick, and five feet long at the bottom, and at the top three feet and two palms long; therefore it narrows gradually, and in the upper part are laid seven bricks, the middle ones of which are set upright, and the end ones inclined; they are all thickly coated with lute. In front of the hearth is a dipping-pot, whose pit is a foot deep, and a foot and three palms wide at the top, and gradually narrows. When the masses of lead are to be melted, the workman first places the wood in the hearth so that one end of each billet faces the wall, and the other end the dipping-pot. Then, assisted by other workmen, he pushes the mass of lead forward with crowbars on to a low trolley, and draws it to the crane. The trolley consists of planks fastened together, is two and one-half feet wide and five feet long, and has two small iron axles, around which at each end revolve small iron wheels, two palms in diameter and as many digits wide. The trolley has a tongue, and attached to this is a rope, by which it is drawn to the crane. The crane is exactly similar to those in the second part of the works, except that the crane-arm is not so long. The tongs in whose jaws[6] the masses of lead are seized, are two feet a palm and two digits long; both of the jaws, when struck with a hammer, impinge upon the mass and are driven into it. The upper part of both handles of the tongs are curved back, the one to the right, the other to the left, and each handle is engaged in one of the lowest links of two short chains, which are three links long. The upper links are engaged in a large round ring, in which is fixed the hook of a chain let down from the pulley of the crane-arm. When the crank of the crane is turned, the mass is lifted and is carried by the crane-arm to the hearth and placed on the wood. The workmen wheel up one mass after another and place them in a similar manner on the wood of the hearth; masses which weigh a total of about a hundred and sixty _centumpondia_[7] are usually placed upon the wood and melted at one time. Then a workman throws charcoal on the masses, and all are made ready in the evening. If he fears that it may rain, he covers it up with a cover, which may be moved here and there; at the back this cover has two legs, so that the rain which it collects may flow down the slope on to the open ground. Early in the morning of the following day, he throws live coals on the charcoal with a shovel, and by this method the masses of lead melt, and from time to time charcoal is added. The lead, as soon as it begins to run into the dipping-pot, is ladled out with an iron ladle into copper moulds such as the refiners generally use. If it does not cool immediately he pours water over it, and then sticks the pointed pick into it and pulls it out. The pointed end of the pick is three palms long and the round end is two digits long. It is necessary to smear the moulds with a wash of lute, in order that, when they have been turned upside down and struck with the broad round end of the pick, the cakes of lead may fall out easily. If the moulds are not washed over with the lute, there is a risk that they may be melted by the lead and let it through. Others take hold of a billet of wood with their left hand, and with the heavy lower end of it they pound the mould, and with the right hand they stick the point of the pick into the cake of lead, and thus pull it out. Then immediately the workman pours other lead into the empty moulds, and this he does until the work of melting the lead is finished. When the lead is melted, something similar to litharge is produced; but it is no wonder that it should be possible to make it in this case, when it used formerly to be produced at Puteoli from lead alone when melted by a fierce fire in the cupellation furnace.[8] Afterward these cakes of lead are carried into the lead store-room. [Illustration 501 (Stamp-mill for breaking copper cakes): A--Block of wood. B--Upright posts. C--Transverse beams. D--Head of the stamp. E--Its tooth. F--The hole in the stamp-stem. G--Iron bar. H--Masses of lead. I--The bronze saddle. K--Axle. L--Its arms. M--Little iron axle. N--Bronze pipe.] The cakes of copper, put into wheelbarrows, are carried into the third part of the building, where each is laid upon a saddle, and is broken up by the impact of successive blows from the iron-shod stamp. This machine is made by placing upon the ground a block of oak, five feet long and three feet wide and thick; it is cut out in the middle for a length of two feet and two palms, a width of two feet, and a depth of three palms and two digits, and is open in front; the higher part of it is at the back, and the wide part lies flat in the block. In the middle of it is placed a bronze saddle. Its base is a palm and two digits wide, and is planted between two masses of lead, and extends under them to a depth of a palm on both sides. The whole saddle is three palms and two digits wide, a foot long, and two palms thick. Upon each end of the block stands a post, a cubit wide and thick, the upper end of which is somewhat cut away and is mortised into the beams of the building. At a height of four feet and two digits above the block there are joined to the posts two transverse beams, each of which is three palms wide and thick; their ends are mortised into the upright posts, and holes are bored through them; in the holes are driven iron claves, horned in front and so driven into the post that one of the horns of each points upward and the other downward; the other end of each clavis is perforated, and a wide iron wedge is inserted and driven into the holes, and thus holds the transverse beams in place. These transverse beams have in the middle a square opening three palms and half a digit wide in each direction, through which the iron-shod stamp passes. At a height of three feet and two palms above these transverse beams there are again two beams of the same kind, having also a square opening and holding the same stamp. This stamp is square, eleven feet long, three palms wide and thick; its iron shoe is a foot and a palm long; its head is two palms long and wide, a palm two digits thick at the top, and at the bottom the same number of digits, for it gradually narrows. But the tail is three palms long; where the head begins is two palms wide and thick, and the further it departs from the same the narrower it becomes. The upper part is enclosed in the stamp-stem, and it is perforated so that an iron bolt may be driven into it; it is bound by three rectangular iron bands, the lowest of which, a palm wide, is between the iron shoe and the head of the stamp; the middle band, three digits wide, follows next and binds round the head of the stamp, and two digits above is the upper one, which is the same number of digits wide. At a distance of two feet and as many digits above the lowest part of the iron shoe, is a rectangular tooth, projecting from the stamp for a distance of a foot and a palm; it is two palms thick, and when it has extended to a distance of six digits from the stamp it is made two digits narrower. At a height of three palms upward from the tooth there is a round hole in the middle of the stamp-stem, into which can be thrust a round iron bar two feet long and a digit and a half in diameter; in its hollow end is fixed a wooden handle two palms and the same number of digits long. The bar rests on the lower transverse beam, and holds up the stamp when it is not in use. The axle which raises the stamp has on each side two arms, which are two palms and three digits distant from each other, and which project from the axle a foot, a palm and two digits; penetrating through them are bolts, driven in firmly; the arms are each a palm and two digits wide and thick, and their round heads, for a foot downward on either side, are covered with iron plates of the same width as the arms and fastened by iron nails. The head of each arm has a round hole, into which is inserted an iron pin, passing through a bronze pipe; this little axle has at the one end a wide head, and at the other end a perforation through which is driven an iron nail, lest this little axle should fall out of the arms. The bronze pipe is two palms long and one in diameter; the little iron axle penetrates through its round interior, which is two digits in diameter. The bronze pipe not only revolves round the little iron axle, but it also rotates with it; therefore, when the axle revolves, the little axle and the bronze tube in their turn raise the tooth and the stamp. When the little iron axle and the bronze pipe have been taken out of the arms, the tooth of the stamps is not raised, and other stamps may be raised without this one. Further on, a drum with spindles fixed around the axle of a water-wheel moves the axle of a toothed drum, which depresses the sweeps of the bellows in the adjacent fourth part of the building; but it turns in the contrary direction; for the axis of the drum which raises the stamps turns toward the north, while that one which depresses the sweeps of the bellows turns toward the south. [Illustration 504 (Hearths for heating copper cakes): A--Back wall. B--Walls at the sides. C--Upright posts. D--Chimney. E--The cakes arranged. F--Iron plates. G--Rocks. H--Rabble with two prongs. I--Hammers.] Those cakes which are too thick to be rapidly broken by blows from the iron-shod stamp, such as are generally those which have settled in the bottom of the crucible,[9] are carried into the first part of the building. They are there heated in a furnace, which is twenty-eight feet distant from the second long wall and twelve feet from the second transverse wall. The three sides of this furnace are built of rectangular rocks, upon which bricks are laid; the back furnace wall is three feet and a palm high, and the rear of the side walls is the same; the side walls are sloping, and where the furnace is open in front they are only two feet and three palms high; all the walls are a foot and a palm thick. Upon these walls stand upright posts not less thick, in order that they may bear the heavy weight placed upon them, and they are covered with lute; these posts support the sloping chimney and penetrate through the roof. Moreover, not only the ribs of the chimney, but also the rafters, are covered thickly with lute. The hearth of the furnace is six feet long on each side, is sloping, and is paved with bricks. The cakes of copper are placed in the furnace and heated in the following way. They are first of all placed in the furnace in rows, with as many small stones the size of an egg between, so that the heat of the fire can penetrate through the spaces between them; indeed, those cakes which are placed at the bottom of the crucible are each raised upon half a brick for the same reason. But lest the last row, which lies against the mouth of the furnace, should fall out, against the mouth are placed iron plates, or the copper cakes which are the first taken from the crucible when copper is made, and against them are laid exhausted liquation cakes or rocks. Then charcoal is thrown on the cakes, and then live coals; at first the cakes are heated by a gentle fire, and afterward more charcoal is added to them until it is at times three-quarters of a foot deep. A fiercer fire is certainly required to heat the hard cakes of copper than the fragile ones. When the cakes have been sufficiently heated, which usually occurs within the space of about two hours, the exhausted liquation cakes or the rocks and the iron plate are removed from the mouth of the furnace. Then the hot cakes are taken out row after row with a two-pronged rabble, such as the one which is used by those who "dry" the exhausted liquation cakes. Then the first cake is laid upon the exhausted liquation cakes, and beaten by two workmen with hammers until it breaks; the hotter the cakes are, the sooner they are broken up; the less hot, the longer it takes, for now and then they bend into the shape of copper basins. When the first cake has been broken, the second is put on to the other fragments and beaten until it breaks into pieces, and the rest of the cakes are broken up in the same manner in due order. The head of the hammer is three palms long and one wide, and sharpened at both ends, and its handle is of wood three feet long. When they have been broken by the stamp, if cold, or with hammers if hot, the fragments of copper or the cakes are carried into the store-room for copper. The foreman of the works, according to the different proportions of silver in each _centumpondium_ of copper, alloys it with lead, without which he could not separate the silver from the copper.[10] If there be a moderate amount of silver in the copper, he alloys it fourfold; for instance, if in three-quarters of a _centumpondium_ of copper there is less than the following proportions, _i.e._: half a _libra_ of silver, or half a _libra_ and a _sicilicus_, or half a _libra_ and a _semi-uncia_, or half a _libra_ and _semi-uncia_ and a _sicilicus_, then rich lead--that is, that from which the silver has not yet been separated--is added, to the amount of half a _centumpondium_ or a whole _centumpondium_, or a whole and a half, in such a way that there may be in the copper-lead alloy some one of the proportions of silver which I have just mentioned, which is the first alloy. To this "first" alloy is added such a weight of de-silverized lead or litharge as is required to make out of all of these a single liquation cake that will contain approximately two _centumpondia_ of lead; but as usually from one hundred and thirty _librae_ of litharge only one hundred _librae_ of lead are made, a greater proportion of litharge than of de-silverized lead is added as a supplement. Since four cakes of this kind are placed at the same time into the furnace in which the silver and lead is liquated from copper, there will be in all the cakes three _centumpondia_ of copper and eight _centumpondia_ of lead. When the lead has been liquated from the copper, it weighs six _centumpondia_, in each _centumpondium_ of which there is a quarter of a _libra_ and almost a _sicilicus_ of silver. Only seven _unciae_ of the silver remain in the exhausted liquation cakes and in that copper-lead alloy which we call "liquation thorns"; they are not called by this name so much because they have sharp points as because they are base. If in three-quarters of a _centumpondium_ of copper there are less than seven _uncia_ and a _semi-uncia_ or a _bes_ of silver, then so much rich lead must be added as to make in the copper and lead alloy one of the proportions of silver which I have already mentioned. This is the "second" alloy. To this is again to be added as great a weight of de-silverized lead, or of litharge, as will make it possible to obtain from that alloy a liquation cake containing two and a quarter _centumpondia_ of lead, in which manner in four of these cakes there will be three _centumpondia_ of copper and nine _centumpondia_ of lead. The lead which liquates from these cakes weighs seven _centumpondia_, in each _centumpondium_ of which there is a quarter of a _libra_ of silver and a little more than a _sicilicus_. About seven _unciae_ of silver remain in the exhausted liquation cakes and in the liquation thorns, if we may be allowed to make common the old name (_spinae_ = thorns) and bestow it upon a new substance. If in three-quarters of a _centumpondium_ of copper there is less than three-quarters of a _libra_ of silver, or three-quarters and a _semi-uncia_, then as much rich lead must be added as will produce one of the proportions of silver in the copper-lead alloy above mentioned; this is the "third" alloy. To this is added such an amount of de-silverized lead or of litharge, that a liquation cake made from it contains in all two and three-quarters _centumpondia_ of lead. In this manner four such cakes will contain three _centumpondia_ of copper and eleven _centumpondia_ of lead. The lead which these cakes liquate, when they are melted in the furnace, weighs about nine _centumpondia_, in each _centumpondium_ of which there is a quarter of a _libra_ and more than a _sicilicus_ of silver; and seven _unciae_ of silver remain in the exhausted liquation cakes and in the liquation thorns. If, however, in three-quarters of a _centumpondium_ of copper there is less than ten-twelfths of a _libra_ or ten-twelfths of a _libra_ and a _semi-uncia_ of silver, then such a proportion of rich lead is added as will produce in the copper-lead alloy one of the proportions of silver which I mentioned above; this is the "fourth" alloy. To this is added such a weight of de-silverized lead or of litharge, that a liquation cake made from it contains three _centumpondia_ of lead, and in four cakes of this kind there are three _centumpondia_ of copper and twelve _centumpondia_ of lead. The lead which is liquated therefrom weighs about ten _centumpondia_, in each _centumpondium_ of which there is a quarter of a _libra_ and more than a _semi-uncia_ of silver, or seven _unciae_; a _bes_, or seven _unciae_ and a _semi-uncia_, of silver remain in the exhausted liquation cakes and in the liquation thorns. [Illustration 508 (Blast Furnaces): A--Furnace in which "slags" are re-smelted. B--Furnace in which copper is alloyed with lead. C--Door. D--Forehearths on the ground. E--Copper moulds. F--Rabble. G--Hook. H--Cleft stick. I--Arm of the crane. K--The hook of its chain.] Against the second long wall in the second part of the building, whose area is eighty feet long by thirty-nine feet wide, are four furnaces in which the copper is alloyed with lead, and six furnaces in which "slags" are re-smelted. The interior of the first kind of furnace is a foot and three palms wide, two feet three digits long; and of the second is a foot and a palm wide and a foot three palms and a digit long. The side walls of these furnaces are the same height as the furnaces in which gold or silver ores are smelted. As the whole room is divided into two parts by upright posts, the front part must have, first, two furnaces in which "slags" are re-melted; second, two furnaces in which copper is alloyed with lead; and third, one furnace in which "slags" are re-melted. The back part of the room has first, one furnace in which "slags" are re-melted; next, two furnaces in which copper is alloyed with lead; and third, two furnaces in which "slags" are re-melted. Each of these is six feet distant from the next; on the right side of the first is a space of three feet and two palms, and on the left side of the last one of seven feet. Each pair of furnaces has a common door, six feet high and a cubit wide, but the first and the tenth furnace each has one of its own. Each of the furnaces is set in an arch of its own in the back wall, and in front has a forehearth pit; this is filled with a powder compound rammed down and compressed in order to make a crucible. Under each furnace is a hidden receptacle for the moisture,[11] from which a vent is made through the back wall toward the right, which allows the vapour to escape. Finally, to the right, in front, is the copper mould into which the copper-lead alloy is poured from the forehearth, in order that liquation cakes of equal weight may be made. This copper mould is a digit thick, its interior is two feet in diameter and six digits deep. Behind the second long wall are ten pairs of bellows, two machines for compressing them, and twenty instruments for inflating them. The way in which these should be made may be understood from Book IX. The smelter, when he alloys copper with lead, with his hand throws into the heated furnace, first the large fragments of copper, then a basketful of charcoal, then the smaller fragments of copper. When the copper is melted and begins to run out of the tap-hole into the forehearth, he throws litharge into the furnace, and, lest part of it should fly away, he first throws charcoal over it, and lastly lead. As soon as he has thrown into the furnace the copper and the lead, from which alloy the first liquation cake is made, he again throws in a basket of charcoal, and then fragments of copper are thrown over them, from which the second cake may be made. Afterward with a rabble he skims the "slag" from the copper and lead as they flow into the forehearth. Such a rabble is a board into which an iron bar is fixed; the board is made of elder-wood or willow, and is ten digits long, six wide, and one and a half digits thick; the iron bar is three feet long, and the wooden handle inserted into it is two and a half feet long. While he purges the alloy and pours it out with a ladle into the copper mould, the fragments of copper from which he is to make the second cake are melting. As soon as this begins to run down he again throws in litharge, and when he has put on more charcoal he adds the lead. This operation he repeats until thirty liquation cakes have been made, on which work he expends nine hours, or at most ten; if more than thirty cakes must be made, then he is paid for another shift when he has made an extra thirty. At the same time that he pours the copper-lead alloy into the copper mould, he also pours water slowly into the top of the mould. Then, with a cleft stick, he takes a hook and puts its straight stem into the molten cake. The hook itself is a digit and a half thick; its straight stem is two palms long and two digits wide and thick. Afterward he pours more water over the cakes. When they are cold he places an iron ring in the hook of the chain let down from the pulley of the crane arm; the inside diameter of this ring is six digits, and it is about a digit and a half thick; the ring is then engaged in the hook whose straight stem is in the cake, and thus the cake is raised from the mould and put into its place. The copper and lead, when thus melted, yield a small amount of "slag"[12] and much litharge. The litharge does not cohere, but falls to pieces like the residues from malt from which beer is made. _Pompholyx_ adheres to the walls in white ashes, and to the sides of the furnace adheres _spodos_. In this practical manner lead is alloyed with copper in which there is but a moderate portion of silver. If, however, there is much silver in it, as, for instance, two _librae_, or two _librae_ and a _bes_, to the _centumpondium_,--which weighs one hundred and thirty-three and a third _librae_, or one hundred and forty-six _librae_ and a _bes_,[13]--then the foreman of the works adds to a _centumpondium_ of such copper three _centumpondia_ of lead, in each _centumpondium_ of which there is a third of a _libra_ of silver, or a third of a _libra_ and a _semi-uncia_. In this manner three liquation cakes are made, which contain altogether three _centumpondia_ of copper and nine _centumpondia_ of lead.[14] The lead, when it has been liquated from the copper, weighs seven _centumpondia_; and in each _centumpondium_--if the _centumpondium_ of copper contain two _librae_ of silver, and the lead contain a third of a _libra_--there will be a _libra_ and a sixth and more than a _semi-uncia_ of silver; while in the exhausted liquation cakes, and in the liquation thorns, there remains a third of a _libra_. If a _centumpondium_ of copper contains two _librae_ and a _bes_ of silver, and the lead a third of a _libra_ and a _semi-uncia_, there will be in each liquation cake one and a half _librae_ and a _semi-uncia_, and a little more than a _sicilicus_ of silver. In the exhausted liquation cakes there remain a third of a _libra_ and a _semi-uncia_ of silver. [Illustration 510 (Furnaces enriching copper bottoms): A--Furnace. B--Forehearth. C--Dipping-Pot. D--Cakes.] If there be in the copper only a minute proportion of silver, it cannot be separated easily until it has been re-melted in other furnaces, so that in the "bottoms" there remains more silver and in the "tops" less.[15] This furnace, vaulted with unbaked bricks, is similar to an oven, and also to the cupellation furnace, in which the lead is separated from silver, which I described in the last book. The crucible is made of ashes, in the same manner as in the latter, and in the front of the furnace, three feet above the floor of the building, is the mouth out of which the re-melted copper flows into a forehearth and a dipping-pot. On the left side of the mouth is an aperture, through which beech-wood may be put into the furnace to feed the fire. If in a _centumpondium_ of copper there were a sixth of a _libra_ and a _semi-uncia_ of silver, or a quarter of a _libra_, or a quarter of a _libra_ and a _semi-uncia_--there is re-melted at the same time thirty-eight _centumpondia_ of it in this furnace, until there remain in each _centumpondium_ of the copper "bottoms" a third of a _libra_ and a _semi-uncia_ of silver. For example, if in each _centumpondium_ of copper not yet re-melted, there is a quarter of a _libra_ and a _semi-uncia_ of silver, then the thirty-eight _centumpondia_ that are smelted together must contain a total of eleven _librae_ and an _uncia_ of silver. Since from fifteen _centumpondia_ of re-melted copper there was a total of four and a third _librae_ and a _semi-uncia_ of silver, there remain only two and a third _librae_. Thus there is left in the "bottoms," weighing twenty-three _centumpondia_, a total of eight and three-quarter _librae_ of silver. Therefore, each _centumpondium_ of this contains a third of a _libra_ and a _semi-uncia_, a _drachma_, and the twenty-third part of a _drachma_ of silver; from such copper it is profitable to separate the silver. In order that the master may be more certain of the number of _centumpondia_ of copper in the "bottoms," he weighs the "tops" that have been drawn off from it; the "tops" were first drawn off into the dipping-pot, and cakes were made from them. Fourteen hours are expended on the work of thus dividing the copper. The "bottoms," when a certain weight of lead has been added to them, of which alloy I shall soon speak, are melted in the blast furnace; liquation cakes are then made, and the silver is afterward separated from the copper. The "tops" are subsequently melted in the blast furnace, and re-melted in the refining furnace, in order that red copper shall be made[16]; and the "tops" from this are again smelted in the blast furnace, and then again in the refining furnace, that therefrom shall be made _caldarium_ copper. But when the copper, yellow or red or _caldarium_ is re-smelted in the refining furnace, forty _centumpondia_ are placed in it, and from it they make at least twenty, and at most thirty-five, _centumpondia_. About twenty-two _centumpondia_ of exhausted liquation cakes and ten of yellow copper and eight of red, are simultaneously placed in this latter furnace and smelted, in order that they may be made into refined copper. The copper "bottoms" are alloyed in three different ways with lead.[17] First, five-eighths of a _centumpondium_ of copper and two and three-quarters _centumpondia_ of lead are taken; and since one liquation cake is made from this, therefore two and a half _centumpondia_ of copper and eleven _centumpondia_ of lead make four liquation cakes. Inasmuch as in each _centumpondium_ of copper there is a third of a _libra_ of silver, there would be in the whole of the copper ten-twelfths of a _libra_ of silver; to these are added four _centumpondia_ of lead re-melted from "slags," each _centumpondium_ of which contains a _sicilicus_ and a _drachma_ of silver, which weights make up a total of an _uncia_ and a half of silver. There is also added seven _centumpondia_ of de-silverized lead, in each _centumpondium_ of which there is a _drachma_ of silver; therefore in the four cakes of copper-lead alloy there is a total of a _libra_, a _sicilicus_ and a _drachma_ of silver. In each single _centumpondium_ of lead, after it has been liquated from the copper, there is an _uncia_ and a _drachma_ of silver, which alloy we call "poor" argentiferous lead, because it contains but little silver. But as five cakes of that kind are placed together in the furnace, they liquate from them usually as much as nine and three-quarters _centumpondia_ of poor argentiferous lead, in each _centumpondium_ of which there is an _uncia_ and a _drachma_ of silver, or a total of ten _unciae_ less four _drachmae_. Of the liquation thorns there remain three _centumpondia_, in each _centumpondium_ of which there are three _sicilici_ of silver; and there remain four _centumpondia_ of exhausted liquation cakes, each _centumpondium_ of which contains a _semi-uncia_ or four and a half _drachmae_. Inasmuch as in a _centumpondium_ of copper "bottoms" there is a third of a _libra_ and a _semi-uncia_ of silver, in five of those cakes there must be more than one and a half _unciae_ and half a _drachma_ of silver. Then, again, from another two and a half _centumpondia_ of copper "bottoms," together with eleven _centumpondia_ of lead, four liquation cakes are made. If in each _centumpondium_ of copper there was a third of a _libra_ of silver, there would be in the whole of the _centumpondia_ of base metal five-sixths of a _libra_ of the precious metal. To this copper is added eight _centumpondia_ of poor argentiferous lead, each _centumpondium_ of which contains an _uncia_ and a _drachma_ of silver, or a total of three-quarters of a _libra_ of silver. There is also added three _centumpondia_ of de-silverized lead, in each _centumpondium_ of which there is a _drachma_ of silver. Therefore, four liquation cakes contain a total of a _libra_, seven _unciae_, a _sicilicus_ and a _drachma_ of silver; thus each _centumpondium_ of lead, when it has been liquated from the copper, contains an _uncia_ and a half and a _sicilicus_ of silver, which alloy we call "medium" silver-lead. Then, again, from another two and a half _centumpondia_ of copper "bottoms," together with eleven _centumpondia_ of lead, they make four liquation cakes. If in each _centumpondium_ of copper there were likewise a third of a _libra_ of silver, there will be in all the weight of the base metal five-sixths of a _libra_ of the precious metal. To this is added nine _centumpondia_ of medium silver-lead, each _centumpondium_ of which contains an _uncia_ and a half and a _sicilicus_ of silver; or a total of a _libra_ and a quarter and a _semi-uncia_ and a _sicilicus_ of silver. And likewise they add two _centumpondia_ of poor silver-lead, in each of which there is an _uncia_ and a _drachma_ of silver. Therefore the four liquation cakes contain two and a third _librae_ of silver. Each _centumpondium_ of lead, when it has been liquated from the copper, contains a sixth of a _libra_ and a _semi-uncia_ and a _drachma_ of silver. This alloy we call "rich" silver-lead; it is carried to the cupellation furnace, in which lead is separated from silver. I have now mentioned in how many ways copper containing various proportions of silver is alloyed with lead, and how they are melted together in the furnace and run into the casting pan. [Illustration 514 (Crane for liquation cakes): A--Crane. B--Drum consisting of rundles. C--Toothed drum. D--Trolley and its wheels. E--Triangular board. F--Cakes. G--Chain of the crane. H--Its hook. I--Ring. K--The tongs.] Now I will speak of the method by which lead is liquated from copper simultaneously with the silver. The liquation cakes are raised from the ground with the crane, and placed on the copper plates of the furnaces. The hook of the chain let down from the arm of the crane, is inserted in a ring of the tongs, one jaw of which has a tooth; a ring is engaged in each of the handles of the tongs, and these two rings are engaged in a third, in which the hook of the chain is inserted. The tooth on the one jaw of the tongs is struck by a hammer, and driven into the hole in the cake, at the point where the straight end of the hook was driven into it when it was lifted out of the copper mould; the other jaw of the tongs, which has no tooth, squeezes the cake, lest the tooth should fall out of it; the tongs are one and a half feet long, each ring is a digit and a half thick, and the inside is a palm and two digits in diameter. Those cranes by which the cakes are lifted out of the copper pans and placed on the ground, and lifted up again from there and placed in the furnaces, are two in number--one in the middle space between the third transverse wall and the two upright posts, and the other in the middle space between the same posts and the seventh transverse wall. The rectangular crane-post of both of these is two feet wide and thick, and is eighteen feet from the third long wall, and nineteen from the second long wall. There are two drums in the framework of each--one drum consisting of rundles, the other being toothed. The crane-arm of each extends seventeen feet, three palms and as many digits from the post. The trolley of each crane is two feet and as many palms long, a foot and two digits wide, and a palm and two digits thick; but where it runs between the beams of the crane-arm it is three digits wide and a palm thick; it has five notches, in which turn five brass wheels, four of which are small, and the fifth much larger than the rest. The notches in which the small wheels turn are two palms long and as much as a palm wide; those wheels are a palm wide and a palm and two digits in diameter; four of the notches are near the four corners of the trolley; the fifth notch is between the two front ones, and it is two palms back from the front. Its pulley is larger than the rest, and turns in its own notch; it is three palms in diameter and one palm wide, and grooved on the circumference, so that the iron chain may run in the groove. The trolley has two small axles, to the one in front are fastened three, and to the one at the back, the two wheels; two wheels run on the one beam of the crane-arm, and two on the other; the fifth wheel, which is larger than the others, runs between those two beams. Those people who have no cranes place the cakes on a triangular board, to which iron cleats are affixed, so that it will last longer; the board has three iron chains, which are fixed in an iron ring at the top; two workmen pass a pole through the ring and carry it on their shoulders, and thus take the cake to the furnace in which silver is separated from copper. From the vicinity of the furnaces in which copper is mixed with lead and the "slags" are re-melted, to the third long wall, are likewise ten furnaces, in which silver mixed with lead is separated from copper. If this space is eighty feet and two palms long, and the third long wall has in the centre a door three feet and two palms wide, then the spaces remaining at either side of the door will be thirty-eight feet and two palms; and if each of the furnaces occupies four feet and a palm, then the interval between each furnace and the next one must be a foot and three palms; thus the width of the five furnaces and four interspaces will be twenty-eight feet and a palm. Therefore, there remain ten feet and a palm, which measurement is so divided that there are five feet and two digits between the first furnace and the transverse wall, and as many feet and digits between the fifth furnace and the door; similarly in the other part of the space from the door to the sixth furnace, there must be five feet and two digits, and from the tenth furnace to the seventh transverse wall, likewise, five feet and two digits. The door is six feet and two palms high; through it the foreman of the _officina_ and the workmen enter the store-room in which the silver-lead alloy is kept. [Illustration 517 (Liquation Furnace): A--Sole-stones. B--Rectangular stones. C--Copper plates. D--Front panel. E--Side panels. F--Bar. G--Front end of the long iron rods. H--Short chain. I--Hooked rod. K--Wall which protects the third long wall from injury by fire. L--Third long wall. M--Feet of the panels. N--Iron blocks. O--Cakes. P--Hearth. Q--Receiving-pit.] Each furnace has a bed, a hearth, a rear wall, two sides and a front, and a receiving-pit. The bed consists of two sole-stones, four rectangular stones, and two copper plates; the sole-stones are five feet and a palm long, a cubit wide, a foot and a palm thick, and they are sunk into the ground, so that they emerge a palm and two digits; they are distant from each other about three palms, yet the distance is narrower at the back than the front. Each of the rectangular stones is two feet and as many palms long, a cubit wide, and a cubit thick at the outer edge, and a foot and a palm thick on the inner edge which faces the hearth, thus they form an incline, so that there is a slope to the copper plates which are laid upon them. Two of these rectangular stones are placed on one sole-stone; a hole is cut in the upper edge of each, and into the holes are placed iron clamps, and lead is poured in; they are so placed on the sole-stones that they project a palm at the sides, and at the front the sole-stones project to the same extent; if rectangular stones are not available, bricks are laid in their place. The copper plates are four feet two palms and as many digits long, a cubit wide, and a palm thick; each edge has a protuberance, one at the front end, the other at the back; these are a palm and three digits long, and a palm wide and thick. The plates are so laid upon the rectangular stones that their rear ends are three digits from the third long wall; the stones project beyond the plate the same number of digits in front, and a palm and three digits at the sides. When the plates have been joined, the groove which is between the protuberances is a palm and three digits wide, and four feet long, and through it flows the silver-lead which liquates from the cakes. When the plates are corroded either by the fire or by the silver-lead, which often adheres to them in the form of stalactites, and is chipped off, they are exchanged, the right one being placed to the left, and the left one, on the contrary, to the right; but the left side of the plates, which, when the fusion of the copper took place, came into contact with the copper, must lie flat; so that when the exchange of the plates has been carried out, the protuberances, which are thus on the underside, raise the plate from the stones, and they have to be partially chipped off, lest they should prove an impediment to the work; and in each of their places is laid a piece of iron, three palms long, a digit thick at both ends, and a palm thick in the centre for the length of a palm and three digits. The passage under the plates between the rectangular stones is a foot wide at the back, and a foot and a palm wide at the front, for it gradually widens out. The hearth, which is between the sole-stones, is covered with a bed of hearth-lead, taken from the crucible in which lead is separated from silver. The rear end is the highest, and should be so high that it reaches to within six digits of the plates, from which point it slopes down evenly to the front end, so that the argentiferous lead alloy which liquates from the cakes can flow into the receiving-pit. The wall built against the third long wall in order to protect it from injury by fire, is constructed of bricks joined together with lute, and stands on the copper plates; this wall is two feet, a palm and two digits high, two palms thick, and three feet, a palm and three digits wide at the bottom, for it reaches across both of them; at the top it is three feet wide, for it rises up obliquely on each side. At each side of this wall, at a height of a palm and two digits above the top of it, there is inserted in a hole in the third long wall a hooked iron rod, fastened in with molten lead; the rod projects two palms from the wall, and is two digits wide and one digit thick; it has two hooks, the one at the side, the other at the end. Both of these hooks open toward the wall, and both are a digit thick, and both are inserted in the last, or the adjacent, links of a short iron chain. This chain consists of four links, each of which is a palm and a digit long and half a digit thick; the first link is engaged in the first hole in a long iron rod, and one or other of the remaining three links engages the hook of the hooked rod. The two long rods are three feet and as many palms and digits long, two digits wide, and one digit thick; both ends of both of these rods have holes, the back one of which is round and a digit in diameter, and in this is engaged the first link of the chain as I have stated; the hole at the front end is two digits and a half long and a digit and a half wide. This end of each rod is made three digits wide, while for the rest of its length it is only two digits, and at the back it is two and a half digits. Into the front hole of each rod is driven an iron bar, which is three feet and two palms long, two digits wide and one thick; in the end of this bar are five small square holes, two-thirds of a digit square; each hole is distant from the other half a digit, the first being at a distance of about a digit from the end. Into one of these holes the refiner drives an iron pin; if he should desire to make the furnace narrower, then he drives it into the last hole; if he should desire to widen it, then into the first hole; if he should desire to contract it moderately, then into one of the middle holes. For the same reason, therefore, the hook is sometimes inserted into the last link of the chain, and sometimes into the third or the second. The furnace is widened when many cakes are put into it, and contracted when there are but few, but to put in more than five is neither usual nor possible; indeed, it is because of thin cakes that the walls are contracted. The bar has a hump, which projects a digit on each side at the back, of the same width and thickness as itself. These humps project, lest the bar should slip through the hole of the right-hand rod, in which it remains fixed when it, together with the rods, is not pressing upon the furnace walls. [Illustration 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 spaces, 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 passage, 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 passage, 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 passage. 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 passage, 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 passage into the receiving-pit, and has been poured out into copper moulds, the thorns are drawn out of the passage 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 stalactites 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. [Illustration 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 assistant chips off the stalactites from the exhausted liquation cakes. They then carry the cakes to the furnace, and put the stalactites 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 passages, 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 passages 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. [Illustration 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 space 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 space 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 space; 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 passages, 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. [Illustration 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 principal 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 passages 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 passages 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. [Illustration 528 (Drying Furnace for Liquation): A--The door raised. B--Hooked bar. C--Two-pronged 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-pronged rake with which the "dried" cakes are drawn over to the left side so that they may be seized with tongs; the prongs 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 assistants, 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 passages; 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. [Illustration 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 assistants 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] [Illustration 532 (Copper Refining Furnace): A--Hearth of the furnace. B--Chimney. C--Common pillar. D--Other pillars. The partition wall is behind the common pillar and not to be seen. E--Arches. F--Little walls which protect the partition 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 space is sixty-three feet and two palms long, and since each of these furnaces occupies thirteen feet, the space 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 spaces 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 partition wall. The partition 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 partition wall. Imposed upon these arches and the partition 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 partition 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 partition wall, and has a little wall built of bricks cemented together with lute; this little wall protects the partition wall from injury by the fire. On the contrary, the second furnace has the left side open and the right side is against the partition wall, where also it has its own little wall which protects the partition 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 partition 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 passed 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 snowballs. 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, passing 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 brassy 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] [Illustration 534 (Copper Refining): A--Pointed bar. B--Thin copper layer. C--Anvil. D--Hammer.] [Illustration 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 pass 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 assistant 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 assistant, 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 assistant 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 space in the copper, and he separates the cake from the rest of the mass. 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 assistant 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 assistant 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 assistant 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 assistant 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 passes 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 substituted 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. [Illustration 543 (Copper Refining): A--Furnace. B--Forehearth. C--Oblong moulds.] The _cadmia_,[32] as it is called by us, is made from the "slags" which the master, who makes copper from "dried" cakes, draws off together with other re-melted base "slags"; for, indeed, if the copper cakes made from such "slags" are broken, the fragments are called _cadmia_; from this and yellow copper is made _caldarium_ copper in two ways. For either two parts of _cadmia_ are mixed with one of yellow copper in the blast furnaces, and melted; or, on the contrary, two parts of yellow copper with one of _cadmia_, so that the _cadmia_ and yellow copper may be well mixed; and the copper which flows down from the furnace into the forehearth is poured out with a ladle into oblong copper moulds heated beforehand. These moulds are sprinkled over with charcoal dust before the _caldarium_ copper is to be poured into them, and the same dust is sprinkled over the copper when it is poured in, lest the _cadmia_ and yellow copper should freeze before they have become well mixed. With a piece of wood the assistant cleanses each cake from the dust, when it is turned out of the mould. Then he throws it into the tub containing hot water, for the _caldarium_ copper is finer if quenched in hot water. But as I have so often made mention of the oblong copper moulds, I must now speak of them a little; they are a foot and a palm long, the inside is three palms and a digit wide at the top, and they are rounded at the bottom. The concentrates are of two kinds--precious and base.[33] The first are obtained from the accretions of the blast furnace, when liquation cakes are made from copper and lead, or from precious liquation thorns, or from the better quality "slags," or from the best grade of concentrates, or from the sweepings and bricks of the furnaces in which exhausted liquation cakes are "dried"; all of these things are crushed and washed, as I explained in Book VIII. The base concentrates are made from accretions formed when cakes are cast from base thorns or from the worst quality of slags. The smelter who makes liquation cakes from the precious concentrates, adds to them three wheelbarrowsful of litharge and four barrowsful of hearth-lead and one of ash-coloured copper, from all of which nine or ten liquation cakes are melted out, of which five at a time are placed in the furnace in which silver-lead is liquated from copper; a _centumpondium_ of the lead which drips from these cakes contains one _uncia_ of silver. The liquation thorns are placed apart by themselves, of which one basketful is mixed with the precious thorns to be re-melted. The exhausted liquation cakes are "dried" at the same time as other good exhausted liquation cakes. The thorns which are drawn off from the lead, when it is separated from silver in the cupellation furnace[34], and the hearth-lead which remains in the crucible in the middle part of the furnaces, together with the hearth material which has become defective and has absorbed silver-lead, are all melted together with a little slag in the blast furnaces. The lead, or rather the silver-lead, which flows from the furnace into the forehearth, is poured out into copper moulds such as are used by the refiners; a _centumpondium_ of such lead contains four _unciae_ of silver, or, if the hearth was defective, it contains more. A small portion of this material is added to the copper and lead when liquation cakes are made from them, if more were to be added the alloy would be much richer than it should be, for which reason the wise foreman of the works mixes these thorns with other precious thorns. The hearth-lead which remains in the middle of the crucible, and the hearth material which absorbs silver-lead, is mixed with other hearth-lead which remains in the cupellation furnace crucible; and yet some cakes, made rich in this manner, may be placed again in the cupellation furnaces, together with the rest of the silver-lead cakes which the refiner has made. The inhabitants of the Carpathian Mountains, if they have an abundance of finely crushed copper[35] or lead either made from "slags," or collected from the furnace in which the exhausted liquation cakes are dried, or litharge, alloy them in various ways. The "first" alloy consists of two _centumpondia_ of lead melted out of thorns, litharge, and thorns made from hearth-lead, and of half a _centumpondium_ each of lead collected in the furnace in which exhausted liquation cakes are "dried," and of copper _minutum_, and from these are made liquation cakes; the task of the smelter is finished when he has made forty liquation cakes of this kind. The "second" alloy consists of two _centumpondia_ of litharge, of one and a quarter _centumpondia_ of de-silverized lead or lead from "slags," and of half a _centumpondium_ of lead made from thorns, and of as much copper _minutum_. The "third" alloy consists of three _centumpondia_ of litharge and of half a _centumpondium_ each of de-silverized lead, of lead made from thorns, and of copper _minutum contusum_. Liquation cakes are made from all these alloys; the task of the smelters is finished when they have made thirty cakes. The process by which cakes are made among the Tyrolese, from which they separate the silver-lead, I have explained in Book IX. Silver is separated from iron in the following manner. Equal portions of iron scales and filings and of _stibium_ are thrown into an earthenware crucible which, when covered with a lid and sealed, is placed in a furnace, into which air is blown. When this has melted and again cooled, the crucible is broken; the button that settles in the bottom of it, when taken out, is pounded to powder, and the same weight of lead being added, is mixed and melted in a second crucible; at last this button is placed in a cupel and the lead is separated from the silver.[36] There are a great variety of methods by which one metal is separated from other metals, and the manner in which the same are alloyed I have explained partly in the eighth book of _De Natura Fossilium_, and partly I will explain elsewhere. Now I will proceed to the remainder of my subject. END OF BOOK XI. FOOTNOTES: [1] The whole of this Book is devoted to the subject of the separation of silver from copper by liquation, except pages 530-9 on copper refining, and page 544 on the separation of silver from iron. We believe a brief outline of the liquation process here will refresh the mind of the reader, and enable him to peruse the Book with more satisfaction. The fundamental principle of the process is that if a copper-lead alloy, containing a large excess of lead, be heated in a reducing atmosphere, above the melting point of lead but below that of copper, the lead will liquate out and carry with it a large proportion of the silver. As the results are imperfect, the process cannot be carried through in one operation, and a large amount of bye-products is created which must be worked up subsequently. The process, as here described, falls into six stages. 1st, Melting the copper and lead in a blast furnace to form "liquation cakes"--that is, the "leading." If the copper contain too little silver to warrant liquation directly, then the copper is previously enriched by melting and drawing off from a settling pot the less argentiferous "tops" from the metal, liquation cakes being made from the enriched "bottoms." 2nd, Liquation of the argentiferous lead from the copper. This work was carried out in a special furnace, to which the admission of air was prevented as much as possible in order to prevent oxidation. 3rd, "Drying" the residual copper, which retained some lead, in a furnace with a free admission of air. The temperature was raised to a higher degree than in the liquation furnace, and the expelled lead was oxidized. 4th, Cupellation of the argentiferous lead. 5th, Refining of the residual copper from the "drying" furnace by oxidation of impurities and poling in a "refining furnace." 6th, Re-alloy and re-liquation of the bye-products. These consist of: _a_, "slags" from "leading"; _b_, "slags" from "drying"; _c_, "slags" from refining of the copper. All of these "slags" were mainly lead oxides, containing some cuprous oxides and silica from the furnace linings; _d_, "thorns" from liquation; _e_, "thorns" from "drying"; _f_, "thorns" from skimmings during cupellation; these were again largely lead oxides, but contained rather more copper and less silica than the "slags"; _g_, "ash-coloured copper," being scales from the "dried" copper, were cuprous oxides, containing considerable lead oxides; _h_, concentrates from furnace accretions, crushed bricks, &c. The discussion of detailed features of the process has been reserved to notes attached to the actual text, to which the reader is referred. As to the general result of liquation, Karsten (see below) estimates the losses in the liquation of the equivalent of 100 lbs. of argentiferous copper to amount to 32-35 lbs. of lead and 5 to 6 lbs. of copper. Percy (see below) quotes results at Lautenthal in the Upper Harz for the years 1857-60, showing losses of 25% of the silver, 9.1% of the copper, and 36.37 lbs. of lead to the 100 lbs. of copper, or say, 16% of the lead; and a cost of L8 6s. per ton of copper. The theoretical considerations involved in liquation have not been satisfactorily determined. Those who may wish to pursue the subject will find repeated descriptions and much discussion in the following works, which have been freely consulted in the notes which follow upon particular features of the process. It may be mentioned that Agricola's treatment of the subject is more able than any down to the 18th century. Ercker (_Beschreibung Allerfuernemsten Mineralischen_, etc., Prague, 1574). Lohneys (_Bericht vom Bergwercken_, etc., Zellerfeldt, 1617). Schlueter (_Gruendlicher Unterricht von Huette-Werken_, Braunschweig, 1738). _Karsten_ (_System der Metallurgie V._ and _Archiv fuer Bergbau und Huettenwesen_, 1st series, 1825). Berthier (_Annales des Mines_, 1825, II.). Percy (Metallurgy of Silver and Gold, London, 1880). NOMENCLATURE.--This process held a very prominent position in German metallurgy for over four centuries, and came to have a well-defined nomenclature of its own, which has never found complete equivalents in English, our metallurgical writers to the present day adopting more or less of the German terms. Agricola apparently found no little difficulty in adapting Latin words to his purpose, but stubbornly adhered to his practice of using no German at the expense of long explanatory clauses. The following table, prepared for convenience in translation, is reproduced. The German terms are spelled after the manner used in most English metallurgies, some of them appear in Agricola's Glossary to _De Re Metallica_. English. Latin. German. Blast furnace _Prima fornax_ _Schmeltzofen_ Liquation furnace _Fornax in qua argentum et _Saigernofen_ plumbum ab aere secernuntur_ Drying furnace _Fornax in qua aerei panes _Darrofen_ fathiscentes torrentur_ Refining hearth _Fornax in qua panes aerei _Gaarherd_ torrefacti coquuntur_ Cupellation _Secunda fornax_, or _Treibherd_ furnace _fornax in qua plumbum ab argento separatur_ Leading _Mistura_ _Frischen_ Liquating _Stillare_, or _distillare_ _Saigern_ "Drying" _Torrere_ _Darren_ Refining _Aes ex panibus torrefactis _Gaarmachen_ conficere_ Liquation cakes _Panes ex aere ac plumbo misti_ _Saigerstock_ Exhausted _Panes fathiscentes_ _Kiehnstock_, liquation cakes or _Kinstocke_ "Dried" cakes _Panes torrefacti_ _Darrlinge_ Slags from leading _Recrementa_ _Frischschlacke_ (with explanatory phrases) Slags from drying _Recrementa_ _Darrost_ (with explanatory phrases) Slags from refining _Recrementa_ _Gaarschlacke_ (with explanatory phrases) Liquation thorns _Spinae_ _Saigerdoerner_, (with explanatory phrases) or _Roestdoerner_ Thorns from "drying" _Spinae_ _Darrsoehle_ (with explanatory phrases) Thorns from _Spinae_ _Abstrich_ cupellation (with explanatory phrases) Silver-lead or _Stannum_ _Saigerwerk_ or liquated _saigerblei_ silver-lead Ash-coloured copper _Aes cinereum_ _Pickschiefer_ or _schifer_ Furnace accretions _Cadmiae_ _Offenbrueche_ or "accretions" HISTORICAL NOTE.--So far as we are aware, this is the first complete discussion of this process, although it is briefly mentioned by one writer before Agricola--that is, by Biringuccio (III, 5, 8), who wrote ten years before this work was sent to the printer. His account is very incomplete, for he describes only the bare liquation, and states that the copper is re-melted with lead and re-liquated until the silver is sufficiently abstracted. He neither mentions "drying" nor any of the bye-products. In his directions the silver-lead alloy was cupelled and the copper ultimately refined, obviously by oxidation and poling, although he omits the pole. In A.D. 1150 Theophilus (p. 305, Hendrie's Trans.) describes melting lead out of copper ore, which would be a form of liquation so far as separation of these two metals is concerned, but obviously not a process for separating silver from copper. This passage is quoted in the note on copper smelting (Note on p. 405). A process of such well-developed and complicated a character must have come from a period long before Agricola; but further than such a surmise, there appears little to be recorded. Liquation has been during the last fifty years displaced by other methods, because it was not only tedious and expensive, but the losses of metal were considerable. [2] _Paries_,--"Partition" or "wall." The author uses this term throughout in distinction to _murus_, usually applying the latter to the walls of the building and the former to furnace walls, chimney walls, etc. In order to gain clarity, we have introduced the term "hood" in distinction to "chimney," and so far as possible refer to the _paries_ of these constructions and furnaces as "side of the furnace," "side of the hood," etc. [4] From this point on, the construction of the roofs, in the absence of illustration, is hopeless of intelligent translation. The constant repetition of "_tignum_," "_tigillum_," "_trabs_," for at least fifteen different construction members becomes most hopelessly involved, especially as the author attempts to distinguish between them in a sort of "House-that-Jack-built" arrangement of explanatory clauses. [5] In the original text this is given as the "fifth," a manifest impossibility. [6] _Chelae_,--"claws." [7] If Roman weights, this would be 5.6 short tons, and 7.5 tons if German _centner_ is meant. [8] This is, no doubt, a reference to Pliny's statement (XXXIII, 35) regarding litharge at Puteoli. This passage from Pliny is given in the footnote on p. 466. Puteoli was situated on the Bay of Naples. [9] By this expression is apparently meant the "bottoms" produced in enriching copper, as described on p. 510. [10] The details of the preparation of liquation cakes--"leading"--were matters of great concern to the old metallurgists. The size of the cakes, the proportion of silver in the original copper and in the liquated lead, the proportion of lead and silver left in the residual cakes, all had to be reached by a series of compromises among militant forces. The cakes were generally two and one-half to three and one-half inches thick and about two feet in diameter, and weighed 225 to 375 lbs. This size was wonderfully persistent from Agricola down to modern times; and was, no doubt, based on sound experience. If the cakes were too small, they required proportionately more fuel and labour; whilst if too large, the copper began to melt before the maximum lead was liquated. The ratio of the copper and lead was regulated by the necessity of enough copper to leave a substantial sponge mass the shape of the original cake, and not so large a proportion as to imprison the lead. That is, if the copper be in too small proportion the cakes break down; and if in too large, then insufficient lead liquates out, and the extraction of silver decreases. Ercker (p. 106-9) insists on the equivalent of about 3 copper to 9.5 lead; Lohneys (p. 99), 3 copper to 9 or 10 lead. Schlueter (p. 479, etc.) insists on a ration of 3 copper to about 11 lead. Kerl (_Handbuch Der Metallurgischen Huettenkunde_, 1855; Vol. III., p. 116) gives 3 copper to 6 to 7 parts lead. Agricola gives variable amounts of 3 parts copper to from 8 to 12 parts lead. As to the ratio of silver in the copper, or to the cakes, there does not, except the limit of payability, seem to have been any difficulty on the minimum side. On the other hand, Ercker, Lohneys, Schlueter, and Karsten all contend that if the silver ran above a certain proportion, the copper would retain considerable silver. These authors give the outside ratio of silver permissible for good results in one liquation at what would be equivalent to 45 to 65 ozs. per ton of cakes, or about 190 to 250 ozs. per ton on the original copper. It will be seen, however, that Agricola's cakes greatly exceed these values. A difficulty did arise when the copper ran low in silver, in that the liquated lead was too poor to cupel, and in such case the lead was used over again, until it became rich enough for this purpose. According to Karsten, copper containing less than an equivalent of 80 to 90 ozs. per ton could not be liquated profitably, although the Upper Harz copper, according to Kerl, containing the equivalent of about 50 ozs. per ton, was liquated at a profit. In such a case the cakes would run only 12 to 14 ozs. per ton. It will be noticed that in the eight cases given by Agricola the copper ran from 97 to over 580 ozs. per ton, and in the description of enrichment of copper "bottoms" the original copper runs 85 ozs., and "it cannot be separated easily"; as a result, it is raised to 110 ozs. per ton before treatment. In addition to the following tabulation of the proportions here given by Agricola, the reader should refer to footnotes 15 and 17, where four more combinations are tabulated. It will be observed from this table that with the increasing richness of copper an increased proportion of lead was added, so that the products were of similar value. It has been assumed (see footnote 13 p. 509), that Roman weights are intended. It is not to be expected that metallurgical results of this period will "tie up" with the exactness of the modern operator's, and it has not been considered necessary to calculate beyond the nearest pennyweight. Where two or more values are given by the author the average has been taken. 1ST CHARGE. 2ND CHARGE. 3RD CHARGE. 4TH CHARGE. Amount of 211.8 lbs. 211.8 lbs. 211.8 lbs. 211.8 lbs. argentiferous copper Amount of lead 564.8 " 635.4 " 776.6 " 847.2 " Weight of each cake 193.5 " 211.5 " 247.1 " 264.75 " Average value of 56 ozs. 62 ozs. 64 ozs. 66 ozs. charge 3dwts. 4dwts. 4dwts. 7dwts. Per cent. of copper 27.2% 25% 21.4% 20% Average value of 207 ozs. 251 ozs. 299 ozs. 332 ozs. original copper 4dwts. 3dwts. 15dwts. 3dwts. per ton Weight of 423.6 lbs. 494.2 lbs. 635.4 lbs. 706 lbs. argentiferous lead liquated out Average value of 79 ozs. 79 ozs. 79 ozs. 85 ozs. liquated lead per ton Weight of residues 353 lbs. 353 lbs. 353 lbs. 353 lbs. (residual copper and thorns) Average value of 34 ozs. 34 ozs. 34 ozs. 34 ozs. to residues per ton 38 ozs. Extraction of 76.5% 73.4% 79% 85.3% silver into the argentiferous lead [11] See p. 356. [12] An analysis of this "slag" by Karsten (_Archiv_. 1st Series IX, p. 24) showed 63.2% lead oxide, 5.1% cuprous oxide, 20.1% silica (from the fuel and furnace linings), together with some iron alumina, etc. The _pompholyx_ and _spodos_ were largely zinc oxide (see note, p. 394). [13] This description of a _centumpondium_ which weighed either 133-1/3 _librae_, or 146-3/4 _librae_, adds confusion to an already much mixed subject (see Appendix C.). Assuming the German _pfundt_ to weigh 7,219 troy grains, and the Roman _libra_ 4,946 grains, then a _centner_ would weigh 145.95 _librae_, which checks up fairly well with the second case; but under what circumstances a _centner_ can weigh 133-1/3 _librae_ we are unable to record. At first sight it might appear from this statement that where Agricola uses the word _centumpondium_ he means the German _centner_. On the other hand, in the previous five or six pages the expressions one-third, five-sixths, ten-twelfths of a _libra_ are used, which are even divisions of the Roman 12 _unciae_ to one _libra_, and are used where they manifestly mean divisions of 12 units. If Agricola had in mind the German scale, and were using the _libra_ for a _pfundt_ of 16 _untzen_, these divisions would amount to fractions, and would not total the _sicilicus_ and _drachma_ quantities given, nor would they total any of the possibly synonymous divisions of the German _untzen_ (see also page 254). [14] If we assume Roman weights, the charge in the first case can be tabulated as follows, and for convenience will be called the fifth charge:-- 5TH CHARGE (3 cakes). Amount of copper 211.8 lbs. Amount of lead 635.4 lbs. Weight of each cake 282.4 lbs. Average value of charge 218 ozs. 18 dwts. Per cent. of copper 25% Average value of original copper per ton 583 ozs. 6 dwts. 16 grs. Weight of argentiferous lead liquated out 494.2 lbs. Average value of liquated lead per ton 352 ozs. 8 dwts. Weight of residues 353 lbs. Average value of residues per ton 20 ozs. (about). Extraction of silver into the argentiferous lead 94% The results given in the second case where the copper contains 2 _librae_ and a _bes_ per _centumpondium_ do not tie together at all, for each liquation cake should contain 3 _librae_ 9-1/2 _unciae_, instead of 1-1/2 _librae_ and 1/2 _uncia_ of silver. [15] In this enrichment of copper by the "settling" of the silver in the molten mass the original copper ran, in the two cases given, 60 ozs. 15 dwts. and 85 ozs. 1 dwt. per ton. The whole charge weighed 2,685 lbs., and contained in the second case 114 ozs. Troy, omitting fractions. On melting, 1,060 lbs. were drawn off as "tops," containing 24 ozs. of silver, or running 45 ozs. per ton, and there remained 1,625 lbs. of "bottoms," containing 90 ozs. of silver, or averaging 110 ozs. per ton. It will be noticed later on in the description of making liquation cakes from these copper bottoms, that the author alters the value from one-third _librae_, a _semi-uncia_ and a _drachma_ per _centumpondium_ to one-third of a _libra_, _i.e._, from 110 ozs. to 97 ozs. 4 dwts. per ton. In the Glossary this furnace is described as a _spleisofen_, _i.e._, a refining hearth. [16] The latter part of this paragraph presents great difficulties. The term "refining furnace" is given in the Latin as the "second furnace," an expression usually applied to the cupellation furnace. The whole question of refining is exhaustively discussed on pages 530 to 539. Exactly what material is meant by the term red (_rubrum_), yellow (_fulvum_) and _caldarium_ copper is somewhat uncertain. They are given in the German text simply as _rot_, _geel_, and _lebeter kupfer_, and apparently all were "coarse" copper of different characters destined for the refinery. The author states in _De Natura Fossilium_ (p. 334): "Copper has a red colour peculiar to itself; this colour in smelted copper is considered the most excellent. It, however, varies. In some it is red, as in the copper smelted at Neusohl.... Other copper is prepared in the smelters where silver is separated from copper, which is called yellow copper (_luteum_), and is _regulare_. In the same place a dark yellow copper is made which is called _caldarium_, taking its name among the Germans from a caldron.... _Regulare_ differs from _caldarium_ in that the former is not only fusible, but also malleable; while the latter is, indeed, fusible, but is not ductile, for it breaks when struck with the hammer." Later on in _De Re Metallica_ (p. 542) he describes yellow copper as made from "baser" liquation thorns and from exhausted liquation cakes made from thorns. These products were necessarily impure, as they contained, among other things, the concentrates from furnace accretions. Therefore, there was ample source for zinc, arsenic or other metallics which would lighten the colour. _Caldarium_ copper is described by Pliny (see note, p. 404), and was, no doubt, "coarse" copper, and apparently Agricola adopted this term from that source, as we have found it used nowhere else. On page 542 the author describes making _caldarium_ copper from a mixture of yellow copper and a peculiar _cadmia_, which he describes as the "slags" from refining copper. These "slags," which are the result of oxidation and poling, would contain almost any of the metallic impurities of the original ore, antimony, lead, arsenic, zinc, cobalt, etc. Coming from these two sources the _caldarium_ must have been, indeed, impure. [17] The liquation of these low-grade copper "bottoms" required that the liquated lead should be re-used again to make up fresh liquation cakes, in order that it might eventually become rich enough to warrant cupellation. In the following table the "poor" silver-lead is designated (A) the "medium" (B) and the "rich" (C). The three charges here given are designated sixth, seventh, and eighth for purposes of reference. It will be seen that the data is insufficient to complete the ninth and tenth. Moreover, while the author gives directions for making four cakes, he says the charge consists of five, and it has, therefore, been necessary to reduce the volume of products given to this basis. 6TH CHARGE. 7TH CHARGE. 8TH CHARGE. Amount of copper 176.5 lbs. 176.5 lbs. 176.5 lbs. bottoms Amount of lead 282.4 lbs. 564.8 lbs. 635.4 lbs. (slags) of (A) of (B) Amount of 494.2 lbs. 211.8 lbs. 141.2 lbs. (A) de-silverized lead Weight of each cake 238.3 lbs. 238.3 lbs. 238.3 lbs. Average value of 22 ozs. 35 ozs. 50 ozs. charge per ton 5dwts. 15dwts. 5dwts. Per cent. of copper 18.5% 18.5% 18.5% Average value per 97 ozs. 97 ozs. 97 ozs. ton original copper 4dwts. 4dwts. 4dwts. Average value per 90 ozs. 28 ozs. 28 ozs. ton of 2dwts. (slags) 5dwts. (A) 5dwts. (A) Average value per 3 ozs. 3 ozs. 42 ozs. ton of 1dwt. (lead) 1dwt. (lead) 10dwts. (B) Weight of liquated 550.6 lbs. lead Average value of 28 ozs. 42 ozs. 63 ozs. the liquated lead 5dwts. (A) 10dwts. (B) 16dwts. (C) per ton Weight of exhausted 225.9 lbs. liquation cakes Average value of 12 ozs. the exhausted 3dwts. liquation cakes per ton Weight of liquation 169.4 lbs. thorns Average value of 18 ozs. the liquation 4dwts. thorns per ton Extraction of 71% silver into the liquated lead [18] For the liquation it was necessary to maintain a reducing atmosphere, otherwise the lead would oxidize; this was secured by keeping the cakes well covered with charcoal and by preventing the entrance of air as much as possible. Moreover, it was necessary to preserve a fairly even temperature. The proportions of copper and lead in the three liquation products vary considerably, depending upon the method of conducting the process and the original proportions. From the authors consulted (see note p. 492) an average would be about as follows:--The residual copper--exhausted liquation cakes--ran from 25 to 33% lead; the liquated lead from 2 to 3% copper; and the liquation thorns, which were largely oxidized, contained about 15% copper oxides, 80% lead oxides, together with impurities, such as antimony, arsenic, etc. The proportions of the various products would obviously depend upon the care in conducting the operation; too high temperature and the admission of air would increase the copper melted and oxidize more lead, and thus increase the liquation thorns. There are insufficient data in Agricola to adduce conclusions as to the actual ratios produced. The results given for the 6th charge (note 17, p. 512) would indicate about 30% lead in the residual copper, and would indicate that the original charge was divided into about 24% of residual copper, 18% of liquation thorns, and 57% of liquated lead. This, however, was an unusually large proportion of liquation thorns, some of the authors giving instances of as low as 5%. [19] The first instance given, of 44 _centumpondia_ (3,109 lbs.) lead and one _centumpondium_ (70.6 lbs.) copper, would indicate that the liquated lead contained 2.2% copper. The second, of 46 _centumpondia_ (3,250 lbs.) lead and 1-1/2 _centumpondia_ copper (106 lbs.), would indicate 3% copper; and in the third, 120 _centumpondia_ (8,478 lbs.) lead and six copper (424 lbs.) would show 4.76% copper. This charge of 120 _centumpondia_ in the cupellation furnace would normally make more than 110 _centumpondia_ of litharge and 30 of hearth-lead, _i.e._, saturated furnace bottoms. The copper would be largely found in the silver-lead "which does not melt," at the margin of the crucible. These skimmings are afterward referred to as "thorns." It is difficult to understand what is meant by the expression that the silver which is in the copper is mixed with the remaining (_reliquo_) silver. The coppery skimmings from the cupellation furnace are referred to again in Note 28, p. 539. [20] A further amount of lead could be obtained in the first liquation, but a higher temperature is necessary, which was more economical to secure in the "drying" furnace. Therefore, the "drying" was really an extension of liquation; but as air was admitted the lead and copper melted out were oxidized. The products were the final residual copper, called by Agricola the "dried" copper, together with lead and copper oxides, called by him the "slags," and the scale of copper and lead oxides termed by him the "ash-coloured copper." The German metallurgists distinguished two kinds of slag: the first and principal one, the _darrost_, and the second the _darrsoehle_, this latter differing only in that it contained more impurities from the floor of the furnace, and remained behind until the furnace cooled. Agricola possibly refers to these as "more liquation thorns," because in describing the treatment of the bye-products he refers to thorns from the process, whereas in the description of "drying" he usually refers to "slags." A number of analyses of these products, given by Karsten, show the "dried" copper to contain from 82.7 to 90.6% copper, and from 9.4 to 17.3% lead; the "slag" to contain 76.5 to 85.1% lead oxide, and from 4.1 to 7.8% cuprous oxide, with 9 to 13% silica from the furnace bottoms, together with some other impurities; the "ash-coloured copper" to contain about 60% cuprous oxide and 30% lead oxide, with some metallic copper and minor impurities. An average of proportions given by various authors shows, roughly, that out of 100 _centners_ of "exhausted" liquation cakes, containing about 70% copper and 30% lead, there were about 63 _centners_ of "dried" copper, 38 _centners_ of "slag," and 6-1/2 _centners_ of "ash-coloured copper." According to Karsten, the process fell into stages; first, at low temperature some metallic lead appeared; second, during an increasing temperature for over 14 to 15 hours the slags ran out; third, there was a period of four hours of lower temperature to allow time for the lead to diffuse from the interior of the cakes; and fourth, during a period of eight hours the temperature was again increased. In fact, the latter portion of the process ended with the economic limit between leaving some lead in the copper and driving too much copper into the "slags." Agricola gives the silver contents of the "dried" copper as 3 _drachmae_ to 1 _centumpondium_, or equal to about 9 ozs. per ton; and assuming that the copper finally recovered from the bye-products ran no higher, then the first four charges (see note on p. 506) would show a reduction in the silver values of from 95 to 97%; the 7th and 8th charges (note on p. 512) of about 90%. [21] If Roman weights, this would equal from 6,360 lbs. to 7,066 lbs. [22] One half _uncia_, or three _drachmae_ of silver would equal either 12 ozs. or 9 ozs. per ton. If we assume the values given for residual copper in the first four charges (note p. 506) of 34 ozs., this would mean an extraction of, roughly, 65% of the silver from the exhausted liquation cakes. [23] See note 29, p. 540. [24] Assuming Roman weights: 2 _centumpondia_ = 141.3 lbs. 2-1/2 " = 176.6 " 3 " = 211.9 " 3-1/2 " = 248.2 " 6 " = 423.9 " [25] This description of refining copper in an open hearth by oxidation with a blast and "poling"--the _gaarmachen_ of the Germans--is so accurate, and the process is so little changed in some parts of Saxony, that it might have been written in the 20th century instead of the 16th. The best account of the old practice in Saxony after Agricola is to be found in Schlueter's _Huette Werken_ (Braunschweig, 1738, Chap. CXVIII.). The process has largely been displaced by electrolytic methods, but is still in use in most refineries as a step in electrolytic work. It may be unnecessary to repeat that the process is one of subjecting the molten mass of impure metal to a strong and continuous blast, and as a result, not only are the impurities to a considerable extent directly oxidized and taken off as a slag, but also a considerable amount of copper is turned into cuprous oxide. This cuprous oxide mostly melts and diffuses through the metallic copper, and readily parting with its oxygen to the impurities further facilitates their complete oxidation. The blast is continued until the impurities are practically eliminated, and at this stage the molten metal contains a great deal of dissolved cuprous oxide, which must be reduced. This is done by introducing a billet of green wood ("poling"), the dry distillation of which generates large quantities of gases, which reduce the oxide. The state of the metal is even to-day in some localities tested by dipping into it the point of an iron rod; if it be at the proper state the adhering copper has a net-like appearance, should be easily loosened from the rod by dipping in water, is of a reddish-copper colour and should be quite pliable; if the metal is not yet refined, the sample is thick, smooth, and detachable with difficulty; if over-refined, it is thick and brittle. By allowing water to run on to the surface of the molten metal, thin cakes are successively formed and taken off. These cakes were the article known to commerce over several centuries as "rosetta copper." The first few cakes are discarded as containing impurities or slag, and if the metal be of good quality the cakes are thin and of a red colour. Their colour and thinness, therefore, become a criterion of purity. The cover of charcoal or charcoal dust maintained upon the surface of the metal tended to retard oxidation, but prevented volatilization and helped to secure the impurities as a slag instead. Karsten (_Archiv._, 1st series, p. 46) gives several analyses of the slag from refining "dried" copper, showing it to contain from 51.7 to 67.4% lead oxide, 6.2 to 19.2% cuprous oxide, and 21.4 to 23.9 silica (from the furnace bottoms), with minor quantities of iron, antimony, etc. The "bubbles" referred to by Agricola were apparently the shower of copper globules which takes place upon the evolution of sulphur dioxide, due to the reaction of the cuprous oxide upon any remaining sulphide of copper when the mass begins to cool. HISTORICAL NOTE.--It is impossible to say how the Ancients refined copper, beyond the fact that they often re-smelted it. Such notes as we can find are set out in the note on copper smelting (note 42, p. 402). The first authentic reference to poling is in Theophilus (1150 to 1200 A.D., Hendrie's translation, p. 313), which shows a very good understanding of this method of refining copper:--"Of the Purification of Copper. Take an iron dish of the size you wish, and line it inside and out with clay strongly beaten and mixed, and it is carefully dried. Then place it before a forge upon the coals, so that when the bellows act upon it the wind may issue partly within and partly above it, and not below it. And very small coals being placed round it, place the copper in it equally, and add over it a heap of coals. When by blowing a long time this has become melted, uncover it and cast immediately fine ashes of coals over it, and stir it with a thin and dry piece of wood as if mixing it, and you will directly see the burnt lead adhere to these ashes like a glue, which being cast out again superpose coals, and blowing for a long time, as at first, again uncover it, and then do as you did before. You do this until at length by cooking it you can withdraw the lead entirely. Then pour it over the mould which you have prepared for this, and you will thus prove if it be pure. Hold it with the pincers, glowing as it is, before it has become cold, and strike it with a large hammer strongly over the anvil, and if it be broken or split you must liquefy it anew as before. If, however, it should remain sound, you will cool it in water, and you cook other (copper) in the same manner." Biringuccio (III, 8) in 1540 describes the process briefly, but omits the poling, an essential in the production of malleable copper. [26] _Pompholyx_ and _spodos_ were impure zinc oxides (see note 26, p. 394). The copper flowers were no doubt cupric oxide. They were used by the Ancients for medicinal purposes. Dioscorides (V, 48) says: "Of flowers of copper, which some call the scrapings of old nails, the best is friable; it is gold-coloured when rubbed, is like millet in shape and size, is moderately bright, and somewhat astringent. It should not be mixed with copper filings, with which it is often adulterated. But this deception is easily detected, for when bitten in the teeth the filings are malleable. It (the flowers) is made when the copper fused in a furnace has run into the receptacle through the spout pertaining to it, for then the workmen engaged in this trade cleanse it from dirt and pour clear water over it in order to cool it; from this sudden condensation the copper spits and throws out the aforesaid flowers." Pliny (XXXIV, 24) says: "The flower, too, of copper (_aeris flos_) is used in medicine. This is made by fusing copper, and then removing it to another furnace, where the repeated blast makes the metal separate into small scales like millet, known as flowers. These scales also fall off when the cakes of metal are cooled in water; they become red, too, like the scales of copper known as '_lepis_,' by use of which the flowers of copper are adulterated, it being also sold for it. These are made when hammering the nails that are made from the cakes of copper. All these methods are carried on in the works of Cyprus; the difference between these substances is that the _squamae_ (copper scales) are detached from hammering the cakes, while the flower falls off spontaneously." Agricola (_De Nat. Fos._, p. 352) notes that "flowers of copper (_flos aeris_) have the same properties as 'roasted copper.'" [27] It seems scarcely necessary to discuss in detail the complicated "flow scheme" of the various minor bye-products. They are all re-introduced into the liquation circuit, and thereby are created other bye-products of the same kind _ad infinitum_. Further notes are given on:-- Liquation thorns Note 28. Slags " 30. Ash-coloured copper " 29. Concentrates " 33. _Cadmia_ " 32. There are no data given, either by Agricola or the later authors, which allow satisfactory calculation of the relative quantities of these products. A rough estimate from the data given in previous notes would indicate that in one liquation only about 70% of the original copper came out as refined copper, and that about 70% of the original lead would go to the cupellation furnace, _i.e._, about 30% of the original metal sent to the blast furnace would go into the "thorns," "slags," and "ash-coloured copper." The ultimate losses were very great, as given before (p. 491), they probably amounted to 25% of the silver, 9% copper, and 16% of the lead. [28] There were the following classes of thorns:-- 1st. From liquation. 2nd. From drying. 3rd. From cupellation. In a general way, according to the later authors, they were largely lead oxide, and contained from 5% to 20% cuprous oxide. If a calculation be made backward from the products given as the result of the charge described, it would appear that in this case they must have contained at least one-fifth copper. The silver in these liquation cakes would run about 24 ozs. per ton, in the liquated lead about 36 ozs. per ton, and in the liquation thorns 24 ozs. per ton. The extraction into the liquated lead would be about 80% of the silver. [29] The "ash-coloured copper" is a cuprous oxide, containing some 3% lead oxide; and if Agricola means they contained two _unciae_ of silver to the _centumpondium_, then they ran about 48 ozs. per ton, and would contain much more silver than the mass. [30] There are three principal "slags" mentioned-- 1st. Slag from "leading." 2nd. Slag from "drying." 3rd. Slag from refining the copper. From the analyses quoted by various authors these ran from 52% to 85% lead oxide, 5% to 30% cuprous oxide, and considerable silica from the furnace bottoms. They were reduced in the main into liquation cakes, although Agricola mentions instances of the metal reduced from "slags" being taken directly to the "drying" furnace. Such liquation cakes would run very low in silver, and at the values given only averaged 12 ozs. per ton; therefore the liquated lead running the same value as the cakes, or less than half that of the "poor" lead mentioned in Note 17, p. 512, could not have been cupelled directly. [31] See Note 16, p. 511, for discussion of yellow and _caldarium_ copper. [32] This _cadmia_ is given in the Glossary and the German translation as _kobelt_. A discussion of this substance is given in the note on p. 112; and it is sufficient to state here that in Agricola's time the metal cobalt was unknown, and the substances designated _cadmia_ and _cobaltum_ were arsenical-cobalt-zinc minerals. A metal made from "slag" from refining, together with "base" thorns, would be very impure; for the latter, according to the paragraph on concentrates a little later on, would contain the furnace accretions, and would thus be undoubtedly zincky. It is just possible that the term _kobelt_ was used by the German smelters at this time in the sense of an epithet--"black devil" (see Note 21, p. 214). [33] It is somewhat difficult to see exactly the meaning of base (_vile_) and precious (_preciosum_) in this connection. While "base" could mean impure, "precious" could hardly mean pure, and while "precious" could mean high value in silver, the reverse does not seem entirely _apropos_. It is possible that "bad" and "good" would be more appropriate terms. [34] The skimmings from the molten lead in the early stages of cupellation have been discussed in Note 28, p. 539. They are probably called thorns here because of the large amount of copper in them. The lead from liquation would contain 2% to 3% of copper, and this would be largely recovered in these skimmings, although there would be some copper in the furnace bottoms--hearth-lead--and the litharge. These "thorns" are apparently fairly rich, four _unciae_ to the _centumpondium_ being equivalent to about 97 ozs. per ton, and they are only added to low-grade liquation material. [35] _Particulis aeris tusi_. Unless this be the fine concentrates from crushing the material mentioned, we are unable to explain the expression. [36] This operation would bring down a button of antimony under an iron matte, by de-sulphurizing the antimony. It would seem scarcely necessary to add lead before cupellation. This process is given in an assay method, in the _Probierbuechlein_ (folio 31) 50 years before _De Re Metallica_: "How to separate silver from iron: Take that silver which is in iron _plechen_ (_plachmal_), pulverize it finely, take the same iron or _plec_ one part, _spiesglasz_ (antimony sulphide) one part, leave them to melt in a crucible placed in a closed _windtofen_. When it is melted, let it cool, break the crucible, chip off the button that is in the bottom, and melt it in a crucible with as much lead. Then break the crucible, and seek from the button in the cupel, and you will find what silver it contains."