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.
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.
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.