Chapter XXV: Book IX: 1 (2)

The assistant, having prepared the forehearth, returns to the furnace and besmears both sides as well as the top of the mouth with simple lute. In the lower part of the mouth he places lute that has been dipped in charcoal dust, to guard against the risk of the lute attracting to itself the powder of the hearth and vitiating it. Next he lays in the mouth of the furnace a straight round rod three quarters of a foot long and three digits in diameter. Afterward he places a piece of charcoal on the lute, of the same length and width as the mouth, so that it is entirely closed up; if there be not at hand one piece of charcoal so large, he takes two instead. When the mouth is thus closed up, he throws into the furnace a wicker basket full of charcoal, and in order that the piece of charcoal with which the mouth of the furnace is closed should not then fall out, the master holds it in with his hand. The pieces of charcoal which are thrown into the furnace should be of medium size, for if they are large they impede the blast of the bellows and prevent it from blowing through the tap-hole of the furnace into the forehearth to heat it. Then the master covers over the charcoal, placed at the mouth of the furnace, with lute and extracts the wooden rod, and thus the furnace is prepared. Afterward the assistant throws four or five larger baskets full of charcoal into the furnace, filling it right up; he also throws a little charcoal into the forehearth, and places glowing coals upon it in order that it may be kindled, but in order that the flames of this fire should not enter through the tap-hole of the furnace and fire the charcoal inside, he covers the tap-hole with lute or closes it with fragments of pottery. Some do not warm the forehearth the same evening, but place large charcoals round the edge of it, one leaning on the other; those who follow the first method sweep out the forehearth in the morning, and clean out the little pieces of charcoal and cinders, while those who follow the latter method take, early in the morning, burning firebrands, which have been prepared by the watchman of the works, and place them on the charcoal.

At the fourth hour the master begins his work. He first inserts a small piece of glowing coal into the furnace, through the bronze nozzle-pipe of the bellows, and blows up the fire with the bellows; thus within the space of half an hour the forehearth, as well as the hearth, becomes warmed, and of course more quickly if on the preceding day ores have been smelted in the same furnace, but if not then it warms more slowly. If the hearth and forehearth are not warmed before the ore to be smelted is thrown in, the furnace is injured and the metals lost; or if the powder from which both are made is damp in summer or frozen in winter, they will be cracked, and, giving out a sound like thunder, they will blow out the metals and other substances with great peril to the workmen. After the furnace has been warmed, the master throws in slags, and these, when melted, flow out through the tap-hole into the forehearth. Then he closes up the tap-hole at once with mixed lute and charcoal dust; this plug he fastens with his hand to a round wooden rammer that is five digits thick, two palms high, with a handle three feet long. The smelter extracts the slags from the forehearth with a hooked bar; if the ore to be smelted is rich in gold or silver he puts into the forehearth a _centumpondium_ of lead, or half as much if the ore is poor, because the former requires much lead, the latter little; he immediately throws burning firebrands on to the lead so that it melts. Afterward he performs everything according to the usual manner and order, whereby he first throws into the furnace as many cakes melted from pyrites[12], as he requires to smelt the ore; then he puts in two wicker baskets full of ore with litharge and hearth-lead[13], and stones which fuse easily by fire of the second order, all mixed together; then one wicker basket full of charcoal, and lastly the slags. The furnace now being filled with all the things I have mentioned, the ore is slowly smelted; he does not put too much of it against the back wall of the furnace, lest sows should form around the nozzles of the bellows and the blast be impeded and the fire burn less fiercely.

This, indeed, is the custom of many most excellent smelters, who know how to govern the four elements[14]. They combine in right proportion the ores, which are part earth, placing no more than is suitable in the furnaces; they pour in the needful quantity of water; they moderate with skill the air from the bellows; they throw the ore into that part of the fire which burns fiercely. The master sprinkles water into each part of the furnace to dampen the charcoal slightly, so that the minute parts of ore may adhere to it, which otherwise the blast of the bellows and the force of the fire would agitate and blow away with the fumes. But as the nature of the ores to be smelted varies, the smelters have to arrange the hearth now high, now low, and to place the pipe in which the nozzles of the bellows are inserted sometimes on a great and sometimes at a slight angle, so that the blast of the bellows may blow into the furnace in either a mild or a vigorous manner. For those ores which heat and fuse easily, a low hearth is necessary for the work of the smelters, and the pipe must be placed at a gentle angle to produce a mild blast from the bellows. On the contrary, those ores that heat and fuse slowly must have a high hearth, and the pipe must be placed at a steep incline in order to blow a strong blast of the bellows, and it is necessary, for this kind of ore, to have a very hot furnace in which slags, or cakes melted from pyrites, or stones which melt easily in the fire[15], are first melted, so that the ore should not settle in the hearth of the furnace and obstruct and choke up the tap-hole, as the minute metallic particles that have been washed from the ores are wont to do. Large bellows have wide nozzles, for if they were narrow the copious and strong blast would be too much compressed and too acutely blown into the furnace, and then the melted material would be chilled, and would form sows around the nozzle, and thus obstruct the opening into the furnace, which would cause great damage to the proprietors' property. If the ores agglomerate and do not fuse, the smelter, mounting on the ladder placed against the side of the furnace, divides the charge with a pointed or hooked bar, which he also pushes down into the pipe in which the nozzle of the bellows is placed, and by a downward movement dislodges the ore and the sows from around it.

After a quarter of an hour, when the lead which the assistant has placed in the forehearth is melted, the master opens the tap-hole of the furnace with a tapping-bar. This bar is made of iron, is three and a half feet long, the forward end pointed and a little curved, and the back end hollow so that into it may be inserted a wooden handle, which is three feet long and thick enough to be well grasped by the hand. The slag first flows from the furnace into the forehearth, and in it are stones mixed with metal or with the metal adhering to them partly altered, the slag also containing earth and solidified juices. After this the material from the melted pyrites flows out, and then the molten lead contained in the forehearth absorbs the gold and silver. When that which has run out has stood for some time in the forehearth, in order to be able to separate one from the other, the master first either skims off the slags with the hooked bar or else lifts them off with an iron fork; the slags, as they are very light, float on the top. He next draws off the cakes of melted pyrites, which as they are of medium weight hold the middle place; he leaves in the forehearth the alloy of gold or silver with the lead, for these being the heaviest, sink to the bottom. As, however, there is a difference in slags, the uppermost containing little metal, the middle more, and the lowest much, he puts these away separately, each in its own place, in order that to each heap, when it is re-smelted, he may add the proper fluxes, and can put in as much lead as is demanded for the metal in the slag; when the slag is re-melted, if it emits much odour, there is some metal in it; if it emits no odour, then it contains none. He puts the cakes of melted pyrites away separately, as they were nearest in the forehearth to the metal, and contain a little more of it than the slags; from all these cakes a conical mound is built up, by always placing the widest of them at the bottom. The hooked bar has a hook on the end, hence its name; otherwise it is similar to other bars.

Afterward the master closes up the tap-hole and fills the furnace with the same materials I described above, and again, the ores having been melted, he opens the tap-hole, and with a hooked bar extracts the slags and the cakes melted from pyrites, which have run down into the forehearth. He repeats the same operation until a certain and definite part of the ore has been smelted, and the day's work is at an end; if the ore was rich the work is finished in eight hours; if poor, it takes a longer time. But if the ore was so rich as to be smelted in less than eight hours, another operation is in the meanwhile combined with the first, and both are performed in the space of ten hours. When all the ore has been smelted, he throws into the furnace a basket full of litharge or hearth-lead, so that the metal which has remained in the accretions may run out with these when melted. When he has finally drawn out of the forehearth the slags and the cakes melted from pyrites, he takes out, with a ladle, the lead alloyed with gold or silver and pours it into little iron or copper pans, three palms wide and as many digits deep, but first lined on the inside with lute and dried by warming, lest the glowing molten substances should break through. The iron ladle is two palms wide, and in other respects it is similar to the others, all of which have a sufficiently long iron shaft, so that the fire should not burn the wooden part of the handle. When the alloy has been poured out of the forehearth, the smelter foreman and the mine captain weigh the cakes.

Then the master breaks out the whole of the mouth of the furnace with a crowbar, and with that other hooked bar, the rabble and the five-toothed rake, he extracts the accretions and the charcoal. This crowbar is not unlike the other hooked one, but larger and wider; the handle of the rabble is six feet long and is half of iron and half of wood. The furnace having cooled, the master chips off the accretions clinging to the walls with a rectangular spatula six digits long, a palm broad, and sharp on the front edge; it has a round handle four feet long, half of it being of iron and half of wood. This is the first method of smelting ores.

Because they generally consist of unequal constituents, some of which melt rapidly and others slowly, the ores rich in gold and silver cannot be smelted as rapidly or as easily by the other methods as they can by the first method, for three important reasons. The first reason is that, as often as the closed tap-hole of the furnace is opened with a tapping-bar, so often can the smelter observe whether the ore is melting too quickly or too slowly, or whether it is flaming in scattered bits, and not uniting in one mass; in the first case the ore is smelting too slowly and not without great expense; in the second case the metal mixes with the slag which flows out of the furnace into the forehearth, wherefore there is the expense of melting it again; in the third case, the metal is consumed by the violence of the fire. Each of these evils has its remedy; if the ore melts slowly or does not come together, it is necessary to add some amount of fluxes which melt the ore; or if they melt too readily, to decrease the amount.

The second reason is that each time that the furnace is opened with a tapping-bar, it flows out into the forehearth, and the smelter is able to test the alloy of gold and lead or of silver with lead, which is called _stannum_.[16] When the tap-hole is opened the second or third time, this test shows us whether the alloy of gold or silver has become richer, or whether the lead is too debilitated and wanting in strength to absorb any more gold or silver. If it has become richer, some portion of lead added to it should renew its strength; if it has not become richer, it is poured out of the forehearth that it may be replaced with fresh lead.

The third reason is that if the tap-hole of the furnace is always open when the ore and other things are being smelted, the fluxes, which are easily melted, run out of the furnace before the rich gold and silver ores, for these are sometimes of a kind that oppose and resist melting by the fire for a longer period. It follows in this case, that some part of the ore is either consumed or is mixed with the accretions, and as a result little lumps of ore not yet melted are now and then found in the accretions. Therefore when these ores are being smelted, the tap-hole of the furnace should be closed for a time, as it is necessary to heat and mix the ore and the fluxes at the same time; since the fluxes fuse more rapidly than the ore, when the molten fluxes are held in the furnace, they thus melt the ore which does not readily fuse or mix with the lead. The lead absorbs the gold or silver, just as tin or lead when melted in the forehearth absorbs the other unmelted metal which has been thrown into it. But if the molten matter is poured upon that which is not molten, it runs off on all sides and consequently does not melt it. It follows from all this that ores rich in gold or silver, when put into a furnace with its tap-hole always open, cannot for that reason be smelted so successfully as in one where the tap-hole is closed for a time, so that during this time the ore may be melted by the molten fluxes. Afterward, when the tap-hole has been opened, they flow into the forehearth and mix there with the molten lead. This method of smelting the ores is used by us and by the Bohemians.

The three remaining methods of smelting ores are similar to each other in that the tap-holes of the furnaces always remain open, so that the molten metals may continually run out. They differ greatly from each other, however, for the tap-hole of the first of this kind is deeper in the furnace and narrower than that of the third, and besides it is invisible and concealed. It easily discharges into the forehearth, which is one and a half feet higher than the floor of the building, in order that below it to the left a dipping-pot can be made. When the forehearth is nearly full of the slags, which well up from the invisible tap-hole of the furnace, they are skimmed off from the top with a hooked bar; then the alloy of gold or silver with lead and the melted pyrites, being uncovered, flow into the dipping-pot, and the latter are made into cakes; these cakes are broken and thrown back into the furnace so that all their metal may be smelted out. The alloy is poured into little iron moulds.

The smelter, besides lead and cognate things, uses fluxes which combine with the ore, of which I gave a sufficient account in Book VII. The metals which are melted from ores that fuse readily in the fire, are profitable because they are smelted in a short time, while those which are difficult to fuse are not as profitable, because they take a long time. When fluxes remain in the furnace and do not melt, they are not suitable; for this reason, accretions and slags are the most convenient for smelting, because they melt quickly. It is necessary to have an industrious and experienced smelter, who in the first place takes care not to put into the furnace more ores mixed with fluxes than it can accommodate.

The powder out of which this furnace hearth and the adjoining forehearth and the dipping-pot are usually made, consists mostly of equal proportions of charcoal dust and of earth, or of equal parts of the same and of ashes. When the hearth of the furnace is prepared, a rod that will reach to the forehearth is put into it, higher up if the ore to be smelted readily fuses, and lower down if it fuses with difficulty. When the dipping-pot and forehearth are finished, the rod is drawn out of the furnace so that the tap-hole is open, and through it the molten material flows continuously into the forehearth, which should be very near the furnace in order that it may keep very hot and the alloy thus be made purer. If the ore to be smelted does not melt easily, the hearth of the furnace must not be made too sloping, lest the molten fluxes should run down into the forehearth before the ore is smelted, and the metal thus remain in the accretions on the sides of the furnace. The smelter must not ram the hearth so much that it becomes too hard, nor make the mistake of ramming the lower part of the mouth to make it hard, for it could not breathe[17], nor could the molten matter flow freely out of the furnace. The ore which does not readily melt is thrown as much as possible to the back of the furnace, and toward that part where the fire burns very fiercely, so that it may be smelted longer. In this way the smelter may direct it whither he wills. Only when it glows at the part near the bellows' nozzle does it signify that all the ore is smelted which has been thrown to the side of the furnace in which the nozzles are placed. If the ore is easily melted, one or two wicker baskets full are thrown into the front part of the furnace so that the fire, being driven back by it, may also smelt the ore and the sows that form round about the nozzles of the bellows. This process of smelting is very ancient among the Tyrolese[18], but not so old among the Bohemians.

The second method of smelting ores stands in a measure midway between that one performed in a furnace of which the tap-hole is closed intermittently, and the first of the methods performed in a furnace where the tap-hole is always open. In this manner are smelted the ores of gold and silver that are neither very rich nor very poor, but mediocre, which fuse easily and are readily absorbed by the lead. It was found that in this way a large quantity of ore could be smelted at one operation without much labour or great expense, and could thus be alloyed with lead. This furnace has two crucibles, one of which is half inside the furnace and half outside, so that the lead being put into this crucible, the part of the lead which is in the furnace absorbs the metals of the ores which easily fuse; the other crucible is lower, and the alloy and the molten pyrites run into it. Those who make use of this method of smelting, tap the alloy of gold or silver with lead from the upper crucible once or twice if need be, and throw in other lead or litharge, and each absorbs that flux which is nearest. This method of smelting is in use in Styria[19].

The furnace in the third method of smelting ores has the tap-hole likewise open, but the furnace is higher and wider than the others, and its bellows are larger; for these reasons a larger charge of the ore can be thrown into it. When the mines yield a great abundance of ore for the smelter, they smelt in the same furnace continuously for three days and three nights, providing there be no defect either in the hearth or in the forehearth. In this kind of a furnace almost every kind of accretion will be found. The forehearth of the furnace is not unlike the forehearth of the first furnace of all, except that it has a tap-hole. However, because large charges of ore are smelted uninterruptedly, and the melted material runs out and the slags are skimmed off, there is need for a second forehearth crucible, into which the molten material runs through an opened tap-hole when the first is full. When a smelter has spent twelve hours' labour on this work, another always takes his place. The ores of copper and lead and the poorest ores of gold and silver are smelted by this method, because they cannot be smelted by the other three methods on account of the greater expense occasioned. Yet by this method a _centumpondium_ of ore containing only one or two _drachmae_ of gold, or only a half to one _uncia_, of silver,[20] can be smelted; because there is a large amount of ore in each charge, smelting is continuous, and without expensive fluxes such as lead, litharge, and hearth-lead. In this method of smelting we must use only cupriferous pyrites which easily melt in the fire, in truth the cakes melted out from this, if they no longer absorb much gold or silver, are replenished again from crude pyrites alone. If from this poor ore, with melted pyrites alone, material for cakes cannot be made, there are added other fluxes which have not previously been melted. These fluxes are, namely, lead ore, stones easily fused by fire of the second order and sand made from them, limestone, _tophus_, white schist, and iron stone[21].

Although this method of smelting ores is rough and might not seem to be of great use, yet it is clever and useful; for a great weight of ores, in which the gold, silver, or copper are in small quantities, may be reduced into a few cakes containing all the metal. If on being first melted they are too crude to be suitable for the second melting, in which the lead absorbs the precious metals that are in the cakes, or in which the copper is melted out of them, yet they can be made suitable if they are repeatedly roasted, sometimes as often as seven or eight times, as I have explained in the last book. Smelters of this kind are so clever and expert, that in smelting they take out all the gold and silver which the assayer in assaying the ores has stated to be contained in them, because if during the first operation, when he makes the cakes, there is a _drachma_ of gold or half an _uncia_ of silver lost from the ores, the smelter obtains it from the slags by the second smelting. This method of smelting ores is old and very common to most of those who use other methods.

Although lead ores are usually smelted in the third furnace--whose tap-hole is always open,--yet not a few people melt them in special furnaces by a method which I will briefly explain. The _Carni_[22] first burn such lead ores, and afterward break and crush them with large round mallets. Between the two low walls of a hearth, which is inside a furnace made of and vaulted with a rock that resists injury by the fire and does not burn into chalk, they place green wood with a layer of dry wood on the top of it; then they throw the ore on to this, and when the wood is kindled the lead drips down and runs on to the underlying sloping hearth[23]. This hearth is made of pulverised charcoal and earth, as is also a large crucible, one-half of which lies under the furnace and the other half outside it, into which runs the lead. The smelter, having first skimmed off the slags and other things with a hoe, pours the lead with a ladle into moulds, taking out the cakes after they have cooled. At the back of the furnace is a rectangular hole, so that the fire may be allowed more draught, and so that the smelter can crawl through it into the furnace if necessity demands.

The Saxons who inhabit Gittelde, when smelting lead ore in a furnace not unlike a baking oven, put the wood in through a hole at the back of the furnace, and when it begins to burn vigorously the lead trickles out of the ore into a forehearth. When this is full, the smelting being accomplished, the tap-hole is opened with a bar, and in this way the lead, together with the slags, runs into the dipping-pots below. Afterward the cakes of lead, when they are cold, are taken from the moulds.

In Westphalia they heap up ten wagon-loads of charcoal on some hillside which adjoins a level place, and the top of the heap being made flat, straw is thrown upon it to the thickness of three or four digits. On the top of this is laid as much pure lead ore as the heap can bear; then the charcoal is kindled, and when the wind blows, it fans the fire so that the ore is smelted. In this wise the lead, trickling down from the heap, flows on to the level and forms broad thin slabs. A few hundred pounds of lead ore are kept at hand, which, if things go well, are scattered over the heap. These broad slabs are impure and are laid upon dry wood which in turn is placed on green wood laid over a large crucible, and the former having been kindled, the lead is re-melted.

The Poles use a hearth of bricks four feet high, sloping on both sides and plastered with lute. On the upper level part of the hearth large pieces of wood are piled, and on these is placed small wood with lute put in between; over the top are laid wood shavings, and upon these again pure lead ore covered with large pieces of wood. When these are kindled, the ore melts and runs down on to the lower layer of wood; and when this is consumed by the fire, the metal is collected. If necessity demand, it is melted over and over again in the same manner, but it is finally melted by means of wood laid over the large crucible, the slabs of lead being placed upon it.

The concentrates from washing are smelted together with slags (fluxes?) in a third furnace, of which the tap-hole is always open.

It is worth while to build vaulted dust-chambers over the furnaces, especially over those in which the precious ores are to be smelted, in order that the thicker part of the fumes, in which metals are not wanting, may be caught and saved. In this way two or more furnaces are combined under the same vaulted ceiling, which is supported by the wall, against which the furnaces are built, and by four columns. Under this the smelters of the ore perform their work. There are two openings through which the fumes rise from the furnaces into the wide vaulted chamber, and the wider this is the more fumes it collects; in the middle of this chamber over the arch is an opening three palms high and two wide. This catches the fumes of both furnaces, which have risen up from both sides of the vaulted chamber to its arch, and have fallen again because they could not force their way out; and they thus pass out through the opening mentioned, into the chimney which the Greeks call [Greek: kapnodoche], the name being taken from the object. The chimney has thin iron plates fastened into the walls, to which the thinner metallic substances adhere when ascending with the fumes. The thicker metallic substances, or _cadmia_,[25] adhere to the vaulted chamber, and often harden into stalactites. On one side of the chamber is a window in which are set panes of glass, so that the light may be transmitted, but the fumes kept in; on the other side is a door, which is kept entirely closed while the ores are being smelted in the furnaces, so that none of the fumes may escape. It is opened in order that the workman, passing through it, may be enabled to enter the chamber and remove the soot and _pompholyx_[26] and chip off the _cadmia_; this sweeping is done twice a year. The soot mixed with _pompholyx_ and the _cadmia_, being chipped off, is thrown down through a long chute made of four boards joined in the shape of a rectangle, that they should not fly away. They fall on to the floor, and are sprinkled with salt water, and are again smelted with ore and litharge, and become an emolument to the proprietors. Such chambers, which catch the metallic substances that rise with the fumes, are profitable for all metalliferous ores; but especially for the minute metallic particles collected by washing crushed ores and rock, because these usually fly out with the fire of the furnaces.

I have explained the four general methods of smelting ores; now I will state how the ores of each metal are smelted, or how the metal is obtained from the ore. I will begin with gold. Its sand, the concentrates from washing, or the gold dust collected in any other manner, should very often not be smelted, but should be mixed with quicksilver and washed with tepid water, so that all the impurities may be eliminated. This method I explained in Book VII. Or they are placed in the _aqua_ which separates gold from silver, for this also separates its impurities. In this method we see the gold sink in the glass ampulla, and after all the _aqua_ has been drained from the particles, it frequently remains as a gold-coloured residue at the bottom; this powder, when it has been moistened with oil made from argol[27], is then dried and placed in a crucible, where it is melted with borax or with saltpetre and salt; or the same very fine dust is thrown into molten silver, which absorbs it, and from this it is again parted by _aqua valens_[28].

It is necessary to smelt gold ore either outside the blast furnace in a crucible, or inside the blast furnace; in the former case a small charge of ore is used, in the latter a large charge of it. _Rudis_ gold, of whatever colour it is, is crushed with a _libra_ each of sulphur and salt, a third of a _libra_ of copper, and a quarter of a _libra_ of argol; they should be melted in a crucible on a slow fire for three hours, then the alloy is put into molten silver that it may melt more rapidly. Or a _libra_ of the same crude gold, crushed up, is mixed together with half a _libra_ of _stibium_ likewise crushed, and put into a crucible with half an _uncia_ of copper filings, and heated until they melt, then a sixth part of granulated lead is thrown into the same crucible. As soon as the mixture emits an odour, iron-filings are added to it, or if these are not at hand, iron hammer-scales, for both of these break the strength of the _stibium_. When the fire consumes it, not alone with it is some strength of the _stibium_ consumed, but some particles of gold and also of silver, if it be mixed with the gold[29]. When the button has been taken out of the crucible and cooled, it is melted in a cupel, first until the antimony is exhaled, and thereafter until the lead is separated from it.

Crushed pyrites which contains gold is smelted in the same way; it and the _stibium_ should be of equal weight and in truth the gold may be made from them in a number of different ways[30]. One part of crushed material is mixed with six parts of copper, one part of sulphur, half a part of salt, and they are all placed in a pot and over them is poured wine distilled by heating liquid argol in an ampulla. The pot is covered and smeared over with lute and is put in a hot place, so that the mixture moistened with wine may dry for the space of six days, then it is heated for three hours over a gentle fire that it may combine more rapidly with the lead. Finally it is put into a cupel and the gold is separated from the lead[31].

Or else one _libra_ of the concentrates from washing pyrites, or other stones to which gold adheres, is mixed with half a _libra_ of salt, half a _libra_ of argol, a third of a _libra_ of glass-galls, a sixth of a _libra_ of gold or silver slags, and a _sicilicus_ of copper. The crucible into which these are put, after it has been covered with a lid, is sealed with lute and placed in a small furnace that is provided with small holes through which the air is drawn in, and then it is heated until it turns red and the substances put in have alloyed; this should take place within four or five hours. The alloy having cooled, it is again crushed to powder and a pound of litharge is added to it; then it is heated again in another crucible until it melts. The button is taken out, purged of slag, and placed in a cupel, where the gold is separated from the lead.

Or to a _libra_ of the powder prepared from such metalliferous concentrates, is added a _libra_ each of salt, of saltpetre, of argol, and of glass-galls, and it is heated until it melts. When cooled and crushed, it is washed, then to it is added a _libra_ of silver, a third of copper filings, a sixth of litharge, and it is likewise heated again until it melts. After the button has been purged of slag, it is put into the cupel, and the gold and silver are separated from the lead; the gold is parted from the silver with _aqua valens_. Or else a _libra_ of the powder prepared from such metalliferous concentrates, a quarter of a _libra_ of copper filings, and two _librae_ of that second powder[32] which fuses ores, are heated until they melt. The mixture when cooled is again reduced to powder, roasted and washed, and in this manner a blue powder is obtained. Of this, and silver, and that second powder which fuses ores, a _libra_ each are taken, together with three _librae_ of lead, and a quarter of a _libra_ of copper, and they are heated together until they melt; then the button is treated as before. Or else a _libra_ of the powder prepared from such metalliferous concentrates, half a _libra_ of saltpetre, and a quarter of a _libra_ of salt are heated until they melt. The alloy when cooled is again crushed to powder, one _libra_ of which is absorbed by four pounds of molten silver. Or else a _libra_ of the powder made from that kind of concentrates, together with a _libra_ of sulphur, a _libra_ and a half of salt, a third of a _libra_ of salt made from argol, and a third of a _libra_ of copper resolved into powder with sulphur, are heated until they melt. Afterward the lead is re-melted, and the gold is separated from the other metals. Or else a _libra_ of the powder of this kind of concentrates, together with two _librae_ of salt, half a _libra_ of sulphur, and one _libra_ of litharge, are heated, and from these the gold is melted out. By these and similar methods concentrates containing gold, if there be a small quantity of them or if they are very rich, can be smelted outside the blast furnace.

If there be much of them and they are poor, then they are smelted in the blast furnace, especially the ore which is not crushed to powder, and particularly when the gold mines yield an abundance of it[33]. The gold concentrates mixed with litharge and hearth-lead, to which are added iron-scales, are smelted in the blast furnace whose tap-hole is intermittently closed, or else in the first or the second furnaces in which the tap-hole is always open. In this manner an alloy of gold and lead is obtained which is put into the cupellation furnace. Two parts of roasted pyrites or _cadmia_ which contain gold, are put with one part of unroasted, and are smelted together in the third furnace whose tap-hole is always open, and are made into cakes. When these cakes have been repeatedly roasted, they are re-smelted in the furnace whose tap-hole is temporarily closed, or in one of the two others whose tap-holes are always open. In this manner the lead absorbs the gold, whether pure or argentiferous or cupriferous, and the alloy is taken to the cupellation furnace. Pyrites, or other gold ore which is mixed with much material that is consumed by fire and flies out of the furnace, is melted with stone from which iron is melted, if this is at hand. Six parts of such pyrites, or of gold ore reduced to powder and sifted, four of stone from which iron is made, likewise crushed, and three of slaked lime, are mixed together and moistened with water; to these are added two and a half parts of the cakes which contain some copper, together with one and a half parts of slag. A basketful of fragments of the cakes is thrown into the furnace, then the mixture of other things, and then the slag. Now when the middle part of the forehearth is filled with the molten material which runs down from the furnace, the slags are first skimmed off, and then the cakes made of pyrites; afterward the alloy of copper, gold and silver, which settles at the bottom, is taken out. The cakes are gently roasted and re-smelted with lead, and made into cakes, which are carried to other works. The alloy of copper, gold, and silver is not roasted, but is re-melted again in a crucible with an equal portion of lead. Cakes are also made much richer in copper and gold than those I spoke of. In order that the alloy of gold and silver may be made richer, to eighteen _librae_ of it are added forty-eight _librae_ of crude ore, three _librae_ of the stone from which iron is made, and three-quarters of a _libra_ of the cakes made from pyrites, and mixed with lead, all are heated together in the crucible until they melt. When the slag and the cakes melted from pyrites have been skimmed off, the alloy is carried to other furnaces.

There now follows silver, of which the native silver or the lumps of _rudis_ silver[34] obtained from the mines are not smelted in the blast furnaces, but in small iron pans, of which I will speak at the proper place; these lumps are heated and thrown into molten silver-lead alloy in the cupellation furnace when the silver is being separated from the lead, and refined. The tiny flakes or tiny lumps of silver adhering to stones or marble or rocks, or again the same little lumps mixed with earth, or silver not pure enough, should be smelted in the furnace of which the tap-hole is only closed for a short time, together with cakes melted from pyrites, with silver slags, and with stones which easily fuse in fire of the second order.

In order that particles of silver should not fly away[35] from the lumps of ore consisting of minute threads of pure silver and twigs of native silver, they are enclosed in a pot, and are placed in the same furnace where the rest of the silver ores are being smelted. Some people smelt lumps of native silver not sufficiently pure, in pots or triangular crucibles, whose lids are sealed with lute. They do not place these pots in the blast furnace, but arrange them in the assay furnace into which the draught of the air blows through small holes. To one part of the native silver they add three parts of powdered litharge, as many parts of hearth-lead, half a part of galena[36], and a small quantity of salt and iron-scales. The alloy which settles at the bottom of the other substances in the pot is carried to the cupellation furnace, and the slags are re-melted with the other silver slags. They crush under the stamps and wash the pots or crucibles to which silver-lead alloy or slags adhere, and having collected the concentrates they smelt them together with the slags. This method of smelting _rudis_ silver, if there is a small quantity of it, is the best, because the smallest portion of silver does not fly out of the pot or the crucible, and get lost.

If bismuth ore or antimony ore or lead ore[37] contains silver, it is smelted with the other ores of silver; likewise galena or pyrites, if there is a small amount of it. If there be much galena, whether it contain a large or a small amount of silver, it is smelted separately from the others; which process I will explain a little further on.

Because lead and copper ores and their metals have much in common with silver ores, it is fitting that I should say a great deal concerning them, both now and later on. Also in the same manner, pyrites are smelted separately if there be much of them. To three parts of roasted lead or copper ore and one part of crude ore, are added concentrates if they were made by washing the same ore, together with slags, and all are put in the third furnace whose tap-hole is always open. Cakes are made from this charge, which, when they have been quenched with water, are roasted. Of these roasted cakes generally four parts are again mixed with one part of crude pyrites and re-melted in the same furnace. Cakes are again made from this charge, and if there is a large amount of copper in these cakes, copper is made immediately after they have been roasted and re-melted; if there is little copper in the cakes they are also roasted, but they are re-smelted with a little soft slag. In this method the molten lead in the forehearth absorbs the silver. From the pyritic material which floats on the top of the forehearth are made cakes for the third time, and from them when they have been roasted and re-smelted is made copper. Similarly, three parts of roasted _cadmia_[38] in which there is silver, are mixed with one part of crude pyrites, together with slag, and this charge is smelted and cakes are made from it; these cakes having been roasted are re-smelted in the same furnace. By this method the lead contained in the forehearth absorbs the silver, and the silver-lead is taken to the cupellation furnace. Crude quartz and stones which easily fuse in fire of the third order, together with other ores in which there is a small amount of silver, ought to be mixed with crude roasted pyrites or _cadmia_, because the roasted cakes of pyrites or _cadmia_ cannot be profitably smelted separately. In a similar manner earths which contain little silver are mixed with the same; but if pyrites and _cadmia_ are not available to the smelter, he smelts such silver ores and earths with litharge, hearth-lead, slags, and stones which easily melt in the fire. The concentrates[39] originating from the washing of _rudis_ silver, after first being roasted[40] until they melt, are smelted with mixed litharge and hearth-lead, or else, after being moistened with water, they are smelted with cakes made from pyrites and _cadmia_. By neither of these methods do (the concentrates) fall back in the furnace, or fly out of it, driven by the blast of the bellows and the agitation of the fire. If the concentrates originated from galena they are smelted with it after having been roasted; and if from pyrites, then with pyrites.

Pure copper ore, whether it is its own colour or is tinged with chrysocolla or azure, and copper glance, or grey or black _rudis_ copper, is smelted in a furnace of which the tap-hole is closed for a very short time, or else is always open[41]. If there is a large amount of silver in the ore it is run into the forehearth, and the greater part of the silver is absorbed by the molten lead, and the remainder is sold with the copper to the proprietor of the works in which silver is parted from copper[42]. If there is a small amount of silver in the ore, no lead is put into the forehearth to absorb the silver, and the above-mentioned proprietors buy it in with the copper; if there be no silver, copper is made direct. If such copper ore contains some minerals which do not easily melt, as pyrites or _cadmia metallica fossilis_[43], or stone from which iron is melted, then crude pyrites which easily fuse are added to it, together with slag. From this charge, when smelted, they make cakes; and from these, when they have been roasted as much as is necessary and re-smelted, the copper is made. But if there be some silver in the cakes, for which an outlay of lead has to be made, then it is first run into the forehearth, and the molten lead absorbs the silver.

Indeed, _rudis_ copper ore of inferior quality, whether ash-coloured or purple, blackish and occasionally in parts blue, is smelted in the first furnace whose tap-hole is always open. This is the method of the Tyrolese. To as much _rudis_ copper ore as will fill eighteen vessels, each of which holds almost as much as seven Roman _moduli_[44], the first smelter--for there are three--adds three cartloads of lead slags, one cartload of schist, one fifth of a _centumpondium_ of stones which easily fuse in the fire, besides a small quantity of concentrates collected from copper slag and accretions, all of which he smelts for the space of twelve hours, and from which he makes six _centumpondia_ of primary cakes and one-half of a _centumpondium_ of alloy. One half of the latter consists of copper and silver, and it settles to the bottom of the forehearth. In every _centumpondium_ of the cakes there is half a _libra_ of silver and sometimes half an _uncia_ besides; in the half of a _centumpondium_ of the alloy there is a _bes_ or three-quarters of silver. In this way every week, if the work is for six days, thirty-six _centumpondia_ of cakes are made and three _centumpondia_ of alloy, in all of which there is often almost twenty-four _librae_ of silver. The second smelter separates from the primary cakes the greater part of the silver by absorbing it in lead. To eighteen _centumpondia_ of cakes made from crude copper ore, he adds twelve _centumpondia_ of hearth-lead and litharge, three _centumpondia_ of stones from which lead is smelted, five _centumpondia_ of hard cakes rich in silver, and two _centumpondia_ of exhausted liquation cakes[45]; he adds besides, some of the slags resulting from smelting crude copper, together with a small quantity of concentrates made from accretions, all of which he melts for the space of twelve hours, and makes eighteen _centumpondia_ of secondary cakes, and twelve _centumpondia_ of copper-lead-silver alloy; in each _centumpondium_ of the latter there is half a _libra_ of silver. After he has taken off the cakes with a hooked bar, he pours the alloy out into copper or iron moulds; by this method they make four cakes of alloy, which are carried to the works in which silver is parted from copper. On the following day, the same smelter, taking eighteen _centumpondia_ of the secondary cakes, again adds twelve _centumpondia_ of hearth-lead and litharge, three _centumpondia_ of stones from which lead is smelted, five _centumpondia_ of hard cakes rich in silver, together with slags from the smelting of the primary cakes, and with concentrates washed from the accretions which are usually made at that time. This charge is likewise smelted for the space of twelve hours, and he makes as many as thirteen _centumpondia_ of tertiary cakes and eleven _centumpondia_ of copper-lead-silver alloy, each _centumpondium_ of which contains one-third of a _libra_ and half an _uncia_ of silver. When he has skimmed off the tertiary cakes with a hooked bar, the alloy is poured into copper moulds, and by this method four cakes of alloy are made, which, like the preceding four cakes of alloy, are carried to the works in which silver is parted from copper. By this method the second smelter makes primary cakes on alternate days and secondary cakes on the intermediate days. The third smelter takes eleven cartloads of the tertiary cakes and adds to them three cartloads of hard cakes poor in silver, together with the slag from smelting the secondary cakes, and the concentrates from the accretions which are usually made at that time. From this charge when smelted, he makes twenty _centumpondia_ of quaternary cakes, which are called "hard cakes," and also fifteen _centumpondia_ of those "hard cakes rich in silver," each _centumpondium_ of which contains a third of a _libra_ of silver. These latter cakes the second smelter, as I said before, adds to the primary and secondary cakes when he re-melts them. In the same way, from eleven cartloads of quaternary cakes thrice roasted, he makes the "final" cakes, of which one _centumpondium_ contains only half an _uncia_ of silver. In this operation he also makes fifteen _centumpondia_ of "hard cakes poor in silver," in each _centumpondium_ of which is a sixth of a _libra_ of silver. These hard cakes the third smelter, as I have said, adds to the tertiary cakes when he re-smelts them, while from the "final" cakes, thrice roasted and re-smelted, is made black copper[46].

The _rudis_ copper from which pure copper is made, if it contains little silver or if it does not easily melt, is first smelted in the third furnace of which the tap-hole is always open; and from this are made cakes, which after being seven times roasted are re-smelted, and from these copper is melted out; the cakes of copper are carried to a furnace of another kind, in which they are melted for the third time, in order that in the copper "bottoms" there may be more silver, while in the "tops" there may be less, which process is explained in Book XI.

Pyrites, when they contain not only copper, but also silver, are smelted in the manner I described when I treated of ores of silver. But if they are poor in silver, and if the copper which is melted out of them cannot easily be treated, they are smelted according to the method which I last explained.

Finally, the copper schists containing bitumen or sulphur are roasted, and then smelted with stones which easily fuse in a fire of the second order, and are made into cakes, on the top of which the slags float. From these cakes, usually roasted seven times and re-melted, are melted out slags and two kinds of cakes; one kind is of copper and occupies the bottom of the crucible, and these are sold to the proprietors of the works in which silver is parted from copper; the other kind of cakes are usually re-melted with primary cakes. If the schist contains but a small amount of copper, it is burned, crushed under the stamps, washed and sieved, and the concentrates obtained from it are melted down; from this are made cakes from which, when roasted, copper is made. If either chrysocolla or azure, or yellow or black earth containing copper and silver, adheres to the schist, it is not washed, but is crushed and smelted with stones which easily fuse in fire of the second order.