De Re Metallica Part 39

The pots, lest they should become defective, are moulded from the best potters' clay, for if there are defects the quicksilver flies out in the fumes. If the fumes give out a very sweet odour it indicates that the quicksilver is being lost, and since this loosens the teeth, the smelters and others standing by, warned of the evil, turn their backs to the wind, which drives the fumes in the opposite direction; for this reason, the building should be open around the front and the sides, and exposed to the wind. If these pots are made of cast copper they last a long time in the fire. This process for reducing the ores of quicksilver is used by most people.

In a similar manner the antimony ore,[57] if free from other metals, is reduced in upper pots which are twice as large as the lower ones. Their size, however, depends on the cakes, which have not the same weight everywhere; for in some places they are made to weigh six _librae_, in other places ten, and elsewhere twenty. When the smelter has concluded his operation, he extinguishes the fire with water, removes the lids from the pots, throws earth mixed with ash around and over them, and when they have cooled, takes out the cakes from the pots.

[Ill.u.s.tration 429 (Quicksilver distillation Furnaces): A--Pots.

B--Opercula. C--Nozzles. D--Gourd-shaped earthenware vessels.]

Other methods for reducing quicksilver are given below. Big-bellied pots, having been placed in the upper rectangular open part of a furnace, are filled with the crushed ore. Each of these pots is covered with a lid with a long nozzle--commonly called a _campana_--in the shape of a bell, and they are cemented. Each of the small earthenware vessels shaped like a gourd receives two of these nozzles, and these are likewise cemented. Dried wood having been placed in the lower part of the furnace and kindled, the ore is heated until all the quicksilver has risen into the operculum which is over the pot; it then flows from the nozzle and is caught in the earthenware gourd-shaped vessel.

[Ill.u.s.tration 430 (Quicksilver distillation Furnaces): A--Enclosed chamber. B--Door. C--Little windows. D--Mouths through the walls.

E--Furnace in the enclosed chamber. F--Pots.]

Others build a hollow vaulted chamber, of which the paved floor is made concave toward the centre. Inside the thick walls of the chamber are the furnaces. The doors through which the wood is put are in the outer part of the same wall. They place the pots in the furnaces and fill them with crushed ore, then they cement the pots and the furnaces on all sides with lute, so that none of the vapour may escape from them, and there is no entrance to the furnaces except through their mouths. Between the dome and the paved floor they arrange green trees, then they close the door and the little windows, and cover them on all sides with moss and lute, so that none of the quicksilver can exhale from the chamber. After the wood has been kindled the ore is heated, and exudes the quicksilver; whereupon, impatient with the heat, and liking the cold, it escapes to the leaves of the trees, which have a cooling power. When the operation is completed the smelter extinguishes the fire, and when all gets cool he opens the door and the windows, and collects the quicksilver, most of which, being heavy, falls of its own accord from the trees, and flows into the concave part of the floor; if all should not have fallen from the trees, they are shaken to make it fall.

[Ill.u.s.tration 431 (Quicksilver distillation Furnaces): A--Larger pot.

B--Smaller. C--Tripod. D--Tub in which the sand is washed.]

The following is the fourth method of reducing ores of quicksilver. A larger pot standing on a tripod is filled with crushed ore, and over the ore is put sand or ashes to a thickness of two digits, and tamped; then in the mouth of this pot is inserted the mouth of another smaller pot and cemented with lute, lest the vapours are emitted. The ore heated by the fire exhales the quicksilver, which, penetrating through the sand or the ashes, takes refuge in the upper pot, where condensing into drops it falls back into the sand or the ashes, from which the quicksilver is washed and collected.

[Ill.u.s.tration 432 (Quicksilver distillation Furnaces): A--Pots. B--Lids.

C--Stones. D--Furnace.]

The fifth method is not very unlike the fourth. In the place of these pots are set other pots, likewise of earthenware, having a narrow bottom and a wide mouth. These are nearly filled with crushed ore, which is likewise covered with ashes to a depth of two digits and tamped in. The pots are covered with lids a digit thick, and they are smeared over on the inside with liquid litharge, and on the lid are placed heavy stones.

The pots are set on the furnace, and the ore is heated and similarly exhales quicksilver, which fleeing from the heat takes refuge in the lid; on congealing there, it falls back into the ashes, from which, when washed, the quicksilver is collected.

By these five methods quicksilver may be made, and of these not one is to be despised or repudiated; nevertheless, if the mine supplies a great abundance of ore, the first is the most expeditious and practical, because a large quant.i.ty of ore can be reduced at the same time without great expense.[58]

[Ill.u.s.tration 434 (Bis.m.u.th Smelting): A--Pit across which wood is placed. B--Forehearth. C--Ladle. D--Iron mould. E--Cakes. F--Empty pot lined with stones in layers. G--Troughs. H--Pits dug at the foot of the troughs. I--Small wood laid over the troughs. K--Wind.]

Bis.m.u.th[59] ore, free from every kind of silver, is smelted by various methods. First a small pit is dug in the dry ground; into this pulverised charcoal is thrown and tamped in, and then it is dried with burning charcoal. Afterward, thick dry pieces of beech wood are placed over the pit, and the bis.m.u.th ore is thrown on it. As soon as the kindled wood burns, the heated ore drips with bis.m.u.th, which runs down into the pit, from which when cooled the cakes are removed. Because pieces of burnt wood, or often charcoal and occasionally slag, drop into the bis.m.u.th which collects in the pit, and make it impure, it is put back into another kind of crucible to be melted, so that pure cakes may be made. There are some who, bearing these things in mind, dig a pit on a sloping place and below it put a forehearth, into which the bis.m.u.th continually flows, and thus remains clean; then they take it out with ladles and pour it into iron pans lined inside with lute, and make cakes of it. They cover such pits with flat stones, whose joints are besmeared with a lute of mixed dust and crushed charcoal, lest the joints should absorb the molten bis.m.u.th. Another method is to put the ore in troughs made of fir-wood and placed on sloping ground; they place small firewood over it, kindling it when a gentle wind blows, and thus the ore is heated. In this manner the bis.m.u.th melts and runs down from the troughs into a pit below, while there remains slag, or stones, which are of a yellow colour, as is also the wood laid across the pit. These are also sold.

[Ill.u.s.tration 435 (Bis.m.u.th Smelting): A--Wood. B--Bricks. C--Pans.

D--Furnace. E--Crucible. F--Pipe. G--Dipping-pot.]

Others reduce the ore in iron pans as next described. They lay small pieces of dry wood alternately straight and transversely upon bricks, one and a half feet apart, and set fire to it. Near it they put small iron pans lined on the inside with lute, and full of broken ore; then when the wind blows the flame of the fierce fire over the pans, the bis.m.u.th drips out of the ore; wherefore, in order that it may run, the ore is stirred with the tongs; but when they decide that all the bis.m.u.th is exuded, they seize the pans with the tongs and remove them, and pour out the bis.m.u.th into empty pans, and by turning many into one they make cakes. Others reduce the ore, when it is not mixed with _cadmia_,[60] in a furnace similar to the iron furnace. In this case they make a pit and a crucible of crushed earth mixed with pulverised charcoal, and into it they put the broken ore, or the concentrates from washing, from which they make more bis.m.u.th. If they put in ore, they reduce it with charcoal and small dried wood mixed, and if concentrates, they use charcoal only; they blow both materials with a gentle blast from a bellows. From the crucible is a small pipe through which the molten bis.m.u.th runs down into a dipping-pot, and from this cakes are made.

[Ill.u.s.tration 436 (Bis.m.u.th Smelting): A--Hearth in which ore is melted.

B--Hearth on which lie drops of bis.m.u.th. C--Tongs. D--Basket. E--Wind.]

On a dump thrown up from the mines, other people construct a hearth exposed to the wind, a foot high, three feet wide, and four and a half feet long. It is held together by four boards, and the whole is thickly coated at the top with lute. On this hearth they first put small dried sticks of fir wood, then over them they throw broken ore; then they lay more wood over it, and when the wind blows they kindle it. In this manner the bis.m.u.th drips out of the ore, and afterward the ashes of the wood consumed by the fire and the charcoals are swept away. The drops of bis.m.u.th which fall down into the hearth are congealed by the cold, and they are taken away with the tongs and thrown into a basket. From the melted bis.m.u.th they make cakes in iron pans.

[Ill.u.s.tration 437 (Bis.m.u.th Smelting): A--Box. B--Pivot. C--Transverse wood beams. D--Grate. E--Its feet. F--Burning wood. G--Stick. H--Pans in which the bis.m.u.th is melted. I--Pans for moulds. K--Cakes. L--Fork.

M--Brush.]

Others again make a box eight feet long, four feet wide, and two feet high, which they fill almost full of sand and cover with bricks, thus making the hearth. The box has in the centre a wooden pivot, which turns in a hole in two beams laid transversely one upon the other; these beams are hard and thick, are sunk into the ground, both ends are perforated, and through these holes wedge-shaped pegs are driven, in order that the beams may remain fixed, and that the box may turn round, and may be turned toward the wind from whichever quarter of the sky in may blow. In such a hearth they put an iron grate, as long and wide as the box and three-quarters of a foot high; it has six feet, and there are so many transverse bars that they almost touch one another. On the grate they lay pine-wood and over it broken ore, and over this they again lay pine-wood. When it has been kindled the ore melts, out of which the bis.m.u.th drips down; since very little wood is burned, this is the most profitable method of smelting the bis.m.u.th. The bis.m.u.th drips through the grate on to the hearth, while the other things remain upon the grate with the charcoal. When the work is finished, the workman takes a stick from the hearth and overturns the grate, and the things which have been acc.u.mulated on it; with the brush he sweeps up the bis.m.u.th and collects it in a basket, and then he melts it in an iron pan and makes cakes. As soon as possible after it is cool, he turns the pans over, so that the cakes may fall out, using for this purpose a two-p.r.o.nged fork of which one p.r.o.ng is again forked. And immediately afterward he returns to his labours.

END OF BOOK IX.

FOOTNOTES:

[1] The history of the fusion of ores and of metals is the history of individual processes, and such information as we have been able to discover upon the individual methods previous to Agricola we give on the pages where such processes are discussed. In general the records of the beginnings of metallurgy are so nebular that, if one wishes to shirk the task, he can adopt the explanation of William Pryce one hundred and fifty years ago: "It is very probable that the nature and use of Metals were not revealed to Adam in his state of innocence: the toil and labour necessary to procure and use those implements of the iron age could not be known, till they made part of the curse incurred by his fall: 'In the sweat of thy face shalt thou eat bread, till thou return unto the ground; in sorrow shalt thou eat of it all the days of thy life'

(Genesis). That they were very early discovered, however, is manifest from the Mosaick account of Tubal Cain, who was the first instructor of every artificer in Bra.s.s [_sic_] and Iron" (_Mineralogia Cornubiensis_, p. 2).

It is conceivable that gold could be found in large enough pieces to have had general use in pre-historic times, without fusion; but copper, which was also in use, must have been smelted, and therefore we must a.s.sume a considerable development of human knowledge on the subject prior to any human record. Such incidental mention as exists after record begins does not, of course, extend to the beginning of any particular branch of the art--in fact, special arts obviously existed long before such mention, and down to the complete survey of the state of the art by Agricola our dates are necessarily "prior to" some first mention in literature, or "prior to" the known period of existing remains of metallurgical operations. The scant Egyptian records, the Scriptures, and the Shoo King give a little insight prior to 1000 B.C.

The more extensive Greek literature of about the 5th to the 3rd centuries B.C., together with the remains of Greek mines, furnish another datum point of view, and the Roman and Greek writers at the beginning of the Christian era give a still larger view. After them our next step is to the Monk Theophilus and the Alchemists, from the 12th to the 14th centuries. Finally, the awakening of learning at the end of the 15th and the beginning of the 16th centuries, enables us for the first time to see practically all that was known. The wealth of literature which exists subsequent to this latter time makes history thereafter a matter of some precision, but it is not included in this undertaking.

Considering the great part that the metals have played in civilization, it is astonishing what a minute amount of information is available on metallurgy. Either the ancient metallurgists were secretive as to their art, or the ancient authors despised such common things, or, as is equally probable, the very partial preservation of ancient literature, by painful transcription over a score of centuries, served only for those works of more general interest. In any event, if all the direct or indirect material on metallurgy prior to the 15th century were compiled, it would not fill 40 pages such as these.

It may be of service to give a tabular summary indicating approximately the time when evidence of particular operations appear on the historical horizon:

Gold washed from alluvial Prior to recorded civilization

Copper reduced from ores by smelting Prior to recorded civilization

Bitumen mined and used Prior to recorded civilization

Tin reduced from ores by smelting Prior to 3500 B.C.

Bronze made Prior to 3500 B.C.

Iron reduced from ores by smelting Prior to 3500 B.C.

Soda mined and used Prior to 3500 B.C.

Gold reduced from ores by concentration Prior to 2500 B.C.

Silver reduced from ores by smelting Prior to 2000 B.C.

Lead reduced from ores by smelting Prior to 2000 B.C.

(perhaps prior to 3500 B.C.)

Silver parted from lead by cupellation Prior to 2000 B.C.

Bellows used in furnaces Prior to 1500 B.C.

Steel produced Prior to 1000 B.C.

Base metals separated from ores by water Prior to 500 B.C.

concentration

Gold refined by cupellation Prior to 500 B.C.

Sulphide ores smelted for lead Prior to 500 B.C.

Mercury reduced from ores by (?) Prior to 400 B.C.

White-lead made with vinegar Prior to 300 B.C.

Touchstone known for determining gold and silver Prior to 300 B.C.

fineness