De Re Metallica, Translated from the First Latin Edition of 1556

by Georg Agricola

Gold may be parted without injury from silver goblets and from other gilt vessels and articles[22], by means of a powder, which consists of one part of sal-ammoniac and half a part of sulphur. The gilt goblet or other article is smeared with oil, and the powder is dusted on; the article is seized in the hand, or with tongs, and is carried to the fire and sharply tapped, and by this means the gold falls into water in vessels placed underneath, while the goblet remains uninjured.

Gold is also parted from silver on gilt articles by means of quicksilver. This is poured into an earthen crucible, and so warmed by the fire that the finger can bear the heat when dipped into it; the silver-gilt objects are placed in it, and when the quicksilver adheres to them they are taken out and placed on a dish, into which, when cooled, the gold falls, together with the quicksilver. Again and frequently the same silver-gilt object is placed in heated quicksilver, and the same process is continued until at last no more gold is visible on the object; then the object is placed in the fire, and the quicksilver which adheres to it is exhaled. Then the artificer takes a hare's foot, and brushes up into a dish the quicksilver and the gold which have fallen together from the silver article, and puts them into a cloth made of woven cotton or into a soft leather; the quicksilver is squeezed through one or the other into another dish.[23] The gold remains in the cloth or the leather, and when collected is placed in a piece of charcoal hollowed out, and is heated until it melts, and a little button is made from it. This button is heated with a little stibium in an earthen crucible and poured out into another little vessel, by which method the gold settles at the bottom, and the stibium is seen to be on the top; then the work is completed. Finally, the gold button is put in a hollowed-out brick and placed in the fire, and by this method the gold is made pure. By means of the above methods gold is parted from silver and also silver from gold.

Now I will explain the methods used to separate copper from gold[24]. The salt which we call sal-artificiosus,[25] is made from a libra each of vitriol, alum, saltpetre, and sulphur not exposed to the fire, and half a libra of sal-ammoniac; these ingredients when crushed are heated with one part of lye made from the ashes used by wool dyers, one part of unslaked lime, and four parts of beech ashes. The ingredients are boiled in the lye until the whole has been dissolved. Then it is immediately dried and kept in a hot place, lest it turn into oil; and afterward when crushed, a libra of lead-ash is mixed with it. With each libra of this powdered compound one and a half unciae of the copper is gradually sprinkled into a hot crucible, and it is stirred rapidly and frequently with an iron rod. When the crucible has cooled and been broken up, the button of gold is found.

The second method for parting is the following. Two librae of sulphur not exposed to the fire, and four librae of refined salt are crushed and mixed; a sixth of a libra and half an uncia of this powder is added to a bes of granules made of lead, and twice as much copper containing gold; they are heated together in an earthen crucible until they melt. When cooled, the button is taken out and purged of slag. From this button they again make granules, to a third of a libra of which is added half a libra of that powder of which I have spoken, and they are placed in alternate layers in the crucible; it is well to cover the crucible and to seal it up, and afterward it is heated over a gentle fire until the granules melt. Soon afterward, the crucible is taken off the fire, and when it is cool the button is extracted. From this, when purified and again melted down, the third granules are made, to which, if they weigh a sixth of a libra, is added one half an uncia and a sicilicus of the powder, and they are heated in the same manner, and the button of gold settles at the bottom of the crucible.

The third method is as follows. From time to time small pieces of sulphur, enveloped in or mixed with wax, are dropped into six librae of the molten copper, and consumed; the sulphur weighs half an uncia and a sicilicus. Then one and a half sicilici of powdered saltpetre are dropped into the same copper and likewise consumed; then again half an uncia and a sicilicus of sulphur enveloped in wax; afterward one and a half sicilici of lead-ash enveloped in wax, or of minium made from red-lead. Then immediately the copper is taken out, and to the gold button, which is now mixed with only a little copper, they add stibium to double the amount of the button; these are heated together until the stibium is driven off; then the button, together with lead of half the weight of the button, are heated in a cupel. Finally, the gold is taken out of this and quenched, and if there is a blackish colour settled in it, it is melted with a little of the chrysocolla which the Moors call borax; if too pale, it is melted with stibium, and acquires its own golden-yellow colour. There are some who take out the molten copper with an iron ladle and pour it into another crucible, whose aperture is sealed up with lute, and they place it over glowing charcoal, and when they have thrown in the powders of which I have spoken, they stir the whole mass rapidly with an iron rod, and thus separate the gold from the copper; the former settles at the bottom of the crucible, the latter floats on the top. Then the aperture of the crucible is opened with the red-hot tongs, and the copper runs out. The gold which remains is re-heated with stibium, and when this is exhaled the gold is heated for the third time in a cupel with a fourth part of lead, and then quenched.

The fourth method is to melt one and a third librae of the copper with a sixth of a libra of lead, and to pour it into another crucible smeared on the inside with tallow or gypsum; and to this is added a powder consisting of half an uncia each of prepared sulphur, verdigris, and saltpetre, and an uncia and a half of sal coctus. The fifth method consists of placing in a crucible one libra of the copper and two librae of granulated lead, with one and a half unciae of sal-artificiosus; they are at first heated over a gentle fire and then over a fiercer one. The sixth method consists in heating together a bes of the copper and one-sixth of a libra each of sulphur, salt, and stibium. The seventh method consists of heating together a bes of the copper and one-sixth each of iron scales and filings, salt, stibium, and glass-galls. The eighth method consists of heating together one libra of the copper, one and a half librae of sulphur, half a libra of verdigris, and a libra of refined salt. The ninth method consists of placing in one libra of the molten copper as much pounded sulphur, not exposed to the fire, and of stirring it rapidly with an iron rod; the lump is ground to powder, into which quicksilver is poured, and this attracts to itself the gold.

Gilded copper articles are moistened with water and placed on the fire, and when they are glowing they are quenched with cold water, and the gold is scraped off with a brass rod. By these practical methods gold is separated from copper.

Either copper or lead is separated from silver by the methods which I will now explain.[26] This is carried on in a building near by the works, or in the works in which the gold or silver ores or alloys are smelted. The middle wall of such a building is twenty-one feet long and fifteen feet high, and from this a front wall is distant fifteen feet toward the river; the rear wall is nineteen feet distant, and both these walls are thirty-six feet long and fourteen feet high; a transverse wall extends from the end of the front wall to the end of the rear wall; then fifteen feet back a second transverse wall is built out from the front wall to the end of the middle wall. In that space which is between those two transverse walls are set up the stamps, by means of which the ores and the necessary ingredients for smelting are broken up. From the further end of the front wall, a third transverse wall leads to the other end of the middle wall, and from the same to the end of the rear wall. The space between the second and third transverse walls, and between the rear and middle long walls, contains the cupellation furnace, in which lead is separated from gold or silver. The vertical wall of its chimney is erected upon the middle wall, and the sloping chimney-wall rests on the beams which extend from the second transverse wall to the third; these are so located that they are at a distance of thirteen feet from the middle long wall and four from the rear wall, and they are two feet wide and thick. From the ground up to the roof-beams is twelve feet, and lest the sloping chimney-wall should fall down, it is partly supported by means of many iron rods, and partly by means of a few tie-beams covered with lute, which extend from the small beams of the sloping chimney-wall to the beams of the vertical chimney-wall. The rear roof is arranged in the same way as the roof of the works in which ore is smelted. In the space between the middle and the front long walls and between the second[27] and the third transverse walls are the bellows, the machinery for depressing and the instrument for raising them. A drum on the axle of a water-wheel has rundles which turn the toothed drum of an axle, whose long cams depress the levers of the bellows, and also another toothed drum on an axle, whose cams raise the tappets of the stamps, but in the opposite direction. So that if the cams which depress the levers of the bellows turn from north to south, the cams of the stamps turn from south to north.