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BOOK X.
is separated from gold or silver. The vertical wall of its chimney iserected upon the middle wall, and the sloping chimney-wall rests on thebeams which extend from the second transverse wall to the third; these areso located that they are at a distance of thirteen feet from the middle longwall 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 slopingchimney-wall should fall down, it is partly supported by means of manyiron rods, and partly by means of a few tie-beams covered with lute, whichextend from the small beams of the sloping chimney-wall to the beams of thevertical chimney-wall. The rear roof is arranged in the same way as the roof
“ from Attica, the second (best) from Spain ; after that the kinds made in Puteoli, in Campania,“ and at Baia in Sicily, for in these places it is mostly produced by burning lead plates. The“ best of all is that which is a bright golden colour, called chrysitis, that from Sicily (is called)“ argyritis, that made from silver is called lauritis.” Pliny refers in several passages tolitharge ( spuma argenti) and to what is evidently cupellation, (xxxm, 31): “ And this the“ same agency of fire separates part into lead, which floats on the silver like oil on water ”(xxxiv, 47). “ The metal which flows liquid at the first melting is called stannum, the second
“ melting is silver ; that which remains in the furnace is galena, which is added to a third part“ of the ore. This being again melted, produced lead with a deduction of two-ninths.”Assuming stannum to be silver-lead alloy, and galena to be molybdaena, and thereforelitharge, this becomes a fairly clear statement of cupellation (see note 23, p. 392). He furtherstates (xxxiii, 35) : “ There is made in the same mines what is called spuma argenti (litharge).“ There are three varieties of it; the best, known as chrysitis ; the second best, which is called“ argyritis ; and a third kind, which is called molybditis. And generally all these colours“ are to be found in the same tubes (see p. 480). The most approved kind is that of Attica ;“ the next, that which comes from Spain. Chrysitis is the product from the ore itself;“ argyritis is made from the silver, and molybditis is the result of smelting of lead, which is“ done at Puteoli, and from this has its name. All three are made as the material when“ smelted flows from an upper crucible into a lower one. From this last it is raised with an“ iron bar, and is then twirled round in the flames in order to make it less heavy (made in“ tubes). Thus, as may be easily perceived from the name, it is in reality the spuma of a“ boiling substance—of the future metal, in fact. It differs from slag in the same way that“ the scum of a liquid differs from the lees, the one being purged from the material while“ purifying itself, the other an excretion of the metal when purified.”
The works of either Theophilus (1150-1200 a.d.) or Geber (prior to the 14th century)are the first where adequate description of the cupel itself can be found. The uncertainty ofdates renders it difficult to say which is earliest. Theophilus (Hendrie’s Trans., p. 317)says : “ How gold is separated from copper : But if at any time you have broken copper“ or silver-gilt vessels, or any other work, you can in this manner separate the gold. Take“ the bones of whatever animal you please, which (bones) you may have found in the street,“ and burn them, being cold, grind them finely, and mix with them a third part of beech-“ wood ashes, and make cups as we have mentioned above in the purification of silver ; you“ will dry these at the fire or in the sun. Then you carefully scrape the gold from the copper,“ and you will fold this scraping in lead beaten thin, and one of these cups being placed in“ the embers before the furnace, and now become warm, you place in this fold of lead with the“ scraping, and coals being heaped upon it you will blow it. And when it has become“ melted, in the same manner as silver is accustomed to be purified, sometimes by removing“ the embers and by adding lead, sometimes by re-cooking and warily blowing, you burn it“ until, the copper being entirely absorbed, the gold may appear pure.”
We quote Geber from the Nuremberg edition of 1545, p. 152 : “ Now we describe the“ method of this. Take sifted ashes or calx, or the powder of the burned bones of animals,“ or all of them mixed, or some of them ; moisten with water, and press it with your hand to“ make the mixture firm and solid, and in the middle of this bed make a round solid crucible“ and sprinkle a quantity of crushed glass. Then permit it to dry. When it is dry, place“ into the crucible that which we have mentioned which you intend to test. On it kindle“ a strong fire, and blow upon the surface of the body that is being tested until it melts, which,“ when melted, piece after piece of lead is thrown upon it, and blow over it a strong flame.“ When you see it agitated and moved with strong shaking motion it is not pure. Then wait“ until all of the lead is exhaled. If it vanishes and does not cease its motion it is not purified.“ Then again throw lead and blow again until the lead separates. If it does not become quiet“ again, throw in lead and blow on it until it is quiet and you see it bright and clear on the“ surface.”
Cupellation is mentioned by most of the alchemists, but as a metallurgical operationon a large scale the first description is by Biringuccio in 1540.