| Abzug | 2 | centners, | containing | 64% | lead |
| Abstrich | 51/2 | " | " | 73% | " |
| Herdtplei | 211/2 | " | " | 60% | " |
| Impure litharge | 18 | " | " | 85% | " |
| Litharge | 66 | " | " | 89% | " |
| Total | 113 | centners |
He estimates the lead loss at from 8% to 15%, and gives the average silver contents of blicksilber as about 90%. Many analyses of the various products may be found in Percy (Metallurgy of Lead, pp. 198-201), Schnabel and Lewis (Metallurgy, Vol. I, p. 581); but as they must vary with every charge, a repetition of them here is of little purpose.
Historical Note on Cupellation. The cupellation process is of great antiquity, and the separation of silver from lead in this manner very probably antedates the separation of gold and silver. We can be certain that the process has been used continuously for at least 2,300 years, and was only supplanted in part by Pattinson's crystallization process in 1833, and further invaded by Parks' zinc method in 1850, and during the last fifteen years further supplanted in some works by electrolytic methods. However, it yet survives as an important process. It seems to us that there is no explanation possible of the recovery of the large amounts of silver possessed from the earliest times, without assuming reduction of that metal with lead, and this necessitates cupellation. If this be the case, then cupellation was practised in 2500 B.C. The subject has been further discussed on p. [389]. The first direct evidence of the process, however, is from the remains at Mt. Laurion ([note 6, p. 27]), where the period of greatest activity was at 500 B.C., and it was probably in use long before that time. Of literary evidences, there are the many metaphorical references to "fining silver" and "separating dross" in the Bible, such as Job (XXVIII, 1), Psalms (XII, 6, LXVI, 10), Proverbs (XVII, 3). The most certain, however, is Jeremiah (VI, 28-30): "They are all brass [sic] and iron; they are corrupters. The bellows are burned, the lead is consumed in the fire, the founder melteth in vain; for the wicked are not plucked away. Reprobate silver shall men call them." Jeremiah lived about 600 B.C. His contemporary Ezekiel (XXII, 18) also makes remark: "All they are brass and tin and iron and lead in the midst of the furnace; they are even the dross of the silver." Among Greek authors Theognis (6th century B.C.) and Hippocrates (5th century B.C.) are often cited as mentioning the refining of gold with lead, but we do not believe their statements will stand this construction without strain. Aristotle (Problems XXIV, 9) makes the following remark, which has been construed not only as cupellation, but also as the refining of silver in "tests." "What is the reason that boiling water does not leap out of the vessel ... silver also does this when it is purified. Hence those whose office it is in the silversmiths' shops to purify silver, derive gain by appropriation to themselves of the sweepings of silver which leap out of the melting-pot."
The quotation of Diodorus Siculus from Agatharchides (2nd century B.C.) on gold refining with lead and salt in Egypt we give in [note 8, p. 279]. The methods quoted by Strabo (63 B.C.-24 A.D.) from Polybius (204-125 B.C.) for treating silver, which appear to involve cupellation, are given in [note 8, p. 281]. It is not, however, until the beginning of the Christian era that we get definite literary information, especially with regard to litharge, in Dioscorides and Pliny. The former describes many substances under the terms scoria, molybdaena, scoria argyros and lithargyros, which are all varieties of litharge. Under the latter term he says (V, 62): "One kind is produced from a lead sand (concentrates?), which has been heated in the furnaces until completely fused; another (is made) out of silver; another from lead. The best is [Pg 466]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 to litharge (spuma argenti) and to what is evidently cupellation, (XXXIII, 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 therefore litharge, this becomes a fairly clear statement of cupellation (see [note 23, p. 392]). He further states (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 of dates 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 beechwood 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 operation on a large scale the first description is by Biringuccio in 1540.
[Pg 467][27] In Agricola's text this is "first,"—obviously an error.
[Pg 472][28] The Roman sextarius was about a pint.
[29] This sentence continues, Ipsa vero media pars praeterea digito, to which we are unable to attribute any meaning.