De Re Metallica Part 47

The next mention is by Geber, of whose date and authenticity there is great doubt, but, in any event, the work bearing his name is generally considered to be prior to the 14th, although he has been placed as early as the 8th Century. We quote from Russell's translation, pp. 17 and 224, which we have checked with the Latin edition of 1542: "Sol, or gold, is beaten into thin plates and with them and common salt very well prepared lay upon lay in a vessel of calcination which set into the furnace and calcine well for three days until the whole is subtily calcined. Then take it out, grind well and wash it with vinegar, and dry it in the sun.

Afterwards grind it well with half its weight of cleansed _sal-armoniac_; then set it to be dissolved until the whole be dissolved into most clear water." Further on: "Now we will declare the way of cementing. Seeing it is known to us that cement is very necessary in the examen of perfection, we say it is compounded of inflammable things. Of this kind are, all blackening, flying, penetrating, and burned things; as is vitriol, _sal-armoniac_, _flos aeris_ (copper oxide scales) and the ancient _fictile_ stone (earthen pots), and a very small quant.i.ty, or nothing, of sulphur, and urine with like acute and penetrating things. All these are impasted with urine and spread upon thin plates of that body which you intend shall be examined by this way of probation.

Then the said plates must be laid upon a grate of iron included in an earthen vessel, yet so as one touch not the other that the virtue of the fire may have free and equal access to them. Thus the whole must be kept in fire in a strong earthen vessel for the s.p.a.ce of three days. But here great caution is required that the plates may be kept but not melt."

Albertus Magnus (1205-1280) _De Mineralibus et Rebus Metallicis_, Lib.

IV, describes the process as follows:--"But when gold is to be purified an earthen vessel is made like a cucurbit or dish, and upon it is placed a similar vessel; and they are luted together with the tenacious lute called by alchemists the lute of wisdom. In the upper vessel there are numerous holes by which vapour and smoke may escape; afterwards the gold in the form of short thin leaves is arranged in the vessel, the leaves being covered consecutively with a mixture obtained by mixing together soot, salt, and brick dust; and the whole is strongly heated until the gold becomes perfectly pure and the base substances with which it was mixed are consumed." It will be noted that salt is the basis of all these cement compounds. We may also add that those of Biringuccio and all other writers prior to Agricola were of the same kind, our author being the first to mention those with nitre.

PARTING WITH NITRIC ACID. The first mention of nitric acid is in connection with this purpose, and, therefore, the early history of this reagent becomes the history of the process. Mineral acids of any kind were unknown to the Greeks or Romans. The works of the Alchemists and others from the 12th to the 15th Centuries, have been well searched by chemical historians for indications of knowledge of the mineral acids, and many of such suspected indications are of very doubtful order. In any event, study of the Alchemists for the roots of chemistry is fraught with the greatest difficulty, for not only is there the large ratio of fraud which characterised their operations, but there is even the much larger field of fraud which characterised the authorship and dates of writing attributed to various members of the cult. The mention of saltpetre by Roger Bacon (1214-94), and Albertus Magnus (1205-80), have caused some strain to read a knowledge of mineral acids into their works, but with doubtful result. Further, the Monk Theophilus (1150-1200) is supposed to have mentioned products which would be mineral acids, but by the most careful scrutiny of that work we have found nothing to justify such an a.s.sertion, and it is of importance to note that as Theophilus was a most accomplished gold and silver worker, his failure to mention it is at least evidence that the process was not generally known. The transcribed ma.n.u.scripts and later editions of such authors are often altered to bring them "up-to-date." The first mention is in the work attributed to Geber, as stated above, of date prior to the 14th Century. The following pa.s.sage from his _De Inventione Veritatis_ (Nuremberg edition, 1545, p. 182) is of interest:--"First take one _libra_ of vitriol of Cyprus and one-half _libra_ of saltpetre and one-quarter of alum of Jameni, extract the _aqua_ with the redness of the alembic--for it is very solvative--and use as in the foregoing chapters. This can be made acute if in it you dissolve a quarter of sal-ammoniac, which dissolves gold, sulphur, and silver." Distilling vitriol, saltpetre and alum would produce nitric acid. The addition of sal-ammoniac would make _aqua regia_; Geber used this solvent water--probably without being made "more acute"--to dissolve silver, and he crystallized out silver nitrate. It would not be surprising to find all the Alchemists subsequent to Geber mentioning acids. It will thus be seen that even the approximate time at which the mineral-acids were first made cannot be determined, but it was sometime previous to the 15th Century, probably not earlier than the 12th Century. Beckmann (Hist. of Inventions II, p. 508) states that it appears to have been an old tradition that acid for separating the precious metals was first used at Venice by some Germans; that they chiefly separated the gold from Spanish silver and by this means acquired great riches. Beckmann considers that the first specific description of the process seems to be in the work of William Budaeus (_De a.s.se_, 1516, III, p. 101), who speaks of it as new at this time. He describes the operation of one, Le Conte, at Paris, who also acquired a fortune through the method.

Beckmann and others have, however, entirely overlooked the early _Probierbuchlein_. If our conclusions are correct that the first of these began to appear at about 1510, then they give the first description of inquartation. This book (see appendix) is made up of recipes, like a cook-book, and four or five different recipes are given for this purpose; of these we give one, which sufficiently indicates a knowledge of the art (p. 39): "If you would part them do it this way: Beat the silver which you suppose to contain gold, as thin as possible; cut it in small pieces and place it in 'strong' water (_starkwa.s.ser_).

Put it on a mild fire till it becomes warm and throws up blisters or bubbles. Then take it and pour off the water into a copper-bowl; let it stand and cool. Then the silver settles itself round the copper bowl; let the silver dry in the copper bowl, then pour the water off and melt the silver in a crucible. Then take the gold also out of the gla.s.s _kolken_ and melt it together." Biringuccio (1540, Book VI.) describes the method, but with much less detail than Agricola. He made his acid from alum and saltpetre and calls it _lacque forti_.

PARTING WITH SULPHUR. This process first appears in Theophilus (1150-1200), and in form is somewhat different from that mentioned by Agricola. We quote from Hendrie's Translation, p. 317, "How gold is separated from silver. When you have sc.r.a.ped the gold from silver, place this sc.r.a.ping in a small cup in which gold or silver is accustomed to be melted, and press a small linen cloth upon it, that nothing may by chance be abstracted from it by the wind of the bellows, and placing it before the furnace, melt it; and directly lay fragments of sulphur in it, according to the quant.i.ty of the sc.r.a.ping, and carefully stir it with a thin piece of charcoal until its fumes cease; and immediately pour it into an iron mould. Then gently beat it upon the anvil lest by chance some of that black may fly from it which the sulphur has burnt, because it is itself silver. For the sulphur consumes nothing of the gold, but the silver only, which it thus separates from the gold, and which you will carefully keep. Again melt this gold in the same small cup as before, and add sulphur. This being stirred and poured out, break what has become black and keep it, and do thus until the gold appear pure. Then gather together all that black, which you have carefully kept, upon the cup made from the bone and ash, and add lead, and so burn it that you may recover the silver. But if you wish to keep it for the service of niello, before you burn it add to it copper and lead, according to the measure mentioned above, and mix with sulphur." This process appears in the _Probierbuchlein_ in many forms, different recipes containing other ingredients besides sulphur, such as salt, saltpetre, sal-ammoniac, and other things more or less effective. In fact, a series of hybrid methods between absolute melting with sulphur and cementation with salt, were in use, much like those mentioned by Agricola on p. 458.

PARTING WITH ANTIMONY SULPHIDE. The first mention of this process lies either in Basil Valentine's "Triumphant Chariot of Antimony" or in the first _Probierbuchlein_. The date to be a.s.signed to the former is a matter of great doubt. It was probably written about the end of the 15th Century, but apparently published considerably later. The date of the _Probierbuchlein_ we have referred to above. The statement in the "Triumphal Chariot" is as follows (Waite's Translation, p. 117-118): "The elixir prepared in this way has the same power of penetrating and pervading the body with its purifying properties that antimony has of penetrating and purifying gold.... This much, however, I have proved beyond a possibility of doubt, that antimony not only purifies gold and frees it from foreign matter, but it also ameliorates all other metals, but it does the same for animal bodies." There are most specific descriptions of this process in the other works attributed to Valentine, but their authenticity is so very doubtful that we do not quote. The _Probierbuchlein_ gives several recipes for this process, all to the same metallurgical effect, of which we quote two: "How to separate silver from gold. Take 1 part of golden silver, 1 part of _spiesgla.s.s_, 1 part copper, 1 part lead; melt them together in a crucible. When melted pour into the crucible pounded sulphur and directly you have poured it in cover it up with soft lime so that the fumes cannot escape, and let it get cold and you will find your gold in a b.u.t.ton. Put that same in a pot and blow on it." "How to part gold and silver by melting or fire. Take as much gold-silver as you please and granulate it; take 1 _mark_ of these grains, 1 _mark_ of powder; put them together in a crucible. Cover it with a small cover, put it in the fire, and let it slowly heat; blow on it gently until it melts; stir it all well together with a stick, pour it out into a mould, strike the mould gently with a knife so that the b.u.t.ton may settle better, let it cool, then turn the mould over, strike off the b.u.t.ton and twice as much _spiesglas_ as the b.u.t.ton weighs, put them in a crucible, blow on it till it melts, then pour it again into a mould and break away the b.u.t.ton as at first. If you want the gold to be good always add to the b.u.t.ton twice as much _spiesgla.s.s_. It is usually good gold in three meltings. Afterward take the b.u.t.ton, place it on a cupel, blow on it till it melts. And if it should happen that the gold is covered with a membrane, then add a very little lead, then it shines (_plickt_) and becomes clearer." Biringuccio (1540) also gives a fairly clear exposition of this method. All the old refiners varied the process by using mixtures of salt, antimony sulphide, and sulphur, in different proportions, with and without lead or copper; the net effect was the same. Later than Agricola these methods of parting bullion by converting the silver into a sulphide and carrying it off in a regulus took other forms. For instance, Schluter (_Hutte-Werken_, Braunschweig, 1738) describes a method by which, after the granulated bullion had been sulphurized by cementation with sulphur in pots, it was melted with metallic iron. Lampadius (_Grundriss Einer Allgemeinen Huttenkunde_, Gottingen, 1827) describes a treatment of the bullion, sulphurized as above, with litharge, thus creating a lead-silver regulus and a lead-silver-gold bullion which had to be repeatedly put through the same cycle. The princ.i.p.al object of these processes was to reduce silver bullion running low in gold to a ratio acceptable for nitric acid treatment.

Before closing the note on the separation of gold and silver, we may add that with regard to the three processes largely used to-day, the separation by solution of the silver from the bullion by concentrated sulphuric acid where silver sulphate is formed, was first described by D'Arcet, Paris, in 1802; the separation by introducing chlorine gas into the molten bullion and thus forming silver chlorides was first described by Lewis Thompson in a communication to the Society of Arts, 1833, and was first applied on a large scale by F. B. Miller at the Sydney Mint in 1867-70; we do not propose to enter into the discussion as to who is the inventor of electrolytic separation.

[22] There were three methods of gilding practised in the Middle Ages--the first by hammering on gold leaf; the second by laying a thin plate of gold on a thicker plate of silver, expanding both together, and fabricating the articles out of the sheets thus prepared; and the third by coating over the article with gold amalgam, and subsequently driving off the mercury by heat. Copper and iron objects were silver-plated by immersing them in molten silver after coating with sal-ammoniac or borax. Tinning was done in the same way.

[23] See note 12, p. 297, for complete discussion of amalgamation.

[24] These nine methods of separating gold from copper are based fundamentally upon the sulphur introduced in each case, whereby the copper is converted into sulphides and separated off as a matte. The various methods are much befogged by the introduction of extraneous ingredients, some of which serve as fluxes, while others would provide metallics in the shape of lead or antimony for collection of the gold, but others would be of no effect, except to increase the matte or slag.

Inspection will show that the amount of sulphur introduced in many instances is in so large ratio that unless a good deal of volatilization took place there would be insufficient metallics to collect the gold, if it happened to be in small quant.i.ties. In a general way the auriferous b.u.t.ton is gradually impoverished in copper until it is fit for cupellation with lead, except in one case where the final stage is accomplished by amalgamation. The lore of the old refiners was much after the order of that of modern cooks--they treasured and handed down various efficacious recipes, and of those given here most can be found in identical terms in the _Probierbuchlein_, some editions of which, as mentioned before, were possibly fifty years before _De Re Metallica_.

This knowledge, no doubt, acc.u.mulated over long experience; but, so far as we are aware, there is no description of sulphurizing copper for this purpose prior to the publication mentioned.

[25] _Sal artificiosus_. The compound given under this name is of quite different ingredients from the stock fluxes given in Book VII under the same term. The method of preparation, no doubt, dehydrated this one; it would, however, be quite effective for its purpose of sulphurizing the copper. There is a compound given in the _Probierbuchlein_ identical with this, and it was probably Agricola's source of information.

[26] Throughout the book the cupellation furnace is styled the _secunda fornax_ (Glossary, _Treibeherd_). Except in one or two cases, where there is some doubt as to whether the author may not refer to the second variety of blast furnace, we have used "cupellation furnace." Agricola's description of the actual operation of the old German cupellation is less detailed than that of such authors as Schluter (_Hutte-Werken_, Braunschweig, 1738) or Winkler (_Beschreibung der Freyberger Schmelz Huttenprozesse_, Freyberg, 1837). The operation falls into four periods.

In the first period, or a short time after melting, the first sc.u.m--the _abzug_--arises. This material contains most of the copper, iron, zinc, or sulphur impurities in the lead. In the second period, at a higher temperature, and with the blast turned on, a second sc.u.m arises--the _abstrich_. This material contains most of the antimony and a.r.s.enical impurities. In the third stage the litharge comes over. At the end of this stage the silver brightens--"_blicken_"--due to insufficient litharge to cover the entire surface. Winkler gives the following average proportion of the various products from a charge of 100 _centners_:--

_Abzug_ 2 _centners_, containing 64% lead _Abstrich_ 5-1/2 " " 73% "

_Herdtplei_ 21-1/2 " " 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 a.n.a.lyses 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 repet.i.tion 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 a.s.suming 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 bra.s.s [_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 bra.s.s 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 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 pa.s.sages to litharge (_spuma argenti_) and to what is evidently cupellation, (x.x.xIII, 31): "And this the same agency of fire separates part into lead, which floats on the silver like oil on water"

(x.x.xIV, 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."

a.s.suming _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 (x.x.xIII, 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 sc.u.m 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 sc.r.a.pe the gold from the copper, and you will fold this sc.r.a.ping 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 sc.r.a.ping, 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 quant.i.ty of crushed gla.s.s. 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.

[27] In Agricola's text this is "first,"--obviously an error.

[28] The Roman _s.e.xtarius_ was about a pint.

[29] This sentence continues, _Ipsa vero media pars praeterea digito_, to which we are unable to attribute any meaning.

[30] _Thus_, or _tus_--"incense."

[31] One _centumpondium_, Roman, equals about 70.6 lbs. avoirdupois; one _centner_, old German, equals about 114.2 lbs. avoirdupois. Therefore, if German weights are meant, the maximum charge would be about 5.7 short tons; if Roman weights, about 3.5 short tons.

[32] See description, p. 269.

[33] _Stannum_, as a term for lead-silver alloys, is a term which Agricola (_De Natura Fossilium_, pp. 341-3) adopted from his views of Pliny. In the _Interpretatio_ and the Glossary he gives the German equivalent as _werk_, which would sufficiently identify his meaning were it not obvious from the context. There can be little doubt that Pliny uses the term for lead alloys, but it had come into general use for tin before Agricola's time. The Roman term was _plumb.u.m candidum_, and as a result of Agricola's insistence on using it and _stannum_ in what he conceived was their original sense, he managed to give considerable confusion to mineralogic literature for a century or two. The pa.s.sages from Pliny, upon which he bases his use, are (x.x.xIV, 47): "The metal which flows liquid at the first melting in the furnace is called _stannum_, the second melting is silver," etc. (x.x.xIV, 48): "When copper vessels are coated with _stannum_ they produce a less disagreeable flavour, and it prevents verdigris. It is also remarkable that the weight is not increased.... At the present day a counterfeit _stannum_ is made by adding one-third of white copper to tin. It is also made in another way, by mixing together equal parts of tin and lead; this last is called by some _argentarium_.... There is also a composition called _tertiarium_, a mixture of two parts of lead and one of tin. Its price is twenty _denarii_ per pound, and it is used for soldering pipes.

Persons still more dishonest mix together equal parts of _tertiarium_ and tin, and calling the compound _argentarium_, when it is melted coat articles with it." Although this last pa.s.sage probably indicates that _stannum_ was a tin compound, yet it is not inconsistent with the view that the genuine _stannum_ was silver-lead, and that the counterfeits were made as stated by Pliny. At what period the term _stannum_ was adopted for tin is uncertain. As shown by Beckmann (Hist. of Inventions II, p. 225), it is used as early as the 6th century in occasions where tin was undoubtedly meant. We may point out that this term appears continuously in the official doc.u.ments relating to Cornish tin mining, beginning with the report of William de Wrotham in 1198.

[34] The Latin term for litharge is _spuma argenti_, spume of silver.

[35] Pliny, x.x.xIII, 35. This quotation is given in full in the footnote p. 466. Agricola ill.u.s.trates these "tubes" of litharge on p. 481.

[36] a.s.suming Roman weights, three _unciae_ and three _drachmae_ per _centumpondium_ would be about 82 ozs., and the second case would equal about 85 ozs. per short ton.

[37] Agricola uses throughout _De Re Metallica_ the term _molybdaena_ for this substance. It is obvious from the context that he means saturated furnace bottoms--the _herdpley_ of the old German metallurgists--and, in fact, he himself gives this equivalent in the _Interpretatio_, and describes it in great detail in _De Natura Fossilium_ (p. 353). The derivatives coined one time and another from the Greek _molybdos_ for lead, and their applications, have resulted in a stream of wasted ink, to which we also must contribute. Agricola chose the word _molybdaena_ in the sense here used from his interpretation of Pliny. The statements in Pliny are a hopeless confusion of _molybdaena_ and _galena_. He says (x.x.xIII, 35): "There are three varieties of it (litharge)--the best-known is _chrysitis_; the second best is called _argyritis_; and a third kind is called _molybditis_.... _Molybditis_ is the result of the smelting of lead.... Some people make two kinds of litharge, which they call _scirerytis_ and _peumene_; and a third variety being _molybdaena_, will be mentioned with lead." (x.x.xIV, 53): "_Molybdaena_, which in another place I have called _galena_, is an ore of mixed silver and lead. It is considered better in quality the nearer it approaches to a golden colour and the less lead there is in it; it is also friable and moderately heavy. When it is boiled with oil it becomes liver-coloured, adheres to the gold and silver furnaces, and in this state it is called _metallica_." From these two pa.s.sages it would seem that _molybdaena_, a variety of litharge, might quite well be hearth-lead. Further (in x.x.xIV, 47), he says: "The metal which flows liquid at the first melting in the furnace is called _stannum_, at the second melting is silver, that which remains in the furnace is _galena_." If we still maintain that _molybdaena_ is hearth-lead, and _galena_ is its equivalent, then this pa.s.sage becomes clear enough, the second melting being cupellation. The difficulty with Pliny, however, arises from the pa.s.sage (x.x.xIII, 31), where, speaking of silver ore, he says: "It is impossible to melt it except with lead ore, called _galena_, which is generally found next to silver veins." Agricola (_Bermannus_, p. 427, &c.), devotes a great deal of inconclusive discussion to an attempt to reconcile this conflict of Pliny, and also that of Dioscorides. The probable explanation of this conflict arises in the resemblance of cupellation furnace bottoms to lead carbonates, and the native _molybdaena_ of Dioscorides; and some of those referred to by Pliny may be this sort of lead ores. In fact, in one or two places in Book IX, Agricola appears to use the term in this sense himself. After Agricola's time the term _molybdaenum_ was applied to substances resembling lead, such as graphite, and what we now know as _molybdenite_ (_MoS_{2}_). Some time in the latter part of the 18th century, an element being separated from the latter, it was dubbed _molybdenum_, and confusion was five times confounded.

[38] Agricola here refers to the German word used in this connection, _i.e._, _hundt_, a dog.

[39] If Agricola means the German _centner_, this charge would be from about 4.6 to 5.7 short tons. If he is using Roman weights, it would be from about 3 to 3.7 short tons.

[40] The refining of silver in "tests" (Latin _testa_) is merely a second cupellation, with greater care and under stronger blast. Stirring the ma.s.s with an iron rod serves to raise the impurities which either volatilize as litharge or, floating to the edges, are absorbed into the "test." The capacity of the tests, from 15 _librae_ to 50 _librae_, would be from about 155 to 515 ozs. Troy.

[41] A _drachma_ of impurities in a _bes_, would be one part in 64, or 984.4 fine. A loss of a _sicilicus_ of silver to the _bes_, would be one part in 32, or about 3.1%; three _drachmae_ would equal 4.7%, and half an _uncia_ 6.2%, or would indicate that the original bullion had a fineness in the various cases of about 950, 933, and 912.

[42] _Praefectus Regis_.

BOOK XI.

Different methods of parting gold from silver, and, on the other hand, silver from gold, were discussed in the last book; also the separation of copper from the latter, and further, of lead from gold as well as from silver; and, lastly, the methods for refining the two precious metals. Now I will speak of the methods by which silver must be separated from copper, and likewise from iron.[1]

[Ill.u.s.tration 493 (Building Plan for Refinery): Six long walls: A--The first. B--The first part of the second. C--The further part of the second. D--The third. E--The fourth. F--The fifth. G--The sixth.

Fourteen transverse walls: H--The first. I--The second. K--The third.

L--The fourth. M--The fifth. N--The sixth. O--The seventh. P--The eighth. Q--The ninth. R--The tenth. S--The eleventh. T--The twelfth.

V--The thirteenth. X--The fourteenth.]