De Re Metallica Part 43

[54] _Aureo nummo_. German Translation gives _reinschen gulden_, which was the equivalent of about $1.66, or 6.9 s.h.i.+llings. The purchasing power of money was, however, several times as great as at present.

[55] In the following descriptions of iron-smelting, we have three processes described; the first being the direct reduction of malleable iron from ore, the second the transition stage then in progress from the direct to indirect method by way of cast-iron; and the third a method of making steel by cementation. The first method is that of primitive iron-workers of all times and all races, and requires little comment. A pasty ma.s.s was produced, which was subsequently hammered to make it exude the slag, the hammered ma.s.s being the ancient "bloom." The second process is of considerable interest, for it marks one of the earliest descriptions of working iron in "a furnace similar to a blast furnace, but much wider and higher." This original German _Stuckofen_ or high bloomery furnace was used for making "ma.s.ses" of wrought-iron under essentially the same conditions as its progenitor the forge--only upon a larger scale. With high temperatures, however, such a furnace would, if desired, yield molten metal, and thus the step to cast-iron as a preliminary to wrought-iron became very easy and natural, in fact Agricola mentions above that if the iron is left to settle in the furnace it becomes hard. The making of malleable iron by subsequent treatment of the cast-iron--the indirect method--originated in about Agricola's time, and marks the beginning of one of those subtle economic currents destined to have the widest bearing upon civilization. It is to us uncertain whether he really understood the double treatment or not.

In the above paragraph he says from ore "once or twice smelted they make iron," etc., and in _De Natura Fossilium_ (p. 339) some reference is made to pouring melted iron, all of which would appear to be cast-iron.

He does not, however, describe the 16th Century method of converting cast into wrought iron by way of in effect roasting the pig iron to eliminate carbon by oxidation, with subsequent melting into a "ball" or "ma.s.s." It must be borne in mind that puddling for this purpose did not come into use until the end of the 18th Century. A great deal of discussion has arisen as to where and at what time cast-iron was made systematically, but without satisfactory answer; in any event, it seems to have been in about the end of the 14th Century, as cast cannon began to appear about that time. It is our impression that the whole of this discussion on iron in _De Re Metallica_ is an abstract from Biringuccio, who wrote 15 years earlier, as it is in so nearly identical terms. Those interested will find a translation of Biringuccio's statement with regard to steel in Percy's Metallurgy of Iron and Steel, London, 1864, p. 807.

HISTORICAL NOTE ON IRON SMELTING. The archaeologists' division of the history of racial development into the Stone, Bronze, and Iron Ages, based upon objects found in tumuli, burial places, etc., would on the face of it indicate the prior discovery of copper metallurgy over iron, and it is generally so maintained by those scientists. The metallurgists have not hesitated to protest that while this distinction of "Ages" may serve the archaeologists, and no doubt represents the sequence in which the metal objects are found, yet it by no means follows that this was the order of their discovery or use, but that iron by its rapidity of oxidation has simply not been preserved. The arguments which may be advanced from our side are in the main these. Iron ore is of more frequent occurrence than copper ores, and the necessary reduction of copper oxides (as most surface ores must have been) to fluid metal requires a temperature very much higher than does the reduction of iron oxides to wrought-iron blooms, which do not necessitate fusion. The comparatively greater simplicity of iron metallurgy under primitive conditions is well exemplified by the hill tribes of Northern Nigeria, where in village forges the negroes reduce iron sufficient for their needs, from hemat.i.te. Copper alone would not be a very serviceable metal to primitive man, and he early made the advance to bronze; this latter metal requires three metallurgical operations, and presents immeasurably greater difficulties than iron. It is, as Professor Gowland has demonstrated (Presidential Address, Inst. of Metals, London, 1912) quite possible to make bronze from melting stanniferous copper ores, yet such combined occurrence at the surface is rare, and, so far as known, the copper sources from which Asia Minor and Egypt obtained their supply do not contain tin. It seems to us, therefore, that in most cases the separate fusions of different ores and their subsequent re-melting were required to make bronze. The arguments advanced by the archaeologists bear mostly upon the fact that, had iron been known, its superiority would have caused the primitive races to adopt it, and we should not find such an abundance of bronze tools. As to this, it may be said that bronze weapons and tools are plentiful enough in Egyptian, Mycenaean, and early Greek remains, long after iron was demonstrably well known. There has been a good deal p.r.o.nounced by etymologists on the history of iron and copper, for instance, by Max Muller, (Lectures on the Science of Language, Vol. II, p. 255, London, 1864), and many others, but the amazing lack of metallurgical knowledge nullifies practically all their conclusions. The oldest Egyptian texts extant, dating 3500 B.C., refer to iron, and there is in the British Museum a piece of iron found in the Pyramid of Kephron (3700 B.C.) under conditions indicating its co-incident origin. There is exhibited also a fragment of oxidized iron lately found by Professor Petrie and placed as of the VI Dynasty (B.C.

3200). Despite this evidence of an early knowledge of iron, there is almost a total absence of Egyptian iron objects for a long period subsequent to that time, which in a measure confirms the view of its disappearance rather than that of ignorance of it. Many writers have a.s.sumed that the Ancients must have had some superior art of hardening copper or bronze, because the cutting of the gigantic stonework of the time could not have been done with that alloy as we know it; no such hardening appears among the bronze tools found, and it seems to us that the argument is stronger that the oldest Egyptian stoneworkers employed mostly iron tools, and that these have oxidized out of existence. The reasons for preferring copper alloys to iron for decorative objects were equally strong in ancient times as in the present day, and accounts sufficiently for these articles, and, therefore, iron would be devoted to more humble objects less likely to be preserved. Further, the Egyptians at a later date had some prejudices against iron for sacred purposes, and the media of preservation of most metal objects were not open to iron. We know practically nothing of very early Egyptian metallurgy, but in the time of Thotmes III. (1500 B.C.) bellows were used upon the forge.

Of literary evidences the earliest is in the Shoo King among the Tribute of Yu (2500 B.C.?). Iron is frequently mentioned in the Bible, but it is doubtful if any of the early references apply to steel. There is scarcely a Greek or Latin author who does not mention iron in some connection, and of the earliest, none are so suggestive from a metallurgical point of view as Homer, by whom "laboured" ma.s.s (wrought-iron?) is often referred to. As, for instance, in the Odyssey (I., 234) Pallas in the guise of Mentes, says according to Pope:

"Freighted with iron from my native land I steer my voyage to the Brutian strand, To gain by commerce for the laboured ma.s.s A just proportion of refulgent bra.s.s."

(Bra.s.s is modern poetic licence for copper or bronze). Also, in the Odyssey (IX, 465) when Homer describes how Ulysses plunged the stake into Cyclop's eye, we have the first positive evidence of steel, although hard iron mentioned in the Tribute of Yu, above referred to, is sometimes given as steel:

"And as when armourers temper in the ford The keen-edg'd pole-axe, or the s.h.i.+ning sword, The red-hot metal hisses in the lake."

No doubt early wrought-iron was made in the same manner as Agricola describes. We are, however, not so clear as to the methods of making steel. Under primitive methods of making wrought-iron it is quite possible to carburize the iron sufficiently to make steel direct from ore. The primitive method of India and j.a.pan was to enclose lumps of wrought-iron in sealed crucibles with charcoal and sawdust, and heat them over a long period. Neither Pliny nor any of the other authors of the period previous to the Christian Era give us much help on steel metallurgy, although certain obscure expressions of Aristotle have been called upon (for instance, St. John V. Day, Prehistoric Use of Iron and Steel, London, 1877, p. 134) to prove its manufacture by immersing wrought-iron in molten cast-iron.

[56] _Quae vel aerosa est, vel cocta_. It is by no means certain that _cocta_, "cooked" is rightly translated, for the author has not hitherto used this expression for heated. This may be residues from roasting and leaching pyrites for vitriol, etc.

[57] Agricola draws no sharp line of distinction between antimony the metal, and its sulphide. He uses the Roman term _stibi_ or _stibium_ (_Interpretatio_,--_Spiesglas_) throughout this book, and evidently in most cases means the sulphide, but in others, particularly in parting gold and silver, metallic antimony would be reduced out. We have been in much doubt as to the term to introduce into the text, as the English "stibnite" carries too much precision of meaning. Originally the "antimony" of trade was the sulphide. Later, with the application of that term to the metal, the sulphide was termed "grey antimony," and we have either used _stibium_ for lack of better alternative, or adopted "grey antimony." The method described by Agricola for treating antimony sulphide is still used in the Harz, in Bohemia, and elsewhere. The stibnite is liquated out at a low heat and drips from the upper to the lower pot. The resulting purified antimony sulphide is the modern commercial "crude antimony" or "grey antimony."

HISTORICAL NOTE ON THE METALLURGY OF ANTIMONY. The Egyptologists have adopted the term "antimony" for certain cosmetics found in Egyptian tombs from a very early period. We have, however, failed to find any reliable a.n.a.lyses which warrant this a.s.sumption, and we believe that it is based on the knowledge that antimony was used as a base for eye ointments in Greek and Roman times, and not upon proper chemical investigation. It may be that the ideograph which is interpreted as antimony may really mean that substance, but we only protest that the chemist should have been called in long since. In St. Jerome's translation of the Bible, the cosmetic used by Jezebel (II. Kings IX, 30) and by the lady mentioned by Ezekiel (XXIII, 40), "who didst wash thyself and paintedst thine eyes" is specifically given as _stibio_. Our modern translation carries no hint of the composition of the cosmetic, and whether some of the Greek or Hebrew MSS. do furnish a basis for such translation we cannot say. The Hebrew term for this mineral was _kohl_, which subsequently pa.s.sed into "alcool" and "alkohol" in other languages, and appears in the Spanish Bible in the above pa.s.sage in Ezekiel as _alcoholaste_. The term _antimonium_ seems to have been first used in Latin editions of Geber published in the latter part of the 15th Century. In any event, the metal is clearly mentioned by Dioscorides (1st Century), who calls it _stimmi_, and Pliny, who termed it _stibium_, and they leave no doubt that it was used as a cosmetic for painting the eyebrows and dilating the eyes. Dioscorides (V, 59) says: "The best _stimmi_ is very brilliant and radiant. When broken it divides into layers with no part earthy or dirty; it is brittle. Some call it _stimmi_, others _platyophthalmon_ (wide eyed); others _larbason_, others _gynaekeion_ (feminine).... It is roasted in a ball of dough with charcoal until it becomes a cinder.... It is also roasted by putting it on live charcoal and blowing it. If it is roasted too much it becomes lead." Pliny states (x.x.xIII, 33 and 34): "In the same mines in which silver is found, properly speaking there is a stone froth. It is white and s.h.i.+ning, not transparent; is called _stimmi_, or _stibi_, or _alabastrum_, and _larbasis_. There are two kinds of it, the male and the female. The most approved is the female, the male being more uneven, rougher, less heavy, not so radiant, and more gritty. The female kind is bright and friable, laminar and not globular. It is astringent and refrigerative, and its princ.i.p.al use is for the eyes.... It is burned in manure in a furnace, is quenched with milk, ground with rain water in a mortar, and while thus turbid it is poured into a copper vessel and purified with nitrum ... above all in roasting it care should be taken that it does not turn to lead." There can be little doubt from Dioscorides' statement of its turning to lead that he had seen the metal antimony, although he thought it a species of lead. Of further interest in connection with the ancient knowledge of the metal is the Chaldean vase made of antimony described by Berthelot (_Comptes Rendus_, 1887, CIV, 265). It is possible that Agricola knew the metal, although he gives no details as to de-sulphurizing it or for recovering the metal itself. In _De Natura Fossilium_ (p. 181) he makes a statement which would indicate the metal, "_Stibium_ when melted in the crucible and refined has as much right to be regarded as a metal as is accorded to lead by most writers. If when smelted a certain portion be added to tin, a printer's alloy is made from which type is cast that is used by those who print books." Basil Valentine, in his "Triumphal Chariot of Antimony," gives a great deal that is new with regard to this metal, even if we can accredit the work with no earlier origin than its publication--about 1600; it seems possible however, that it was written late in the 15th Century (see Appendix B). He describes the preparation of the metal from the crude ore, both by roasting and reduction from the oxide with argol and saltpetre, and also by fusing with metallic iron.

While the first description of these methods is usually attributed to Valentine, it may be pointed out that in the _Probierbuchlein_ (1500) as well as in Agricola the separation of silver from iron by antimony sulphide implies the same reaction, and the separation of silver and gold with antimony sulphide, often attributed to Valentine, is repeatedly set out in the _Probierbuchlein_ and in _De Re Metallica_.

Biringuccio (1540) has nothing of importance to say as to the treatment of antimonial ores, but mentions it as an alloy for bell-metal, which would imply the metal.

[58] HISTORICAL NOTE ON THE METALLURGY OF QUICKSILVER. The earliest mention of quicksilver appears to have been by Aristotle (_Meteorologica_ IV, 8, 11), who speaks of it as fluid silver (_argyros chytos_). Theophrastus (105) states: "Such is the production of quicksilver, which has its uses. This is obtained from cinnabar rubbed with vinegar in a bra.s.s mortar with a bra.s.s pestle." (Hill's Trans., p.

139). Theophrastus also (103) mentions cinnabar from Spain and elsewhere. Dioscorides (V, 70) appears to be the first to describe the recovery of quicksilver by distillation: "Quicksilver (_hydrargyros_, _i.e._, liquid silver) is made from _ammion_, which is called _cinnabari_. An iron bowl containing _cinnabari_ is put into an earthen vessel and covered over with a cup-shaped lid smeared with clay. Then it is set on a fire of coals and the soot which sticks to the cover when wiped off and cooled is quicksilver. Quicksilver is also found in drops falling from the walls of the silver mines. Some say there are quicksilver mines. It can be kept only in vessels of gla.s.s, lead, tin (?), or silver, for if put in vessels of any other substances it consumes them and flows through." Pliny (x.x.xIII, 41): "There has been discovered a way of extracting _hydrargyros_ from the inferior _minium_ as a subst.i.tute for quicksilver, as mentioned. There are two methods: either by pounding _minium_ and vinegar in a bra.s.s mortar with a bra.s.s pestle, or else by putting _minium_ into a flat earthen dish covered with a lid, well luted with potter's clay. This is set in an iron pan and a fire is then lighted under the pan, and continually blown by a bellows. The perspiration collects on the lid and is wiped off and is like silver in colour and as liquid as water." Pliny is somewhat confused over the _minium_--or the text is corrupt, for this should be the genuine _minium_ of Roman times. The methods of condensation on the leaves of branches placed in a chamber, of condensing in ashes placed over the mouth of the lower pot, and of distilling in a retort, are referred to by Biringuccio (A.D. 1540), but with no detail.

[59] Most of these methods depend upon simple liquation of native bis.m.u.th. The sulphides, oxides, etc., could not be obtained without fusing in a furnace with appropriate de-sulphurizing or reducing agents, to which Agricola dimly refers. In _Bermannus_ (p. 439), he says: "_Bermannus_.--I will show you another kind of mineral which is numbered amongst metals, but appears to me to have been unknown to the Ancients; we call it _bisemutum_. _Naevius_.--Then in your opinion there are more kinds of metals than the seven commonly believed? _Bermannus_.--More, I consider; for this which just now I said we called _bisemutum_, cannot correctly be called _plumb.u.m candidum_ (tin) nor _nigrum_ (lead), but is different from both, and is a third one. _Plumb.u.m candidum_ is whiter and _plumb.u.m nigrum_ is darker, as you see. _Naevius_.--We see that this is of the colour of _galena_. _Ancon_.--How then can _bisemutum_, as you call it, be distinguished from _galena_? _Bermannus_.--Easily; when you take it in your hands it stains them with black unless it is quite hard.

The hard kind is not friable like _galena_, but can be cut. It is blacker than the kind of crude silver which we say is almost the colour of lead, and thus is different from both. Indeed, it not rarely contains some silver. It generally shows that there is silver beneath the place where it is found, and because of this our miners are accustomed to call it the 'roof of silver.' They are wont to roast this mineral, and from the better part they make metal; from the poorer part they make a pigment of a kind not to be despised." This pigment was cobalt blue (see note on p. 112), indicating a considerable confusion of these minerals.

This quotation is the first description of bis.m.u.th, and the above text the first description of bis.m.u.th treatment. There is, however, bare mention of the mineral earlier, in the following single line from the _Probierbuchlein_ (p. 1): "Jupiter (controls) the ores of tin and _wismundt_." And it is noted in the _Nutzliche Bergbuchlein_ in a.s.sociation with silver (see Appendix B).

[60] This _cadmia_ is given in the German translation as _kobelt_. It is probably the cobalt-a.r.s.enic-bis.m.u.th minerals common in Saxony. A large portion of the world's supply of bis.m.u.th to-day comes from the cobalt treatment works near Schneeberg. For further discussion of _cadmia_ see note on p. 112.

BOOK X.

Questions as to the methods of smelting ores and of obtaining metals I discussed in Book IX. Following this, I should explain in what manner the precious metals are parted from the base metals, or on the other hand the base metals from the precious[1]. Frequently two metals, occasionally more than two, are melted out of one ore, because in nature generally there is some amount of gold in silver and in copper, and some silver in gold, copper, lead, and iron; likewise some copper in gold, silver, lead, and iron, and some lead in silver; and lastly, some iron in copper[2]. But I will begin with gold.

Gold is parted from silver, or likewise the latter from the former, whether it be mixed by nature or by art, by means of _aqua valens_[3], and by powders which consist of almost the same things as this _aqua_.

In order to preserve the sequence, I will first speak of the ingredients of which this _aqua_ is made, then of the method of making it, then of the manner in which gold is parted from silver or silver from gold.

Almost all these ingredients contain vitriol or alum, which, by themselves, but much more when joined with saltpetre, are powerful to part silver from gold. As to the other things that are added to them, they cannot individually by their own strength and nature separate those metals, but joined they are very powerful. Since there are many combinations, I will set out a few. In the first, the use of which is common and general, there is one _libra_ of vitriol and as much salt, added to a third of a _libra_ of spring water. The second contains two _librae_ of vitriol, one of saltpetre, and as much spring or river water by weight as will pa.s.s away whilst the vitriol is being reduced to powder by the fire. The third consists of four _librae_ of vitriol, two and a half _librae_ of saltpetre, half a _libra_ of alum, and one and a half _librae_ of spring water. The fourth consists of two _librae_ of vitriol, as many _librae_ of saltpetre, one quarter of a _libra_ of alum, and three-quarters of a _libra_ of spring water. The fifth is composed of one _libra_ of saltpetre, three _librae_ of alum, half a _libra_ of brick dust, and three-quarters of a _libra_ of spring water.

The sixth consists of four _librae_ of vitriol, three _librae_ of saltpetre, one of alum, one _libra_ likewise of stones which when thrown into a fierce furnace are easily liquefied by fire of the third order, and one and a half _librae_ of spring water. The seventh is made of two _librae_ of vitriol, one and a half _librae_ of saltpetre, half a _libra_ of alum, and one _libra_ of stones which when thrown into a glowing furnace are easily liquefied by fire of the third order, and five-sixths of a _libra_ of spring water. The eighth is made of two _librae_ of vitriol, the same number of _librae_ of saltpetre, one and a half _librae_ of alum, one _libra_ of the lees of the _aqua_ which parts gold from silver; and to each separate _libra_ a sixth of urine is poured over it. The ninth contains two _librae_ of powder of baked bricks, one _libra_ of vitriol, likewise one _libra_ of saltpetre, a handful of salt, and three-quarters of a _libra_ of spring water. Only the tenth lacks vitriol and alum, but it contains three _librae_ of saltpetre, two _librae_ of stones which when thrown into a hot furnace are easily liquefied by fire of the third order, half a _libra_ each of verdigris[4], of _stibium_, of iron scales and filings, and of asbestos[5], and one and one-sixth _librae_ of spring water.

All the vitriol from which the _aqua_ is usually made is first reduced to powder in the following way. It is thrown into an earthen crucible lined on the inside with litharge, and heated until it melts; then it is stirred with a copper wire, and after it has cooled it is pounded to powder. In the same manner saltpetre melted by the fire is pounded to powder when it has cooled. Some indeed place alum upon an iron plate, roast it, and make it into powder.

Although all these _aquae_ cleanse gold concentrates or dust from impurities, yet there are certain compositions which possess singular power. The first of these consists of one _libra_ of verdigris and three-quarters of a _libra_ of vitriol. For each _libra_ there is poured over it one-sixth of a _libra_ of spring or river water, as to which, since this pertains to all these compounds, it is sufficient to have mentioned once for all. The second composition is made from one _libra_ of each of the following, artificial orpiment, vitriol, lime, alum, ash which the dyers of wool use, one quarter of a _libra_ of verdigris, and one and a half _unciae_ of _stibium_. The third consists of three _librae_ of vitriol, one of saltpetre, half a _libra_ of asbestos, and half a _libra_ of baked bricks. The fourth consists of one _libra_ of saltpetre, one _libra_ of alum, and half a _libra_ of sal-ammoniac.[6]

[Ill.u.s.tration 442 (Nitric Acid Making): A--Furnace. B--Its round hole.

C--Air-holes. D--Mouth of the furnace. E--Draught opening under it.

F--Earthenware crucible. G--Ampulla. H--Operculum. I--Its spout.

K--Other ampulla. L--Basket in which this is usually placed lest it be broken.]

The furnace in which _aqua valens_ is made[7] is built of bricks, rectangular, two feet long and wide, and as many feet high and a half besides. It is covered with iron plates supported with iron rods; these plates are smeared on the top with lute, and they have in the centre a round hole, large enough to hold the earthen vessel in which the gla.s.s ampulla is placed, and on each side of the centre hole are two small round air-holes. The lower part of the furnace, in order to hold the burning charcoal, has iron plates at the height of a palm, likewise supported by iron rods. In the middle of the front there is the mouth, made for the purpose of putting the fire into the furnace; this mouth is half a foot high and wide, and rounded at the top, and under it is the draught opening. Into the earthen vessel set over the hole is placed clean sand a digit deep, and in it the gla.s.s ampulla is set as deeply as it is smeared with lute. The lower quarter is smeared eight or ten times with nearly liquid lute, each time to the thickness of a blade, and each time it is dried again, until it has become as thick as the thumb; this kind of lute is well beaten with an iron rod, and is thoroughly mixed with hair or cotton thread, or with wool and salt, that it should not crackle. The many things of which the compounds are made must not fill the ampulla completely, lest when boiling they rise into the operculum.

The operculum is likewise made of gla.s.s, and is closely joined to the ampulla with linen, cemented with wheat flour and white of egg moistened with water, and then lute free from salt is spread over that part of it.

In a similar way the spout of the operculum is joined by linen covered with lute to another gla.s.s ampulla which receives the distilled _aqua_.

A kind of thin iron nail or small wooden peg, a little thicker than a needle, is fixed in this joint, in order that when air seems necessary to the artificer distilling by this process he can pull it out; this is necessary when too much of the vapour has been driven into the upper part. The four air-holes which, as I have said, are on the top of the furnace beside the large hole on which the ampulla is placed, are likewise covered with lute.

All this preparation having been accomplished in order, and the ingredients placed in the ampulla, they are gradually heated over burning charcoal until they begin to exhale vapour and the ampulla is seen to trickle with moisture. But when this, on account of the rising of the vapour, turns red, and the _aqua_ distils through the spout of the operculum, then one must work with the utmost care, lest the drops should fall at a quicker rate than one for every five movements of the clock or the striking of its bell, and not slower than one for every ten; for if it falls faster the gla.s.ses will be broken, and if it drops more slowly the work begun cannot be completed within the definite time, that is within the s.p.a.ce of twenty-four hours. To prevent the first accident, part of the coals are extracted by means of an iron implement similar to pincers; and in order to prevent the second happening, small dry pieces of oak are placed upon the coals, and the substances in the ampulla are heated with a sharper fire, and the air-holes on the furnace are re-opened if need arise. As soon as the drops are being distilled, the gla.s.s ampulla which receives them is covered with a piece of linen moistened with water, in order that the powerful vapour which arises may be repelled. When the ingredients have been heated and the ampulla in which they were placed is whitened with moisture, it is heated by a fiercer fire until all the drops have been distilled[8]. After the furnace has cooled, the _aqua_ is filtered and poured into a small gla.s.s ampulla, and into the same is put half a _drachma_ of silver[9], which when dissolved makes the turbid _aqua_ clear. This is poured into the ampulla containing all the rest of the _aqua_, and as soon as the lees have sunk to the bottom the _aqua_ is poured off, removed, and reserved for use.

Gold is parted from silver by the following method[10]. The alloy, with lead added to it, is first heated in a cupel until all the lead is exhaled, and eight ounces of the alloy contain only five _drachmae_ of copper or at most six, for if there is more copper in it, the silver separated from the gold soon unites with it again. Such molten silver containing gold is formed into granules, being stirred by means of a rod split at the lower end, or else is poured into an iron mould, and when cooled is made into thin leaves. As the process of making granules from argentiferous gold demands greater care and diligence than making them from any other metals, I will now explain the method briefly. The alloy is first placed in a crucible, which is then covered with a lid and placed in another earthen crucible containing a few ashes. Then they are placed in the furnace, and after they are surrounded by charcoal, the fire is blown by the blast of a bellows, and lest the charcoal fall away it is surrounded by stones or bricks. Soon afterward charcoal is thrown over the upper crucible and covered with live coals; these again are covered with charcoal, so that the crucible is surrounded and covered on all sides with it. It is necessary to heat the crucibles with charcoal for the s.p.a.ce of half an hour or a little longer, and to provide that there is no deficiency of charcoal, lest the alloy become chilled; after this the air is blown in through the nozzle of the bellows, that the gold may begin to melt. Soon afterward it is turned round, and a test is quickly taken to see whether it be melted, and if it is melted, fluxes are thrown into it; it is advisable to cover up the crucible again closely that the contents may not be exhaled. The contents are heated together for as long as it would take to walk fifteen paces, and then the crucible is seized with tongs and the gold is emptied into an oblong vessel containing very cold water, by pouring it slowly from a height so that the granules will not be too big; in proportion as they are lighter, more fine and more irregular, the better they are, therefore the water is frequently stirred with a rod split into four parts from the lower end to the middle.

The leaves are cut into small pieces, and they or the silver granules are put into a gla.s.s ampulla, and the _aqua_ is poured over them to a height of a digit above the silver. The ampulla is covered with a bladder or with waxed linen, lest the contents exhale. Then it is heated until the silver is dissolved, the indication of which is the bubbling of the _aqua_. The gold remains in the bottom, of a blackish colour, and the silver mixed with the _aqua_ floats above. Some pour the latter into a copper bowl and pour into it cold water, which immediately congeals the silver; this they take out and dry, having poured off the _aqua_[11]. They heat the dried silver in an earthenware crucible until it melts, and when it is melted they pour it into an iron mould.

The gold which remains in the ampulla they wash with warm water, filter, dry, and heat in a crucible with a little _chrysocolla_ which is called borax, and when it is melted they likewise pour it into an iron mould.

Some workers, into an ampulla which contains gold and silver and the _aqua_ which separates them, pour two or three times as much of this _aqua valens_ warmed, and into the same ampulla or into a dish into which all is poured, throw fine leaves of black lead and copper; by this means the gold adheres to the lead and the silver to the copper, and separately the lead from the gold, and separately the copper from the silver, are parted in a cupel. But no method is approved by us which loses the _aqua_ used to part gold from silver, for it might be used again[12].

[Ill.u.s.tration 446 (Parting precious metals with nitric acid): A--Ampullae arranged in the vessels. B--An ampulla standing upright between iron rods. C--Ampullae placed in the sand which is contained in a box, the spouts of which reach from the opercula into ampullae placed under them. D--Ampullae likewise placed in sand which is contained in a box, of which the spouts from the opercula extend crosswise into ampullae placed under them. E--Other ampullae receiving the distilled _aqua_ and likewise arranged in sand contained in the lower boxes.

F--Iron tripod, in which the ampulla is usually placed when there are not many particles of gold to be parted from the silver. G--Vessel.]

A gla.s.s ampulla, which bulges up inside at the bottom like a cone, is covered on the lower part of the outside with lute in the way explained above, and into it is put silver bullion weighing three and a half Roman _librae_. The _aqua_ which parts the one from the other is poured into it, and the ampulla is placed in sand contained in an earthen vessel, or in a box, that it may be warmed with a gentle fire. Lest the _aqua_ should be exhaled, the top of the ampulla is plastered on all sides with lute, and it is covered with a gla.s.s operculum, under whose spout is placed another ampulla which receives the distilled drops; this receiver is likewise arranged in a box containing sand. When the contents are heated it reddens, but when the redness no longer appears to increase, it is taken out of the vessel or box and shaken; by this motion the _aqua_ becomes heated again and grows red; if this is done two or three times before other _aqua_ is added to it, the operation is sooner concluded, and much less _aqua_ is consumed. When the first charge has all been distilled, as much silver as at first is again put into the ampulla, for if too much were put in at once, the gold would be parted from it with difficulty. Then the second _aqua_ is poured in, but it is warmed in order that it and the ampulla may be of equal temperature, so that the latter may not be cracked by the cold; also if a cold wind blows on it, it is apt to crack. Then the third _aqua_ is poured in, and also if circ.u.mstances require it, the fourth, that is to say more _aqua_ and again more is poured in until the gold a.s.sumes the colour of burned brick. The artificer keeps in hand two _aquae_, one of which is stronger than the other; the stronger is used at first, then the less strong, then at the last again the stronger. When the gold becomes of a reddish yellow colour, spring water is poured in and heated until it boils. The gold is washed four times and then heated in the crucible until it melts. The water with which it was washed is put back, for there is a little silver in it; for this reason it is poured into an ampulla and heated, and the drops first distilled are received by one ampulla, while those which come later, that is to say when the operculum begins to get red, fall into another. This latter _aqua_ is useful for testing the gold, the former for was.h.i.+ng it; the former may also be poured over the ingredients from which the _aqua valens_ is made.

The _aqua_ that was first distilled, which contains the silver, is poured into an ampulla wide at the base, the top of which is also smeared with lute and covered by an operculum, and is then boiled as before in order that it may be separated from the silver. If there be so much _aqua_ that (when boiled) it rises into the operculum, there is put into the ampulla one lozenge or two; these are made of soap, cut into small pieces and mixed together with powdered argol, and then heated in a pot over a gentle fire; or else the contents are stirred with a hazel twig split at the bottom, and in both cases the _aqua_ effervesces, and soon after again settles. When the powerful vapour appears, the _aqua_ gives off a kind of oil, and the operculum becomes red. But, lest the vapours should escape from the ampulla and the operculum in that part where their mouths communicate, they are entirely sealed all round. The _aqua_ is boiled continually over a fiercer fire, and enough charcoal must be put into the furnace so that the live coals touch the vessel. The ampulla is taken out as soon as all the _aqua_ has been distilled, and the silver, which is dried by the heat of the fire, alone remains in it; the silver is shaken out and put in an earthenware crucible, and heated until it melts. The molten gla.s.s is extracted with an iron rod curved at the lower end, and the silver is made into cakes.

The gla.s.s extracted from the crucible is ground to powder, and to this are added litharge, argol, gla.s.s-galls, and saltpetre, and they are melted in an earthen crucible. The b.u.t.ton that settles is transferred to the cupel and re-melted.

If the silver was not sufficiently dried by the heat of the fire, that which is contained in the upper part of the ampulla will appear black; this when melted will be consumed. When the lute, which was smeared round the lower part of the ampulla, has been removed, it is placed in the crucible and is re-melted, until at last there is no more appearance of black[13].

If to the first _aqua_ the other which contains silver is to be added, it must be poured in before the powerful vapours appear, and the _aqua_ gives off the oily substance, and the operculum becomes red; for he who pours in the _aqua_ after the vapour appears causes a loss, because the _aqua_ generally spurts out and the gla.s.s breaks. If the ampulla breaks when the gold is being parted from the silver or the silver from the _aqua_, the _aqua_ will be absorbed by the sand or the lute or the bricks, whereupon, without any delay, the red hot coals should be taken out of the furnace and the fire extinguished. The sand and bricks after being crushed should be thrown into a copper vessel, warm water should be poured over them, and they should be put aside for the s.p.a.ce of twelve hours; afterward the water should be strained through a canvas, and the canvas, since it contains silver, should be dried by the heat of the sun or the fire, and then placed in an earthen crucible and heated until the silver melts, this being poured out into an iron mould. The strained water should be poured into an ampulla and separated from the silver, of which it contains a minute portion; the sand should be mixed with litharge, gla.s.s-galls, argol, saltpetre, and salt, and heated in an earthen crucible. The b.u.t.ton which settles at the bottom should be transferred to a cupel, and should be re-melted, in order that the lead may be separated from the silver. The lute, with lead added, should be heated in an earthen crucible, then re-melted in a cupel.

We also separate silver from gold by the same method when we a.s.say them.

For this purpose the alloy is first rubbed against a touchstone, in order to learn what proportion of silver there is in it; then as much silver as is necessary is added to the argentiferous gold, in a _bes_ of which there must be less than a _semi-uncia_ or a _semi-uncia_ and a _sicilicus_[14] of copper. After lead has been added, it is melted in a cupel until the lead and the copper have exhaled, then the alloy of gold with silver is flattened out, and little tubes are made of the leaves; these are put into a gla.s.s ampulla, and strong _aqua_ is poured over them two or three times. The tubes after this are absolutely pure, with the exception of only a quarter of a _siliqua_, which is silver; for only this much silver remains in eight _unciae_ of gold[15].

As great expense is incurred in parting the metals by the methods that I have explained, as night vigils are necessary when _aqua valens_ is made, and as generally much labour and great pains have to be expended on this matter, other methods for parting have been invented by clever men, which are less costly, less laborious, and in which there is less loss if through carelessness an error is made. There are three methods, the first performed with sulphur, the second with antimony, the third by means of some compound which consists of these or other ingredients.

[Ill.u.s.tration 449 (Parting precious metals with sulphur): A--Pot.

B--Circular fire. C--Crucibles. D--Their lids. E--Lid of the pot.

F--Furnace. G--Iron rod.]

In the first method,[16] the silver containing some gold is melted in a crucible and made into granules. For every _libra_ of granules, there is taken a sixth of a _libra_ and a _sicilicus_ of sulphur (not exposed to the fire); this, when crushed, is sprinkled over the moistened granules, and then they are put into a new earthen pot of the capacity of four _s.e.xtarii_, or into several of them if there is an abundance of granules. The pot, having been filled, is covered with an earthen lid and smeared over, and placed within a circle of fire set one and a half feet distant from the pot on all sides, in order that the sulphur added to the silver should not be distilled when melted. The pot is opened, the black-coloured granules are taken out, and afterward thirty-three _librae_ of these granules are placed in an earthen crucible, if it has such capacity. For every _libra_ of silver granules, weighed before they were sprinkled with sulphur, there is weighed out also a sixth of a _libra_ and a _sicilicus_ of copper, if each _libra_ consists either of three-quarters of a _libra_ of silver and a quarter of a _libra_ of copper, or of three-quarters of a _libra_ and a _semi-uncia_ of silver and a sixth of a _libra_ and a _semi-uncia_ of copper. If, however, the silver contains five-sixths of a _libra_ of silver and a sixth of a _libra_ of copper, or five-sixths of a _libra_ and a _semi-uncia_ of silver and an _uncia_ and a half of copper, then there are weighed out a quarter of a _libra_ of copper granules. If a _libra_ contains eleven-twelfths of a _libra_ of silver and one _uncia_ of copper, or eleven-twelfths and a _semi-uncia_ of silver and a _semi-uncia_ of copper, then are weighed out a quarter of a _libra_ and a _semi-uncia_ and a _sicilicus_ of copper granules. Lastly, if there is only pure silver, then as much as a third of a _libra_ and a _semi-uncia_ of copper granules are added. Half of these copper granules are added soon afterward to the black-coloured silver granules. The crucible should be tightly covered and smeared over with lute, and placed in a furnace, into which the air is drawn through the draught-holes. As soon as the silver is melted, the crucible is opened, and there is placed in it a heaped ladleful more of granulated copper, and also a heaped ladleful of a powder which consists of equal parts of litharge, of granulated lead, of salt, and of gla.s.s-galls; then the crucible is again covered with the lid. When the copper granules are melted, more are put in, together with the powder, until all have been put in.

A little of the regulus is taken from the crucible, but not from the gold lump which has settled at the bottom, and a _drachma_ of it is put into each of the cupels, which contain an _uncia_ of molten lead; there should be many of these cupels. In this way half a _drachma_ of silver is made. As soon as the lead and copper have been separated from the silver, a third of it is thrown into a gla.s.s ampulla, and _aqua valens_ is poured over it. By this method is shown whether the sulphur has parted all the gold from the silver, or not. If one wishes to know the size of the gold lump which has settled at the bottom of the crucible, an iron rod moistened with water is covered with chalk, and when the rod is dry it is pushed down straight into the crucible, and the rod remains bright to the height of the gold lump; the remaining part of the rod is coloured black by the regulus, which adheres to the rod if it is not quickly removed.

If when the rod has been extracted the gold is observed to be satisfactorily parted from the silver, the regulus is poured out, the gold b.u.t.ton is taken out of the crucible, and in some clean place the regulus is chipped off from it, although it usually flies apart. The lump itself is reduced to granules, and for every _libra_ of this gold they weigh out a quarter of a _libra_ each of crushed sulphur and of granular copper, and all are placed together in an earthen crucible, not into a pot. When they are melted, in order that the gold may more quickly settle at the bottom, the powder which I have mentioned is added.