Book X

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 pass 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]

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 glass 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 glass 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 glass, 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 glass 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 glasses will be broken, and if it drops more slowly the work begun cannot be completed within the definite time, that is within the space 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 glass 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 glass 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 space 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 glass 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].

A glass 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 glass 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 circumstances require it, the fourth, that is to say more aqua and again more is poured in until the gold assumes 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 washing 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 glass is extracted with an iron rod curved at the lower end, and the silver is made into cakes. The glass extracted from the crucible is ground to powder, and to this are added litharge, argol, glass-galls, and saltpetre, and they are melted in an earthen crucible. The button 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 glass 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 space 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, glass-galls, argol, saltpetre, and salt, and heated in an earthen crucible. The button 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 assay 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 glass 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.

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 sextarii, 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 glass-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 glass 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 button 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.

Although minute particles of gold appear to scintillate in the regulus of copper and silver, yet if all that are in a libra do not weigh as much as a single sesterce, then the sulphur has satisfactorily parted the gold from the silver; but if it should weigh a sesterce or more, then the regulus is thrown back again into the earthen crucible, and it is not advantageous to add sulphur, but only a little copper and powder, by which method a gold lump is again made to settle at the bottom; and this one is added to the other button which is not rich in gold.

When gold is parted from sixty-six librae of silver, the silver, copper, and sulphur regulus weighs one hundred and thirty-two librae. To separate the copper from the silver we require five hundred librae of lead, more or less, with which the regulus is melted in the second furnace. In this manner litharge and hearth-lead are made, which are re-smelted in the first furnace. The cakes that are made from these are placed in the third furnace, so that the lead may be separated from the copper and used again, for it contains very little silver. The crucibles and their covers are crushed, washed, and the sediment is melted together with litharge and hearth-lead.

Those who wish to separate all the silver from the gold by this method leave one part of gold to three of silver, and then reduce the alloy to granules. Then they place it in an ampulla, and by pouring aqua valens over it, part the gold from the silver, which process I explained in Book VII.

If sulphur from the lye with which sal artificiosus is made, is strong enough to float an egg thrown into it, and is boiled until it no longer emits fumes, and melts when placed upon glowing coals, then, if such sulphur is thrown into the melted silver, it parts the gold from it.

Silver is also parted from gold by means of stibium[17]. If in a bes of gold there are seven, or six, or five double sextulae of silver, then three parts of stibium are added to one part of gold; but in order that the stibium should not consume the gold, it is melted with copper in a red hot earthen crucible. If the gold contains some portion of copper, then to eight unciae of stibium a sicilicus of copper is added; and if it contains no copper, then half an uncia, because copper must be added to stibium in order to part gold from silver. The gold is first placed in a red hot earthen crucible, and when melted it swells, and a little stibium is added to it lest it run over; in a short space of time, when this has melted, it likewise again swells, and when this occurs it is advisable to put in all the remainder of the stibium, and to cover the crucible with a lid, and then to heat the mixture for the time required to walk thirty-five paces. Then it is at once poured out into an iron pot, wide at the top and narrow at the bottom, which was first heated and smeared over with tallow or wax, and set on an iron or wooden block. It is shaken violently, and by this agitation the gold lump settles to the bottom, and when the pot has cooled it is tapped loose, and is again melted four times in the same way. But each time a less weight of stibium is added to the gold, until finally only twice as much stibium is added as there is gold, or a little more; then the gold lump is melted in a cupel. The stibium is melted again three or four times in an earthen crucible, and each time a gold lump settles, so that there are three or four gold lumps, and these are all melted together in a cupel.

To two librae and a half of such stibium are added two librae of argol and one libra of glass-galls, and they are melted in an earthen crucible, where a lump likewise settles at the bottom; this lump is melted in the cupel. Finally, the stibium with a little lead added, is melted in the cupel, in which, after all the rest has been consumed by the fire, the silver alone remains. If the stibium is not first melted in an earthen crucible with argol and glass-galls, before it is melted in the cupel, part of the silver is consumed, and is absorbed by the ash and powder of which the cupel is made.

The crucible in which the gold and silver alloy are melted with stibium, and also the cupel, are placed in a furnace, which is usually of the kind in which the air is drawn in through holes; or else they are placed in a goldsmith's forge.

Just as aqua valens poured over silver, from which the sulphur has parted the gold, shows us whether all has been separated or whether particles of gold remain in the silver; so do certain ingredients, if placed in the pot or crucible "alternately" with the gold, from which the silver has been parted by stibium, and heated, show us whether all have been separated or not.

We use cements[18] when, without stibium, we part silver or copper or both so ingeniously and admirably from gold. There are various cements. Some consist of half a libra of brick dust, a quarter of a libra of salt, an uncia of saltpetre, half an uncia of sal-ammoniac, and half an uncia of rock salt. The bricks or tiles from which the dust is made must be composed of fatty clays, free from sand, grit, and small stones, and must be moderately burnt and very old.

Another cement is made of a bes of brick dust, a third of rock salt, an uncia of saltpetre, and half an uncia of refined salt. Another cement is made of a bes of brick dust, a quarter of refined salt, one and a half unciae of saltpetre, an uncia of sal-ammoniac, and half an uncia of rock salt. Another has one libra of brick dust, and half a libra of rock salt, to which some add a sixth of a libra and a sicilicus of vitriol. Another is made of half a libra of brick dust, a third of a libra of rock salt, an uncia and a half of vitriol, and one uncia of saltpetre. Another consists of a bes of brick dust, a third of refined salt, a sixth of white vitriol[19], half an uncia of verdigris, and likewise half an uncia of saltpetre. Another is made of one and a third librae of brick dust, a bes of rock salt, a sixth of a libra and half an uncia of sal-ammoniac, a sixth and half an uncia of vitriol, and a sixth of saltpetre. Another contains a libra of brick dust, a third of refined salt, and one and a half unciae of vitriol.

Those ingredients above are peculiar to each cement, but what follows is common to all. Each of the ingredients is first separately crushed to powder; the bricks are placed on a hard rock or marble, and crushed with an iron implement; the other things are crushed in a mortar with a pestle; each is separately passed through a sieve. Then they are all mixed together, and are moistened with vinegar in which a little sal-ammoniac has been dissolved, if the cement does not contain any. But some workers, however, prefer to moisten the gold granules or gold-leaf instead.

The cement should be placed, alternately with the gold, in new and clean pots in which no water has ever been poured. In the bottom the cement is levelled with an iron implement, and afterward the gold granules or leaves are placed one against the other, so that they may touch it on all sides; then, again, a handful of the cement, or more if the pots are large, is thrown in and levelled with an iron implement; the granules and leaves are laid over this in the same manner, and this is repeated until the pot is filled. Then it is covered with a lid, and the place where they join is smeared over with artificial lute, and when this is dry the pots are placed in the furnace.

The furnace has three chambers, the lowest of which is a foot high; into this lowest chamber the air penetrates through an opening, and into it the ashes fall from the burnt wood, which is supported by iron rods, arranged to form a grating. The middle chamber is two feet high, and the wood is pushed in through its mouth. The wood ought to be oak, holmoak, or turkey-oak, for from these the slow and lasting fire is made which is necessary for this operation. The upper chamber is open at the top so that the pots, for which it has the depth, may be put into it; the floor of this chamber consists of iron rods, so strong that they may bear the weight of the pots and the heat of the fire; they are sufficiently far apart that the fire may penetrate well and may heat the pots. The pots are narrow at the bottom, so that the fire entering into the space between them may heat them; at the top the pots are wide, so that they may touch and hold back the heat of the fire. The upper part of the furnace is closed in with bricks not very thick, or with tiles and lute, and two or three air-holes are left, through which the fumes and flames may escape.

The gold granules or leaves and the cement, alternately placed in the pots, are heated by a gentle fire, gradually increasing for twenty-four hours, if the furnace was heated for two hours before the full pots were stood in it, and if this was not done, then for twenty-six hours. The fire should be increased in such a manner that the pieces of gold and the cement, in which is the potency to separate the silver and copper from the gold, may not melt, for in this case the labour and cost will be spent in vain; therefore, it is ample to have the fire hot enough that the pots always remain red. After so many hours all the burning wood should be drawn out of the furnace. Then the refractory bricks or tiles are removed from the top of the furnace, and the glowing pots are taken out with the tongs. The lids are removed, and if there is time it is well to allow the gold to cool by itself, for then there is less loss; but if time cannot be spared for that operation, the pieces of gold are immediately placed separately into a wooden or bronze vessel of water and gradually quenched, lest the cement which absorbs the silver should exhale it. The pieces of gold, and the cement adhering to them, when cooled or quenched, are rolled with a little mallet so as to crush the lumps and free the gold from the cement. Then they are sifted by a fine sieve, which is placed over a bronze vessel; in this manner the cement containing the silver or the copper or both, falls from the sieve into the bronze vessel, and the gold granules or leaves remain on it. The gold is placed in a vessel and again rolled with the little mallet, so that it may be cleansed from the cement which absorbs silver and copper.

The particles of cement, which have dropped through the holes of the sieve into the bronze vessel, are washed in a bowl, over a wooden tub, being shaken about with the hands, so that the minute particles of gold which have fallen through the sieve may be separated. These are again washed in a little vessel, with warm water, and scrubbed with a piece of wood or a twig broom, that the moistened cement may be detached. Afterward all the gold is again washed with warm water, and collected with a bristle brush, and should be washed in a copper full of holes, under which is placed a little vessel. Then it is necessary to put the gold on an iron plate, under which is a vessel, and to wash it with warm water. Finally, it is placed in a bowl, and, when dry, the granules or leaves are rubbed against a touchstone at the same time as a touch-needle, and considered carefully as to whether they be pure or alloyed. If they are not pure enough, the granules or the leaves, together with the cement which attracts silver and copper, are arranged alternately in layers in the same manner, and again heated; this is done as often as is necessary, but the last time it is heated as many hours as are required to cleanse the gold.

Some people add another cement to the granules or leaves. This cement lacks the ingredients of metalliferous origin, such as verdigris and vitriol, for if these are in the cement, the gold usually takes up a little of the base metal; or if it does not do this, it is stained by them. For this reason some very rightly never make use of cements containing these things, because brick dust and salt alone, especially rock salt, are able to extract all the silver and copper from the gold and to attract it to themselves.

It is not necessary for coiners to make absolutely pure gold, but to heat it only until such a fineness is obtained as is needed for the gold money which they are coining.

The gold is heated, and when it shows the necessary golden yellow colour and is wholly pure, it is melted and made into bars, in which case they are either prepared by the coiners with chrysocolla, which is called by the Moors borax, or are prepared with salt of lye made from the ashes of ivy or of other salty herbs.

The cement which has absorbed silver or copper, after water has been poured over it, is dried and crushed, and when mixed with hearth-lead and de-silverized lead, is smelted in the blast furnace. The alloy of silver and lead, or of silver and copper and lead, which flows out, is again melted in the cupellation furnace, in order that the lead and copper may be separated from the silver. The silver is finally thoroughly purified in the refining furnace, and in this practical manner there is no silver lost, or only a minute quantity.

There are besides this, certain other cements[20] which part gold from silver, composed of sulphur, stibium and other ingredients. One of these compounds consists of half an uncia of vitriol dried by the heat of the fire and reduced to powder, a sixth of refined salt, a third of stibium, half a libra of prepared sulphur (not exposed to the fire), one sicilicus of glass, likewise one sicilicus of saltpetre, and a drachma of sal-ammoniac.[21] The sulphur is prepared as follows: it is first crushed to powder, then it is heated for six hours in sharp vinegar, and finally poured into a vessel and washed with warm water; then that which settles at the bottom of the vessel is dried. To refine the salt it is placed in river water and boiled, and again evaporated. The second compound contains one libra of sulphur (not exposed to fire) and two librae of refined salt. The third compound is made from one libra of sulphur (not exposed to the fire), half a libra of refined salt, a quarter of a libra of sal-ammoniac, and one uncia of red-lead. The fourth compound consists of one libra each of refined salt, sulphur (not exposed to the fire) and argol, and half a libra of chrysocolla which the Moors call borax. The fifth compound has equal proportions of sulphur (not exposed to the fire), sal-ammoniac, saltpetre, and verdigris.

The silver which contains some portion of gold is first melted with lead in an earthen crucible, and they are heated together until the silver exhales the lead. If there was a libra of silver, there must be six drachmae of lead. Then the silver is sprinkled with two unciae of that powdered compound and is stirred; afterward it is poured into another crucible, first warmed and lined with tallow, and then violently shaken. The rest is performed according to the process I have already explained.

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

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

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

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

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

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

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

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

Lead is separated from gold or silver in a cupellation furnace, of which the structure consists of rectangular stones, of two interior walls of which the one intersects the other transversely, of a round sole, and of a dome. Its crucible is made from powder of earth and ash; but I will first speak of the structure and also of the rectangular stones. A circular wall is built four feet and three palms high, and one foot thick; from the height of two feet and three palms from the bottom, the upper part of the interior is cut away to the width of one palm, so that the stone sole may rest upon it. There are usually as many as fourteen stones; on the outside they are a foot and a palm wide, and on the inside narrower, because the inner circle is much smaller than the outer; if the stones are wider, fewer are required, if narrower more; they are sunk into the earth to a depth of a foot and a palm. At the top each one is joined to the next by an iron staple, the points of which are embedded in holes, and into each hole is poured molten lead. This stone structure has six air-holes near the ground, at a height of a foot above the ground; they are two feet and a palm from the bottom of the stones; each of these air-holes is in two stones, and is two palms high, and a palm and three digits wide. One of them is on the right side, between the wall which protects the main wall from the fire, and the channel through which the litharge flows out of the furnace crucible; the other five air-holes are distributed all round at equal distances apart; through these escapes the moisture which the earth exhales when heated, and if it were not for these openings the crucible would absorb the moisture and be damaged. In such a case a lump would be raised, like that which a mole throws up from the earth, and the ash would float on the top, and the crucible would absorb the silver-lead alloy; there are some who, because of this, make the rear part of the structure entirely open. The two inner walls, of which one intersects the other, are built of bricks, and are a brick in thickness. There are four air-holes in these, one in each part, which are about one digit's breadth higher and wider than the others. Into the four compartments is thrown a wheelbarrowful of slag, and over this is placed a large wicker basket full of charcoal dust. These walls extend a cubit above the ground, and on these, and on the ledge cut in the rectangular stones, is placed the stone sole; this sole is a palm and three digits thick, and on all sides touches the rectangular stones; if there are any cracks in it they are filled up with fragments of stone or brick. The front part of the sole is sloped so that a channel can be made, through which the litharge flows out. Copper plates are placed on this part of the sole-stone so that the silver-lead or other alloy may be more rapidly heated.

A dome which has the shape of half a sphere covers the crucible. It consists of iron bands and of bars and of a lid. There are three bands, each about a palm wide and a digit thick; the lowest is at a distance of one foot from the middle one, and the middle one a distance of two feet from the upper one. Under them are eighteen iron bars fixed by iron rivets; these bars are of the same width and thickness as the bands, and they are of such a length, that curving, they reach from the lower band to the upper, that is two feet and three palms long, while the dome is only one foot and three palms high. All the bars and bands of the dome have iron plates fastened on the underside with iron wire. In addition, the dome has four apertures; the rear one, which is situated opposite the channel through which the litharge flows out, is two feet wide at the bottom; toward the top, since it slopes gently, it is narrower, being a foot, three palms, and a digit wide; there is no bar at this place, for the aperture extends from the upper band to the middle one, but not to the lower one. The second aperture is situated above the channel, is two and a half feet wide at the bottom, and two feet and a palm at the top; and there is likewise no bar at this point; indeed, not only does the bar not extend to the lower band, but the lower band itself does not extend over this part, in order that the master can draw the litharge out of the crucible. There are besides, in the wall which protects the principal wall against the heat, near where the nozzles of the bellows are situated, two apertures, three palms wide and about a foot high, in the middle of which two rods descend, fastened on the inside with plates. Near these apertures are placed the nozzles of the bellows, and through the apertures extend the pipes in which the nozzles of the bellows are set. These pipes are made of iron plates rolled up; they are two palms three digits long, and their inside diameter is three and a half digits; into these two pipes the nozzles of the bellows penetrate a distance of three digits from their valves. The lid of the dome consists of an iron band at the bottom, two digits wide, and of three curved iron bars, which extend from one point on the band to the point opposite; they cross each other at the top, where they are fixed by means of iron rivets. On the under side of the bars there are likewise plates fastened by rivets; each of the plates has small holes the size of a finger, so that the lute will adhere when the interior is lined. The dome has three iron rings engaged in wide holes in the heads of iron claves, which fasten the bars to the middle band at these points. Into these rings are fastened the hooks of the chains with which the dome is raised, when the master is preparing the crucible.

On the sole and the copper plates and the rock of the furnace, lute mixed with straw is placed to a depth of three digits, and it is pounded with a wooden rammer until it is compressed to a depth of one digit only. The rammer-head is round and three palms high, two palms wide at the bottom, and tapering upward; its handle is three feet long, and where it is set into the rammer-head it is bound around with an iron band. The top of the stonework in which the dome rests is also covered with lute, likewise mixed with straw, to the thickness of a palm. All this, as soon as it becomes loosened, must be repaired.

The artificer who undertakes the work of parting the metals, distributes the operation into two shifts of two days. On the one morning he sprinkles a little ash into the lute, and when he has poured some water over it he brushes it over with a broom. Then he throws in sifted ashes and dampens them with water, so that they could be moulded into balls like snow. The ashes are those from which lye has been made by letting water percolate through them, for other ashes which are fatty would have to be burnt again in order to make them less fat. When he has made the ashes smooth by pressing them with his hands, he makes the crucible slope down toward the middle; then he tamps it, as I have described, with a rammer. He afterward, with two small wooden rammers, one held in each hand, forms the channel through which the litharge flows out. The heads of these small rammers are each a palm wide, two digits thick, and one foot high; the handle of each is somewhat rounded, is a digit and a half less in diameter than the rammer-head, and is three feet in length; the rammer-head as well as the handle is made of one piece of wood. Then with shoes on, he descends into the crucible and stamps it in every direction with his feet, in which manner it is packed and made sloping. Then he again tamps it with a large rammer, and removing his shoe from his right foot he draws a circle around the crucible with it, and cuts out the circle thus drawn with an iron plate. This plate is curved at both ends, is three palms long, as many digits wide, and has wooden handles a palm and two digits long, and two digits thick; the iron plate is curved back at the top and ends, which penetrate into handles. There are some who use in the place of the plate a strip of wood, like the rim of a sieve; this is three digits wide, and is cut out at both ends that it may be held in the hands. Afterward he tamps the channel through which the litharge discharges. Lest the ashes should fall out, he blocks up the aperture with a stone shaped to fit it, against which he places a board, and lest this fall, he props it with a stick. Then he pours in a basketful of ashes and tamps them with the large rammer; then again and again he pours in ashes and tamps them with the rammer. When the channel has been made, he throws dry ashes all over the crucible with a sieve, and smooths and rubs it with his hands. Then he throws three basketsful of damp ashes on the margin all round the edge of the crucible, and lets down the dome. Soon after, climbing upon the crucible, he builds up ashes all around it, lest the molten alloy should flow out. Then, having raised the lid of the dome, he throws a basketful of charcoal into the crucible, together with an iron shovelful of glowing coals, and he also throws some of the latter through the apertures in the sides of the dome, and he spreads them with the same shovel. This work and labour is finished in the space of two hours.

An iron plate is set in the ground under the channel, and upon this is placed a wooden block, three feet and a palm long, a foot and two palms and as many digits wide at the back, and two palms and as many digits wide in front; on the block of wood is placed a stone, and over it an iron plate similar to the bottom one, and upon this he puts a basketful of charcoal, and also an iron shovelful of burning charcoals. The crucible is heated in an hour, and then, with the hooked bar with which the litharge is drawn off, he stirs the remainder of the charcoal about. This hook is a palm long and three digits wide, has the form of a double triangle, and has an iron handle four feet long, into which is set a wooden one six feet long. There are some who use instead a simple hooked bar. After about an hour's time, he stirs the charcoal again with the bar, and with the shovel throws into the crucible the burning charcoals lying in the channel; then again, after the space of an hour, he stirs the burning charcoals with the same bar. If he did not thus stir them about, some blackness would remain in the crucible and that part would be damaged, because it would not be sufficiently dried. Therefore the assistant stirs and turns the burning charcoal that it may be entirely burnt up, and so that the crucible may be well heated, which takes three hours; then the crucible is left quiet for the remaining two hours.

When the hour of eleven has struck, he sweeps up the charcoal ashes with a broom and throws them out of the crucible. Then he climbs on to the dome, and passing his hand in through its opening, and dipping an old linen rag in a bucket of water mixed with ashes, he moistens the whole of the crucible and sweeps it. In this way he uses two bucketsful of the mixture, each holding five Roman sextarii,[28] and he does this lest the crucible, when the metals are being parted, should break open; after this he rubs the crucible with a doe skin, and fills in the cracks. Then he places at the left side of the channel, two fragments of hearth-lead, laid one on the top of the other, so that when partly melted they remain fixed and form an obstacle, that the litharge will not be blown about by the wind from the bellows, but remain in its place. It is expedient, however, to use a brick in the place of the hearth-lead, for as this gets much hotter, therefore it causes the litharge to form more rapidly. The crucible in its middle part is made two palms and as many digits deeper.[29]

There are some who having thus prepared the crucible, smear it over with incense[30], ground to powder and dissolved in white of egg, soaking it up in a sponge and then squeezing it out again; there are others who smear over it a liquid consisting of white of egg and double the amount of bullock's blood or marrow. Some throw lime into the crucible through a sieve.

Afterward the master of the works weighs the lead with which the gold or silver or both are mixed, and he sometimes puts a hundred centumpondia[31] into the crucible, but frequently only sixty, or fifty, or much less. After it has been weighed, he strews about in the crucible three small bundles of straw, lest the lead by its weight should break the surface. Then he places in the channel several cakes of lead alloy, and through the aperture at the rear of the dome he places some along the sides; then, ascending to the opening at the top of the dome, he arranges in the crucible round about the dome the cakes which his assistant hands to him, and after ascending again and passing his hands through the same aperture, he likewise places other cakes inside the crucible. On the second day those which remain he, with an iron fork, places on the wood through the rear aperture of the dome.

When the cakes have been thus arranged through the hole at the top of the dome, he throws in charcoal with a basket woven of wooden twigs. Then he places the lid over the dome, and the assistant covers over the joints with lute. The master himself throws half a basketful of charcoal into the crucible through the aperture next to the nozzle pipe, and prepares the bellows, in order to be able to begin the second operation on the morning of the following day. It takes the space of one hour to carry out such a piece of work, and at twelve all is prepared. These hours all reckoned up make a sum of eight hours.

Now it is time that we should come to the second operation. In the morning the workman takes up two shovelsful of live charcoals and throws them into the crucible through the aperture next to the pipes of the nozzles; then through the same hole he lays upon them small pieces of fir-wood or of pitch pine, such as are generally used to cook fish. After this the water-gates are opened, in order that the machine may be turned which depresses the levers of the bellows. In the space of one hour the lead alloy is melted; and when this has been done, he places four sticks of wood, twelve feet long, through the hole in the back of the dome, and as many through the channel; these sticks, lest they should damage the crucible, are both weighted on the ends and supported by trestles; these trestles are made of a beam, three feet long, two palms and as many digits wide, two palms thick, and have two spreading legs at each end. Against the trestle, in front of the channel, there is placed an iron plate, lest the litharge, when it is extracted from the furnace, should splash the smelter's shoes and injure his feet and legs. With an iron shovel or a fork he places the remainder of the cakes through the aperture at the back of the dome on to the sticks of wood already mentioned.

The native silver, or silver glance, or grey silver, or ruby silver, or any other sort, when it has been flattened out[32], and cut up, and heated in an iron crucible, is poured into the molten lead mixed with silver, in order that impurities may be separated. As I have often said, this molten lead mixed with silver is called stannum[33].

When the long sticks of wood are burned up at the fore end, the master, with a hammer, drives into them pointed iron bars, four feet long and two digits wide at the front end, and beyond that one and a half digits wide and thick; with these he pushes the sticks of wood forward and the bars then rest on the trestles. There are others who, when they separate metals, put two such sticks of wood into the crucible through the aperture which is between the bellows, as many through the holes at the back, and one through the channel; but in this case a larger number of long sticks of wood is necessary, that is, sixty; in the former case, forty long sticks of wood suffice to carry out the operation. When the lead has been heated for two hours, it is stirred with a hooked bar, that the heat may be increased.

If it be difficult to separate the lead from the silver, he throws copper and charcoal dust into the molten silver-lead alloy. If the alloy of argentiferous gold and lead, or the silver-lead alloy, contains impurities from the ore, then he throws in either equal portions of argol and Venetian glass or of sal-ammoniac, or of Venetian glass and of Venetian soap; or else unequal portions, that is, two of argol and one of iron rust; there are some who mix a little saltpetre with each compound. To one centumpondium of the alloy is added a bes or a libra and a third of the powder, according to whether it is more or less impure. The powder certainly separates the impurities from the alloy. Then, with a kind of rabble he draws out through the channel, mixed with charcoal, the scum, as one might say, of the lead; the lead makes this scum when it becomes hot, but that less of it may be made it must be stirred frequently with the bar.

Within the space of a quarter of an hour the crucible absorbs the lead; at the time when it penetrates into the crucible it leaps and bubbles. Then the master takes out a little lead with an iron ladle, which he assays, in order to find what proportion of silver there is in the whole of the alloy; the ladle is five digits wide, the iron part of its handle is three feet long and the wooden part the same. Afterward, when they are heated, he extracts with a bar the litharge which comes from the lead and the copper, if there be any of it in the alloy. Wherefore, it might more rightly be called spuma of lead than of silver[34]. There is no injury to the silver, when the lead and copper are separated from it. In truth the lead becomes much purer in the crucible of the other furnace, in which silver is refined. In ancient times, as the author Pliny[35] relates, there was under the channel of the crucible another crucible, and the litharge flowed down from the upper one into the lower one, out of which it was lifted up and rolled round with a stick in order that it might be of moderate weight. For which reason, they formerly made it into small tubes or pipes, but now, since it is not rolled round a stick, they make it into bars.

If there be any danger that the alloy might flow out with the litharge, the foreman keeps on hand a piece of lute, shaped like a cylinder and pointed at both ends; fastening this to a hooked bar he opposes it to the alloy so that it will not flow out.

Now when the colour begins to show in the silver, bright spots appear, some of them being almost white, and a moment afterward it becomes absolutely white. Then the assistant lets down the water-gates, so that, the race being closed, the water-wheel ceases to turn and the bellows are still. Then the master pours several buckets of water on to the silver to cool it; others pour beer over it to make it whiter, but this is of no importance since the silver has yet to be refined. Afterward, the cake of silver is raised with the pointed iron bar, which is three feet long and two digits wide, and has a wooden handle four feet long fixed in its socket. When the cake of silver has been taken from the crucible, it is laid upon a stone, and from part of it the hearth-lead, and from the other part the litharge, is chipped away with a hammer; then it is cleansed with a bundle of brass wire dipped in water. When the lead is separated from the silver, more silver is frequently found than when it was assayed; for instance, if before there were three unciae and as many drachmae in a centumpondium, they now sometimes find three unciae and a half[36]. Often the hearth-lead remaining in the crucible is a palm deep; it is taken out with the rest of the ashes and is sifted, and that which remains in the sieve, since it is hearth-lead, is added to the hearth-lead[37].

The ashes which pass through the sieve are of the same use as they were at first, for, indeed, from these and pulverised bones they make the cupels. Finally, when much of it has accumulated, the yellow pompholyx adhering to the walls of the furnace, and likewise to those rings of the dome near the apertures, is cleared away.

I must also describe the crane with which the dome is raised. When it is made, there is first set up a rectangular upright post twelve feet long, each side of which measures a foot in width. Its lower pinion turns in a bronze socket set in an oak sill; there are two sills placed crosswise so that the one fits in a mortise in the middle of the other, and the other likewise fits in the mortise of the first, thus making a kind of a cross; these sills are three feet long and one foot wide and thick. The crane-post is round at its upper end and is cut down to a depth of three palms, and turns in a band fastened at each end to a roof-beam, from which springs the inclined chimney wall. To the crane-post is affixed a frame, which is made in this way: first, at a height of a cubit from the bottom, is mortised into the crane-post a small cross-beam, a cubit and three digits long, except its tenons, and two palms in width and thickness. Then again, at a height of five feet above it, is another small cross-beam of equal length, width, and thickness, mortised into the crane-post. The other ends of these two small cross-beams are mortised into an upright timber, six feet three palms long, and three-quarters wide and thick; the mortise is transfixed by wooden pegs. Above, at a height of three palms from the lower small cross-beam, are two bars, one foot one palm long, not including the tenons, a palm three digits wide, and a palm thick, which are mortised in the other sides of the crane-post. In the same manner, under the upper small cross-beam are two bars of the same size. Also in the upright timber there are mortised the same number of bars, of the same length as the preceding, but three digits thick, a palm two digits wide, the two lower ones being above the lower small cross-beam. From the upright timber near the upper small cross-beam, which at its other end is mortised into the crane-post, are two mortised bars. On the outside of this frame, boards are fixed to the small cross-beams, but the front and back parts of the frame have doors, whose hinges are fastened to the boards which are fixed to the bars that are mortised to the sides of the crane-post.

Then boards are laid upon the lower small cross-beam, and at a height of two palms above these there is a small square iron axle, the sides of which are two digits wide; both ends of it are round and turn in bronze or iron bearings, one of these bearings being fastened in the crane-post, the other in the upright timber. About each end of the small axle is a wooden disc, of three palms and a digit radius and one palm thick, covered on the rim with an iron band; these two discs are distant two palms and as many digits from each other, and are joined with five rundles; these rundles are two and a half digits thick and are placed three digits apart. Thus a drum is made, which is a palm and a digit distant from the upright timber, but further from the crane-post, namely, a palm and three digits. At a height of a foot and a palm above this little axle is a second small square iron axle, the thickness of which is three digits; this one, like the first one, turns in bronze or iron bearings. Around it is a toothed wheel, composed of two discs a foot three palms in diameter, a palm and two digits thick; on the rim of this there are twenty-three teeth, a palm wide and two digits thick; they protrude a palm from the wheel and are three digits apart. And around this same axle, at a distance of two palms and as many digits toward the upright timber, is another disc of the same diameter as the wheel and a palm thick; this turns in a hollowed-out place in the upright timber. Between this disc and the disc of the toothed wheel another drum is made, having likewise five rundles. There is, in addition to this second axle, at a height of a cubit above it, a small wooden axle, the journals of which are of iron; the ends are bound round with iron rings so that the journals may remain firmly fixed, and the journals, like the little iron axles, turn in bronze or iron bearings. This third axle is at a distance of about a cubit from the upper small cross-beam; it has, near the upright timber, a toothed wheel two and a half feet in diameter, on the rim of which are twenty-seven teeth; the other part of this axle, near the crane-post, is covered with iron plates, lest it should be worn away by the chain which winds around it. The end link of the chain is fixed in an iron pin driven into the little axle; this chain passes out of the frame and turns over a little pulley set between the beams of the crane-arm.

Above the frame, at a height of a foot and a palm, is the crane-arm. This consists of two beams fifteen feet long, three palms wide, and two thick, mortised into the crane-post, and they protrude a cubit from the back of the crane-post and are fastened together. Moreover, they are fastened by means of a wooden pin which penetrates through them and the crane-post; this pin has at the one end a broad head, and at the other a hole, through which is driven an iron bolt, so that the beams may be tightly bound into the crane-post. The beams of the crane-arm are supported and stayed by means of two oblique beams, six feet and two palms long, and likewise two palms wide and thick; these are mortised into the crane-post at their lower ends, and their upper ends are mortised into the beams of the crane-arm at a point about four feet from the crane-post, and they are fastened with iron nails. At the back of the upper end of these oblique beams, toward the crane-post, is an iron staple, fastened into the lower sides of the beams of the crane-arm, in order that it may hold them fast and bind them. The outer end of each beam of the crane-arm is set in a rectangular iron plate, and between these are three rectangular iron plates, fixed in such a manner that the beams of the crane-arm can neither move away from, nor toward, each other. The upper sides of these crane-arm beams are covered with iron plates for a length of six feet, so that a trolley can move on it.

The body of the trolley is made of wood from the Ostrya or any other hard tree, and is a cubit long, a foot wide, and three palms thick; on both edges of it the lower side is cut out to a height and width of a palm, so that the remainder may move backward and forward between the two beams of the crane-arm; at the front, in the middle part, it is cut out to a width of two palms and as many digits, that a bronze pulley, around a small iron axle, may turn in it. Near the corners of the trolley are four holes, in which as many small wheels travel on the beams of the crane-arm. Since this trolley, when it travels backward and forward, gives out a sound somewhat similar to the barking of a dog, we have given it this name[38]. It is propelled forward by means of a crank, and is drawn back by means of a chain. There is an iron hook whose ring turns round an iron pin fastened to the right side of the trolley, which hook is held by a sort of clavis, which is fixed in the right beam of the crane-arm.

At the end of the crane-post is a bronze pulley, the iron axle of which is fastened in the beams of the crane-arm, and over which the chain passes as it comes from the frame, and then, penetrating through the hollow in the top of the trolley, it reaches to the little bronze pulley of the trolley, and passing over this it hangs down. A hook on its end engages a ring, in which are fixed the top links of three chains, each six feet long, which pass through the three iron rings fastened in the holes of the claves which are fixed into the middle iron band of the dome, of which I have spoken.

Therefore when the master wishes to lift the dome by means of the crane, the assistant fits over the lower small iron axle an iron crank, which projects from the upright beam a palm and two digits; the end of the little axle is rectangular, and one and a half digits wide and one digit thick; it is set into a similar rectangular hole in the crank, which is two digits long and a little more than a digit wide. The crank is semi-circular, and one foot three palms and two digits long, as many digits wide, and one digit thick. Its handle is straight and round, and three palms long, and one and a half digits thick. There is a hole in the end of the little axle, through which an iron pin is driven so that the crank may not come off. The crane having four drums, two of which are rundle-drums and two toothed-wheels, is more easily moved than another having two drums, one of which has rundles and the other teeth.

Many, however, use only a simple contrivance, the pivots of whose crane-post turn in the same manner, the one in an iron socket, the other in a ring. There is a crane-arm on the crane-post, which is supported by an oblique beam; to the head of the crane-arm a strong iron ring is fixed, which engages a second iron ring. In this iron ring a strong wooden lever-bar is fastened firmly, the head of which is bound by a third iron ring, from which hangs an iron hook, which engages the rings at the ends of the chains from the dome. At the other end of the lever-bar is another chain, which, when it is pulled down, raises the opposite end of the bar and thus the dome; and when it is relaxed the dome is lowered.

In certain places, as at Freiberg in Meissen, the upper part of the cupellation furnace is vaulted almost like an oven. This chamber is four feet high and has either two or three apertures, of which the first, in front, is one and a half feet high and a foot wide, and out of this flows the litharge; the second aperture and likewise the third, if there be three, are at the sides, and are a foot and a half high and two and a half feet wide, in order that he who prepares the crucible may be able to creep into the furnace. Its circular bed is made of cement, it has two passages two feet high and one foot wide, for letting out the vapour, and these lead directly through from one side to the other, so that the one passage crosses the other at right angles, and thus four openings are to be seen; these are covered at the top by rocks, wide, but only a palm thick. On these and on the other parts of the interior of the bed made of cement, is placed lute mixed with straw, to a depth of three digits, as it was placed over the sole and the plates of copper and the rocks of that other furnace. This, together with the ashes which are thrown in, the master or the assistant, who, upon his knees, prepares the crucible, tamps down with short wooden rammers and with mallets likewise made of wood.

The cupellation furnace in Poland and Hungary is likewise vaulted at the top, and is almost similar to an oven, but in the lower part the bed is solid, and there is no opening for the vapours, while on one side of the crucible is a wall, between which and the bed of the crucible is a passage in place of the opening for vapours; this passage is covered by iron bars or rods extending from the wall to the crucible, and placed a distance of two digits from each other. In the crucible, when it is prepared, they first scatter straw, and then they lay in it cakes of silver-lead alloy, and on the iron bars they lay wood, which when kindled heats the crucible. They melt cakes to the weight of sometimes eighty centumpondia and sometimes a hundred centumpondia[39]. They stimulate a mild fire by means of a blast from the bellows, and throw on to the bars as much wood as is required to make a flame which will reach into the crucible, and separate the lead from the silver. The litharge is drawn out on the other side through an aperture that is just wide enough for the master to creep through into the crucible. The Moravians and Carni, who very rarely make more than a bes or five-sixths of a libra of silver, separate the lead from it, neither in a furnace resembling an oven, nor in the crucible covered by a dome, but on a crucible which is without a cover and exposed to the wind; on this crucible they lay cakes of silver-lead alloy, and over them they place dry wood, and over these again thick green wood. The wood having been kindled, they stimulate the fire by means of a bellows.

I have explained the method of separating lead from gold or silver. Now I will speak of the method of refining silver, for I have already explained the process for refining gold. Silver is refined in a refining furnace, over whose hearth is an arched chamber built of bricks; this chamber in the front part is three feet high. The hearth itself is five feet long and four wide. The walls are unbroken along the sides and back, but in front one chamber is placed over the other, and above these and the wall is the upright chimney. The hearth has a round pit, a cubit wide and two palms deep, into which are thrown sifted ashes, and in this is placed a prepared earthenware "test," in such a manner that it is surrounded on all sides by ashes to a height equal to its own. The earthenware test is filled with a powder consisting of equal portions of bones ground to powder, and of ashes taken from the crucible in which lead is separated from gold or silver; others mix crushed brick with the ashes, for by this method the powder attracts no silver to itself. When the powder has been made up and moistened with water, a little is thrown into the earthenware test and tamped with a wooden pestle. This pestle is round, a foot long, and a palm and a digit wide, out of which extend six teeth, each a digit thick, and a digit and a third long and wide, and almost a digit apart; these six teeth form a circle, and in the centre of them is the seventh tooth, which is round and of the same length as the others, but a digit and a half thick; this pestle tapers a little from the bottom up, that the upper part of the handle may be round and three digits thick. Some use a round pestle without teeth. Then a little powder is again moistened, and thrown into the test, and tamped; this work is repeated until the test is entirely full of the powder, which the master then cuts out with a knife, sharp on both sides, and turned upward at both ends so that the central part is a palm and a digit long; therefore it is partly straight and partly curved. The blade is one and a half digits wide, and at each end it turns upward two palms, which ends to the depth of a palm are either not sharpened or they are enclosed in wooden handles. The master holds the knife with one hand and cuts out the powder from the test, so that it is left three digits thick all round; then he sifts the powder of dried bones over it through a sieve, the bottom of which is made of closely-woven bristles. Afterward a ball made of very hard wood, six digits in diameter, is placed in the test and rolled about with both hands, in order to make the inside even and smooth; for that matter he may move the ball about with only one hand. The tests[40] are of various capacities, for some of them when prepared hold much less than fifteen librae of silver, others twenty, some thirty, others forty, and others fifty. All these tests thus prepared are dried in the sun, or set in a warm and covered place; the more dry and old they are the better. All of them, when used for refining silver, are heated by means of burning charcoal placed in them. Others use instead of these tests an iron ring; but the test is more useful, for if the powder deteriorates the silver remains in it, while there being no bottom to the ring, it falls out; besides, it is easier to place in the hearth the test than the iron ring, and furthermore it requires much less powder. In order that the test should not break and damage the silver, some bind it round with an iron band.

In order that they may be more easily broken, the silver cakes are placed upon an iron grate by the refiner, and are heated by burning charcoal placed under them. He has a brass block two palms and two digits long and wide, with a channel in the middle, which he places upon a block of hard wood. Then with a double-headed hammer, he beats the hot cakes of silver placed on the brass block, and breaks them in pieces. The head of this hammer is a foot and two digits long, and a palm wide. Others use for this purpose merely a block of wood channelled in the top. While the fragments of the cake are still hot, he seizes them with the tongs and throws them into a bowl with holes in the bottom, and pours water over them. When the fragments are cooled, he puts them nicely into the test by placing them so that they stand upright and project from the test to a height of two palms, and lest one should fall against the other, he places little pieces of charcoal between them; then he places live charcoal in the test, and soon two twig basketsful of charcoal. Then he blows in air with the bellows. This bellows is double, and four feet two palms long, and two feet and as many palms wide at the back; the other parts are similar to those described in Book VII. The nozzle of the bellows is placed in a bronze pipe a foot long, the aperture in this pipe being a digit in diameter in front and quite round, and at the back two palms wide. The master, because he needs for the operation of refining silver a fierce fire, and requires on that account a vigorous blast, places the bellows very much inclined, in order that, when the silver has melted, it may blow into the centre of the test. When the silver bubbles, he presses the nozzle down by means of a small block of wood moistened with water and fastened to an iron rod, the outer end of which bends upward. The silver melts when it has been heated in the test for about an hour; when it is melted, he removes the live coals from the test and places over it two billets of fir-wood, a foot and three palms long, a palm two digits wide, one palm thick at the upper part, and three digits at the lower. He joins them together at the lower edges, and into the billets he again throws the coals, for a fierce fire is always necessary in refining silver. It is refined in two or three hours, according to whether it was pure or impure, and if it is impure it is made purer by dropping granulated copper or lead into the test at the same time. In order that the refiner may sustain the great heat from the fire while the silver is being refined, he lets down an iron door, which is three feet long and a foot and three palms high; this door is held on both ends in iron plates, and when the operation is concluded, he raises it again with an iron shovel, so that its edge holds against the iron hook in the arch, and thus the door is held open. When the silver is nearly refined, which may be judged by the space of time, he dips into it an iron bar, three and a half feet long and a digit thick, having a round steel point. The small drops of silver that adhere to the bar he places on the brass block and flattens with a hammer, and from their colour he decides whether the silver is sufficiently refined or not. If it is thoroughly purified it is very white, and in a bes there is only a drachma of impurities. Some ladle up the silver with a hollow iron implement. Of each bes of silver one sicilicus is consumed, or occasionally when very impure, three drachmae or half an uncia[41].

The refiner governs the fire and stirs the molten silver with an iron implement, nine feet long, a digit thick, and at the end first curved toward the right, then curved back in order to form a circle, the interior of which is a palm in diameter; others use an iron implement, the end of which is bent directly upward. Another iron implement has the shape of tongs, with which, by compressing it with his hands, he seizes the coals and puts them on or takes them off; this is two feet long, one and a half digits wide, and the third of a digit thick.

When the silver is seen to be thoroughly refined, the artificer removes the coals from the test with a shovel. Soon afterward he draws water in a copper ladle, which has a wooden handle four feet long; it has a small hole at a point half-way between the middle of the bowl and the edge, through which a hemp seed just passes. He fills this ladle three times with water, and three times it all flows out through the hole on to the silver, and slowly quenches it; if he suddenly poured much water on it, it would burst asunder and injure those standing near. The artificer has a pointed iron bar, three feet long, which has a wooden handle as many feet long, and he puts the end of this bar into the test in order to stir it. He also stirs it with a hooked iron bar, of which the hook is two digits wide and a palm deep, and the iron part of its handle is three feet long and the wooden part the same. Then he removes the test from the hearth with a shovel or a fork, and turns it over, and by this means the silver falls to the ground in the shape of half a sphere; then lifting the cake with a shovel he throws it into a tub of water, where it gives out a great sound. Or else, having lifted the cake of silver with a fork, he lays it upon the iron implement similar to tongs, which are placed across a tub full of water; afterward, when cooled, he takes it from the tub again and lays it on the block made of hard wood and beats it with a hammer, in order to break off any of the powder from the test which adheres to it. The cake is then placed on the implement similar to tongs, laid over the tub full of water, and cleaned with a bundle of brass wire dipped into the water; this operation of beating and cleansing is repeated until it is all clean. Afterward he places it on an iron grate or tripod; the tripod is a palm and two digits high, one and a half digits wide, and its span is two palms wide; then he puts burning charcoal under the tripod or grate, in order again to dry the silver that was moistened by the water. Finally, the Royal Inspector[42] in the employment of the King or Prince, or the owner, lays the silver on a block of wood, and with an engraver's chisel he cuts out two small pieces, one from the under and the other from the upper side. These are tested by fire, in order to ascertain whether the silver is thoroughly refined or not, and at what price it should be sold to the merchants. Finally he impresses upon it the seal of the King or the Prince or the owner, and, near the same, the amount of the weight.

There are some who refine silver in tests placed under iron or earthenware muffles. They use a furnace, on the hearth of which they place the test containing the fragments of silver, and they place the muffle over it; the muffle has small windows at the sides, and in front a little bridge. In order to melt the silver, at the sides of the muffle are laid bricks, upon which the charcoal is placed, and burning firebrands are put on the bridge. The furnace has an iron door, which is covered on the side next to the fire with lute in order that it may not be injured. When the door is closed it retains the heat of the fire, but it has a small window, so that the artificers may look into the test and may at times stimulate the fire with the bellows. Although by this method silver is refined more slowly than by the other, nevertheless it is more useful, because less loss is caused, for a gentle fire consumes fewer particles than a fierce fire continually excited by the blast of the bellows. If, on account of its great size, the cake of silver can be carried only with difficulty when it is taken out of the muffle, they cut it up into two or three pieces while it is still hot, with a wedge or a hammer-chisel; for if they cut it up after it has cooled, little pieces of it frequently fly off and are lost.

END OF BOOK X.

FOOTNOTES:

[1] Vile a precioso.Return to passage

[2] The reagents mentioned in this Book are much the same as those of Book VII, where (p. 220) a table is given showing the Latin and Old German terms. Footnotes in explanation of our views as to these substances may be most easily consulted through the index.Return to passage

[3] Aqua valens, literally strong, potent, or powerful water. It will appear later, from the method of manufacture, that hydrochloric, nitric, and sulphuric acids and aqua regia were more or less all produced and all included in this term. We have, therefore, used either the term aqua valens or simply aqua as it occurs in the text. The terms aqua fortis and aqua regia had come into use prior to Agricola, but he does not use them; the Alchemists used various terms, often aqua dissolvia. It is apparent from the uses to which this reagent was put in separating gold and silver, from the method of clarifying it with silver and from the red fumes, that Agricola could have had practical contact only with nitric acid. It is probable that he has copied part of the recipes for the compounds to be distilled from the Alchemists and from such works as the Probierbuechlein. In any event he could not have had experience with them all, for in some cases the necessary ingredients for making nitric acid are not all present, and therefore could be of no use for gold and silver separation. The essential ingredients for the production of this acid by distillation, were saltpetre, water, and either vitriol or alum. The other substances mentioned were unnecessary, and any speculation as to the combinations which would result, forms a useful exercise in chemistry, but of little purpose here. The first recipe would no doubt produce hydrochloric acid.Return to passage

[4] Agricola, in the Interpretatio, gives the German equivalent for the Latin aerugo as Spanschgruen--"because it was first brought to Germany from Spain; foreigners call it viride aeris (copper green)." The English "verdigris" is a corruption of vert de grice. Both verdigris and white lead were very ancient products, and they naturally find mention together among the ancient authors. The earliest description of the method of making is from the 3rd Century B.C., by Theophrastus, who says (101-2): "But these are works of art, as is also Ceruse (psimythion) to make which, lead is placed in earthen vessels over sharp vinegar, and after it has acquired some thickness of a kind of rust, which it commonly does in about ten days, they open the vessels and scrape off, as it were, a kind of foulness; they then place the lead over the vinegar again, repeating over and over again the same method of scraping it till it is wholly dissolved; what has been scraped off they then beat to powder and boil for a long time; and what at last subsides to the bottom of the vessel is the white lead.... Also in a manner somewhat resembling this, verdigris (ios) is made, for copper is placed over lees of wine (grape refuse?), and the rust which it acquires by this means is taken off for use. And it is by this means that the rust which appears is produced." (Based on Hill's translation.) Vitruvius (VII, 12), Dioscorides (V, 51), and Pliny (XXXIV, 26 and 54), all describe the method of making somewhat more elaborately.Return to passage

[5] Amiantus (Interpretatio gives federwis, pliant, salamanderhar). From Agricola's elaborate description in De Natura Fossilium (p. 252) there can be no doubt that he means asbestos. This mineral was well-known to the Ancients, and is probably earliest referred to (3rd Century B.C.) by Theophrastus in the following passage (29): "There is also found in the mines of Scaptesylae a stone, in its external appearance somewhat resembling wood, on which, if oil be poured, it burns; but when the oil is burnt away, the burning of the stone ceases, as if it were in itself not liable to such accidents." There can be no doubt that Strabo (X, 1) describes the mineral: "At Carystus there is found in the earth a stone, which is combed like wool, and woven, so that napkins are made of this substance, which, when soiled, are thrown into the fire and cleaned, as in the washing of linen." It is also described by Dioscorides (V, 113) and Pliny (XIX, 4). Asbestos cloth has been found in Pre-Augustinian Roman tombs.Return to passage

[6] This list of four recipes is even more obscure than the previous list. If they were distilled, the first and second mixtures would not produce nitric acid, although possibly some sulphuric would result. The third might yield nitric, and the fourth aqua regia. In view of the water, they were certainly not used as cements, and the first and second are deficient in the vital ingredients.Return to passage

[7] Distillation, at least in crude form, is very old. Aristotle (Meteorologica, IV.) states that sweet water can be made by evaporating salt-water and condensing the steam. Dioscorides and Pliny both describe the production of mercury by distillation (note 58, p. 432). The Alchemists of the Alexandrian School, from the 1st to the 6th Centuries, mention forms of imperfect apparatus--an ample discussion of which may be found in Kopp, Beitraege zur Geschichte der Chemie, Braunschweig, 1869, p. 217.Return to passage

[8] It is desirable to note the contents of the residues in the retort, for it is our belief that these are the materials to which the author refers as "lees of the water which separates gold from silver," in many places in Book VII. They would be strange mixtures of sodium, potassium, aluminium sulphates, with silica, brickdust, asbestos, and various proportions of undigested vitriol, salt, saltpetre, alum, iron oxides, etc. Their effect must have been uncertain. Many old German metallurgies also refer to the Todenkopf der Scheidwasser, among them the Probierbuechlein before Agricola, and after him Lazarus Ercker (Beschreibung Allerfuernemsten, etc., Prague, 1574). See also note 16, p. 234.Return to passage

[9] This use of silver could apply to one purpose only, that is, the elimination of minor amounts of hydrochloric from the nitric acid, the former originating no doubt from the use of salt among the ingredients. The silver was thus converted into a chloride and precipitated. This use of a small amount of silver to purify the nitric acid was made by metallurgists down to fairly recent times. Biringuccio (IV, 2) and Lazarus Ercker (p. 71) both recommend that the silver be dissolved first in a small amount of acid, and the solution poured into the newly-manufactured supply. They both recommend preserving this precipitate and its cupellation after melting with lead--which Agricola apparently overlooked.Return to passage

[10] In this description of parting by nitric acid, the author digresses from his main theme on pages 444 and 445, to explain a method apparently for small quantities where the silver was precipitated by copper, and to describe another cryptic method of precipitation. These subjects are referred to in notes 11 and 12 below. The method of parting set out here falls into six stages: a--cupellation, b--granulation, c--solution in acid, d--treatment of the gold residues, e--evaporation of the solution, f--reduction of the silver nitrate. For nitric acid parting, bullion must be free from impurities, which cupellation would ensure; if copper were left in, it would have the effect he mentions if we understand "the silver separated from the gold soon unites with it again," to mean that the silver unites with the copper, for the copper would go into solution and come down with the silver on evaporation. Agricola does not specifically mention the necessity of an excess of silver in this description, although he does so elsewhere, and states that the ratio must be at least three parts silver to one part gold. The first description of the solution of the silver is clear enough, but that on p. 445 is somewhat difficult to follow, for the author states that the bullion is placed in a retort with the acid, and that distillation is carried on between each additional charge of acid. So far as the arrangement of a receiver might relate to the saving of any acid that came over accidentally in the boiling, it can be understood, but to distill off much acid would soon result in the crystallization of the silver nitrate, which would greatly impede the action of subsequent acid additions, and finally the gold could not be separated from such nitrate in the way described. The explanation may be (apart from incidental evaporation when heating) that the acids used were very weak, and that by the evaporation of a certain amount of water, not only was the acid concentrated, but room was provided for the further charges. The acid in the gold wash-water, mentioned in the following paragraph, was apparently thus concentrated. The "glass" mentioned as being melted with litharge, argols, nitre, etc., was no doubt the silver nitrate. The precipitation of the silver from the solution as a chloride, by the use of salt, so generally used during the 18th and 19th Centuries, was known in Agricola's time, although he does not mention it. It is mentioned in Geber and the Probierbuechlein. The clarity of the latter on the subject is of some interest (p. 34a): "How to pulverise silver and again make it into silver. Take the silver and dissolve it in water with the starckenwasser, aqua fort, and when that is done, take the silver water and pour it into warm salty water, and immediately the silver settles to the bottom and becomes powder. Let it stand awhile until it has well settled, then pour away the water from it and dry the settlings, which will become a powder like ashes. Afterward one can again make it into silver. Take the powder and put it on a test, and add thereto the powder from the settlings from which the aqua forte has been made, and add lead. Then if there is a great deal, blow on it until the lead has incorporated itself ... blow it until it plickt (blickens). Then you will have as much silver as before."Return to passage

[11] The silver is apparently precipitated by the copper of the bowl. It would seem that this method was in considerable use for small amounts of silver nitrate in the 16th Century. Lazarus Ercker gives elaborate directions for this method (Beschreibung Allerfuernemsten, etc., Prague, 1574, p. 77).Return to passage

[12] We confess to a lack of understanding of this operation with leaves of lead and copper.Return to passage

[13] We do not understand this "appearance of black." If the nitrate came into contact with organic matter it would, of course, turn black by reduction of the silver, and sunlight would have the same effect.Return to passage

[14] This would be equal to from 62 to 94 parts of copper in 1,000.Return to passage

[15] As 144 siliquae are 1 uncia, then 1/4 siliqua in 8 unciae would equal one part silver in 4,608 parts gold, or about 999.8 fine.Return to passage

[16] The object of this treatment with sulphur and copper is to separate a considerable portion of silver from low-grade bullion (i.e., silver containing some gold), in preparation for final treatment of the richer gold-silver alloy with nitric acid. Silver sulphide is created by adding sulphur, and is drawn off in a silver-copper regulus. After the first sentence, the author uses silver alone where he obviously means silver "containing some gold," and further he speaks of the "gold lump" (massula) where he likewise means a button containing a great deal of silver. For clarity we introduced the term "regulus" for the Latin mistura. The operation falls into six stages: a, granulation; b, sulphurization of the granulated bullion; c, melting to form a combination of the silver sulphide with copper into a regulus, an alloy of gold and silver settling out; d, repetition of the treatment to abstract further silver from the "lump;" e, refining the "lump" with nitric acid; f, recovery of the silver from the regulus by addition of lead, liquation and cupellation.Return to passage

The use of a "circle of fire" secures a low temperature that would neither volatilize the sulphur nor melt the bullion. The amount of sulphur given is equal to a ratio of 48 parts bullion and 9 parts sulphur. We are not certain about the translation of the paragraph in relation to the proportion of copper added to the granulated bullion; because in giving definite quantities of copper to be added in the contingencies of various original copper contents in the bullion, it would be expected that they were intended to produce some positive ratio of copper and silver. However, the ratio as we understand the text in various cases works out to irregular amounts, i.e., 48 parts of silver to 16, 12.6, 24, 20.5, 20.8, 17.8, or 18 parts of copper. In order to obtain complete separation there should be sufficient sulphur to have formed a sulphide of the copper as well as of the silver, or else some of the copper and silver would come down metallic with the "lump". The above ratio of copper added to the sulphurized silver, in the first instance would give about 18 parts of copper and 9 parts of sulphur to 48 parts of silver. The copper would require 4.5 parts of sulphur to convert it into sulphide, and the silver about 7 parts, or a total of 11.5 parts required against 9 parts furnished. It is plain, therefore, that insufficient sulphur is given. Further, the litharge would probably take up some sulphur and throw down metallic lead into the "lump". However, it is necessary that there should be some free metallics to collect the gold, and, therefore, the separation could not be complete in one operation. In any event, on the above ratios the "gold lump" from the first operation was pretty coppery, and contained some lead and probably a good deal of silver, because the copper would tend to desulphurize the latter. The "powder" of glass-galls, salt, and litharge would render the mass more liquid and assist the "gold lump" to separate out.

The Roman silver sesterce, worth about 2-1/8 pence or 4.2 American cents, was no doubt used by Agricola merely to indicate an infinitesimal quantity. The test to be applied to the regulus by way of cupellation and parting of a sample with nitric acid, requires no explanation. The truth of the description as to determining whether the gold had settled out, by using a chalked iron rod, can only be tested by actual experiment. It is probable, however, that the sulphur in the regulus would attack the iron and make it black. The re-melting of the regulus, if some gold remains in it, with copper and "powder" without more sulphur, would provide again free metallics to gather the remaining gold, and by desulphurizing some silver this button would probably not be very pure.

From the necessity for some free metallics besides the gold in the first treatment, it will be seen that a repetition of the sulphur addition and re-melting is essential gradually to enrich the "lump". Why more copper is added is not clear. In the second melting, the ratio is 48 parts of the "gold lump", 12 parts of sulphur and 12 parts copper. In this case the added copper would require about 3 parts sulphur, and if we consider the deficiency of sulphur in the first operations pertained entirely to the copper, then about 2.5 parts would be required to make good the shortage, or in other words the second addition of sulphur is sufficient. In the final parting of the "lump" it will be noticed that the author states that the silver ratio must be arranged as three of silver to one of gold. As to the recovery of the silver from the regulus, he states that 66 librae of silver give 132 librae of regulus. To this, 500 librae of lead are added, and it is melted in the "second" furnace, and the litharge and hearth-lead made are re-melted in the "first" furnace, the cakes made being again treated in the "third" furnace to separate the copper and lead. The "first" is usually the blast furnace, the "second" furnace is the cupellation furnace, and the "third" the liquation furnace. It is difficult to understand this procedure. The charge sent to the cupellation furnace would contain between 3% and 5% copper, and between 3% and 5% sulphur. However, possibly the sulphur and copper could be largely abstracted in the skimmings from the cupellation furnace, these being subsequently liquated in the "third" furnace. It may be noted that two whole lines from this paragraph are omitted in the editions of De Re Metallica after 1600. For historical note on sulphur separation see page 461.

[17] There can be no doubt that in most instances Agricola's stibium is antimony sulphide, but it does not follow that it was the mineral stibnite, nor have we considered it desirable to introduce the precision of either of these modern terms, and have therefore retained the Latin term where the sulphide is apparently intended. The use of antimony sulphide to part silver from gold is based upon the greater affinity of silver than antimony for sulphur. Thus the silver, as in the last process, is converted into a sulphide, and is absorbed in the regulus, while the metallic antimony alloys with the gold and settles to the bottom of the pot. This process has several advantages over the sulphurization with crude sulphur; antimony is a more convenient vehicle of sulphur, for it saves the preliminary sulphurization with its attendant difficulties of volatilization of the sulphur; it also saves the granulation necessary in the former method; and the treatment of the subsequent products is simpler. However, it is possible that the sulphur-copper process was better adapted to bullion where the proportion of gold was low, because the fineness of the bullion mentioned in connection with the antimonial process was apparently much higher than the previous process. For instance, a bes of gold, containing 5, 6, or 7 double sextulae of silver would be .792, .750 or .708 fine. The antimonial method would have an advantage over nitric acid separation, in that high-grade bullion could be treated direct without artificial decrease of fineness required by inquartation to about .250 fine, with the consequent incidental losses of silver involved.Return to passage

The process in this description falls into six operations: a, sulphurization of the silver by melting with antimony sulphide; b, separation of the gold "lump" (massula) by jogging; c, re-melting the regulus (mistura) three or four times for recovery of further "lumps"; d, re-melting of the "lump" four times, with further additions of antimony sulphide; e, cupellation of the regulus to recover the silver; f, cupellation of the antimony from the "lump" to recover the gold. Percy seems to think it difficult to understand the insistence upon the addition of copper. Biringuccio (IV, 6) states, among other things, that copper makes the ingredients more liquid. The later metallurgists, however, such as Ercker, Lohneys, and Schlueter, do not mention this addition; they do mention the "swelling and frothing," and recommend that the crucible should be only partly filled. As to the copper, we suggest that it would desulphurize part of the antimony and thus free some of that metal to collect the gold. If we assume bullion of the medium fineness mentioned and containing no copper, then the proportions in the first charge would be about 36 parts gold, 12 parts silver, 41 parts sulphur, 103 parts antimony, and 9 parts copper. The silver and copper would take up 4.25 parts of sulphur, and thus free about 10.6 parts of antimony as metallics. It would thus appear that the amount of metallics provided to assist the collection of the gold was little enough, and that the copper in freeing 5.6 parts of the antimony was useful. It appears to have been necessary to have a large excess of antimony sulphide; for even with the great surplus in the first charge, the reaction was only partial, as is indicated by the necessity for repeated melting with further antimony.

The later metallurgists all describe the separation of the metallic antimony from the gold as being carried out by oxidation of the antimony, induced by a jet of air into the crucible, this being continued until the mass appears limpid and no cloud forms in the surface in cooling. Agricola describes the separation of the silver from the regulus by preliminary melting with argols, glass-gall, and some lead, and subsequent cupellation of the lead-silver alloy. The statement that unless this preliminary melting is done, the cupel will absorb silver, might be consonant with an attempt at cupellation of sulphides, and it is difficult to see that much desulphurizing could take place with the above fluxes. In fact, in the later descriptions of the process, iron is used in this melting, and we are under the impression that Agricola had omitted this item for a desulphurizing reagent. At the Dresden Mint, in the methods described by Percy (Metallurgy Silver and Gold, p. 373) the gold lumps were tested for fineness, and from this the amount of gold retained in the regulus was computed. It is not clear from Agricola's account whether the test with nitric acid was applied to the regulus or to the "lumps". For historical notes see p. 461.

[18] As will be shown in the historical note, this process of separating gold and silver is of great antiquity--in all probability the only process known prior to the Middle Ages, and in any event, the first one used. In general the process was performed by "cementing" the disintegrated bullion with a paste and subjecting the mass to long-continued heat at a temperature under the melting point of the bullion. The cement (compositio) is of two different species; in the first species saltpetre and vitriol and some aluminous or silicious medium are the essential ingredients, and through them the silver is converted into nitrate and absorbed by the mass; in the second species, common salt and the same sort of medium are the essentials, and in this case the silver is converted into a chloride. Agricola does not distinguish between these two species, for, as shown by the text, his ingredients are badly mixed.Return to passage

The process as here described falls into five operations: a, granulation of the bullion or preparation of leaves; b, heating alternate layers of cement and bullion in pots; c, washing the gold to free it of cement; d, melting the gold with borax or soda; e, treatment of the cement by way of melting with lead and cupellation to recover the silver. Investigation by Boussingault (Ann. De Chimie, 1833, p. 253-6), D'Elhuyar (Bergbaukunde, Leipzig, 1790, Vol. II, p. 200), and Percy (Metallurgy of Silver and Gold, p. 395), of the action of common salt upon silver under cementation conditions, fairly well demonstrated the reactions involved in the use of this species of cement. Certain factors are essential besides salt: a, the admission of air, which is possible through the porous pots used; b, the presence of some moisture to furnish hydrogen; c, the addition of alumina or silica. The first would be provided by Agricola in the use of new pots, the second possibly by use of wood fuel in a closed furnace, the third by the inclusion of brickdust. The alumina or silica at high temperatures decomposes the salt, setting free hydrochloric acid and probably also free chlorine. The result of the addition of vitriol in Agricola's ingredients is not discussed by those investigators, but inasmuch as vitriol decomposes into sulphuric acid under high temperatures, this acid would react upon the salt to free hydrochloric acid, and thus assist to overcome deficiencies in the other factors. It is possible also that sulphuric acid under such conditions would react directly upon the silver to form silver sulphates, which would be absorbed into the cement. As nitric acid is formed by vitriol and saltpetre at high temperatures, the use of these two substances as a cementing compound would produce nitric acid, which would at once attack the silver to form silver nitrate, which would be absorbed into the melted cement. In this case the brickdust probably acted merely as a vehicle for the absorption, and to lower the melting point of the mass and prevent fusion of the metal. While nitric acid will only part gold and silver when the latter is in great excess, yet when applied as fumes under cementation conditions it appears to react upon a minor ratio of silver. While the reactions of the two above species of compounds can be accounted for in a general way, the problem furnished by Agricola's statements is by no means simple, for only two of his compounds are simply salt cements, the others being salt and nitre mixtures. An inspection of these compounds produces at once a sense of confusion. Salt is present in every compound, saltpetre in all but two, vitriol in all but three. Lewis (Traite Singulier de Metallique, Paris, 1743, II, pp. 48-60), in discussing these processes, states that salt and saltpetre must never be used together, as he asserts that in this case aqua regia would be formed and the gold dissolved. Agricola, however, apparently found no such difficulty. As to the other ingredients, apart from nitre, salt, vitriol, and brickdust, they can have been of no use. Agricola himself points out that ingredients of "metallic origin" corrupt the gold and that brickdust and common salt are sufficient. In a description of this process in the Probierbuechlein (p. 58), no nitre is mentioned. This booklet does mention the recovery of the silver from the cement by amalgamation with mercury--the earliest mention of silver amalgamation.

[19] While a substance which we now know to be natural zinc sulphate was known to Agricola (see note 11, p. 572), it is hardly possible that it is referred to here. If green vitriol be dehydrated and powdered, it is white.Return to passage

[20] The processes involved by these "other" compounds are difficult to understand, because of the lack of information given as to the method of operation. It might be thought that these were five additional recipes for cementing pastes, but an inspection of their internal composition soon dissipates any such assumption, because, apart from the lack of brickdust or some other similar necessary ingredient, they all contain more or less sulphur. After describing a preliminary treatment of the bullion by cupellation, the author says: "Then the silver is sprinkled with two unciae of that powdered compound and is stirred. Afterward it is poured into another crucible ... and violently shaken. The rest is performed according to the process I have already explained." As he has already explained four or five parting processes, it is not very clear to which one this refers. In fact, the whole of this discussion reads as if he were reporting hearsay, for it lacks in every respect the infinite detail of his usual descriptions. In any event, if the powder was introduced into the molten bullion, the effect would be to form some silver sulphides in a regulus of different composition depending upon the varied ingredients of different compounds. The enriched bullion was settled out in a "lump" and treated "as I have explained," which is not clear.Return to passage

[21] HISTORICAL NOTE ON PARTING GOLD AND SILVER. Although the earlier Classics contain innumerable references to refining gold and silver, there is little that is tangible in them, upon which to hinge the metallurgy of parting the precious metals. It appears to us, however, that some ability to part the metals is implied in the use of the touchstone, for we fail to see what use a knowledge of the ratio of gold and silver in bullion could have been without the power to separate them. The touchstone was known to the Greeks at least as early as the 5th Century B.C. (see note 37, p. 252), and a part of Theophrastus' statement (LXXVIII.) on this subject bears repetition in this connection: "The nature of the stone which tries gold is also very wonderful, as it seems to have the same power as fire; which is also a test of that metal.... The trial by fire is by the colour and the quantity lost by it, but that of the stone is made only by rubbing," etc. This trial by fire certainly implies a parting of the metals. It has been argued from the common use of electrum--a gold-silver alloy--by the Ancients, that they did not know how to part the two metals or they would not have wasted gold in such a manner, but it seems to us that the very fact that electrum was a positive alloy (20% gold, 80% silver), and that it was deliberately made (Pliny XXXIII, 23) and held of value for its supposed superior brilliancy to silver and the belief that goblets made of it detected poison, is sufficient answer to this.Return to passage

To arrive by a process of elimination, we may say that in the Middle Ages, between 1100 and 1500 A.D., there were known four methods of parting these metals: a, parting by solution in nitric acid; b, sulphurization of the silver in finely-divided bullion by heating it with sulphur, and the subsequent removal of the silver sulphide in a regulus by melting with copper, iron, or lead; c, melting with an excess of antimony sulphide, and the direct conversion of the silver to sulphide and its removal in a regulus; d, cementation of the finely-divided bullion with salt, and certain necessary collateral re-agents, and the separation of the silver by absorption into the cement as silver chloride. Inasmuch as it can be clearly established that mineral acids were unknown to the Ancients, we can eliminate that method. Further, we may say at once that there is not, so far as has yet been found, even a remote statement that could be applied to the sulphide processes. As to cementation with salt, however, we have some data at about the beginning of the Christian Era.

Before entering into a more detailed discussion of the history of various processes, it may be useful, in a word, to fix in the mind of the reader our view of the first authority on various processes, and his period.

(1) Separation by cementation with salt, Strabo (?) 63 B.C.-24 A.D.; Pliny 23-79 A.D.

(2) Separation by sulphur, Theophilus, 1150-1200 A.D.

(3) Separation by nitric acid, Geber, prior to 14th Century.

(4) Separation by antimony sulphide, Basil Valentine, end 14th Century, or Probierbuechlein, beginning 15th Century.

(5) Separation by antimony sulphide and copper, or sulphur and copper, Probierbuechlein, beginning 15th Century.

(6) Separation by cementation with saltpetre, Agricola, 1556.

(7) Separation by sulphur and iron, Schlueter, 1738.

(8) Separation by sulphuric acid, D'Arcet, 1802.

(9) Separation by chloride gas, Thompson, 1833.

(10) Separation electrolytically, latter part 19th Century.

PARTING BY CEMENTATION. The following passage from Strabo is of prime interest as the first definite statement on parting of any kind (III, 2, 8): "That when they have melted the gold and purified it by means of a kind of aluminous earth, the residue left is electrum. This, which contains a mixture of silver and gold, being again subjected to the fire, the silver is separated and the gold left (pure); for this metal is easily dissipated and fat, and on this account gold is most easily molten by straw, the flame of which is soft, and bearing a similarity (to the gold) causes it easily to dissolve, whereas coal, besides wasting a great deal, melts it too much, by reason of its vehemence, and carries it off (in vapour)." This statement has provoked the liveliest discussion, not only on account of the metallurgical interest and obscurity, but also because of differences of view as to its translation; we have given that of Mr. H. C. Hamilton (London, 1903). A review of this discussion will be found in Percy's Metallurgy of Gold and Silver, p. 399. That it refers to cementation at all hangs by a slender thread, but it seems more nearly this than anything else.

Pliny (XXXIII, 25) is a little more ample: "(The gold) is heated with double its weight of salt and thrice its weight of misy, and again with two portions of salt and one of a stone which they call schistos. The virus is drawn out when these things are burnt together in an earthen crucible, itself remaining pure and incorrupt, the remaining ash being preserved in an earthen pot and mixed with water as a lotion for lichen (ring-worm) on the face." Percy (Metallurgy Silver and Gold, p. 398) rightly considers that this undoubtedly refers to the parting of silver and gold by cementation with common salt. Especially as Pliny further on states that with regard to misy, "In purifying gold they mix it with this substance." There can be no doubt from the explanations of Pliny and Dioscorides that misy was an oxidized pyrite, mostly iron sulphate. Assuming the latter case, then all of the necessary elements of cementation, i.e., vitriol, salt, and an aluminous or silicious element, are present.

The first entirely satisfactory evidence on parting is to be found in Theophilus (12th Century), and we quote the following from Hendrie's translation (p. 245): "Of Heating the Gold. Take gold, of whatsoever sort it may be, and beat it until thin leaves are made in breadth three fingers, and as long as you can. Then cut out pieces that are equally long and wide and join them together equally, and perforate through all with a fine cutting iron. Afterwards take two earthen pots proved in the fire, of such size that the gold can lie flat in them, and break a tile very small, or clay of the furnace burned and red, weigh it, powdered, into two equal parts, and add to it a third part salt for the same weight; which things being slightly sprinkled with urine, are mixed together so that they may not adhere together, but are scarcely wetted, and put a little of it upon a pot about the breadth of the gold, then a piece of the gold itself, and again the composition, and again the gold, which in the digestion is thus always covered, that gold may not be in contact with gold; and thus fill the pot to the top and cover it above with another pot, which you carefully lute round with clay, mixed and beaten, and you place it over the fire, that it may be dried. In the meantime compose a furnace from stones and clay, two feet in height, and a foot and a half in breadth, wide at the bottom, but narrow at the top, where there is an opening in the middle, in which project three long and hard stones, which may be able to sustain the flame for a long time, upon which you place the pots with the gold, and cover them with other tiles in abundance. Then supply fire and wood, and take care that a copious fire is not wanting for the space of a day and night. In the morning taking out the gold, again melt, beat and place it in the furnace as before. Again also, after a day and night, take it away and mixing a little copper with it, melt it as before, and replace it upon the furnace. And when you have taken it away a third time, wash and dry it carefully, and so weighing it, see how much is wanting, then fold it up and keep it."

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 quantity, 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 space 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 assertion, 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 manuscripts 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 passage 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 Asse, 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 Probierbuechlein. 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 (starkwasser). 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 glass 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 scraped the gold from silver, place this scraping 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 quantity of the scraping, 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 Probierbuechlein 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 Probierbuechlein. The date to be assigned 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 Probierbuechlein 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 Probierbuechlein 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 spiesglass, 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 button. 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 button may settle better, let it cool, then turn the mould over, strike off the button and twice as much spiesglas as the button weighs, put them in a crucible, blow on it till it melts, then pour it again into a mould and break away the button as at first. If you want the gold to be good always add to the button twice as much spiesglass. It is usually good gold in three meltings. Afterward take the button, 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, Schlueter (Huette-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 Huettenkunde, Goettingen, 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 principal 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.Return to passage

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

[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 quantities. In a general way the auriferous button 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 Probierbuechlein, some editions of which, as mentioned before, were possibly fifty years before De Re Metallica. This knowledge, no doubt, accumulated 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.Return to passage

[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 Probierbuechlein identical with this, and it was probably Agricola's source of information.Return to passage

[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 Schlueter (Huette-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 scum--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 scum arises--the abstrich. This material contains most of the antimony and arsenical 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:--Return to passage

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 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 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.

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

[28] The Roman sextarius was about a pint.Return to passage

[29] This sentence continues, Ipsa vero media pars praeterea digito, to which we are unable to attribute any meaning.Return to passage

[30] Thus, or tus--"incense."Return to passage

[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.Return to passage

[32] See description, p. 269.Return to passage

[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 plumbum 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 passages from Pliny, upon which he bases his use, are (XXXIV, 47): "The metal which flows liquid at the first melting in the furnace is called stannum, the second melting is silver," etc. (XXXIV, 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 passage 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 documents relating to Cornish tin mining, beginning with the report of William de Wrotham in 1198.Return to passage

[34] The Latin term for litharge is spuma argenti, spume of silver.Return to passage

[35] Pliny, XXXIII, 35. This quotation is given in full in the footnote p. 466. Agricola illustrates these "tubes" of litharge on p. 481.Return to passage

[36] Assuming 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.Return to passage

[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 (XXXIII, 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." (XXXIV, 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 passages it would seem that molybdaena, a variety of litharge, might quite well be hearth-lead. Further (in XXXIV, 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 passage becomes clear enough, the second melting being cupellation. The difficulty with Pliny, however, arises from the passage (XXXIII, 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.Return to passage

[38] Agricola here refers to the German word used in this connection, i.e., hundt, a dog.Return to passage

[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.Return to passage

[40] The refining of silver in "tests" (Latin testa) is merely a second cupellation, with greater care and under stronger blast. Stirring the mass 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.Return to passage

[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.Return to passage

[42] Praefectus Regis.Return to passage