Chapter XXXIX: Book XII (2)

The sulphurous mixture, whether it consists of stone and sulphur only, or of stone and sulphur and metal, may be heated in similar pots, but with perforated bottoms. Before the furnace is constructed, against the "second" wall of the works two lateral partitions are built seven feet high, three feet long, one and a half feet thick, and these are distant from each other twenty-seven feet. Between them are seven low brick walls, that measure but two feet and the same number of digits in height, and, like the other walls, are three feet long and one foot thick; these little walls are at equal distances from one another, consequently they will be two and one half feet apart. At the top, iron bars are fixed into them, which sustain iron plates three feet long and wide and one digit thick, so that they can bear not only the weight of the pots, but also the fierceness of the fire. These plates have in the middle a round hole one and a half digits wide; there must not be more than eight of these, and upon them as many pots are placed. These pots are perforated at the bottom, and the same number of whole pots are placed underneath them; the former contain the mixture, and are covered with lids; the latter contain water, and their mouths are under the holes in the plates. After wood has been arranged round the upper pots and ignited, the mixture being heated, red, yellow, or green sulphur drips from it and flows down through the hole, and is caught by the pots placed underneath the plates, and is at once cooled by the water. If the mixture contains metal, it is reserved for smelting, and, if not, it is thrown away. The sulphur from such a mixture can best be extracted if the upper pots are placed in a vaulted furnace, like those which I described among other metallurgical subjects in Book VIII., which has no floor, but a grate inside; under this the lower pots are placed in the same manner, but the plates must have larger holes.

Others bury a pot in the ground, and place over it another pot with a hole at the bottom, in which pyrites or _cadmia_, or other sulphurous stones are so enclosed that the sulphur cannot exhale. A fierce fire heats the sulphur, and it drips away and flows down into the lower pot, which contains water. (Illustration p. 582).

Bitumen[14] is made from bituminous waters, from liquid bitumen, and from mixtures of bituminous substances. The water, bituminous as well as salty, at Babylon, as Pliny writes, was taken from the wells to the salt works and heated by the great heat of the sun, and condensed partly into liquid bitumen and partly into salt. The bitumen being lighter, floats on the top, while the salt being heavier, sinks to the bottom. Liquid bitumen, if there is much floating on springs, streams and rivers, is drawn up in buckets or other vessels; but, if there is little, it is collected with goose wings, pieces of linen, _ralla_, shreds of reeds, and other things to which it easily adheres, and it is boiled in large brass or iron pots by fire and condensed. As this bitumen is put to divers uses, some mix pitch with the liquid, others old cart-grease, in order to temper its viscosity; these, however long they are boiled in the pots, cannot be made hard. The mixtures containing bitumen are also treated in the same manner as those containing sulphur, in pots having a hole in the bottom, and it is rare that such bitumen is not highly esteemed.

Since all solidified juices and earths, if abundantly and copiously mixed with the water, are deposited in the beds of springs, streams or rivers, and the stones therein are coated by them, they do not require the heat of the sun or fire to harden them. This having been pondered over by wise men, they discovered methods by which the remainder of these solidified juices and unusual earths can be collected. Such waters, whether flowing from springs or tunnels, are collected in many wooden tubs or tanks arranged in consecutive order, and deposit in them such juices or earths; these being scraped off every year, are collected, as _chrysocolla_[15] in the Carpathians and as ochre in the Harz.

There remains glass, the preparation of which belongs here, for the reason that it is obtained by the power of fire and subtle art from certain solidified juices and from coarse or fine sand. It is transparent, as are certain solidified juices, gems, and stones; and can be melted like fusible stones and metals. First I must speak of the materials from which glass is made; then of the furnaces in which it is melted; then of the methods by which it is produced.

It is made from fusible stones and from solidified juices, or from other juicy substances which are connected by a natural relationship. Stones which are fusible, if they are white and translucent, are more excellent than the others, for which reason crystals take the first place. From these, when pounded, the most excellent transparent glass was made in India, with which no other could be compared, as Pliny relates. The second place is accorded to stones which, although not so hard as crystal, are yet just as white and transparent. The third is given to white stones, which are not transparent. It is necessary, however, first of all to heat all these, and afterward they are subjected to the pestle in order to break and crush them into coarse sand, and then they are passed through a sieve. If this kind of coarse or fine sand is found by the glass-makers near the mouth of a river, it saves them much labour in burning and crushing. As regards the solidified juices, the first place is given to soda; the second to white and translucent rock-salt; the third to salts which are made from lye, from the ashes of the musk ivy, or from other salty herbs. Yet there are some who give to this latter, and not to the former, the second place. One part of coarse or fine sand made from fusible stones should be mixed with two parts of soda or of rock-salt or of herb salts, to which are added minute particles of _magnes_.[16] It is true that in our day, as much as in ancient times, there exists the belief in the singular power of the latter to attract to itself the vitreous liquid just as it does iron, and by attracting it to purify and transform green or yellow into white; and afterward fire consumes the _magnes_. When the said juices are not to be had, two parts of the ashes of oak or holmoak, or of hard oak or Turkey oak, or if these be not available, of beech or pine, are mixed with one part of coarse or fine sand, and a small quantity of salt is added, made from salt water or sea-water, and a small particle of _magnes_; but these make a less white and translucent glass. The ashes should be made from old trees, of which the trunk at a height of six feet is hollowed out and fire is put in, and thus the whole tree is consumed and converted into ashes. This is done in winter when the snow lies long, or in summer when it does not rain, for the showers at other times of the year, by mixing the ashes with earth, render them impure; for this reason, at such times, these same trees are cut up into many pieces and burned under cover, and are thus converted into ashes.

Some glass-makers use three furnaces, others two, others only one. Those who use three, melt the material in the first, re-melt it in the second, and in the third they cool the glowing glass vessels and other articles. Of these the first furnace must be vaulted and similar to an oven. In the upper chamber, which is six feet long, four feet wide, and two feet high, the mixed materials are heated by a fierce fire of dry wood until they melt and are converted into a vitreous mass. And if they are not satisfactorily purified from dross, they are taken out and cooled and broken into pieces; and the vitreous pieces are heated in pots in the same furnace.

The second furnace is round, ten feet in diameter and eight feet high, and on the outside, so that it may be stronger, it is encompassed by five arches, one and one half feet thick; it consists in like manner of two chambers, of which the lower one is vaulted and is one and one half feet thick. In front this chamber has a narrow mouth, through which the wood can be put into the hearth, which is on the ground. At the top and in the middle of its vault, there is a large round hole which opens to the upper chamber, so that the flames can penetrate into it. Between the arches in the walls of the upper chamber are eight windows, so large that the big-bellied pots may be placed through them on to the floor of the chamber, around the large hole. The thickness of these pots is about two digits, their height the same number of feet, and the diameter of the belly one and a half feet, and of the mouth and bottom one foot. In the back part of the furnace is a rectangular hole, measuring in height and width a palm, through which the heat penetrates into a third furnace which adjoins it.

This third furnace is rectangular, eight feet long and six feet wide; it also consists of two chambers, of which the lower has a mouth in front, so that firewood may be placed on the hearth which is on the ground. On each side of this opening in the wall of the lower chamber is a recess for oblong earthenware receptacles, which are about four feet long, two feet high, and one and a half feet wide. The upper chamber has two holes, one on the right side, the other on the left, of such height and width that earthenware receptacles may be conveniently placed in them. These latter receptacles are three feet long, one and a half feet high, the lower part one foot wide, and the upper part rounded. In these receptacles the glass articles, which have been blown, are placed so that they may cool in a milder temperature; if they were not cooled slowly they would burst asunder. When the vessels are taken from the upper chamber, they are immediately placed in the receptacles to cool.

Some who use two furnaces partly melt the mixture in the first, and not only re-melt it in the second, but also replace the glass articles there. Others partly melt and re-melt the material in different chambers of the second furnace. Thus the former lack the third furnace, and the latter, the first. But this kind of second furnace differs from the other second furnace, for it is, indeed, round, but the interior is eight feet in diameter and twelve feet high, and it consists of three chambers, of which the lowest is not unlike the lowest of the other second furnace. In the middle chamber wall there are six arched openings, in which are placed the pots to be heated, and the remainder of the small windows are blocked up with lute. In the middle top of the middle chamber is a square opening a palm in length and width. Through this the heat penetrates into the upper chamber, of which the rear part has an opening to receive the oblong earthenware receptacles, in which are placed the glass articles to be slowly cooled. On this side, the ground of the workshop is higher, or else a bench is placed there, so that the glass-makers may stand upon it to stow away their products more conveniently.

Those who lack the first furnace in the evening, when they have accomplished their day's work, place the material in the pots, so that the heat during the night may melt it and turn it into glass. Two boys alternately, during night and day, keep up the fire by throwing dry wood on to the hearth. Those who have but one furnace use the second sort, made with three chambers. Then in the evening they pour the material into the pots, and in the morning, having extracted the fused material, they make the glass objects, which they place in the upper chamber, as do the others.

The second furnace consists either of two or three chambers, the first of which is made of unburnt bricks dried in the sun. These bricks are made of a kind of clay that cannot be easily melted by fire nor resolved into powder; this clay is cleaned of small stones and beaten with rods. The bricks are laid with the same kind of clay instead of lime. From the same clay the potters also make their vessels and pots, which they dry in the shade. These two parts having been completed, there remains the third.

The vitreous mass having been made in the first furnace in the manner I described, is broken up, and the assistant heats the second furnace, in order that the fragments may be re-melted. In the meantime, while they are doing this, the pots are first warmed by a slow fire in the first furnace, so that the vapours may evaporate, and then by a fiercer fire, so that they become red in drying. Afterward the glass-makers open the mouth of the furnace, and, seizing the pots with tongs, if they have not cracked and fallen to pieces, quickly place them in the second furnace, and they fill them up with the fragments of the heated vitreous mass or with glass. Afterward they close up all the windows with lute and bricks, with the exception that in each there are two little windows left free; through one of these they inspect the glass contained in the pot, and take it up by means of a blow-pipe; in the other they rest another blow-pipe, so that it may get warm. Whether it is made of brass, bronze, or iron, the blow-pipe must be three feet long. In front of the window is inserted a lip of marble, on which rests the heaped-up clay and the iron shield. The clay holds the blow-pipe when it is put into the furnace, whereas the shield preserves the eyes of the glass-maker from the fire. All this having been carried out in order, the glass-makers bring the work to completion. The broken pieces they re-melt with dry wood, which emits no smoke, but only a flame. The longer they re-melt it, the purer and more transparent it becomes, the fewer spots and blisters there are, and therefore the glass-makers can carry out their work more easily. For this reason those who only melt the material from which glass is made for one night, and then immediately make it up into glass articles, make them less pure and transparent than those who first produce a vitreous mass and then re-melt the broken pieces again for a day and a night. And, again, these make a less pure and transparent glass than do those who melt it again for two days and two nights, for the excellence of the glass does not consist solely in the material from which it is made, but also in the melting. The glass-makers often test the glass by drawing it up with the blowpipes; as soon as they observe that the fragments have been re-melted and purified satisfactorily, each of them with another blow-pipe which is in the pot, slowly stirs and takes up the glass which sticks to it in the shape of a ball like a glutinous, coagulated gum. He takes up just as much as he needs to complete the article he wishes to make; then he presses it against the lip of marble and kneads it round and round until it consolidates. When he blows through the pipe he blows as he would if inflating a bubble; he blows into the blow-pipe as often as it is necessary, removing it from his mouth to re-fill his cheeks, so that his breath does not draw the flames into his mouth. Then, twisting the lifted blow-pipe round his head in a circle, he makes a long glass, or moulds the same in a hollow copper mould, turning it round and round, then warming it again, blowing it and pressing it, he widens it into the shape of a cup or vessel, or of any other object he has in mind. Then he again presses this against the marble to flatten the bottom, which he moulds in the interior with his other blow-pipe. Afterward he cuts out the lip with shears, and, if necessary, adds feet and handles. If it so please him, he gilds it and paints it with various colours. Finally, he lays it in the oblong earthenware receptacle, which is placed in the third furnace, or in the upper chamber of the second furnace, that it may cool. When this receptacle is full of other slowly-cooled articles, he passes a wide iron bar under it, and, carrying it on the left arm, places it in another recess.

The glass-makers make divers things, such as goblets, cups, ewers, flasks, dishes, plates, panes of glass, animals, trees, and ships, all of which excellent and wonderful works I have seen when I spent two whole years in Venice some time ago. Especially at the time of the Feast of the Ascension they were on sale at Morano, where are located the most celebrated glass-works. These I saw on other occasions, and when, for a certain reason, I visited Andrea Naugerio in his house which he had there, and conversed with him and Francisco Asulano.

END OF BOOK XII.

FOOTNOTES:

[1] The history of salt-making in salt-pans, from sea-water or salt springs, goes further back than human records. From an historical point of view the real interest attached to salt lies in the bearing which localities rich in either natural salt or salt springs, have had upon the movements of the human race. Many ancient trade routes have been due to them, and innumerable battles have been fought for their possession. Salt has at times served for currency, and during many centuries in nearly every country has served as a basis of taxation. These subjects do not, however, come within the scope of this text. For the quotation from Pliny referred to, see Note 14 below, on bitumen.

[2] The first edition gives _graviorem_, the latter editions _gratiorem_, which latter would have quite the reverse meaning from the above.

[3] The following are approximately the English equivalents:--

Pints. Quarts. Gallons.
1 _Cyathus_ .08
3 _Cyathi_ = 1 _Quartarius_ .24
4 _Quartarii_ = 1 _Sextarius_ .99
6 _Sextarii_ = 1 _Congius_ 5.94 2.97
16 _Sextarii_ = 1 _Modius_ 15.85 7.93 1.98
8 _Congii_ = 1 _Amphora_ 47.57 23.78 5.94

The dipper mentioned would thus hold about one and one quarter gallons, and the cask ten gallons.

[4] The salt industry, founded upon salt springs, is still of importance to this city. It was a salt centre of importance to the Germanic tribes before Charles, the son of Charlemagne, erected a fortress here in 806. Mention of the salt works is made in the charter by Otto I., conveying the place to the Diocese of Magdeburg, in 968.

[5] Pliny XXXI., 39-40. "In the Gallic provinces in Germany they pour salt water upon burning wood. The Spaniards in a certain place draw the brine from wells, which they call _Muria_. They indeed think that the wood turns to salt, and that the oak is the best, being the kind which is itself salty. Elsewhere the hazel is praised. Thus the charcoal even is turned into salt when it is steeped in brine. Whenever salt is made with wood it is black."

[6] We have elsewhere in this book used the word "soda" for the Latin term _nitrum_, because we believe as used by Agricola it was always soda, and because some confusion of this term with its modern adaptation for saltpetre (nitre) might arise in the mind of the reader. Fortunately, Agricola usually carefully mentions other alkalis, such as the product from lixiviation of ashes, separately from his _nitrum_. In these paragraphs, however, he has soda and potash hopelessly mixed, wherefore we have here introduced the Latin term. The actual difference between potash and soda--the _nitrum_ of the Ancients, and the _alkali_ of Geber (and the glossary of Agricola), was not understood for two hundred years after Agricola, when Duhamel made his well-known determinations; and the isolation of sodium and potassium was, of course, still later by fifty years. If the reeds and rushes described in this paragraph grew near the sea, the salt from lixiviation would be soda, and likewise the Egyptian product was soda, but the lixiviation of wood-ash produces only potash; as seen above, all are termed _nitrum_ except the first.

HISTORICAL NOTES.--The word _nitrum_, _nitron_, _nitri_, _neter_, _nether_, or similar forms, occurs in innumerable ancient writings. Among such references are Jeremiah (II., 22) Proverbs (XXV., 20), Herodotus (II., 86, 87), Aristotle (_Prob._ I., 39, _De Mirab._ 54), Theophrastus (_De Igne_ 435 ed. Heinsii, Hist. Plants III., 9), Dioscorides (V., 89), Pliny (XIV., 26, and XXXI., 46). A review of disputations on what salts this term comprised among the Ancients would itself fill a volume, but from the properties named it was no doubt mostly soda, more rarely potash, and sometimes both mixed with common salt. There is every reason to believe from the properties and uses mentioned, that it did not generally comprise nitre (saltpetre)--into which superficial error the nomenclature has led many translators. The preparation by way of burning, and the use of _nitrum_ for purposes for which we now use soap, for making glass, for medicines, cosmetics, salves, painting, in baking powder, for preserving food, embalming, etc., and the descriptions of its taste in "nitrous" waters,--all answer for soda and potash, but not for saltpetre. It is possible that the common occurrence of saltpetre as an efflorescence on walls might naturally lead to its use, but in any event its distinguishing characteristics are nowhere mentioned. As sal-ammoniac occurred in the volcanoes in Italy, it also may have been included in the _nitrum_ mentioned. _Nitrum_ was in the main exported from Egypt, but Theophrastus mentions its production from wood-ash, and Pliny very rightly states that burned lees of wine (argol) had the nature of _nitrum_. Many of the ancient writers understood that it was rendered more caustic by burning, and still more so by treatment with lime. According to Beckmann (Hist. of Inventions II., p. 488), the form of the word _natron_ was first introduced into Europe by two travellers in Egypt, Peter Ballon and Prosper Alpinus, about 1550. The word was introduced into mineralogy by Linnaeus in 1736. In the first instance _natron_ was applied to soda and potash in distinction to _nitre_ for saltpetre, and later _natron_ was applied solely to soda.

It is desirable to mention here two other forms of soda and potash which are frequently mentioned by Agricola. "Ashes which wool dyers use" (_cineres quo infectores lanarum utuntur_).--There is no indication in any of Agricola's works as to whether this was some special wood-ash or whether it was the calcined residues from wool washing. The "yolk" or "suint" of wool, originating from the perspiration of the animal, has long been a source of crude potash. The water, after washing the wool, is evaporated, and the residue calcined. It contains about 85% K_{2}CO_{3}, the remainder being sodium and potassium sulphates. Another reason for assuming that it was not a wood-ash product, is that these products are separately mentioned. In either event, whether obtained from wool residues or from lixiviation of wood-ash, it would be an impure potash. In some methods of wool dyeing, a wash of soda was first given, so that it is barely possible that this substance was sodium carbonate.

"Salt made from the ashes of musk ivy" (_sal ex anthyllidis cinere factus_,--Glossary, _salalkali_). This would be largely potash.

[7] This wondrous illustration of soda-making from Nile water is no doubt founded upon Pliny (XXXI., 46). "It is made in almost the same manner as salt, except that sea-water is put into salt pans, whereas in the nitrous pans it is water of the Nile; these, with the subsidence of the Nile during the forty days, are impregnated with _nitrum_."

[8] This paragraph displays hopeless ignorance. Borax was known to Agricola and greatly used in his time; it certainly was not made from these compounds, but was imported from Central Asia. Sal-ammoniac was also known in his time, and was used like borax as a soldering agent. The reaction given by Agricola would yield free ammonia. The following historical notes on borax and sal-ammoniac may be of service.

BORAX.--The uncertainties of the ancient distinctions in salts involve borax deeply. The word _Baurach_ occurs in Geber and the other early Alchemistic writings, but there is nothing to prove that it was modern borax. There cannot be the slightest doubt, however, that the material referred to by Agricola as _borax_ was our borax, because of the characteristic qualities incidentally mentioned in Book VII. That he believed it was an artificial product from _nitrum_ is evident enough from his usual expression "_chrysocolla_ made from _nitrum_, which the Moors call _borax_." Agricola, in _De Natura Fossilium_ (p. 206-7), makes the following statements, which could leave no doubt on the subject:--"Native _nitrum_ is found in the earth or on the surface.... It is from this variety that the Venetians make _chrysocolla_, which I call _borax_.... The second variety of artificial _nitrum_ is made at the present day from the native _nitrum_, called by the Arabs _tincar_, but I call it usually by the Greek name _chrysocolla_; it is really the Arabic _borax_.... This _nitrum_ does not decrepitate nor fly out of the fire; however, the native variety swells up from within." The application of the word _chrysocolla_ (_chrysos_, gold; _colla_, solder) to soldering materials, and at the same time to the copper mineral, is of Greek origin. If any further proof were needed as to the substance meant by Agricola, it lies in the word _tincar_. For a long time the borax of Europe was imported from Central Asia, through Constantinople and Venice, under the name of _tincal_ or _tincar_. When this trade began, we do not know; evidently before Agricola's time. The statement here of making borax from alum and sal-ammoniac is identical with the assertion of Biringuccio (II., 9).

SAL-AMMONIAC.--The early history of this--ammonium chloride--is also under a cloud. Pliny (XXXI., 39) speaks of a _sal-hammoniacum_, and Dioscorides (V., 85) uses much the same word. Pliny describes it as from near the temple of Ammon in Egypt. None of the distinctive characteristics of sal-ammoniac are mentioned, and there is every reason to believe it was either common salt or soda. Herodotus, Strabo, and others mention common salt sent from about the same locality. The first authentic mention is in Geber, who calls it _sal-ammoniacum_, and describes a method of making, and several characteristic reactions. It was known in the Middle Ages under various names, among them _sal-aremonicum_. Agricola (_De Nat. Fos._, III., p. 206) notes its characteristic quality of volatilization. "Sal-ammoniac ... in the fire neither crackles nor flies out, but is totally consumed." He also says (p. 208): "Borax is used by goldsmiths to solder gold, likewise silver. The artificers who make iron needles (tacks?) similarly use sal-ammoniac when they cover the heads with tin." The statement from Pliny mentioned in this paragraph is from XXXIII., 29, where he describes the _chrysocolla_ used as gold solder as made from verdigris, _nitrum_, and urine in the way quoted. It is quite possible that this solder was sal-ammoniac, though not made in quite this manner. Pliny refers in several places (XXXIII., 26, 27, 28, and 29, XXXV., 28, etc.) to _chrysocolla_, about which he is greatly confused as between gold-solder, the copper mineral, and a green pigment, the latter being of either mineral origin.

[9] Saltpetre was secured in the Middle Ages in two ways, but mostly from the treatment of calcium nitrate efflorescence on cellar and similar walls, and from so-called saltpetre plantations. In this description of the latter, one of the most essential factors is omitted until the last sentence, _i.e._, that the nitrous earth was the result of the decay of organic or animal matter over a long period. Such decomposition, in the presence of potassium and calcium carbonates--the lye and lime--form potassium and calcium nitrates, together with some magnesium and sodium nitrates. After lixiviation, the addition of lye converts the calcium and magnesium nitrates into saltpetre, _i.e._, Ca(NO_{3})_{2} + K_{2}CO_{3} = CaCO_{3} + 2KNO_{3}. The carbonates precipitate out, leaving the saltpetre in solution, from which it was evaporated and crystallized out. The addition of alum as mentioned would scarcely improve the situation.

The purification by repeated re-solution and addition of lye, and filtration, would eliminate the remaining other salts. The purification with sulphur, however, is more difficult to understand. In this case the saltpetre is melted and the sulphur added and set alight. Such an addition to saltpetre would no doubt burn brilliantly. The potassium sulphate formed would possibly settle to the bottom, and if the "greasy matter" were simply organic impurities, they might be burned off. This method of refining appears to have been copied from Biringuccio (X., 1), who states it in almost identical terms.

HISTORICAL NOTE.--As mentioned in Note 6 above, it is quite possible that the Ancients did include efflorescence of walls under _nitrum_; but, so far as we are aware, no specific mention of such an occurrence of _nitrum_ is given, and, as stated before, there is every reason to believe that all the substances under that term were soda and potash. Especially the frequent mention of the preparation of _nitrum_ by way of burning, argues strongly against saltpetre being included, as they would hardly have failed to notice the decrepitation. Argument has been put forward that Greek fire contained saltpetre, but it amounts to nothing more than argument, for in those receipts preserved, no salt of any kind is mentioned. It is most likely that the leprosy of house-walls of the Mosaic code (Leviticus XIV., 34 to 53) was saltpetre efflorescence. The drastic treatment by way of destruction of such "unclean" walls and houses, however, is sufficient evidence that this salt was not used. The first certain mention of saltpetre (_sal petrae_) is in Geber. As stated before, the date of this work is uncertain; in any event it was probably as early as the 13th Century. He describes the making of "solvative water" with alum and saltpetre, so there can be no doubt as to the substance (see Note on p. 460, on nitric acid). There is also a work by a nebulous Marcus Graecus, where the word _sal petrosum_ is used. And it appears that Roger Bacon (died 1294) and Albertus Magnus (died 1280) both had access to that work. Bacon uses the term _sal petrae_ frequently enough, and was the first to describe gunpowder (_De Mirabili Potestate Artis et Naturae_ 1242). He gives no mention of the method of making his _sal petrae_. Agricola uses throughout the Latin text the term _halinitrum_, a word he appears to have coined himself. However, he gives its German equivalent in the _Interpretatio_ as _salpeter_. The only previous description of the method of making saltpetre, of which we are aware, is that of Biringuccio (1540), who mentions the boiling of the excrescences from walls, and also says a good deal about boiling solutions from "nitrous" earth, which may or may not be of "plantation" origin. He also gives this same method of refining with sulphur. In any event, this statement by Agricola is the first clear and complete description of the saltpetre "plantations." Saltpetre was in great demand in the Middle Ages for the manufacture of gunpowder, and the first record of that substance and of explosive weapons necessarily involves the knowledge of saltpetre. However, authentic mention of such weapons only begins early in the 14th Century. Among the earliest is an authority to the Council of Twelve at Florence to appoint persons to make cannon, etc., (1326), references to cannon in the stores of the Tower of London, 1388, &c.

[10] There are three methods of manufacturing alum described by Agricola, the first and third apparently from shales, and the second from alum rock or "alunite." The reasons for assuming that the first process was from shales, are the reference to the "aluminous earth" as ore (_venae_) coming from "veins," and also the mixture of vitriol. In this process the free sulphuric acid formed by the oxidation of pyrites reacts upon the argillaceous material to form aluminium sulphate. The decomposed ore is then placed in tanks and lixiviated. The solution would contain aluminium sulphate, vitriol, and other impurities. By the addition of urine, the aluminium sulphate would be converted into ammonia alum. Agricola is, of course, mistaken as to the effect of the addition, being under the belief that it separated the vitriol from the alum; in fact, this belief was general until the latter part of the 18th Century, when Lavoisier determined that alum must have an alkali base. Nor is it clear from this description exactly how they were separated. In a condensed solution allowed to cool, the alum would precipitate out as "alum meal," and the vitriol would "float on top"--in solution. The reference to "meal" may represent this phenomenon, and the re-boiling referred to would be the normal method of purification by crystallization. The "asbestos" and gypsum deposited in the caldrons were no doubt feathery and mealy calcium sulphate. The alum produced would, in any event, be mostly ammonia alum.

The second process is certainly the manufacture from "alum rock" or "alunite" (the hydrous sulphate of aluminium and potassium), such as that mined at La Tolfa in the Papal States, where the process has been for centuries identical with that here described. The alum there produced is the double basic potassium alum, and crystallizes into cubes instead of octahedra, _i.e._, the Roman alum of commerce. The presence of much ferric oxide gives the rose colour referred to by Agricola. This account is almost identical with that of Biringuccio (II., 4), and it appears from similarity of details that Agricola, as stated in his preface, must have "refreshed his mind" from this description; it would also appear from the preface that he had himself visited the locality.

The third process is essentially the same as the first, except that the decomposition of the pyrites was hastened by roasting. The following obscure statement of some interest occurs in Agricola's _De Natura Fossilium_, p. 209:--"... alum is made from vitriol, for when oil is made from the latter, alum is distilled out (_expirat_). This absorbs the clay which is used in cementing glass, and when the operation is complete the clay is macerated with pure water, and the alum is soon afterward deposited in the shape of small cubes." Assuming the oil of vitriol to be sulphuric acid and the clay "used in cementing glass" to be kaolin, we have here the first suggestion of a method for producing alum which came into use long after.

"Burnt alum" (_alumen coctum_).--Agricola frequently uses this expression, and on p. 568, describes the operation, and the substance is apparently the same as modern dehydrated alum, often referred to as "burnt alum."

HISTORICAL NOTES.--Whether the Ancients knew of alum in the modern sense is a most vexed question. The Greeks refer to a certain substance as _stypteria_, and the Romans refer to this same substance as _alumen_. There can be no question as to their knowledge and common use of vitriol, nor that substances which they believed were entirely different from vitriol were comprised under the above names. Beckmann (Hist. of Inventions, Vol. I., p. 181) seems to have been the founder of the doctrine that the ancient _alumen_ was vitriol, and scores of authorities seem to have adopted his arguments without inquiry, until that belief is now general. One of the strongest reasons put forward was that alum does not occur native in appreciable quantities. Apart from the fact that the weight of this argument has been lost by the discovery that alum does occur in nature to some extent as an aftermath of volcanic action, and as an efflorescence from argillaceous rocks, we see no reason why the Ancients may not have prepared it artificially. One of the earliest mentions of such a substance is by Herodotus (II., 180) of a thousand talents of _stypteria_, sent by Amasis from Egypt as a contribution to the rebuilding of the temple of Delphi. Diodorus (V., 1) mentions the abundance which was secured from the Lipari Islands (Stromboli, etc.), and a small quantity from the Isle of Melos. Dioscorides (V., 82) mentions Egypt, Lipari Islands, Melos, Sardinia, Armenia, etc., "and generally in any other places where one finds red ochre (_rubrica_)." Pliny (XXXV., 52) gives these same localities, and is more explicit as to how it originates--"from an earthy water which exudes from the earth." Of these localities, the Lipari Islands (Stromboli, etc.), and Melos are volcanic enough, and both Lipari and Melos are now known to produce natural alum (Dana. Syst. Min., p. 95; and Tournefort, "_Relation d'un voyage du Levant_." London, 1717, _Lettre_ IV., Vol. 1.). Further, the hair-like alum of Dioscorides, repeated by Pliny below, was quite conceivably fibrous _kalinite_, native potash alum, which occurs commonly as an efflorescence. Be the question of native alum as it may--and vitriol is not much more common--our own view that the ancient _alumen_ was alum, is equally based upon the artificial product. Before entering upon the subject, we consider it desirable to set out the properties of the ancient substance, a complete review of which is given by Pliny (XXXV., 52), he obviously quoting also from Dioscorides, which, therefore, we do not need to reproduce. Pliny says:--

"Not less important, or indeed dissimilar, are the uses made of _alumen_; by which name is understood a sort of salty earth. Of this, there are several kinds. In Cyprus there is a white _alumen_, and a darker kind. There is not a great difference in their colour, though the uses made of them are very dissimilar,--the white _alumen_ being employed in a liquid state for dyeing wool bright colours, and the dark-coloured _alumen_, on the other hand, for giving wool a sombre tint. Gold is purified with black _alumen_. Every kind of _alumen_ is from a _limus_ water which exudes from the earth. The collection of it commences in winter, and it is dried by the summer sun. That portion of it which first matures is the whitest. It is obtained in Spain, Egypt, Armenia, Macedonia, Pontus, Africa, and the islands of Sardinia, Melos, Lipari, and Strongyle; the most esteemed, however, is that of Egypt, the next best from Melos. Of this last there are two kinds, the liquid _alumen_, and the solid. Liquid _alumen_, to be good, should be of a limpid and milky appearance; when rubbed, it should be without roughness, and should give a little heat. This is called _phorimon_. The mode of detecting whether it has been adulterated is by pomegranate juice, for, if genuine, the mixture turns black. The other, or solid, is pale and rough and turns dark with nut-galls; for which reason it is called _paraphoron_. Liquid _alumen_ is naturally astringent, indurative, and corrosive; used in combination with honey, it heals ulcerations.... There is one kind of solid _alumen_, called by the Greeks _schistos_, which splits into filaments of a whitish colour; for which reason some prefer calling it _trichitis_ (hair like). _Alumen_ is produced from the stone _chalcitis_, from which copper is also made, being a sort of coagulated scum from that stone. This kind of _alumen_ is less astringent than the others, and is less useful as a check upon bad humours of the body.... The mode of preparing it is to cook it in a pan until it has ceased being a liquid. There is another variety of _alumen_ also, of a less active nature, called _strongyle_. It is of two kinds. The fungous, which easily dissolves, is utterly condemned. The better kind is the pumice-like kind, full of small holes like a sponge, and is in round pieces, more nearly white in colour, somewhat greasy, free from grit, friable, and does not stain black. This last kind is cooked by itself upon charcoal until it is reduced to pure ashes. The best kind of all is that called _melinum_, from the Isle of Melos, as I have said, none being more effectual as an astringent, for staining black, and for indurating, and none becomes more dry.... Above all other properties of _alumen_ is its remarkable astringency, whence its Greek name.... It is injected for dysentry and employed as a gargle." The lines omitted refer entirely to medical matters which have no bearing here. The following paragraph (often overlooked) from Pliny (XXXV., 42) also has an important bearing upon the subject:--"In Egypt they employ a wonderful method of dyeing. The white cloth, after it is pressed, is stained in various places, not with dye stuffs, but with substances which absorb colours. These applications are not apparent on the cloth, but when it is immersed in a caldron of hot dye it is removed the next moment brightly coloured. The remarkable circumstance is that although there be only one dye in the caldron yet different colours appear in the cloth."

It is obvious from Pliny's description above, and also from the making of vitriol (see Note 11, p. 572), that this substance was obtained from liquor resulting from natural or artificial lixiviation of rocks--in the case of vitriols undoubtedly the result of decomposition of pyritiferous rocks (such as _chalcitis_). Such liquors are bound to contain aluminum sulphate if there is any earth or clay about, and whether they contained alum would be a question of an alkali being present. If no alkali were present in this liquor, vitriol would crystallize out first, and subsequent condensation would yield aluminum sulphate. If alkali were present, the alum would crystallize out either before or with the vitriol. Pliny's remark, "that portion of it which first matures is whitest", agrees well enough with this hypothesis. No one will doubt that some of the properties mentioned above belong peculiarly to vitriol, but equally convincing are properties and uses that belong to alum alone. The strongly astringent taste, white colour, and injection for dysentry, are more peculiar to alum than to vitriol. But above all other properties is that displayed in dyeing, for certainly if we read this last quotation from Pliny in conjunction with the statement that white _alumen_ produces bright colours and the dark kind, sombre colours, we have the exact reactions of alum and vitriol when used as mordants. Therefore, our view is that the ancient salt of this character was a more or less impure mixture ranging from alum to vitriol--"the whiter the better." Further, considering the ancient knowledge of soda (_nitrum_), and the habit of mixing it into almost everything, it does not require much flight of imagination to conceive its admixture to the "water," and the absolute production of alum.

Whatever may have been the confusion between alum and vitriol among the Ancients, it appears that by the time of the works attributed to Geber (12th or 13th Century), the difference was well known. His work (_Investigationes perfectiones_, IV.) refers to _alumen glaciale_ and _alumen jameni_ as distinguished from vitriol, and gives characteristic reactions which can leave no doubt as to the distinction. We may remark here that the repeated statement apparently arising from Meyer (History of Chemistry, p. 51) that Geber used the term _alum de rocca_ is untrue, this term not appearing in the early Latin translations. During the 15th Century alum did come to be known in Europe as _alum de rocca_. Various attempts have been made to explain the origin of this term, ranging from the Italian root, a "rock," to the town of Rocca in Syria, where alum was supposed to have been produced. In any event, the supply for a long period prior to the middle of the 15th Century came from Turkey, and the origin of the methods of manufacture described by Agricola, and used down to the present day, must have come from the Orient.

In the early part of the 15th Century, a large trade in alum was done between Italy and Asia Minor, and eventually various Italians established themselves near Constantinople and Smyrna for its manufacture (Dudae, _Historia Byzantina Venetia_, 1729, p. 71). The alum was secured by burning the rock, and lixiviation. With the capture of Constantinople by the Turks (1453), great feeling grew up in Italy over the necessity of buying this requisite for their dyeing establishments from the infidel, and considerable exertion was made to find other sources of supply. Some minor works were attempted, but nothing much eventuated until the appearance of one John de Castro. From the Commentaries of Pope Pius II. (1614, p. 185), it appears that this Italian had been engaged in dyeing cloth in Constantinople, and thus became aware of the methods of making alum. Driven out of that city through its capture by the Turks, he returned to Italy and obtained an office under the Apostolic Chamber. While in this occupation he discovered a rock at Tolfa which appeared to him identical with that used at Constantinople in alum manufacture. After experimental work, he sought the aid of the Pope, which he obtained after much vicissitude. Experts were sent, who after examination "shed tears of joy, they kneeling down three times, worshipped God and praised His kindness in conferring such a gift on their age." Castro was rewarded, and the great papal monopoly was gradually built upon this discovery. The industry firmly established at Tolfa exists to the present day, and is the source of the Roman alum of commerce. The Pope maintained this monopoly strenuously, by fair means and by excommunication, gradually advancing the price until the consumers had greater complaint than against the Turks. The history of the disputes arising over the papal alum monopoly would alone fill a volume.

By the middle of the 15th Century alum was being made in Spain, Holland, and Germany, and later in England. In her efforts to encourage home industries and escape the tribute to the Pope, Elizabeth (see Note on p. 283) invited over "certain foreign chymistes and mineral masters" and gave them special grants to induce them to "settle in these realmes." Among them was Cornelius Devoz, to whom was granted the privilege of "mining and digging in our Realm of England for allom and copperas." What Devoz accomplished is not recorded, but the first alum manufacture on a considerable scale seems to have been in Yorkshire, by one Thomas Chaloner (about 1608), who was supposed to have seduced workmen from the Pope's alum works at Tolfa, for which he was duly cursed with all the weight of the Pope and Church. (Pennant, Tour of Scotland, 1786).

[11] The term for vitriol used by the Roman authors, followed by Agricola, is _atramentum sutorium_, literally shoemaker's blacking, the term no doubt arising from its ancient (and modern) use for blackening leather. The Greek term was _chalcanthon_. The term "vitriol" seems first to appear in Albertus Magnus (_De Mineralibus_, _Liber_ V.), who died in 1280, where he uses the expression "_atramentum viride a quibusdam vitreolum vocatur_." Agricola (_De Nat. Foss._, p. 213) states, "In recent years the name _vitriolum_ has been given to it." The first adequate description of vitriol is by Dioscorides (V., 76), as follows:--"Vitriol (_chalcanthon_) is of one genus, and is a solidified liquid, but it has three different species. One is formed from the liquids which trickle down drop by drop and congeal in certain mines; therefore those who work in the Cyprian mines call it _stalactis_. Petesius calls this kind _pinarion_. The second kind is that which collects in certain caverns; afterward it is poured into trenches, where it congeals, whence it derives its name _pectos_. The third kind is called _hephthon_ and is mostly made in Spain; it has a beautiful colour but is weak. The manner of preparing it is as follows: dissolving it in water, they boil it, and then they transfer it to cisterns and leave it to settle. After a certain number of days it congeals and separates into many small pieces, having the form of dice, which stick together like grapes. The most valued is blue, heavy, dense, and translucent." Pliny (XXXIV., 32) says:--"By the name which they have given to it, the Greeks indicate the similar nature of copper and _atramentum sutorium_, for they call it _chalcanthon_. There is no substance of an equally miraculous nature. It is made in Spain from wells of this kind of water. This water is boiled with an equal quantity of pure water, and is then poured into wooden tanks (fish ponds). Across these tanks there are fixed beams, to which hang cords stretched by little stones. Upon these cords adheres the _limus_ (Agricola's 'juice') in drops of a vitreous appearance, somewhat resembling a bunch of grapes. After removal, it is dried for thirty days. It is of a blue colour, and of a brilliant lustre, and is very like glass. Its solution is the blacking used for colouring leather. _Chalcanthon_ is made in many other ways: its kind of earth is sometimes dug from ditches, from the sides of which exude drops, which solidify by the winter frosts into icicles, called _stalagmia_, and there is none more pure. When its colour is nearly white, with a slight tinge of violet, it is called _leukoion_. It is also made in rock basins, the rain water collecting the _limus_ into them, where it becomes hardened. It is also made in the same way as salt by the intense heat of the sun. Hence it is that some distinguish two kinds, the mineral and the artificial; the latter being paler than the former and as much inferior to it in quality as it is in colour."

While Pliny gives prominence to blue vitriol, his solution for colouring leather must have been the iron sulphate. There can be no doubt from the above, however, that both iron and copper sulphates were known to the Ancients. From the methods for making vitriol given here in _De Re Metallica_, it is evident that only the iron sulphate would be produced, for the introduction of iron strips into the vats would effectually precipitate any copper. It is our belief that generally throughout this work, the iron sulphate is meant by the term _atramentum sutorium_. In _De Natura Fossilium_ (p. 213-15) Agricola gives three varieties of _atramentum sutorium_,--_viride_, _caeruleum_, and _candidum_, _i.e._, green, blue, and white. Thus the first mention of white vitriol (zinc sulphate) appears to be due to him, and he states further (p. 213): "A white sort is found, especially at Goslar, in the shape of icicles, transparent like crystals." And on p. 215: "Since I have explained the nature of vitriol and its relatives, which are obtained from cupriferous pyrites, I will next speak of an acrid solidified juice which commonly comes from _cadmia_. It is found at Annaberg in the tunnel driven to the Saint Otto mine; it is hard and white, and so acrid that it kills mice, crickets, and every kind of animal. However, that feathery substance which oozes out from the mountain rocks and the thick substance found hanging in tunnels and caves from which saltpetre is made, while frequently acrid, does not come from _cadmia_." Dana (Syst. of Min., p. 939) identifies this as _Goslarite_--native zinc sulphate. It does not appear, however, that artificial zinc vitriol was made in Agricola's time. Schlueter (_Huette-Werken_, Braunschweig 1738, p. 597) states it to have been made for the first time at Rammelsberg about 1570.