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reviously I have dealt with the methods of separating silver from copper. There now remains the portion which treats of solidified juices; and whereas they might be considered as alien to things metallic, nevertheless, the reasons why they should not be separated from it I have explained in thesecond book.
Solidified juices are either prepared from waters in which nature or art has infused them, or they are produced from the liquid juices themselves, or from stony minerals. Sagacious people, at first observing the waters of some lakes to be naturally full of juices which thickened on being dried up by the heat of the sun and thus became solidified juices, drew such waters into other places, or diverted them into low-lying places adjoining hills, so that the heat of the sun should likewise cause them to condense. Subsequently, because they observed that in this wise the solidified juices could be made only in summer, and then not in all countries, but only in hot and temperate regions in which it seldom rains in summer, they boiled them in vessels over a fire until they began to thicken. In this manner, at all times of the year, in all regions, even the coldest, solidified juices could be obtained from solutions of such juices, whether made by nature or by art. Afterward, when they saw juices drip from some roasted stones, they cooked these in pots in order to obtain solidified juices in this wise also. It is worth the trouble to learn the proportions and the methods by which these are made.
I will therefore begin with salt, which is made from water either salty by nature, or by the labour of man, or else from a solution of salt, or from lye, likewise salty. Water which is salty by nature, is condensed and converted into salt in salt-pits by the heat of the sun, or else by the heat of a fire in pans or pots or trenches. That which is made salty by art, is also condensed by fire and changed into salt. There should be as many salt-pits dug as the circumstance of the place permits, but there should not be more made than can be used, although we ought to make as much salt as we can sell. The depth of salt-pits should be moderate, and the bottom should be level, so that all the water is evaporated from the salt by the heat of the sun. The salt-pits should first be encrusted with salt, so that they may not suck up the water. The method of pouring or leading sea-water into salt-pits is very old, and is still in use in many places. The method is not less old, but less common, to pour well-water into salt-pits, as was done in Babylon, for which Pliny is the authority, and in Cappadocia, where they used not only well-water, but also spring-water. In all hot countries salt-water and lake-water are conducted, poured or carried into salt-pits, and, being dried by the heat of the sun, are converted intosalt.[1]While the salt-water contained in the salt-pits is being heated by the sun, if they be flooded with great and frequent showers of rain the evaporation is hindered. If this happens rarely, the salt acquires a disagreeable[2]flavour, and in this case the salt-pits have to be filled with other sweet water.
Salt PansA—Sea. B—Pool. C—Gate. D—Trenches. E—Salt basins. F—Rake. G—Shovel.[Pg 547]Salt from sea-water is made in the following manner. Near that part of the seashore where there is a quiet pool, and there are wide, level plains which the inundations of the sea do not overflow, three, four, five, or six trenches are dug six feet wide, twelve feet deep, and six hundred feet long, or longer if the level place extends for a longer distance; they are two hundred feet distant from one another; between these are three transverse trenches. Then are dug the principal pits, so that when the water has been raised from the pool it can flow into the trenches, and from thence into the salt-pits, of which there are numbers on the level ground between the trenches. The salt-pits are basins dug to a moderate depth; these are banked round with the earth which was dug in sinking them or in cleansing them, so that between the basins, earth walls are made a foot high, which retain the water let into them. The trenches have openings, through which the first basins receive the water; these basins also have openings, through which the water flows again from one into the other. There should be a slight fall, so that the water may flow from one basin into the other, and can thus be replenished. All these things having been done rightly and in order, the gate is raised that opens the mouth of the pool which contains sea-water mixed with rain-water or river-water; and thus all of the trenches are filled. Then the gates of the first basins are opened, and thus the remaining basins are filled with the water from the first; when this salt-water condenses, all these basins are incrusted, and thus made clean from earthy matter. Then again the first basins are filled up from the nearest trench with the same kind of water, and left until much of the thin liquid is converted into vapour by the heat of the sun and dissipated, and the remainder is considerably thickened. Then their gates being opened, the water passes into the second basins; and when it has remained there for a certain space of time the gates are opened, so that it flows into the third basins, where it is all condensed into salt. After the salt has been taken out, the basins are filled again and again with sea-water. The salt is raked up with wooden rakes and thrown out with shovels.
Salt WellsA—Shed. B—Painted signs. C—First room. D—Middle room. E—Third room. F—Two little windows in the end wall. G—Third little window in the roof. H—Well. I—Well of another kind. K—Cask. L—Pole. M—Forked sticks in which the porters rest the pole when they are tired.[Pg 549]Salt-water is also boiled in pans, placed in sheds near the wells from which it is drawn. Each shed is usually named from some animal or other thing which is pictured on a tablet nailed to it. The walls of these sheds are made either from baked earth or from wicker work covered with thickmud, although some may be made of stones or bricks. When of brick they are often sixteen feet high, and if the roof rises twenty-four feet high, then the walls which are at the ends must be made forty feet high, as likewise the interior partition walls. The roof consists of large shingles four feet long, one foot wide, and two digits thick; these are fixed on long narrow planks placed on the rafters, which are joined at the upper end and slope in opposite directions. The whole of the under side is plastered one digit thick with straw mixed with lute; likewise the roof on the outside is plastered one and a half feet thick with straw mixed with lute, in order that the shed should not run any risk of fire, and that it should be proof against rain, and be able to retain the heat necessary for drying the lumps of salt. Each shed is divided into three parts, in the first of which the firewood and straw are placed; in the middle room, separated from the first room by a partition, is the fireplace on which is placed the caldron. To the right of the caldron is a tub, into which is emptied the brine brought into the shed by the porters; to the left is a bench, on which there is room to lay thirty pieces of salt. In the third room, which is in the back part of the house, there is made a pile of clay or ashes eight feet higher than the floor, being the same height as the bench. The master and his assistants, when they carry away the lumps of salt from the caldrons, go from the former to the latter. They ascend from the right side of the caldron, not by steps, but by a slope of earth. At the top of the end wall are two small windows, and a third is in the roof, through which the smoke escapes. This smoke, emitted from both the back and the front of the furnace, finds outlet through a hood through which it makes its way up to the windows; this hood consists of boards projecting one beyond the other, which are supported by two small beams of the roof. Opposite the fireplace the middle partition has an open door eight feet high and four feet wide, through which there is a gentle draught which drives the smoke into the last room; the front wall also has a door of the same height and width. Both of these doors are large enough to permit the firewood or straw or the brine to be carried in, and the lumps of salt to be carried out; these doors must be closed when the wind blows, so that the boiling will not be hindered. Indeed, glass panes which exclude the wind but transmit the light, should be inserted in the windows in the walls.
They construct the greater part of the fireplace of rock-salt and of clay mixed with salt and moistened with brine, for such walls are greatly hardened by the fire. These fireplaces are made eight and a half feet long, seven and three quarters feet wide, and, if wood is burned in them, nearly four feet high; but if straw is burned in them, they are six feet high. An iron rod, about four feet long, is engaged in a hole in an iron foot, which stands on the base of the middle of the furnace mouth. This mouth is three feet in width, and has a door which opens inward; through it they throw in the straw.
Salt CaldronA—Fireplace. B—Mouth of fireplace. C—Caldron. D—Posts sunk into the ground. E—Cross-beams. F—Shorter bars. G—Iron hooks. H—Staples. I—Longer bars. K—Iron rod bent to support the caldron.[Pg 551]The caldrons are rectangular, eight feet long, seven feet wide, and half a foot high, and are made of sheets of iron or lead, three feet long and of the same width, all but two digits. These plates are not very thick, so that thewater is heated more quickly by the fire, and is boiled away rapidly. The more salty the water is, the sooner it is condensed into salt. To prevent the brine from leaking out at the points where the metal plates are fastened with rivets, the caldrons are smeared over with a cement made of ox-liver and ox-blood mixed with ashes. On each side of the middle of the furnace two rectangular posts, three feet long, and half a foot thick and wide are set into the ground, so that they are distant from each other only one and a half feet. Each of them rises one and a half feet above the caldron. After the caldron has been placed on the walls of the furnace, two beams of the same width and thickness as the posts, but four feet long, are laid on these posts, and are mortised in so that they shall not fall. There rest transversely upon these beams three bars, three feet long, three digits wide, and two digits thick, distant from one another one foot. On each of these hang three iron hooks, two beyond the beams and one in the middle; these are a foot long, and are hooked at both ends, one hook turning to the right, the other to the left. The bottom hook catches in the eye of a staple, whose ends are fixed in the bottom of the caldron, and the eye projects from it. There are besides, two longer bars six feet long, one palm wide, and three digits thick, which pass under the front beam and rest upon the rear beam. At the rear end of each of the bars there is an iron hook two feet and three digits long, the lower end of which is bent so as to support the caldron. The rear end of the caldron does not rest on the two rear corners of the fireplace, but is distant from the fireplace two thirds of a foot, so that the flame and smoke can escape; this rear end of the fireplace is half a foot thick and half a foot higher than the caldron. This is also the thickness and height of the wall between the caldron and the third room of the shed, to which it is adjacent. This back wall is made of clay and ashes, unlike the others which are made of rock-salt. The caldron rests on the two front corners and sides of the fireplace, and is cemented with ashes, so that the flames shall not escape. If a dipperful of brine poured into the caldron should flow into all the corners, the caldron is rightly set upon the fireplace.
The wooden dipper holds ten Romansextarii, and the cask holds eight dippers full[3]. The brine drawn up from the well is poured into such casks and carried by porters, as I have said before, into the shed and poured into a tub, and in those places where the brine is very strong it is at once transferred with the dippers into the caldron. That brine which is less strong is thrown into a small tub with a deep ladle, the spoon and handle of which are hewn out of one piece of wood. In this tub rock-salt is placed in orderthat the water should be made more salty, and it is then run off through a launder which leads into the caldron. From thirty-seven dippersful of brine the master or his deputy, at Halle in Saxony,[4]makes two cone-shaped pieces of salt. Each master has a helper, or in the place of a helper his wife assists him in his work, and, in addition, a youth who throws wood or straw under the caldron. He, on account of the great heat of the workshop, wears a straw cap on his head and a breech cloth, being otherwise quite naked. As soon as the master has poured the first dipperful of brine into the caldron the youth sets fire to the wood and straw laid under it. If the firewood is bundles of faggots or brushwood, the salt will be white, but if straw is burned, then it is not infrequently blackish, for the sparks, which are drawn up with the smoke into the hood, fall down again into the water and colour it black.
Salt CaldronA—Wooden dipper. B—Cask. C—Tub. D—Master. E—Youth. F—Wife. G—Wooden spade. H—Boards. I—Baskets. K—Hoe. L—Rake. M—Straw. N—Bowl. O—Bucket containing the blood. P—Tankard which contains beer.[Pg 553]In order to accelerate the condensation of the brine, when the master has poured in two casks and as many dippersful of brine, he adds about a Romancyathusand a half of bullock's blood, or of calf's blood, or buck's blood, or else he mixes it into the nineteenth dipperful of brine, in order that it may be dissolved and distributed into all the corners of the caldron; in other places the blood is dissolved in beer. When the boiling water seems to be mixed with scum, he skims it with a ladle; this scum, if he be working with rock-salt, he throws into the opening in the furnace through which the smoke escapes, and it is dried into rock-salt; if it be not from rock-salt, he pours it on to the floor of the workshop. From the beginning to the boiling and skimming is the work of half-an-hour; after this it boils down for another quarter-of-an-hour, after which time it begins to condense into salt. When it begins to thicken with the heat, he and his helper stir it assiduously with a wooden spatula, and then he allows it to boil for an hour. After this he pours in acyathusand a half of beer. In order that the wind should not blow into the caldron, the helper covers the front with a board seven and a half feet long and one foot high, and covers each of the sides with boards three and three quarters feet long. In order that the front board may hold more firmly, it is fitted into the caldron itself, and the side-boards are fixed on the front board and upon the transverse beam. Afterward, when the boards have been lifted off, the helper places two baskets, two feet high and as many wide at the top, and a palm wide at the bottom, on the transverse beams, and into them the master throws the salt with a shovel, taking half-an-hour to fill them. Then, replacing the boards on the caldron, he allows the brine to boil for three quarters of an hour. Afterward the salt has again to be removed with a shovel, and when the baskets are full, they pile up the salt in heaps.
In different localities the salt is moulded into different shapes. In the baskets the salt assumes the form of a cone; it is not moulded in baskets alone, but also in moulds into which they throw the salt, which are made inthe likeness of many objects, as for instance tablets. These tablets and cones are kept in the higher part of the third room of the house, or else on the flat bench of the same height, in order that they may dry better in the warm air. In the manner I have described, a master and his helper continue one after the other, alternately boiling the brine and moulding the salt, day and night, with the exception only of the annual feast days. No caldron is able to stand the fire for more than half a year. The master pours in water and washes it out every week; when it is washed out he puts straw under it and pounds it; new caldrons he washes three times in the first two weeks, and afterward twice. In this manner the incrustations fall from the bottom; if they are not cleared off, the salt would have to be made more slowly over a fiercer fire, which requires more brine and burns the plates of the caldron. If any cracks make their appearance in the caldron they are filled up with cement. The salt made during the first two weeks is not so good, being usually stained by the rust at the bottom where incrustations have not yet adhered.
Although salt made in this manner is prepared only from the brine ofsprings and wells, yet it is also possible to use this method in the case of river-, lake-, and sea-water, and also of those waters which are artificially salted. For in places where rock-salt is dug, the impure and the broken pieces are thrown into fresh water, which, when boiled, condenses into salt. Some, indeed, boil sea-salt in fresh water again, and mould the salt into the little cones and other shapes.
Salt BoilingA—Pool. B—Pots. C—Ladle. D—Pans. E—Tongs.[Pg 554]Some people make salt by another method, from salt water which flows from hot springs that issue boiling from the earth. They set earthenware pots in a pool of the spring-water, and into them they pour water scooped up with ladles from the hot spring until they are half full. The perpetual heat of the waters of the pool evaporates the salt water just as the heat of the fire does in the caldrons. As soon as it begins to thicken, which happens when it has been reduced by boiling to a third or more, they seize the pots with tongs and pour the contents into small rectangular iron pans, which have also been placed in the pool. The interior of these pans is usually three feet long, two feet wide, and three digits deep, and they stand on four heavy legs, so that the water flows freely all round, but not into them. Since the water flows continuously from the pool through the little canals, and the springalways provides a new and copious supply, always boiling hot, it condenses the thickened water poured into the pans into salt; this is at once taken out with shovels, and then the work begins all over again. If the salty water contains other juices, as is usually the case with hot springs, no salt should be made from them.
Salt BoilingA—Pots. B—Tripod. C—Deep ladle.[Pg 555]Others boil salt water, and especially sea-water, in large iron pots; this salt is blackish, for in most cases they burn straw under them. Some people boil in these pots the brine in which fish is pickled. The salt which they make tastes and smells of fish.
Salt evaporated on faggotsA—Trench. B—Vat into which the salt water flows. C—Ladle. D—Small bucket with pole fastened into it.[Pg 556]Those who make salt by pouring brine over firewood, lay the wood in trenches which are twelve feet long, seven feet wide, and two and one half feet deep, so that the water poured in should not flow out. These trenches are constructed of rock-salt wherever it is to be had, in order that they should not soak up the water, and so that the earth should not fall in on the front, back and sides. As the charcoal is turned into salt at the same time as thesalt liquor, the Spaniards think, as Pliny writes[5], that the wood itself turns into salt. Oak is the best wood, as its pure ash yields salt; elsewhere hazel-wood is lauded. But with whatever wood it be made, this salt is not greatly appreciated, being black and not quite pure; on that account this method of salt-making is disdained by the Germans and Spaniards.
Lye MakingA—Large vat. B—Plug. C—Small tub. D—Deep ladle. E—Small vat. F—Caldron.[Pg 557]The solutions from which salt is made are prepared from salty earth or from earth rich in salt and saltpetre. Lye is made from the ashes of reeds and rushes. The solution obtained from salty earth by boiling, makes salt only; from the other, of which I will speak more a little later, salt and saltpetre are made; and from ashes is derived lye, from which its own salt is obtained. The ashes, as well as the earth, should first be put into a large vat; then fresh water should be poured over the ashes or earth, and it should be stirred for about twelve hours with a stick, so that it may dissolve the salt. Then the plug is pulled out of the large vat; the solution of salt or the lye is drained into a small tub and emptied with ladles into small vats; finally, such a solution is transferred into iron or lead caldrons and boiled, until the water having evaporated, the juices are condensed into salt. The above are the various methods for making salt. (Illustration p.557.)
Nitrum-pitsA—Nile. B—Nitrum-pits, such as I conjecture them to be.[7][Pg 559]Nitrum[6]is usually made fromnitrouswaters, or from solutions or from lye. In the same manner as sea-water or salt-water is poured into salt-pits and evaporated by the heat of the sun and changed into salt, so thenitrousNile is led intonitrumpits and evaporated by the heat of the sun and convertedintonitrum. Just as the sea, in flowing of its own will over the soil of this same Egypt, is changed into salt, so also the Nile, when it overflows in the dog days, is converted intonitrumwhen it flows into thenitrumpits. The solution from whichnitrumis produced is obtained from fresh water percolating throughnitrousearth, in the same manner as lye is made from fresh water percolating through ashes of oak or hard oak. Both solutions are taken out of vats and poured into rectangular copper caldrons, and are boiled until at last they condense intonitrum.
Soda MakingA—Vat in which the soda is mixed. B—Caldron. C—Tub in whichchrysocollais condensed. D—Copper wires. E—Mortar.[Pg 561]Native as well as manufacturednitrumis mixed in vats with urine and boiled in the same caldrons; the decoction is poured into vats in which are copper wires, and, adhering to them, it hardens and becomeschrysocolla, which the Moors callborax. Formerlynitrumwas compounded with Cyprian verdigris, and ground with Cyprian copper in Cyprian mortars, as Pliny writes. Somechrysocollais made of rock-alum and sal-ammoniac.[8]
Saltpetre MakingA—Caldron. B—Large vat into which sand is thrown. C—Plug. D—Tub. E—Vat containing the rods.[Pg 563]Saltpetre[9]is made from a dry, slightly fatty earth, which, if it be retained for a while in the mouth, has an acrid and salty taste. This earth, together with a powder, are alternately put into a vat in layers a palm deep. The powder consists of two parts of unslaked lime and three parts of ashes of oak, or holmoak, or Italian oak, or Turkey oak, or of some similar kind. Each vat is filled with alternate layers of these to within three-quarters of a foot of the top, and then water is poured in until it is full. As the water percolates through the material it dissolves the saltpetre; then, the plug being pulled out from the vat, the solution is drained into a tub and ladled out into smallvats. If when tested it tastes very salty, and at the same time acrid, it is good; but, if not, then it is condemned, and it must be made to percolate again through the same material or through a fresh lot. Even two or three waters may be made to percolate through the same earth and become full of saltpetre, but the solutions thus obtained must not be mixed together unless all have the same taste, which rarely or never happens. The first of these solutions is poured into the first vat, the next into the second, the third into the third vat; the second and third solutions are used instead of plain water to percolate through fresh material; the first solution is made in this manner from both the second and third. As soon as there is an abundance of this solution it is poured into the rectangular copper caldron and evaporated to one half by boiling; then it is transferred into a vat covered with a lid, in which the earthy matter settles to the bottom. When the solution is clear it is poured back into the same pan, or into another, and re-boiled. When it bubbles and forms a scum, in order that it should not run over and that it may be greatly purified, there is poured into it three or four pounds of lye, made from three parts of oak or similar ash and one of unslaked lime. But in the water, prior to its being poured in, is dissolved rock-alum, in the proportion of one hundred and twentylibraeof the former to fivelibraeof the latter. Shortly afterward the solution will be found to be clear and blue. It is boiled until the waters, which are easily volatile (subtiles), are evaporated, and then the greater part of the salt, after it has settled at the bottom of the pan, is taken out with iron ladles. Then the concentrated solution is transferred to the vat in which rods are placed horizontally and vertically, to which it adheres when cold, and if there be much, it is condensed in three or four days into saltpetre. Then the solution which has not congealed, is poured out and put on one side or re-boiled. The saltpetre being cut out and washed with its own solution, is thrown on to boards that it may drain and dry. The yield of saltpetre will be much or little in proportion to whether the solution has absorbed much or little; when the saltpetre has been obtained from lye, which purifies itself, it is somewhat clear and pure.
The purest and most transparent, because free from salt, is made if it is drawn off at the thickening stage, according to the following method. Thereare poured into the caldron the same number ofamphoraeof the solution as ofcongiiof the lye of which I have already spoken, and into the same caldron is thrown as much of the already made saltpetre as the solution and lye will dissolve. As soon as the mixture effervesces and forms scum, it is transferred to a vat, into which on a cloth has been thrown washed sand obtained from a river. Soon afterward the plug is drawn out of the hole at the bottom, and the mixture, having percolated through the sand, escapes into a tub. It is then reduced by boiling in one or another of the caldrons, until the greater part of the solution has evaporated; but as soon as it is well boiled and forms scum, a little lye is poured into it. Then it is transferred to another vat in which there are small rods, to which it adheres and congeals in two days if there is but little of it, or if there is much in three days, or at the most in four days; if it does not condense, it is poured back into the caldron and re-boiled down to half; then it is transferred to the vat to cool. The process must be repeated as often as is necessary.
Others refine saltpetre by another method, for with it they fill a pot made of copper, and, covering it with a copper lid, set it over live coals, where it is heated until it melts. They do not cement down the lid, but it has a handle, and can be lifted for them to see whether or not the melting has taken place. When it has melted, powdered sulphur is sprinkled in, and if the pot set on the fire does not light it, the sulphur kindles, whereby the thick, greasy matter floating on the saltpetre burns up, and when it is consumed the saltpetre is pure. Soon afterward the pot is removed from the fire, and later, when cold, the purest saltpetre is taken out, which has the appearance of white marble, the earthy residue then remains at the bottom. The earths from which the solution was made, together with branches of oak or similar trees, are exposed under the open sky and sprinkled with water containing saltpetre. After remaining thus for five or six years, they are again ready to be made into a solution.
Pure saltpetre which has rested many years in the earth, and that which exudes from the stone walls of wine cellars and dark places, is mixed with the first solution and evaporated by boiling.
Thus far I have described the methods of makingnitrum, which are not less varied or multifarious than those for making salt. Now I propose to describe the methods of making alum,[10]which are likewise neither all alike, nor simple, because it is made from boiling aluminous water until it condenses to alum, or else from boiling a solution of alum which is obtained from a kind of earth, or from rocks, or from pyrites, or other minerals.
Vitriol MakingA—Tanks. B—Stirring poles. C—Plug. D—Trough. E—Reservoir. F—Launder. G—lead caldron. H—Wooden tubs sunk into the earth. I—Vats in which twigs are fixed.[Pg 567]This kind of earth having first been dug up in such quantity as would make three hundred wheelbarrow loads, is thrown into two tanks; then the water is turned into them, and if it (the earth) contains vitriol it must be diluted with urine. The workmen must many times a day stir the ore with long, thick sticks in order that the water and urine may be mixed with it; then the plugs having been taken out of both tanks, the solution is drawn off into a trough, which is carved out of one or two trees. If the locality is supplied with an abundance of such ore, it should not immediately be thrown into the tanks, but first conveyed into open spaces and heaped up, for the longer it is exposed to the air and the rain, the better it is; after some months, during which the ore has been heaped up in open spaces into mounds, there are generated veinlets of far better quality than the ore. Then it is conveyed into six or more tanks, nine feet in length and breadth and five in depth, and afterward water is drawn into them of similar solution. After this, when the water has absorbed the alum, the plugs are pulled out, and the solution escapes into a round reservoir forty feet wide and three feet deep. Then the ore is thrown out of the tanks into other tanks, and water again being run into the latter and the urine added and stirred by means of poles, the plugs are withdrawn and the solution is run off into the same reservoir. A few days afterward, the reservoirs containing the solution are emptied through a small launder, and run into rectangular lead caldrons; it is boiled in them until thegreater part of the water has evaporated. The earthy sediment deposited at the bottom of the caldron is composed of fatty and aluminous matter, which usually consists of small incrustations, in which there is not infrequently found a very white and very light powder of asbestos or gypsum. The solution now seems to be full of meal. Some people instead pour the partly evaporated solution into a vat, so that it may become pure and clear; then pouring it back into the caldron, they boil it again until it becomes mealy. By whichever process it has been condensed, it is then poured into a wooden tub sunk into the earth in order to cool it. When it becomes cold it is poured into vats, in which are arranged horizontal and vertical twigs, to which the alum clings when it condenses; and thus are made the small white transparent cubes, which are laid to dry in hot rooms.
If vitriol forms part of the aluminous ore, the material is dissolved in water without being mixed with urine, but it is necessary to pour that into the clear and pure solution when it is to be re-boiled. This separates the vitriol from the alum, for by this method the latter sinks to the bottom of the caldron, while the former floats on the top; both must be poured separately into smaller vessels, and from these into vats to condense. If, however, when the solution was re-boiled they did not separate, then they must be poured from the smaller vessels into larger vessels and covered over; then the vitriol separating from the alum, it condenses. Both are cut out and put to dry in the hot room, and are ready to be sold; the solution which did not congeal inthe vessels and vats is again poured back into the caldron to be re-boiled. The earth which settled at the bottom of the caldron is carried back to the tanks, and, together with the ore, is again dissolved with water and urine. The earth which remains in the tanks after the solution has been drawn off is emptied in a heap, and daily becomes more and more aluminous in the same way as the earth from which saltpetre was made, but fuller of its juices, wherefore it is again thrown into the tanks and percolated by water.
Alum MakingA—Furnace. B—Enclosed space. C—Aluminous rock. D—Deep ladle. E—Caldron. F—Launder. G—Troughs.[Pg 571]Aluminous rock is first roasted in a furnace similar to a lime kiln. At the bottom of the kiln a vaulted fireplace is made of the same kind of rock; the remainder of the empty part of the kiln is then entirely filled with the same aluminous rocks. Then they are heated with fire until they are red hot and have exhaled their sulphurous fumes, which occurs, according to their divers nature, within the space of ten, eleven, twelve, or more hours. One thing the master must guard against most of all is not to roast the rock either too much or too little, for on the one hand they would not soften when sprinkled with water, and on the other they either would be too hard or would crumble into ashes; from neither would much alum be obtained, for the strength which they have would be decreased. When the rocks are cooled they are drawn out and conveyed into an open space, where they are piled one upon the other in heaps fifty feet long, eight feet wide, and four feet high, which are sprinkled for forty days with water carried in deep ladles. In spring the sprinkling is done both morning and evening, and in summer atnoon besides. After being moistened for this length of time the rocks begin to fall to pieces like slaked lime, and there originates a certain new material of the future alum, which is soft and similar to theliquidae medullaefound in the rocks. It is white if the stone was white before it was roasted, and rose-coloured if red was mixed with the white; from the former, white alum is obtained, and from the latter, rose-coloured. A round furnace is made, the lower part of which, in order to be able to endure the force of the heat, is made of rock that neither melts nor crumbles to powder by the fire. It is constructed in the form of a basket, the walls of which are two feet high, made of the same rock. On these walls rests a large round caldron made of copper plates, which is concave at the bottom, where it is eight feet in diameter. In the empty space under the bottom they place the wood to be kindled with fire. Around the edge of the bottom of the caldron, rock is built in cone-shaped, and the diameter of the bottom of the rock structure is seven feet, and of the top ten feet; it is eight feet deep. The inside, after being rubbed over with oil, is covered with cement, so that it may be able to hold boiling water; the cement is composed of fresh lime, of which the lumps are slaked with wine, of iron-scales, and of sea-snails, ground and mixed with the white of eggs and oil. The edges of the caldron are surmounted with a circle of wood a foot thick and half a foot high, on which the workmen rest the wooden shovels with which they cleanse the water of earth and of the undissolved lumps of rock that remain atthe bottom of the caldron. The caldron, being thus prepared, is entirely filled through a launder with water, and this is boiled with a fierce fire until it bubbles. Then little by little eight wheelbarrow loads of the material, composed of roasted rock moistened with water, are gradually emptied into the caldron by four workmen, who, with their shovels which reach to the bottom, keep the material stirred and mixed with water, and by the same means they lift the lumps of undissolved rock out of the caldron. In this manner the material is thrown in, in three or four lots, at intervals of two or three hours more or less; during these intervals, the water, which has been cooled by the rock and material, again begins to boil. The water, when sufficiently purified and ready to congeal, is ladled out and run off with launders into thirty troughs. These troughs are made of oak, holm oak, or Turkey oak; their interior is six feet long, five feet deep, and four feet wide. In these the water congeals and condenses into alum, in the spring in the space of four days, and in summer in six days. Afterward the holes at the bottom of the oak troughs being opened, the water which has not congealed is drawn off into buckets and poured back into the caldron; or it may be preserved in empty troughs, so that the master of the workmen, having seen it, may order his helpers to pour it into the caldron, for the water which is not altogether wanting in alum, is considered better than that which has none at all. Then the alum is hewn out with a knife or a chisel. It is thick and excellent according to the strength of the rock, either white or pink according to the colour of the rock. The earthy powder, which remains three to four digits thick as the residue of the alum at the bottom of the trough is again thrown into the caldron and boiled with fresh aluminous material. Lastly, the alum cut out is washed, and dried, and sold.
Alum is also made from crude pyrites and other aluminous mixtures. It is first roasted in an enclosed area; then, after being exposed for somemonths to the air in order to soften it, it is thrown into vats and dissolved. After this the solution is poured into the leaden rectangular pans and boiled until it condenses into alum. The pyrites and other stones which are not mixed with alum alone, but which also contain vitriol, as is most usually the case, are both treated in the manner which I have already described. Finally, if metal is contained in the pyrites and other rock, this material must be dried, and from it either gold, silver, or copper is made in a furnace.
Vitriol[11]can be made by four different methods; by two of these methodsfrom water containing vitriol; by one method from a solution ofmelanteria,soryandchalcitis; and by another method from earth or stones mixed with vitriol.
Vitriol MakingA—Tunnel. B—Bucket. C—Pit.[Pg 574]Vitriol MakingA—Caldron. B—Tank. C—Cross-bars. D—Ropes. E—Little stones.[Pg 575]The vitriol water is collected into pools, and if it cannot be drained into them, it must be drawn up and carried to them in buckets by a workman.In hot regions or in summer, it is poured into out-of-door pits which have been dug to a certain depth, or else it is extracted from shafts by pumps and poured into launders, through which it flows into the pits, where it is condensed by the heat of the sun. In cold regions and in winter these vitriol waters are boiled down with equal parts of fresh water in rectangular leaden caldrons; then, when cold, the mixture is poured into vats or into tanks, which Pliny calls wooden fish-tanks. In these tanks light cross-beams are fixed to the upper part, so that they may be stationary, and from them hang ropes stretched with little stones; to these the contents of the thickened solutions congeal and adhere in transparent cubes or seeds of vitriol, like bunches of grapes.
By the third method vitriol is made out ofmelanteriaandsory. If the mines give an abundant supply ofmelanteriaandsory, it is better to reject thechalcitis, and especially themisy, for from these the vitriol is impure, particularly from themisy. These materials having been dug and thrown into the tanks, they are first dissolved with water; then, in order to recover the pyrites from which copper is not rarely smelted and which forms a sediment at the bottom of the tanks, the solution is transferred to other vats, which are nine feet wide and three feet deep. Twigs and wood which float on the surface are lifted out with a broom made of twigs, and afterward all the sediment settles at the bottom of this vat. The solution is poured into a rectangular leaden caldron eight feet long, three feet wide, and the same in depth. In this caldron it is boiled until it becomes thick and viscous, when it is poured into a launder, through which it runs into another leaden caldron of the same size as the one described before.Vitriol MakingA—Wooden tub. B—Cross-bars. C—Laths. D—Sloping floor of the chamber. E—Tub placed under it.[Pg 576]When cold, the solution is drawn off through twelve little launders, out of which it flows into as many wooden tubs four and a half feet deep and three feet wide. Upon these tubs are placed perforated crossbars distant from each other from four to six digits, and from the holes hang thin laths, which reach to the bottom, withpegs or wedges driven into them. The vitriol adheres to these laths, and within the space of a few days congeals into cubes, which are taken away and put into a chamber having a sloping board floor, so that the moisture which drips from the vitriol may flow into a tub beneath. This solution is re-boiled, as is also that solution which was left in the twelve tubs, for, by reason of its having become too thin and liquid, it did not congeal, and was thus not converted into vitriol.