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heap of wood, and setting the pile on fire, in conformity to the manner in which ores were smelted during the burning of forests; but as the force of the fire is greatly diminished by the dispersion of its flame, and as the air acts more forcibly in exciting fire when it rushes upon it with greater velocity, it is likely that the heap of wood and ore would soon be surrounded with a wall of stone, in which sufficient openings would be left for the entrance of the air, and thus a kind of furnace would be constructed.

The Peruvians, we are told, had discovered the art of smelting and refining silver, either by the simple application of fire, or, where the ore was more stubborn and impregnated with foreign substances, by placing it in small ovens or furnaces on high grounds, so artificially constructed, that the draught of air performed the function of a bellows, a machine with which they were totally unacquainted. This method of smelting ores on high grounds, without the assistance of a bellows, or at least of bellows moved by water, seems to have been formerly practised in other countries as well as in Peru. There are several places in Derbyshire, called boles by the inhabitants, where lead has been anciently smelted, before the invention of moving bellows by water; these boles were always situated upon high grounds, and mostly upon that side of a hill which faces the west, probably because the wind proceeds most frequently from that quarter. From a pig of lead, dug up in 1766 at one of these boles, near Matlock, and bearing an inscription in relievo, from which it appears to have been smelted in the age of Adrian, many of the boles in Derbyshire seem to be of high antiquity. However, this method of smelting ore by the variable action of the wind, being a very troublesome and precarious process, has been universally disused, and the more regular blast of a bellows has been introduced in its stead.

As the metals are generally intimately mixed and blended with earthy matter or spar, or often with other metallic matter of inferior value, before the processes of smelting or reduction by fire are resorted to, various mechanical operations are used to free them from such admixtures as much as possible, so that they may be rendered as pure as these means will allow before they go to the furnace.

The following is a brief account of the processes of dressing :-The ores, when first raised from the mines, are in various states; some in large masses from other matter, other large masses containing ores, spars, &c.; small pieces both of pure ore and that which is mixed, and much that is crumbled to small minute frag

ments.

The first operations relate to separating them into proper sizes and qualities by spulling or knocking, sifting or gridling, and picking. The purer parts are then separated, and are often removed at once for smelting after having been broken down to a certain degree of fineness or size. The other or mixed parts are submitted to various processes of washing, but first must be put into a proper state of division by being bruised and sifted to uniform sizes: this is done

either by cobbing and bucking, manual operations; or by crushing and stamping by machines. The processes of washing are very various, but depend on one general principle, that the metallic may be separated from the earthy parts by their different specific gravities. Thus, if both are agitated together in water, the heaviest will sink or be deposited first. This principle is applied by throwing the ores into streams of water, running over planes gently inclined. The ores settle at the upper, and the spar and earthy parts at the lower.

Another way much in use is by agitating the whole in sieves, so fine as to permit but little of the solid matter to pass, but to admit the water freely. By this agitation in water, the ore settles to the bottom of the sieve, and the spar or matrix floats at the top, where it is skimmed off and thrown away, and this is called jegging. When the ores are cleaned by dressing, they are fitted for the operations of reduction or smelting.

The following simple method of smelting is practised by the natives of the province of Mekran in Persia; which, although it may at times leave a trifling portion of the earth mixed with the metal, is, from its ingenuity, worthy of notice. When a sufficient quantity of the ore is collected, it is placed upon a pile of wood, which is set on fire, and constantly replenished with fresh fuel, until the ore melts and falls to the bottom, when it is separated from the ashes, and found to be considerably clearer than wher. first taken from the mine. It is then placed in a pit, made of earthern tiles, so constructed as to admit a fire under it. The ore is again melted in this pit, and a considerable quantity of the dirt and dross removed, by skimming the surface. After this process the metal is lifted out in a liquid state, poured into hollow cylinders of clay, and then sold.

To come to a complete understanding, relative to the processes of smelting, we must bear in mind the compound nature of these substances; observing, first, that all the ores are much mixed with earthy matter, even after the operation of dressing or washing, so that these earthy parts often bear a large proportion to the whole. Secondly, that volatile mineralisers, or substances which may be dissipated or evaporated by heat alone, enter in most cases into the composition of the ores. These, as has been mentioned, are sulphur, arsenic, carbonic acid, as the most common, and having therefore considerable influence on the processes. Thirdly, that other substances are found combined with the metals which cannot be evaporated simply, but may be separated by the addition of other bodies, to which they have greater chemical affinity. These are first and principally oxygen, and occasionally some acids. Lastly, that the metals being obtained, when the foregoing admixtures are got rid of, in a state of union one with the other, or at least to a certain extent, it must follow that, to have the one which we want in a pure state, the other should be separated or destroyed.

The processes which are employed for all these objects are, calcination or roasting; fusion or melting; refining, which is performed in se

veral modes. All these operations require the application of heat; and in most of them it is urged to a great degree of intensity.

The furnaces employed are of two classes. Blast furnaces, where the fire is excited by the use of bellows, or air cylinders constantly working; and air furnaces, where the effect is produced by strong draught, occasioned by the height or construction of the stacks of chimneys. Blast furnaces are almost entirely employed in the reduction of the ores of iron, and are for that purpose constructed of large dimensions. Of a smaller size they are very commonly used in iron foundries, where pig-iron is simply melted for making various articles of cast-iron; and similar furnaces are in use in what are called the blowing-houses in Cornwall, for the finer kind of tin, called grain-tin. Blast furnaces of a small kind, called hearths, are much employed also in Cumberland and Yorkshire for melting lead ore; but they are nearly confined to this district, as the Derbyshire and Welsh smelters prefer air furnaces. The fuel mostly in use for the blast furnaces is coke, or coal charred so as to drive off its bituminous part; this is common for iron. In lead ores the principal fuel is peat or turf, with a small mixture of coal. And for tin ores they employ wood charcoal; coal would not answer, as it would cake together, and prevent the proper action of the furnace.

Air furnaces for smelting are of a construction which is usually called a reverberatory, though they have also some other local appellations. It is not unlike a large flat oven with the fire-place at one end, and the chimney at the other; so that the matter to be acted upon being placed in the bottom, between the flame playing over it, and reverberating upon it, produces the effect desired. These furnaces are used with a gentle draught and a moderate red heat for calcining or roasting, and with a stronger draught and an intense heat for fusion or flowing, and also for refining. They are the furnaces for copper ores, for lead ores in many places, and for the greater part of the tin ores. Common coal is the fuel used in them, and is the best adapted for them, as the strong flame it gives is just what is required, and the fire-places are so constructed that the fire can be stirred and supplied at pleasure.

The first operation which we shall notice, as it is the first in order in the large way, is that of calcination or roasting. The object here is to evaporate the volatile substances, or such as may be driven off by heat, or converted into a gaseous or aëriform state. These are most commonly sulphur or arsenic, and occasionally some acids.

In the roasting of ores, the following attentions must be given :-1. To reduce the mineral previously into small lumps, that the surface may be increased; but they must not be so small, nor placed so compactly, as to prevent the passage of the air and flame. 2. The larger pieces must be placed at the bottom of the pile, where the greatest heat is. 3. The heat must be gradually applied, that the sulphur may not be melted, which would greatly retard its expulsion; and that the spars, fluors, and stones, in

termixed with the ore, may not crack, fly, and be dispersed. 4..The ores not thoroughly roasted by one operation must be exposed to a second. 5. The fire may be increased towards the end, that the noxious matters more strongly adhering may be expelled. 6. Fuel which yields much flame, as wood and fossil coals free from sulphur, is said to be preferable to charcoal or cokes. Sometimes cold water is thrown on the calcined ore, at the end of the operation, while the ore is yet hot, to render it more friable. No general rule can be given concerning the duration or degree of the fire, these being very various according to the difference of the ores. A roasting during a few hours or days is sufficient for many ores; while some, such as the ore of Rammelsberg, require that it should be continued during several months.

Schlutter enumerates five methods of roasting ores. 1. By constructing a pile of ores and fuel placed in alternate strata, in the open air, without any furnace. 2. By confining such a pile within walls, but without a roof. 3. By placing the pile under a roof, without lateral walls. 4. By placing the pile in a furnace consisting of walls and a roof. 5. By roasting the ore in a reverberatory furnace, in which it must be continually stirred with an iron rod.

The German process for extracting_sulphur from pyrites may be thus described :—It ought, in the first instance, to be exposed to a heat sufficient to sublime the sulphur, or to make it distil in vessels, which must be close to prevent its burning. The furnaces employed for this operation are oblong, like vaulted galleries; and in the vaulted roofs are made several openings. These are called furnaces for extracting sulphur. In these furnaces are placed earthenware tubes, filled with pyrites broken into pieces of the size of small nuts. Each of these tubes contains about fifty pounds of pyrites. They are placed in the furnace almost horizontally, and have scarcely more than an inch of descent. The ends, which come out of the furnace five or six inches, become gradually narrower. Within each tube is fixed a piece of baked earth in form of a star, at the place where it begins to come narrower, in order to prevent the pyrites from falling out, or choking the mouth of the tube. To each tube is fitted a receiver, covered with a leaden, pipe, pierced with a small hole to give air to the sulphur. The other end of the tube is exactly closed. A moderate fire is made with wood, and in eight hours the sulphur of the pyrites is found to have passed into the receivers. The residuum of the pyrites, after distillation, is drawn out at the large end, and fresh pyrites is put in its place. From this residuum, which is called burnings of sulphur, vitriol is extracted.

The eleven tubes, into which were put, at three several distillations, in all 900lbs. of pyrites, yield from 100lbs. to 150lbs. of crude sulphur, which is so impure as to require to be purified by a second distillation. This purification of crude sulphur is also done in a furnace in form of a gallery, in which five cucurbits are arranged on each side. These cucurbits are placed in a sloping direction, and contain about eight quintals and a half of crude sulphur. To them are

Juted earthen tubes, so disposed as to answer the purpose of capitals. The nose of each of these Lubes is inserted into an earthen pot, called the forerunner. This pot has three openings; namely, that which receives the nose of the tube; a second smaller hole, which is left open to give air; and a third in its lower part, which is stopped with a wooden peg.

When the preparations are made, a fire is lighted, about seven o'clock in the evening, and is a little abated when the sulphur begins to distil. At three o'clock in the morning the wooden pegs, which stop the lower holes of the forerunners, are for the first time drawn out, and the sulphur flows out of each of them into an earthen pot with two handles, placed below for its reception. In this distillation the fire must be moderately and prudently conducted; otherwise less sulphur will be obtained, and it would also be of a gray color, and not of the fine yellow which it ought to have when pure. The ordinary loss in the purification of eight quintals of crude sulphur is, at most, one quintal.

When all the sulphur has flowed out, and has cooled a little in the earthen pots, it is cast into moulds made of beech-tree, which have been previously dipped in water, and set to drain. As soon as the sulphur is cooled in the moulds, they are opened, and the cylinders of sulphur are taken out and put up in casks. These are called roll-brimstone.

There are some ores which contain so much sulphur that part of it is actually collected in the ordinary operation of roasting, without much trouble for that purpose. Such is the ore of Ramelsberg, in the country of Hartz. This ore, which is of lead, containing silver, is partly very pure, and partly mixed with cupreous pyrites and silver; hence it is necessary to roast it. The roasting is performed by laying alternate strata of ore and wood upon each other in an open field, taking care to diminish the size of the strata as they rise higher; so that the whole mass shall be a quadrangular pyramid truncated above, whose base is about thirty-one feet square. Below, some passages are left open, to give free entrance to the air; and the sides and top of the pyramid are covered over with small ore, to concentrate the heat and make it last longer. In the centre of this pyramid there is a channel which descends vertically from the top to the base. When all is properly arranged, ladles full of redhot scoria, from the smelting furnace are thrown down the channel, by which means the shrubs and wood placed below for that purpose are kindled, and the fire is from them communicated to all the wood of the pile, which continues burning till the third day. At that time the sulphur of the mineral becomes capable of burning spontaneously, and of continuing the fire after the wood is consumed.

When this roasting has been continued fifteen days the mineral becomes greasy; that is, it is covered over with a kind of varnish; twenty or twenty-five holes or hollows are then made in the upper part of the pile, in which the sulphur is collected. From these cavities the sulphur is taken out thrice every day, and thrown into water. This sulphur is not pure, but crude; and is

therefore sent to the manufacturers of sulphur, to be purified in the manner above related. The calcination of copper, lead, and tin ores, is performed in reverberatory furnaces at a moderate red heat. In the copper works in South Wales, each furnace contains full three tons of raw ores, which are frequently burned, to expose fresh surfaces, for twelve hours. Lead ores are treated in the same manner, in the same furnace often, which, with a higher heat, is used to melt them, and the charge seldom exceeds a ton. Tin ores being simple oxides, and not decomposable in this way, are roasted or calcined principally to alter the specific gravity of the pyrites with which they are mixed, which thus may be separated by subsequent dressing or washing. The furnaces for this purpose, in Cornwall, are called burning-houses. Iron ores, though commonly oxides, are often mixed with sulphurets or iron pyrites, and are roasted to free them from the sulphur; this, however, is not done in furnaces, but the ore is stratified with refuse coal, and burnt in large heaps in the open air.

At the Paris and Mona copper mines in the island of Anglesey, where the ores are poor in metal, but contain a large proportion of sulphur, they are treated in the same way, except that they do not find it necessary to use coal, as a small quantity of wood is sufficient to set the ore on fire, and combustion goes slowly on, owing to the sulphur; a heap of 300 or 400 tons is eight months in burning, and some of the sulphur is sublimed and is condensed in chambers or vaults, to which the flues are conducted.

In the process of calcination sulphur is generally inflamed, and, uniting with the oxygen of the atmosphere, is converted into sulphurous acid gas; which mixed, as it is, with the vapor of certain volatile metals, such as arsenic, zinc, antimony, or lead, forms a dense or suffocating smoke destructive of vegetation; but it does not appear so prejudicial to animal life, except where lead is prevalent. Whoever has seen the country round the copper works at Swansea, will have observed the desolating effect of the smoke; and yet it is proved, on the best evidence, that the men are not subject to any peculiar disease. One set of works there, belonging to Messrs. Vivians, who purchase the ores from the mines in Cornwall, sometimes work at the rate of 600 tons per week. These gentlemen have some time back constructed, at a great expense, erections to condense the noxious vapors, and upon which they have consulted Mr. Philips and other eminent chemists. They have altogether eightyfour reverberatory furnaces, of which twenty-five are used for calcining.

The ores being deprived of sulphur, or at least to a certain degree (for one calcination does not effect this completely), the next step in smelting is to get rid of all the earthy matter, which is done at once by the simple operation of bringing the whole into a state of fusion. It has already been stated that some of the metallic oxides combine with certain earths in fusion, and act powerfully as a flux, which is a term employed for substances that promote the fusibility of others in the fire. It is also necessary to remark, that although a single earth, as silex, for instance, is nearly in

fusible by itself in our strongest fires; yet, by mixing the earths together, their infusibility is increased, and we obtain the power of rendering them all fluid by heat. Further, that some of the earths and some of the metallic oxides possess this influence in a greater degree than others. Thus lime, in all its states, but particularly in that of fluor-spar, and oxide of lead, are the most powerful assistants of the fusion of earthy matter in general, or the best fluxes. Many salts, indeed, possess this property to a much greater extent; but they are far too expensive for use in the larger operations of smelting, though they are much used for trials in the small way, called assays.

Now as the ores commonly contain different mixtures in different mines, and as it results from what has been said that such a combination as may be thus expected is useful in promoting the fusion of the whole, the smelters find it desirable to mix the ores from different veins on this account; but, as even this does not always succeed sufficiently, an addition is commonly made of lime, limestone, or fluor-spar. With a mixture of these the ores are submitted to the strongest action of the fire; complete fusion of the whole mass takes place; the earthy parts form a fluid impure glass, being completely vitrified; the metallic parts of the ore, either quite free from sulphur, or in a degree combined with it, are also entirely melted, and a perfect separation takes place; owing to the great difference in the specific gravity of the substances: the earthy glass in a liquid state, which is now called slag or scoria, occupying the upper place, and the metallic part by its weight sinking down and forming a liquid stratum of melted metal underneath, where also it is prevented from oxidation and evaporation from the intense heat applied. The whole is in some cases stirred, to assist the precipitation of the metallic matter to the bottom of the furnace; in other cases this is left to take place of itself.

The fusion of copper ore is conducted in reverberatory furnaces at a high degree of heat, and the slag is raked off in a fluid state. Lead and tin ores are treated in a nearly similar manner.

Iron smelting is carried on in blast furnaces of very large dimensions. in which coke is employed as fuel, and limestone is used as a flux. Copper of the first flowing is in part combined with sulphur, so as to require subsequent calcinations and repeated fusions before it comes to the refining process. Lead is generally produced pure in one operation from the reverberatory furnace, and also from the blast-furnace, where the sulphur is dissipated partly by the application of heat, and partly by combining with the lime which is used. Tin, being produced from an oxide, some carbonaceous matter, such as small-coal, is used in mixture with the ores, the carbon unites with the oxygen and leaves the metal pure, except as it may happen to be mixed with other metallic substances.

By the operations which have been described the whole metallic contents of the ores are produced in a separate state, the volatile part being dissipated by calcination, and the earthy part by being converted into slag, which is easily detached from

the metal. It is evident, however, that if more metals than one exist in the ores they will all be reduced by the same treatment, and therefore we may, and often do, procure an alloy more or less complicated.

The purification of the metals is performed by various processes of refining, which are suited to their several qualities, and advantage is taken of the different properties in each to effect this. Thus, some metals are refined by their having less affinity for oxygen than others; such as gold, silver, and copper; these, not being easily oxidised in the fire, may be exposed to a strong and continued heat, which converting the inferior metals into oxides, they rise to the surface of the melted mass, from which they may be removed by various means. An example of this is the separation of lead from silver. This operation is called testing or cupellation. Another mode of refining is, when one metal is more fusible than another, whereby a separation of the two may effected. Thus tin of the first melting often contains some iron or copper, but, being melted at a very low red heat, the tin oxides, leaving the others, which do not flow but at a higher temperature. Silver is separated from copper when it is in small proportions, by adding lead to the whole infusion. The silver unites with the lead, and is separated with it afterwards by a heat which melts it out from the copper. This process is called eliquation. The silver is separated from the lead afterwards by cupellation, which is a process adapted also to procuring gold.

Where metals in the state of oxide are to be reduced into their malleable or proper form, it is done by fusion, in contact with carbon, as was described in the case of tin ores; and they are therefore mixed with small-coal, wood, or charcoal. The oxygen leaves the metal, and forms, with the carbon, carbonic acid, which escapes. Thus litharge, which is the oxide of lead obtained by cupellation, is again brought into the state of lead: this process is called reviving. Iron, in its perfect state, is nearly infusible, and it must be largely combined with carbon to make it melt freely; on which account we see the use of smelting the ores in contact with coke. The carbon is separated when it is converted into bar-iron; and, in converting this into steel, carbon is again made to combine in another proportion. Copper requires, after it is freed as much as possible from the other metals, a peculiar treatment with charcoal, and a continued melting heat; which process is called toughening. The melted metal is much stirred with wood poles, and after a time assumes the required properties of extending under the hammer without being subject to crack. The theory of this process is rather obscure. The volatile metals would of course be dissipated if they were exposed to the heat requisite for melting them out from the substances with which they are mixed in their ores in open furnaces; they are therefore distilled in retorts, which are generally made of iron. Distillation is employed in this country for obtaining zinc, and abroad also for this metal and in the mines of mercury.

The mode of extracting the precious metals most in use in Hungary and other parts of Ger

many, as well as in all the American mines, is that of amalgamation of the ores with mercury. By this process the gold or silver is dissolved by the mercury and separated from the earthy mixture, and also from baser metals, which do not so readily combine with mercury. This process requires, however, that the ores should be previously calcined to decompose the sulphurets, and an addition of common salt is added to facilitate this decomposition; the whole is then finely powdered and triturated in water with the mercury by machines. Subsequent distillation separates and preserves the mercury, and the gold or silver is refined in the usual way.

The metals raised in this country form an important part of our national wealth: they are exported in considerable quantities in their unmanufactured state; but a greater proportion are worked up into innumerable forms, and thus contribute much more largely to the general stock, in the employment and encouragement of industry and ingenuity. The most important metals produced in Great Britain are, iron, copper, lead, tin. With respect to the first, the iron-works of this country, as is well known, are of immense extent, and are rapidly increasing in produce. By improved methods of manufacture iron has, of late years, been much reduced in price, and this has increased the demand both at home and abroad. The manufacture of iron may be computed at Wales

150,000 tons.

[blocks in formation]

The quantity of copper raised is about 10,000 tons; of which about 8000 tons are produced in Cornwall, and the remainder in Anglesey, Devon, Ireland, and Staffordshire. In the year 1800 the quantity of copper raised in the Cornish mines was between 5000 and 6000 tons; so that there has been an increase since that time of from 2000 to 3000 tons. The value of the whole quantity of copper in its unmanufactured state is about £1,000,000.

The lead of Great Britain probably amounts to from 30,000 to 32,000 tons. The northern parts of the kingdom, Cumberland, Durham, and Northumberland, produce North Wales and Shropshire

12,000 tons.

8,000

Yorkshire

4,500

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quantities of zinc, manganese, silver, antimony, and cobalt; but of these it is difficult to estimate the quantity or value.

The aggregate value of the metals of the kingdom is thus more than £4,000,000, but is increased enormously when manufactured; and they are the foundation of important branches of our commerce in our unrivalled fabrication of hardware.

Iron is exported to almost all parts of the world in its raw, as well as in its manufactured states, and in an infinite diversity of useful and ornamental forms which it would be tedious to attempt to describe.

Copper is employed largely in its simple state, particularly rolled into sheet; and is also very much used in mixture with other metals, it being the principal constituent in brass, gun-metal, and pot-metal. The town of Birmingham alone is said to require 2000 tons a year for its varied manufactures. About 3000 tons have of late been annually sent to the East Indies and America, United States; the West Indies and different countries in Europe take from us considerable supplies.

Of the large portion of lead which our mines produce a considerable part is worked up into forms which at once destroy it, so that it does not return again for use. Thus 5000 tons a year are made into small shot, partly for home consumption and partly for exportation. The quantity made into white and red-lead and principally used as pigments, and part converted into the glazing of pottery, or an ingredient of glassmaking, is little, if at all, short of 10,000 tons.

Tin is an article of export to most countries; a great deal is often sent to China; and, in the manufacture of tin plate, or thin rolled iron coated with tin in the manner before described, is a large article of commerce.

Swedenborgius has very industriously and exactly described the different processes used in most parts of Europe, for the smelting of ores of iron, for the forging of that metal, and for the conversion of it into steel; but we do not find that he, or any other author, have, by experiments and discoveries, contributed much to the illustration or to the improvement of this part of metallurgy; unless, perhaps, we except those of M. Reaumur, concerning the softening of castiron by cementation with earthy substances. The ores of iron are known to vary much in their appearance, in their contents, in their degrees of fusibility, in the methods necessary for the extraction of their contained metal, and in the qualities of the metal when extracted.

Most ores require to be roasted previously to their fusion; some more slightly, and others with a more violent and long-continued fire. Those which contain much sulphur, arsenic, or vitriolic acid, require a long-continued and repeated roasting, that the volatile matters may be expelled. Of this kind is the black iron ore, from which the Swedish iron is said to be obtained.. Some ores require a very slight roasting only, that they may be dried and rendered friable. Such are the ores called bog ores, and others, which being in a calcined state, and containing little sulphureous matter, would, by a farther

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