REDUCTION AND ANALYSIS OF.

In the treatment of metallic ores, it has been already hinted, that two objects are in view: the one is to obtain a knowledge of the nature and proportions of their component parts; and the other is to be acquainted with the best methods of separating the metals which they contain, that they may be applied in their pure or uncombined state to useful purposes. In the following treatise, therefore, we shall keep in view the same objects; and under each of the metals we shall first detail the most improved methods of analysing its different ores; and, secondly, give a short account of the best and most approved processes that are employed in their reduction. The last object, however, refers only to some of the metals, others not being found in sufficient quantity, or not being applicable to useful purposes.

In this treatise we shall consider the metals in the same order in which they have been described under Mineralogy, and to each metal we shall devote a particular chapter.

CHAP. I. Of the Ores of Platina.

Platina, on account of its insusibility, density, and indestructibility, is one of the most important and useful of the metals yet known, and particularly for different chemical instruments and utensils, because there are few chemical agents whose effects it cannot resist. Platina is only found in the state of alloy, with rhodium and palladium, two of the newly discovered metals; and it is accompanied also with another alloy, iridium and osmium, also newly discovered metals, as well as with particles of iron, gold and some other substances. The discovery of these metals, and the importance of platina itself, have rendered the ores of this metal peculiarly interesting. We shall therefore in the present chapter, give a pretty full detail of the methods of analysing the ore, and of working it for the purposes of manufacture. These subjects will occupy the two following sections.

SECT. I. Of the Analysis of the Ores of Platina.

The whole of the platina which is brought to Europe, has been previously subjected to the process of amalgamation in South America; and hence it happens, that a small quantity of mercury remains in it, sometimes in very small distinct particles, but more commonly in a state of combination with gold, in the form of an amalgam. In treating the ores of platina, therefore, the first object is to separate the mercury, and the easiest process is to drive it off by means of heat, either in an open ladle, if it be not intended to collect the mercury, or in an earthen retort, if the object of the operator be to retain that metal. The platina remaining after the mercury is thus driven off, appears much yellower, because the particles of gold dispersed through it exhibit their peculiar colour. The ore is next to be spread out thin on a smooth table, and by means of a pair of common bellows, the lighter particles may be separated with tolerable Platina, lighter accuracy from the heavier ones. The lighter particles in the ore are found, on examination, to be minute crystals and fragments of quartz, and two kinds of iron ore, which are also in fragments, or in the form of small octahedrons. Some of the particles of iron are attracted by the magnet, forming the ore of iron called magnetic iron-sand; but others, which are not attracted by the magnet, give out, when roasted, a slight sulphurous odour.

The lighter particles being separated by mechanical action, the heavier particles are to be treated with a small quantity of slightly diluted nitro-muriatic acid, and by this means the whole of the gold is taken up, with a portion of iron, and a small quantity of platina and other ingredients. The gold may be thrown down from this solution by adding green sulphate of iron, and it may be purified by mixing it with nitre and borax. If the quantity of platina to be purified be considerable, it is an object worth the attention of the chemist, to separate and collect the gold, because the proportion of the latter contained in crude platina is not small. Prost obtained seven ounces of gold from a quantity of platina consisting of 100 ounces; and from another quantity of the same weight he separated not less than 13 ounces of gold*. It may be observed that the platina which is whitest, is found to be the richest in gold, and that the black varieties scarcely contain any at all.

The gold being separated, the platina is next to be digested in nitro-muriatic acid, and excepting a black matter, the whole is dissolved. This black matter, when first observed, was supposed to be plumbago; but it appears from the discovery of Mr Tennant, to be a compound of two new metals, to which he has given the names of osmium and iridium. By adding muriate of ammonia to the nitro-muriatic solution, almost the whole of the platina is precipitated in the form of a yellow powder. This powder is a muriate of ammonia and platina, and it is nearly insoluble. The solution being next treated with zinc, the whole of its metallic contents, excepting the iron, are thrown down. The precipitate thus obtained is to be washed and digested in nitric acid much diluted. By this means the copper and lead with which crude platina is usually contaminated, are separated. The remainder is to be dissolved in nitro-muriatic acid; to the latter solution add common salt, and evaporate the whole to dryness; the salt remaining contains the muriates of soda and of platina, palladium and rhodium; and as the salt of rhodium is found to be insoluble in alcohol, it may, by means of it, be separated from the former. The platina and palladium now remain in the alcoholic solution, and from this the greater part of the platina may be separated by means of muriate of ammonia; and after diluting the solution by adding prussiate of potash, a deep orange precipitate is obtained, which is palladium. By concentrating the remaining liquor, the platina may be precipitated by means of muriate of ammonia.

Sect. II. Of the Methods of working Platina.

Platina, on account of its peculiar properties in resisting great degrees of heat and the action of many of the most powerful chemical agents, is by far the most important and valuable of the metals yet known for the purpose of constructing various instruments and utensils, which are found highly useful in chemical analysis. But the refractory nature of this metal has presented many difficulties, and has greatly exercised the ingenuity and skill of chemists and artists to rendered it malleable and capable of assuming the requisite forms. It has been observed that the largest and whitest grains picked out from crude platina have a considerable degree of malleability even when cold; but when they are heated, this property appears in greater perfection: and if two of these grains be brought into contact, and subjected to the highest degree of white heat, the stroke of a hammer will make them adhere more or less perfectly. In this way, a small mass of metal may be obtained by the union of a few grains. But it is obvious that the patience and dexterity required in this slow and tedious process will prevent it from being practically useful.

In the progress of experiments made on platina it was discovered that arsenic combined readily with that metal, and formed an alloy of easy fusibility. The great volatility of the arsenic, particularly when in contact with charcoal, gave reason to hope that the whole of it, by proper management, might be driven off, leaving the platina behind in a mass, and retaining its peculiar and characteristic properties. In this way different chemists succeeded in forming, of this alloy, crucibles and other chemical utensils, which were found to be less fusible than silver, and were capable of resisting many of the common chemical agents. The most successful method of rendering platina malleable, and working it by means of this alloy, was discovered by Jeanety, a Parisian silversmith, who long directed his attention to this object. An account of his method has been given by Berthollet and Pelletier, of which the following is an abstract*.

The crude platina being first ground in water, and washed for the purpose of separating the earthy matters, three half pounds of the metal, three pounds of white arsenic, and one pound of pearl ashes, are to be well mixed together. A crucible, capable of holding 20 pounds of this mixture, is then to be placed in a furnace of any convenient construction. When the crucible is thoroughly red hot, introduce one-third of the mixture, and continue stirring it with a rod of platina till it comes to a state of quiet fusion; then add another one-third, stirring it in the same manner till the fusion is completed, and afterwards add the remaining one-third, and apply a strong heat, so that the whole may become very fluid. Then withdraw the crucible, and when it has cooled gradually, break it up; a well formed metallic button will be found in it, covered by blackish brown scoriae, which has a considerable action on the magnetic needle. The button, which is very brittle, being broken to pieces, is to be fused again with white arsenic and pearl ashes as before, and the metallic mass obtained from this second fusion is generally found to have no effect on the magnetic needle; but if this should not be the case, a third fusion in the same way becomes necessary.

The first step of the process is now completed. A flat-bottomed cylindrical crucible, about three inches and a half in diameter, is to be made thoroughly hot in a furnace, and charged with one pound and a half of the arsenicated platina, mixed with a equal weight of white arsenic, and one half pound of pot-ash; and when this mixture... Platinum mixture has been completely fluid, the crucible is to be removed from the fire, and allowed to cool in a horizontal position, that the thickness of the cake of metal may be uniform. When the crucible is cold, it is to be carefully broken, and the scoriae being removed, a cake of metal is obtained, well-formed and sonorous, weighing three ounces more than the arsenicated platinum employed. The metal is now quite saturated with arsenic. It has been observed, that there is no inconvenience from incorporating too much arsenic, for it would appear that the full success and rapidity of the purification of the platinum, are exactly in proportion to the quantity of arsenic with which it has been previously combined.

The mass of metal thus obtained, is placed in a muffle, and the heat is gradually increased, till the evaporation of the arsenic commences; after which the temperature is to be kept up as nearly as possible at the same degree, for the space of six hours, carefully watching not to increase it, lest the cake should be brought to a state of fusion. At the end of the six hours, the cake has usually become considerably porous; it is then to be withdrawn, and extinguished in common oil; after which it is returned to the muffle, by which means a further quantity of arsenic is drawn off; and this alternate heating and application of oil are to be continued till the arsenic no longer makes its appearance. In proportion as the arsenic is driven off, the fusibility of the mass diminishes, so that a greater degree of heat may be applied in the latter stage of the process. After having carefully burnt off at a high degree of heat the whole of the charcoal which is produced by the decomposition of the oil, the spongy cake of metal is to be digested in nitrous acid, and then edulcorated by repeated boiling in water. Three or more of the cakes are then to be placed in a crucible, and exposed to the highest degree of heat in a powerful furnace, and while they are thus rendered soft, an iron pestle let down upon them, will make them cohere; and being withdrawn from the crucible, they are to be heated to the utmost in a smith's fire, and carefully forged like iron on the anvil, into compact bars.

The cheapness of the process now detailed is the only advantage which it holds out, for the platinum does not require to be previously dissolved in nitromuriatic acid; but it is to be observed, that the metal by this treatment is by no means perfectly pure; a small portion of arsenic and iron still adhering to it, and probably some lead and copper, which may have been accidentally mixed with the ore, while it contains the whole of the palladium, osmium, iridium, and rhodium; and thus contaminated, it is obvious, that it must be less capable of resisting the action of alkalis, and high degrees of heat without injury, than when it is brought to a state of greater purity. Accordingly, other processes for the purification of this valuable metal, have been contrived and practised.

The following is the processes proposed by Count Mousin Poushskin, to render platinum malleable. 1. Precipitate the platinum from its solution by muriate of ammonia, and wash the precipitate with a little cold water.

2. Reduce it in a convenient crucible to the well-known spongy metallic texture, which wash two or three times with boiling water to carry off any portion of saline matter which may have escaped the action of the fire.

3. Boil it for about half an hour in as much water, mixed with one-tenth part of muriatic acid, as will cover the mass to the depth of about half an inch, in a convenient glass vessel. This will carry off any quantity of iron that might still exist in the metal.

4. Decant the acid water, and edulcorate or strongly ignite the platinum.

5. To one part of this metal take two parts of mercury, and amalgamate in a glass or porphyry mortar. This amalgamation takes place very readily. The proper method of conducting it is to take about two drams of mercury to three drams of platinum, and amalgamate them together; and to this amalgam may be added alternate small quantities of platinum and mercury till the whole of the two metals are combined. Several pounds may be thus amalgamated in a few hours, and in the large way a proper mill might shorten the operation.

6. After the amalgam is completely produced, it must be quickly moulded in bars or plates, or any other forms that may be preferred; taking care that these moulded pieces should at least be half an inch in thickness, and of a proper length to manage them afterwards in the fire; it is also requisite that the mould should be perfectly even and smooth. Half an hour after the pieces are formed they begin to harden by the oxidation of the mercury, and change their brilliant metallic colour for a dull leaden ore.

7. As soon as the pieces have acquired a proper degree of hardness to be handled without danger of breaking, which commonly takes place in a little more than an hour, place them in a proper furnace, and keep them ignited under a muffle or in a small reverberatory. No other precaution is necessary in this operation, but that of not breaking the pieces during their transport. The mercury flies off during the heat, and the platinum remains perfectly solid; so that, after being strongly ignited two or three times before the bellows, it may be forged, or laminated in the same manner as gold or silver; care being taken, at the commencement of the forging, or of passing it between rollers, not to apply too great a force till the metal has acquired all its density. It is almost superfluous to add, that in evaporating the mercury from large quantities of amalgam, a proper apparatus, such as in the silver amalgamation, must be employed, to receive the volatilized mercury; but for small quantities, where the loss of this metal is of no consequence, the furnace must have a proper chimney to carry off the metallic vapours. When the platinum comes out of the first fire, its dimensions are about two thirteenth parts smaller every year than the original amalgam from the mould. The whole of this operation seems to be governed by the pressure of the atmosphere and the laws of cohesive attraction: for the air is driven out from between the molecules of the platinum, which by their solution in mercury are most probably in their primitive and consequently uniform figure. It is very visible, and at the same time a very amusing phenomenon to observe, (during the process of ignition, which is performed in four or five minutes), how the platinum contracts every way into itself, as if pressed by some external force."

The count then adds, "that, as soon as my amalgam of mercury is made, I compress the same in tubes of wood, by the pressure of an iron screw upon a cylinder of wood, adapted to the bore of the tube. This forces out the superabundant mercury from the amalgam, and A simpler method for rendering platina malleable, at the same time not less effectual, has been proposed by Mr Knight. The following is an account of this method in the words of the author.

"To a given quantity of crude platina, I add fifteen times its weight of nitro-muriatic acid (composed of equal parts of nitric and muriatic acid) in a tubulated glass retort, with a tubulated receiver adapted to it. It is then boiled, by means of an Argand's lamp, till the acid has assumed a deep saffron colour; it is then poured off; and if any platina remain undissolved, more acid is added, and it is again boiled until the whole is taken up. The liquor, being suffered to rest till quite clear, is again decanted: a solution of sal-ammoniac is then added, by little and little, till it no longer gives a cloudiness. By this means the platina is thrown down in the form of a lemon-coloured precipitate, which having subsided, the liquor is poured off, and the precipitate repeatedly washed with distilled water till it ceases to give an acid taste; (too much water is injurious, the precipitate being in a certain degree soluble in that liquid): the water is then poured off, and the precipitate evaporated to dryness.

"So far my process is in a great measure similar to that which some others have also followed; but my method of managing the subsequent, and which are indeed the principal manipulations, will be found to possess many advantages over any that has yet been made public. The best process hitherto followed has been, to give the precipitate a white heat in a crucible, which in some measure agglutinates the particles; and then to throw the mass into a red-hot mortar, or any similar implement, and endeavour to unite them by using a pestle or stamper. But the mass is so spongy that it is hardly possible to get a single stroke applied to it before the welding heat is gone; and though by peculiar dexterity and address some have in this way succeeded, it has been found to require such innumerable beatings and hammerings, that most of those who have attempted it, have either failed entirely, or given it up as being too laborious and expensive. I have succeeded in obviating all these difficulties by adopting the following simple, easy, and expeditions method:

"A strong, hollow, inverted cone of crucible earth being procured, with a corresponding stopper to fit it, made of the same materials, the point of the latter is cut off about three-fourths from the base. The platina, now in the state of a light yellow powder, is pressed tight into the cone, and a cover being fixed slightly on, it is placed in an air furnace, and the fire raised gradually to a strong white heat. In the mean time the conical stopper, fixed in a pair of iron tongs suitable for the purpose, is brought to a red or to a bright red heat. The cover being then removed from the cone, the tongs with the heated stopper is introduced through a hole in the cover of the furnace, and pressed at first gently on the platina, at this time in a state nearly as soft as dough, till it at length acquires a more solid consistence. It is then repeatedly struck with the stopper, as hard as the nature of the materials will admit, till it appears to receive no farther impression. The cone is then removed from the furnace, and being struck lightly with a hammer, the platina falls out in a metallic button, from which state it may be drawn, by repeatedly heating and gently hammering, into a bar fit for flatting, drawing into wire, planishing, &c.

"Besides the comparative facility of this process, it has the farther advantage of rendering the platina much purer than when red-hot iron is obliged to be had recourse to; for platina, when of a white heat, has a strong affinity for iron, and, with whatever care it may have been previously separated from that metal, will be found to have taken up a portion of it, when it is employed of a red heat, to serve to unite the particles of the platina. To the superior purity of platina, rendered malleable by the process before described, I attribute the greater specific gravity which I find it to possess, than that prepared by other methods. Having taken the specific gravity of about ten pennyweights of it, which I had previously passed repeatedly through a flatting mill, I found it to be 22.267."

Another method, which has been successfully practised, was contrived by Mr Cock. The following is an account of his process. After the solution of the platina in nitro-muriatic acid, the liquor is filtered through clean sand, for the purpose of separating the black powder which floats in it. The clear solution is then decomposed by means of sal ammoniac; the yellow precipitate being collected, is to be moderately well washed in warm water and dried; and being distributed into saucers placed in a small oven, constructed for the purpose, in which they are to be exposed for a short time to a low red heat, that the platina may be brought to the metallic state, and the greater part of the sal ammoniac may be sublimed. When the platina, after this treatment, is withdrawn, it is in the form of a gray coloured, spongy mass; and in this state half an ounce of it is to be put into a strong iron mould, one inch and a half wide, and two and a half long. It is then to be compressed as strongly as possible, by striking with a mallet upon a wooden pestle accurately cut to fit the mould; another half ounce is then added, and treated in the same manner, till six ounces have been forced into the mould; a loose iron cover, just capable of sliding down the mould, is then laid upon the platina. This part of the process requires particular care; for if any material quantity of air be left in the mass, the bar into which it is formed is extremely apt to scale and be full of flaws in the subsequent operations. The pressure being properly made, the mould is to be taken to pieces, and the platina will be found in the form of a dense compact parallelopiped. It is next to be placed in a forge fire of charcoal, and heated to the most intense white heat, in order to drive off the muriate of ammonia which remains: this being done, it is to be quickly placed on a clear bright anvil, and gently hammered in every direction by a clean hammer. This is several times to be repeated, at the end of which the mass will be perfectly compact, and fit to be laminated or wrought in any other manner at the pleasure of the artist. It is to be observed, that while the platina is heating, it must be loose in the fire, for if it were held by the tongs, they would infallibly become welded to the platina, and by this means greatly damage it. When the platina is thus drawn down to a compact bar, it will be covered by a semivitreous crust, somewhat somewhat reddish, chiefly proceeding from particles of the ashes melted down upon it, and extended by the hammer over its surface. To remove this, the bar, after being made red hot, is to be sprinkled over with glass of borax reduced to powder, and then kept at a white heat for a few minutes; it is to be plunged into diluted muriatic acid when moderately cool, by which the borax and other vitreous matters will be dissolved, and the platina with a perfectly clean white surface left behind.

**CHAP. II. Of the Ores of Gold.**

Gold exists in nature only in the metallic state; but it is scarcely ever found perfectly pure, for it is alloyed in different proportions with silver, copper, tellurium, and some other metals. When it is alloyed with silver or copper, or even with both, the gold retains its ductility; but when combined with tellurium, its distinctive characters entirely disappear.

**Sect. I. Of the Analysis of the Ores of Gold.**

The method of analysing gold ores is very simple. The principal difficulty with which it is attended arises from the small proportion of this metal contained in the greater part, even of those ores which are considered as very rich. Native gold contains invariably, but generally in small proportion, silver or copper, and sometimes both, and the gangue is often a very hard quartz. In this case the following is an approved mode of proceeding. Reduce the ore to fine powder, mix it with six times its weight of carbonate of soda, or, what answers better, with four parts of carbonate of soda, and one of glass of borax: put the mixture into an earthen crucible, and melt it. Pour out the fused mass on a stone slab, and detach the small portion remaining in the crucible by means of a little diluted muriatic acid. Reduce the mass to coarse powder; put it into a flask with the muriatic solution; add strong muriatic acid, and apply a gentle heat. Continue the digestion, adding from time to time a little nitrous acid, till no farther action is produced, and the undissolved residue becomes of a pure white colour. Then pour off the liquor, wash the residue, and add the washings to the liquor.

1. After the insoluble residue is dried, expose it to the sun, and if it contain any muriate of silver, it will assume a purplish colour. When this is the case, let it be mixed with three times its weight of pearl-ash, and fused in an earthen crucible for five minutes. The silver will thus be reduced to metallic globules, and will be obtained pure by digesting it in muriatic acid, which combines with the earth and alkali, but does not act on the silver.

2. The nitro-muriatic solution is now to be carefully neutralized by means of soda or of potash; and a solution of green sulphate of iron is to be added, as long as any precipitate is formed. The precipitate thus obtained is gold, and this being carefully collected, is to be fused in a small crucible with nitre just in sufficient quantity to cover its surface.

3. The residual liquor, after being decomposed by the carbonate of an alkali, and the precipitate being well washed, is to be digested in liquid ammonia, to dissolve the copper. The ammoniacal solution being slightly super-

saturated with muriatic acid, a rod of zinc being introduced, will precipitate the copper in the metallic state.

**Auriferous pyrites.** It appears that iron pyrites of a bronze yellow colour in masses, or in striated cubes, and hepatic pyrites, which are found in veins in primitive mountains, contain a quantity of pure gold, or of gold alloyed with silver, which is worth the trouble and expense of extracting it. A considerable proportion, not only of the American, but also of the Hungarian gold, is obtained from ore of this kind. The produce of the latter sometimes does not exceed a few grains of gold in the quintal, but occasionally the auriferous pyrites of the Hungarian mines yield not less than 450 ounces of gold in the quintal of the ore.

The following is the method of analysis to be followed in ores of this kind. The pyrites being reduced to powder, is digested in muriatic acid, occasionally adding a small portion of nitric acid, till every thing soluble is taken up. The residue, after being well washed and dried, is to be weighed, and exposed to a heat which is just sufficient to burn off the sulphur, the quantity of which is indicated by the loss of weight. The residue is again to be digested in nitro-muriatic acid, and this solution is to be added to the first. The earthy residue, which contains the silver in the state of muriate, is then to be fused with an equal weight of glass of borax, and three times the quantity of pearl ashes. By this process the silver is reduced, and may be separated from the alkali and the earth by means of muriatic acid very much diluted. The nitro-muriatic solution is to be neutralized by a fixed alkali, and if it be afterwards treated with nitrate of mercury prepared in the cold, the gold will be thrown down in the state of a brown powder. It may be reduced to the metallic state by fusing it with nitre. The oxide of iron which remains in solution, may be obtained in the usual way in the state of magnetic oxide.

**Auriferous galena.—Galena, or the native sulphuret of lead, almost always contains a small portion of silver, and very often it is in such quantity as to be worth the trouble of extracting it. Galena sometimes has also combined with it a little gold as well as silver, and it is worked as one of the ores of gold. This is the case with some of the galena of Hungary, as that of Boicza yields 1½ oz. of alloy in the quintal, of which 31 parts are silver, and one of gold.**

The analysis of auriferous galena is to be conducted nearly in the same way as the auriferous pyrites. The pulverised ore being digested in nitro-muriatic acid, the gold and the lead, and, if any are present, the iron and antimony, are taken up; leaving behind the earthy matters, as well as the sulphur and silver, which may be separated according to the method employed in the former process. By gradually evaporating the nitro-muriatic solution, a crystallized muriate of lead is obtained; and by again diluting the solution with water, the gold may be separated by adding nitrate of mercury.

The analysis of the ores of gold containing tellurium, will be given under the head of that metal.

**Sect. II. Reduction of the Ores of Gold.**

Many of the most profitable veins of gold are of trifling magnitude, but at the same time yield ample returns to the miner, although they are mixed with so large large proportion of stony matter and other impurities as would render the working of any other metal altogether unprofitable. This obviously arises from the great commercial importance of gold compared with other metals, which no doubt is owing as well to its rarity as to its peculiar properties. In the Hungarian gold mines, which are the richest yet known in the old continent, the attention of the miner is not merely limited to the strings of ore, but to the whole contents of the vein, which are usually extracted and raised to the surface in large masses. These masses are distributed to the workmen, who break them down, first with large hammers, and afterwards with smaller ones, till they are reduced to pieces of the size of a walnut. In the course of this process, every piece is carefully examined, and arranged according to its value. The smallest visible grain of native gold is separated from the quartz in which it is chiefly imbedded, and put by itself. The auriferous pyrites and galena are also put into separate heaps; even the small splinters that are detached in breaking down the masses, and the sand and mud of the mine, are all collected, washed, and sifted, and ranged according to their apparent richness. What has been rejected in the first examination, is re-examined by boys, whose labour is not of great value, and who pick out almost the whole that has been overlooked by the men, and arrange it in the same manner.

The native gold with the matrix attached to it, is again to be broken by hand into still smaller pieces, by which means other impurities and stony matters are separated. The ore is then introduced into a wooden box floored with cast-iron plates; and by the action of two or more heavy spars of oak, which are shod with iron, and alternately worked like the common stamping mill, it is reduced to a fine powder. This powder, which is called flour, is then removed into a vessel like a large basin, and is mixed with such a quantity of salt and water as will render it damp. The workman then takes a thin porous leather bag, introduces a quantity of mercury into it, and by a regular and continued pressure forces the mercury in very minute drops through the leather. In this divided state it falls upon the pulverized ore, and is immediately kneaded up with it, till the requisite quantity, which depends on the proportion of gold, has been added. After completing this part of the process, the next object is to incorporate the mercury and the gold. This is effected by rubbing the mixture together for some time by means of a wooden pestle. The mixture is then heated in a proper vessel, and subjected for three or four days, to the temperature of boiling water; and, lastly, the mixture is to be carefully washed by small parcels at a time, so that the earthy particles may be carried off by the water. The mercury combined with the gold, only remains behind, in the form of amalgam. A portion of this mercury is then separated by pressure in a leathern bag, and the remainder is driven off by distillation, leaving behind the gold, and silver with which it may be alloyed.

But a more complicated process is requisite in separating that portion of the gold which is invisibly dispersed in the pyrites, in galena, and other metallic substances, as well as the stony parts of the matrix. In the treatment and sorting already described, those ores are separated, not only according to their apparent richness, but they are arranged also according to the degrees of hardness. They are then carried to the stamping mill, of which the principal parts are, 1. The coifers or cisterns, in which the ore is reduced to powder, and through which a stream of water continually passes, and so managed as to be increased or diminished at pleasure; 2. The stampers, or vertical beams, which are shod with iron; and, 3. The axle, which is fixed horizontally, and one end of which works in a pivot, while the other is riveted into the centre of a large water wheel. The mode of action of this apparatus is obvious. A stream of water falls upon the wheel, and turns it round, as well as the axle to which it is attached. The cogs, which are fastened to the axle, alternately raise the stampers to a given height, and then let them fall upon the ore placed in the coifers. And as the ore is sufficiently broken, it is carried by the stream of water continually passing through, out at the sides of the coifer into the labyrinths, where the stony and metallic contents of the ore are deposited, according to their specific gravity, nearer to or at a greater distance from the aperture. The coifer is a rectangular hole sunk below the level of the ground, and it is about five feet in length, two feet and sometimes less in width, and four feet deep. Five stampers are employed; they are strong oaken beams shod with iron, and weighing about 200 pounds each. They are placed side by side, at the distance of about 2½ inches from each other.

When the ore is to be pounded, the first thing is to cover the bottom of the coifer with a flooring or pavement, composed of large pieces of the hardest and poorest part of the vein. These pieces are to be close set together, and a floor of this kind is found to answer better than an iron floor. The thickness of the floor is to be proportioned according to the degree of hardness of the ore to be pounded; for it is obvious that the higher it is, the smaller will be the space through which the stampers fall; and their momentum will therefore be proportionally diminished. One precaution must be invariably observed, that the part of the floor immediately under the middle stamper be about two inches lower than that below the stamper on each side, and that this again be an inch lower than that beneath the two outermost stampers.

After the coifer is thus prepared, the machinery is set in motion, a small stream of water being allowed to flow into the coifer. The ore is to be carefully thrown in, just below the middle stamper, or the proper quantity is supplied by means of a hopper. The ore being thus broken down by the middle stamper, is gradually delivered to the stampers on each side, where it is still further reduced to powder, and from them it passes on to the two outermost stampers, where it is reduced to such a degree of fineness as to be for a time suspended in the water, and carried along with the stream through the openings at the ends of the coifer.

In stamping the ores of gold and silver, great attention is necessary, that no pieces of ore be subjected to the process that can be conveniently separated from the gangue by the hand; and that the ore be reduced to a coarse or fine powder, according to its nature. When native gold is dispersed in minute particles, in a hard siliceous matrix, it is found impossible to separate the whole of the metal, unless it be very finely pulverized; and in this case the ore may be reduced to fine powder, both on account of the great difference of the specific gravity of the two ingredients of the ore, and also because the siliceous particles, however minute, acquire no degree of tenacity, so as to adhere to the particles of gold. stamping ores of this kind, therefore, the coffers may be set very low, that the stampers may have the greater power, and a small stream of water only may be let in, that the current which passes out may carry with it only the smaller particles. But when the gold is dispersed in an indurated and ochrey clay, or in calcareous spar; if the ore in this case be not finely pulverized, a great proportion of the metal will be retained in the earthy matrix; and if the stamping be continued too long, the whole will be brought to a fluid mud, which will prevent the subsidence of the particles of gold. In the management of this part of the process, no small degree of skill and experience is requisite, to obtain the greatest produce of gold.

The reduction of the ore to grains of a uniform size, greatly facilitates the washing which follows the stamping, and yields a greater product of metal. This is effected by taking care that the ore, when first introduced into the coffer, shall fall under the middle stamper, and also by the velocity of the water wheel being properly regulated. When the motion of the stampers is too slow, loss of time is the only consequence; but when the motion is greatly accelerated, the water is violently thrown about, carrying with it to the apertures at the end of the coffer, pieces of the ore that are not sufficiently comminuted.

The ore being reduced to particles of a sufficient degree of fineness to be carried by the force of the water out of the coffer, passes into shallow channels of different dimensions. These channels or troughs, the whole series of which is called a labyrinth, are constructed of wood or stone, and communicate with each other at the extremities. The various parts of the ore are deposited in these channels, according to their specific gravities; the heaviest particles are detained in the first, and the lightest are carried along, and subside in the last and lowest. Each of the channels has a groove at its lowest extremity, and thus admits of being closed at pleasure by pieces of wood about an inch in height, which slide down upon each other. By varying the rapidity of the current through the channels, the heavy particles can be more accurately separated from the lighter ones, which is done by diminishing the slope, and increasing the width and length of the channels.

But with whatever care the first operation of the washing may be conducted, it is by no means sufficient to separate the whole of the sand from the ore. A second washing on tables, as they are called, is requisite. These tables are long wooden planes, which are considerably inclined, and are crossed at regular distances by narrow shallow grooves. A long wicker basket, or perforated wooden trough, filled with the washed ore, is fixed to the upper extremity of the table, and a small stream of water is admitted, which passing between the twigs of the basket, carries with it particles of the ore. These particles are either carried by the current off the table, or are deposited, according to their specific gravity, in the grooves, the heaviest particles subsiding first. In this way the auriferous ores of iron and copper pyrites, galena, &c. are sufficiently separated from the quartz and other stony matter, to be fit for the furnace; but for the ores of native gold, a third washing is necessary. This is performed in small quantities at a time, in a wooden vessel resembling in shape a common fire-shovel without a handle, but having the sides more elevated, and being furnished with two ears, by which it is held during the operation. The ore is put into this vessel, which is gently immersed in water, and a circular motion is communicated to it by a peculiar dexterity, which can only be acquired by practice. By this motion in the water the lighter particles are gradually thrown out of the vessel, and scarcely anything remains behind but the gold, which is either amalgamated or fused with the addition of a little nitre, in an earthen crucible. Here it may be added, that the separation of the gold which is found in alluvial soil, or in the sands of rivers, is conducted precisely in the same way, only that it is not necessary to be subjected to the process of stamping previous to washing.

The produce of the proper auriferous ores is seldom of sufficient value to admit of the same attention in washing as native gold; and therefore it is always found, after this operation, mixed with a considerable proportion of earthy matters. When the metallic part is composed of pyrites, which is frequently the case, it may be useful, previous to the fusion of the ore, to give it a moderate roasting, for the purpose of expelling the greater part of the sulphur; but it must be observed, that this process is to be regulated by the quantity, and refractory nature of the stony part of the ore; because the sulphur in the subsequent fusion acts the part of a flux, and therefore the cleaner the ore, the more perfectly it may be roasted. This part of the process being completed, a little quicklime, as a flux, is added, and carefully mixed with the ore, and a portion of galena, according to the proportion of gold and silver contained in the pyrites, previously discovered by assaying it. This mixture is next to be introduced into a reverberatory furnace, which is to be raised to a red heat; and when the mixture begins to clot together, it is to be stirred from time to time, and kept at a temperature inferior to that of fusion, till part of the sulphur is expelled; and when this is accomplished, the fire is to be increased, so that the whole may be brought to a state of thin fusion, after which it is let out in the usual way, and received in a mould of sand. During the process of fusion, the iron having a very strong affinity for sulphur, recombines with that portion of which it had been deprived by the roasting, in consequence of the decomposition of the sulphurics of lead and copper with which it is mixed; and these metals, by their specific gravity, fall in drops through the vitreous ferruginous scoriae, and carry with them the gold and silver, with which they unite at the bottom into a dense mass of metal. Thus it happens that the pig formed in the mould consists of two parts, which adhere to each other, but may be easily separated by the hammer. The superior and the larger portion, is a cellular mass of scoriae, and the lower is a black, heavy, compact mass, containing the gold and silver, along with lead, copper, and a portion of sulphur and iron. It is again broken into pieces, and roasted and fused once or twice, till the whole of the sulphur and other impurities are separated, and nothing remains but the metallic substances.

In the farther treatment of the ores of gold, the object of the refiner is to separate it from the metallic substances with which it is alloyed. We shall now mention the different methods which are followed in separating the metals from gold with which it is usually alloyed. 1. Separation of gold from platina.—As platina, like gold itself, is not susceptible of oxidation by exposure to heat and air, it cannot be separated by the process of cupellation; and platina having as little affinity for sulphur as gold itself, that substance, or the sulphurated metals, cannot be successfully employed for this purpose. It has been found that mercury combines more readily with gold than with platina, and from the knowledge of this circumstance a method has been devised of separating these metals. When the proportion of platina is so large, that the mass is brittle, it must be reduced to powder in a mortar; but if it be ductile, it may be reduced to small pieces by granulation. A quantity of mercury equal to seven or eight times the weight of the alloy, is then to be heated in an iron crucible, and raised to the boiling point. The alloy being first made red hot, is to be dropped in, and the whole kept for half an hour nearly at the same temperature. The mixture is then emptied into an iron mortar, and being covered with hot water, is to be carefully triturated for some hours, the water being renewed from time to time. In this way the gold combines with the mercury, and a considerable proportion of the platina will rise to the surface of the amalgam in the state of a black powder, which may be easily scraped off. In this way the alloy is to be purified as much as possible, and the superfluous mercury may be separated by straining through leather, and the amalgam deprived of the remaining mercury by the process of distillation. The gold, which still holds a small quantity of platina, is now to be melted with three times its weight of silver; and the mixture being granulated, is to be parted by means of nitrous acid. It has been found (although it be a singular circumstance) that pure platina, or even when mixed with gold, is perfectly insoluble in this acid; but, when combined with a large proportion of silver, it is readily dissolved, and the solution is of a dark yellowish brown colour; and, therefore, by digesting this triple alloy of gold, platina, and silver, in nitrous acid, the silver and platina are dissolved, and the gold remains behind. But it may be necessary to ascertain whether the whole of the platina be separated. This is done by melting a few grains of the gold, after careful washing, with three times their weight of silver, and treating it as before with nitrous acid. If it contain one half per cent. or even a smaller proportion of platina, the acid will be perceptibly coloured, and this being the case, the process must be repeated again on the whole mass. But this is rarely necessary when the previous trituration with mercury has been carefully performed. By adding to the remaining nitrous solution, a solution of common salt, the silver will be precipitated, leaving the platina in the solution.

By the following method, which is still more commodious, gold may be separated from platina. The alloy is dissolved in nitro-muriatic acid, and the gold is precipitated by means of carbonate of soda, or a large quantity of green sulphate of iron, neither of which has the effect of decomposing the solution of platina. The precipitated gold being dried, and mixed with a little borax and nitre, is subjected to fusion, after which it will be found in a state of perfect purity.

2. Separation of gold from silver.—In ores in which the proportion of gold is small, the silver may be conveniently separated by means of sulphur. The alloy is first melted, and granulated, by pouring it into cold water, which is kept in constant agitation with a rod or wicker brush. From an eighth to a fifth of the granulated metal is reserved, and the remainder is carefully mixed with about one-eighth of its weight of powdered sulphur, which adheres readily to the moist grains. The mixture is introduced into a covered crucible, and kept for some time at a gentle heat, that the metal may be completely penetrated by the sulphur, after which the heat is increased till the whole mass is brought into fusion. This sulphuret of silver becomes a tough viscous fluid, which retains the particles of gold, and prevents them from subsiding. The mass being kept in fusion for about an hour, that the union of the sulphur and silver may be completed, and any excess may be burnt off, a third part of the reserved silver in grains is to be added, and when it is melted, is to be stirred with a wooden rod, that it may be accurately mixed with the other materials, and brought into contact with the gold, with which it immediately enters into combination. The fusion being continued another hour, a similar quantity of grained silver is to be added, and after a third hour has elapsed, the remaining third is introduced, and treated in the same manner. The crucible, which is now to be kept carefully covered, is to be exposed to a high temperature for three hours, while the melted mass is stirred from the bottom every half hour. At the end of this time the surface of the mass, instead of being dark brown, becomes whitish as the sulphur escapes, and some bright white drops of melted silver, about the size of peas, make their appearance. The fused mass is now to be poured into a greased cone; and when it is cold, it will be found to be composed of a mass of sulphuret of silver, resting upon a white metallic button, which is nearly equal in weight to the added silver, and contains the whole of the gold that originally existed in the entire mass. If it appears that any of the gold remains among the sulphuret of silver, it may be separated by fusion in an open crucible. By this process part of the sulphur is burnt off, and a corresponding quantity of silver is reduced to the metallic state, which being carefully mixed with the remainder, and repeatedly stirred with a piece of stick, the whole of the gold remaining in the silver, which is still sulphurated, will be attracted; and by being poured into a cone, will be collected at the bottom in a mass.

The silver containing the gold, which is collected in these two operations, being melted and granulated, is subjected to one or more repetitions of the same process, till the silver that remains is found to contain a sufficient proportion of gold, to render it worth while to proceed to the process of parting by means of aquafortis. The whole of the silver may be separated by means of sulphur; but when the proportion of gold is considerable, the sulphuret of silver always takes up a part of it, which cannot again be entirely separated without repeated fusions; and therefore, when the gold is equal to $\frac{1}{3}$th of the silver, a further purification by means of sulphur, will scarcely be found advantageous.

An ingenious and economical method of separating the gold from old gilt silver lace or wire, has been extensively practised in Saxony. This method proceeds on the principle, that the affinity of gold for copper, and of silver for lead, is much greater than the affinity which subsists between gold and silver; and it is conducted... ducted in the following manner. The alloyed metal is first granulated, and \( \frac{1}{5} \) of it is mixed with \( \frac{1}{5} \) its weight of litharge, and \( \frac{1}{3} \) of sandiver. This is called the precipitating mixture. The next is mixed with \( \frac{1}{5} \) of powdered sulphur, and is brought into fusion, which being complete, as will appear from the flashing at the surface, \( \frac{1}{5} \) of the precipitating mixture is added at three different times, allowing an interval of five minutes between each time; and the fusion is then continued for ten minutes longer.

Part of the sulphurated silver is taken out with a small crucible made red hot, and the remainder being poured into the melting cone, a quantity of metallic silver combined with the greatest part of the gold, subsides to the bottom. The sulphuret of silver is again melted, and the remaining part of the precipitating mixture is added as at first, and thus a second portion of gold alloyed with silver is obtained. But as the sulphuret still retains a small portion of gold, it is to be fused a third time; and a precipitating mixture, equal in weight to the former, but consisting of an alloy of equal parts of copper and lead, is to be added, and thus a third precipitate of gold holding silver is obtained, and the sulphuret is now deprived of the whole of its gold.

The different metallic masses thus obtained, are melted with \( \frac{1}{5} \) of lead, then granulated, and treated in the same way as at first, with sulphur and the precipitating mixtures. The silver thus obtained being rich in gold, is first to be granulated, then mixed with \( \frac{1}{5} \) of sulphur, and kept in fusion for about half an hour without any addition; and being poured into a cone, the sulphuret is separated from the metal, and this last is treated two or three times more with sulphur, in a similar manner. The metallic button obtained, which now appears of a yellow colour, is to be melted with one sixteenth of copper, then granulated, and mixed with one sixteenth of sulphur; and the mixture being first gently heated in a covered crucible, and kept in fusion for about a quarter of an hour, is poured into a cone, at the bottom of which the gold is collected of a brass colour, and about eighteen carats fine. The purification is afterwards completed by means of sulphuret of antimony, a process which will be afterwards described.

3. Parting operation.—When the proportion of the gold and silver, alloyed together, is such, that the former is not much less than one sixteenth, or greater than one fourth of the whole mass, the operation of parting may be followed. In this method the gold is separated from the silver by means of diluted nitric acid, or, as it is termed by manufacturers, aquafortis, which dissolves the silver, and leaves the gold untouched. The button of gold and silver is prepared for this process by flattening with the hammer, again heating it red hot, and slowly cooling to anneal it for the purpose of increasing its malleability. It is then to be extended into a small plate as thin as a wafer, by passing it between rollers of polished steel, again heated, but only to redness, and last of all rolled up in the form of a small loose coil or spiral, called a cornet. The annealing is useful in allowing the metal to be rolled up without cracking, and at the same time the freer action of the acid, in consequence of the texture of the metal being somewhat opened.

The cornet thus prepared is introduced into a pear-shaped matress, called a parting-glass, and three or four times its weight of pure nitric acid of 1.25 specific gravity are added; the mouth being slightly covered to keep out the dust, the glass is set on a sand bath, or over charcoal, to boil. As soon as it becomes warm, the acid begins to act on the silver, and dissolves it with the evolution of nitrous fumes. During the whole action of the acid, the cornet appears all over studded with minute bubbles, and when these discontinue, or run into one another, forming a few large ones, the action of the acid is nearly over. The process is usually completed in about fifteen or twenty minutes from the time that the acid begins to boil. The cornet now appears corroded throughout, and has lost during the solution the whole of the silver; and the remaining gold which is slender and brittle, retains the same spiral form. Indeed it is of considerable importance that it should not be broken, for much of the accuracy of the operation depends on having the gold in one piece and not in fragments.

The acid solution of silver, while yet hot, is next to be carefully poured off, and a portion of fresh acid, somewhat stronger, is to be added, to separate all the remains of silver; the boiling is to be repeated as before, but only for five or six minutes; it is then poured off and added to the former solution, and the parting-glass is filled with hot distilled water, to wash off the remains of the solution. The cornet, which is now of a brown colour and spongy texture, and has little of the metallic appearance, is taken out in the following manner. A small crucible is inverted over the mouth of the parting-glass, while it is yet filled with the distilled water, and the latter being rapidly inverted upon the crucible, the cornet falls softly through the water down the neck of the glass into the crucible, where it is deposited, and the water is carefully poured off. The crucible after being dried is next heated to redness under a muffle. The cornet contracts greatly in all directions, becomes of a firm texture, and resumes its metallic lustre; and after being brought to a red heat and cooled, it exhibits the appearance of a cornet of pure gold, having all the splendour, softness, and flexibility of this precious metal. By accurate weighing, the amount of the product is precisely ascertained, and thus the operation of parting is completed.

But if the proportion of gold amount to one third of the mass, it combines with part of the silver, and protects the latter by its insolubility from being acted on by the acid, so that in the process of parting, too great a proportion of gold in the alloy must be avoided; and farther, as the acid is expensive, unless the silver be rich in gold, this process, which is in many respects convenient, will not be found economical. In reducing the fineness of the alloy which is too rich in gold to be advantageously parted by itself, it will be the object of the refiner not to employ pure silver, but such as contains a small portion of gold; and at the same time it will be his study to save the quantity of acid.

The following is the usual method of conducting the process of parting. After selecting a proper quantity of rich and poor ingots of mixed metal, the whole is to be fused in an iron crucible; and being well mixed by frequent stirring, it is to be removed by a clean iron ladle, and granulated in cold water. The parting-glasses, which are nearly of the form of a truncated cone with a rounded bottom, are about twelve inches high and seven inches wide at the lower extremity, and they should be of equal thickness, well annealed, and free from any kind of flaws. About forty ounces of metal are introduced into each glass, and the nitrous acid, half saturat- ted with silver, is added till it stand two or three fingers breadth above the surface of the metal. Twenty or even more of these glasses are placed in a sand bath, and the heat, which should at first be moderate, is gradually increased till it nearly reach the boiling point about the time that the acid is saturated. The nitrate of silver is poured off, a new portion of stronger acid is added, and boiled as before till it is nearly saturated, when almost the whole of the silver is taken up, and what remains undissolved has the appearance of a brown mud, and consists of the gold finely divided with a small portion of silver. The acid again saturated is poured off, and a third portion of still stronger acid is added, which is kept at the boiling temperature till the evolution of nitrous gas ceases, and the bubbles are enlarged, which shews that all the silver is taken up. The acid is then decanted off, and reserved for the first part of a future process of the same kind; and the gold is repeatedly washed with fresh portions of hot water till the washings dropped on a polished copper plate produce no stain; and the powder, being dried and mixed with little nitre and borax, is fused, and is then in a state of purity.

To decompose the nitrate of silver with the view of procuring the pure metal, the solution is poured into a wooden vessel lined with copper, and in which are placed plates of copper that the silver may be precipitated from its solution in consequence of the greater affinity of the nitrous acid for the copper. The surface of the plates is to be cleared from time to time of the silver crust, that a fresh surface of copper may be exposed to the action of the acid, and the decomposition of the nitrate of silver may be promoted; after which the nitrate of copper formed in the solution is decanted off, the plates are scraped, and the silver being washed is fused with nitre, and is also obtained in a state of purity.

4. Separation of gold from silver or other metals by sulphuret of antimony.—All the common metals, excepting zinc, which come under the denomination of imperfect metals, may be separated from gold by this process; for as gold is incapable of combining with sulphur, and as the affinity of almost all the other metals for sulphur is stronger than that of antimony, it is sufficiently obvious, that an alloy of gold with any of these metals, as for instance gold and copper, being added to sulphuret of antimony, the sulphur will combine with the copper, and the antimony will form an alloy with the gold. When common crucibles are employed for this process, some previous preparation is necessary. A well burned crucible is selected, and soaked for two or three days in linseed oil, which is then to be cleared away from the inner surface till some finer powdered glass of borax dusted upon it shall just adhere, when it is to be put into a dry place for two or three weeks, after which it is fit for use.

The gold alloy is first melted in the crucible, and then about twice its weight of coarsely-powdered sulphuret of antimony is thrown in at two or three different times. At each addition the mixture froths and swells up, so that the crucible must be larger than the quantity contained, and great caution must be observed to prevent any bits of charcoal dropping into the crucible; for then the mass of melted matter would certainly flow over. When the mixture begins to sparkle on the surface, and appears to be perfectly fluid, it is to be poured into a melting cone which has been previously heated and greased, and the settling of the gold at the bottom is promoted by communicating a tremulous motion to the cone by means of slight blows. When the matter has become cold, it is removed from the cone by giving it a few blows in an inverted position. The mass is composed of an alloy of gold and antimony, covered with scorie consisting of the metal formerly alloyed with the gold now in combination with the sulphur or the antimony. But the gold still retains a little of its alloy, and from this it is to be freed; the same process is to be repeated not only a second, but even a third and fourth time, with a similar quantity of sulphuret of antimony. The metals from which gold may be advantageously purified by this process are iron, copper, tin, lead, and silver.

5. Separation of gold from antimony.—When the proportion of antimony exceeds that of the gold, the alloy is brittle. It must be reduced to small pieces, mixed with one-fourth its weight of sulphur, melted in a covered earthen crucible, and after the fusion is completed, poured into a melting cone previously heated and greased. When examined after being cooled, it will be found to consist of two parts, which may be easily separated by melting the alloy, exposing it to a high temperature, and at the same time directing a stream of air from a pair of bellows into the crucible which contains it. By this means the antimony is oxidated, and driven off in the form of white vapour. The gold having acquired a clear bright green colour, it is to be poured out and melted again in a small crucible with a little nitre. The remaining portions of antimony will be oxidated, and driven off from the gold as before. The small proportion of gold which remains attached to the sulphuret of antimony may be separated by bringing the whole mass into thin fusion, and precipitating part of the antimony by adding about one-fifth of its weight of iron filings. In this way the gold falls down in the form of alloy with the antimony, and it may be separated by means of the process described above.

Separation of gold from lead by cupellation.—This is the most economical method of separating gold from lead. The nature of the process of cupellation, and the method of conducting it, have been already described under Chemistry, No. 2026, p. 682. But besides lead, other metals may be separated from gold, by employing that metal as a flux, the effects of which in scoriifying and carrying down most of the imperfect metals, are such, that by the process of cupellation with lead, which is to be repeated according to the proportion of the alloy, and its affinity for the gold, almost every particle of the metals combined with it, may be separated. This method is usually followed where the proportion of alloy is but small; but when it is more considerable, some of the other methods are preferable. It is found however, that in the cupellation of pure gold with lead, it always retains a small portion of this metal, which affects its colour and ductility. But if the alloy to be purified contain, beside lead, to the amount of one-twenty-fourth of the gold of copper, the whole of the lead may be separated, but scarcely any of the copper; and if it contain silver in a greater proportion than that of copper, the latter may be separated by the process of cupellation, and a little of the lead remains. But if the silver exceed... Gold, exceed the gold, or be equal to it, the copper and lead may be entirely separated, while the gold and silver remain behind. From a knowledge of these facts, the refiners, in separating the base metals from gold, by the process of cupellation, add to the mixture a considerable proportion of silver. When the gold is alloyed with tin, cupellation with lead alone will not succeed, because the tin, with part of the lead, forms a spongy refractory oxide, and floats on the surface of the fluid metal, and at the same time retains part of the gold. But as iron is found to combine with tin into an alloy that may be scorified by lead, the addition of iron filings during the process removes the difficulty.

The following table shews the quantity of gold which is got from the different countries of the old and new world, taken on an average, between the years 1792 and 1802.

| Old Continent | Kilogrammes | |---------------|-------------| | Siberia | 1700 | | Africa | 1500 | | Hungary | 650 | | Salzburg | 75 | | Norway | 75 | | Total of the Old Continent | 4000 |

| New Continent | Kilogrammes | |---------------|-------------| | North America | 1300 | | South America | | | Spanish possessions | 5000 | | Portuguese possessions | 7500 | | Total of the New Continent | 13800 |

* The kilogramme being equal to 2lbs. 3oz. 5drs. avoirdupois, the whole amount is equal to about 39,285 pounds avoirdupois.

**CHAP. III. Of the Ores of Mercury.**

The ores of mercury present less variety than those of many other metals; and on account of its peculiar properties, the management of its ores, whether for the purposes of analysis or reduction, is less complicated and difficult.

**SECT. I. Of the Analysis of the Ores of Mercury.**

To analyze the ore of native mercury, or native amalgam, it is to be digested in nitric acid of moderate strength; the mercury and silver, and bismuth, will be dissolved, and if the ore should contain a minute portion of gold, it will remain untouched in the form of a brown powder at the bottom of the solution. The nitrous solution is next to be gently evaporated till it is so far concentrated as to be on the point of crystallizing. It is then to be poured into a large quantity of pure water, by which means the most part of the bismuth will be separated, and a solution of common salt, or any other neutral muriate, being added to the filtered liquor, the silver and mercury will be precipitated in the form of muriate. After this is separated, add to the clear liquor some carbonated alkali, while any precipitation takes place; then boil the liquor, and separate the precipitate by filtration. The muriatic precipitate is next to be digested in nitro-muriatic acid moderately diluted, which takes up every thing excepting the muriate of silver, from which, after being washed and dried, the proportion of silver in the ore may be easily ascertained. The nitro-muriatic solution is now to be decomposed at a boiling heat, by a carbonated alkali, and the white precipitate thus obtained being added to the former carbonated precipitate, mix them with a little oil, or what answers better, sugar, and distil in a small coated glass retort. Raise it gradually to a red heat, and continue at that temperature while any mercury comes over. The residue in the retort consists of a little metallic bismuth and charcoal.

**Native amalgam.—** With the view of ascertaining the proportion of mercury and silver in this ore, Klaproth examined some of the garnet-like crystals from the quicksilver mines of Deux Ponts. Some pure crystals weighing 33½ grains were introduced into a barometer tube of a larger diameter than usual, and closed at the lower end. This end was placed in sand, within a small crucible; heat was applied, and its intensity gradually increased to the degree of ignition. After cooling, he cut off the lower end of the tube, and found that it contained the silver, which had undergone ignition in its former crystalline form, and weighing 12 grains. On collecting the mercury which had been sublimed in the tube, he obtained 21 grains. Therefore since the deficiency of one-third of a grain may be reckoned as a loss of quicksilver, the following will be the proportion of the parts in 100 of this crystallized amalgam of silver.

| Silver | 36 | |--------|----| | Mercury | 64 | | | 100 |

**Cinnabar.—** The analysis of cinnabar may be conducted in the following manner. The ore being reduced to a fine powder, is repeatedly digested in a mixture of 1 part of nitric acid, and 3 of muriatic, moderately diluted, by which every thing in the ore is dissolved excepting the siliceous earth and the sulphur. The residue being washed, dried, and weighed, is subjected to a red heat, and the remaining silic being deducted, the difference of weight shews the amount of the sulphur. The nitro-muriatic solution is next to be decomposed at a boiling heat, by carbonated alkali, and the precipitate obtained being mixed with a little lamp-black, and distilled, the mercury passes over in the metallic form. The residue in the retort consists of magnetic oxide of iron, and any accidental earth excepting silic that is contained in the ore, together with a little charcoal, which may be separated in the usual way.

**Hepatic ores.—** The hepatic ores of mercury, and such as contain bituminous substances, may be treated in the same way; but these ores are sometimes combined with a little silver, and therefore the matter which remains undissolved in nitro-muriatic acid, may be muriate of silver, as well as sulphur and silic. When the sulphur is burnt off, the residue is to be mixed with twice its weight of pearl-ash, and being strongly ignited in an earthen crucible, diluted muriatic acid is added, by which the alkali and the earth will be taken up, and Mercury, the silver will remain behind in the form of small metallic grains.

Corrosive ore of mercury.—To analyze this species of mercurial ore, let it be digested in a little distilled vinegar, by which the native mercury which is dispersed though the ore will be left behind. Add to the clear solution nitrate of barytes, by which the sulphuric acid will be separated in the state of sulphate of barytes; and this being removed, drop in nitrate of silver, by which the muriatic acid will be separated in the form of muriate of silver. The mercury now remains in solution in the state of nitrate, and being precipitated by means of iron, it is afterwards washed in muriatic acid, and thus appears in the metallic state. It may also be reduced to the metallic state by precipitating by carbonated alkali, and distilling the precipitate with a little lamp black.

A simple and easy process is followed in assaying the ore of mercury in the dry way. The ore to be examined is first to be reduced to powder, and carefully mixed with one-fourth of its weight of quicklime, and an equal portion of iron filings. It is then to be exposed to a red heat in an iron or earthen retort, as long as any mercury passes over into the receiver.

Sect. II. Of the Reduction of the Ores of Mercury.

A very simple process is followed for reducing the ores of mercury. The following is the method practised at the celebrated mines of Almaden in Spain. The pieces of pure cinnabar are first selected and separated from the ore, to be sold to painters and manufacturers of sealing-wax. The rest is sorted into three parts, of which the first is the richest, and is broken into pieces of a moderate size; the second, containing a smaller proportion of metal, is broken into smaller pieces; and the third consists of the dust and smaller fragments of the other two. These are kneaded up with clay, and being formed into bricks, are carefully dried in the sun. The furnace which is used for extracting the mercury is built in an oblong form, and is divided horizontally by an iron grate, into an upper and lower compartment, and near its top it communicates with a series of aludels. In charging the furnace, a stratum of flat rough stones is placed on the grate, intervals between each of the stones being left for the passage of the fire. A bed of ore of the second quality is laid on the stratum of stones, and then a stratum of the ore of the first quality, after which another of the second kind, and last of all a stratum of the third kind, which has been made up into bricks. A few faggots are then thrown into the lower cavity of the furnace, and lighted up; and a gentle fire is to be kept up by occasionally adding faggots for eight or twelve hours, according to the previous state of the ore with regard to moisture. After the moisture is separated, which is known by the vapour ceasing to be exhaled, the fireplace is filled again with faggots, and by the time they are consumed, a sufficient heat will be communicated to the ore, to allow the combustion to go on, by means of the sulphur which it contains, without requiring any more fuel. In the course of the next two days, while the sulphur burns slowly away, the mercury rises in the state of vapour, and passes into the aludels, where it is condensed. When the whole of the metal is extracted, the scoria is taken out of the furnace, and the aludels are emptied of their contents. But besides the mercury, they are found to contain a quantity of black matter like soot. This matter is easily separated by spreading the whole about on an inclined table, so that the mercury may run to the lower extremity, where it is collected in a channel, and the impure sooty matter remains behind.

The method of extracting mercury from its ores now described, is advantageous, on account of the simplicity of the apparatus, and the smaller expense of fuel; but it would appear that a portion of the mercury remaining in the ore is lost. There is besides a considerable loss in throwing away the soot, after separating the running mercury on the tables, not only because many of the globules of the metal itself are thrown away, but also the calomel, and cinnabar, which are found to be in considerable proportion, are wasted. Hence it has been recommended as a more profitable method, 1. To separate the sulphate of ammonia, which, according to the examination of Proust, forms part of the matter deposited in the aludels, and then by mixing what remains, with 12 or 15 per cent. of quicklime, distil it in an iron retort, by which means the whole of the running mercury would be obtained, as well as that which is produced by the decomposition of the calomel and cinnabar.

A more improved process is practised at the mines of Deux Ponts, and Idria. The ore, as it is brought out of the mine, is carefully sorted by the hand, and these parts that seem destitute of metal, are rejected. This process, although tedious and expensive, is found to be more advantageous than the older method of separating the cinnabar by washing, in which there is a great loss of metal. The ore being thus sorted, it is reduced to powder, and accurately mixed with one-fifth of quicklime, which has fallen to powder by exposing it to the air; but it ought to be observed that the quantity of quick lime is to be regulated by the proportion of cinnabar contained in the ore. The mixture being thus prepared, is introduced into iron retorts, which are capable of holding about 60lbs. weight. The retorts, to the number of 40 or 50, are fixed in a long furnace, and a glass receiver is attached to each, but it is not luted. A moderate heat is then applied for the purpose of driving off the whole of the moisture; and when this is done, the joinings of the vessels are to be closely stopt with tempered clay, and a full red heat is to be applied, and continued for seven or eight hours, at the end of which time the whole of the mercury will be volatilized, and condensed in the receiver. By this process it is found, that 100lb. of the ore yield from 6 oz. to 10 oz. of metal.

Chap. IV. Of the Ores of Silver.

The ores of silver present a considerable variety. Sometimes it is found in the metallic state in masses of from 30lbs. to 40lbs. weight, but it is often combined with sulphur in the state of sulphuret; with other metals, especially antimony, arsenic, iron, copper, lead, and bismuth; or with acids, as the carbonate and the muriatic, forming the carbonate and muriate of silver. The analysis and reduction of these different ores, it is scarcely necessary to observe, must be conducted according to Sect. I. Of the Analysis of the Ores of Silver.

When a silver ore is to be examined, and the only object in view is to ascertain the proportion of silver it contains, the operation is usually conducted in the dry way. The ore is first roasted and reduced to powder; it is then mixed with litharge in proportion to the earthy matter combined with the ore, and quickly vitrified. The mass thus obtained is again reduced to powder, and being mixed with black flux, is to be fused in a crucible, with a sufficient degree of heat. By this process the lead of the litharge is revived, and collected at the bottom of the crucible, carrying with it the whole of the silver, as well as some of the other metals which may be combined with the ore. The button thus obtained is to be subjected to the process of cupellation, with the requisite quantity of pure lead, and in this way the base metals are scorified, and the silver remains behind in a state of purity, or combined only with the gold, which many of the ores of silver contain in small proportion. The gold is to be separated by some of the methods which we have already described, in treating of the ores of gold. This operation, in which the object only is to ascertain, as in this case, the quantity of silver, is called assaying. In the examination of ores in this view, more assays than one should always be performed, that an accurate and nearly invariable result may be obtained.

But in examining metallic ores, it is always more satisfactory to ascertain the whole of the ingredients of which they are composed. We shall therefore proceed to give an account of the best conducted analysis of the ores of silver.

Corneous silver ore.—The following is the analysis of this ore by Klaproth.

"Upon 200 grains of the corneous silver ore I poured three times their weight of pure nitric acid; but no action took place, either in the cold or in the heat of boiling; only a subtle brown red iron-ochre was separated, which, being washed off from the remaining ore, and dried, amounted to four grains. Caustic ammonia, added to the nitric acid employed, precipitated five grains more of iron. When it was afterwards mixed with muriatic acid, only a pale milky colour was produced, but no real corneous silver ore deposited. It followed from this, that neither any free native silver, nor any portion of it mineralized by sulphur, had been contained in that ore. The horn-silver, after treatment with nitric acid, was reduced by twice its weight of salt of tartar, and yielded 133 grains of reguline-silver.

"1. For the purpose of finding out, more accurately, its constituent parts, I mixed 200 grains with 600 grains of the purest alkali prepared from tartar, and brought the mixture into the state of fusion in a glass retort, applying the necessary degree of heat. After refrigeration, I broke off the upper half of the retort, softened the fused mass, which was of a light-brown colour, with hot distilled water, filtered the whole, and edulcorated the residue.

"2. This residue was then dissolved in nitric acid. The solution acquired a brown tinge, and the scum floating upon the liquor assumed the colour of bricks. When the argentous parts were completely dissolved, there remained 8½ grains of a brown-red powder, which imparted a golden yellow colour to the aqua regia, with which it was digested, and left a white residue behind. This last consisted of horn-silver, mingled with a slight portion of the gangue, or matrix of the ore, and afforded, on reduction, two grains more of silver. Caustic ammonia precipitated from the yellow solution seven grains of oxydied iron.

"3. The nitric solution of the silver was precipitated by common salt; and the muriate of silver thus obtained weighed, after reduction by means of soda, 134½ grains of reguline silver.

"4. The fluid, left after the separation of the horn-silver, had a pale-yellow colour, owing to a portion of iron; which, precipitated by pure ammonia, weighed five grains.

"5. After this, I proceeded to examine the saline mass, dissolved in distilled water, and separated from the silver, after the corneous ore had been fused with pure alkali. On saturating this mass with distilled vinegar, the solution was rendered turbid, and a loose white earth deposited, which, collected and dried, amounted to three grains and a half of argillaceous earth.

"6. The alumina being separated, the solution was reduced to a dry salt by evaporation, and the alcohol, affused upon it, took up the acetite of pot ash. The neutral salt, which was left behind by this process, and which consisted of the mineralizing muriatic acid and the alkali employed, I dissolved in water, and obtained from it, by repeated evaporation and crystallization, 117½ grains of muriate of potash.

"7. In order to learn whether and in what proportion sulphuric acid, which by some writers has been mentioned as one of the constituent parts of the corneous silver ore, were really present in it, I again dissolved that salt in distilled water, and dropped into it liquid muriate of barytes. The mixture became turbid, exhibiting that appearance which indicates the presence of only a slight quantity of sulphuric acid. I continued to add the barytes, until no more turbidness appeared. The weight of the precipitate thus obtained was three grains: but, as in these three grains of sulphated barytes the acid cannot properly be estimated to be more than half a grain, I think this quantity is too trifling to be considered as one of the essential constituent parts of the corneous silver ore. But if that half grain of sulphuric acid be estimated equal to 1½ grain of sulphur of potash, and be subtracted from the above 117½ grains of digestive salt, or muriate of potash, there will remain of the latter only 116 grains, in which the concentrated muriatic acid amounts to 42 grains. Therefore,

"One hundred parts of this corneous ore contain

| Silver | 67.75 | | Muriatic acid | 21 | | Oxide of iron | 6 | | Alumina | 1.75 | | Sulphuric acid | 0.25 |

96.75."

Red silver ore.—The following is the analysis of this ore, also by Klaproth. "Upon 500 grains of bright, crystalline, red silver ore, most finely pulverized, I poured six times their quantity of a mixture of equal parts of nitric acid of 1.350 specific gravity and distilled water. The phial was kept for several hours in a low digesting heat, so that the agency of the acid would be but moderate. I then diluted the solution with water; caused it to boil; and, after the residuum had subsided to the bottom, I decanted the clear solution. Upon the remaining pulverulent ore, a quantity of nitric acid and water, equal to the preceding, was again affused; and, in the same manner, proceeded with as at first. The ore appeared now to have been effectually decomposed; and for this reason the solutions, together with the residuum, were put on the filter, and the latter properly washed.

"The filtered nitric solution had no colour at all, having been very much diluted by the water by which the residue had been edulcorated. I subjected it to evaporation to ¼th part, and found the bottom of the evaporating glass vessel, after cooling, covered with copious, finely grained, resplendent, and heavy crystals of a gray white. To ascertain their nature, I procured, by a separate process, a quantity of a solution of the same red silver-ore, sufficient for this enquiry, and found that they were sulphate of silver. Being assured of this, I dissolved that sulphate by a proportionate quantity of water, assisted by heat, added it again to the nitric solution, and combined this last with muriatic acid, as long as any muriate of silver would precipitate; which, when collected, edulcorated, and dried, was found to weigh 39½ grains.

"The fluid, from which the horn-silver had been thus separated, was then reduced to a smaller bulk, by distillation from a retort. This concentrated fluid became turbid, and left another grain of muriated silver on the filter. At this time it contained no other foreign substance, except a considerable portion of sulphuric acid.

"What remained undissolved by the nitric acid, consisted of an ash-gray, pretty loose, or flocculent powder, of 20½ grains in weight. When this had been gently digested for half an hour, with a mixture of five parts of muriatic acid, mixed with one part of the nitric, and then diluted with half its quantity of water, there remained, after filtering, careful edulcoration, and drying, 65 grains; which were the sulphureous contents of the ore. When this residue had been gently heated, the sulphur deflagrated, leaving 64½ grains of muriated silver behind. This sulphur, therefore, consisted of 8½ grains.

"After the filtered solution had been evaporated in part, it was poured into a large quantity of water. By management, a white precipitate immediately ensued, which being separated by the filter, edulcorated, and dried, and lastly heated in a porcelain cup, gave 133 grains in weight. But I could not find the least trace of arsenic in it, though I had subjected it to all the trials deemed proper for discovering its presence. On the contrary, it was manifest, that this precipitate wholly consisted of oxide of antimony, quite of the same nature with that which is produced when muriatic solutions of antimony are precipitated by water. On exposing it to heat, a small portion of moisture still evaporated, attended with a muriatic smell, which was hardly perceptible. When again put on a test, and mingled with a third part of charcoal dust, the coaly powder was slowly consumed, by burning, without any arsenical smell, and left behind it the metallic oxide, possessed of a gray colour, and partly blended, partly covered, with a quantity of fine, gray-white, shining, acicular crystals, or the flowers of antimony, as they are called. But when it was fused in a covered crucible with tartar and powdered charcoal, it was completely revived into reguline antimony, which, being blown off with the bellows, a bead of silver was left, weighing half a grain.

"The liquor also, from which the antimonial oxide was separated, contained free sulphuric acid. On this account, I put it into a retort, together with the nitric acid, from which the silver had been precipitated in the state of horn-silver, by means of muriatic acid, and continued the distillation until, at this temperature, nothing more would pass over; but, on raising the heat, thick white vapours had begun to rise. The fluid left behind in the retort was found upon trial, to be concentrated sulphuric acid. Upon diluting this last with water, and subsequent affusion of muriated barytes, the sulphate of barytes from thence produced, amounted, after edulcoration and desiccation, to 19½ grains.

"Consequently, the constituent parts discovered by these researches, are, silver, antimony, sulphur, and sulphuric acid."

Vitreous silver ore.—This has been also analyzed by Klapproth, according to the following method.

1. If ductile vitreous silver ore be fused upon a piece of charcoal, by the assistance of the blow-pipe, its sulphur is quickly volatilized, and a button of pure silver remains. But it is otherwise with the brittle ore: for the bead left after the evaporation of the sulphur is brittle, and cannot be purified by the addition of borax. However, if a little nitrate of potash be added to the red-hot bead, it will destroy the portion of baser metal which it contains, and then the borate of soda causes it to yield a pure button of silver.

2. One hundred grains of ore, previously levigated, were gently boiled in a sufficient quantity of nitric acid, diluted with an equal quantity of water. This operation was repeatedly performed, till the black colour of the powdered ore disappeared, and the insoluble portion had become of a loose texture, and had acquired a gray-yellow colour. When filtered and dried, this residue weighed 26 grains.

3. On adding a solution of common salt to the above filtered solution, which had assumed a pale-greenish colour, a copious precipitate of horn-silver ensued, which, edulcorated and dried, gave 88½ grains. Four parts of this afforded three of silver, by fusion with soda.

4. The remaining solution was next combined with sulphate of soda; but neither any turbidness, nor any indication of the presence of lead, appeared. Upon this, caustic ammonia was affused to excess; and the gray precipitate, which then fell down, and which the volatile alkali could not again render soluble, weighed five grains. Urged by heat, it melted into a consistence like pap, at the same time that a weak arsenical smell was perceived. After this precipitate had been once more dissolved in nitric acid, the addition of soda caused it to yield a whitish yellow, alkaline sulphuret a dirty brown, and Prussian alkali a deep blue precipitate, liable to the attraction of the loadstone, after ignition. Therefore, it consisted of iron, with a slight trace of arsenic. 5. The proportion of copper, indicated by a blue colour, in consequence of the addition of ammonia, and which still remained in the solution, was but slight. For, after the solution had been saturated with sulphuric acid, polished iron immersed in it, was invested with so slight a coppery crust, that no copper to any amount could be collected.

6. Those 26 grains, which continued insoluble in the nitric acid (2.), were digested in nitro-muriatic acid, till nothing appeared to remain but the mere sulphur. Its weight amounted to 13 grains; but after deflagration, it left behind it about one grain of quartzose matter of the mine.

7. From this it is obvious, that 13 grains, or one-half of the above 26 grains, were held in solution by the nitro-muriatic acid; and these were precipitated entirely in the form of a white powder, upon the affusion of 20 parts of water. When ignited, this precipitate assumed a yellowish colour; but there was nothing either of arsenic, or any other volatile substance, perceptible. By combination with soda, it became reduced to pure reguline antimony; which, as such, admitted of being blown off, without leaving any residue, in its usual form of a thick white smoke, adhering to the contiguous bodies in the form of needle-shaped flowers (oxide) of antimony. Those 13 grains of oxidized antimony are equivalent to ten grains of that matter in the reguline state.*

For the analysis of some of the other ores of silver, we must refer our readers to the ingenious and elaborate Essays of the sagacious Klaproth, from which we have extracted what is given above on this subject.

Sect. II. Reduction of the Ores of Silver.

Although the ores of silver contain a larger proportion of extraneous matters than the ores of some other metals, the value of that metal being greater than that of many others, admits of greater expense in the processes employed for their reduction. The ores of silver are reduced either by fusion, or amalgamation.

Reduction of silver ores by fusion.—Native sulphuret of lead, or galena, commonly contains a portion of silver, and often in such quantity, as to make its separation from the lead a profitable undertaking. The proportion of silver contained in lead is very variable. The greatest produce of silver which we have heard of, was got from the lead ore of Craven in Yorkshire, which amounted to 250 ounces of silver in the ton of lead. The mines of Cardiganshire yielded formerly 80 ounces per ton; the Durham and Westmoreland mines afford lead, from which 17 ounces of silver are obtained upon an average per ton. The lead procured from the mines of Islay, one of the Western islands of Scotland, yielded, we have been informed, 40 ounces per ton; and the average produce of lead at the refinery at Poullaouen, in Brittany in France, is above 39 ounces of silver per ton. The following is the process carried on at the latter establishment, for separating the silver from the lead.

After the lead has been extracted from the ore, the object of the refiner is to obtain the silver in a separate state, which is dispersed through the mass of lead. This is performed by the process of cupellation on a large scale, or refining, as it is usually termed. The floor of the reverberatory furnace, in which the process is conducted, is horizontal, and it is lined with wood ashes and sand mixed together, and well beaten, and formed into a shallow basin, which is the cupel. There is an aperture at one side of the cupel, which forms a right angle with the flue by which the flame from the fireplace passes into the cavity of the furnace. Through this aperture the lead, brought to the state of litharge, runs; and opposite to it there is another aperture by which a blast of air is admitted. The top of the furnace has a circular aperture directly above, and corresponds in extent with the cupel, which may be shut up with a frame work of iron filled with bricks. When the furnace is ready, the cupel is lined with hay, and is then charged with about 177 quintals of lead, in bars or pigs, through the circular aperture, and the cover being put on, the fire is lighted up. In the course of six hours, the whole of the lead being melted, and brought to a red heat, a blast of air is directed upon the surface of the lead, and the ashes of the hay, and other impurities are removed with a wooden rake. The blast being continued for half an hour and more, the surface of the lead begins to be covered with a thick crust of oxide, which is scraped off, and is soon succeeded by another, but it is not till the surface has been cleared five or six times that the true litharge appears. When this is the case, the temperature is raised to a cherry red, and by the action of the blast, with the occasional aid of the workman, the litharge flows out through the aperture mentioned above. The intense heat volatilizes a considerable portion of lead, and so fills the interior of the furnace with vapour, that a person of experience only can discover what is going on in the cupel. At the end of 38 or 40 hours from the time that the fire is lighted, the contents of the cupel are reduced to about six quintals, and the litharge which comes over at this time is kept separate, because it contains a small portion of silver. At last the litharge ceases to flow, and the surface of the melted metal appears covered only by a thin pellicle. It then becomes gradually convex at the edges; the pellicle breaks up, and the surface of the metal appears quite bright. The blast is now to be turned off, the fire damped, and an aperture in the furnace, previously stopped with clay, is opened to admit a tin plate tube, through which a stream of water is poured into the cupel, in order to cool the metal rapidly, that it may be prevented from spitting, which would be the case, if this precaution were not observed at the moment of congelation. But the silver thus obtained is still contaminated with a portion of lead, from which it is freed by a second cupellation, which is performed in a moveable cupel containing about 700 or 800 ounces, and is placed in a small reverberatory furnace, which being heated about three hours, is charged with silver of the first cupellation. After the fusion of the silver, a proper working heat is kept up for four or five hours, when the refining is usually completed. The loss of lead by volatilization during the refining process is estimated at about eight per cent. When the quantity of litharge produced is large, it is reconverted into lead, by being returned into the reverberatory furnace, and treated in the same manner as the ore. This forms lead of the best and softest quality, because it is in a state of the greatest purity. And besides, the scoriae that remain after the reduction of the ore, and the litharge, along along with the old cupels, and the metallic soot which is deposited in the chimney of the furnace, are treated in a common blast furnace, and a considerable portion of lead is thus obtained.

A different practice is followed in the English refineries. A common reverberatory furnace, having the area perforated with a large oval hole to receive the cupel, is employed. The cupel is formed of six parts of well burnt bone ashes, and one of good fern ashes, mixed together, and moistened to a proper consistence. A quantity of this mixture is strewed to the depth of about two inches in an iron frame, which consists of a raised elliptical rim, with five broad bars rivetted to its bottom, so as to occupy nearly one-half of its area. The ashes are rammed down very close with a wooden beater, and particularly within the bars of the frame, as it is laid on a flat floor. More ashes are then added, and beaten carefully in, till the frame is quite full. By means of a sharp-edged spade, five inches square, a cavity is formed in the test for containing the melted metal, and at one end of the frame a semi-elliptical hole is cut through the breast, which latter is to be left of sufficient solidity and thickness. The test is now to be turned on its side, and dressed from all superfluous ashes adhering to the bottom, taking care that none shall be left flush with the bottom of the frame or cross bars, otherwise the test might be bulged, by fixing it at the bottom of the furnace. The rim being plastered with clay or moistened ashes, the test is placed upon the supporting cross bars, and fixed firmly with wedges against the bottom of the furnace, the breast being next to the feeding hole. A moderate heat is now applied, and gradually increased till the test be red hot; and when it ceases to emit steam from the under side, it is sufficiently dry. This previous preparation being completed, the following is the method of operation as it is described by Mr Sadler*.

"Lead previously melted in an iron pot is ladled into the test until the hollow part be nearly filled, the operator closes the feeding aperture, and increases the heat of the furnace until the surface of the lead is well covered with litharge; he then removes the door from the feeding hole, and with an iron rod, which has one end bent down at right angles about three inches, and made flat or chisel-shaped, scrapes the small gutter or channel until the litharge just flows into it; the blast from a pair of double bellows is then directed from the back part over the surface of the test, the litharge is urged forward, and flows from the gutter upon the floor of the refinery; the operation now goes forward, gradually adding lead as the escape of litharge makes it necessary, until the gutter is so worn down that the test does not contain more than an inch in depth of lead, the blast is then taken off; the gutter filled up with moistened ashes, and a fresh one made on the other side the breast; the test is again filled, though not so full as at first, and the operation carried on until this gutter also is worn down and the test contain from about 50 to 70 pounds of alloy. This quantity is run into an iron pot, and set by until a sufficient number of pieces have been collected to make it worth while to take off a plate of pure silver from them.

"The quantity of alloy left in the working off each test must depend in a great measure upon the quantity of silver which by estimation it is supposed to contain. A sufficient quantity of lead should always be left in the alloy to make it fuse easily in the iron pot.

"When the test is removed from the furnace and broken up, the litharge will be found to have penetrated to an inconsiderable but an equal depth in the ashes; that part not impregnated with litharge may be pulverized, mixed with fresh ashes, and again used for another test.

"The operation of taking off the silver pure differs in no respect from the foregoing, only more care is observed in the working, not to suffer the escape of any metallic particles with the litharge, as that would occasion considerable waste of silver. As the process advances, and the proportion of silver to lead increases, the litharge assumes a darker colour, a greater heat becomes necessary, and at last the brightening takes place; the interior of the furnace, which during the whole of the process had been very obscure and misty, clears up. When the operator observes the surface of the silver to be free from litharge, he removes the blast of the bellows, and suffers the furnace to cool gradually; as the silver cools many protuberances arise on the surface, and fluid silver is ejected from them with considerable force, which falling again on the plate, spots it very fantastically with small globules.

"The latter portions of litharge bring over a considerable quantity of silver with them; this is generally reduced by itself and again refined.

"The litharge as it falls upon the floor of the refinery is occasionally removed; it is in clots at first, but after a short time as it cools it falls for the most part like slaked lime, and appears in the brilliant scales it is met with in commerce: if it is intended as an article for sale, nothing more is necessary than to sift it from the clots which have not fallen, and pack it in barrels.

"If, on the contrary, it is intended to be manufactured into pure lead, it is placed in a reverberatory furnace, mixed with clean small-coal, and exposed to a heat just sufficient to fuse the litharge. The metal as it is reduced flows through an aperture into an iron pot, and is cast into pigs for sale. During the reducing, care is taken to keep the whole surface of the litharge in the furnace covered with small coal.

"In some smelt works, instead of a reverberatory furnace for reducing, a blast furnace is made use of, on account of the greater produce, but the lead so reduced is never so pure as that made in the wind furnace. The oxides of the metals, which require a greater heat to reduce than the lead, are in the blast furnace generally reduced with it.

"The volatile oxides, as zinc, antimony, and arsenic, are mostly carried off by evaporation during refining; a considerable portion of the oxide of lead itself is carried off by evaporation, making the interior of the furnace so misty and obscure that a person unused to refining cannot see more than a few inches into it.

"A considerable portion of these oxides is driven by the blast of the bellows through the feeding aperture, and would be dissipated in the refining-house, to the great injury of the workmen's healths; to prevent their ill effects, the arch or dome over the feeding hole is erected to carry the fume into the stack of the furnace."

We shall now describe the method of treating the Silver proper ores of silver, as it is conducted by Schreiber at Allcmont in France. These ores are native silver, and the sulphuret of silver mixed with arsenical cobalt, pyrites, iron ochre, clay, calcareous spar, and some other earthly minerals. The silver being dispersed in very minute grains through the gangue, cannot be separated from the stony parts by washing. After the ore is picked by the hand, it is pounded dry in the stamping mill, and is reduced to the consistence of coarse sand. Roasting, previous to fusion, is not required; but the ore being refractory, it is found necessary to employ a flux composed of quicklime, scorice from a preceding fusion, and slag from the iron forges. To supply the proper quantity of lead, powdered galena, with the litharge and scorice furnished by the refinery, and with old cupels ground to powder, is added to the ore in such proportions that the lead, which is obtained by the fusion, may contain two per cent. of silver, allowing 20 per cent. of the lead at least to be lost by evaporation, or combining with the scorice. After being properly mixed, the materials are subjected to the heat of a powerful blast-furnace, with alternate charges of charcoal. The products of the fusion are lead combined with silver, a black, compact, sulphureous, semi-metallic substance which is called matt, and some scorice. The scorice thus obtained is neglected, excepting a certain proportion, which is reserved as a flux for the next parcel of ore. But the matt, which is tolerably rich in silver, is again melted with litharge, and the lead carries with it almost the whole of the silver; and although this second matt contains a portion of silver, it is not found worth while to subject it to a second fusion. After refining the lead procured by these operations, it is found to yield about two per cent. of silver. The process of cupellation is performed at a higher heat than usual, which it is supposed is necessary by the presence of a small portion of iron; but the consequence of employing this high temperature is to increase the waste of the metal by evaporation; for instead of seven or eight per cent. it amounts to no less than 20 per cent. And as every pound avoirdupois of the lead thus volatilized, contains from six to ten grains of silver, the loss in this process is very great. Perhaps it might be diminished by mixing a larger proportion of lead with the silver ore.

But other silver ores afford both lead and copper, and in this case a more complicated operation becomes requisite. In the first part of the process the poorest kinds of silver ore, or such as contain but a small proportion of copper and lead, and a great deal of stony matter, are to be mixed with the poorer pyritical ores, or such as contain little silver and copper, and a great deal of sulphur and iron. A portion of scorice obtained from a former process, and containing the oxides of lead and copper, with some silver, is added to this mixture by way of flux. The materials thus prepared being exposed to heat in a blast-furnace, react on each other, and enter into fusion. The stony matter is dissolved, and the melted mass separates into two distinct parts, of which the heaviest occupying the bottom of the furnace forms about one-fourth of the whole mass. This is called matt, and contains all the silver, with the greater part of the copper, most of the lead, iron, and sulphur, and generally zinc and arsenic. The slag which swims on the surface, as being the lighter portion, consists of the greater part of the sulphur, oxide of iron, and earthy matters; the small proportion of lead and copper is not worth the trouble of extraction.

To drive off part of the sulphur and other volatile impurities, the crude matt obtained in the preceding operation is roasted, and being mixed with one and a half times its weight of a richer kind of silver ore, and twice its weight of lead scorice, by way of flux, it is again fused, and thus a rich matt is procured, which may contain from nine to ten pounds of lead, from three to four pounds of copper, and from six to seven ounces of silver in the quintal, besides a quantity of scorice which holds a little silver, and which may therefore be successfully employed as a flux in subsequent fusions. This rich matt being roasted, is mixed with half its weight of litharge and scorice in equal proportions, and again subjected to fusion. The product of this fusion is a quantity of metallic lead, containing from six to eight ounces of silver in the quintal; a similar quantity of copper matt, which contains from 30 to 40 pounds of copper, and about four ounces of silver in the quintal; and lastly a quantity of scorice, which contains from six to ten pounds of lead, and about 40 grains of silver in the quintal.

The copper matt of the above operation is next roasted, and fused with a quantity of lead and copper scorice, and the product obtained is black copper, which contains from 60 to 80 pounds of copper, and from five to ten ounces of silver in the quintal. This black copper being melted with litharge and scorice, the most part of the silver combines with the lead, and after one or two fusions, the copper is entirely freed, not only from the lead and silver, but also from the sulphur, iron, and other impurities.

Liquation.—The affinity between lead and silver is much stronger than the affinity between lead and copper. In consequence of this affinity, lead and silver are easily separated from copper, by being exposed to a moderate heat. This process is called liquation or eliquation. When the black unrefined copper, or copper matt, contains the proper proportion of silver for this operation, it is first used with lead or litharge, or with a mixture of the two, and an alloy consisting of copper, lead, and silver, is thus obtained. This is cast into moulds, so that the metallic product shall be in the form of round masses or leaves, which being set in a furnace on an inclined plane of iron, with a small channel grooved out, are exposed to a moderate red heat. By this process the lead melts, or, as it were, sweats out of the loaf, and carrying the silver along with it, on account of its stronger affinity for this metal, runs down the groove, while the copper remains behind as a dark red spongy mass. The lead containing the silver being subjected to the process of cupellation, the latter is obtained separate. But, in adopting this process, the proportion of the three metals must be attended to. The lead should not be more than four times the weight of the copper, otherwise the alloy becomes so fusible, that part of the copper will be melted and carried along with the lead and silver; or, if too great a degree of heat is applied, the whole loaf of liquation will be fused, and the process must again be repeated. The proportion of lead should at least be 2½ times the quantity of copper, otherwise a considerable proportion of it, and also part of the silver, will remain in the loaf after heating. But as this process is now more rarely followed, we we shall not enter into any farther detail of the particulars connected with it.

Reduction of silver ores by amalgamation.—This process, by which silver ores are reduced, and which is now pretty generally followed in different parts of Europe, was first practised by the Spaniards in South America. The ores which are subjected to amalgamation, are such as contain only a small quantity of lead or copper; but it is of some importance that there should be a certain proportion of iron pyrites, and if this proportion be not naturally mixed with the ore, it is a good practice to supply the deficiency, by adding what is wanting to the dressed ore, so that the pyritical contents may, as nearly as possible, be in a certain proportion to the quantity of silver, which is to be ascertained by previously assaying a portion of the ore.

The ore being reduced to the consistence of coarse sand, is carefully mixed with common salt, in the proportion of eight or nine per cent. when the silver in the ore amounts to eight ounces per quintal; and when the latter amounts to 32 ounces, or even a greater proportion, from 10 to 12 per cent. of salt is to be added. The next process is roasting the ore, in which about three quintals are spread on the floor of a reverberatory furnace, and subjected to a moderate red heat. During the roasting the ore is to be turned twice or thrice, that every part of it may be equally exposed to the heat. The first charge being withdrawn, an experienced workman knows by its appearance whether the proportion of salt be too little or too much, and, as may be required, more salt or ore is added to the unroasted parcel. When the whole of the ore is roasted, it is ground in a mill, passed through sieves, by which it is made as fine as meal, and is then prepared for the proper process of amalgamation. This is performed in the following manner. A number of small barrels, which are made to revolve rapidly on their axes by means of machinery, or fixed tubs, either open or covered, having in the centre of each an instrument resembling a chocolate mill, which may be turned rapidly by similar machinery. The tubs or barrels are filled about one-third with water, and afterwards a sufficient quantity of roasted ore and mercury, in nearly equal proportions, is introduced, so that the whole may be of the consistence of thin mud. The machinery is put in motion, and continued without interruption for 30 or 48 hours, according to the nature of the ore, when the amalgamation is completed. About a quarter of an hour after the agitation of the matter in the barrels has ceased, the greater part of it falls to the bottom, and is withdrawn by opening a hole made for the purpose. The earthy residue is carefully washed by small portions at a time, and thus a good deal of the amalgam which, from being very minutely divided, could not sink through and mix with the rest, is recovered. The earth, however, if originally rich in silver, still retains a small proportion. It is therefore dried, and being mixed with about 3 per cent. of salt, is again roasted, but at a higher temperature than at first; and the process of amalgamation being again repeated, the whole of the silver is extracted. The fluid amalgam is strained through a closely woven bag, and is thus separated into nearly pure mercury and a stiff amalgam; and the latter being subjected to distillation, the mercury is driven over, and the silver remains behind. The copper, which is combined with the silver, is separated by cupellation.

The process of amalgamation is thus explained. The greater part of the sulphur of the silver and pyrites is, by roasting, burnt off, and converted into sulphurous acid, which latter, as soon as it is formed, and assisted also by the affinity of the silver for muriatic acid, decomposes the common salt, forming a sulphate or sulphite of soda, while the muriatic acid combining with the silver, forms muriate of silver. In the amalgamation which follows, the mercury, being in great proportion, decomposes the muriate of silver, and is partly converted into calomel. Hence it appears, that the loss of mercury, which is sometimes very considerable in this process, arises, first, from the conversion of part of it into calomel; and, secondly, from the extremely minute division of another part, so that it is carried off in washing the earthy residue; but the proportion of the latter depends much on management.

By the following method silver may be separated from copper, according to Napiere, without the expensive and complicated process of liquation. The mixed metal is melted; a quantity of sulphur is sprinkled over its surface, while the whole is stirred about with a stick by an assistant, so that the sulphur may combine with the copper into a matt, which floats above the metal, and is to be removed with a pair of tongs, previously moistening its surface with water, to make it solid. Another portion of sulphur is next to be stirred in, and the second matt produced is to be removed in the same manner. This process being repeated a sufficient number of times, the greater part of the copper is converted into matt, holding a small proportion of silver, while the remaining copper, which retains the most of the silver, originally diffused through the whole mass, becomes rich enough to be sent immediately to the refinery. In treating the matt, it is first to be reduced to powder, mixed with common salt and quicklime, in the proportion of 12 per cent. of each, roasted for 10 hours, amalgamated as before; and after three successive roastings and amalgamations, the whole of the silver may be extracted.

Table of the quantity of Silver introduced into Commerce, taken at an average between the years 1790 and 1802.

| Old Continent | Kilogrammes | |---------------|------------| | Siberia | 17,500 | | Hungary | 20,000 | | Austrian States | 5000 | | Hartz and Hesse | 5000 | | Saxony | 10,000 | | Norway | 10,000 | | France | 5000 |

Total: 72,500

| New Continent | Kilogrammes | |---------------|------------| | North America | 600,000 | | Spanish possessions in South America | 275,000 |

Total: 875,000

Kilogrammes: 947,500, or about 2,091,162 lbs. avoirdupois. The ores of copper are very various. This metal is found native, in the state of oxide, in the state of sulphuret, and in that of salt, combined with carbonic, muriatic, phosphoric, and arsenic acids.

Sect. I. Of the Analysis of the Ores of Copper.

The analysis of the ores of copper, it is obvious, must vary, according to the nature of the substances with which they are combined; but as a great proportion of the ores of that metal are combined with sulphur or arsenic, when they are to be treated in the dry way, they are first roasted, for the purpose of expelling those substances. To effect this, the ore is mixed with about one half its bulk of charcoal powder, or fine saw-dust, and then subjected to a low red heat, on a flat tile or muffle, on which it should be thinly spread. The sulphur or the arsenic rises in fumes; and to accelerate the separation of these substances, the mixture should be frequently stirred, observing at the same time not to increase the heat to such a degree as to make the ore clot together, which is one of the objects in the use of the saw-dust or charcoal. When it appears that the fumes cease to rise, and the whole of the charcoal is burnt off, the part of the ore remaining is now in the state of oxide, but mixed with a quantity of sulphur or arsenic, which cannot be entirely separated by roasting, and with the earthy matters with which the ore was originally combined.

The next object is to reduce the oxides, thus obtained, to the metallic state; and in this process of reduction the oxide is exposed to a high temperature, in contact with some carbonaceous matter, and secluded from the air. It has been a common practice to add some alkaline matters by way of flux, to promote the fusion of the extraneous matters combined with the ore; but the experience and observation of more enlightened chemists have proved, that a portion of the metallic oxide is always dissolved by saline fluxes, so that by assays in the dry way with saline fluxes, a less proportion of metal than the ore really contains, is obtained from it. The loss, according to Klaproth, between the treatment of a copper ore in the dry way, and the same ore, in the moist way, amounted to no less than 9 per cent. To obviate this inconvenience, a flux is employed by some, composed of fusible glass, into which a large proportion of alkali and silica enters, without any metallic matter; or fluor spar, lime, and particularly borax. By the latter, a thinner fusion of the vitrifying mixture, than by an equal quantity of any other substance, is produced, so that a smaller proportion of borax than of the alkaline matters answers all the purposes of a flux; and thus the loss of the metallic oxide, by solution, is less.

But in reducing the pure oxides, or the carbonated oxides of copper, the method which is attended with scarcely any loss, is by subjecting them in contact with charcoal, in a covered crucible, to an intense heat. It is indeed in this way that the reduction of roasted copper ores is conducted on a large scale; but as these latter contain sulphur, arsenic, iron, and other impurities, the process must be many times repeated before the copper is brought to a malleable state.

In reducing the sulphurated ores of copper, a button of metal, of considerable purity, may be sometimes obtained by means of a single operation. The tedious process of roasting is avoided, by adding to the ore two or three times its weight of nitre, and projecting it into a hot crucible. When thrown into the crucible, a deflagration takes place, in which the sulphur is burnt, and converted into sulphuric acid, which unites with the potash of the decomposed nitre. The metal being now freed from the sulphur, is in a state of complete oxidation by the nitric acid, and may be reduced by adding a flux of tartar and pitch, or other similar matters, and applying a strong heat for a sufficient length of time. But it seems to be more advisable to separate the metallic oxide after deflagration. This may be done by washing the mixture, after which the oxide is to be reduced by the proper flux.

In the analysis of copper ores in the moist way, the metal is obtained separate in three states; either in the metallic state, in the state of black oxide, or in that of green carbonate. If a polished piece of iron be introduced into an acid solution of copper, it is immediately covered with a coating of shining metallic copper, which is owing to a part of the iron being dissolved by the acid, and a corresponding portion of copper being separated from the solution. The whole of the copper may be precipitated in this way, and at last the solution contains only iron. The precipitate, which is in the form of ragged filaments, may be washed, dried, and weighed, so that the proportion of the metal in the ore examined may be ascertained. It may be added, that the precipitation is greatly promoted, by boiling for a short time, especially towards the end of the process, which produces the separation of the last portions of the copper; and it should be farther observed, that a perfect separation of copper from iron is obtained only when the solution is made in sulphuric or muriatic acid, and not in nitric acid. The method of separating copper from silver has been already mentioned. It may be separated from lead, by adding sulphate of soda to the solution, by which an insoluble sulphate of lead is obtained, and the copper remains behind. To separate copper from antimony, the oxides of copper and antimony are digested with nitric acid; the copper is dissolved, and the antimony is left. By immersing a piece of metallic tin in the solution, copper may be separated from tin; for by this means the copper only is precipitated. Arsenic is separated from copper by dissolving in nitrous acid, and adding acetate or nitrate of lead, which produces an insoluble arseniate of lead, and leaves the copper behind. In case there should be an excess of lead, the addition of sulphate of soda will throw it down in the form of insoluble sulphate. When nickel is combined with copper, it is usually conjoined with iron. Ammonia precipitates all the three metals; but, when added in excess, redissolves the nickel and copper. To obtain the latter separate, supersaturate with muriatic acid, and introduce a polished piece of iron, by which the copper is precipitated, and the nickel remains in the solution.

To ascertain the quantity of precipitated copper obtained from the examination of an ore, it is to be washed and dried, put into a small crucible, moistened with a drop or two of oil, and covered with borax. Thus prepared, it is subjected to strong heat for a few minutes, Copper, and a solid button of malleable copper is produced, which may be accurately weighed. But if the product of the analysis be in the state of green carbonate, which is obtained by adding carbonate of potash or soda to a solution of copper, the green precipitate thus formed, is to be washed and dried at the temperature of boiling water. An hundred and eighty parts of this carbonate are equivalent to 100 of metallic copper. The quantity of copper obtained by analysis may be estimated also in the state of black oxide. If the green carbonate be boiled for a few moments in caustic potash, it shrinks and becomes a deep brownish black fine powder, which is a pure oxide of copper in its highest state of oxidation. One hundred parts of this oxide, after being well washed, and dried in a low red heat, for a minute or two, are constantly found to contain 80 parts of pure metallic copper.

We shall now give a few examples of the analyses of particular ores of copper.

**Vitreous copper ore, or sulphuret of copper from Siberia.**—The following is the mode of analysis of vitreous copper ore by Klaproth.

"1. Upon 200 grains of the ore, coarsely powdered, moderately strong nitric acid was affused, which attacked and dissolved them with frothing and extrication of red vapours. The solution was clear, and the sulphur alone in the ore was left behind, floating in the fluid, in gray, loose flocculi, without any other residue; which indicated that no antimony was present. The sulphur collected on the filter was heated in a small crucible to inflammation, and it burned with its peculiar odour, without any trace of arsenic; yet leaving a slight portion of oxidated iron and siliceous earth.

"2. The solution, which had a pure blue colour, was treated first with muriate, and then with sulphate of soda. But none of these, nor any other salt, rendered it turbid, or produced any other alteration; by which it appears, that this ore contains neither silver nor lead.

"3. To determine, with proper accuracy, the proportion of the constituent parts, I repeated the examination in the following manner. Two hundred grains of the powdered ore were combined and heated with muriatic acid, to the degree of boiling. But as this alone manifested no action on it; I added nitric acid gradually, by drops, which exerted a strong attack in each instance. When the solution of the ore had been accomplished, I separated the fluid from the sulphur floating on the surface; and digested this last once more with a fresh quantity of muriatic acid, dropping into it some nitric acid, after which I collected it upon the filter. This sulphur, washed and desiccated, weighed 38½ grs. out of which, after its combustion, 1½ grain of siliceous earth remained; so that the true amount of sulphur was 37 grains.

"4. The solution exhibited a glass-green colour. I divided it into two parts. Into one half polished iron was immersed, upon which the copper precipitated of a dendritical form, and pure metallic brilliance. It weighed 7½ grs., when washed, and immediately desiccated in a moderate temperature.

"5. In order to ascertain the proportion of iron contained in the ore, I combined the other half of the solution with caustic ammonia added to excess of saturation. The precipitated iron remained behind, in the form of a subtle brown mud, which, collected on the filter, desiccated and ignited, weighed three grains. But as the iron is contained in the mixture of the ore, not in this calciform state, but in the reguline, which last is to the first in the proportion of 3 to 4, these three grains of oxidated iron give 2½ of metallic iron to be added in the computation.

"Therefore, an hundred parts of the Siberian vitreous copper ore consist of,

| Copper | 78.50 | |--------|-------| | Iron | 2.25 | | Sulphur| 18.50 | | Silice | 0.75 |

100.00

**Variegated copper ore.**—This ore was analysed by Klaproth, in the following manner.

"1. One hundred grains of the pulverized ore were subjected to gentle digestion with nitric acid, whose action upon it was but moderate. From the residue, the sulphur was driven out by combustion. This residue, when a second time digested with nitric acid, dissolved in it, leaving only a slight portion of a red oxide of iron. On examining the solution, first by common salt, and then by Glauber salt, it continued limpid and unchanged.

"2. Upon 200 grains of the powdered ore, muriatic acid was affused, the mixture heated, and then combined in small portions with nitric acid. The solution, which was thus performed, had a brown colour while concentrated; but as soon as it was diluted with water, it acquired a green. The remaining sulphur was gray, tenacious, and spongy, and weighed 72 grains when dry. By slow combustion it left 35 grains, of which, after extraction by muriatic acid, five grains still remained behind. These lost one grain more of sulphur by burning, and the remaining four grains dissolved entirely in muriatic acid. Whence the quantity of sulphur amounted to 38 grains.

"3. The muriatic solution was divided into two equal parts; and the copper was precipitated from one of them by means of iron. It amounted to 69½ grains.

"4. The other half was supersaturated with caustic ammonia, and the oxide of iron which fell down was collected. This, when moistened with linseed oil, and exposed to a low red heat, weighed 10 grains; which are equal to 7½ grains of metallic or reguline iron.

"Thus, in 100 parts of this variegated copper ore from Norway were found,

| Copper | 69.50 | |--------|-------| | Sulphur| 19. | | Iron | 7.50 | | Oxygen | 4. |

100.00

"In supplying the deficiency in the sum of weights of the copper, iron, and sulphur, from the hundred, by putting oxygen in the account, I mean to characterize this last as a constant constituent part of variegated copper ore, producing in it those variegated colours: in the same manner, as in steel, in copper pyrites, and other..." other metallic substances, the beginning of their oxidation is indicated by a similar diversity of colours.

"In the last-mentioned substances, however, the changeable colours are only owing to external causes; for which reason they present themselves only on the surface, when long exposed to air. On the contrary, the variegated copper ore is penetrated throughout its whole mass by the oxidating principle. This corresponds with the deficiency of weight to make up the sum of the fixed constituent parts of the ore here analysed; whereas no such loss is observable in the vitreous copper ore, treated and decomposed by the same method. It is on this account also, that the action of the nitric acid is less strong, and the disengagement of nitrous gas is less copious, in the variegated than in the vitreous copper ore."

Malachite, or carbonate of copper.—Klaproth analysed a Siberian ore of this species, according to the following process.

"1. One thousand grains of compact reniform malachite, from the Turjin mines, on the Ural, were reduced to powder, and heated to complete redness in a small glass retort, connected with the pneumatic apparatus. Much carbonic acid gas was disengaged in this process, to the amount of 252 cubic inches, without reckoning that part which was absorbed by the water of the apparatus. This gas was entirely absorbed by lime water, at the same time that a proportionate quantity of carbonate or crude calcareous earth was produced. In the intermediate small receiver a moisture collected, weighing 78 grains, which, upon trial, proved to be pure water.

2. The pulverulent residue taken out of the retort appeared of a black colour, and weighed 716 grains. To serve for the following experiments, it was divided into four parts, at 179 grams each; and hence corresponding to 250 grams of rough malachite.

3. One hundred and seventy-nine grains of ignited malachite, combined with three times its quantity of black flux, were put into an assay crucible, without lining it, and covered with muriated soda. In this situation it was committed to the fire of the blast furnace, and when the coals had become red hot without the action of the bellows, it was kept melting for the space of 20 minutes. After cooling, it was observed that, in the broken retort, the whole mixture, under the covering of common salt, had run into an uniform, compact, and opaque mass, of the bright red colour of ordinary sealing-wax, and that no metallic button had been formed.

"It follows from this, that there was not carbone enough present to take up entirely the oxygen of the metallic oxide. Therefore the copper has, by means of this small remainder of oxygen still united with it, been brought into the state of red oxide of copper; and, as such, it has diffused itself uniformly through the alkaline salt.

4. One hundred and seventy-nine grains of ignited malachite were mingled with three times their quantity of black flux, and one-tenth of powdered charcoal. When fused in this state, during 20 minutes, under a stratum of common salt, in an assay crucible not lined in the inside, they afforded a button of reguline copper, which had run well together, and weighed 136½ grains.

5. Another 179 grams of ignited malachite, mixed with thrice as many grains of black flux, and one-fifth part of their weight of colophony, and likewise fused for 20 minutes, under a cover of muriate of soda, in a crucible not secured by lining, yielded a well-melted button of reguline copper, weighing 138 grams.

6. The remaining 179 grams of ignited malachite were, like the preceding, melted during the time of 20 minutes, under a cover of common salt. But the assay crucible had previously been lined with powdered charcoal, and the malachite mingled with an equal weight of calcined borax, with half its quantity of white glass, and one-fourth part of colophony, or boiled turpentine. By this process I obtained, indeed, a well-fused button of reguline copper; but with a considerable loss, as it weighed only 105½ grams.

"In order to discover more accurately the constituent parts of the malachite, I performed the following experiments.

7. One hundred grains of malachite, reduced to powder by trituration, were dissolved in nitric acid; which was effected without leaving any residue. The solution had a bright-blue colour, and was saturated to excess with caustic of ammonia; but the precipitate produced was entirely, and without turbidness, redissolved by the excess of the alkali. This shewed that the malachite here examined was perfectly free from iron, and similar admixtures.

8. I combined 100 grams of triturated malachite with a sufficient quantity of sulphuric acid, previously diluted with five parts of water, and accurately weighed together with the vessel. After the malachite had been wholly dissolved, which was effected gradually, and with a moderately strong effervescence, the loss of weight, occasioned by the carbonic acid gas that was extricated, was found to consist of 18 grams.

9. One hundred grams of the same powdered malachite were ignited, at a moderate heat, in a covered crucible. The black residue had lost 29½ grams in weight. If from these be subtracted 18 grams for the carbonic acid, the remaining 11½ grams of loss will consist of water.

10. And lastly, 100 grams, which had been dissolved in diluted sulphuric acid, and precipitated by zinc, yielded 58 grams of pure copper.

"In consequence of these experiments, the Siberian malachite consists, in the 100, of,

| Copper | 58 | |--------|----| | Carbonic acid | 18 | | Oxygen | 12.50 | | Water | 11.50 |

100.00 *."

Muriate of copper.—This ore, when exposed upon charcoal to the action of the blow-pipe, gave to the flame a blue and green colour; the muriatic acid was soon driven off, and a metallic button of pure copper remained.

This ore of copper was examined and analyzed by Klaproth in the following manner. A portion of the ore being reduced to powder, and boiled with water, communicated no colour to the solution; and, with the addition of a solution of nitrate of silver, afforded a small quantity of a white precipitate which blackened... in the day light. This experiment shows, that the proportion of muriatic acid is too small to give a compound soluble in water.

"1. One hundred grains of the elutriated mineral dissolved readily and quietly in nitric acid affused in the cold. The solution possessed a pure blue colour, and deposited a little of a brown iron ochre, which, separated by filtering, weighed a grain and a half. It was then diluted with water, and treated with a nitric solution of silver. The precipitated muriate of silver, when edulcorated, dried, and melted at a moderate degree of heat, in a silver pan, weighed $64\frac{1}{2}$ grains.

"One hundred parts of metallic silver yield by such combination $133$ parts of muriated silver. But as this metal, to be rendered soluble in acids, takes up $12$ per cent. of oxygen, these must be subtracted; so that of this increase of weight by $33$ parts, there remain $20\frac{1}{2}$ for the muriatic acid.

"These principles being laid down, the above $64\frac{1}{2}$ grains of muriated silver will fix the proportion of the muriatic acid, contained in $100$ parts of the ore, very nearly to $10$ grains.

"2. That I might be sure of having completely separated the muriatic acid from the nitric solution of this copper ore, I added the nitrated silver in a small degree of excess; and this silver I afterwards threw down with muriatic acid, and filtered it off. Which done, the copper was precipitated in the metallic state, by means of a piece of polished iron immersed in the solution. It amounted to $57\frac{1}{2}$ grains when collected and carefully dried.

"The copper, however, is contained in the ore as an oxide. In this state its weight is increased $25$ per cent. by the oxygen; which, for those $57.50$ grains of metallic copper, just now mentioned, gives, by calculation, $14.38$ grains.

"Now, since what is deficient from the first weight of the ore employed is to be considered for the greatest part as its water of crystallization, and since those $15$ grains of ferruginous ochre do not belong to the composition of the ore, the constituent parts of the muriated ore of copper may be said to be in the $100$ as follows:

| Oxide of copper | 73 | |-----------------|----| | Muriatic acid | 10.1 | | Water of crystallization | 16.9 |

*100.0.*

Phosphate of copper.—The following is the method of analysis adopted by Klaproth, in the examination of this ore.

"1. Because this ore is very much intermixed with its quartzose matrix, I pulverized a portion of it, previously freed as much as possible from the stony matter, and ascertained the weight of quartz still united with it, by solution in nitric acid. The quartz amounted to $16$ parts in $100$ of the purified ore.

"On this consideration, I weighed $116$ grains of the powdered ore, and poured nitric acid upon it. The mixture became of itself moderately warm. When the solution, assisted by a little heat, was thoroughly brought about, and by means of filtration freed from the undissolved quartzy matrix, it showed by its pure sky-blue colour, that it contained no iron.

Vol. XV. Part II.

"After the small portion of the predominant acid had been saturated with potash, I added to the solution dissolved acetate of lead, until no farther precipitation took place. The precipitate was at first drenched for a while with weak acetic acid, then elixivated with water, and at last perfectly dried in a low heat. It weighed $138$ grains.

"That this precipitate was a combination of lead with phosphoric acid, of this I had myself assured by a previous experiment, made with another portion of the same fossil. It exhibited the phenomenon, which is peculiar to phosphated lead; namely, that under the blow-pipe it runs into a pearl, which in the very moment of fixation, rapidly assumes a garnet-like form with shining surfaces.

"Upon another portion of that precipitate, half its weight of sulphuric acid, sufficiently weakened with water, was poured and digested with it. The clear fluid, which had been filtered off from the generated sulphate of lead, and contained free phosphoric acid, was first half saturated with soda, and upon this perfectly neutralized with ammonia. By crystallization, it yielded microcosmic salt, or phosphate of soda and ammonia.

"3. In order to discover the proportion of the phosphoric acid combined with those $138$ grains of the precipitate mentioned before, I proceeded to the following experiment.

"I burned pure phosphorus under a large glass-bell, dissolved the obtained dry phosphoric acid in water, passed it through the filter, and reduced it by evaporation, in a sand heat, to a smaller volume. When towards the end of this process, flames of phosphorated hydrogen gas appeared, I added nitric acid by drops till no longer any red vapours were disengaged.

"Of this perfectly oxygenated unctuous liquid phosphoric acid, I diluted $100$ grains with water, and neutralized the liquor with finely powdered white marble; of which $324$ grains were employed. The mixture was evaporated to dryness, and the dry mass kept in a moderate red heat for half an hour. This ignited phosphate of lime weighed $256\frac{1}{2}$ grains. In the $324$ grains of marble employed in this experiment, the portion of lime, or pure calcareous earth, amounts to $178.20$ grains, which if subtracted from the above $256.50$ grains, determine the quantity of the phosphoric acid ingredient in that calcareous phosphate to be $78.30$ grains.

"From these data, taken together, it now was rendered evident, that in those $138$ grains of phosphated lead, which have been produced by the combination of lead with the phosphoric acid, constituting a component principle of the portion of the ore examined,—the concrete phosphoric acid amounts to $30.95$ grams.

"4. The remaining part of the solution, which yet contained the cuprous part of the ore, was first treated with sulphate of soda, to separate the small portion of lead it still held dissolved from a slight excess of acetated lead added in the process (2.). Which done, it was mixed with a little of uncombined sulphuric acid, and a piece of polished iron put into it to precipitate the copper, which I found to weigh $54.50$ grains. But as this metal is contained in the ore in an oxidated state, which requires $25$ per cent. of oxygen; there must $68.13$ grains be reckoned for the oxide of copper." "One hundred grains of this phosphated ore of copper, therefore, consist of,

Oxide of copper. 68.13 Phosphoric acid, 30.95

* 99.08."

Arseniate of copper, or needle-shaped copper ore.—This ore was examined by Klaproth, according to the following process.

"1. Under the blow-pipe, upon charcoal, this ore detonates, emits a white arsenical smoke, and runs into small reddish-gray globules, which, when again fluxed with borax, yield a pure regulus of copper.

"2. A pure, massive specimen of this ore, weighing 50 grains, was kept in a porcelain crucible, during 15 minutes, in a moderate red heat. Its figure was not altered by the fire; but its dark olive colour was changed into a bright grass green, inclining to that of the siskin. Its weight was diminished by 1½ grain.

"3. Nitric acid dissolves it quietly in the cold, and the solution possesses an undefined blue colour. By the addition of nitrated silver, the mixture is not in the least rendered turbid. Acetate of barytes produces a precipitate which entirely disappears upon dilution with water. The effusion of dissolved acetate of lead, forms with this solution a white precipitate, which upon the charcoal emits arsenical vapours, and is reduced to metallic lead, when combined with an excess of ammonia, the precipitate falling down at first, is directly redissolved, no cloudiness left behind, and the deep-blue colour is restored to the liquor.

"4. Also by the acetic acid this ore is gradually dissolved. Upon the evaporation of the solvent, a dark-green salt of a dendritical form remains behind.

"5. One hundred grains of the acicular olive copper ore, which had previously been freed, by means of elutriation, from the admixed reddish iron ochre, soon dissolved in nitric acid, and without the application of heat. The solution, being accurately neutralized with carbonated potash, was combined with dissolved acetate of lead, until all precipitation ceased. The obtained precipitate, when edulcorated and dried in a raised temperature, weighed 133½ grains.

"6. To be more convinced that this precipitate was an arseniated lead, I drenched it with water, and digested it with half its weight of sulphuric acid. The liquor, separated by filtration, contained uncombined arsenic acid. I neutralized it with soda, and treated part of it with a solution of nitrated silver. This produced a copious precipitate of arseniated silver, which possessed the brick-red colour peculiar to it, emitted arsenical vapours upon the charcoal, and was readily reduced to pure silver. The remaining part of the solution, when mixed with liquid nitrate of iron, afforded the common whitish precipitate of arseniated iron.

"Now in order to ascertain, by means of a comparative experiment, the proportion of the acid of arsenic combined with the 133½ grains of the above precipitate (1), I dissolved in water 100 grains of solid arsenical acid, and added to it a solution of acetated lead in small portions so long as any precipitate would appear. The arseniated lead then obtained weighed 297 grains after edulcoration and drying in a warm place. Hence it followed, that the quantity of concreted acid of arsenic combined with those 133½ grains of the precipitate, which the acid of arsenic contained in the ore had produced, must be estimated at 45 grains.

"And to be more assured that all the arsenical acid had been separated from the nitric solution of the ore, I added a little more of acetated lead than would have been absolutely requisite. This was afterwards again precipitated as sulphate of lead, by adding sulphated soda, and filtered off. To the solution, thus freed from the last precipitate, I added uncombined sulphuric acid, and precipitated the copper, now disengaged from its mineralizing acid, by means of a polished piece of iron, in the metallic state. Thus I obtained of it 40½ grains.

"But since in the composition of the olive copper ore the copper is contained in the state of an oxide, it yet remained to discover the proportion of oxygen. To attain this end, I dissolved 200 grains of pure copper in nitric acid, diluted the solution with a sufficient quantity of water, and again precipitated the metal with a lixivium of caustic potash. The precipitate had a light blue colour; but after the mixture had stood a couple of days in a moderately warm place, that blue colour was changed into a brown. When separated by filtration, washed with a large quantity of water, and desiccated in a low heat, this precipitate amounted to 269 grains. Upon ignition it weighed only 250 grains, and appeared in the form of a very subtile, fully-black powder.

"Therefore, because according to this experiment, copper acquires an increase of 25 per cent. of weight, by combining with oxygen, it is obvious, that for the above 40½ grains of metallic copper, we must put in the account 50.62 grains of oxidated copper.

"In consequence of this decomposition, 100 parts of the olive copper ore contain,

Oxid of copper, - 50.62 Acid of arsenic, - 45. Water of crystallization, 3.50

* 99.12."

Sect. II. Of the Reduction of the Ores of Copper.

The processes employed for the reduction of copper ores in the large way are extremely simple. It scarcely ever happens, it has been remarked, that the same order in conducting the different reducing processes, even in cases where the quality of the ore is found to be the same, is observed at two works. The same remark, however, might probably be made with regard to other manufactories, where the same practical management being long established, and attended with ordinary success, its inconveniences or advantages are rarely investigated, with regard to the abridgement of labour, or the diminution of expense. We shall now describe the processes for the reduction of copper ores, which are followed in different places, by which our readers, who are interested in the subject, will be enabled to appreciate the advantages of each, or to suggest improvements of which they are susceptible; and with this view, we shall describe the operations for reducing copper ores which are followed in Cornwall, and in Anglesea.

Method Method of reducing copper ores in Cornwall.—The ore is first broken to pieces, of the size of a hazel nut. This operation is known by the name of cobbining. The richer pieces of ore are then picked out by the hand. The next operation is roasting, which is performed in large reverberatory furnaces, 16 feet long, and 14 feet broad. The bottom of the furnace is composed of fire bricks, covered with sand, two feet thick. This sand becomes a semivitrified mass by the intense heat. The height of the chimney is from 40 to 50 feet, the draught of which is so strong, that the sulphur and arsenic, separated during the roasting, are carried almost entirely through it. The ore is introduced through a kind of funnel, and spread to the thickness of a foot over the bottom of the furnace. The fuel is placed at the anterior part of the furnace, so that the flame must pass over the surface of the ore as it is directed by the current of air towards the chimney. The ore is roasted in this furnace with a dull red heat for 12 hours, and is frequently stirred with an iron rake, to expose fresh surfaces to the flame.

The ore being sufficiently roasted, is carried to another furnace, nine feet long by six wide, where it is exposed to a fusing heat, without addition, except that of a little calcareous sand, when the slag does not rise freely. It is raked out at the end of every four hours, when it is of the consistence of soft dough, and is introduced into oblong moulds, a little water being sprinkled upon it, to make it sink down. The slag being raked off, a fresh quantity of calcined ore is introduced into the furnace, and the copper is tapped off by a hole in its side, which had been stopped up with wet clay mixed with one-fourth part of new coal, which prevents the clay from becoming so hard as to render it difficult to open the hole by means of an iron pick. As the rough copper flows from the furnace, it is conducted by a gutter into a large bucket, suspended by chains in a well, through which a stream of water is passing. The metal, as it falls into the water, is granulated, without explosion or danger, and is afterwards taken out by raising the bucket.

But in this state the copper is very impure, being quite brittle, and mixed with arsenic and sulphur, which can only be separated by other processes. For this purpose it is again melted, and granulated two or three times. Each time a slag is thrown up in the furnace; but as it contains some copper, it is not, like the first slag, rejected, but worked over and over again with new charges of calcined ore. The nature of the ore must determine the number of fusions and granulations. After the granulation, the mass is melted and cast into pigs, which have a blistered appearance on the surface. These are again broken up, and melted and roasted several times, by which the metal becomes purer, and is then cast into iron moulds, after which it is carried to the refining furnace; and being again melted with the addition of some charcoal, it is brought to such a degree of purity as to bear the hammer, and be fit for the market. In this way, by repeated calcination and fusion, the common ores of copper are freed from arsenic, sulphur, and earthy matters, and brought to the metallic state. Here it is proper to add, that where there is variety of ores, no small degree of judgment is requisite in sorting and distributing them for the furnace, that the more fusible ores being mixed with such as are more refractory, will render the poorer ores, by the addition of a portion of the richer, worth the working.

Method of reducing copper ores in Anglesea.—The ore, which is the sulphuret of copper, is broken into small pieces, and exposed to heat in a kiln, which is close covered. A little fire is applied to the mass of ore in different places, by which the whole is gradually kindled. The kiln is furnished with flues, which open into a long, close, pent-house gallery, for the purpose of collecting the sulphur, which rises in the state of vapour to the top of the kiln, passes through the flues into the long gallery, where it is slowly condensed, is afterwards taken out, and farther prepared for sale. The mass of ore, after it is once kindled, burns of itself for about six months, and in this time the sulphur chamber is four times cleared out. The improved sulphur chambers are constructed in the form of lime kilns, having the ore at the bottom, and the sulphur subliming at the top. The richer part of the roasted ore is exported without being subjected to any other preparation, but the poorest part is melted on the spot, and contains, besides a great deal of sulphur, many other impurities. The smelting houses consist of a range of large reverberatory furnaces, having chimneys above 40 feet high, thus producing a very strong current of air. Thirty one of these furnaces are arranged side by side under the same roof. The fuel, which is coal, is burnt on a grate at the anterior part of the furnace, and the flame is carried over the ore placed on the bottom of it, by the draught of air. Twelve hundred weight of roasted ore is introduced into the furnace, mixed with a small portion of coal dust. Here the ore is melted, and brought to an impure regulus, and when it is sufficiently fused, it is drawn off into earthen moulds. Each charge of the furnace is worked off in about five hours, and yields about half a hundred weight of rough copper, which after being farther purified, affords about 50 per cent. of pure metal.

In reducing copper ores at Neusol in Hungary, lead is employed in the refining part of the process. The rough copper is spread out on the rough bed of a furnace, and after being six hours in fusion, a quantity of lead, in the proportion of from six to eight per cent. of the copper, is thrown in. This immediately begins to vitrify, and form a thick scoria, along with the impurities of the copper. The scoriae are successively removed, till the whole is separated, and the copper is purified. The scoriae retain a portion of the copper, and are employed in a future operation. The process continues from ten to twelve hours, with fifty quintals of raw copper.

Some of the fine copper ores contain such a proportion of silver as to render it worth while to extract the metal. In the different roastings and fusions which are employed to bring the copper to a state of purity, the silver always remains combined with it, so that it must be separated by another process. The method of separating silver from copper has been already described, in treating of the reduction of the ores of silver.

The springs which are found in copper mines, or flow from rocks which afford copper ores, are often so strongly impregnated with blue vitriol or native sulphate of copper, as to yield a considerable quantity of this metal. It is obtained by the following process. Large square open pits, are formed of rammed clay, two or three three feet deep. Into these pits the vitriol water is pumped; a quantity of refuse iron is thrown in, which being allowed to remain for a considerable time, the iron is dissolved by its stronger affinity for the acid, and the copper being separated, is precipitated in the form of brown mud. After the water appears to be exhausted of the copper, the oxide of copper collected at the bottom is raked out, and being dried in the sun, may be reduced in the usual way. This material which is the richest employed in obtaining metallic copper, yielding fifty per cent. although contaminated with some iron and clay, is rarely smelted, excepting along with the poorer ores, some of which do not afford more than five per cent. of pure metal.

The plates of copper of a fine red colour, usually known by the name of rosette copper, are made by a particular management. When the metal is found to be in a state of sufficient purity, the surface while in fusion is well scummed, and allowed to cool till it is just ready to fix. At this time the workman brushes it over with a wet broom, by which the surface is immediately fixed, and a thin plate is separated from the metal below, which is still in a fluid state. The plate thus produced is taken off and thrown into water, where it becomes of a high red colour. The same operation is repeated and continued successively till the whole of the fluid metal is converted into thin irregular plates of the above description.

**Chap. VI. Of the Ores of Iron.**

The ores of iron, which present a considerable variety, are reduced, on account of the refractory nature of this metal, with no small difficulty. The most powerful agents must be employed for this purpose. And as the construction of furnaces is a matter of the greatest importance in the smelting of iron ores, we were led, when treating of that subject, to enter into a pretty full account of the processes themselves; to this account the reader is referred for information on the methods followed in the reduction of these ores. The present chapter therefore will be only occupied in giving an abridged view of their analysis.

**Sect. I. Of the Analysis of Iron Ores.**

*Native Iron.*—In analysing this ore, it may be dissolved in diluted nitric acid; the lead may be separated by adding sulphate of soda, thus forming an insoluble sulphate of lead; the oxides of iron and copper may be precipitated by means of caustic fixed alkali at a boiling heat; the addition of caustic ammonia will dissolve the copper, and the iron will remain behind.

*Pyrites.*—Iron pyrites is either magnetical, or is destitute of this property. When the ore is magnetical, it may be either proper magnetical pyrites, or common pyrites with a mixture of magnetic iron, either in the metallic state, or in that of black oxide. If the magnetism be owing to black oxide mixed with common pyrites, no hydrogen gas will be produced by digesting it in muriatic acid; and if metallic iron and pyrites be combined together, the gas obtained will be hydrogen gas: but if the ore examined be magnetic pyrites, the gas evolved by muriatic acid will be sulphurated hydrogen. The following analysis is applicable to both species of pyrites. 1. After reducing the pyrites to a very fine powder, let it be digested in nitric acid of moderate strength, and boiled almost to dryness; then add a fresh portion of acid, and repeat this process till the whole sulphur is converted into sulphuric acid. 2. Pour off the liquor, edulcorate the undissolved residue, and add the washings to the liquor. 3. Add to this carbonate of soda to a slight excess, and separate the precipitate, if any take place. 4. After neutralising the residual liquor by a little nitrous acid, it may be decomposed by muriate of barytes, which is to be added while any precipitate takes place. A hundred parts of this precipitate indicate 14.5 of sulphur in the ore. 5. The insoluble residue (2.) is next to be digested with caustic soda, and being evaporated to dryness and slightly ignited, the precipitate (3.) is to be added, and the whole dissolved in muriatic acid, and boiled nearly to dryness. By the diffusion of water the silica will be left in the state of a white insoluble powder. 6. Mix the muriatic solution with ammonia in slight excess, and the alumina and oxide of iron will be precipitated together, leaving the lime, if there should be any, in the solution, from which it may be obtained in the state of carbonate, by a mild alkali. 7. The iron and alumina may be separated by boiling in nitric acid, which leaves the metallic oxide untouched, or by digestion in caustic potash or soda, which produces a similar effect.

*Magnetic Iron Ore, Specula Iron Ore,* and *Red Iron Ore,*—are composed chiefly of oxide of iron, with an accidental quantity of silica and alumina. These ores are with difficulty acted on by acids alone. In conducting the analysis, therefore, 1. The ore is to be reduced to a fine powder, and heated in a silver crucible, with caustic soda in solution. When the whole moisture is evaporated, the remaining matter is to be ignited to a low degree for a few minutes; next dissolve the whole contents of the crucible in diluted muriatic acid; evaporate the solution nearly to dryness, and boil the residue in distilled water; acidulated with a little muriatic acid, and the silica will remain behind undissolved. 2. The solution being considerably reduced by evaporation, add caustic soda to a slight excess, and boil it upon the precipitate which is thus obtained. This precipitate, after being edulcorated, is pure oxide of iron, and being heated with a little wax, it may brought to the state of magnetic oxide, one hundred parts of which indicate seventy-three of metallic iron. In this way the quantity of iron in the ore may be estimated. 3. The alkaline solution contains the alumina, which may be separated by muriate of ammonia, and after being washed and ignited, its quantity may be ascertained.

*Black Iron Ore,* and *Brown Iron Ore.*—Besides the ingredients contained in the former species, these ores are combined with a portion of manganese; the precipitate obtained, therefore, is a mixture of the oxides of iron and manganese. These oxides may be separated by dissolving them in muriatic acid, and adding to the hot solution caustic soda, drop by drop, till the liquor becomes colourless, or till the precipitate thrown down at each addition of the alkali begins to be white. In this way the oxide of iron is precipitated, while that of the manganese remains in solution. The iron being removed, the oxide of manganese may be obtained, by continuing the addition of soda till no farther precipitate is produced. The two oxides may also be separated by adding succinate... succinate of soda to the muriatic solution, by which means the iron is precipitated, and the manganese remains in solution.

Sparry Iron Ore.—This ore of iron, which is supposed to contain carbonic acid, the oxides of iron and manganese, lime, magnesia and barytes, in the state of carbonate, with a small portion of silica and alumina, may be examined according to the following analysis.

1. Digest the ore reduced to very fine powder, in muriatic acid, with a little nitric acid; a slight effervescence takes place, and the loss of weight indicates the quantity of carbonic acid driven off. 2. The insoluble portion of the ore, after being twice or thrice digested in muriatic acid, is silica. 3. The muriatic solutions and washings, being mixed together, are to be concentrated by evaporation, and decomposed at a boiling heat, by adding caustic soda in excess. 4. Boil the precipitate and supernatant fluid together for a short time, the alumina only will be dissolved. 5. The insoluble portion is next to be well washed and ignited, and being once abstracted with nitric acid, the lime, barytes, and magnesia, will be dissolved, leaving behind the oxides of iron and manganese. 6. To separate the oxides, digest the mixture with a gentle heat in diluted nitric acid, with the addition of a small bit of sugar; the manganese is dissolved, and the remaining oxide of iron may be brought to the magnetic state, by heating it with wax. 7. The nitrate of manganese may be precipitated by carbonate of soda, and after washing and drying it at a heat below redness, pure carbonate of manganese is obtained, one hundred parts of which indicate fifty-five of metallic manganese. 8. To the nitric solution (i.), a good deal diluted with water, add sulphuric acid as long as any precipitate is formed. The sulphate of barytes thus obtained being removed, the other earths may be thrown down by means of the carbonate of an alkali; they are again dissolved in diluted sulphuric acid, and the sulphates of lime and magnesia thus produced, being precipitated by alcohol, may be separated from each other by cold water. In this way the sulphate of magnesia is dissolved, with only a very inconsiderable quantity of the sulphate of lime.

Argillaceous iron ore, bog iron ore, blue earthy and green earthy iron ores,—are chiefly composed of the oxides of iron and manganese, phosphate of iron, silica, alumina, and lime. The analysis of these ores may be conducted according to the following process. 1. After the ore is reduced to powder, and ignited, abstract it two or three times with nitric acid; pour off the acid, and wash the residue with a small portion of strong nitric acid. 2. Add the acids together, evaporate nearly to dryness, wash the residue with cold water; the phosphate of iron remains behind. 3. Ignite the insoluble residue (i.) with caustic soda, and separate the silica as in a former analysis, by muriatic acid. 4. Mix the nitric and muriatic liquors, boil them with an excess of caustic soda, and the alumina will be dissolved, while the metallic oxides and lime are precipitated. 5. After ignition, abstract the compound precipitate with nitric acid; the lime is now dissolved, and nothing remains but the oxides of iron and manganese, which may be separated according to the preceding analysis.

Arseniate of Iron.—This ore is found to contain oxides of iron and copper, with arsenic acid, besides a portion of silica, and sometimes lime. It was analysed by Mr. Chenevix, according to the following process. Being reduced to powder, and subjected to less than a red heat, the water of crystallization is driven off; the residue is next boiled with caustic potash, and the alkaline solution being separated by filtration, is to be neutralized with nitric acid. The addition of nitrate of lead affords a precipitate of arseniate of lead, one hundred parts of which indicate thirty-three of arsenic acid. Muriatic acid is next to be added to the residue, which is insoluble in potash; the iron and copper are thus dissolved, and the silica remains behind. By supersaturating the muriatic solution with ammonia, the oxide of iron will be precipitated, and the oxide of copper will remain in solution by the alkali.

But, for practical purposes, we shall give a short view of the simpler methods of assaying the ores of iron, which are chiefly employed in manufacture, with the view of ascertaining the quantity of metal to be obtained from them, when treated in the large way. Among the older metallurgists it was usual to employ active saline fluxes in assaying the ores of iron; but as the metallic part of the ore can only be brought into fusion at a very high temperature, the same degree of heat effects the vitrification of the earthy matters, when aided by lime and bottle glass, so that the use of borax, or alkaline salts, which are more expensive, may be dispensed with.

To assay the richer varieties of magnetic iron ore, particularly iron sand, reduce them to a fine powder, add one-twelfth of charcoal, or double the quantity of fine saw dust, and expose the mixture in a covered crucible for an hour to the heat of a powerful wood furnace. After this the iron will be found at the bottom of the crucible, in the form of an irregular button, and covered with a small portion of cellular scoriae. This process will be sufficient where the quantity of earthy matter is small; but as the common magnetic iron ore contains a considerable portion of silica, a flux of the following materials may be necessary. For every eight parts of ore take eight of bottle glass, six of limestone or chalk, and one of charcoal; mix the whole carefully together with the ore, and expose the mixture to heat as in the former case. If the operation have succeeded, a button of iron will be found at the bottom of the crucible, covered by a compact, vitreous, greenish slag.

As the specular iron ore generally contains a portion of sulphur, from the admixture of pyrites, it must be roasted at a moderate red heat, till the sulphureous odour is no longer perceptible; then to eight parts of the ore, add eight of bottle glass, six of chalk, and one twelfth of charcoal, and treat the mixture as before. The red, brown, and black iron ores, may be assayed in the same way.

Sparry iron ore may be assayed without roasting, by reducing it to powder, and placing it in a crucible lined with a mixture of charcoal and clay, and then covering it with about one-fourth of its weight of calcined borax.

In assaying argillaceous and bog ores of iron, they are first to be roasted, and then mixed with eight parts of bottle glass, seven of chalk, and one and a half of charcoal, to eight parts of ore, and subjected to fusion in an unlined crucible. It is scarcely necessary to observe, that the proportion of chalk may be diminished in treat- Sect. II. Of the Reduction of the Ores of Iron.

In treating of the construction of furnaces, the proper form and management of which are of the utmost importance in extracting the metal from the ores of iron, we were led to enter pretty fully into the nature and effects of the smelting process, or the method of reducing iron ores. We shall not, therefore, resume the subject in this place. See Furnace.

Chap. VII. Of Lead.

In the present chapter we shall first give an account of the most improved methods of analysing the ores of lead; and secondly, treat of the best methods of reducing or smelting these ores.

Sect. I. Of the Analysis of Lead Ores.

The analysis of the ores of lead is less difficult than that of the other metals of which we have just now treated; and when accuracy is wanted, the humid way of analysis is to be preferred. The method of separating lead from silver has been already noticed, as well as that by which it is separated from iron and copper. The same process as that employed for separating iron and copper from lead, may be followed with regard to the separation of lead from tin, cobalt, and zinc. We shall now give an account of the analysis of particular lead ores.

Galena, or sulphuret of lead.—This species, which is the most common ore of lead, was analysed by Vaucelin, by the following process*. 1. Three hundred parts of the ore, reduced to powder, were roasted; and lost, during the process, twelve per cent. 2. Three hundred parts of the same ore were heated with nitric acid very much diluted; a strong odour of sulphurated hydrogen was perceived, and the solution of the lead being completed and filtered, there remained on the filter pure silica, which being heated to redness and cooled, weighed fifty grains, or 16.67 parts per cent. 3. The solution of lead in nitric acid being decomposed by means of sulphate of soda, and the sulphate of lead precipitated being washed and dried, weighed 250 grains, or 63.1 of metallic lead per cent. 4. After the sulphate of lead was separated, ammonia was added, and a precipitate of oxide of iron was obtained, which being subjected to a red heat, weighed ten grains, or was equal to 3.33 per cent. 5. Carbonate of potash being added to the residual liquor, threw down nine grains of carbonate of lime, which is equal to three per cent. The sulphuret of lead thus analyzed, afforded in one hundred parts,

| Substance | Weight | |-----------------|--------| | Sulphur | 12 | | Silica | 16.67 | | Metallic lead | 63.1 | | Oxide of iron | 3.33 | | Carbonate of lime| 3 | | Loss | 1.9 |

To assay galena in the dry way, it is to be mixed after roasting with three times its weight of black flux, covered with salt, and melted. A button of lead will be found at the bottom of the crucible, but the silver and other metals which existed in the ore, are still combined with the metallic lead.

Sulphuret of lead, antimony and copper.—An ore of this kind was analysed by Mr Hatchett, by the following process. Two hundred grains of the ore were heated in a matrass, with two ounces of muriatic acid, and nitric acid was very slowly added, till the whole exhibited a moderate effervescence. Being gently heated for an hour, the solution assumed a green colour, and a quantity of sulphur which floated on the surface, being collected, digested separately with a little muriatic acid, and washed and dried, weighed thirty-four grains; and as it burnt entirely away without any residuum, in a red earthen cup, it was perfectly pure. The solution with the muriatic acid, in which the sulphur had been washed, was first boiled, and afterwards mixed with six pints of boiling distilled water, to which it communicated a milky appearance. It was filtered while hot, and the filter washed with another portion of boiling water. The white precipitate, which was oxide of antimony, was dried in a sand bath, and weighed sixty-three grains. When the liquor with the washings cooled, some crystals of muriate of lead were deposited. The liquor was afterwards evaporated nearly to dryness, and a few drops of sulphuric acid were added, to separate the lead which remained in solution. The residue being again dissolved in boiling water, was entirely decomposed by sulphate of soda, and the sulphate of lead thus obtained being added to the former portion, was washed and dried on a sand bath. It weighed 120 grains.

The liquor, which was now bluish green, assumed a deep blue colour by the addition of ammonia; a small portion of the oxide of iron was separated, which, when dried and heated with wax, became magnetic, and amounted to 2.43 grains. The liquor, after being evaporated nearly to dryness, was boiled with a strong solution of potash, till it was nearly dry, and the residue being washed with water, a black oxide of copper remained; which, after being dried, weighed thirty-two grains.

White lead ore, or carbonate of lead.—The white tabular lead ore, from Leadhills in Scotland, was analysed by Klapproth, according to the following process.

1. One hundred grains of it, in pure specimens, and previously triturated to a powder, were by small portions introduced into a mixture of 200 of nitric acid with 300 grains of water, and put in equilibrium upon the balance. The ore dissolved readily, and with a strong effervescence, without leaving any residue. By the carbonic acid that escaped, there was a loss of 16 grains of weight.

2. The solution, which was clear and colourless, was diluted with water, and a cylinder of zinc put into it. After 24 hours, the whole of the lead had shot into beautiful metallic laminae, which collected, washed, and both quickly and carefully dried, to the end that no oxidation might take place, afforded 77 grains of lead in the reguline state, which correspond with 82 grains of oxidated lead.

Consequently, the constituent parts of this tabular and carbonated white lead ore, bear to each other the following proportion:

| Oxide of lead | 82 | |---------------|----| | Carbonic acid | 16 | | Water | 2 |

+ 100

Green lead ore, or phosphate of lead.—The following is an example of the method of analysing this species of ore, adopted by Klaproth.

"1. An hundred grains of this ore, in very pure specimens, left on solution in dilute nitric acid one half grain of the quartzose matrix behind; which I separated and replaced by an equal quantity of pure ore. The colourless solution, treated with nitrate of silver, yielded 10 grains of muriated silver; which indicates 1.54 of concrete muriatic acid, contained in 100 of the ore.

"2. In the next instance, the ingredient lead was separated by means of sulphuric acid. The collected sulphate of lead, after gentle ignition, weighed 104½ grains; for which 77.10 grains of oxidated lead must be put in the account.

"3. When after this the nitric solution had been freed, by nitrated barytes, from the portion of sulphuric acid added to excess, and subsequently treated with ammonia so far, that the acid still predominated, I continued adding a solution of acetated lead, till no more turbidness was effected. The generated phosphate of lead, when collected and exposed to a gentle red heat, proved to weigh 85 grains; and consequently, the proportion of the phosphoric acid must have been 19 grains.

"4. The remaining fluid was mixed with muriatic acid, the mixture evaporated to dryness, and extracted with ardent spirit. The residue, after completely evaporating the spirit, was again dissolved in water, and treated with Prussian alkali. A precipitation of prussitated iron ensued, which indicated the amount of oxide of iron 10 grains.

From the results of this decomposition it follows, that the constituent parts of green lead ore, and their proportion to each other, are:

| Oxide of lead | 77.10 | |---------------|-------| | Phosphoric acid | 19 | | Muriatic acid | 1.54 | | Oxide of iron | 0.10 |

+ 97.74

Red lead ore, or chromate of lead.—In analysing this ore, Vanquelin adopted the following simple process. Equal weights of the ore reduced to fine powder, strong muriatic acid, and distilled water, were digested together at a moderate temperature, and stirred from time to time. The chromate of lead is thus decomposed, and converted, for the most part, to muriate of lead, which is of a white colour. When the acid has ceased to act, pour off the liquor, add fresh muriatic acid, diluted as before with an equal quantity of water, and to the amount of about one fourth of the former quantity, and digest till the whole of the orange-coloured particles among the white muriate disappear. This liquor is to be added to the former, along with the washings; the whole is to be heated, and placed in a cool place for a few days, that the small portion of muriate of lead which it holds in solution, may be deposited; and this being removed, add very gradually oxide of silver, precipitated from its solution in nitric acid by caustic potash, till the last portions assume a red purple colour. In this way the whole of the muriatic acid is separated, and the liquors contain only chromic acid, which is deposited by slow evaporation in the form of small, prismatic, ruby red crystals. The quantity of muriate of lead obtained by this process being ascertained, will shew the quantity of metallic lead contained in the ore.

Yellow lead ore, or molybdate of lead.—Klaproth analysed this ore in the following manner:

"1. A hundred grams of the crystals were carefully freed from the adhering calcareous earth and ochre of iron, and then finely pulverized. They were then dissolved in muriatic acid, assisted by heat, alternately affusing upon them the acid, and a large quantity of water. In this instance a trace of siliceous earth, though scarcely discernible, appeared.

"2. The greatest part of muriate of lead, generated in the process, was deposited in fine needles, even before the solution had completely grown cold. The supernatant clear fluid was then poured off, reduced to a smaller volume by evaporation, and freed from the muriated lead, which still separated. The muriated metal, collected with care, and briskly desiccated, weighed 74½ grams. By dissolving it in hot water, and steeping into the solution a polished piece of iron, the lead precipitated upon this last in fine lamellae, and in the metallic state.

"3. But in order to find more accurately what proportion this muriated lead might bear to pure oxide of lead, I made the following experiment.

Two hundred grams of lead, cut into shreds, were dissolved in 300 grams of nitric acid, diluted with 10 ounces of water, and, with the assistance of digestion, in a boiling heat. The solution was then divided into two parts.

"a. Into one half I dropped muriated acid, as long as it produced any turbidness; evaporating afterwards the mixture to the most perfect dryness of the residue. The muriate of lead here produced weighed 133 grams.

"b. From the second half of the nitric solution I precipitated the oxide of lead by dissolved caustic potash. This oxide, when educorated and briskly dried till it began to turn yellowish, amounted to 115 grams.

"From this it followed that those 74½ grams of muriated lead, obtained from 100 grams of the yellow molybdate of lead (2.) are equal to 64.42 grams of pure oxide of lead.

"4. The concentrated muriatic solution of molybdene, which had a blue colour, was mixed with nitric acid, and lodged in a sand bath for farther evaporation. Being thus circumstanced, it was again divested of its blue colour, and a yellow oxide of molybdene separated. But when the evaporation had been carried on to complete dryness, I collected and weighed the remaining lemon-yellow oxide of molybdene; and found it amount to 34½ grams.

"Therefore, one hundred parts of the purest crystals of the yellow lead ore, from Carinthia, contain, Sulphate of lead.—This ore of lead was analysed by Klaproth according to the following process.

1. One hundred grains of tabular sulphate of lead from Wanlockhead, in select pure specimens, lost 2½ grains, by being heated in a covered crucible. When finely pulverized and ignited in a platina crucible with 400 grains of carbonate of potash, they yielded a brownish yellow, moderately concrete mass. Upon this substance, previously triturated, water was affixed and heat applied to promote the solution of the soluble parts. As in the case of the preceding fossil, so in this, an oxide of lead deposited from the liquor, which, when washed, dried, and moderately ignited, weighed 70½ grains. Diluted nitric acid took the whole of it up, without the assistance of heat, and afforded a clear solution, from which the lead has been precipitated in the reguline state, by means of zinc. The metallic lead, thus obtained, when collected, washed and quickly dried, amounted to 65½ grains.

2. In order to ascertain the quantity of sulphuric acid contained in the alkaline solution, it was combined with nitric acid added to supersaturation in some degree, and, in the next instance, treated with acetate of barytes. By this management sulphate of barytes was formed and precipitated, to the amount of 76 grains, after being heated to redness, which indicates 25½ grains of concrete sulphuric acid.

According to this decomposition, an hundred parts of this tabular sulphate of lead consist of,

| Oxide of lead | 70.50 | |--------------|-------| | Sulphuric acid | 25.75 | | Water of crystallization | 2.25 |

Total 98.50.

Sect. II. Of the Reduction of the Ores of Lead.

Galena is by far the most abundant ore of lead, and indeed almost the only ore which is subjected to the process of reduction. The treatment of this ore of lead in this way is very simple. The first object in dressing the ore, is to separate the extraneous matters or impurities, such as iron pyrites, blende, calcareous spar, quartz, &c. The purer part of the ore is broken to pieces about the size of a hazel nut, and washed from any earthy matters which adhere to it, and then it is ready to be smelted. A ton, or a greater quantity, of the ore, is spread on the floor of a common reverberatory furnace with a low arch, and with the flame of pit coal it is quickly brought to a red heat; being, during this time, occasionally stirred with iron rakes, to expose fresh surfaces to the action of the heat. When it begins to assume the consistence of paste, the heat is lowered, and kept at a dull red, till the whole of the sulphur is nearly driven off; when the heat is increased, and the ore brought to perfect fusion. The mass consists of two fluids, the upper being a vitreous slag, and the lower metallic lead. The fire is now damped, and a few spadefuls of quicklime thrown in, by which the scorish become suddenly solid, and are removed to the side of the furnace. The tap hole is now opened, and the lead runs into moulds, in which oblong masses or pigs, about 60 pounds each, are formed. After the lead has run out of the furnace, the hole is again closed, the scorish are replaced in the bed; and the heat being raised to a glowing red, they are soon melted. The greater part of the lead separates from the slag, and collects in a mass at the bottom. The scorish become solid with the addition of a little lime, and the lead is let off into the mould. The second scorish still contain a portion of lead, from six to eight per cent.; but as it is not worth the expense of extracting, it is thrown away. It is found that the first running of lead is the best; the second, which is obtained from the scorish, being considerably harder, on account of a greater proportion of iron combined with it.

The process which is followed, at least in most parts of Scotland, is somewhat different from that now described, particularly in the previous preparation of the ore. The masses of ore, as it is brought from the mine, being separated from any adhering impurities, are reduced to small pieces, well washed, and then pulverised. In this state it is ready for the smelting process, which till of late was usually performed in an open furnace.

In some mining countries there is a considerable proportion of white lead ore mixed with the galena; doubts have been entertained whether it be profitable to retain this ore, even although it contain a large proportion of metal, because in the reverberatory furnace it is vitrified immediately on the appellation of the heat, and acting as a powerful flux, the whole is brought into fusion before the sulphur be entirely separated; so that the proportion of scorish in this case is greatly augmented, with very little increase in the produce of lead.

Chap. VIII. Of the Ores of Tin.

There is no great variety of the ores of tin. It is usually found in the state of oxide, or in that of sulphuret, when it is also combined with copper, and a small proportion of iron.

Sect. I. Analysis of the Ores of Tin.

Before treating of the analysis of the ore of tin, we shall first describe a very simple process for assaying it. The ore is first reduced to the consistence of coarse sand, and separated from the stony matters by washing. If it appear, by subjecting a grain or two to the action of the blow-pipe, that it contains arsenic, 200 grains of the ore mixed with a little charcoal, are to be roasted in a calcining test at a low red heat, till the whole of the arsenic is driven off. The residue is withdrawn, mixed with a little pitch and fine saw-dust, introduced into a crucible lined with charcoal, and after a cover is fitted on, placed in a large furnace, whose heat is to be raised to a bright red. In about 20 minutes the reduction is completed, the crucible is removed, and a button of metallic tin is found at the bottom, covered with a little scorish. But if the ore should contain no arsenic, the previous process of roasting is unnecessary.

Tin-stone.—The best method of analysing the ores of tin, is that contrived by Klaproth, by means of the fixed alkalies, which was conducted according to the following process. One hundred grains of tin-stone from Alternon, in Cornwall, previously ground to a subtile powder, were mixed in a silver vessel with a lixivium containing 600 grains of caustic potash. This mixture was evaporated to dryness in a sand heat, and then moderately ignited for half an hour. When the gray-white mass, thus obtained, had been softened while yet warm, with boiling water, it left on the filter 11 grains of an undissolved residue.

These 11 grains, again ignited with six times their weight of caustic potash, and dissolved in boiling water, left now only 1½ grain of a fine yellowish-gray powder behind.

The alkaline solution (1. and 2.), which was in some degree colourless, was saturated with muriatic acid. A brilliant white, tender oxide of tin was thrown down, giving to the mixture a milky appearance. This precipitate, re-dissolved by an additional quantity of muriatic acid, was precipitated afresh by means of carbonated soda. When lixiviated and dried in a gentle heat, it acquired the form of bright yellowish transparent lumps, having in their fracture a vitreous lustre.

This precipitate, being finally powdered, soon and entirely dissolved in muriatic acid, assisted by a gentle heat. Into the colourless solution, previously diluted with from two to three parts of water, I put a stick of zinc; and the oxide of tin, thus reduced, gathered around it in delicate dendritic laminae of a metallic lustre. These, when collected, washed, and fused, under a cover of tallow, in a capsule placed upon charcoal, yielded a button of pure metallic tin, weighing 77.50 grains.

The above-mentioned residue of 1½ grain, left by the treatment with caustic potash (2.), afforded with muriatic acid a yellowish solution; from which, by means of a little piece of zinc introduced into it, one half grain of tin was still deposited. Prussian alkali, added to the remainder of the solution, produced a small portion of a light-blue precipitate; of which, after subtracting the oxide of tin now combined with it, hardly one-fourth of a grain remained, to be put to the account of the iron contained in the tin-stone, here examined.

In these experiments, (excepting only a slight indication of silex, amounting to about three-fourths of a grain), no trace has appeared, either of tungstic oxide, which some mineralogists have supposed to be one of the constituent parts of tin-stone, or of any other fixed substance. Therefore, what is deficient in the sum, to make up the original weight of the fossil analysed, must be ascribed to the loss of oxygen; and thus the constituent parts of pure tin-stone from Alternon are to each other in the following proportion:

| Tin | 77.50 | |-----|------| | Iron | 0.25 | | Silex | 0.75 | | Oxygen | 21.50 |

100.00

The analysis of grained tin ore, or wood tin, may be conducted in the same way as the former.

**Tin pyrites.**—The following is the process which Khlaproth adopted in the analysis of this species of tin ore.

Two drams of finely triturated tin pyrites were treated with an aqua regia, composed of one ounce of muriatic and a half ounce of nitric acid. Within 24 hours the greatest part of the metallic portion was dissolved in it, without application of heat; while the sulphur rose up, and floated on the surface of the menstruum. After the mixture had been digested upon it for some time in a low sand heat, I diluted it with water, and filtered it. It left 43 grains of sulphur on the paper, still, however, mixed with metallic particles. When the sulphur had been gently burnt off on a test, there still remained 13 grains; of which eight were dissolved by nitro-muriatic acid. The remaining part was then ignited with a little wax; upon which the magnet attracted one grain of it.—What remained was part of the siliceous matrix, and weighed three grains.

The solution of the metallic portion (1.) was combined with carbonate of potash; and the dirty green precipitate, thus obtained, was re-dissolved in muriatic acid, diluted with three parts of water. Into this fluid a cylinder of pure metallic tin, weighing 217 grains, was immersed. The result was, that the portion of copper contained in the solution, deposited itself on the cylinder of tin; at the same time that the fluid began to lose its green colour, from the bottom upwards; until, after the complete precipitation of the copper in the reguline state, it became quite colourless.

The copper thus obtained weighed 44 grains. By brisk digestion in nitric acid, it dissolved, forming a blue tincture, and left one grain of tin behind, in the character of a white oxide. Thus the portion of pure copper consisted of 43 grains.

The cylinder of tin, employed to precipitate the copper, now weighed 128 grains; so that 89 grains of it had entered into the muriatic solution. From this, by means of a cylinder of zinc, I re-produced the whole of its dissolved tin, which was loosely deposited on the zinc in a tender dendritical form. Upon being assured, that all the tin had been precipitated, I collected it carefully, lixiviated it cleanly, and suffered it to dry. It weighed 130 grains. I made it to melt into grains, having it previously mixed with tallow, and under a cover of charcoal dust, in a small crucible; which done, I separated the powder of the coal by elutriation. Among the washed grains of tin, I observed some black particles of iron, which were attracted by the magnet, and weighed one grain. Deducting this, there remain 129 grains for the weight of the tin. By subtracting again from these last, those 89 grains, which proceeded from the cylinder of tin employed for the precipitation of the copper (2.) there remained 40 grains for the portion of tin contained in the tin pyrites examined. Hence, including that one grain of tin, which had been separated from the solution of the copper (3.), the portion of pure tin contained in this ore amounts to 41 grains. An hundred parts yielded,

| Sulphur | 25 | | Tin | 34 | | Copper | 36 | | Iron | 2 | | Earthy matters | 13 |

100. Sect. II. Of the Reduction of the Ores of Tin.

Tin stone, or vein tin, as it is called in Cornwall, contains a large proportion of stony matters. It is first broken by hammers into pieces of the size of a hen's egg, when it is ready for the operation of stamping, which is performed in the way already described for the ores of gold, excepting that there are only three stampers. A tin plate about a foot square, and pierced with holes to admit a moderate sized knitting-needle, is inserted in front of the trough, and that surface of the plate with the rough extremities of the holes is on the inside, by which the holes are prevented from being plugged up with the ore. As the ore is reduced to the proper fineness, it passes with the water through the holes into the labyrinth, where it is collected, and after being washed on a wooden table, when it is ready for roasting. In this state it has a considerable proportion of copper and iron pyrites, and is called black tin. After being calcined at a low red heat for several hours, in a large reverberatory furnace, the ore comes out of a bright ochre red colour, owing to the decomposition and oxidation of some of the metallic substances; but the oxide of tin, when the operation is properly conducted, remains unaltered. The ore is washed a second time, to separate the remaining impurities; and the water which is impregnated with sulphate of copper, is retained and decomposed by means of old iron.

The reduction of the ore is the next step in the process. Seven cwt. of roasted ore, with one fifth of its bulk of small coal, are introduced into a reverberatory furnace, which is about seven feet long, and 3½ wide. No lime, or indeed flux of any kind is required. A brisk heat is kept up for about six hours; the tin sinking down as it is reduced, and covered with black scoriae. The furnace is now tapt, and the metal flows into a shallow pit. When the whole of the metal has run out, the scoriae are removed from the furnace, and a fresh charge is made. The metal in the pit throws up a slag, rich in metal, which is immediately returned into the furnace; and after the melted tin has cooled a little, it is taken out with iron ladles, and poured into granite moulds. Each charge affords an average from four to five cwt. of metal; but as the first scoriae are not entirely free from metal, they are again stamped and washed, and mixed with a new parcel of roasted ore. The pigs of tin are next put into a small reverberatory furnace; where, without any addition, they are subjected to a very gentle heat; the purest part of the tin melts first, and is drawn off, forming what is called common grained tin; the other part contains some copper, arsenic and iron, which is brought to a state of fusion, and cast into pigs, forming common tin.

Stream tin ore, which is peculiar to Cornwall, is prepared for the furnace by reducing it to powder, and passing it through wire sieves, which have 16 meshes in the square inch. A blast furnace is employed, which is about seven feet high, and is supplied with air from two cylinders washed by an overshot water wheel. The method of managing the furnace, after being fully heated, is the following. Three or four shovels full of ore, and two or three half bushels of charcoal, without any kind of flux, form a charge with which the furnace is fed at short intervals. There is a small channel at the bottom of the furnace, through which the reduced tin is constantly flowing into a pit below, and the slag which accompanies it is removed from time to time, and returned into the furnace. When the pit is full, the melted metal is removed into an iron boiler three feet in diameter, having a small fire under it, to keep the metal in fusion. Two or three large pieces of charcoal are then placed upon the tin, and forced to the bottom by means of an iron instrument resembling a wheel, with a long handle fixed in the axle. This produces a violent ebullition, and a little slag, before mixed with the metal, rises to the surface, and is removed. In a minute or two the metal is tried, as it is called, by taking up a ladleful, and returning it again into the mass; when, if it assume a bright silver-like appearance, and a uniform consistence, the purification is complete. When cool to the proper degree, it is removed into the moulds, where it is formed into pigs of two or three cwt. Stream tin ore yields from 65 to 75 per cent. of the best and purest tin.

Chap. IX. Of the Ores of Bismuth.

Bismuth is found in the metallic state, accompanied by native silver, blende, and galena, some other metals, and earthly substances. It is also met with in the state of oxide, and also in the state of sulphuret.

Sect. I. Of the Analysis of the Ores of Bismuth.

In conducting the analysis of the ores of bismuth, previous roasting is not requisite. The native bismuth, or oxide of bismuth, dissolves readily in nitrous acid, diluted with about one third of water, and either in the cold, or with a moderate heat; but boiling is necessary for the sulphuret, to precipitate the sulphur, and dissolve the bismuth. The greater part of the nitrate of bismuth may be precipitated from the solution, and separated from the metals with which it is usually alloyed, by adding a large quantity of water. But to separate the bismuth totally, evaporate the clear liquor which remains over the precipitated oxide to a small bulk, so as to retain in solution the nitrates of the other metals. Add muriatic acid by drops, as long as any white cloud is formed. This last precipitate consists of the remaining portion of the oxide of bismuth, mixed with muriate of silver, if the ore examined contain any of that metal. Then add a few drops of strong nitric acid, which dissolves the bismuth, and leaves the silver; and to this portion of the nitrate of bismuth add water, which separates the whole by precipitation. To ascertain whether the solution contains any silver, expose the precipitate by muriatic acid to the light, which will become of a bluish or slaty colour, if any silver has been dissolved; but if not, the pure white colour remains unaltered. As the oxide of bismuth is composed of 81.3 per cent. of metal, and 18.7 of oxygen, the proportion of metal in the ore may be precisely ascertained by weighing it. The other metals held in solution by the nitrous acid, which are chiefly lead, iron, copper and cobalt, may be separated in the usual way.

Sect. II. Of the Reduction of the Ores of Bismuth.

The low degree of heat at which bismuth is fusible, renders renders the reduction of the ores of this metal a very simple process. In the treatment of the native metal, and the oxide, the weight of the ore of black flux is put into a crucible along with it, covered with salt, to about a finger's breadth, and melted for 5 minutes with a brisk fire; when it is cold, the bismuth is found in a clean button. The flux employed by others is one part of borax, and the same quantity of powdered glass, to two of the ore, and the fusion is effected in a crucible lined with charcoal. With the oxide, a little oil, rosin, or charcoal, should also be mixed. Previous roasting is necessary in the treatment of the sulphuret of bismuth, to separate the sulphur; the other part of the treatment is the same with that now described.

But in the large way, the ores of bismuth are reduced merely by heating them along with burning fuel. Sometimes a shallow hole is made in the ground, and filled loosely with pieces of wood and bushes, and after the fire is kindled, the ore reduced to small pieces is thrown in; and sometimes the stump of a hollow pine tree is filled with wood and ore alternately, and set on fire; the bismuth separates from its matrix, and collects in a mass at the bottom.

**CHAP. X. Of the Ores of Zinc.**

The ores of zinc are, the native carbonate, or common calamine, the oxide of zinc, and the sulphuret.

**SECT. I. Analysis of the Ores of Zinc.**

On account of the great volatility of zinc, it cannot be examined in the dry way, or subjected to assay, without particular precaution. In assaying blende, or the sulphuret of zinc, the ore, after being bruised, is to be carefully separated from particles of galena, or other impurities. It is then to be roasted, and the sulphur being driven off, to be reduced to fine powder, mixed with half its weight of charcoal, introduced into an earthen retort, to which a tube is fitted. The retort being exposed to a strong heat in a wind furnace, for three quarters of an hour, is to be gradually cooled, and on breaking it, the zinc is found in the neck, in metallic drops. The object may be accomplished in another way. Prepare the ore as before, and having mixed it with charcoal, let it be stratified in a crucible, with its own weight of copper clippings; and having luted on a perforated cover, subject it for nearly an hour to a low white heat. Allow it to cool, and examine and wash the contents. The globules of brass formed are thus easily separated from the other impurities, and the excess of weight of the brass above the copper, indicates the quantity of zinc given out by the ore.

**Blende, or sulphuret of zinc.**—This ore is found to contain not only zinc and sulphur, but sometimes iron, lead, copper, and arsenic, with silica, alumina, and a portion of water. It may be analyzed by the following process:

1. Introduce into a small coated glass retort, 200 grains of ore reduced to powder, and let it be gently ignited for a quarter of an hour. The fluid collected in the receiver will be found to be water.

2. Digest another portion of ore in repeated quantities of diluted nitric acid, till every thing soluble is taken up; wash the residue; weigh and ignite it; the loss of weight indicates the quantity of sulphur which is burnt off.

3. Digest the residue in a little nitro-muriatic acid, till the insoluble portion becomes quite white, which is pure silica.

4. Add to the nitric solution (2.) a few drops of sulphate of soda; evaporate gently, and continue to add sulphate of soda while a precipitate is formed, and after being evaporated nearly to dryness, digest in diluted muriatic acid; the sulphate of lead remains behind.

5. Add together the nitro-muriatic solutions (3. & 4.), decompose by carbonate of soda, and digest the precipitate in caustic ammonia; the zinc and copper are thus dissolved.

6. Let the ammoniacal solution (5.) be saturated with muriatic acid; boil it, and add caustic soda, while a precipitate takes place: this is the brown oxide of copper.

7. Oxide of zinc now only remains in the soda solution, which is to be saturated with muriatic acid, and decomposed by carbonate of soda. The precipitate obtained after ignition is oxide of zinc.

8. The residue which was insoluble in ammonia (5.), is to be treated repeatedly with nitric acid, and digested in caustic soda. Oxide of iron, contaminated slightly with arsenic, remains insoluble.

9. Having saturated the soda solution (8.) with nitric acid, add nitrate of lead, till no farther precipitate is formed; the precipitate is arseniate of lead.

10. And to the residual liquor, add first, sulphate of soda, to separate any nitrate of lead that may remain; filter the liquor, decompose it by carbonate of ammonia; the precipitate, washed and ignited, is pure alumina.

**Calamine, or carbonate of zinc.**—The ores of this species contain, besides the carbonate of zinc, the carbonates of lead, iron, and lime. The following is the mode of analysis.

1. The ore reduced to powder is to be dissolved in diluted nitric acid; the loss of weight during the solution indicates the quantity of carbonic acid. Neutralize the solution with caustic soda, evaporate gently, and add from time to time a few drops of sulphate of soda while any precipitate is formed.

2. Having thus cautiously brought it nearly to dryness, digest it in highly rectified alcohol, and afterwards in a little cold water, which will take up every thing but the sulphates of lead and lime.

3. These may then be separated by digestion in sulphuric acid very much diluted, which will take up the sulphate of lime, leaving the sulphate of lead pure.

4. Neutralize the muriatic solution by soda, and evaporate nearly to dryness; then add alcohol to the residue, which will throw down the sulphate of lime with a little sulphate of soda, which latter may then be washed away by a little cold water.

5. The alcoholic solution (2.) after evaporation to dryness, may be digested in caustic ammonia, which will take up the oxide of zinc, and leave behind the oxide of iron.

6. The alkaline solution, after being slightly supersaturated with muriatic acid, is to be decomposed by a perfectly carbonated alkali, by which the zinc is pro- cured in the state of carbonate; and this, after edulcoration, being dissolved by sulphuric acid, and the solution ignited in a platina crucible, affords dry sulphate of zinc, containing 50 per cent. of oxide of zinc.

7. Thus, all the constituent parts are ascertained except the water: to determine the proportion of this, take a fresh parcel of the ore, weigh it, and then ignite it for half an hour, note the loss of weight, and transfer the residue into muriatic acid; if while it dissolves in this fluid it gives out any gas, let the loss of weight be noted; then add together the losses by ignition and solution; deduct from the sum the known weight of the carbonic acid, and the residue is water.

Sect. II. Of the Reduction of the Ores of Zinc.

The ore being reduced to small pieces, and the different impurities being separated, it is next calcined in a reverberatory furnace at a moderate red heat, and if the ore be calamine, the carbonic acid is driven off; and if blende, it is deprived of its sulphur. After this it is washed, and the metallic oxide being separated from the earthy parts, it is dried, and carefully mixed with about one-eighth of its weight of charcoal, by grinding the ingredients together in a mill, and is now ready for the smelting process. This is performed in a circular furnace, in which are fixed six large earthen pots, about four feet high and nearly of the shape of oil jars. An iron tube is inserted into the bottom of each pot, and, passing through the arched floor of the furnace, terminates in a vessel of water placed beneath, while the other end of the tube rises within the crucible to a few inches of the top. The crucibles are then filled with the mixture of the ore and charcoal, to the level of the tube, the cover of each is carefully luted on, and an intense heat is to be kept up for several hours. The zinc, as the process of reduction goes on, rises in the form of vapour to the top of the pot; but as it cannot escape, it descends through the iron tube, passes into the water, and is condensed in small drops. The globules are afterwards fused, and cast into the form of ingots, when it is fit for the market.

But as common zinc contains a little of other metals, as copper, lead, arsenic, iron, and manganese, which impair its quality, these impurities are partially separated by melting the zinc in a crucible, and stirring into it, with a stick or earthen rod, a mixture of sulphur and fat; by the latter the zinc is preserved from oxidation, and the sulphur combines with all the other metals except the zinc, and converting them into sulphurets, they rise to the top in the form of scorize, which may be removed. This process is to be repeated as long as any scorize appear. The method of purifying zinc proposed by Proust, is simple distillation in an earthen retort. The zinc passes over, and the oxides of the other metals remain behind. But it is supposed that the arsenic or lead cannot be separated in this way.

Chap. XI. Of the Ores of Antimony.

Native antimony is a very rare production; the most common ore of antimony is the sulphuret; but it is also sometimes found in the state of oxide.

Sect. I. Of the Analysis of the Ores of Antimony.

Gray ore of antimony, or sulphuret of antimony.—As the sulphurets of antimony are the principal ores of this metal, we shall only describe the process by which the analysis of these ores may be conducted.

1. Five hundred grains being reduced to fine powder, are to be digested with 1500 grains of pure nitric acid, of specific gravity 1.25, and 1000 grams of water, for half an hour, at 150° Fahrenheit; then add a quantity of pure water, equal to the rest of the fluid; mix the whole well together, and pour off the liquor as soon as it becomes clear. This consists of the nitrates of silver, lead, and copper, and perhaps a little iron dissolved in an excess of acid. By simple boiling and filtration, the iron is separated in the state of red oxide.

2. Add to the solution muriate of soda, while any precipitate takes place, and let the whole stand till the supernatant liquor becomes clear; the precipitate is pure muriate of silver.

3. The solution (2.) is next to be saturated with potash or soda, and concentrated by evaporation to one-third of its bulk. The addition of caustic ammonia in excess throws down the lead in the state of oxide, and the copper remains in solution.

4. Acidulate slightly the solution (3.) with nitrous acid; add carbonate of potash, by which the green oxide of copper will be precipitated, and being subjected to a low red heat, is reduced to the state of brown oxide, of which 100 parts indicate 8½ parts of metal.

5. The portion of ore (1.) which was insoluble, is next to be digested at a degree of heat below boiling, with successive portions of nitromuriatic acid, composed of nitric acid, as long as anything is taken up. The different solutions are then mixed, concentrated by evaporation, and poured into a large portion of pure water; a precipitate immediately takes place, which is the white oxide of antimony, which, after being separated and washed, is to be mixed with twice its weight of crude tartar and a little nitre, and then exposed to a full red heat, which in a few minutes reduces it to the metallic state.

6. The solution (4.) contains now a little sulphuric acid and iron, with some earthy matters. By adding nitrate of barytes while any precipitate is produced, the quantity of acid may be ascertained, and then adding caustic potash in excess, which, assisted by a boiling heat, will precipitate the iron, and retain the alumina and silica.

7. The insoluble residue (6.) contains sulphur and earth; it is decomposed by a red heat, the sulphur being dissipated, and the earth remains.

Sect. II. Of the Reduction of the Ores of Antimony.

The ore of antimony, which is found in sufficient quantity to be employed in the process of reduction in the large way, is the sulphuret, the analysis of which has now been detailed. The ore being separated from the greater part of the stony matters which adhere to it, is placed on the bed of a reverberatory furnace, and covered with charcoal powder; and being brought to a low red heat, the sulphuret enters into fusion, and the earthy The metal is obtained in a state of purity from the crude antimony, or sulphuret, by different processes. The following is recommended as one of the best, and most frequently practised. The sulphuret being reduced to small pieces, is strewed thinly on the floor of a reverberatory furnace, to drive off the sulphur. The heat at first must not exceed that of the melting point of tin, otherwise the antimony will melt. A lamplight blue flame is observed over the surface of the ore, which proceeds from the combustion of the sulphur; the metal is deprived of its lustre, and is converted into a grayish oxide. In the course of some hours, by carefully stirring the ore, and cautiously increasing the temperature, as the fusibility diminishes, it at last ceases to give out sulphurous vapours, and can bear a moderate red heat without melting. After the roasting, the ore is removed from the fire, and is found changed into an ash-gray oxide, weighing from 30 to 36 per cent. less than the sulphuret, but it is not yet entirely free from sulphur. To reduce the oxide, mix it with half its weight of crude tartar, and subject to a full red heat in a covered crucible. The oxide is decomposed by the carbonaceous part of the tartar, and the antimony, reduced to the metallic form, is collected at the bottom of the crucible. A small proportion, however, still remains, dissolved by the sulphuret of potash, formed by the alkaline base of the tartar and the sulphur of the oxide. The quantity of metal which is thus obtained in the large way, amounts to 66 or 70 per cent. of the oxide employed. The loss, however, would be greater, if the ore has not been properly roasted.

The reduction is effected also by another process, which is supposed to be more economical. The roasted oxide is mixed with oil or fat, and a little powdered charcoal, and then introduced into a crucible; and as the metal begins to appear, powdered nitre, in the proportion of an ounce to a pound of oxide, is gradually injected, after which the whole mass is brought to thin fusion, affording a pure metal, and in greater proportion than in the usual way.

The only other process which we shall mention, for reducing sulphuret of antimony, is that by means of some of the other metals, for which the sulphur has a greater affinity than for the antimony. Proceeding on this principle, iron, copper, lead, silver, and tin, may be employed in the process; but as iron is not only more effectual, but also cheaper, it is preferred. The antimony obtained by this process, was formerly called martial regulus, not only on account of the iron being used in the preparation, but, not improperly, on account of a small portion of that metal which still adheres to it. The proportions recommended are the following: Eight ounces of small iron nails are heated in a crucible almost to whiteness; 16 ounces of crude or roasted sulphuret of antimony, coarsely pounded, are then added; the crucible is covered, and the fire kept up; and in a few minutes, when the whole is melted, three ounces of nitre are to be added: after a slight detonation has taken place, the whole is brought to perfect fusion. It is then put into an iron cone previously heated and greased, and as the mass becomes solid, the sides of the cone are struck, to promote the precipitation of the metal. When cold and weighed, a mass of antimony is obtained, equal to about 20 ounces of the sulphuret employed, covered with alkaline ferruginous scoriae, from which it is easily separated by a blow of the hammer.

But the metal is not yet entirely free from iron and sulphur; to purify it still farther, therefore, it is to be remelted, two ounces of crude antimony, and three of nitre being added; and when the detonation has ceased, it is poured into a cone, and the metal is separated as before, from the scoriae. Fuse the metal again; project upon it three ounces of nitre; separate the purified metal from the scoriae; remelt with a strong heat, projecting gradually three ounces of nitre, and immediately pour it into a cone. About eight ounces of a beautiful stellated regulus, covered with yellowish white scoriae, are thus obtained.

**CHAP. XII. Of the Ores of Cobalt.**

Cobalt exists usually in a state of combination with arsenic and sulphur, or in the state of oxide. Scarcely any of its ores are free from arsenic and iron. Nickel is also sometimes abundantly mixed with the ores of cobalt, and occasionally a little manganese and copper.

**Sect. I. Of the Analysis of the Ores of Cobalt.**

White and gray cobalt ores, consisting chiefly of arsenic and cobalt, may be examined in the dry way, according to the following process, which, however, is not to be considered as very perfect. The ore is to be mixed with charcoal or saw-dust, and roasted to drive off the arsenic. The oxide after calcination is mixed with four times its weight of an equal mixture of carbonate of potash and tartar, and heated intensely, at the temperature which is required for melting cast-iron. A button of metallic cobalt is found beneath the scoriae, which are always of a deep blue, or nearly black colour, owing to the combination of part of the oxide of cobalt. A hundred grains of this ore, treated by Klaproth according to this process, yielded 44 grains of metallic cobalt; but if the ore contained iron, copper, or nickel, it must have been alloyed with these metals, and perhaps not entirely free from arsenic.

But the analysis may be conducted with more accuracy according to the following process by Tassart:

1. With a view to ascertain the quantity of arsenic, he digested 100 parts of cobalt ore with diluted nitric acid. The whole was dissolved in a few hours, and deposited, on cooling, white crystalline grains. By evaporation more crystals were deposited; the whole collected and dried, weighed 56 parts, and, excepting three parts, the whole was sublimed. These 53 parts are oxide of arsenic, and indicate 49 per cent. of metal in the ore.

2. Three hundred parts of the ore digested with four times as much nitric acid, afforded a rose-coloured solution. After partial evaporation, and with the addition of water and heat, a pale-red precipitate (1.) was formed, leaving a rose-coloured solution. The solution being boiled with an excess of potash, afforded an oxide of cobalt, which was rose coloured, and then green, and when dried in a red heat, black. The amount was 85 parts. 3. These 85 parts, dissolved in nitro-muriatic acid, gave, with the addition of pure ammonia, a black precipitate, which, excepting a small portion, was again dissolved by an excess of alkali. The undissolved portion treated again with nitro-muriatic acid and ammonia, was reduced to four parts, and appeared to be oxide of iron.

4. The rose-coloured precipitate (2.), which was a mixture of arseniate of cobalt and iron, being decomposed by caustic potash in excess, afforded a precipitate, which weighed, after being dried, 100 parts.

5. The 100 parts (4.) being again dissolved in nitric acid, and the solution being partially evaporated, and then diluted with water, gave a precipitate of 27 parts of oxide of iron, and left a clear solution of cobalt.

6. The nitrate of cobalt (5.) was decomposed by ammonia; and the precipitate redissolved by an excess of the alkali, excepting an insoluble oxide of iron, amounting to 15 parts. The solution was then added to the ammoniated cobalt (3.).

7. The insoluble precipitates of oxide of iron (3., 5., and 6.) were then mixed and examined. With borax they gave a blue glass, indicating a portion of cobalt still combined. They were then dissolved in nitro-muriatic acid, precipitated by ammonia, and the wet precipitate was introduced into acetic acid, which at first dissolved the whole, but by boiling and evaporation nearly to dryness, four times successively, the oxide of iron became insoluble, while the cobalt remained in solution, and as it was more freed from iron, it assumed more of a fine rose colour. The solution of acetate of cobalt was supersaturated with ammonia, and the solution of ammoniated cobalt was added to the different portions of the same, obtained in former experiments. To expel the ammonia, the whole solution was boiled, and, by adding potash, the whole oxide of cobalt, was precipitated, which being washed and dried, amounted to 133 parts. The oxide being reduced in a crucible lined with charcoal, afforded pure metallic cobalt, of specific gravity 8.538.

8. To determine the quantity of sulphur, 100 parts of the ore were separately boiled with 500 of nitric acid, and diluted with water, to separate the whole of the oxide of arsenic that deposited spontaneously. The sulphur was now converted into sulphuric acid; nitrate of barytes was added, and a precipitate of sulphate of barytes was formed, the quantity of which being ascertained, the proportion of sulphur might in this way be estimated.

Sect. II. Of the Reduction of the Ores of Cobalt.

As cobalt in the metallic state is not applied to any useful purpose, the reduction of its ores in this view is not an object of manufacture. But as it is extensively employed in the state of oxide, to give a fine blue colour to glass, porcelain, &c. we shall here give a short account of the method of preparing the ores for this purpose. When the oxide of cobalt is simply mixed, after calcination, with a quantity of vitrifiable earth, it is then known by the name of zaffre, and it is in the form of a brown, gritty powder; but if it be melted with a quantity of vitrifiable matters, it yields a glass of a very deep blue colour, which being reduced to a fine powder, constitutes the smalt of commerce.

Preparation of zaffre.—This substance is chiefly prepared in the large way, in different parts of Germany, but particularly in Saxony, and the following is the method of its preparation. The furnace employed is somewhat like a baker's oven, and is so constructed, that the flame of wood may be reverberated on all sides. The cobalt ore is placed on the hearth of the furnace, and by the action of the flame soon becomes red hot; a dense arsenical vapour arises, which is conducted through a horizontal wooden square trough or chimney, sometimes 120 fathoms long. In this chimney the arsenic is chiefly condensed, yet it is said, that some of the vapours, on account of their great volatility, escape. The calcination is continued till the exhalation of vapours nearly ceases: the ore is then reduced to powder, calcined a second time, again ground, and passed through a fine sieve. The powder is then mixed with two parts of powdered flint or quartz, after which it is moistened, and packed into barrels, where it acquires a great degree of hardness. This is the zaffre of commerce, in the state in which it is exported; the exportation of the simple coloured oxide being prohibited under heavy penalties, it is said that the flints are added with a view to conceal the real nature of the substance.

Preparation of Smalt.—This is also sometimes called zaffre, and when reduced to a very fine powder, it is called azure blue. It is prepared with about equal parts of calcined cobalt ore, potash, and ground flints. This mixture is first fritted, and afterwards made into glass, in pots like those of the glass-house. Eight or ten hours are required for its fusion. When the blue colour is perfect, the fused matter is taken out with iron ladles, and dropped into cold water, which makes it crack in all directions, so that it is easily reduced to fine powder. This operation is performed in a mill of very hard stone, inclosed in a wooden case. In the preparation of the smalt by the above process, a portion of bismuth, which usually accompanies the ores of cobalt, is found. Above it there is also a mixed alloy of iron, copper, and arsenic.

Chap. XIII. Of the Ores of Nickel.

Nickel, as it is found in the state of ore, is usually combined with arsenic and sulphur, copper and iron, or with oxygen, in the form of oxide.

Sect. I. Of the Analysis of the Ores of Nickel.

When the ore contains, beside nickel, arsenic, sulphur, copper, and iron, with which it is usually accompanied, cobalt, silver, and bismuth, with some earthy matters, the analysis may be conducted according to the following process.

1. The ore being reduced to an impalpable powder, is to be two or three times digested in nitric acid, considerably diluted, after which every thing soluble will be taken up. During the process, nitrous gas is given out.

2. The insoluble part consists mostly of sulphur and silica, which after being dried, weighed and heated, the sulphur burns off, and the difference of weight before and after ignition, indicates its amount. The residue, after boiling in a little nitrous acid, is pure silica.

3. Saturate the two nitrous solutions (1. and 2.) with pure pure soda, evaporate considerably, and pour the solution into cold distilled water; the oxide of bismuth is precipitated.

4. Add muriate of soda by drops to the filtered solution, while any precipitate is formed, which is the muriate of silver.

5. Evaporate the solution nearly to dryness, boil it with strong nitric acid while nitrous gas is given out; red oxide of iron is precipitated during the process.

6. Remove the oxide of iron, saturate the liquor with soda, and add nitrate of lead while any precipitate takes place. This is the arseniate of lead, which may be separated by filtration.

7. Decompose the nitrous solution by carbonate of soda: digest the washed precipitate in liquid ammonia; the oxide of iron mixed with alumina, is left behind, and may be separated by caustic fixed alkali.

8. Let the ammoniacal solution be slightly supersaturated with nitric acid, and a polished bar of iron introduced; in this way the copper will be separated: then decompose the liquid by carbonate of soda, and digest the precipitate in ammonia, and the iron employed in separating the copper will be removed.

9. The solution now contains only nickel and cobalt. Let it be evaporated till the excess of ammonia be expelled. This is the case when the vapour ceases to discolour moist turmeric paper. Then add pure potash or soda to the solution largely diluted, while any precipitation takes place. The precipitate is the oxide of nickel. The cobalt now only remaining in the solution, may be separated in the usual way. To reduce the oxide of nickel, mix it with glass of borax and a small quantity of carbonaceous matter, and then subject it in a crucible to the most powerful furnace heat. A button of pure nickel is thus produced.

As the ores of nickel are not very abundant, and as this metal is little employed for purposes of manufacture, the reduction of its ores does not extend beyond chemical analysis, which we have now detailed.

**Chap. XIV. Of the Ores of Manganese.**

Manganese usually exists in the state of oxide, combined with a small proportion of iron, or in the state of carbonate, and sometimes in that of sulphuret.

**Sect. I. Of the Analysis of the Ores of Manganese.**

Radiated gray ore of manganese.—This ore was analysed by Klapproth according to the following process.

1. Two hundred grains of the ore, in grossly broken crystals, were heated to a thorough redness in a small coated glass retort, connected with the pneumatic apparatus. The gas collected amounted only to nine grains, upon deducting the common air of the apparatus; but showed by the lively combustion of an iron wire confined in it, that it was pure oxygen gas.

2. In the small intermediate hollow glass sphere of the apparatus, a considerable quantity of moisture has condensed, which weighed 14 grains, and was pure water.

3. The manganese, having sustained that ignition, weighed 181 grains. The external lustre of the crystals was very much diminished, and their gray colour turned blackish.

"One hundred parts of this ore have, consequently, been decomposed into,

| Black oxide of manganese | 90.50 | |-------------------------|------| | Water | 7 | | Oxygen gas | 2.25 |

99.75"

As manganese is chiefly employed for economical purposes, in the state of oxide, the reduction of its ores forms no object of manufacture.

**Chap. XV. Of the Ores of Molybdena.**

For an account of the treatment of the ores of molybdena, which exists in the state of sulphuret and in that of oxide only, see Chemistry; see also the analysis of the molybdate of lead, in the chapter on lead, in this article.

**Chap. XVI. Of the Ores of Arsenic.**

Arsenic is found native, when it is alloyed with a small portion of iron, and sometimes also with a little gold or silver; in the state of sulphuret, or in the state of oxide.

**Sect. I. Of the Analysis of the Ores of Arsenic.**

The method of analysing the ores of arsenic by Bergman, has been already given under Arsenic in the article Chemistry, as well as the method of subliming the metal in close vessels, to obtain it in a state of purity. The following is recommended as a successful process for preparing this metal for nice chemical purposes. Mix a quantity of arseniate of potash with about \( \frac{1}{8} \) part of charcoal, and let it be sublimed in a close glass vessel, slowly heated to redness. The metallic arsenic thus obtained is in the form of beautiful brilliant crystals.

**Sect. II. Preparation of White Arsenic and Orpiment.**

White arsenic.—In the large way, this is prepared, by roasting the arsenical ores, previously ground to powder, and mixed with charcoal or saw dust, at a low red heat for several hours. The roasted ore is then subjected to a second sublimation, according to the following method; which is practised in Bohemia. The vessels in which the sublimation is performed, are strong square boxes of cast iron furnished with conical heads, which are closely luted with clay. These boxes are arranged in a spacious brick area, which is heated by fires proceeding from two furnaces, placed a little below them. When the impure arsenic has become red hot, it is removed into the boxes by 15 pounds at a time, where it is brought into fusion, and about an hour after begins to sublimate into the conical head. When the arsenic ceases to rise, another quantity is introduced into the vessel, and treated in the same way. These additions are continued till about 150 pounds of arsenic have been thus treated in each vessel; a period of about 12 hours is requisite for the sublimation of the whole quantity. When the vessels are cold, the conical head is taken off, and the sublimed arsenic is broken off with hammers, at the same time any impurities that adhere to it are separated, for a second operation.