Effaying dish Memoirs, a water flowing through a mine in Norway containing silver. Another instance is also mentioned of a silver guhr, in the Act. Erud. Upsal. 1720.

8. Mr Von Justi pretends, that he has found silver mineralised by an alkaline substance; but he has not spoken sufficiently distinctly concerning it, to know whether he means a saline or earthy alkaline matter. Henckel also pretends, that by treating calcareous earth or certain clays with pyrites, silver may be obtained.

§ 2. Ores of silver may be effayed by the same methods which are employed for the extraction of that metal from large quantities of ores; which methods are different, and suited to the different qualities of the different ores. See Part III. Or, in general, ores and earths containing silver may be effayed by the following processes, which are copied from Dr Mortimer's English edition of Cramer's Art of Effaying Metals, Part II. Process I.

PROCESS I.

To precipitate Silver by means of Lead from fusible Ores.

"Pound the ore in a very clean iron mortar into fine powder: of this weigh one docimatical centner or quintal, and eight of the like centners of granulated lead.

"Then have at hand the docimatical test, which must not as yet have served to any operation: pour into it about half of the granulated lead, and spread it with your finger thro' the cavity of it.

"Put upon this lead the pounded ore; and then cover it quite with the remainder of the granulated lead.

"Put the test thus loaded under the muffle of an effay-furnace, and in the hinder part of it: then make your fire, and encrease it gradually. If you look thro' the holes of either of the sliders, you will soon see that the pounded ore will be raised out of the melted lead, and swim upon it. A little after, it will grow clammy, melt, and be thrown towards the border of the test: then the surface of the lead will appear in the middle of the test like a bright disc, and you will see it smok and boil: so soon as you see this, it will be proper to diminish the fire a small matter for a quarter of an hour; so that the boiling of the lead may almost cease. Then again, increase the fire to such a degree, that all may turn into a thin fluid, and the lead may be seen, as before, smoking and boiling with great violence. The surface of it will then diminish by degrees, and be covered over with a mass of scoriae. Finally, have at hand an iron hook ready heated, wherewith the whole mass must be stirred, especially towards the border; that in case any small parcels of the ore not yet dissolved should be adherent there, they may be brought down, taking great care not to stir any the least thing out of the test.

"Now, if what is adherent to the hook during the stirring, when you raise it above the test, melts quickly again, and the extremity of the hook grown cold is covered with a thin, smooth, shining crust; it is a sign that the scorification is perfect; and it will be the more so as the said crust adherent to the hook shall be coloured equally on every side: but in case, while the scoriaes are stirred, you perceive any considerable clamminess in them, and when they adhere in good quantity to the hook, though red-hot, and are inequally tinged, and seem dusty or rough with grains interspersed here and there; it is a sign that the ore is not entirely turned into scoriae. In this case, you must with a hammer strike off what is adherent to the hook, pulverize it, and with a ladle put it again into the test, without any loss or mixture of any foreign body, and continue the fire in the same degree till the scoria has acquired its perfection and the abovementioned qualities. This once obtained, take the test with a pair of tongs out of the fire, and pour the lead, together with the scoria swimming upon it, into a cone made hot and rubbed with tallow. Thus will the first operation of the process be performed, which does not commonly indeed last above three quarters of an hour.

"With a hammer strike the scoriaes off from the regulus grown cold, and again examine whether they have the characteristics of a perfect scorification; if they have, you may thence conclude, that the silver has been precipitated out of the ore turned to scoriae, and received by the lead.

"When the scorification lasts longer than we mentioned, the lead at last turns to scoriae or litharge, and the silver remains at the bottom of the vessel: but the fire must be moderately supplied, and the vessels be extremely good, to produce this effect; for they seldom relish to the strength of the scoriae long enough; so that the whole scorification may be brought to an end; which has afterwards this inconvenience, that the silver is dissipated by grains in the small hollows of the corroded ore, and can hardly be well collected again, when the ore has but little silver in it. Nay, there is still more time to be consumed to obtain the perfect destruction of the lead, by means of the combined actions of the fire and air, because the scoriaes swimming at the top retard it considerably.

"In this process, the sulphur and the arsenic of the silver-ore, when the ore is broken small, and extended widely in a small quantity, are in part easily dissipated by the fire, and in part absorbed by the lead; the lighter part of which, swimming upon the heavier, becomes very clammy by means of the sulphur which is in the ore; but when this is dissipated by the violence of fire, it turns into glaas or scoriae: but when arsenic is predominant in the ore, the plumbous part turns immediately into a very penetrating and very fusible glaas, having a dissolving efficacy, unless the arsenic lies hidden in a white pyrite or cobalt. For this reason, the fixed part of the ore, which is no silver, is dissolved by that glaas, melts, and assumes the form of scoriae. The unmetallic earths and the pure copper or lead ores thereto adherent are of this kind. The silver then remains immutable; and being freed of these heterogeneous bodies, which are partly dissipated and partly melted, it is precipitated and received by the remaining regulus of lead. Therefore this process is completed by three distinct operations; viz. 1. By roasting. 2. By scorification. 3. By the melting precipitation of the silver, which is the result of the two former operations.

"The "The ore must be pulverised very fine, in order to increase the surface, that the dissipation of the volatiles and the dissolution by litharge may be sooner effected. This pulverising must then be done before the ore is weighed, because there is always some part of the ore adherent to the mortar or iron plate on which it is made fine; which part being lost, the operation is not exact. Erker was in the right when he prescribed eight centners of lead for the subduing of fusible ores. Nevertheless, it must be owned, that this quantity is superfluous in some cases. However, as the flexibility of the silver-ore depends from the absence of stones, pyrites, &c., it is easy to see, that there are an infinite number of degrees of fluxibility which it would be needless to determine exactly, and most commonly very difficult to determine by the bare sight. Besides, a little more lead does not render the process imperfect; on the contrary, if you use too small a quantity of lead, the scoriafication is never completely made. Nay, there are a great many ores containing sulphur and arsenic in plenty, that destroy a considerable quantity of lead: such are the red silver-ore, and that wherein there is a great deal of the steel-grained lead-ore. If the fire must be sometimes diminished in the middle of the process, it is in order to hinder the too much attenuated litharge, which is continually generated out of the lead, from penetrating the pores of the test, and from corroding it; which is easily done when the fire is over-strong; for then the surface of the vessel which is contiguous to the lead contracts cavities, or, being totally consumed by small holes, lets the regulus flow out of it. The vessels that are most subject to this inconvenience are those in the materials of which lime, plaster, and chalk are mixed. Nay, these bodies, which are of their nature refractory, being eroded during their scoriafication, at the same time communicate a great clamminess to the scoria; so that a great quantity of the mass remains adherent to the test in the form of protuberances, when you pour it out; whereby a great many grains of the regulus are detained."

**PROCESS II.**

The regulus obtained by the process I. contains all the silver of the ore, and the unscoriafied part of the lead. The silver may be afterwards separated from the lead, and obtained pure by cupellation; which process is described under the article Essay (of the value of Silver.)

**PROCESS III.**

If the silver-ore cannot be washed clean, or if it be rendered refractory by a mixture of unmetallic earths and stones, the scoriafication of these earthly matters frequently cannot be completed by the process I. Cramer therefore directs, that such ores shall be treated in the following manner.

"Bruise the ore into an impalpable powder, by grinding in a mortar; to a docimatical centner of it, add a like quantity of glass of lead finely pulverised; for the more exactly these two are mixed together, the more easily the scoriafication afterwards succeeds. Put this mixture, together with 12 centners of lead, into the test, according to process I. then put the test under the muffle.

"Make first under it a strong fire, till the lead boils very well; when you see it so, diminish the violence of the heat, as was directed in the first process; but keep it thus diminished a little longer: then, finally, again increase the fire to such a degree, till you perceive the signs of a perfect scoriafication and fusion. See the whole process I. Now this process lasts a little longer than the foregoing, and requires a greater fire towards the end.

"It sometimes happens that a very refractory ore cannot be dissolved by litharge; and that a mass, which has the clamminess of pitch, swims upon the regulus and upon the scoriae themselves which are already subdued in part: when you see this, shut the vents of the furnace to diminish the fire; then gently touch this refractory body with a small iron cold hook, to which it will immediately stick; take it off softly, not to lose any thing; pound it into a fine powder, adding a little glass of lead, and put it again into the test; then continue the scoriafication till it is brought to its perfection. But you must always examine the scoria of your refractory ore, to see whether there may not be some grains of regulus dispersed in it: for sometimes the scoriae that grow clammy retain something of the metal; which if you suspect, pound the scoriae into a fine dust, and thus the grains of metal will appear if there are any left, because they can never be pounded fine. The silver is separated from this regulus by cupelling, as in Process II.

"All earths and stones are refractory in the fire: for, although some of them melt naturally in the fire, as those that are vitrifiable do; nevertheless, all the others, a very few excepted, melt much more difficulty than metals, and never become so thin in the fusion as is required for the sufficient precipitation of a precious metal. But litharge itself does not conveniently dissolve these refractory matters by the help of fire alone, unless you add some mechanical mixture to them; for the very moment the said litharge penetrates through the interstices of the refractory ore, and begins to dissolve it, a tenacious mass is produced, which hardly admits any farther dilution by the litharge. You may see it plain, if you make coloured glasses with metallic calxes; if you pour carefully upon them a calx that gives a colour, you will never obtain that they may be equally dyed on every side, even although you should torture them for whole days together in a great fire. Nay, glasses already made can never be diluted by only pouring salts and litharge upon it. Wherefore, you must use the artifice of glass-makers, who, in the making of the most perfect glasses, take great care, before they put the species of their ingredients into the fire, to have a mechanical mixture precede, or at least accede during the fusion itself, which is done here by pounding glasses of lead mixed with the ore: but if you think that your glasses of lead is not sufficiently fusible, you may add to it litharge melted first, and then pounded into a fine powder.

"As this scoriafication requires a longer and a greater fire than the foregoing, and as a greater quantity of litharge is moreover requisite to subdue the refractory scoria; it is easy to see why a much greater quantity of lead must be used here than in Process I.; and, although less lead is often sufficient, it Part II.

Eflaying it is nevertheless proper always to use the greatest quantity that can be necessary; lest, for instance, it should be necessary to try so many times the lead alone, to make it evident how much silver the lead when alone leaves in the coppel. Nor need you fear lest any thing of the silver be taken away by the lead, provided the coppels be good, and the coppeiling duly put in execution: for you can hardly collect a ponderable quantity of silver out of the collected fume of the lead, which rises during the coppeiling, as well as out of the litharge that is withdrawn into the coppel."

PROCESS IV.

If the ore be rendered refractory by pyrites, Cramer directs that the silver should be precipitated by lead in the following manner. (Art of Assaying, Part II. proc. 4.)

"Break your ore into a rough powder, and put a centner of it into the teft: put upon this another teft in the manner of a tile; put it under the muffle hardly red-hot: increase the fire by degrees. There will always be a crackling: which being ended, take away the upper-teft; for when the vessels have been red-hot about one minute, the ore ceases to split. Leave the ore under the muffle till the arsenic and the sulphur are for the most part evaporated; which you will know from the cessation of the visible smoke, of the smell of garlic, or the acid; then take away the teft, and leave it in a place not too cold, that it may cool of itself.

"Pour out, without any dissipation, the roasted ore, and with a knife take away what is adherent to the vessel; pound it to a most subtile powder, and grind it together with an equal weight of glafs of lead; and, finally, scorify the whole collected ore in the same teft wherein the testing was made, unless it has contracted chinks, as was described in Process III.

"Remarks. Yellow pyrites-ores contain a very great quantity of sulphur, even greater than is necessary to saturate the metal that lies hidden in them. For which reason this superfluous sulphur dissipates in a middling fire; but if it had been mixed with lead, it would have rendered it refractory, nor could it afterwards be dissipated from it without a considerable destruction of the lead. The white arsenical pyrites turn also a great quantity of lead into glafs, on account of the abundance of the arsenic they contain. For which reason these ores must be previously roasted, that the sulphur and arsenic may be dissipated. Nor need you fear lest any part of the silver be carried away with the arsenic; for when arsenic is separated from any fixed body, by a certain degree of fire, it carries nothing of that body away with it."

PROCESS V.

SILVER may be precipitated from its ore by cupellation only, in the following Process, given by Cramer, [Art of Assaying, Part II. Proc. 9.]

"Pound one centner of ore; roast it in the manner directed in the last process; beat it to a most subtile powder; and if it melts with difficulty on the fire, grind it together with one centner of litharge, which is not necessary when the ore melts easily: then divide the mixture or the powder of the ore alone into five or six parts, and wrap up every one of them severally in such bits of paper as can contain no more than this small portion.

"Put a very large coppel under the muffle; roast it well first, and then put into it fifteen centners of lead: when the lead begins to smoke and boil, put upon it one of the said portions with the small paper it was wrapped in, and diminish the fire immediately, in the same manner as if you would make a scorification in a teft, but in a lesser time. The small paper, which turns presently to ashes, goes off of itself, and does not sensibly increase the mats of the scoriae. The ore proceeding therefrom is cast on the border, and turns to scoriae very soon. Increase the fire again immediately, and, at the same time, put another portion of the ore into the coppel, as was just now said. The same effects will be produced. Go on in the same manner, till all the portions are thrown in and consumed in the lead. Finally, destroy the remaining lead with a stronger fire.

"The silver that was in the ore and in the lead will remain in the coppel. If you deduct from it the lead proceeding from the lead, you will have the weight of the silver contained in the ore. If the ore employed was easy to be melted, all the scoria vanishes; but if it was refractory or not fusible, all the scoria does not always go away, but there remains something of it now and then in the form of dust. A great many ores and metals may be tried in this way, except only such as split and corrode the coppels. There are likewise some of them which must be previously prepared in the same manner as is required to render them fit for going through a scorification. See the foregoing Processes.

"Remarks. The ore thrown at several times upon lead boiling in a coppel may be dissolved without the foregoing scorification; but this is very far from having an equal success with all kinds of ores; for there are ores and metals which resist very much to their dissolution by litharge; and which being on this account thrown on the border, are not sufficiently dissolved; because the litharge steals away soon into the coppel. Nevertheless, there are some others which vanish entirely by this method, except the silver and gold that was contained in them.

"A previous roasting is necessary, first, for the reasons mentioned, and then because the ore thrown upon boiling lead should not crackle and leap out; for, having once passed the fire, it bears the most sudden heat."

PROCESS VI.

Silver may be precipitated out of the same bodies as were mentioned in the foregoing processes by scorification in a crucible. [Cramer, Proc. 15.]

"The body out of which you intend to precipitate silver must be previously prepared for a scorification by pounding and roasting, as mentioned in the former processes. Then, in the same manner, and with the same quantity of lead, put it into a crucible strictly examined, that it be entire, solid, not speckled with black spots, like the scoria of iron, especially at its inferior parts, and capable of containing three times Native metallic silver may be separated from the stones and earths with which it is intermixed, by amalgamation with mercury, which operation is to be performed in the same manner as for the separation of native gold; a detail of which see in Part III. sect. iii.

The corneous ore, if it really be, as Cronstedt says, a luna cornea, ought to be treated in some of the methods directed for the reduction of luna cornea. See Chemistry, no 366, 367.

Sect. IV. Ores of Copper.

§ 1. Copper is found underground in three different forms. 1. Native or virgin copper diversely ramified, which is much more rare than native silver. This native copper is not so ductile as copper purified by fusions from the ore (a). 2. Copper is found in form of calx, of verdigris, of precipitates. Such are the minerals called silky copper ores, and several white and green earths. These matters are only copper almost pure but little mineralized, but which has been corroded, dissolved, precipitated, calcined by saline matters, by the action of the air, of water, and of earths (b). 3. Copper is frequently in a truly mineral state, that is, combined with sulphur, and with arsenic, with other metallic matters mixed with earths, and enveloped in different matrixes. These are the true copper ores. They have no regular forms except they partake of the nature of pyrites. Their colours are very different, which depend chiefly on the proportion of the mineral substances composing them. Lastly, in most all of them we may perceive green or blue colours, which always indicate an erosion or calcination of the copper. Most copper ores contain also some iron or ferruginous earth, to which the ochre colour is to be attributed, which might make us believe them to be ores of iron. Ores which contain much iron are the most difficultly fusible.

Copper ores have almost all a yellow, golden, and shining colour, by which they are easily distinguished. Some of them are coloured with irises, and frequently have spots of verdigris, by which also they are distinguishable from other ores.

Many copper ores are also rich in silver. Such is that called the white copper ore, the colour of which is rather occasioned by arsenic than by silver, although it contains so much silver as to be enumerated by several names.

(a) Native Copper is solid; or consisting of friable masses, formed by precipitation of cuprous vitriolic waters, called cement or ziment copper; or forming crystallized cubes, or grains, leaves, branches, or filaments.

(b) Calciform ores are either pure calxes of copper, or are mixed with heterogeneous matters. 1. The pure are, loose friable ochre, called ceruleum montanum, mountain-blue, and viride montanum, mountain-green; and the red indurated calx, called improperly glass copper ore. 2. Mixed calciform ores are those in which the calx of copper is mixed; with calcareous earth, forming a mountain blue; with iron, forming a black calx; with gypsum, an indurated green ore, called malachites; and with quartz, a red ore.

(c) Copper is mineralized, 1. By sulphur, forming the grey copper ore, improperly called vitreous (minera cupri vitrea Wallerii). 2. By fulgurated iron, forming the hepatic copper ore (minera cupri hepatica Wallerii) of a brown yellow colour. It is a kind of cuprous pyrites, and is called by Cronstedt minera cupri pyritacea. Sometimes it is of a blackish grey colour, and is then called pyrites cupri griseus (minera cupri grisea Wallerii); sometimes of a reddish yellow, and tarnished with blue irises on its surface, when it is called minera cupri lazurae; when of a yellowish green colour, it is the pyrites cupri flavo-viridefens (cuprum sulphure & ferro mineralifaturn Wallerii); and when of a pale yellow colour, it is the pyrites cupri palide flavus. Most of the above pyritaceous ores contain also some arsenic, but their sulphur is predominant. 3. Copper mineralized by sulphur, iron, and arsenic. White copper ore (Minera cupri alba Wall.) This ore contains also some silver. 4. Copper dissolved by vitriolic acid. Native blue vitriol. 5. Copper united with bitumen. Copper-coal ore. This is a pit-coal, from the ashes of which copper is obtainable. 6. Copper is also found in the mineral called kupfer nickel. Part II.

Effaying of Ores of Copper.

Mineralogists amongst silver ores.

Lastly, the pyrites of a golden yellow colour which contains copper and sulphur, and the white pyrites which contains copper and arsenic, are considered as copper ores by several chemists and naturalists. Henschel and Cramer remark, that no proper ore of copper is known which does not contain a considerable quantity of arsenic.

§ 2. Ores of copper may be effayed in methods similar to those employed for smelting of large quantities of ores, (Part III.) or they may in general be effayed by the following processes.

PROCESS I.

To reduce and precipitate copper from a pure and fusible ore in a close vessel.

"Mix one, or, if you have small weights, two docimastical centners of ore beat extremely fine, with six centners of the black flux; and having put them into a crucible or pot, cover them one inch high with common salt, and press them down with your finger: but let the capacity of the vessel be such, that it may be only half full; shut the vessel close, put it into the furnace; heap coals upon it, so that it may be covered over with them a few inches high; govern the fire in such a manner, that it may first grow slightly red-hot. Soon after you will hear your common salt crackle; and then there will be a gentle hissing noise. So long as this lasts, keep the same degree of fire till it is quite over. Then increase suddenly the fire, either with the funnel and cover put upon the furnace, or with a pair of bellows applied to the hole of the bottom part, that the vessel may grow very red-hot. Thus you will reduce and precipitate your copper in about a quarter of an hour; then take out the vessel, and strike with a few blows the pavement upon which you put it, that all the small grains of copper may be collected in one mass.

Break the vessel, when grown cold, in two, from top to bottom, as nearly as you can: if the whole process has been well performed, you will find a solid, perfectly yellow and malleable regulus adhering to the bottom of the vessel, with scoria remaining at top of a brown colour, solid, hard, and shining, from which the regulus must be separated with several gentle blows of a hammer; this done, weigh it, after having wiped off all the slimes.

A soft, dusty, and very black, scoria, is a sign of a fire not sufficiently strong. Small neat grains of copper reduced but not precipitated, and adhering still to scoriae, especially not very far from the bottom, and an unequal and ramified regulus, are signs of the same thing. A solid, hard, shining, red-coloured scoria, especially about the regulus, or even the regulus itself when covered with a like small crust, are signs of an excess in the degree and duration of the fire.

Remarks. All the ores which are easily melted in the fire are not the objects of this process; for they must also be very pure. Such are the vitreous copper ores." (Mr Cramer means, it is presumed, the red calciform ore called improperly glass ore, and not the minera cupri vitrea of Wallerius, which being composed of copper mineralised by sulphur, could not be treated properly by this process, in which no previous roasting is required. The sulphur of this ore would with the alkali of the black flux form a heap, from which the metal would not precipitate.) "But especially the green and azure-coloured ores, and the ceruleum and viride montanum, which are not very different from them. But if there is a great quantity of arsenic, sulphur, or of the ore of another metal and semimetal joined to the ore of copper, then you will never obtain a malleable regulus of pure copper, tho' ores are not always rendered refractory by the presence of these."

PROCESS II.

To reduce and precipitate copper out of ores rendered refractory by earth and stones that cannot be washed off.

"Beat your ore into a most subtil powder, of which weigh one or two centners, and mix as much sandviper to them. This done, add four times as much of the black flux with respect to the ore; for by this means, the sterile terrestrial parts are better disposed to a scorification, and the reducing and precipitating flux may act more freely upon the metallic particles freed from all their incumbrances.

As for the rest, make the apparatus as in last process; but you must make the fire a little stronger for about half an hour together. When the vessel is grown cold and broken, examine the scoriae, whether they are as they ought to be. The regulus will be as fine and ductile as the foregoing.

Remarks. As these copper ores hardly conceal any sulphur and arsenic in them, the roasting would be of no effect, and much copper would be lost. For no metallic calx, except those of gold and silver, improperly so called, can be roasted, without you find a part of the metal lost after the reduction.

PROCESS III.

To precipitate copper out of an ore (b) that contains iron.

"Do all according to last process. But you will find, after the vessel is broken, a regulus upon no account so fine, but less ductile, wherein the genuine colour of the copper does not perfectly appear, and which must be further purified.

Remarks. The fire used in this operation is not so strong that the iron should turn to a regulus. But as copper is the menstruum of iron, which is of itself very refractory in the fire; for this reason, while the ore and the flux are most intimately mixed and confounded by trituration, the greatest part of the iron being dissolved by the copper, turns into a regulus along with it."

PROCESS IV.

The roasting of a pyrite, sulphureous, arsenical, semi-metallic, copper ore.

Break two docimastical centners of the ore to a coarse powder, put them into a test covered with a tile,

(d) Mr Cramer still means the calciform ores only, and not the mineralised ores of copper. Efusing tile, and place them under the muzzle of a docimastical furnace. But the fire must be so gentle, that the muzzle may be but faintly red-hot. When the ore has decrepitated, open the test, and continue the fire for a few minutes; then increase it by degrees, that you may see the ore perpetually smoking a little: in the mean time, it is also proper now and then to stir it up with an iron hook. The shining particles will assume a dark red or blackish colour. This done, take out the test, that it may grow cold. If the small grains are not melted, nor strongly adherent to each other, hitherto all will be well; but if they run again into one single cake, the process must be made again with another portion of the ore, in a more gentle fire.

When the ore is grown cold, beat it to a powder somewhat finer, and roast it by the same method as before; then take it out, and if the powder is not melted yet, beat it again to a most subtil powder; in this you are to take care that nothing be lost.

Roast the powder in a fire somewhat stronger, but for a few minutes only. If you do not then find the ore any way inclined to melt, add a little tallow, and burn it away under the muzzle, and do the same another time again, till, the fire being very bright, you no longer perceive any sulphureous, arsenical, unpleasant smell, or any smoke; and there remains nothing but a thin, soft powder, of a dark red, or blackish colour.

Remarks. Every pyrites contains iron, with an unmetallic earth: to which sulphur, or arsenic, and most commonly both, always join. Besides, there is copper in many pyrites; but sometimes more, and sometimes less: some of them are altogether destitute of copper; therefore, so much as pyrites differ with regard to the proportion of their constituent particles, so much do they differ as to their disposition in the fire. For instance, the more copper there is in pyrites, the more it inclines to colliquation. The more sulphur and arsenic it has in it, the more quickly the melting of it will be procured, and the reverse: the more iron and unmetallic earth it contains, the more it proves refractory in the fire. Now if such pyrites melt in the roasting, as happens to some of them if they grow but red-hot, the sulphur and arsenic that lies hidden therein are so strictly united with the fixed part, that you would in vain attempt to dissipate them. Nay, in this case, when it is reduced again into a powder, it requires a much greater time and accuracy in the regimen of the fire to perform the operation. For this reason, it is much better to repeat it with new pyrites. But you can roast no more than the double quantity at once of the ore you have a mind to employ in the foregoing experiment; to the end that, the precipitation by fusion not succeeding, there may remain still another portion entire; lest you should be obliged to repeat a tedious roasting. If you see the signs of a ferrous refractory pyrites, the operation must be performed with a greater fire, and much more quickly. However, take care not to do it with too violent a fire: for a great deal of copper is consumed not only by the arsenic, but also by the sulphur; and this happens even in vessels shut very close, when the sulphur is expelled by a fire not quite so strong; which a reiterated and milder sublimation of the sulphur in a vessel both very clean and well closed will clearly shew.

When the greatest part of the sulphur and the arsenic is dissipated by such causes as promote colliquation, you may make a stronger fire: but then it is proper to add a little of some fat body; for this dissolves mineral sulphur: it changes the mixture of it in some part, which, for instance, consists in a certain proportion of acid and phlogiston; and at the same time hinders the metallic earth from being reduced into copper, by being burnt to an excess. From these effects, the reason is plain, why assayers produce less metals in the trying of veins of copper, lead, and tin, than skilful smelters do in large operations. For the former perform the roasting under a muzzle, with a clear fire, and without any oily reducing menstruum; whereas the latter perform it in the middle of charcoal or of wood, which perpetually emit a reductive phlogiston.

The darker and blacker the powder of the roasted ore appears, the more copper you may expect from it. But the redder it looks, the less copper and the more iron it affords; for roasted copper dissolved by sulphur or the acid of it is very black, and iron, on the contrary, very red.

PROCESS V.

The precipitation of copper out of roasted ore of the last process.

Divide the roasted ore into two parts: each of them shall go for a centner: add to it the same weight of sandiver, and four times as much of the black flux, and mix them well together. As for the rest, do all according to the process I.: the precipitated regulus will be half malleable, sometimes quite brittle, now and then pretty much like pure copper in its colour, but sometimes whitish, and even blackish. Whence it is most commonly called black copper, tho' it is not always of so dark a dye.

It is easy to conceive, that there is as great a difference between the several kinds of that metal called black copper, as there is between the pyritose and other copper ores accidentally mixed with other metallic and semi-metallic bodies. For all the metals, the ores of which are intermixed with the copper ores, being reduced, are precipitated together with the copper, which is brought about by means of the black flux. Wherefore iron, lead, tin, the reguline part of antimony, bismuth, most commonly are mixed with black copper in a multitude of different proportions. Nay, it is self-evident, that gold and silver, which are dissolvable by all these matters, are collected in such a regulus when they have been first hidden in the ore. Besides, sulphur and arsenic are not always altogether absent. For they can hardly be expelled so perfectly by the many preceding roastings, but there remain some vestiges of them, which are not dissipated by a sudden melting, especially in a close vessel, wherein the flux swimming at top hinders the action of the air. Nay, arsenic is rather fixed by the black flux, and assumes a reguline semi-metallic form, while it is at the same time preserved from dissipating by the copper. PROCESS VI.

To reduce black copper into pure copper by scoriafication.

"Separate a specimen of your black copper, of the weight of two small docimastical centners at least; and do it in the same manner, and with the same precautions, as if you would detect a quantity of silver in black copper.

"Then with lime and coal-dust, make a bed in the cavity of a test moistened: when this bed is dry, put it under the muffle of the docimastical furnace, in the open orifice of which there must be bright burning coals, wherewith the test must likewise be surrounded on all parts. When the whole is perfectly red-hot, put your copper into the fire, alone, if it contains lead; but if it is altogether destitute of it, add a small quantity of glass of lead, and with a pair of hand-bellows increase the fire, that the whole may melt with all speed: this done, let the fire be made a little violent, and such as will suffice to keep the metallic mass well melted; and not much greater. The melted mass will boil, and scoriae will be produced, that will gather at the circumference. All the heterogeneous matters being at last partly dissipated, and partly turned to scoriae, the surface of the pure melted copper will appear. So soon as you see it, take the pot out of the fire, and extinguish it in water: then examine it in a balance, and if lead has been at first mixed with your black-copper, add to the regulus remaining of the pure copper, one fifth part of its weight which the copper has lost by means of the lead, then break it with a vice; and thus you will be able to judge by its colour and malleability, and by the surface of it after it is broken, whether the purifying of it has been well performed or no. But whatever caution you may use in the performing of this process, the product will nevertheless be always less in proportion than what you can get by a greater operation, provided the copper be well purified in the small trial.

"Remarks. This is the last purifying of copper, whereby the separation of the heterogeneous bodies begun in the foregoing process is completed as perfectly as it possibly can be. For, except gold and silver, all the other metals and semimetals are partly dissipated and partly burnt, together with the sulphur and arsenic. For in the fusion they either turn of themselves to scoria or fumes, or this is performed by means of iron, which chiefly absorbs semimetals, sulphur and arsenic, and the destruction of it is at the same time accelerated by them. Thus the copper is precipitated out of them pure; for it is self-evident, that the unmetallic earth is expelled, the copper being reduced from a vitreous terrestrial to a metallic state, and the arsenic being dissipated by means of which the said earth has been joined to the coarser reguluses of the first fusion. But there is at the same time a good quantity of the copper that gets into the scoriae: however, a great part of it may be reduced out of them by repeating the fusion.

"The fire in this process must be applied with all imaginable speed, to make it soon run: for if you neglect this, much of your copper is burnt; because copper that is only red-hot, cleaves much sooner, and in much greater quantity, into half-scorified scales, than it is diminished in the same time when melted. However, too impetuous a fire, and one much greater than is necessary for the fusion of it, destroys a much greater quantity of it than a fire sufficient only to put it in fusion would do. For this reason, when the purifying is finished, the body melted must be extinguished in water together with the vessel, lest, being already grown hard, it should still remain hot for a while; which must be done very carefully to prevent dangerous explosions.

"The scoria of the above process frequently contains copper. To extract which, let two or three docimastical centners of the scoria, if it be charged with sulphur, be beat to a fusible powder, and mix it, either alone, or, if its refractory nature requires it, with some very fusible common pounded glass without a reducing saline flux, and melt it in a close vessel, and in a fire having a draught of air; by which you will obtain a regulus.

"But when the scoria has little or no sulphur at all in it, take one centner of it, and with the black flux manage it as you do the fusible copper ore, (process I.) by which you will have a pure regulus."

PROCESS VII.

The following process is translated from Mr Gellert's Elements of Effaying, and describes a new method of effaying ores, concerning which, see the section Of Effaying in general, p. 4922, col. 2.

"To effay copper ores.

Roast a quintal of ore [in the manner described in process IV.]; add to it an equal quantity of borax, half a quintal of fusible glass, and a quarter of a quintal of pitch: put the mixture in a crucible, the inner surface of which has been previously rubbed with a fluid paste of charcoal-dust and water: cover the whole with pounded glass mixed with a little borax, or with deprectated tea-fat: put a lid on the crucible, which you will place in an air-furnace, or in a blast-furnace: when the fire shall have extended to the bottom of the coals, let it be excited briskly during half an hour, that the crucible may be of a brick red colour: then withdraw the crucible, and when it is cold break it: observe if the scoria be well made: separate the regulus, which ought to be semi-ductile; and weigh it. This regulus is black copper; which must be purified, as in process VI.

If the ore be very poor, and enveloped in much earthy and stony matters; to a quintal of it, a quintal and a half of borax, a quarter of a quintal of pitch, and ten pounds of calx of lead or minium, must be added. The calx of lead will be revived, and will unite with the scattered particles of the copper, and together with these will fall to the bottom of the crucible, forming a compound regulus. When the ores of copper are very rich, half a quintal of borax and a quarter of a quintal of glass will be sufficient for the reduction. If the ore is charged with much antimony, a half or three quarters of a quintal of clean iron-silings may be added; otherwise the large quantity of antimony might destroy the copper, especially if the ore contained no lead. If iron be contained in copper ore, as in pyrites, some pounds of antimony, or of its regulus, may be PROCESS VII.

To effay Ores of Copper by humid Solution.

Some pyrites and ores contain so small a quantity of copper, that it cannot be separated by the above processes, but is destroyed by the repeated roastings and fusions. These, and indeed any copper-ores, may be effayed by humid solution, or by menstruums.

1. By roasting a sulphureous ore, the sulphur is burnt or decomposed, its phlogiston with part of the acid evaporating, while the remaining part of the acid combines with the metals, especially with the copper and iron contained in the ore. Accordingly, from an ore thus roasted, a vitriolic solution may be obtained by lixiviation with warm water, especially if the ore has been exposed, during a few days after it has been roasted, to a moist air; as the water thus gradually applied unites better with the combination of the metallic calxes with the concentrated vitriolic acid of the sulphur: but all the copper is not thus reduced by one operation to a vitriol. More sulphur must therefore be combined with the residuous ore by fusion, and must be again burnt off, that the remaining part of the copper may be attacked by some of the acid of the sulphur. By repeating this operation, almost all the copper and iron will be reduced to a vitriolic lixivium, from which the copper may be separated and precipitated by adding clean pieces of iron.

2. Copper-ores may be more easily effayed by humid solution in the following manner:

Roast the mineralized ores in the manner directed in Process IV. and pulverize them. If the ores be calciform, they do not require a previous roasting. Put this powder into a matras capable of containing ten times the quantity of the ore; pour upon the ore some water: set the matras in a sand-bath, that the water may boil: pour off the lixivium: add to the residuous ore more water, with some vitriolic or marine acid: digest as before in the sand-bath, and add this lixivium to the former: repeat this operation, till you find that the acid liquor dissolves no more metal.

By adding clean plates of iron you may precipitate the copper, which ought then to be collected, fused with a little borax and charcoal dust, and weighed.

We may remark, that although copper is not soluble by a dilute vitriolic acid, yet the calx of it obtained by roasting the ore, and also the calciform ores, are readily soluble in that acid.

3. Stahl advises to effay copper-ores by boiling them, after they have been roasted and powdered, in water, together with tartar and common salt, or with alum and common salt: but we have not found this method fo effectual as the preceding.

PROCESS VIII.

Dr Fordyce's method of effaying copper ores, by means of Aqua Regia. [Phil. Trans. for 1781, vol. lxxx. art. 3.]

This method consists only in pouring a quantity of an aqua regia composed of equal parts of the nitrous and muriatic acids upon a small quantity of the ore in powder, till a fresh effusion of the menstruum shews no green or blue tinge; by which means all the metalline part of the ore will be dissolved. It is then to be precipitated by means of a solution of fixed alkali, or volatile alkali cautiously managed will answer the same purpose. The metal then appears in form of a green precipitate called green verditer; but is mixed with what calcareous earth might have been contained in the ore; which the acids would dissolve, and the fixed alkali, if that kind was used, would precipitate. The caustic volatile alkali would not throw down this earth, and is therefore to be preferred to any other; but care must be taken to hit the point of saturation very exactly with it, as it violently dissolves the metal if added in too great quantity. Dr Fordyce orders this green calx to be dissolved in vitriolic acid, and then, by adding a piece of clean iron to the solution, all the copper contained in the ore will be obtained in its metallic form.

This method can be subject to no fallacy, unless the ore contains aluminous matter, in which case some of the earth of alum will be mixed with the metal, as that earth will be precipitated by fixed alkali, by caustic volatile alkali, and by iron. This, however, may very effectually be prevented by dissolving the green calx first in volatile alkali, and then in vitriolic acid. It is even probable, that by reducing the ore to a very fine powder, and treating it with caustic alkali, all the metal might be separated from the ore, without the trouble of using aqua regia. For the principles on which this method is conducted, see the article Chemistry passim.

SECT. V. Ores of Lead.

Lead is seldom found native (e) and malleable. Neither, says Mr Macquer (f), is it found in form of calx or precipitate, as copper is, because it is much less liable to lose its phlogiston by the action of air and water: therefore almost all lead is found naturally mineralized.

Lead is generally mineralized by sulphur (g). Its ores have a dark white, but a shining metallic colour.

There

(e) Cronstedt doubts whether any native lead has been found. Linnaeus says, he has seen what externally appeared to be such.

(f) But he is mistaken. As lead unites strongly with vitriolic acid, we might expect to meet ochres of this metal as well as of copper. Accordingly, we find some calciform ores of lead.

1. A pure calx of lead, in form of a friable ochre, cerussa nativa, found on the surface of galena; or it is indurated with a radiated or fibrous texture, of a white or yellowish green colour, and resembling spar; it is called spatium plumbi, sparry lead-ore, and lead-spar.

2. A calx of lead is found mixed with calx of arsenic, forming the ore called arsenicated lead-spar. Sometimes also that calx is mixed with calcareous earth.

(g) Lead is mineralized, 1. With sulphur; such are the several kinds of steel-grained and tessellated galenas, which also contain generally some silver. 2. With sulphurated iron and silver. It is fine-grained or tessellated, and is distin- These ores, although they form irregular masses, are internally regularly disposed, and seem to be composed of cubes of different sizes applied to each other, but not adherent. These ores are generally distinguished by the name of Galena. They commonly contain about three quarters of lead and a quarter of sulphur. They are accordingly heavy and fusible, although much less so than pure lead.

Most lead-ores contain silver; none but those of Wielach in Carinthia are known to be quite free from it: some of them contain so much of it, that they are considered as improper ores of silver. The smaller the cubes of galena are, the larger quantity of silver has been remarked to be generally contained.

§ 2. Lead ores may be effayed, i. By means of the black flux, in the manner directed by Mr Cramer, as follows:

"Let one or more quintals of this ore be grossly powdered, and roasted in a test till no more sulphurous vapours be exhaled, and then reduced to a finer powder; it is then to be accurately mixed with twice its weight of black flux, a fourth part of its weight of clean filings of iron and of borax. The mixture is to be put into a good crucible, or rather into a test; it is then to be covered with a thickness of two or three fingers of decrepitated sea-salt; the crucible is to be closed, and placed in a melting furnace, which is to be filled with unlighted charcoal, so that the top of the crucible shall be covered with it. Lighted coals are then to be thrown upon the unkindled charcoal, and the whole is left to kindle slowly, till the crucible be red-hot; soon after which a hissing noise proceeds from the crucible, which is occasioned by the reduction of the lead: the same degree of fire is to be maintained while this noise continues, and is afterwards to be suddenly increased, so as to make a perfect fusion; in which state it is to be continued during a quarter of an hour; after which it is to be extinguished; and the operation is then finished."—The filings of iron are added to the mixture, to absorb the sulphur, a certain quantity of which generally remains united with the lead-ore, notwithstanding the roasting. We need not fear lest this metal should unite with the lead and alter its purity; because, although the sulphur should not hinder it, these two metals cannot be united. The refractory quality of the iron does not impede the fusion; for the union it forms with the sulphur renders it so fusible, that it becomes itself a kind of flux.—This addition of iron in the effay of lead-ores would be useless, if the ores were sufficiently roasted, so that no sulphur should remain.

Or, 2. By the following process of Mr Gellert.

"Mix a quintal of roasted-lead ore with a quintal of calcined borax, half a quintal of glass finely pulverized, a quarter of a quintal of pitch, and as much of clean iron-filings: put this mixture into a crucible wetted with charcoal-dust and water; place the crucible before the nozzle of the bellows of a forge, and when it is red raise the fire during 15 or 20 minutes; then withdraw the crucible, and break it when cold."

Some very fusible ores, such as the galena of Derbyshire, may be effayed, as large quantities of it are distinguished from the former by yielding a black flag when scorched, whereas the former yields a yellow flag.

3. With sulphurated antimony and silver. Plumbum fibiatum Linnei. Its colour is similar to that of galena, and its texture is striated. 4. With sulphur and arsenic. This cure is soft, almost malleable, like lead. From this ore lead may be melted by the flame of a candle.

Sect. VI. Tin Ores.

§ 1. Tin is very seldom found pure, but almost always mineralized, and chiefly by arsenic.

The richest ore of tin is of an irregular form, of a black or tarnished colour, and almost the heaviest of all ores. The cause of this extraordinary weight is, that it contains much more arsenic than sulphur, whereas most ores contain more sulphur than arsenic.

The most common tin ore is of the colour of rust, which proceeds from a quantity of iron, or of iron-ore mixed with it. The tin-ores of Saxony and Bohemia appear to be all of this kind.

One kind of tin-ore is semi-transparent and like spar. Lastly, several kinds of garnets are enumerated by mineralogists among tin-ores, because they actually contain tin.

The county of Cornwall, in England, is very rich in tin-ores; and the tin contained in them is very pure. From tin-mines in the East Indies tin is brought, called Malacca tin. No mines of tin have been discovered in France; only in Bretagne garnets are found which contain some tin.

Native tin is said to have been found in Saxony and Malacca. Its ores are all of the calciform kind, excepting black-lead, which appears to be tin mineralized by sulphur and iron.

The calciform ores of tin are, 1. Tin-flone, which is of a blackish-brown colour, and of no determinate figure; and tin-grains, or crystals of tin, which resemble garnets, and are of a spherical or polygonal figure, which they have probably acquired by the attrition of their angles. The tin-flone seems to consist of attrited tin-grains. This ore is calx of tin united with calx of arsenic, and frequently with calx of iron. 2. Garnets are said to contain calx of tin united with calx of iron. 3. Manganese is said also to contain tin.

§ 2. Ores of tin may be effayed in the same manner, according to Cramer, as he directed for the effay of lead-ores, supra. He further makes upon this effay the following remarks.

1. Tin-ores, on account of its greater gravity, admits better of being separated, by elutriation or washing, from earths, stones, and lighter ores. 2. A most exact separation of earths and stones ought to be made, because the scorification of these by fluxes requires such a heat as would destroy the reduced tin. 3. The iron ought to be separated by a magnet. 4. By a previous roasting, the arsenic is dissipated, which would otherwise carry off a great deal of tin along with it in a melting. Ores of Iron: heat would change another part of it into ashes, and would vitiate the remaining tin. The effay of tin is very precarious and uncertain; because tin once reduced is easily destructible by the fire, and by the saline fluxes requisite for the reduction.

Mr Gellert directs, that ores of tin should be effayed in the following manner:

"Mix a quintal of tin-ore, washed, pulverized, and twice roasted, with half a quintal of calcined borax, and half a quintal of pulverized pitch: these are to be put into a crucible moistened with charcoal-dust and water, and the crucible placed in an air-furnace: after the pitch is burnt, give a violent fire during a quarter of an hour; and then withdraw your crucible. If the ore be not very well washed from the earthy matters, as it ought to be, a larger quantity of borax is requisite, with some powdered glass, by which the too quick fusion of the borax is retarded, and the precipitation of the earthy matters is prevented. If the ore contains iron, to the above mixture may be added some alkaline salt."

**Sect. VII. Ores of Iron.**

§. 1. Iron is seldom found in its metallic state, and free from admixture; though Cramer gives an account of an ore which needs only to be put into a forge, and heated to a welding heat. Several sands and earths also have the appearance of iron, and are even attractive by a magnet. The ore mentioned by Cramer is found vitrified; with moderate blows the scoriae are thrown out, and a mass of iron obtained, which, by being put into the forge again, gives tough iron without any other process. But in general this metal is found in the state of a calx; or, though it is combined with a great quantity of the principle of inflammability, it has seldom enough of the metallic form; and it is very often intermixed with a certain proportion of sulphur. The minerals wrought for iron are three, viz. iron-ore, iron-stone, and bog-ore.

The iron ore is found in veins as the ores of other metals are, and the appearance is very various; sometimes it has a rusty iron colour resembling that of iron; sometimes it has a reddish cast; often it is formed into a sort of crystallizations which are protuberant knobs on the outside; and these consist of fibres tending to a common centre; and it is of a dark colour like coagulated blood. It is called hematites, or blood-stone; and consists of a calx of iron with a small quantity of vitriolic acid.

Iron-stone in this country is clay found in strata with coal; but which contains a large quantity of iron, so as to make the working profitable. Sometimes it has little appearance of iron; but, when burnt with a certain degree of heat, it becomes of a deep red.

The bog-ore is an ochre of iron, and is found generally in low situations, and in springs containing a small quantity of iron, which flowing over these grounds deposits it in the form of ochre; and after a number of ages it proves a rich mine of iron, and it is extracted from a calx of this kind in many parts of the world. There is also a particular kind of spar found in different countries of a pale blue colour, so that from its first appearance we would expect copper; but it contains a small quantity of iron, and is a combination of the metal with inflammable matter, as in Prussian blue.

The loadstone is a noted iron ore. It is always found in veins, and it is alleged that it is only possessed of its magnetic qualities when near the surface. In appearance, it does not differ from many of the ores of iron, and treated as an ore, it affords a considerable quantity of metal.

Neither is iron generally mineralized so distinctly as other metals are, unless in pyrites and ores of other metals.

Most of the minerals called iron ores have an earthy, rusty, yellowish, or brownish appearance, which proceeds from the facility with which the true iron ores are decomposed.

Iron is the most common and most abundant of all metals. In Europe, at least, we cannot find an earth, a sand, a chalk, a clay, a vitrifiable or calcinable stone, or even the ashes of any substance, which do not contain an earth convertible into iron. All earths and stones which are naturally yellow or red, and all those which acquire these colours by calcination, receive them from the ferruginous earth mixed with them. The yellow and red ochres consist almost solely of this earth: the black and heavy sands are generally very ferruginous.

The iron ore most commonly found is a stone of the colour of rust, of an intermediate weight betwixt those of ores in general and of unmetallic stones. This ore has no determinate form, and easily furnishes an iron of good quality.

Blood-stone or hematites, sanguine or red chalk, and emery, are iron ores; some of which, for instance blood-stone, are almost all iron. Most of these substances require but a slight calcination to be rendered very attractive by a magnet, and soluble in aqua fortis; but the iron obtained from them is of a bad quality, and they are therefore neglected. Iron from the hematites is very brittle; that obtained from ochres is red-short. All these iron ores are so refractory, that they can scarcely be fused.

Iron ores are very various in their form; or rather they have no determinate form. Sometimes they are earths, sometimes stones, sometimes grains. Accordingly, those naturalists who attend only to the external form of things in classing and subdividing minerals, have been obliged to multiply the names of iron ores; hence they are called iron ores in form of pease, of beans, of coriander seeds, of pepper-corns, of cinnamon, &c. which Mr Cramer treats as ridiculous trifles.

§. 2. Ores of iron may be effayed by the following process.

**Process I.**

[Cramer's Art of Affaying, Proc. 54.]

To reduce a precipitate iron out of its ore in a close vessel.

"Roast for a few minutes in a test under a muffle, and with a pretty strong fire, two centners of the small weight of your iron ore grossly pulverised; that the volatiles may be dissipated in part, and the ore itself be softened in case it should be too hard. When it Part II.

Essaying is grown cold, beat it extremely fine, and roast it a second time, as you do the copper-ore, but in a much stronger fire, till it no longer emits any smell; then let it grow cold again. Compose a flux of three parts of the white flux, with one part of fusible pulverised glaas, or of the like sterile unfulphurous scoriae, and add sandliver and coal-dust, of each one half-part; add of this flux three times the quantity of your roasted ore, and mix the whole very well together; then choose a very good crucible, well rubbed with lute within, to stop the pores that may be here and there unseen; put into it the ore mixed with the flux; cover it over with common salt; and shut it close with a tile, and with lute applied to the points.

"Put the wind-furnace upon its bottom-part, having a bed made of coal-dust. Introduce besides into the furnace a small grate supported on its iron bars, and a stone upon it, whereon the crucible may stand as on a support: surround the whole with hard coals, not very large, and light them at top. When the vessel begins to grow red, which is indicated by the common salt's ceasing to crackle, stop with grofs lute the holes of the bottom-part, except that in which the nozzle of the bellows is received: blow the fire, and excite it with great force, adding now and then fresh fuel, that the vessel may never be naked at top: having thus continued your fire in its full strength for three quarters of an hour, or for a whole hour, take next the vessel out of it, and strike several times the pavement upon which it is set, that the small grains of iron which happen to be dispersed may be collected into a regulus, which you will find after having broken the vessel.

"When the regulus is weighed, try its malleability: then make it red-hot; and when so, strike it with a hammer: if it bears the strokes of a hammer, both when red-hot and when cold, and extends a little, you may pronounce your iron very good; but if, when either hot or cold, it proves brittle, you may judge it to be not quite pure, but still in a semi-mineral condition.

"Remarks. The arsenic, but especially the sulphur, must be dissipated by roasting: for the former renders the iron brittle; and the latter not only does the same, but, being managed in a close vessel, with a saline alkaline flux, turns to liver of sulphur; to the action of which iron yielding in every respect, it can upon no account be precipitated; and if not the whole, a great part of it, at least, is retained by the fulphurous scoria; so that in this case you commonly in vain look for a regulus.

"The iron obtained from this first precipitation has hardly ever the requisite ductility, but is rather brittle: the reason of which is, that the sulphur and arsenic remain in it; for notwithstanding that the greatest part of these is dissipated by roasting, yet some part adheres so strictly, that it can never be separated but with absorbent, terrestrial, alkaline ingredients, that change the nature of the sulphur. For which reason, in larger operations, they add quicklime, or marble stones that turn into quicklime; which, while they absorb the said minerals, are, by it, and by help of the destroyed part of the iron, brought to a fusion, and turn to a vitrified scoria; although, at other times, they resist so much by their own nature a

vitrification. Another cause of the brittleness of iron is the unmetallic earth, when it is not yet separated from it; for the iron ore contains a great quantity of it, and in the melting remains joined with the regulus part: whence the iron is rendered very coarse and brittle. Some iron ores are altogether untractable: nevertheless, the reguluses produced out of them, when broken, have sometimes a neat semi-metallic look; which proceeds undoubtedly from a mixture of a small quantity of some other metal or semi-metal."

PROCESS II.

[The following Process for essaying iron ores, and ferruginous stones and earths, is extracted from Mr Gellert's Elements of Essaying.]

"Roast two quintals of iron ore, or of ferruginous earth: divide the roasted matter into two equal parts; to each of which add half a quintal of pulverised glaas, if the substance be fusible and contain much metal; but if otherwise, add also half a quintal of calcined borax. If the roasting has entirely disengaged the sulphur and arsenic, an eighth part, or even half a quintal, of quicklime may be added. With the above matters, mix twelve pounds of charcoal-powder.

"Take a crucible, and cover the bottom and sides of its inner surface with a paste made of three parts of charcoal-dust and one part of clay beat together. In the hollow left in this paste put the above mixture; press it lightly down; cover it with pulverised glaas; and put on the lid of the crucible.

"Place two such crucibles at the distance of about four fingers from the air-pipe, in such a manner that the air shall pass betwixt them at about the third part of the height from the bottom: fill the space betwixt the two crucibles with coals of moderate size: throw lighted coals upon them, that the fire may descend and make them red-hot from top to bottom: at first let the bellows blow softly, and afterwards strongly during an hour, or an hour and a quarter: then take away the crucible, and break it when cold. A regulus will be found in the bottom, and sometimes some small grains of iron in the scoria, which must be separated and weighed along with the regulus: then try the regulus, whether it can be extended under the hammer, when hot and when cold.

"Remarks. To disengage a metal from the earthy matters mixed with it by fire, we must change these matters into scoria or glaas. This change may be effected by adding some substance capable of dissolving these matters; that is, of converting them into a scoria or glaas, from which the metallic matters may, by their weight, separate and form a regulus at bottom. Fixed alkali, which is an ingredient of the black and of the white flux, is a powerful solvent of earths and stones: but the alkali does also dissolve iron, especially when this is in a calcined or earthy state; and this solution is so much more complete, as the fire is longer applied. Hence, in ordinary essays, where an alkaline fault is used, little or no regulus of iron is obtained. Now, glaas acts upon and dissolves earths and stones; but not, or very little, iron: consequently glaas is the best flux for such essays, and experience confirms this assertion. If the ore contains but little iron, we may also add to the glass some borax; but borax cannot be employed singly, because it very soon fuses, and separates from the ore before the metal is revived. Quicklime is added, not only to absorb the sulphur and arsenic remaining in the ore, but also because it dissolves and vitrifies the stony and earthy matters of iron ores, which are generally argillaceous. For which reason, in the large operations for smelting iron ore, quicklime, and even in certain cases gypsum, are commonly added to facilitate the fusion.

The reduction of iron-ore, and even the fusion of iron, requires a violent and long-continued heat; therefore, in this operation, we must not employ an inflammable substance, as pitch, that is soon consumed, but charcoal pulverized, which in close vessels is not sensibly wasted. Too much charcoal must not be added, else it will prevent the action of the glass upon the earthy matter of the ore, and consequently the separation of the metallic part. Experiments have taught me, that one part of charcoal-dust to eight parts of ore was the best proportion.

When iron is surrounded by charcoal, it is not decomposed or destroyed; hence the iron of the ore, which sinks into the hollow made of paste of charcoal-dust and clay, remains there unhurt. The clay is added in this paste to render it more compact, and to keep the fluid iron collected together.

The air is directed betwixt the crucibles; because if it was thrown directly upon them, they would scarcely be able to resist the heat. The space betwixt the air-pipe and the crucibles ought to be constantly filled with charcoal, to prevent the cold air from touching the crucibles. Ductile and malleable iron is seldom obtained in this first operation. The sulphur and arsenic, and frequently also an earthy matter adhering to the iron, prevent these qualities.

**Sect. VIII. Ores of Mercury.**

§ 1. Mercury is sometimes found pure, fluid, and in its proper metallic state, only mixed with earths and stones. Such are the ores of mercury found near Montpelier, in Tuscany, and in other places.

But the largest quantity of the mercury found in the earth is mineralized by sulphur, and consequently is in the form of cinnabar.

Mercury is never mineralized by arsenic. The richest mine of mercury is that of Almaden, in Spain.

Linnaeus and Cronstedt mention a singular ore, in which the mercury is mineralized by sulphur and by copper. It is said to be of a blackish-grey colour, of a glassy texture, and brittle. When the mercury and sulphur are expelled by fire, the copper is discovered by giving an opake red colour to glas of borax, which, by continuance and increase of heat, becomes green and transparent.

§ 2. Cramer directs, that ores of mercury should be assayed by the following Processes.

**Process I.**

To separate Mercury out of an unsulphureous Ore by Distillation.

"Take a lump of the pulverized ore, one common pound, which must stand for one centner; put it into a glass retort perfectly clean, well loricated, or coated up to half the length of its neck: this must be very long, and turned backwards with such a declivity, that a glass recipient may be perpendicularly applied to it; but you must choose a retort small enough, that the belly of it may be filled hardly two-thirds with the ore: this retort must be placed so, that nothing of the fluid adherent to the neck of it may fall into the cavity of the belly, but that the whole may run forward into the recipient. Finally, have a small recipient full of cold water: let it be perpendicularly situated, and receive the neck of the retort in such manner that the extremity of it be hardly one half-inch immersed into the water.

"Let the retort be surrounded with hot burning coals placed at some distance in form of a circle, lest the vessel should burst by too sudden a heat: then by degrees bring the burning coals nearer and nearer, and at last surround the whole retort with them and with fresh charcoal, that it may grow slightly red-hot: this fire having been continued for an hour, let the retort cool of itself: then strike the neck of it gently, that the large drops which are always adherent to it may fall into the recipient: let the recipient be taken away, and the water separated from the mercury by filtration, and let the mercury be weighed. This operation may be more conveniently performed in a sand-bath; in which case the pot containing the sand must be middling red-hot, and the retort be able to touch the bottom of it immediately; nor is it then necessary that the retort be loricated."

**Process II.**

To revivis Mercury from a sulphureous Cinnabar-ore.

"Beat your ore extremely fine, and mix it exactly with an equal portion of iron-filings, not rusty; proceed to distill it with the same apparatus as in the former process, but urge it with the strongest fire that can be made.

"Cinnabar may be separated from stones by sublimation thus: Beat it to a fine powder, and put it into a small narrow glass or earthen cucurbit, the belly of which it must not fill more than one-third part: stop the orifice at top; this must be very narrow, to hinder the free action of the air. Put this small cucurbit in an earthen pot above two inches wide in diameter, and gather sand around this pot about as high as the pulverized ore rises in the cucurbit. Then put it upon burning coals in such manner that the bottom of the pot may be middling red-hot. Thus will your cinnabar ascend and form a solid ponderous ring, which must be got out by breaking the vessel."

**Sect. IX. Ore of the Regulus of Antimony.**

Native regulus of antimony was first observed by Mr Swab, in Sweden, in the mine of Salberg, and described by him in the memoirs of the Swedish Academy in 1749. Mr Wallerius mentions it in his Mineralogy.

Regulus of antimony is generally united with sulphur, with which it forms antimony, which ought to be considered as a true ore of the regulus of antimony.

Another ore of regulus of antimony is also known, Ores of Antimony—of a red colour, in which the regulus is mineralised both by arsenic and by sulphur. This ore resembles some iron ores, and some kinds of blend. It is distinguished by its great fusibility, which is such, that it may be easily melted by the flame of a candle.

The native regulus of antimony, by Von Swed, is said by that author to have differed from the regulus of antimony obtained from ores, in these two properties, that it was capable of being easily amalgamated with mercury, and that its calx shot into crystals during the cooling.

Besides the ores of regulus of antimony enumerated above, this semifinal is also found in ores of other metallic substances, as in the plumose silver-ore, and in the stibiated lead-ore.

§ 2. The ores of antimony may be assayed by the following processes described by Mr Cramer.

**PROCESS I.**

To obtain antimony from its ore.

"Choose a melting crucible, or an earthen pot not glazed, that may contain some common pounds of the ore of antimony, broken into small bits. Bore at the bottom of the crucible some small holes, two lines in diameter. Let the bottom of the vessel be received by the orifice of a smaller one, upon which it must be put; and when the ore is put into it, let it be covered with a tile, and all the joints be stopped with lute.

"Put these vessels upon the pavement of a heath, and put stones all around them at the distance of six inches. Fill this intermediate space with ashes, so high that the inferior pot be covered to the upper brim. Then put fresh and burning coals upon it, and with a pair of hand-bellows excite the fire, till the upper vessels grow red-hot; take off the fire a quarter of an hour after; and when the vessels are grown cold, open them. You will find that the melted antimony has run through the holes made at the bottom of the upper vessel into the inferior one, where it is collected."

**PROCESS II.**

To roast crude antimony, or its ore, with or without addition.

"Choose an earthen, flat, low dish, not glazed; and if it cannot bear being made middling red-hot, cover it over with a coat of lute without. Spread it thinly over with crude antimony, or with its ore, beaten to a pretty coarse powder, not exceeding a few ounces at once. Put the dish upon a fire-pan, having a few burning coals in it: increase the fire till it begins to smoke a little. Meanwhile you must incessantly move the powder with a piece of new tobacco-pipe; for this causes the sulphur to evaporate the sooner. If you increase the fire a little too soon, the powder immediately gathers into large clots, or even begins to melt. When this happens, take it immediately off the fire before it melts entirely. Then pulverise it again, and finally make a gentle fire under it. Your black thinning powder will assume an ash-colour almost like that of earth, and become more refractory in the fire; wherefore you may then increase the fire till your powder grows middling red-hot, and let it last till it ceases to smoke. If you add to your crude antimony pulverised, half or an equal quantity of charcoal-dust, and perform the rest as above, the roasting will be done more conveniently; for it does not gather so easily into clots, and melts with much greater difficulty. When part of the sulphur is evaporated, add some fat to it at several times. Thus you will sooner finish the operation, and the remaining calx will not be burnt to excess. However, if it be thus exposed to too violent and long-lasting a fire, a great quantity of it evaporates; nor does it cease entirely to smoke in a great fire. And it will be enough, if, growing middling red-hot, it does no longer emit the unpleasant smell of the acid of sulphur."

**PROCESS III.**

To reduce a calx of antimony into a semi-metallic regulus.

"Mix some calx of antimony with a quarter part of the black flux, and put it into the crucible. Cover the vessel with a tile; make the fire as quickly as the vessel can bear it, but not greater than is necessary to melt the flux. When the whole has been well in fusion for half a quarter of an hour (which may be tried with a tobacco-pipe, taking off the tile) pour it into the melting cone, which must be warm and done over with tallow. Then immediately strike the cone several times. You will find, when the cone is inverted, a regulus, above which is a false scoria."

The methods of calcining antimony by means of nitre, are described under Chemistry, no 489—459; and those of obtaining a regulus of antimony without a previous calcination or roasting, by throwing a mixture of powdered antimony, tartar, and nitre, into a red-hot crucible, and by fusing this mixture, and of obtaining a martial regulus of antimony, are described at the article REGULUS.

**SECT. X. Ores of Bismuth.**

§ 1. Bismuth is found native, resembling the regulus of bismuth.

An ochre of bismuth, of a whitish yellow colour, is mentioned by Cronstedt; and is different from the ore improperly called flowers of bismuth, which is a calx of cobalt.

Bismuth is mineralised, 1. By sulphur. This ore has the appearance of galena. 2. With sulphurated iron. Bismuth is found also in cobalts, and in some ores of silver.

§ 2. Ores of Bismuth may be assayed by the following process.

**PROCESS I.**

To melt bismuth from its ore.

"Bismuth ore may be melted with the same apparatus as was directed for the fusion of crude antimony out of its ore. Or you may beat your ore to a very fine powder, with the black flux, sandiver, and common salt, in a close vessel, like the ore of lead, or of tin, and melt it in a middling fire, having a draught of air. But as this semi-metal is destructible and volatile, you must as quick as possible apply to it that degree of fire which the flux requires to be melted;" and so soon as it is well melted, the vessel must be taken out of the fire; and when it is grown quite cold and broken, you will find your regulus."

Mr Gellert directs that ores of bismuth should be effayed by fusing a quintal of pulverized ore with half a quintal of calcined borax and half a quintal of pulverized glass, in order to vitrify the adherent earths and stones which envelop the bismuth. But probably the heat requisite for this vitrification would volatilize part of the bismuth.

If the ore be of the kinds above described, mineralized by sulphur, or by sulphur and iron, a previous roasting would be expedient, which may be performed in the same manner as is directed for the roasting of antimony.

**Sect. XI. Ores of the Regulus of Cobalt.**

Cobalt is a grey-coloured mineral, with more or less of a metallic appearance. Its grain is close; it is compact and heavy, and frequently covered with an efflorescence of peach-coloured flowers. Of this several kinds are known*. All the true cobalts contain the semi-metal called regulus of cobalt, the calx of which becomes blue by vitrification. This regulus is mineralized in cobalt by sulphur, and especially by a large quantity of arsenic. Some cobalts also contain bismuth and silver.

Authors have given the name of cobalt to many minerals, although they do not contain the semi-metal above-mentioned, but only because they externally resemble the ore of the regulus of cobalt. But these minerals can only be considered as false cobalts. They are distinguishable from true cobalt by trying whether they can yield the blue glass called finalis, and the sympathetic ink. The red efflorescence is also a mark by which true cobalt is distinguishable from the false; but this efflorescence only happens when the ore has been exposed to a moist air.

The principal mines of cobalt are in Saxony, where they are dug for the sake of obtaining zaffre, azure-blue or smalt, and arsenic. Very fine cobalt is also found in the Pyrenean mountains. It has been likewise found in Cornwall and Scotland. And that it is in the eastern parts of Asia, appears from the blue colouring on old oriental porcelain: but probably the mines discovered in these countries are nearly exhausted, as considerable quantities of zaffre and smalt are exported from Europe to China.

Cobalt is heavier than most other ores, from the large quantity of arsenic it contains; and in this respect it resembles the ore of tin.

Besides the grey or ash-coloured cobalt above described, which is the most frequent, other cobalts are found of various colours and textures, mixed with various substances. Wallerius enumerates six species of cobalts. 1. The ash-coloured ore, which is regulus of cobalt mineralized by arsenic, consisting of shining leaden-coloured grains. Some ores of this kind are compact resembling steel, and others are of a loose texture and friable. 2. The specular ore is black, shining like a mirror, and laminated. This species is very rare; and is supposed by Wallerius to be a foliated spar, or selenites mixed with cobalt. 3. The vitreous, or flag-like ore, is of a bluish, shining colour, compact, or spongy. 4. Crystallized ore, is a grey, deep-coloured cobalt, consisting of clusters of cubical, pyramidal, prismatic crystals. 5. Flowers of cobalt, red, yellow, or violet. These flowers seem to be formed from some of the above-described compact ores, decomposed by exposure to moist air. This decomposition is similar to that which happens to ferruginous and cuprous pyrites. 6. The earthy cobalt is of a greenish white, or of a yellow colour, and of a soft and friable texture. This species seems to be an ochre of cobalt; and is formed perhaps from the flowers of cobalt further decomposed, in the same manner as a martial ochre is formed from the saline efflorescence of decomposing pyrites, when this efflorescence is further decomposed by exposure to moist air; by which the vitriolic acid contained in it is expelled, and the efflorescence is changed from a saline state to that of an ochre or calx.

Besides these proper ores, cobalt is also found in a blue clay along with native silver, in ores of bismuth, and in the mineral called kupfernickel. See Nickel.

The assay of cobalt is described at the article Regulus of Cobalt.

**Sect. XII. Ores of Zinc.**

§ 1. The proper ore of zinc is a substance which has rather an earthy or stony than metallic appearance, and is called calamy, calamine, or lapis calaminaris. This stone, although metallic, is but moderately heavy, and has not the brilliancy of most other ores. Its colour is yellow, and like that of rust. It is also less dense than other metallic minerals. It seems to be an ore naturally decomposed. The calamine is not worked directly to obtain zinc from it, because this would only succeed in close vessels, and consequently with small quantities, according to Mr Margraaf's process. But it is successfully employed for the conversion of copper into brass by cementation, by which the existence of zinc in that stone is sufficiently proved.

Mr Wallerius enumerates also amongst the ores of zinc a very compounded mineral, consisting of zinc, sulphur, iron, and arsenic. This mineral, called blend, resembles externally the ore of lead, and hence has been called false galena. These blends have different forms and colours; but are chiefly red, like the red ore of antimony.

Zinc is obtained from certain minerals in the East Indies, of which we know little.

California ores of zinc, according to Cronstedt, are pure or mixed. The pure are indurated, and sometimes crystallized, resembling lead-spar. The mixed ore contains also some calx of iron. This is calamine. It is whitish, yellowish, reddish, or brown.

Zinc is mineralized, 1. By sulphurated iron. Ore of zinc. Wallerius says, lead is sometimes contained in this ore. It is white, blue, or brown. 2. By sulphur, arsenic, and iron. Blend, or pseudo-galena, or false-galena, or black-jack. These are of various colours, white, yellowish, brown, reddish, greenish, black. They consist of scales, or are tessellated. Mr Cronstedt thinks, that in blends the zinc is mineralized in the state of a calx, and in the ore of zinc in its metallic state.

§ 2. Although the minerals above enumerated have been known, from their property of converting copper into brass, to be ores of zinc, yet the method of effaying Part II.

Ores of Zinc.

saying them so as to obtain the contained zinc was not known, or at least not published, before Mr Margraaf's Memoir of the Berlin Academy for the year 1746, upon that subject. That very able chemist has shown, that zinc may be obtained from its ores, from the flowers, or from any other calx of zinc, by treating these with charcoal-dust, in close vessels, to prevent the combustion of the zinc, which happens immediately upon its reduction when exposed to air. For this purpose, he put a quantity of finely powdered calamine, or roasted blend, or other calx of zinc, well mixed with an eighth part of charcoal-dust, into a strong, luted earthen retort, to which he fitted a receiver. Having placed his retort in a furnace and raised the fire, he applied a violent heat during two hours. When the vessels were cold and broken, he found the zinc in its metallic form adhering to the neck of the retort.

The chief difficulty in this operation is to get an earthen retort sufficiently compact to retain the vapour of the zinc, (for it easily pervades the Hessian crucibles, Stourbridge melting-pots, and similar vessels, as may be seen from the quantity of flowers which appear upon their outer surface, when zinc or its calxes and any inflammable matter have been exposed to heat within these vessels) and at the same time sufficiently strong to resist the violent fire which Mr Margraaf requires.

A pretty exact essay of an ore of zinc may be made in the following manner.

Mix a quantity of pulverised roasted ore or calx of zinc with an eighth part of charcoal-dust. Put this mixture into a crucible capable of containing thrice the quantity. Diffuse equally amongst this mixture a quantity of small grains or thin plates of copper equal to that of the calamine or ore employed, and upon the whole lay another equal quantity of grains or plates of copper; and lastly, cover this latter portion of copper with charcoal-dust. Lute a lid upon the crucible; and apply a red heat during an hour or two. The copper or part of it will unite with the vapour of the zinc, and be thereby converted into brass. By comparing the weight of all the metal after the operation, with the weight of the copper employed; the weight acquired, and consequently the quantity of zinc united with the copper, will be known. The copper which has not been converted into brass, or more copper with fresh charcoal dust, may be again added in the same manner to the remaining ore, and the operation repeated with a heat somewhat more intense, that any zinc remaining in the ore may be thus extracted. A curious circumstance is, that a much greater heat is required to obtain zinc from its ore, by distillation, than in the operation now described of making brass; in which the separation of the zinc from its ore seems to be facilitated by its disposition to unite with copper.

Sect. XIII. Ores of Arsenic.

§ 1. The minerals which contain the largest quantity of arsenic are cobalts and white pyrites; although it is also contained in other ores, it being one of the mineralising substances. But as cobalt must be roasted to obtain the sulphur it contains, the arsenic also which rises during this torrefaction is collected, as we shall see in Part III. (Smelting of Ores,) and the particular articles of each of the metallic substances mentioned in this article.

I. Regulus of arsenic is found native. It is of a leaden colour; it burns with a small flame; and is disipated, leaving generally a very small quantity of calx of bismuth, or of calx of cobalt, and a very little silver. When it is of a solid and teflaceous texture, it has been improperly called teflaceous cobalt, in German scheibencobalt. II. Calx of arsenic is found in form of powder; native flowers of arsenic, or of indurated semitransparent crystals; native crystalline arsenic. III. Calx of arsenic is mixed, 1. With sulphur: when yellow, it is called orpiment; when red, it is called native realgar: the difference of colour depends on the proportion of the two component parts. 2. With calx of tin; tin-grains. 3. With sulphur and silver, in the red silver ore. 4. With calx of lead, in the lead-spar. 5. With calx of cobalt, in the efflorescence of cobalt. IV. Arsenic is mineralised, 1. With sulphurated iron; arsenical pyrites. 2. With iron only; white pyrites, or mifspickle. 3. With cobalt, in almost all cobalt-ores. 4. With silver. 5. With copper. 6. With antimony.

§ 2. Arsenic may be separated from its ore or earthy matter with which it happens to be mixed, by sublimation, according to the following process by Mr Cramer.

"Do every thing as was said about mercury, or sulphur; but let the vessel which is put into the fire with the ore in it be of earth or stone, and the recipient be of glass, and of a middling capacity. Nor is it necessary that this should be filled with water, so it be but well luted. The fire must likewise be stronger, and continued longer than for the extracting of sulphur. Nevertheless every kind of arsenic cannot be extracted in a confined fire: for it adheres to the matrix more strongly than sulphur and mercury. You will find in the part of the vessel which is more remote from the fire, pulverulent and fustle flowers of arsenic; but there will adhere to the posterior of the neck of the retort small solid masses, shining like small crystals, transparent, sometimes gathered into a solid sublimate, and perfectly white, if the ore of the arsenic was perfectly pure; which, nevertheless, happens very seldom. The flowers are most commonly thin, and of a grey colour: which proceeds from the phlogiston mixed with the mass. They are often of a citron or of a golden colour, which is a sign that there is in the mixture some mineral sulphur; and if the sublimate be red or yellow, it is a sign of much sulphur.

"As all the arsenic contained in the ore is not expelled in close vessels, you must weigh the residuum; then roast it in a crucible till it smokes no longer, or rather in an earthen flat vessel not glazed, and in a strong fire to be stirred now and then with a poker, and then weigh it when grown cold: you will be able thus to know how much arsenic remained in the close vessel, unless the ore contain bismuth."

If the arsenic be sulphurated, it may be purified by triturating it with mercury or with fixed alkali, and by subliming the arsenic from the remaining sulphurated mercury or alkali. The method of obtaining a regulus of arsenic is described at the article Regulus of Arsenic. HAVING shown the nature of the principal metallic minerals, and the substances of which they are composed; and also explained the processes by which an exact analysis of these compound minerals may be made, and the nature and quantity of the contained metals may be known; in order to complete what relates to this important subject, we shall describe in this Part the principal operations by which metals, &c., are obtained "in the great," as it is called, or for commercial purposes. What we shall say upon this subject will chiefly be extracted from a Treatise on the Smelting of Ores, by Schlutter, translated from the German into French by M. Hellot; because this, of all the modern works upon that subject, appears to be the most exact. We shall first describe the operations upon pyritous matters for the extraction of sulphur, &c., and afterwards the operations by which metallic substances are extracted from ores properly so called.

Sect. I. Extraction of Sulphur from Pyrites and other Minerals.

In order to obtain sulphur from pyrites, this mineral ought to be exposed to a heat sufficient to sublime the sulphur, or to make it distill in vessels, which must be close, to prevent its burning.

Sulphur is extracted from pyrites at a work at Schwartzemberg, in Saxony, in the high country of the mines; and in Bohemia, at a place called Alten-Sattel.

The furnaces employed for this operation are oblong, like vaulted galleries; and in the vaulted roofs are made several openings. These are called furnaces for extracting sulphur.

In these furnaces are placed earthen-ware tubes, filled with pyrites broken into pieces of the size of small nuts. Each of these tubes contains about 50 pounds of pyrites. They are placed in the furnace almost horizontally, and have scarcely more than an inch of descent. The ends, which come out of the furnace five or six inches, become gradually narrower. Within each tube is fixed a piece of baked earth, in form of a star, at the place where it begins to become narrower, in order to prevent the pyrites from falling out, or choking the mouth of the tube. To each tube is fitted a receiver, covered with a leaden plate, pierced with a small hole to give air to the sulphur. The other end of the tube is exactly closed. A moderate fire is made with wood, and in eight hours the sulphur of the pyrites is found to have passed into the receivers.

The residuum of the pyrites, after the distillation, is drawn out at the large end, and fresh pyrites is put in its place. From this residuum, which is called burnings of sulphur, vitriol is extracted.

The 11 tubes, into which were put, at three several distillations, in all nine quintals or 900 pounds of pyrites, yield from 100 to 150 pounds of crude sulphur, which is so impure as to require to be purified by a second distillation.

This purification of crude sulphur is also done in a furnace in form of a gallery, in which five iron cucurbits are arranged on each side. These cucurbits are placed in a sloping direction, and contain about eight quintals and a half of crude sulphur. To them are fitted earthen tubes, so disposed as to answer the purpose of capitals. The nose of each of these tubes is inserted into an earthen pot called the fore-runner. This pot has three openings; namely, that which receives the nose of the tube; a second smaller hole, which is left open to give air; and a third in its lower-part, which is stopped with a wooden peg.

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

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

As sulphur is not only in pyrites, but also in most metallic minerals, it is evident that it might be obtained by works in the great from the different ores which contain much of it, and from which it must be separated previously to their fusion; but as sulphur is of little value, the trouble of collecting it from ores is seldom taken. Smelters are generally satisfied with freeing their ores from it, by exposing them to a fire sufficient to expel it. This operation is called torrefaction, or roasting of ores.

There are, however, ores which contain so much sulphur, that part of it is actually collected in the ordinary operation of roasting, without much trouble for that purpose. Such is the ore of Ramelsberg in the country of Hartz.

This ore, which is of lead, containing silver, is partly very pure, and partly mixed with cupreous pyrites and silver; hence it is necessary to roast it.

The roasting is performed by laying alternate strata of ore and wood upon each other in an open field, taking care to diminish the size of the strata as they rise higher; so that the whole mass shall be a quadrangular pyramid truncated above, whose base is about 31 feet square. Below, some passages are left open, to give free entrance to the air; and the sides and top of the pyramid are covered over with small ore, to concentrate the heat and make it last longer. In the centre of this pyramid there is a channel which descends vertically from the top to the base. When all is properly arranged, ladlefuls of red-hot scoria from the melting-furnace are thrown down the channel, by which means the shrubs and wood placed below for that purpose are kindled, and the fire is from them communicated to all the wood of the pile, which continues burning till the third day. At that time the sulphur of the mineral becomes capable of burning spontaneously, and of continuing the fire after the wood is consumed.

When this roasting has been continued 15 days, the mineral becomes greasy; that is, it is covered over with a kind of varnish: 20 or 25 holes or hollows are then made in the upper-part of the pile in which the sulphur is collected. From these cavities the sulphur is taken out thrice every day, and thrown into water. This sulphur is not pure, but crude; and is therefore sent to the manufacturers of sulphur, to be purified in the manner above-related.

As this ore of Ramelsberg is very sulphureous, the first roasting, which we are now describing, lasts three months; and during this time, if much rain has not fallen, or if the operation has not failed by the pile falling down or cracking, by which the air has so much free access, that the sulphur is burnt and consumed, from 10 to 20 quintals of crude sulphur are by this method collected.

The sulphur of this ore, like that of most others, was formerly neglected, till, in the year 1570, a person employed in the mines called Christopher Sauder, discovered the method of collecting it, nearly as it is done at present.

Metallic minerals are not the only substances from which sulphur is extracted. This matter is diffused in the earth in such quantities, that the metals cannot absorb it all. Some sulphur is found quite pure, and in different forms, principally in the neighbourhood of volcanoes, in caverns, and in mineral waters. Such are the opaque kind called virgin sulphur; the transparent kind called sulphur of Quito; and the native flowers of sulphur, as those of the waters of Aix-la-Chapelle. It is also found mixed with different earths. Here we may observe, that all those kinds of sulphur which are not mineralized by metallic substances, are found near volcanoes, or hot mineral waters, and consequently in places where nature seems to have formed great subterranean laboratories, in which sulphureous minerals may be analysed and decomposed, and the sulphur separated, in the manner in which it is done in small in our works and laboratories. However that be, certainly one of the best and most famous sulphur-mines in the world is that called Solfatara. The Abbé Nollet has published, in the Memoirs of the Academy, some interesting observations upon this subject, which we shall here abridge.

Near Puzzoli, in Italy, is that great and famous mine of sulphur and alum called at present Solfatara. It is a small oval plain, the greatest diameter of which is about 400 yards, raised about 300 yards above the level of the sea. It is surrounded by high hills and great rocks, which fall to pieces, and whose fragments form very steep banks. Almost all the ground is bare and white, like marble; and is everywhere sensibly warmer than the atmosphere in the greatest heat of summer, so that the feet of persons walking there are burnt through their shoes. It is impossible not to observe the sulphur there; for everywhere may be perceived by the smell a sulphureous vapour, which rises to a considerable height, and gives reason to believe that there is a subterraneous fire below, from which that vapour proceeds.

Near the middle of this field there is a kind of basin three or four feet lower than the rest of the plain, in which a sound may be perceived when a person walks on it, as if there were under his feet some great cavity, the roof of which was very thin. After that, the lake Agnano is perceived, whose waters seem to boil. These waters are indeed hot, but not so hot as boiling water. This kind of ebullition proceeds from vapours which rise from the bottom of the lake, which being set in motion by the action of subterranean fires, have force enough to raise all that mass of water. Near this lake there are pits, not very deep, from which sulphureous vapours are exhaled. Persons who have the itch, come to these pits, and receive the vapours in order to be cured. Finally, there are some deeper excavations, whence a soft stone is procured which yields sulphur. From these cavities vapours exhale, and issue out with noise, and which are nothing else than sulphur bubbling through the crevices. This sulphur adheres to the sides of the rocks, where it forms enormous masses: in calm weather, the vapours may be evidently seen to rise 25 or 30 feet from the surface of the earth.

These vapours, attaching themselves to the sides of rocks, form enormous groups of sulphur, which sometimes fall down by their own weight, and render these places of dangerous access.

In entering the Solfatara, there are warehouses and buildings erected for the refining of sulphur.

Under a great shed, or hangar, supported by a wall behind, and open on the other three sides, the sulphur is procured by distillation from the soft stones we mentioned above. These stones are dug from underground; and those which lie on the surface of the earth are neglected. These last are, however, covered with a sulphur ready formed, and of a yellow colour: but the workmen say they have lost their strength, and that the sulphur obtained from them is not of so good a quality as the sulphur obtained from the stones which are dug out of the ground.

These last mentioned are broken into lumps, and put into pots of earthen ware, containing each about 20 pints Paris measure. The mouths of these pots are as wide as their bottoms; but their bellies, or middle parts, are wider. They are covered with a lid of the same earth, well luted, and are arranged in two parallel lines along two brick walls, which form the two sides of a furnace. The pots are placed within these walls; so that the centre of each pot is in the centre of the thickness of the wall, and that one end of the pots overhangs the wall within, while the other end overhangs the wall without. In each furnace ten of these pots are placed; that is, five in each of the two walls which form the two sides of the furnace. Betwixt Smelting twixt these walls there is a space of 15 or 18 inches; of Ores in which space is covered by a vault resting on the two walls. The whole forms a furnace seven feet long, two feet and a half high, open at one end, and shut at the other, excepting a small chimney through which the smoke passes.

Each of these pots has a mouth in its upper part without the furnace, in order to admit a tube of 18 lines in diameter and a foot in length, which communicates with another pot of the same size placed without the building, and pierced with a round hole in its base of 15 or 18 lines diameter. Lastly, to each of these last-mentioned pots there is a wooden tub placed below, in a bench made for that purpose.

Four or five of these furnaces are built under one hangar, or shed. Fires are kindled in each of them at the same time; and they are thrown down after each distillation, either that the pots may be renewed, or that the residuum may be more easily taken out.

The fire being kindled in the furnace, heats the first pots containing the sulphureous stones. The sulphur rises in fumes into the upper part of the pot, whence it passes through the pipe of communication into the external vessel. There the vapours are condensed, become liquid, and flow through the hole below into the tub, from which the sulphur is easily turned out, because the form of the vessel is that of a truncated cone whose narrower end is placed below, and because the hoops of the tub are so fastened that they may be occasionally loosened. The mass of sulphur is then carried to the buildings mentioned before, where it is remelted for its purification, and cast into rolls, such as we receive it.

Extraction of Vitriol from pyrites. See Chemistry, n° 110, 142, 157.

Extraction of Alum from pyritous substances and from alumious earths. See Chemistry, n° 129.

Sect. II. Smelting of Ores in general.

§ 1. As ores consist of metallic matters combined with sulphur and arsenic, and are besides intermixed with earthy and stony substances of all kinds, the intention of all the operations upon these compound bodies is to separate these different substances from each other. This is effected by several operations founded on the known properties of those substances. We now proceed to give a general idea of these several operations.

First of all, the ore is to be separated from the earths and stones accidentally adherent to it; and when these foreign substances are in large masses, and are not very intimately mixed in small particles with the ore, this separation may be accomplished by mechanical means. This ought always to be the first operation, unless the adherent substance be capable of serving as a flux to the ore. If the unmetallic earths be intimately mixed with the ore, this must necessarily be broken and divided into small particles. This operation is performed by a machine which moves pestles, called bocards or flampers. After this operation, when the parts of the mineral are specifically heavier than those of the unmetallic earth or stone, these latter may be separated from the ore by washing in canals through which water flows. With regard to this washing of ores, it is necessary to observe, that it cannot succeed but when the ore is sensibly heavier than the foreign matters. But the contrary happens frequently, as well because quartz and spar are naturally very ponderous, as because the metallic matter is proportionally so much lighter as it is combined with more sulphur.

When an ore happens to be of this kind, it is necessary to begin by roasting it, in order to deprive it of the greatest part of its sulphur.

It happens frequently that the pyritous matters accompanying the ore are so hard that they can scarcely be pounded. In this case it is necessary to roast it entirely, or partly, and to throw it red-hot into cold water; by which the stones are split, and rendered much more capable of being pulverized.

Thus it happens very frequently, that roasting is the first operation to which an ore is exposed.

When the substance of the ore is very fusible, this first operation may be dispensed with, and the matter may be immediately fused without any previous roasting, or at least with a very slight one. For, to effect this fusion, it is necessary that it retain a great quantity of its sulphur, which, with the other fluxes added, serves to destroy or convert into scoria a considerable part of the stony matter of the mineral, and to reduce the rest into a brittle substance, which is called the matt of lead, or of copper, or other metal contained in the ore. This matt is therefore an intermediate matter betwixt the mineral and the metal; for the metal is there concentrated, and mixed with less useless matter than it was in the ore. But as this matt is always sulphureous, the metal which it contains cannot have its metallic properties. Therefore it must be roasted several times to evaporate the sulphur, before it is remelted, when the pure metal is required. This fusion of an ore not roasted, or but slightly roasted, is called crude fusion.

We may here observe upon the subject of washing and roasting of ores, that as arsenic is heavier than sulphur, and has nearly the weight of metals, the ores in which it prevails are generally very heavy, and consequently are susceptible of being washed, which is a great advantage. But on the other side, as arsenic is capable of volatilising, scorifying, and destroying many metals, these ores have disadvantages in the roasting and fusion, in both which considerable loss is caused by the arsenic. Some ores contain, besides arsenic, other volatile semi-metals, such as antimony and zinc. These are almost untractable, and are therefore neglected. They are called minera rapaces, "rapacious ores."

When the metal has been freed as much as is possible from foreign matters by these preliminary operations, it is to be completely purified by fusions more or less frequently repeated; in which proper additions are made, either to absorb the rest of the sulphur and arsenic, or to complete the vitrification or scorification of the unmetallic stones and earth.

Lastly, as ores frequently contain several different metals, these are to be separated from each other by processes suited to the properties of these metals, of which we shall speak more particularly as we proceed in our examination of the ores of each metal.

§ 2. To facilitate the extraction of metallic substances from the ores and minerals containing them, some operations previous to the fusion or smelting of these Roasting these ores and minerals are generally necessary. These operations consist of, 1. The separation of the ores and metallic matters from the adhering unmetallic earths and stones, by hammers and other mechanical instruments, and by washing with water. 2. Their division or reduction into smaller parts by contusion and trituration, that by another washing with water they may be more perfectly cleansed from extraneous matters, and rendered fitter for the subsequent operations, calcination or roasting, and fusion. 3. Roasting or calcination; the uses of which operation are, to expel the volatile, useless, or noxious substances, as water, vitriolic acid, sulphur, and arsenic; to render the ore more friable, and fitter for the subsequent contusion and fusion; and, lastly, to calcine and destroy the viler metals, for instance the iron of copper-ores, by means of the fire, and of the sulphur and arsenic. Stones, as quartz and flints, containing metallic veins or particles, are frequently made red-hot, and then extinguished in cold water, that they may be rendered sufficiently friable and pulverable, to allow the separation of the metallic particles.

Roasting is unnecessary for native metals; for some of the richer gold and silver ores; for some lead-ores, the sulphur of which may be separated during the fusion; and for many calciform ores, as these do not generally contain any sulphur and arsenic.

In the roasting of ores, the following attentions must be given, 1. To reduce the mineral previously into small lumps, that the surface may be increased; but they must not be so small, nor placed too compactly, as to prevent the passage of the air and flame. 2. The larger pieces must be placed at the bottom of the pile, where the greatest heat is. 3. The heat must be gradually applied, that the sulphur may not be melted, which would greatly retard its expulsion; and that the spars, fluors, and stones, intermixed with the ore, may not crack, fly, and be dispersed. 4. The ores not thoroughly roasted by one operation must be exposed to a second. 5. The fire may be increased towards the end, that the noxious matters more strongly adhering may be expelled. 6. Fuel which yields much flame, as wood and fossil coals free from sulphur, is said to be preferable to charcoal or coaks. Sometimes cold water is thrown on the calcined ore at the end of the operation, while the ore is yet hot, to render it more friable.

No general rule can be given concerning the duration or degree of the fire, these being very various according to the difference of the ores. A roasting during a few hours or days is sufficient for many ores; while some, such as the ore of Rammelsberg, require that it should be continued during several months.

Schlutter enumerates five methods of roasting ores.

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

Several kinds of fusions of ores may be distinguished. 1. When a sulphureous ore is mixed with much earthy matter, from which it cannot be easily separated by mechanical operations, it is frequently melted, in order to disengage it from these earthy matters, and to concentrate its metallic contents. By this fusion, some of the sulphur is distillated, and the ore is reduced to a state intermediate between that of ore and metal. It is then called a matt (lapis sulphureus-metallicus); and is to be afterwards treated like a pure ore by the second kind of fusion, which is properly the smelting, or extraction of the metal by fusion. 2. By this fusion or smelting, the metal is extracted from the ore previously prepared by the above operations, if these be necessary. The ores of some very fusible metals, as of bismuth, may be smelted by applying a heat sufficient only to melt the metals, which are thereby separated from the adhering extraneous matters. This separation of metals by fusion, without the vitrification of extraneous matters, may be called eluation. Generally, a complete fusion of the ore and vitrification of the earthy matters are necessary for the perfect separation of the contained metals. By this method, metals are obtained from their ores, sometimes pure, and sometimes mixed with other metallic substances, from which they must be afterwards separated; as we shall see, when we treat of the extraction of particular metals. To procure this separation of metals from ores, these must be so thinly liquefied, that the small metallic particles may disengage themselves from the scoria; but it must not be so thin as to allow the metal to precipitate before it be perfectly disengaged from any adhering extraneous matter, or to pervade and destroy the containing vessels and furnace. Some ores are sufficiently fusible; but others require certain additions called fluxes, to promote their fusion and the vitrification of their unmetallic parts; and also to render the scoria sufficiently thin to allow the separation of the metallic particles.

Different fluxes are suitable to different ores, according to the quality of the ore, and of the matrix, or stone adherent to it.

The matrixes of two different ores of the same metal frequently serve as fluxes to each other; as, for instance, an argillaceous matrix with one that is calcareous; these two earths being disposed to vitrification when mixed, though each of them is singly unfusible. For this reason, two or more different ores to be smelted are frequently mixed together.

The ores also of different metals require different fluxes. Thus calcareous earth is found to be best suited to iron-ores, and spars and scoria to fusible ores of copper.

The fluxes most frequently employed in the smelting of ores are, calcareous earth, fluors or vitreous spars, quartz and sand, fusible stones, as flates, basaltes, the several kinds of scoria, and pyrites.

Calcareous earth is used to facilitate the fusion of ores of iron, and of some of the poorer ores of copper, and, in general, of ores mixed with argillaceous earths, or with feltspur. This earth has been sometimes added with a view of separating the sulphur, to which it very readily unites: but by this union the sulphur is detained, and a heper is formed, which readily dissolves iron and other metals, and so firmly adheres to them, that they cannot be separated without more difficulty than they could from the original ore. This addition is therefore not to be made till the sulphur be previ- Fluors or fusible spars facilitate the fusion of most metallic minerals, and also of calcareous and argillaceous earths, of fleatites, asbestos, and some other fusible stones, but not of siliceous earths without a mixture of calcareous earth.

Quartz is sometimes added in the fusion of ferruginous copper ores, the use of which is said chiefly to be, to enable the ore to receive a greater heat, and to give a more perfect vitrification to the ferruginous scoria.

The fusible stones, as flints, bafaltes, are so tenacious and thick when fused, that they cannot be considered properly as fluxes, but as matters added to lessen the too great liquidity of some very fusible minerals.

The scoria obtained in the fusion of an ore is frequently useful to facilitate the fusion of an ore of the same metal, and sometimes even of ores of other metals.

Sulphurated pyrites greatly promote the fusibility of the scoria of metals, from the sulphur it contains. It is chiefly added to difficultly-fusible copper-ores, to form the sulphurous compounds called matte, that the ores thus brought into fusion may be separated from the adhering earthy matters, and that the ferruginous matter contained in them may be destroyed, during the subsequent calcination and fusion, by means of the sulphur.

As in the ores called calciform, the metallic matter exists in a calcined state; and as calcination reduces the metals of mineralized ores (excepting the perfect metals) to that state also; therefore all calciform and calcined ores require the addition of some inflammable substance, to reduce them to a metallic state. In great works, the charcoal or other fuel used to maintain the fire produces also this effect.

Metals are sometimes added in the fusion of ores of other more valuable metals, to absorb from these sulphur or arsenic. Thus iron is added to sulphurated, cuprous, and silver ores. Metals are also added in the fusion of ores of other more valuable metals, to unite with and collect the small particles of these dispersed through much earthy matter, and thus to assist their precipitation. With these intentions, lead is frequently added to ores and minerals containing gold, silver, or copper.

Ores of metals are also sometimes added to assist the precipitation of more valuable metals. Thus antimony is frequently added to assist the precipitation of gold intermixed with other metallic matters. Thus far of smelting of ores in general.

**Sect. III. Operations on Ores of Native Gold and Silver, by Washing and by Mercury.**

Earths and sand are at first separated by washing with water; by which operation the greatest part of what is not gold, being lighter, is carried off. After this a second washing is made with mercury, which having the property of uniting with gold, seizes this metal, amalgamates with it, and separates it exactly from the earthy matters, with all which it can form no union.

The mercury thus charged with gold is pressed through shamoy leather, and the gold is retained united with a part of the mercury, from which it may be easily disengaged by exposure to a proper degree of heat, which dissipates and evaporates the mercury, while the gold, being fixed, remains.

This is the foundation of all the operations by which gold is obtained from the rich mines of Peru belonging to the Spaniards. These operations consist in washings, triturations, and amalgams in the great by help of machines.

The ores of native silver are much rarer and less abundant than those of gold. But if any of this kind were found sufficiently rich, they might be treated with mercury exactly in the same manner as the ores of native gold.

Gold is frequently contained in the ores of other metals, either in a native or mineralized state, and in sands, especially those which are black and ferruginous. See Part II. sect. of Ores of Gold.

If gold be contained in ores of other metals, these metals together with the gold may be first extracted by the ordinary processes for smelting these ores; and the gold may be then separated from the metallic mass thus obtained, by mixing and fusing this mass with a quantity of lead, and by the process of cupellation described in the articles Essay of the value of silver, and Refining. Generally, the operations for obtaining gold from ores of imperfect metals are precisely the same as those for obtaining silver, to which therefore we refer. Most frequently a quantity of silver also is contained in these ores; and in this case the perfect metal obtained by cupellation is an alloy of gold and silver, which must be afterwards separated by the processes called parting. See Parting.

Many trials have been made to procure the small quantity of gold contained in the ferruginous sands, at a moderate expense (see Part II. sect. of Ores of Gold); but as no work of this kind is now established, we may presume they have not been successful. The best essays of this kind have been made, according to Schlutter, in the following manner.

The sand is to be made red-hot, and extinguished in cold water four times, by which its colour is changed from the original yellow, red, or black, to a reddish-brown. It is observed to emit, during the first and second calcinations, an arsenical smell; and this smell may be produced again in the following calcinations by adding some inflammable matter. Let an ounce of the calcined sand be mixed with two ounces of granulated lead, and one ounce of black flux, and put into a Hessian crucible, with half an ounce of decrepitated sea-salt upon the surface of the mixture. The crucible is to be placed in a good blast-furnace, and a strong fire is to be excited. The matter contained in the crucible is to be frequently stirred with an iron-rod, and the heat is to be continued till the scoria is thin and perfectly fused. When the crucible is broken, a regulus of lead will be found, containing the gold and silver of the sand. By this method Mr Leberecht obtained, in eleven essays, from 840 to 844 grains of perfect metal from a quintal of sand. Of the perfect metal obtained, from a fourth to a third part was gold. Some parcels of sand have yielded more than 1000 grains, and some not more than 350 grains, per quintal. Instead of the granulated lead, and the black flux, which is too expensive for great operations, some have added, to an ounce of the sand, two ounces of litharge and... Part III.

Smelting of Ores of Silver.

and a little powder of charcoal, by which they have obtained the same quantity of perfect metal. The scoria in these essays has been always found to contain some perfect metal.

The Hungarian copper ores, from which gold and silver are profitably extracted, contain a less quantity of these perfect metals than many ferruginous sands. But they may be formed into a matt, by fusion with pyrites, of which treatment the sands are incapable. From this matt, the gold and silver, along with the copper of the ore, may be precipitated, and separated from the sulphur of the pyrites, by addition of iron, which being more disposed than the other metals to unite with sulphur, disengages these metals, and allows them to precipitate.

Sect. IV. Smelting of Ores of Silver.

§ 1. As silver, even in its proper ores, is always alloyed with some other metals from which it is intended to be separated after that the silver-ore has been well roasted, it must be mixed with a greater or less quantity of lead previous to its fusion.

Lead has the same effect in fusion of gold and silver as mercury has upon these metals by its natural fluidity; that is to say, it unites with them, and separates them from unmetallic matters, which, being lighter, rise always to the surface. But lead has the further advantage of procuring, by its own vitrification, that all metallic substances, excepting gold and silver. Hence it follows, that when gold and silver are obtained by means of mercury, they still remain alloyed with other metallic substances; whereas when they are obtained by fusion and scorification with lead, they are then pure, and not alloyed with any metals but with each other.

In proportion as the lead, which has been united to the gold and silver of the ore, is scorified by the action of the fire, and promotes the scorification of the other metallic matters, it separates the perfect metals, and carries with it all the others to the surface. There it meets the unmetallic substances, which it likewise vitrifies, and which it changes into a perfect scoria, fluid, and such as a scoria ought to be to admit all the perfect metal contained in it to precipitate.

When all heterogeneous matters have been thus disengaged by scorification with lead, the perfect metals, to which some lead still remains united, are to be further purified by the ordinary operation of the cupel.

The common rule for the fusion and scorification of silver-ore with lead, is to add to the ore a quantity of lead so much greater as there is more matter to be scorified, and as these matters are more refractory and of more difficult fusion. Silver ores, or those treated as such, are often rendered refractory by ferruginous earths, pyritous matters, or cobalts, containing always a considerable quantity of an earth which is unmetallic, very subtile, and very refractory, and which renders a considerable augmentation of the quantity of lead necessary.

The quantity of lead which is commonly added to fusible silver ores, that do not contain lead, is eight times the quantity of the ore. But when the ore is refractory, it is necessary to add twelve times the quantity of lead, and even more; also glas of lead, and fluxes, such as the white and black fluxes; to which however borax and powder of charcoal are preferable, on account of the liver of sulphur formed by these alkaline fluxes.

It is necessary to observe, that saline fluxes are only used in small operations, on account of their dearth. To these are substituted, in the great operations, of which we now treat, sandiver, fusible scoria, and other matters of little value.

The greatest part of silver now employed in commerce is not obtained from the proper ores of silver, which are very scarce; but from lead, and even copper ores, which are more or less rich in silver. To give an idea of the manner of treating these kinds of ores, from which silver is extracted in the great works, we shall briefly describe here, after Schütter, the smelting of the ore of Rammelfanger, which contains, as we have already said, several different kinds of metals, but particularly lead and silver.

When this mineral has been disengaged from its sulphur as much as possible by three very long roastings, it is melted in the Lower Hartz in Saxony, in a particular kind of furnace, called a furnace for smelting upon a hollow or caisse. The masonry of this furnace is composed of large thick slates, capable of sustaining great heat, and cemented together by clay. The interior part of the furnace is three feet and a half long, and two feet broad at the back part, and one foot only in the front. Its height is nine feet eight inches. It has a foundation of masonry in the ground; and in this foundation channels are made for the evaporation of the moisture. These channels are covered over with stones called covering stones. The hollow or caisse, which is made above these, is formed of bricks, upon which are placed, first, a bed of clay; then a bed of small ore and sifted vitriols; and, lastly, a bed of charcoal-powder beat down, called light brasque. The anterior wall of the furnace is thinner than the others, and is called the chemise. The back wall, which is pierced to give passage to the pipes of two large wooden bellows, is called the middle wall. When the furnace is thus prepared, charcoal is thrown into the hollow, or caisse; which being kindled, the fire is to be continued during three hours, before the matters to be fused are added. Then these matters are thrown in, which are not the pure ore, but a mixture of several substances, all of which are somewhat profitable. The quantity of these matters is sufficient for one day's work; that is, for a fusion of eighteen hours; and it consists of, 1. Twelve schorbens or measures of well roasted Rammelfanger ore; (the schorben is a measure whose contents are two feet five inches long, one foot seven inches broad, and a little more than a foot deep: it is equal to 32 quintals of that country, Cologn weight, at 123 pounds each quintal.) 2. Six measures of scoria produced by the smelting of the ore of Upper Hartz, which is refractory, and what workmen call cold. 3. Two measures of knobben, which is an impure scoria containing some lead and silver, which has been formerly thrown away as useless, and is now collected by women and children. Besides these, other matters are added, containing lead and silver, as the tests employed in refining, the drops of lead, impure litharge, and and any rubbish containing metal, which was left in the furnace after the foregoing fusion. All these matters being mixed together, are thrown into the furnace; and to each measure of this mixture a measure of charcoal is added. The fusion is then begun by help of bellows; and as it proceeds, the lead falls through the light brasque, or charcoal-bed, into the hollow, or caisse, where it is preserved from burning under the powder of charcoal. The scoria, on the other hand, being lighter and less fluid, is skimmed off from time to time by means of ladles, that it may not prevent the rest of the lead from falling down into the hollow. Thus, while the fusion lasts, fresh matters and fresh charcoal are alternately added, till the whole quantity intended for one fusion, or, as they call it, one day, be thrown in.

There are several essential things to be remarked in this operation, which is very well contrived. First, the mixture of matters from which a little lead and silver is procured, which would otherwise be lost; and which have also this advantage, that they retard the fusion of the Ramelsberg ore, which, however well roasted it has been, retains always enough of the sulphur and iron of the pyrites mixed with it, to render it too fusible or too fluid, so that without the addition of those matters nothing would be obtained but a matt. It is even necessary, notwithstanding these additions, not to hasten the fusion too much, but to give time for the ore to mix with other matters, else it would melt and flow of itself before the rest.

Secondly, the fusion of the ore through charcoal, which is practised in most smelting-houses, and for almost all ores, is an excellent method, the principal advantage of which is the saving of fuel. The action of the burning charcoal directed immediately upon the mineral, at the same time that it melts it more readily and efficaciously, also supplies it with the phlogiston necessary to bring it to a perfect state.

From the Ramelsberg ore after its first roasting, a white vitriol is obtained and prepared at Goflar*, whose basis was zinc: which proves that this ore contains also a certain quantity of this semi-metal. As this ore is smelted in a country where the art is well understood of extracting every thing which a mineral contains, so in this fusion zinc and cadmium are obtained in the following manner: When the furnace is prepared for the fusion, it is necessary to close it up in the fore-part, before the fusion is begun.

First of all, a gritt-stone is to be placed, supported at the height of three inches. This stone is as long as the furnace is broad, and the height of it is level with the hole where the bellows-pipe enters. It is fastened on each side of the furnace, externally and internally, with clay. Upon this stone a kind of receptacle, or, as it is called, the seat of the zinc, is made in the following manner: A flat flaty stone is chosen, as long as the furnace is broad, and eight inches in breadth. This is placed on the gritt-stone above-mentioned, in such a manner that it inclines considerably towards the front of the furnace, and that its bottom touches closely the gritt-stone. It is fastened with clay, which is also laid upon the seat of the zinc. Upon this seat, which is to receive the zinc, two round pieces of charcoal are placed, and also a stone called the zinc stone, which is about a foot and a half in length, and closes one part of the front of the furnace. This stone also is fastened on each of its sides with clay. Clay is likewise put under the stone betwixt the two pieces of charcoal, which hinder it from touching the seat of the zinc. The under-part of this stone is but slightly luted, that the workmen may make an opening for the zinc to flow out. Thus is made the seat or receptacle of the zinc to detain this metallic substance, which would otherwise fall into the hottest part of the fire, called by the workmen the melting-place, and would be there burnt; whereas it is collected upon this receptacle during the fusion, where it is sheltered from the action of the bellows, and consequently from too great heat.

When all the matter to be fused in one day is put into the furnace, the blast of air is continued till that matter has sunk down. When it is half-way down the furnace, they draw out the scoria, that more of the ore and other matters may be exposed to the greatest heat. As soon as the scoria is cooled and fixed a little, two shovel-fulls of small wet scoria or sand is thrown close to the furnace, and beat down with the shovel; then the workmen open the seat or receptacle of zinc, and strike upon the zinc-stone to make the semi-metal flow out. As soon as the purest part of it has flowed out, it is sprinkled with water and carried away. Then the workmen separate entirely the zinc-stone from the wall of the furnace, and they continue to give it little strokes, that the small particles of zinc dispersed among the charcoal may fall down. This being done, the stone is removed; and the zinc is separated from the charcoal by an iron instrument, is cleaned, and remelted along with the zinc that flowed out at first, and is cast into round cakes. The reason why the zinc is withdrawn before the bellows cease to blow, is, that if it was left till the charcoal on the seat or receptacle was consumed, it would be mostly burnt, and little would be obtained. Thus after the zinc is withdrawn, the fusion is finished by blowing the bellows till the end.

Thus the zinc is separated from the ore of Ramelsberg, and is not confounded in the hollow or caisse with the lead and silver, because, being a volatile semi-metal, it cannot support the activity of the fire without rising into vapours, which are condensed in the place least hot, that is to say, upon the stones expressly prepared for that purpose; and which, being much thinner than the other walls of the furnace, are continually cooled by the external air.

It is also in this furnace, and after the fusion of the Ramelsberg ore, that the cadmium of zinc, or the cadmium of furnaces, is obtained. This ore is composed of sulphurous and ferruginous pyrites, of true lead-ore containing silver, and a very hard and compact matter of a dark brownish-grey colour, which is probably a lapis calaminaris, or an ore of zinc. These several matters of the Ramelsberg ore are not separated from each other, either for the roasting or for the fusion. Thus there is zinc in all the parts of the roasted ore; and much more of it would be obtained, if it was not so easily inflammable. All the zinc which is obtained is preserved from burning by falling, while After this digression which we have now made concerning the operation in the great by which zinc and cadmia are obtained, and which we could not infer elsewhere, because of the necessary relation it has with the melting of the Rammelsberg ore, we proceed to the other operations of the same ore; that is to say, to the finery, by which the silver is separated from the lead, which are mixed together, forming what is called the work.

This operation differs from the fining of elay, or in fining, principally in this circumstance, that in the latter method of fining all the litharge is absorbed into the cupel, whereas in the former method the greatest part of this litharge is withdrawn.

The fining in great of the work of Rammelsburg is performed in a furnace called a reverberatory furnace. This furnace is so constructed that the flame of wood burning in a cavity called the fire-place, is determined by a current of air (which is introduced through the ash-holes, and which goes out at an opening on one side of that part of the furnace where the work is, that is, where the lead and silver are), to circulate above, and to give the convenient degree of heat, when the fire is properly managed. In this furnace a great cupel, called a tefi, is disposed. This tefi is made of the ashes of beech-wood, well lixiviated in the usual manner. In some foundries different matters are added, as sand, spar, calcined gypsum, quicklime, clay. When the tefi is well prepared and dried, all the work is put at once upon the cold tefi, to the quantity of 64 quintals for one operation. Then the fire is lighted in the fire-place with faggots; but the fusion is not urged too fast, 1. That the tefi may have time to dry; 2. Because the work of the Rammelsberg ore is alloyed by the mixture of several metallic matters, which it is proper to separate from it, otherwise they would spoil the litharge and the lead procured from it. These metallic matters are, copper, iron, zinc, and matt. As these heterogeneous substances are hard and refractory, they do not melt so soon as the work, that is, as the lead and silver; and when the work is melted, they swim upon its surface like a skin, which is to be taken off. These impurities are called the scum, or the first waft. What remains forms a second scum, which appears when the work is at its greatest degree of heat, but before the litharge begins to form itself. It is a scoria which is to be carefully taken off. It is called the second waft.

When the operation is at this point, it is continued by the help of bellows, the wind of which is directed, not upon the wood or fuel, but upon the very surface of the metal, by means of iron-plates put for that purpose before the blast-hole, which are called papillons. This blast does not so much increase the intensity of the fire, as it facilitates the combustion of the lead, and throws the litharge that is not imbibed by the tefi towards a channel, called the litharge way, through which it flows. The litharge becomes fixed out of the furnace: the matter which is found in the middle of the largest pieces, and which amounts to about a half or a third of the whole, is friable, and falls into powder like sand. This is put into barrels containing each five quintals of it; and is called saleable litharge, because it is sold in that state. The other part which remains solid is called cold litharge, and is again melted... Various processes for extracting Silver.

The fusion is called cold fusion, and the lead obtained from it cold lead, which is good and saleable when the work has been well cleared from the heterogeneous matters mentioned above. The tests and cupels impregnated with litharge are added in the fusion of the ore, as we have already related.

When two thirds, or nearly that quantity, of the lead are converted into litharge, no more of it is formed. The silver then appears covered with a white skin, which the finers call lightening, and the metal lightened or fined silver.

The silver obtained by this process of fining is not yet altogether pure. It still contains some lead, frequently to the quantity of four drams in each marc, or eight ounces. It is delivered to the workmen, who complete its purification by the ordinary method. This last operation is the refining, and the workmen employed to do it are called refiners. A fining of 64 quintals of work, yields from 8 to 10 merces of fined silver, and from 35 to 40 quintals of litharge; that is, from 12 to 18 of saleable litharge, from 22 to 23 of cold litharge, from 20 to 22 quintals of impregnated test, and from 6 to 7 quintals of lead-drofs. The operation lasts from 16 to 18 hours.

§ 2. Ores containing silver may be divided into four kinds. 1. Pure, or those which are not much compounded with other metals. 2. Galenical, in which the silver is mixed with much galena, or ore of lead mineralised by sulphur. 3. Pyritous, in which the silver is mixed with the martial pyrites. 4. Cupreous, in which the silver is contained in copper ores. To extract the silver from these several kinds of ores, different operations are necessary.

Native silver is separated from its adhering earths and stones by amalgamation with mercury, in the manner directed for the separation of gold; or by fusion with lead, from which it may be afterwards separated by cupellation.

Pure ores seldom require a previous calcination; but, when bruised and cleansed from extraneous matters, may be fused directly, and incorporated with a quantity of lead; unless they contain a large proportion of sulphur and arsenic, in which case a calcination may be useful. The lead employed must be in a calcined or vitrified state, which, being mixed with the ore, and gradually reduced by the phlogiston of the charcoal added to it, may be more effectually united with the silver of the ore, than if lead itself had been added, which would too quickly precipitate to the bottom of the containing vessel or furnace. The silver is to be afterwards separated from the lead by cupellation.

Galenical ores, especially those in which pyrites is intermixed, require a calcination, which ought to be performed in an oven, or reverberatory furnace. They are then to be fused together with some inflammable matter, as charcoal, by which the lead is revived, and, together with the silver, is precipitated.

Pyritous ores must be first melted, so as to form a matt. If the sulphur is not sufficient for this kind of fusion, more sulphurated pyrites may be added. This matt contains, besides silver and sulphur, also various metals, as lead, iron, and sometimes cobalt. The matt must be exposed to repeated calcinations till the sulphur is dissipated. By these calcinations most of the iron is destroyed. The calcined matt is to be fused with litharge, and the silver incorporated with the revivèd lead; from which, and from the other imperfect metals with which it may be mixed, it must afterwards be separated by cupellation.

The silver contained in cupreous ores may be obtained, either, 1. By separating it from the copper itself, after this has been extracted along with the silver, in the usual manner, from the ore; or, 2. By precipitating it immediately, from the other matters of the ore.

1. It may be separated from the copper by two methods. One of these is by adding lead, and scoriifying the imperfect metals. By this method much of the copper would be destroyed, and it is therefore not to be used unless the quantity of silver relatively to the copper be considerable. Another method by which silver may be separated from copper is, by eliquation; that is, by mixing the mass of copper and silver with a quantity of lead, and applying such a heat as shall be just sufficient to make the lead eliqueate from the copper, together with the silver, which being more strongly disposed to unite with the lead than with the copper, is thus incorporated with the former metal, and separated from the latter.

2. Silver may also be extracted from these cupreous ores by precipitation. For this purpose, let the ore, previously bruised and cleansed, be formed into a matt, that the earthy matters may be well separated. Let the matt be then fused with a strong heat; and when the scoria has been removed, and the heat is diminished, add to it some clean galena, litharge, and granulated lead. When the fire has been raised, and the additions well incorporated with the matt, let some salt or flint iron be thrown into the liquid mass, which, being more disposed than lead is to unite with sulphur, will separate and precipitate the latter metal, and along with it the silver or gold contained in the matt. This method was introduced by Scheffer, and is practised at Adelhors in Smoland. In this work the proportion of the several materials is, four quintals of matt, two quintals of black copper containing some lead with the perfect metal, one quintal of galena, one quintal of litharge, a fifth part of a quintal of granulated lead, and an equal quantity of salt iron.

The silver in this, and in all other instances where it is united with lead, is to be afterwards separated from the lead by cupellation; which process is described at the articles Essay of the Value of Silver, and Refining.

Sect. V. Smelting of Ores of Copper.

§ 1. The smelting in great of copper ores, and even of several ores of silver and lead, excepting that of Rammelberg, is performed in furnaces not essentially different from that already described; but in this respect only, that the scoria and metal are not drawn out of the furnace, but flow spontaneously, as soon as they are melted, into receiving basins, where the metal is freed from the scoria. These furnaces are generally called pierced furnaces.

Instead of a light brasque, or bed of charcoal-powder, under which the metal lies hid, the bottom of these furnaces is covered with a basin composed of heavy heavy brasque, which is a mixture of charcoal-powder and clay. In the front of the furnace, and at the bottom of the chemife, there is a hole, called the eye, through which the melted matter flows, and runs along a trench or furrow, called the trace, into one or more receiving basins, made of earth, scoria, land, &c. There the metal is separated from the scoria, by making it flow from these basins into another lateral one. These furnaces are also called crooked furnaces.

Different names are given to them according to some difference in their construction. For instance, those which have two eyes, and two traces, through which the melted matter flows alternately into two basins, are called spectacle-furnaces. Their greater or less height gives occasion also to the distinction of high furnaces, and middle furnaces.

The high furnaces are of modern invention. They were first introduced at Mansfeldt in the year 1727; and they are now used in almost all countries where ores are smelted, as in Saxony, Bohemia, Hungary, &c. Their chief advantage consists in simplifying and diminishing the labour. This advantage is effected by the great height of the furnace, which allows the ore to remain there a long time before it falls down into the hottest part of the fire and is melted. Consequently, it suffers successively different degrees of heat; and, before it is melted, it undergoes a roasting which costs nothing; therefore the high furnaces are chiefly employed for crude fusions; and particularly for the slate-copper ore. These furnaces are above 18 feet high. A too great height is attended with an inconvenience, besides the trouble of supplying it with ore and fuel, which is, that the charcoal is mostly consumed before it gets down where the greatest heat is required, and is then rendered incapable of maintaining a fire sufficiently intense.

All the furnaces which we have mentioned are supplied with large bellows, moved by the arbor of a wheel, which is turned round by a current of water.

The only kind of furnace for smelting ores where bellows are not employed, is what is called a reverberatory furnace. The Germans call it a wind-furnace. It is also distinguished by the name of English furnace, because the invention of it is attributed to an English physician of the name of Wright, who was well versed in chemistry; and because the use of it was first introduced in England about the end of the last century, where it is much employed, as well as in several other countries, as at Konigsberg, in Norway.

The length of these furnaces is about 18 feet, comprehending the masonry: their breadth is 12 feet, and their height nine feet and a half. The hearth is raised three feet above the level of the foundry: on one side is the fire-place, under which is an air-hole hollowed in the earth; on the other side is a basin made, which is kept covered with fire when there is occasion: on the anterior side of this furnace there is a chimney, which receives the flame after it has passed over the mineral that is laid upon the hearth. This hearth, which is in the interior part of the furnace, is made of a clay capable of sustaining the fire. The advantage of this furnace is, that bellows are not necessary; and consequently it may be constructed where there is no current of water, and wherever the mine happens to be. This furnace has a hole in its front, through which the scoria is drawn out; and a basin, as we have said, on one side, made with sand, in which are oblong traces for the reception of the matt, and of the black copper, when they flow out of the furnace.

Copper is generally mineralized, not only by sulphur and arsenic, but also by ferrimetallics and pyritous matters, and is frequently mixed with other metals. As this metal has great affinity with sulphur and arsenic, it is almost impossible to disengage it from them entirely by roasting; hence, in the smelting in great, nothing is obtained by the first operation but a copper matt, which contains all the principles of the ore, excepting the earthy and stony parts, particularly when the ore is smelted crude and unroasted. Afterwards this matt must be again roasted and fused. The produce of this second fusion begins still more to resemble copper, but is not malleable. It continues mixed with almost all the minerals, particularly with the metals. As it is frequently of a black colour, it is always called black copper, when it is unworkable, whatever its colour happens really to be.

As, of all the imperfect metals, copper is most difficultly burnt and scorified, it is again remelted several times, in order to burn and scorify the metallic substances mixed with it; and this is done till the copper is perfectly pure, which is then called red or refined copper, and these last fusions are called the fining and refining of it: red copper contains no metals but gold and silver, if any of these happened to be in the ore.

In order to avoid all these fusions, it has been proposed to treat in the humid way certain copper ores, particularly those which are very pyritous. This method consists in making blue vitriol from the ore, by roasting and lixiviating it, and in precipitating pure copper from this lixivium, which is called cement-water, by means of iron: but it is not much practised, because it has been observed, that all the copper contained in the ore was not procured by this means.

As expense is not much regarded in small essays and experiments, these fusions are much abridged and facilitated by adding at first saline and glassy fluxes; and then by refining the black copper with lead in the cupel, as gold and silver are done. In this method of refining, it is to be most carefully observed, that the metal be fused as quickly as possible, and exposed to no more heat than is necessary, lest it be calcined.

When the black copper contains some iron, but not a great deal, the lead presently separates the iron from it, and makes it rise to the surface of the copper: but if the iron be in too large a proportion, it prevents the lead from uniting with the copper. These two phenomena depend on the same cause, which is, that lead and iron cannot unite.

Frequently copper ores contain also a quantity of silver sufficient to make its extraction by particular processes profitable. It was long before any process could be thought of for this purpose which was not too expensive and troublesome: but at length it is accomplished by the excellent operation called eliquation. The copper from which silver has been separated by eliquation must be refined after this operation, as it is generally black copper from which silver is extracted; but even if it had not been black copper which was employed for this operation, it would require to be refined on account of a little lead it always retains. It is therefore carried to the refiner's furnace, when this operation is performed by help of bellows, the blast of which is thrown upon the surface of the melted metal. As in this refining of copper the precise time when it becomes pure cannot be known, because scoria is always formed on its surface, it is necessary to use an essay-iron, the polished end of which being dipped in melted copper, shews that this metal is pure when the copper adhering to the iron falls off as soon as it is dipped in cold water.

When this mark of the purity of the copper has been observed, its surface ought to be well cleaned; and as soon as it begins to fix, it must be sprinkled with a broom or before dipped in cold water. The surface of the copper which is then fixing, being suddenly cooled by the water, detaches itself from the rest of the metal, is taken hold off by tongs, and is thrown red-hot into cold water. By again sprinkling water on the mass of copper, it is all of it reduced into plates which are called rosettes, and these plates are what is called rosette-copper.

2. The copper of pyritous cupreous ores cannot be obtained without several operations, which vary according to the nature of the ores. These operations are chiefly roastings and fusions. By the first fusion a matt is produced, which is afterwards to be roasted; and thus the fusions and roastings are to be alternately applied, till by the last fusion copper is obtained. These methods of treating pyritous copper ores depend on the two following facts: 1. Sulphur is more disposed to unite with iron than with copper. 2. The iron of these ores is destructible by the burning sulphur during the roasting or the fusion of the ores, while the copper is not injured. This fact appears from experiments mentioned by Scheffer and by Wallerius, and from the daily practice of smelting cupreous ores.

From these facts we learn, 1. That sulphur may be employed to separate and destroy iron mixed with copper. 2. That iron may be employed to separate the sulphur from copper, as is sometimes done in the essay of sulphurated copper-ores. 3. That by adjusting the proportion of the iron and sulphur to each other in the smelting of copper-ores, these two substances may be made to destroy each other, and to procure a separation of the copper: and this adjustment may be effected, by adding sulphur or sulphurous pyrites to the copper-ore, when the quantity of sulphur contained in this ore relatively to the iron is too small; or by adding iron when the sulphur predominates; or by roasting, by which the superfluous sulphur may be expelled, and no more left than is sufficient for the destruction of the iron contained in the ore. We shall apply these principles to the following cases.

1. When the quantity of sulphur and of iron in a copper-ore is small, and especially when the iron does not too much abound, a previous roasting will at once calcine the iron, and expel most of the sulphur; so that by one fusion the calcined iron may be scorified, and black copper may be obtained. If the sulphur has not been sufficiently expelled, a second roasting and fusion are requisite; for the whole quantity of sulphur ought not to be expelled during the first roasting; but as much ought to be left as is sufficient for the scorification of the calcined iron; otherwise this might, during the fusion, be again revived and united with the copper.

2. If, in a copper-ore, the quantity of iron be too great, relatively to the sulphur, some sulphurated pyrites, especially that kind which contains copper, ought to be added, that a matt may be obtained, and that the iron may be calcined and scorified.

3. When the quantity of sulphur and iron is very great, that is, when the ore is very pyritous and poor, it ought to be first formed into a matt; by which it is separated from the adherent earths and bones, and the bulk is diminished: then by repeated and alternate roastings and fusions, the copper may be obtained.

4. When the quantity of sulphur in an ore is greater than is sufficient for the forming a matt, the superfluous quantity ought to be previously expelled by roasting.

The copper thus at first obtained is never pure, but is generally mixed with sulphur or with iron. It is called black copper. This may be refined in furnaces, or on hearths.

In the former method, to the copper when melted a small quantity of lead is added, which unites with the sulphur, and is scorified together with the iron, and floats upon the surface of the melted copper. This purification of copper by means of lead is similar to the refining of silver by cupellation; and is founded on the property of lead, by which it is more disposed to unite with sulphur than copper is; and on a property of copper, by which it is less liable than any other imperfect metal to be scorified by lead. But as copper is also capable of being scorified by lead, this operation must be no longer continued, and no more lead must be employed, than is sufficient for the separation of the sulphur, and for the scorification of the iron.

The copper might also be purified from any remaining sulphur by adding a sufficient quantity of iron to engage the sulphur. Thus Mr Scheffer found, that by adding to sulphurated copper from $\frac{1}{4}$th to $\frac{1}{5}$th of old cast iron, he rendered the copper pure and ductile. See his Dissertation on the Parting of Metals amongst the Swedish Memoirs for the year 1752. In this purification, the quantity of iron added ought not to be too little, else all the sulphur will not be separated; and it ought not to be too great, else the superfluous quantity will unite with and injure the purity of the copper. The fusion and scorification, with addition of lead, seems to be the best method for the last purification of copper.

Sect. VI. Smelting, &c. of Ores of Iron.

Notwithstanding the great importance of this subject, and the labours of Reaumur, Swedenborgius, and of some other authors, we have still a very imperfect knowledge of the causes of the differences of the several kinds of ores, of the methods of smelting best adapted to these differences, of the causes of the good and bad qualities of different kinds of iron, and of the means of so meliorating this metal that we may obtain tough and ductile iron from any of its ores. Swedenborgius has very industriously and exactly described the different processes now used in most parts of Europe for the melting of ores of iron, for the forging of that metal, and for the conversion of it into steel; but we do not find that he or any other author have, by experiments and discoveries, contributed much to the illustration or to the improvement of this part of metallurgy, unless perhaps, we except those of Mr. Reaumur, concerning the softening of cast iron by cementation with earthy substances.

The ores of iron are known to vary much in their appearance, in their contents, in their degrees of fusibility, in the methods necessary for the extraction of their contained metal, and in the qualities of the metal when extracted.

Most ores require to be roasted previously to their fusion; some more slightly, and others with a more violent and longer-continued fire. Those which contain much sulphur, arsenic, or vitriolic acid, require a long-continued and repeated roasting, that the volatile matters may be expelled. Of this kind is the black-iron ore, from which the Swedish iron is said to be obtained.

Some ores require a very slight roasting only, that they may be dried and rendered friable. Such are the ores called bog ores, and others, which being in a calcined state, and containing little sulphureous matter, would, by a further calcination, be rendered less capable of being reduced to a metallic state.

The roasting of ores of iron is performed by kindling piles, consisting of strata of fuel and of ore placed alternately upon one another, or in furnaces similar to those commonly employed for the calcination of limestone.

Some authors advise the addition of a calcareous earth to sulphureous ores during the roasting, that the sulphur may be absorbed by this earth when converted into quicklime. But we may observe, that the quicklime cannot absorb the sulphur or sulphurous acid, till these be first extricated from the ore, and does therefore only prevent the distillation of these volatile matters; and, secondly, that the sulphur thus united with the quicklime forms a heap of sulphur, which will unite with and dissolve the ore during its fusion, and prevent the precipitation of the metal.

The next operation is the fusion or melting of the ore. This is generally performed in furnaces or towers, from 20 to 30 feet high, in the bottom of which is a basin for the reception of the fluid metal. When the furnace is sufficiently heated, which must be done at first very gradually, to prevent the cracking of the walls; a quantity of the ore is to be thrown in, from time to time, at the top of the furnace, along with a certain quantity of fuel and of lime-stone, or whatever other flux is employed. While the fuel below is consumed by the fire excited by the wind of the bellows, the ore, together with its proportionable quantity of fuel and of flux, sink gradually down, till they are exposed to the greatest heat in the furnace. There the ore and the flux are fused, the metallic particles are revived by the fuel, are precipitated by means of their weight through the scoria formed of the lighter earthy parts of the flux and of the ore, and unite in the basin at the bottom of the furnace, forming a mass of fluid metal covered by a glassy scoria. When a sufficient quantity of this fluid metal is collected, which is generally twice or thrice in 24 hours, an aperture is made, through which the metal flows into a channel or groove made in a bed of sand; and from thence into smaller lateral or connected channels, or other moulds. There it is cooled, becomes solid, and retains the forms of the channels or moulds into which it flows. The piece of iron formed in the large channel is called a sow, and those formed in the smaller channels are called pigs. Sometimes the fluid iron is taken out of the furnace by means of ladles, and poured into moulds ready prepared, of sand or of clay, and is thus formed into the various utensils and instruments for which cast iron is a proper material.

The scoria must be, from time to time, allowed to flow out, when a considerable quantity of it is formed, through an aperture made in the front of the furnace for that purpose. A sufficient quantity of it must, however, be always left to cover the surface of the melted iron, else the ore which would fall upon it, before the separation of its metallic from its unmetallic parts, would lessen the fluidity and injure the purity of the melted metal. This scoria ought to have a certain degree of fluidity; for if it be too thick, the revived metallic particles will not be able to overcome its tenacity, and collect together into drops, nor be precipitated. Accordingly, a scoria not sufficiently fluid, is always found to contain much metal. If the scoria be too thin, the metallic particles of the ore will be precipitated before they are sufficiently metallized, and separated from the earthy and unmetallic parts. A due degree of fluidity is given to the scoria by applying a proper heat, and by adding fluxes suited to the ore.

Some ores are fusible without addition, and others cannot be melted without the addition of substances capable of facilitating their fusion.

The fusible ores are those which contain sulphur, arsenic, or are mixed with some fusible earth.

The ores difficultly fusible are those which contain no mixture of other substance. Such are most of the ores which contain iron in a state nearly metallic. As iron itself, when purified from all heterogeneous matters, is scarcely fusible without addition, so the metal contained in these purer kinds of ores cannot be easily extracted without the addition of some fusible substance.

1. Those which are mixed with some very refractory substance. Some of these refractory ores contain arsenic; but as this substance facilitates the fusion of iron, we may presume that their refractory quality depends upon a mixture of some unmetallic earth or other unfusible substance. The earth which is mixed with the common calcareous ores is in considerable quantity; and is sometimes calcareous, sometimes siliceous, and sometimes argillaceous.

Perhaps the fusibility of different ores depends greatly on the degree of calcination to which the metal contained in them has been reduced; since we have reason to believe, that, by a very perfect calcination, some metals at least may be reduced to the state of an earth almost unfusible, and incapable of metallization; and since we know, that in every calcination and subsequent reduction of a given quantity of any imperfect Manufacturing of imperfect metal, a sensible part of that quantity is always lost or destroyed, however carefully these operations may have been performed. That some of these ores are already too much calcined, appears from the instance above-mentioned of the bog ores, which are injured by roasting; and even the great height of the common smelting furnaces, although advantageous to many ores that require much roasting, is said to be injurious to those which are already too much calcined, by exposing them to a further calcination, during their very gradual descent, before they arrive at the hottest part of the furnace, where they are fused.

But as too violent calcination renders some ores difficultly fusible, so too slight calcination of other ores injures the purity of the metal, by leaving much of the sulphureous or other volatile matter, which ought to have been expelled.

Various substances are added to assist the fusion of ores difficultly fusible. These are, 1. Ores of a fusible quality, or which, being mixed with others of a different quality, become fusible: accordingly, in the great works for smelting ores of iron, two or more different kinds of ore are commonly mixed, to facilitate the fusion, and also to meliorate the quality of the iron. Thus an ore yielding an iron which is brittle when hot, which quality is called red-short, and another ore which produces iron brittle when cold, or cold-short, are often mixed together; not, as sometimes supposed, that these qualities are mutually destructive of each other, but that each of them is diminished in the mixed mass of iron, as much as this mass is larger than the part of the mass originally possessed of that quality. Thus, if from two such ores the mass of iron obtained consists of equal parts of cold-short and of red-short iron, it will have both these qualities, but will be only half as cold-short as iron obtained solely from one of the ores, and half as red-short as iron obtained only from the other ore. 2. Earths and stones are also generally added to facilitate the fusion of iron ores. These are such as are fusible, or become fusible when mixed with the ore, or with the earth adhering to it. Authors direct that, if this earth be of an argillaceous nature, limestone or some calcareous earth should be added; and that, if the adherent earth be calcareous, an argillaceous or siliceous earth should be added; because these two earths, though singly unfusible, yet, when mixed, mutually promote the fusion of each other: but as limestone is almost always added in the smelting of iron ores, and as in some of these, at least, no argillaceous earth appears to be contained, we are inclined to believe, that it generally facilitates the fusion, not merely by uniting with these earths, but by uniting with that part of the ore which is most perfectly calcined, and least disposed to metallization; since we know, that by mixing a calciform or roasted ore of iron with calcareous earth, without any inflammable matter, these two substances may be totally vitrified. See Experiments made upon quicklime and upon iron, by Mr Brandt, in the Swedish Memoirs for the years 1749 and 1751. Calcareous earth does indeed so powerfully facilitate the fusion of iron ores, that it deserves to be considered whether workmen do not generally use too great a quantity of it, in order to hasten the operation. For when the scoria is rendered too thin, much earthy or unmetallized matter is precipitated, and the cast iron produced is of too vitreous a quality, and not sufficiently approximated to its true metallic state.

Some authors pretend, that a principal use of the addition of limestone in the smelting of iron ores is to absorb the sulphur, or vitriolic acid, of these ores; but, as we have already observed, a heap of sulphur is formed by that mixture of calcareous earth and sulphur, which is capable of dissolving iron in a metallic state; and thus the quantity of metal obtained from an ore not sufficiently divested of its sulphur, or vitriolic acid, (which, by uniting with the fuel, is formed into a sulphur during the smelting,) must be considerably diminished, though rendered purer, by addition of calcareous earth: hence the utility appears of previously expelling the sulphur and vitriolic acid from the ore by a sufficient roasting. 3. The scoria of former smeltings is frequently added to assist the fusion of the ore; and, when the scoria contains much iron, as sometimes happens in ill-conducted operations, it also increases the quantity of metal obtained.

The quantity of these fusible matters to be added varies according to the nature of the ore; but ought in general to be such, that the scoria shall have its requisite degree of thinness, as is mentioned above.

The fuel used in most parts of Europe for the smelting of ores of iron is charcoal. Lately, in several works in England and Scotland, iron ore has been smelted by means of pit-coal, previously reduced to cinders or coals, by a kind of calcination similar to the operation for converting wood into charcoal, by which the aqueous and sulphureous parts of the coal are expelled, while only the more fixed bituminous parts are left behind. In France, pit-coal not calcined has been tried for this purpose, but unsuccessfully. The use of peat has also been introduced in some parts of England.

The quality of the iron depends considerably upon the quality and also upon the quantity of the fuel employed. Charcoal is fitter than coals for producing an iron capable of being rendered malleable by forging.

The quantity of fuel, or the intensity of the heat, must be suited to the greater or less fusibility of the ore. Sulphureous, and other ores easily fusible, require less fuel than ores difficultly fusible. In general, if the quantity of fuel be too small, and the heat not sufficiently intense, all the iron will not be reduced, and much of it will remain in the scoria, which will not be sufficiently thin. This defect of fuel may be known by the blackness and compactness of the scoria; by the qualities of the iron obtained, which in this case is hard, white, light, intermixed with scoria, smooth in its texture, without scales or grains, rough and convex in its surface, and liable to great loss of weight by being forged; and, lastly, it may be known by observing the colour and appearance of the drops of metal falling down from the smelted ore, and of the scoria upon the surface of the fluid metal, both which are darker-coloured than when more fuel is used. When the quantity of fuel is sufficiently large, and the heat is intense enough, the iron is darkercoloured, Part III.

Manufacturing of Iron.

coloured, denser, more tenacious, contains less scoria, and is therefore less fusible, and loses less of its weight by being forged. Its surface is also smoother and somewhat concave; and its texture is generally granulated. The scoria, in this case, is of a lighter colour, and less dense. The drops falling down from the melted ore and the liquid scoria in the furnace appear hotter and of a brighter colour. When the quantity of fuel is too great, and the heat too intense, the iron will appear to have a still darker colour, and more conspicuous grains or plates, and the scoria will be lighter, whiter, and more spungy. The drops falling from the melted ore, and the fluid scoria, will appear to a person looking into the furnace through the blast-hole to be very white and shining hot. The quantity of charcoal necessary to produce five hundred weight of iron, when the ore is rich, the furnace well contrived, and the operation skilfully conducted, is computed to be about 40 cubic feet; but is much more in contrary circumstances.

The time during which the fluid metal ought to be kept in fusion before it is allowed to flow out of the furnace, must be also attended to. How long that time is, and whether it ought not to vary according to the qualities of ores and other circumstances, we cannot determine. In some works the metal is allowed to flow out of the furnace every six or eight, and in others only every 10 or 12 hours. Some workmen imagine, that a considerable time is necessary for the congelation of the metal. This is certain, that the iron undergoes some change by being kept in a fluid state; and that if its fusion be prolonged much beyond the usual time, it is rendered less fluid, and also its cohesion, when it becomes cold, is thereby greatly diminished. The marquis de Courtivron says, that the cohesion may be restored to iron in this state, by adding to it some vitreous earth, which he considers as one of the constituent parts of iron, and which he thinks is destroyed by the fusion too long continued. That the fusibility of cast iron does depend on an admixture of some vitreous earth, appears probable from the great quantity of scoria forced out of iron during its conversion into malleable or forged iron, and from the loss of fusibility which it suffers nearly in proportion to its loss of scoria. The quantity of iron daily obtained from such a furnace as is above described, is from two to five tons in 24 hours, according to the richness and fusibility of the ore, to the construction of the furnace, to the adjustment of the due quantity of flux and of fuel, and to the skill employed in conducting the operation.

The quality of the iron is judged by observing the appearances during its flowing from the furnace, and when it is fixed and cold. If the fluid iron, while it flows, emits many and large sparkles; if many brown spots appear on it while it is yet red-hot; if, when it is fixed and cold, its corners and edges are thick and rough, and its surface is spotted; it is known to have a red-short quality. If, in flowing, the iron seems covered with a thin glassy crust, and if, when cold, its texture be whitish, it is believed to be cold-short. Mr Reaumur says, that dark-coloured cast iron is more impure than that which is white. The marquis de Courtivron is of a contrary opinion. But no certain rules for judging of the quality of iron before it be forged can be given. From brittle cast iron, sometimes ductile forged iron is produced. Cast iron with brilliant plates and points, when forged, becomes sometimes red-short and sometimes cold-short. Large shining plates, large cavities called eyes, want of sufficient density, are almost certain marks of bad iron; but whether it will be cold or red-short cannot be affirmed till it be forged. Whiteness of colour, brittleness, closeness of texture, and hardness, are given to almost any cast iron by sudden cooling; and we may observe, that in general the whiter the metal is, the harder it is also, whether these properties proceed from the quality of the iron, or from sudden cooling; and that, therefore, the darker-coloured iron is fitter for being cast into moulds, because it is capable in some measure of being filed and polished, especially after it has been exposed during several hours to a red-heat in a reverberatory furnace, and very gradually cooled. This operation, called by workmen annealing, changes the texture of the metal, renders it softer, and more capable of being filed than before, and also considerably less brittle.

Mr Reaumur found, that by cementing cast iron with absorbent earths in a red-heat, the metal may be rendered softer, tougher, and consequently a fit material for many utensils formerly made of forged iron. Whether cementation with absorbent earths gives to cast iron a greater degree of these properties than the annealing commonly practised, has not been yet determined.

In Navarre, and in some of the southern parts of France, iron-ore is smelted in furnaces much smaller, and of a very different construction from those above described. A furnace of this kind consists of a wide-mouthed copper-caldron, the inner surface of which is lined with masonry a foot thick. The mouth of the caldron is nearly of an oval or elliptic form. The space or cavity contained by the masonry is the furnace in which the ore is smelted. The depth of this cavity is equal to two feet and a half; the larger diameter of the oval mouth of the cavity is about eight feet, and its smaller diameter is about six feet; the space of the furnace is gradually contracted towards the bottom, the greatest diameter of which does not exceed six feet: eighteen inches above the bottom is a cylindrical channel in one of the longer sides of the caldron and masonry, through which the nozzle of the bellows passes. This channel, and also the bellows-pipe, are so inclined, that the wind is directed towards the lowest point of the opposite side of the furnace. Another cylindrical channel is in one of the shorter sides of the furnace, at the height of a few inches from the bottom, which is generally kept closed, and is opened occasionally to give passage to the scoria; and above this is a third channel in the same side of the furnace, through which an iron instrument is occasionally introduced to stir the fluid metal, and to assist, as is said, the separation of the scoria from it. The greatest height of this channel is at its external aperture on the outside of the furnace, and its smaller height is at its internal aperture; so that the instrument may be directed towards the bottom of the furnace; but the second channel below it has a contrary inclination, that, when an opening is made, the scoria may flow out of the furnace into a bafon bason placed for its reception. When the furnace is heated sufficiently, the workmen begin to throw into it alternate changes of charcoal, and of ore previously roasted. They take care to throw the charcoal chiefly on that side at which the wind enters, and the ore at the opposite side. At the end of about four hours a mass of iron is collected at the bottom of the furnace, which is generally about 600 weight; the bellows are then stopt: and when the mass of iron is become solid, the workmen raise it from the bottom of the furnace, and place it, while yet soft, under a large hammer, where it is forged. The iron produced in these furnaces is of the best quality; the quantity is also very considerable, in proportion to the quantity of ore, and to the quantity of fuel employed. In these furnaces no limestone or other substance is used to facilitate the fusion of the ore. We should receive much instruction concerning the smelting of iron-ore, if we knew upon what part of the process, or circumstance, the excellence of the iron obtained in these furnaces depends; whether on the quality of the ore; on the diffusion of any kind of flux, by which the proportion of vitreous or earthy matter, intermixed with the metallic particles, is diminished; on the forging while the iron is yet soft and hot, as the Marquis de Courtrivron thinks; or on some other cause, not observed.

The iron thus produced by melting ores is very far from being a pure metal; and though its fusibility renders it very useful for the formation of cannon, pots, and a great variety of utensils, yet it wants the strength, toughness, and malleability, which it is capable of receiving by further operations.

Cast-iron seems to contain a large quantity of vitreous or earthy matter mixed with the pure iron; which matter is probably the chief cause of its fusibility, brittleness, hardness, and other properties by which it differs from forged iron. The sulphur, arsenic, and other impurities of the ore, which are sometimes contained in cast-iron, are probably only accidental, and may be the cause of the red-short quality, and of other properties of certain kinds of iron; but the earthy matter above-mentioned seems principally to distinguish cast-iron from forged or malleable iron; for, first, by depriving the former of this earthy matter, it is rendered malleable, as in the common process hereafter to be described; and, secondly, by fusing malleable iron with earthy and vitreous matter, it loses its malleability, and is restored to the state and properties of cast-iron.

The earthy vitreous matter contained in cast-iron consists probably of some of the ferruginous earth or calx of the ore not sufficiently metallified, and also of some unmetallic earth. Perhaps it is only a part of the scoria which adheres to, and is precipitated with, the metallic particles, from which it is more and more separated, as the heat applied is more intense, and as the fusion is longer continued.

To separate these impurities from cast-iron, and to unite the metallic parts more closely and compactly, and thus to give it the ductility and tenacity which render this metal more useful than any other, are the effects produced by the following operations.

The first of these operations is a fusion of the iron, by which much of its impurities is separated in form of scoria; and by the second operation, a further and more complete separation of these impurities, and also a closer compaction of the metallic particles, are effected by the application of mechanical force or pressure, by means of large hammers.

Some differences in the construction of the forge or furnace, in which the fusion or refining of cast-iron is performed, in the method of conducting the operation, and in other circumstances, are observed to occur in different places. We shall describe from Swedenborgius the German method.

The fusion of the cast-iron, which is to be rendered malleable, is performed upon the hearth of a forge similar to that used by blacksmiths: at one side of this hearth is formed a cavity or fire-place, which is intended to contain the fuel and the iron to be melted: this fire-place is 20 inches long, 18 inches broad, and 12 or 14 inches deep: it is bounded on three sides by three plates of cast-iron placed upright; and on the fourth side, which is the front, or that part nearest to which the workmen stand, by a large forge-hammer, through the eye of which the scoria is at certain times allowed to flow. The floor also of the fire-place is another cast-iron plate. The thickness of these plates is from two to four inches. One of the upright side-plates rests against a wall, in an aperture through which a copper tube, called the tuyere, is fitted with clay. This tube is a kind of cage or covering for the pipe of a pair of bellows placed behind the wall, and its direction is therefore parallel to that of the bellows-pipe; but it advances about half a foot further than this pipe into the fire-place; and thus gives greater force to the air, which it keeps concentrated, or prevents the divergency of the air, till it is required to act. The tube rests upon the edge of the side-plate which leans against the wall, nearer to the back-part than to the front of the fire-place, and in such an oblique direction, that the wind shall be impelled towards the furthest part of the floor of the fire-place, or where this floor is intersected by the opposite side-plate. The obliquity of the tuyere ought to vary according to the quality of the iron: and therefore, in every operation, it may be shifted till its proper position is found. The more nearly its direction approaches to a horizontal plane, the more intense is the heat; but a larger quantity of fuel is consumed than is even proportional to the increase of heat, because the flame is not then so well confined. When the iron is easily fusible, great heat is not required: the tuyere may then decline considerably from the horizontal plane, and thus fuel may be saved. This tuyere, though made of copper, a metal more easily fusible than iron, is preserved from fusion by the constant passage of cold air through it. It must be carefully kept open, and cleansed from the scoria, which would be apt to block up its cavity, by which not only the heat would be too much diminished for the success of the operation, but the tube itself would be melted.

To prepare for the fusion, a quantity of scoria of a former operation is thrown into the fire-place, till one-third part of this be full; and the remaining two-thirds of the fire-place are to be filled with smaller scoria, coal-dust, and sparks ejected from hot iron. These matters, being fusible, form a bath for the reception of the iron when melted. Upon this bed of scoria, the mass of cast-iron to be melted is placed; so that one end of it shall be within the fire-place, opposite to the tuyere, and at the distance of about four or five inches from its aperture; and the other end shall stand without the fire-place, to be pushed in, as the former is melted. The upper side of the mass of iron ought to be in the same horizontal plane as the upper part of the orifice of the tuyere, that the wind may, by means of the obliquity of its course, strike upon and pass along the under-side of the mass; but if the iron be difficultly fusible, the tuyere is to be disposed more horizontally, so that the wind shall strike directly upon the mass of iron; and that one part of the blast shall graze along the upper surface, and the other part along the under surface of the iron. The mass of iron weighs generally from 200 to 400 pounds. Sometimes two or three smaller masses are put one above another, so as not to touch. When these are of different qualities, the cold-short piece is placed undermost, that being more fusible than the red-short. The iron being placed, charcoal-powder is thrown on both sides, and coals are accumulated above, so as to cover entirely the iron.

The coals are then to be kindled, and the bellows are made to blow, at first slowly, and afterwards with more and more force. The iron is gradually liquefied, and flows down in drops through the melted scoria to the bottom of the fire-place; during which the workmen frequently turn the iron, so that the end opposed to the blast of wind may be equally exposed to heat, and uniformly fused. While the coals are consumed, more are thrown on, so that the whole may be kept quite covered. During the operation, a workman frequently sounds the bottom and corners of the fire-place by means of a bar or poker, raises up any mass of metal which he finds adhering to these, and exposes them to the greatest heat, that they may be more perfectly fused.

When all the iron is fused, no more coals are to be added; but the melted mass is to remain half uncovered for some time; during which the iron boils and bubbles, and its surface swells and rises higher and higher. When the iron has risen as high as the upper edge of the fire-place, the coals upon its surface must be removed; and by thus exposing it to cold air, its ebullition and swelling subside. In this state, or cocation, the iron is kept during half an hour or more, by adding occasionally pieces of good coal, which maintain a sufficient heat, without covering entirely the surface of the mass. During this cocation, the workmen allow the orifice of the tuyere to be half stopped up by the scoria, that the air may not blow upon the iron with all its force, by which it would be too much cooled. Accordingly, when they think that the cocation has continued sufficiently long, they clear the passage of the tuyere, and the mass is soon cooled by the cold air. At the same time also, they open a passage in the eye of the hammer placed in the front of the fire-place, through which some of the scoria is allowed to flow out. When the iron has become solid, the bellows are stopt, the coals are removed, and the mass is left during an hour; and then the workmen raise it from the fire-place, turn it upside down, and proceed to the second cocation or fusion of the iron.

From this second operation, the mass is to be so placed, that one part of it shall rest upon the tuyere, and the other upon the scoria remaining in the fire-place. This scoria is to be disposed in an oblique direction parallel to the tuyere, by which means the wind of the bellows is obliged to pass along the under side of the mass of iron. About the sides of the mass, charcoal-powder and burnt ashes are thrown; but towards the tuyere, dry and entire pieces of coals are placed, to maintain the fire. When these are kindled, more coals are added, and the fire is gradually excited. The workman attends to the direction of the flame, that it passes equally along the under surface of the iron, quite to the further extremity, and that it do not escape at the sides, nor be reverberated back towards the tuyere, by which this copper tube might be melted. During this fusion, pieces of iron are apt to be separated from the mass, and to fall down unfused to the bottom and corners of the fire-place. These are carefully to be searched for, and exposed to the greatest heat till they are melted. When the whole mass is thus brought into perfect fusion, the coals are removed; and the wind blowing on its surface, whirls and dissipates the small remaining pieces of scoria, and sparks thrown out from the fluid iron. This jet of fire continues about seven or eight minutes, and the whole operation about two hours. In this second fusion the scoria is to be thrice removed, by opening a passage through the eye of the hammer. The first time of removing the scoria is about 20 minutes from the kindling of the fire, the second time is about 40 minutes after the first, and the third time is near the end of the operation.

The mass is then removed from the hearth, and put upon the ground of the forge, where it is cleaned from scoria, and beat into a more uniform shape. It is then placed on an anvil, where, by being forged, it receives a form nearly cubical. This mass is to be divided into five, six, or more pieces, by means of a wedge; and these are to be heated and forged till they are reduced to the form of the bars commonly sold.

In some forges, the iron is fused only once, and in others it suffers three fusions, by which it is said to be rendered very pure. Where only one fusion is practised, it is called the French method. In this, no greater quantity of iron is fused at once than is sufficient to make one bar. The fire-place is of considerable less dimensions, and especially is less deep, than in the German method above described. The fire is also more intense, and the proportion of fuel consumed to the iron is greater. The iron, when melted, is not kept in a state of ebullition as is above described; but this ebullition is prevented by stirring the fluid mass with an iron bar, till it is coagulated, and becomes solid.

By these operations, fusion and forging, the iron loses about \(\frac{1}{3}\) parts of its former weight, sometimes more and sometimes less, according to the quality of the cast-iron employed; it is purified from the vitreous and earthy parts which were intermixed with it, its metallic particles are more closely compacted, its texture is changed, and it is rendered more dense, soft, and malleable, tough, and difficultly fusible.

The degrees, however, of these qualities vary much in different kinds of iron. Thus some iron is tough and malleable, both when it is hot and when it is cold. This is the best and most useful iron. It may be known generally by the equable surface of the forged bar, which is free from transverse fissures or cracks in the edges, and by a clear, white, small-grained, or rather fibrous texture. Another kind is tough when it is heated, but brittle when it is cold. This is called cold-short iron; and is generally known by a texture consisting of large, shining plates, without any fibres. It is less liable to rust than other iron. A third kind of iron, called red-short, is brittle when hot, and malleable when cold. On the surface and edges of the bars of this kind of iron, transverse cracks or fissures may be seen; and its internal colour is dull and dark. It is very liable to rust. Lastly, some iron is brittle both when hot and when cold.

Most authors agree, that the red-short quality of iron proceeds from some sulphur or vitriolic acid being contained in it, because sulphur is known to produce this effect when added to iron, and because the iron obtained from pyritous and other sulphurated ores has generally this quality.

The cause of the cold-short quality of iron is not yet well ascertained. Some imagine, that it proceeds from a mixture of arsenic or of antimony. But this opinion seems to be improbable, when we consider that these metallic substances may in a great measure be dissipated by roasting, whereas the ores which yield a cold-short iron are injured by much roasting; that no arsenic or antimony are observable in most, if in any, of these ores; and lastly, that these semi-metals would render the iron brittle both when hot and when cold. Cramer and other authors impute this vicious quality to a mixture of an unmetallic earth or vitreous matter; and affirm, that it may be destroyed by cementation with phlogiston, and by forging. And lastly, others ascribe the cold-short quality of iron to a defect of phlogiston, or, as Swedenborgius says, of sulphur. To ascertain the causes of the bad qualities of iron, and to discover practical remedies, are still desiderata in metallurgy.

In one bar frequently two or more different kinds of iron may be observed, which run all along its whole length; and scarcely a bar is ever found of entirely pure and homogeneous iron. This difference probably proceeds from the practice we have mentioned of mixing different kinds of ores together, in the melting; and also from the practice of mixing two or more pigs of cast iron of different qualities in the finery of these; by which means, the red-short and cold-short qualities of the different kinds are not, as we have already remarked, mutually counteracted or destroyed by each other, but each of these qualities is diminished in the mixed mass of iron, as much as this mass is larger than the part of the mass originally possessed of that quality: that is, if equal parts of red-short and of cold-short iron be mixed together, the mixed mass will be only half as red-short as the former part, and half as cold-short as the latter. For these different kinds of iron seem as if they were only capable of being interwoven and diffused through each other, but not of being intimately united or combined.

The quality of forged iron may be known by the texture which appears on breaking a bar. The best and toughest iron is that which has the most fibrous texture, and is of a clear greyish colour. This fibrous appearance is given by the resistance which the particles of the iron make to their rupture. The next best iron is that whose texture consists of clear, whitish, small grains, intermixed with fibres. These two kinds are malleable, both when hot and when cold, and have great tenacity. Cold-short iron is known by a texture consisting of large, shining plates, without fibres: and red-short iron is distinguished by its dark dull colour, and by the transverse cracks and fissures on the surface and edges of the bars. The quality of iron may be much improved by violent compression, as by forging and rolling; especially when it is not long exposed to too violent heat, which is known to injure, and at length to destroy its metallic properties.

For the conversion of iron into steel, see the article STEEL.

SECT. VII. Of the Smelting of Tin Ores.

The tin-ores commonly smelted are those which consist of calx of tin combined with calx of arsenic and sometimes with calx of iron. These are either pure, as the tin-grains, or intermixed with spars, stones, pyrites, ores of copper, iron, or of other metals.

The impure ores must be cleansed as much as is possible from all heterogeneous matters. This cleansing is more necessary in ores of tin than of any other metal; because in the smelting of tin-ores a less intense heat must be given than is sufficient for the scorification of earthy matters, lest the tin be calcined. Tin-ores previously bruised may be cleaned by washing, for which operation their great weight and hardness render them well adapted. If they be intermixed with very hard stones or ferruginous ores, a slight roasting will render these impure matters more friable, and consequently fitter to be separated from the tin-ores. Sometimes these operations, the roasting, contusion, and lotion, must be repeated. By roasting, the ferruginous particles are so far revived, that they may be separated by magnets.

The ore, thus cleansed from adhering heterogeneous matters, is to be roasted in an oven or reverberatory furnace with a fire rather intense than long continued, during which it must be frequently stirred to prevent its fusion. By this operation, the arsenic is expelled, and in some works is collected in chambers built purposely above the calcining furnace.

Lastly, the ore cleansed and roasted is to be fused, and reduced to a metallic flake. In this fusion, attention must be given to the following particulars. 1. No more heat is to be applied than is sufficient for the reduction of the ore; because this metal is fusible with very little heat, and is very easily calculable. 2. To prevent this calcination of the reduced metal, a larger quantity of charcoal is used in this than in most other fusions. 3. The scoria must be frequently removed, lest some of the tin should be involved in it, and the melted metal must be covered with charcoal powder to prevent the calcination of its surface. 4. No flux or other substance, excepting the scoria of former smeltings which contains some tin, are to be added, to facilitate the fusion.

SECT. VIII. Smelting of Ores of Lead.

Ores of lead are either pure, that is, containing no Part III.

Smelting no mixture of other metal; or they are mixed with fil- of Tin ores ver, copper, or pyrites. The methods of treating ores of lead containing silver and copper, are de- scribed in the sections of Smelting of Ores of Silver and of Copper; and in the former of these an instance is gi- ven of the method of melting the ore of Rammelsberg, which contains all these three metals.

Pure ores of lead, and those which contain so small a quantity only of silver as not to compensate for the expense of extracting the nobler metal, may be melted in furnaces, and by operations similar to those used at Rammelsberg, or in the following methods. 1. From the lead-ore of Willach in Carinthia, a great part of the lead is obtained by a kind of eliquation, during the roasting of the ore. For this purpose, the ore is thrown upon several strata or layers of wood, placed in a calcining or reverberatory furnace. By kindling this wood, a great part of the lead flows out of the ore, through the layers of fuel, into a bason placed for its reception. The ore which is thus roasted is beat into smaller pieces, and exposed to a second ope- ration similar to the former, by which more metal is eluated; and the remaining ore is afterwards ground, washed, and melted, in the ordinary method.

The lead of Willach is the purest of any known. Schlutter ascribes its great purity to the method used in extracting it, by which the most fusible, and consequently the purest part of the contained lead is separated from any less fusible metal which happens to be mixed with it, and which remains in the roast- ed ore. This method requires a very large quantity of wood.

2. In England, lead ores are smelted either up- on a hearth, or in a reverberatory furnace called a cupel.

In the first of these methods, charcoal is employed as fuel, and the fire is excited by bellows. Small quantities of fuel and of ore are thrown alternately and frequently upon the hearth. The fusion is very quickly effected; and the lead flows from the hearth as fast as it is separated from the ore.

3. In the second method practised in England, pit- coal is used as fuel. The ore is melted by means of the flame passing over its surface; its sulphur is burnt and dissipated, while the metal is separated from the scoria, and collected at the bottom of the furnace. When the ore is well cleansed and pure, no addition is requisite; but when it is mixed with calcareous or earthy matrix, a kind of flour or fusible spar found in the mines is generally added to render the scoria more fluid, and thereby to assist the precipitation of the me- tal. When the fusion has been continued about eight hours, a passage in the side of the furnace is opened, through which the liquid lead flows into an iron ci- tern. But immediately before the lead is allowed to flow out of the furnace, the workmen throw upon the liquid mass a quantity of slackened quicklime, which renders the scoria so thick and tenacious, that it may be drawn out of the furnace by rakes. Schlutter men- tions this addition of quicklime in the smelting of lead ores in England, but thinks that it is intended to fa- cilitate the fusion of the ores; whereas it really has a contrary effect, and is never added till near the end of the operation, when the scoria is to be raked from the surface of the metal.

Sect. IX. Of the Smelting of Ores of Semi-