METALLURGY

M E T A L L U R G Y.

METALLURGY, according to Boerhaave, comprehends the whole art of working metals, from the giebe or ore to the utensil; in which sense essaying, smelting, refining, parting, smithery, gilding, &c. are only branches of metallurgy. But, in the present work, Gilding, Parting, Purifying, Refining, Smithery, &c. are treated under their proper names. With others, therefore, we have chosen to restrain Metallurgy to those operations required to separate metals from their ores for the uses of life. These operations are of two kinds: the smaller, or Essaying; and the larger, or Smelting. But a particular descrip-

tion of the ores themselves seemed likewise necessary to be given; and to this place, too, we have referred a general account of metals, metallisation, mines, and ores, as a proper introduction to the subject. Hence the following division into three parts. The first treating, 1. Of metals and metallisation. 2. Of mines and ores in general. 3. Of the pyrites. 4. Of the essaying of ores in general. The second, Of the particular ores, and the methods of essaying them. The third, Of smelting of ores, or the methods of extracting metals from large quantities of ores for the purposes of commerce or manufacture.

P A R T I.

SECT. I. Of Metals and Metallisation.

UNDER the general name metal, we comprehend here not only the metals properly so called, but also the semimetals, or all matters which have the essential metallic properties which we shall here recount. Thus the word metal and metallic substance will be synonymous in this article.

Metallic substances form a class of bodies, not very numerous, of very great importance in chemistry, medicine, arts, and the ordinary affairs of life. These substances have very peculiar properties, by which they differ from all other bodies.

The natural bodies from which metals differ the least are, earthy and pyritous matters, on account of their solidity and density. Metals and stones are, nevertheless, very different; the heaviest stones which are unmetallic being much lighter than the lightest metals. A cubic foot of marble weighs 252 pounds; and an equal bulk of tin, the lightest of metals, weighs 516 pounds. The difference is much greater when the weight of such stone is compared with that of gold, a cubic foot of which is 1326 pounds.

Opacity is another quality which metals possess eminently, the opacity of metals being much greater than that of any unmetallic substance.

This great opacity of metals is a consequence of their density; and these two properties produce a third, peculiar also to metals, namely, a capacity of reflecting much more light than any other body: hence metals whose surfaces are polished, form mirrors representing the images of bodies more clearly than any other matter. Thus looking-glasses produce their reflection merely by the silvering, which is a covering of metal upon their surfaces. To this reflective property metals owe their peculiar lustre, called the metallic lustre.

Although the several metallic substances differ considerably in hardness and fusibility, we may say in ge-

neral, that they are less hard and less fusible than pure earths.

Metals cannot unite with any earthy substance, not even with their own earths, when these are deprived of their metallic state: hence, when they are melted, they naturally run into globes, as much as the absolute gravity of their mass, and their pressure upon the containing vessels, will allow. Accordingly, the surface of a metal in fusion is always convex. A metal in that state always endeavours to acquire a spherical form, which it does more perfectly as the mass is less. This effect is very sensible in quicksilver, which is nothing but a metal habitually fluid or fused. A mass of several pounds of mercury, contained in a shallow wide-mouthed vessel, is so spread out, that its upper surface is almost flat, and the convexity is not very sensible but at its circumference: on the contrary, if we put very small masses of mercury into the same vessel, as, for instance, masses weighing a grain each, they become so round as to seem perfect globes. This effect is partly occasioned by the inaptitude of metals to unite with the vessels containing them when in fusion, by which quality the whole affinity which subsists betwixt the integrant parts of these metals is capable of acting; and partly also by this affinity, which disposes the integrant parts to come as near to each other as they can, and consequently to form a sphere.

This property is not peculiar to melted metals, but to all fluids, when contiguous to bodies solid or fluid, with which they have no tendency to unite. Thus, for instance, masses of water upon oily bodies, or oily masses upon bodies moistened with water, assume always a form so much nearer to the spherical as they are smaller. Even a large drop of oil poured upon a watery liquor, so that it shall be surrounded with this liquor, becomes a perfect sphere.

All metals are in general soluble by all acids; but often these solutions require particular treatment and circumstances, which are mentioned under CHEMISTRY. With acids, they form a kind of neutral salts, which have

Of Metal-lisation. have all more or less causticity. The affinity of metals is less than of absorbent earths and alkaline salts to acids; and therefore any metal may be separated from any acid by these substances.

Alkaline salts are capable of acting upon all metallic substances, and by proper management will keep them dissolved.

Metals may in general be united with sulphur and liver of sulphur. With sulphur they form compounds resembling the peculiar substance of ores, which are generally nothing else than natural combinations of sulphur and metal. Metals have less affinity with sulphur than with acids; hence sulphur may be separated from them by acids. Some exceptions from these general rules, concerning the affinity of metals to sulphur and liver of sulphur, and concerning their separation from sulphur by acids, may be seen under the articles of the several metals. But these exceptions do probably take place, only because we have not yet found the method of surmounting some obstacles which occur in the ordinary methods of treating certain metals.

All metals may in general be united with each other, with which they form different alloys which have peculiar properties; but this rule also is not without some exceptions.

Metals have a strong affinity with the inflammable principle, and are capable of receiving it superabundantly.

Lastly, oily substances seem to be capable of acting upon all metals. Some metals are easily and copiously dissolved by oils; and perhaps they might all be found to be entirely soluble in oils, if the methods known in chemistry were tried for the accomplishment of these solutions.

The properties above mentioned agree in general to all metallic substances: but, besides the properties peculiar to each metal, some properties are common to a certain number of them; and hence they have been divided into several classes.

Those metallic matters which, when struck by a hammer, or strongly compressed, are extended, lengthened, and flattened, without being broken (which property is called ductility or malleability), and which also remain fixed in the most violent and long continued fire, without diminution of weight, or other sensible alteration, are called perfect metals. These perfect metals are three; gold, silver, platina.

The metallic matters which are ductile and fixed in the fire, to a certain degree, but which are destroyed by the continued action of fire, that is, changed into an earth deprived of all the characteristic properties of metals, are called imperfect metals. Of this kind are four; copper, iron, tin, lead.

The metallic substances which, as well as the imperfect metals, lose their metallic properties by exposure to fire, but which also have no ductility nor fixity, are distinguished from the others by the name of semi-metals. Of this class are seven; regulus of antimony, bismuth, zinc, nickel, regulus of cobalt, regulus of arsenic, and of manganese.

Lastly, mercury, which has all the general properties of metals, makes a class separate from the others; because in purity and gravity it is similar to the per-

fect metals, and in volatility to the semi-metals. Its fusibility also so far surpasses that of any other metallic matter, that it is sufficient to distinguish it from all, and to give it a distinct class. We have enumerated, therefore, in all, 15 metallic substances; four of which were unknown to the ancients, namely, platina, regulus of cobalt, of manganese, and nickel.

As chemists can compound bodies by being capable of separating the principles of such bodies, and even of re-uniting their principles so as to reproduce such compounds as they were originally; and as hitherto they have not been able to accomplish any such decomposition upon the perfect metals; hence, if all the other metallic substances were equally unalterable, we should be very far from having certain notions concerning metals in general: but if we except gold, silver, and platina, all the other metallic matters are susceptible of decomposition and of recomposition, at least to a certain degree; and experiments of this kind have thrown much light on the subject.

We may observe, that even if we had not been able to decompose any metallic substance, we might still, by reflecting on the essential properties of metals, discover sufficiently well the nature of their principles.

The solidity, the consistence, and especially the gravity, which they possess in a degree so superior to all other bodies, would not have allowed us to doubt that the earthy element, of which these are the characteristic properties, enters largely into their composition, and makes their basis.

The facility with which they combine with almost all inflammable matters, and with all those which have great affinity with phlogiston, such as acids; joined to their incapacity of being allayed with meagre matters that are purely earthy or purely watery, which have no disposition to unite with phlogiston; would also have furnished very strong motives to believe, that the inflammable principle enters largely into the composition of metals.

The destructible metals present exactly the same phenomena as all other bodies containing the inflammable principle do, in the state of combustion. When exposed to fire, without access of air, that is, in close vessels, they become red-hot, melt, or sublime, according to their nature: but they receive no alteration in their composition from fire applied in this manner, and they are afterwards found to be exactly in the same state as before. In this respect, they resemble perfectly all bodies which contain no other inflammable matter than pure phlogiston.

But when imperfect metals are exposed to fire, with access of air, as, for instance, under a muffle in a furnace which is made very hot, then they burn more or less sensibly, as their inflammable principle is more or less abundant, or more or less combined. Some of them, as iron and zinc, burn with a very lively and brilliant flame; but this flame is of the same nature as that of charcoal, of sulphur, of all bodies, the combustible principle of which is pure phlogiston, and is not in an oily state, that is, furnishes no foot capable of blackening.

The imperfect metals detonate with nitre, and their phlogiston is consumed by this method much more

more quickly and completely than by ordinary calcination or combustion. Their flame is also much more lively and brilliant: and some of them, as iron and zinc, are used in compositions for fireworks from their very vivid and beautiful flame.

Nitre is alkaliſed by theſe metallic detonations exactly in the ſame manner as in its detonation by coals.

Laſtly, imperfect metals being treated with acids which have an affinity with phlogifton, that is, with the vitriolic and nitrous acids, are deprived by theſe acids of a more or leſs conſiderable part of their inflammable principle; they give a ſulphureous quality to vitriolic acid, and are even capable of producing ſulphur with that acid.

Although the experiments now mentioned were the only proofs of the exiſtence of an inflammable principle in metallic ſubſtances, they would be ſufficient to eſtablish it incontestably. But we ſhall ſee, when we continue to examine the phenomena attending the decomposition of metals, that thoſe are not the only proofs.

If the inflammable matter which ſhows itſelf ſo evidently in the burning of metals, is really one of their conſtituent parts, their eſſential properties muſt be altered in proportion to the quantity of it taken from them: and this evidently happens upon trial: for the reſiduum of metallic matters, after calcination, departs from the metallic character, and approaches to the nature of mere earth. The opacity, brilliancy, ductility, gravity, fuſibility, volatility, in a word, all the properties by which metallic ſubſtances differ from ſimple earths, diminiſh or entirely diſappear, by taking from them their inflammable principle; ſo that when their calcination has been carried as far as is poſſible, they reſemble mere earths, and have no longer any thing in common with metals. Theſe earths can no longer be combined with acids or with metals, but are capable of uniting with pure earths. They are then called calxes or metallic earths. See CHEMISTRY.

We muſt obſerve concerning the decomposition of metals, 1. That when a ſmall quantity of inflammable principle is taken from metals, only a ſmall quantity of calx is formed, and the remaining part continues in the metallic ſtate: hence, as the portion of calcined matter can no longer remain united with that which is deſtroyed, it ſeparates in form of ſcales from the ſurface of the metal when the calcination has been performed without fuſion, as generally happens to iron and to copper: or theſe ſcales float upon the ſurface of the melted matter when the calcination is performed during fuſion, becauſe the calx is ſpecifically lighter than the metal; as happens to the very fuſible metals, as tin, lead, and moſt of the femimetals.

2. The imperfect metals are not all equally eaſily and completely calcinable. In general, as much of their phlogifton may be eaſily taken from them, as is ſufficient to deprive them of their metallic properties; but the remaining portion of their phlogifton cannot be ſo eaſily driven off. Some of them, as copper, reſiſt the firſt calcination more than the reſt; and others, as lead and biſmuth, may be very eaſily calcined, but only to a certain degree, and retain always obſtinately the laſt portions of their inflammable principle; laſtly, others, as tin and regulus of antimony,

may not only be eaſily and quickly calcined, but alſo much more completely. All the other metals partake more or leſs of theſe properties relating to their calcination. In general, if we except the labours of alchemiſts, which are not much to be depended upon, we have not yet made all the proper efforts to arrive at a perfect calcination of the ſeveral metallic ſubſtances; which, however, is abſolutely neceſſary, before we can arrive at a complete knowledge of the nature of their earths, as we ſhall afterwards ſee.

When metallic earths have loſt but little of their phlogifton, and are expoſed to ſtrong fire, they melt, and are reduced to compact maſſes, ſtill heavy and opaque; although much leſs ſo than the metals, and always brittle and abſolutely unmalleable. If the calcination has been more perfect, the metallic earths are ſtill fuſible by fire, but leſs eaſily, and convertible into brittle and tranſparent maſſes poſſeſſed of all the properties of glaſs, and are accordingly called metallic glaſſes. Theſe glaſſes do not poſſeſs any of the properties of their metals, excepting that they are ſpecifically heavier than other glaſſes, that they are capable of being attacked by acids, and that the glaſſes of the femimetals are ſomewhat leſs fixed than unmetallic glaſſes. Laſtly, when the calcination of metals has been carried to its greateſt height, their earths are abſolutely fixed, and unfuſible in the fire of our furnaces, and poſſeſs no longer the ſolubility in acids by which metals are characteriſed.

There are the principal changes which metals ſuffer by loſing their phlogifton. They are thus changed into ſubſtances which have no properties but thoſe of earth. This is a certain proof that the inflammable principle is one of their conſtituent parts. But we have alſo other proofs of this important truth. The reduction of metallic calxes into metal, by the addition of phlogifton alone, completes the proof; and the whole forms one of the cleareſt and moſt ſatisfactory demonstrations in all the ſciences. This reduction is effected in the following manner:

If the earth of a metal be mixed with any inflammable matter, which either is or can be changed into the ſtate of coal, together with ſome ſalt capable of facilitating fuſion, but which, from its quantity or quality, is incapable of receiving the inflammable principle; and if the whole be put into a crucible, and the fuſion promoted by a fire gradually raſed; then an effervescence will happen, accompanied with a hiſſing noiſe, which continues a certain time, during which the fire is not to be increaſed; afterwards, when the whole has been well fuſed, and the crucible taken from the fire and cooled, we ſhall find at the bottom, upon breaking it, the metal, the earth of which was employed for the operation, poſſeſſed of all the properties which it had before calcination and reduction.

We cannot doubt that this transformation of an earthly ſubſtance into a metal, is ſolely cauſed by the phlogifton paſſing from the inflammable matter to the metallic earth. For, firſt, in whatever manner and with whatever ſubſtance metallic earths be treated, they cannot be ever reduced into metals without a concurrence of ſome ſubſtance containing phlogifton. 2dly, The nature of the ſubſtance which is to furniſh phlogifton is quite indifferent, becauſe this principle is the ſame in all bodies containing it. 3dly, If, after the

Of Metallification. the operation, the substance furnishing the phlogiston be examined, we shall find that it has lost as much of that principle as the metallic earth has received. See PHLOGISTON.

The facts related concerning the decomposition and the recomposition of metals, prove incontestably that they are all composed of earth and phlogiston. But we do not yet certainly know whether these two be the only principles of metals. We might affirm this, if we could produce metals by combining phlogiston with some matter which is certainly known to be simple earth. But this hitherto has not been accomplished; for if we try to treat any earth, which has never been metallic, with inflammable matters, we shall perceive that the simple earths are not combinable with phlogiston so as to form metals. We shall even perceive that the metallic earths resist this combination, and are incapable of reduction into metal, when they have been so much calcined as very nearly to approximate the nature of simple earths.

These considerations, added to this, that we cannot easily conceive how, from only two certain principles, so many very different compounds as the several metallic substances are, should result, are capable of inducing a belief that some other principle is added to these two already mentioned in the composition of metals.

Many great chemists, and particularly Becher and Stahl, seem to be of this opinion. Chiefly from the experiments concerning the mercurification of metals, they believe that this third principle exists copiously in mercury; that it is of a mercurial nature; that it also exists in marine acid, to which it gives its specific character; that, by extracting this mercurial principle from marine acid, or any other body containing it copiously, and by combining it with simple earths, these may acquire a metallic character, and be rendered capable of receiving phlogiston, and of being completely metallified.

These chemists admit also, and with probability, a different proportion of metallic principles in the several metals; and believe, that particularly the principle which they call mercurial earth, exists more copiously and sensibly in certain metals than in others. The most mercurial metals, according to them, are mercury, silver, lead, and arsenic. Most chemists distinguish them from the other metals, which they call white metals, lunar metals, or mercurial metals.

All these considerations being united, and others too many to be mentioned, give some probability to the existence of the mercurial principle in metals. We must however acknowledge, that the existence of this principle is merely probable; and, as Stahl observes, is not nearly so well demonstrated as that of the inflammable principle: we may even add, that we have strong motives to doubt of its existence.

To produce metals artificially has justly been reckoned one of the most difficult problems in chemistry.

Metallic substances, although they resemble each other by their general properties, differ nevertheless from each other very evidently by the properties peculiar to each. Do these differences proceed from the different proportion, and from the more or less intimate connection of the inflammable principle with the earthy principle, supposing that this latter should be essentially the same in all metals? or ought they to be attributed to the difference of earths, which in that

case would be distinct and peculiar to each metal? or, Of Metallification. lastly, do metals differ from each other, both by the nature of their earths, and by the proportion and intimacy of connection of their principles? All these things are entirely unknown; and we may easily perceive, that till they are known, we cannot discover what method to pursue in our attempts to accomplish the combinations we are now treating of.

The most essential point then is, to arrive at a knowledge of the true nature of the earths which are in metals; and the only method of arriving at this knowledge is, by reducing them to their greatest simplicity by a perfect calcination. But this cannot be accomplished but by long and difficult operations. We have seen above, that all metals are not calcinable with equal ease; that the perfect metals have not been hitherto calcined truly by any process; and that, in general, the last portions of phlogiston adhere very strongly to calcinable metals.

Some metals, however, as tin and regulus of antimony, may be easily calcined so as to be rendered irreducible. By carrying the calcination still further, we might obtain their earths so pure, that all their essential properties may be discovered, by which they might be easily compared together. This comparison would decide whether their nature be essentially different or not.

If they were found to be composed of earths essentially the same, we might next proceed to compare metallic with unmetallic earths. If the former were found similar to some of the latter kind, we should be then assured that the earth of metals is not peculiar to them, and that ordinary unmetallic earths are susceptible of metallification. From some late experiments, it was imagined that lime and magnesia alba were capable of being converted into metallic substances, but the processes are now found to be erroneous.

The greater the number of metals operated upon, the more general and certain the consequences resulting from these would be: so that, for instance, if the operation were extended to all calcinable metals; and if the result of each of these operations were, that the calces, when perfectly dephlogisticated, do not differ from each other, and are similar to earths already known; we might conclude from analogy, and we should be almost certain, that the earths of the perfect metals are also of the same nature.

They who know the extent and difficulties of chemical operations, will easily perceive that this would be one of the most considerable. Nevertheless, after having determined this essential point, we should only have done half our work: for a knowledge of the nature of the earth of metals, and where it is to be found, would not be sufficient; we must further endeavour to find a method of combining with this earth a sufficient quantity of phlogiston, and in a manner sufficiently intimate, that a metal might be formed by such a combination. But this second difficulty is perhaps greater than the former.

We must observe here, that some famous chemical processes have been considered by many as metallifications, but which are really not so. Such is Becher's famous experiment of the minera arenaria perpetua, by which that chemist proposed to the States-General to extract gold from any kind of sand. Such also is the process of Becher and of Geoffroy, to obtain iron

from all clays by treating them with linseed oil in close vessels. In these, and many other such processes, we only obtain metal that was already formed. Every earth and sand, as the intelligent and judicious Cramer observes, contains some particles of gold. Clays do not commonly contain iron ready formed; but all of them contain a ferruginous earth, naturally disposed to metallisation. (See CLAY.) Accordingly we must conclude, that, by Mr Geoffroy's experiment, iron is only reduced or revived, but is not produced.

The great difficulties which occur in attempting to give a metallic quality to simple earths have induced a belief, that the nature of metals ready formed might be more easily changed, and the less perfect brought to a more perfect state. To effect this, which is one of the principal objects of alchemy, and is called transmutation, numberless trials have been made. As we have not any certain knowledge of what occasions the specific differences of metallic substances, we cannot decide whether transmutation be possible or not. In fact, if each metallic substance have its peculiar earth, essentially different from the earths of the others, and consequently if the differences of metals proceed from the differences of their earths; then, as we cannot change the essential properties of any simple substance, transmutation of metals must be impossible. But if the earths and other principles of metals be essentially the same, if they be combined in different proportions only, and more or less strictly united, and if this be the only cause of the specific difference of metals; we then see no impossibility in their transmutation.

Whatever be the cause of the differences of metals, their transmutation seems to be no less difficult than the production of a new metallic substance; and perhaps it is even more difficult. Alchemists believe that transmutation is possible, and they even affirm that they have effected it. They begin by supposing that all metals are composed of the same principles; and that the imperfect metals do not differ from gold and silver, but because their principles are not so well combined, or because they contain heterogeneous matters. We have then only these two faults to remedy, which, as they say, may be done by a proper coction, and by separating the pure from the impure. As we have but very vague and superficial notions concerning the causes of the differences of metals, we confess that we cannot make any reasonable conjecture upon this matter; and we shall only advise those who would proceed upon good principles, to determine previously, if metals have each a peculiar earth, or only one common to them all. In the second place, if it should be demonstrated that the earthy principle is the same in all metals, and if that be demonstrated as clearly as the identity of the inflammable principle in metals is proved; they must then determine whether these two be the only principles in metals, whether the mercurial principle exists, and whether it be essential to all metals or to some only, and what is the proportion of these two or three principles in the several metallic substances. When we shall clearly understand these principal objects, we may then be able to determine concerning the possibility of transmutation; and if the possibility should be affirmed, we shall then begin to discover the road which we ought to pursue.

We have no reason to believe that any other principle enters into the composition of metals than those above-mentioned: no vestige is perceptible of either air or water. Some chemists have nevertheless advanced that they contain a saline principle. If that were true, they would also contain a watery principle. But all the experiments adduced to prove this opinion are either false, or only show the presence of some saline particles extraneous to the metals, or contained unknown to the chemists in the substances employed in the experiments. For metals perfectly pure, subjected to all trials with substances which do not contain and which cannot produce any thing saline, do not discover any saline property. We must however except arsenic, and even its regulus, these being singular substances, in which the saline are as sensible as the metallic properties.

Arsenic seems to be one of those intermediate substances which nature has placed in almost all its productions betwixt two different kinds, and which partake of the properties of each kind. Arsenic thus placed betwixt metallic and saline substances has properties common to both these kinds of substances, without being either entirely a metal or salt. See ARSENIC.

As water seems to act to a certain degree upon iron, even without the concurrence of air, as the operation of martial ethiops shows, we might thence suspect something saline in that metal. Nevertheless, what happens in that operation has not been so well explained, that any certain consequences can be deduced. 1. The water employed ought to be perfectly pure; that is, distilled rain-water. 2. The iron employed ought also to be perfectly pure, and such is very difficult to be procured. 3. The operation ought to be performed in a bottle accurately closed, that we may be assured that the air contributes nothing to the action upon the iron. 4. After the water has remained a long time, suppose a year, upon the iron, it ought to be carefully filtrated and examined, to ascertain whether it really has dissolved any part of the metal.

In the mean time, we may conclude that metals do not seem to contain any saline principle. And when we consider well their general properties, they seem to be nothing else than earths combined more or less intimately with a large quantity of phlogiston. Although we can demonstrate that their inflammable principle is not in an oily state, and that it is pure phlogiston, they have nevertheless an oily appearance, in this circumstance, that they adhere no more than oils to earthy and aqueous substances, and that they always assume a globular figure when supported by these substances entirely free from phlogiston.

This resemblance is so sensible, that chemists, before they knew the nature of phlogiston, believed that metals contained an oily and fat matter. The cause of this quality of metals is the quantity of phlogiston which they contain. Sulphur, phosphorus, oils, and even fats, have this appearance merely from the inflammable principle which enters into their composition: for this property is communicated by that principle to every compound which contains a certain quantity of it. See PHLOGISTON.

When the phlogiston combines copiously and intimately with earthy matters so as to form metals, it probably

probably so disposes them, that the primitive integrant parts of the new compound, that is, of the metal, approximate and touch each other much more than the integrant parts of simple earths can. This is proved by the great density or specific gravity, and other general properties, of metals.

In fact, as we cannot conceive that a body should be transparent, unless it have pores and interstices through which rays of light can pass; therefore the more dense a body is, that is, the fewer such interstices it has, the less transparent it will be; so that the densest bodies ought to be the most opaque as in metals. The disposition of the pores of bodies contributes also much to their greater or less transparency; and bodies, the pores of which are continued and straight, are more transparent than those whose pores are interrupted, transverse, or oblique; so that a body may be much more transparent than another which is less dense, as we see that glass is more transparent than charcoal. But when other circumstances are equal, the densest bodies are the most opaque. Therefore the opacity of bodies is proportionable to their density, and to the deviation of their pores from right and parallel lines.

From the great opacity of metals, they probably possess both these qualities in an eminent degree. We have seen, at the beginning of this article, that the lustre of metals, and their property of reflecting light much better than any other substance, are necessary consequences of their opacity. This is also self-evident, because the fewer rays any body can transmit, the more it must reflect.

Lastly, the ductility of metals proceeds also from their density, from the disposition of their pores, and from the action of latent heat; for even the most brittle bodies, such as glass, sealing-wax, &c. become ductile by heat. The softness, fusibility, and volatility, of which all metals partake more or less, and which many of them possess in a superior degree, being properties entirely contrary to those of the earthy principle, probably proceed from the inflammable principle.

The order in which metals compared with each other possess most eminently their principal properties, is the same as that in which they are here enumerated, beginning always with that metal in which the property is most considerable.

1. Specific gravity or density. Platina, gold, mercury, lead, silver, copper, iron, and tin.

2. Opacity. We cannot well compare metals with each other in this respect, because it is so considerable in all, that it seems complete. If, however, they differ in this respect, the same order will serve for opacity as for density.

3. Metallic lustre or brilliancy. The same observation which was made concerning the last mentioned property is applicable to this also. We must, however, observe, that as by polish bodies are rendered brighter, and that as whiteness contributes much to the reflexion of light, the whitest and hardest metals therefore reflect best. Hence, according to Mr Macquer, platina ought to be placed first; and then iron, or rather steel, silver, gold, copper, tin, lead.

Hardness of metals may contribute much to the duration of their polish; but certainly soft metals, if their

texture be equally compact, are no less capable of receiving a polish than hard metals. Some hard metallic alloys have been found to be less liable to tarnish than softer compounds, and have for this reason also been chiefly used for speculums. The property of reflecting light seems chiefly to depend on the closeness of the particles or on the density, on the smoothness of the surface, and on the colour being most similar to the colour of the light to be reflected. The white metals, silver, mercury, tin, reflect light more abundantly than others. Gold, being the densest metal next to platina, and perhaps because the colour of solar light has a slightly yellowish tinge, does also reflect light very copiously. Hence speculums made of leaf-gold have been found to be very powerful. Iron or steel reflects much less light than any of the above-mentioned metals, although Mr Macquer has considered it as capable of a greater reflective power. Platina is generally in so small grains, that its reflective power cannot easily be determined. The precise degrees of that power which ought to be assigned to each of the above-mentioned metals, cannot without accurate experiments be ascertained. Perhaps, however, their reflective powers will be found to be more nearly in the following order, than in that above mentioned from Mr Macquer. Silver, quicksilver, tin, gold, copper, iron, lead.

4. Ductility. Gold, silver, copper, iron, tin, lead. The ductility of mercury and that of platina are not yet determined.

5. Hardness. Iron, platina, copper, silver, gold, tin, and lead.

6. Tenacity. By tenacity we understand the force with which the integrant parts of metals resist their separation. This force appears to be in a compound ratio of their ductility and hardness. The comparative tenacity of metals is measured by the weight which wires of the same diameter, made of the several metals, can sustain without breaking. Gold is the most tenacious; then iron, copper, silver, tin, lead. The tenacity of mercury is unknown: that of platina is not yet determined, but is probably considerable.

7. Fusibility. Mercury, tin, lead, silver, gold, copper, iron, and lastly platina, which cannot be fused by the greatest fire of our furnaces, but only by the solar focus, or by a fire excited by dephlogisticated air.

SECT. II. Of Mines and Ores in general.

THE substances found naturally combined with metals in the earth, are, particularly, sulphur and arsenic, sometimes separately, but generally conjointly. Metals combined with these substances are called metals mineralised by sulphur, or by arsenic, or by sulphur and arsenic; and these matters are called mineralising substances.

Besides the sulphur and arsenic with which metals are strictly combined in the mineral state, they are also pretty intimately combined with earthy substances, of different natures, and more or less divided.

These different matters united together form masses which are compact, heavy, brittle, and frequently possessed of much metallic lustre. These substances are properly called ores, or the matter of mines.

These ores are found in earths and stones of different kinds, as sands, flints, crystals, slates, indurated clays, according to the ground in which they are contained. But two kinds of stones in particular seem to accompany ores; and have therefore been considered by several mineralogists as matrixes in which metals are formed. One of these stones is a kind of crystal, generally white, milky, and semi-opaque, striking fire with steel, and of the class of vitrifiable earths. It is called QUARTZ.

The other stone is less hard, which does not strike fire with steel, and is sometimes milky like quartz; sometimes transparent and of different colours, consisting of rhomboidal crystals, which are composed of plates and faces. This stone becomes more soft and friable by being exposed to fire. It is called SPAR. Spar is more like to gypseous stones than to any other, but it differs from gypseous stones in possessing a much greater density. Some spars are so heavy, that they exceed in this respect all other stones. See SPAR.

These earthy and stony substances form the matrix of the ore.

Ores are natural compounds, containing metals alloyed with different substances.

Excepting gold, and a very small quantity of each of the other metals found in some places so pure as to possess all their characteristic properties, nature exhibits to us metals and semimetals differently alloyed not only with each other, but also with several heterogeneous substances, which so alter and disguise their qualities, that in this state they cannot serve for any of the purposes for which they are proper when they are sufficiently pure.

Ores consist, 1. Of metallic substances calcined; or, 2. Of these substances combined with other matters, with which they are said to be mineralised.

Calcined metallic substances, or calciform ores, are metallic substances deprived of phlogiston, and in the state of a calx or metallic earth. Such are all ferruginous ochres, which are calces of iron.

Mineralised ores, are, 1. Simple, containing only one metallic substance: or, 2. Compound, containing two or more metallic substances.

Of the simple, and also of the compound ores, four kinds may be distinguished.

1. Ores consisting of metallic substances mineralised by sulphur. Such is the lead-ore called galena, composed of lead and sulphur.

2. Ores consisting of metallic substances mineralised by arsenic. Such is the white pyrites, containing iron and arsenic.

3. Ores consisting of metallic substances mineralised by sulphur and by arsenic. Such is the red silver-ore, containing silver, arsenic, and sulphur.

4. Ores consisting of metallic substances mineralised by saline matters. Such are the native vitriols. Such also is probably the corncoat silver-ore, which, according to Mr Cronstedt's opinion, is a luna cornea, or silver combined with marine acid. Of this kind of ores, or native metallic salts, is perhaps the scelator salt of borax, which from Mr Cadet's experiments, published in the Memoirs of the Royal Academy for the year 1766, is conjectured to be copper combined with marine acid, and which has been said to be found native. To this class also may be referred the silver mineralised

by an alkaline substance, which Mr Von Justi pretends to have discovered.

Henekel, and after him Cramer, and the author of the Dictionary of Chemistry, pretend, that in mineralised ores, besides the above mentioned metallic and mineralising substances, are also contained a metallic and an unmetallic earth. But Wallerius affirms, that the existence of such earths cannot be shown, and that sulphur is incapable of dissolving unmetallic earths, and even the calces of all metallic substances, excepting those of lead, bismuth, and nickel.

Metals and metalliferous ores are found in various places.

I. Under water; in beds of rivers, lakes, and seas, and chiefly at the flexures of these: such are the auriferous and ferruginous sands, grains of native gold, ochres, and fragments of ores washed from mines.

II. Dissolved in water: such are the vitriolic waters containing iron, copper, or zinc.

III. Upon the surface of the earth. Such are many ochres; metalliferous stones, sands, and clays; and lumps of ores. Mr Gmelin says, that in the northern parts of Asia ores are almost always found upon or near the surface of the ground.

IV. Under the surface of the earth. When the quantity of these collected in one place is considerable, it is called a mine.

Subterranean metals and ores are differently disposed in different places.

1. Some are infix in stones and earths, forming nodules or spots diversely coloured.

2. Some are equably and uniformly diffused through the substance of earths and stones, to which they give colour, density, and other properties. Such are the greatest part of those earths, stones, sands, clays, crystals, flints, gems, and fluors, which are coloured.

3. Some form strata in mountains. Such are the slates containing pyrites, copper-ore, lead-ore, silver-ore, or blend. These lie in the same direction as the strata of stones betwixt which they are placed; but they differ from the ordinary strata in this circumstance, that the thickness of different parts of the same metalliferous stratum is often very various; whereas the thickness of the stony strata is known to be generally very uniform.

4. Fragments of ores are frequently found accumulated in certain subterranean cavities, in fissures of mountains, or interposed betwixt the strata of the earth. These are loose, unconnected, frequently involved in clay, and not accreted to the contiguous rocks or strata immediately, nor by intervention of spar or of quartz, as the ores found in veins are. Tin and iron mines are frequently of the kind here described.

5. Large entire masses of ores are sometimes found in the stony strata of mountains. These are improperly called cumulated veins, because their length, relatively to their breadth and depth, is not considerable.

6. Some instances are mentioned of entire mountains consisting of ore. Such is the mountain Taberg in Smoland; and such are the mountains of Kerunavara and Luofavara in Lapland, the former of which is 1400 perches long and 100 perches broad. These mountains consist of iron-ore.

7. Lastly, and chiefly, metals and ores are found in oblong

Of Pyrites. oblong tracts, forming masses called veins, which lie in the flory strata composing mountains. See the article MINE.

SECT. III. Of the Pyrites.

PYRITE is a mineral resembling the true ores of metals, in the substances of which it is composed, in its colour or lustre, in its great weight, and, lastly, in the parts of the earth in which it is found, since it almost always accompanies ores. It is, like ores, composed of metallic substances, mineralized by sulphur or by arsenic, or by both these matters, and of an unmetallic earth intimately united with its other principles.

Notwithstanding the conformity of pyrites with ores properly so called, some chemists and metallurgists distinguish the former from the latter minerals; because the proportion and connection of the materials composing the pyrites differ much from those of ores. Thus, although sometimes pyrites contains more metal than some ores, yet generally it contains less metal, and a larger quantity of mineralizing substances, sulphur and arsenic, and particularly of unmetallic earth. The connection of these matters is also much stronger in pyrites than in ores, and they are accordingly much harder; so that almost every pyrites can strike sparks from steel.

From the above property of striking sparks from steel, they have been called pyrites; which is a Greek word signifying fire-stone. Pyrites was formerly used for fire-arms, as we now use flints; hence it was called carabine-stone. It is still named by some marcasite. Perhaps no other kind of natural body has received so many names. Persons curious to know the other names less used than those we have mentioned, may find them in Henckel's Pyritologia. We think, with that celebrated chemist, that the subject has been perplexed by this multiplicity of names; for before his great and excellent work, the notions concerning pyrites were very confused and inaccurate.

Pyrite differs also from ores by its forms and positions in the earth. Although pyritous metals generally precede, accompany, and follow veins of ores; they do not, properly speaking, themselves form the oblong and continued masses called veins, as ores do; but they form masses sometimes greater and sometimes smaller, but always distinct from each other. Large quantities of them are often found unaccompanied by ores. They are formed in clays, chalk, marles, marbles, plasters, alabasters, slates, spars, quartz, granites, crystals, in a word, in all earths and stones. Many of them are also found in pit-coals and other bituminous matters.

Pyrites is also distinguishable from ores by its lustre and figure; which is almost always regular and uniform, externally or internally, or both. Some ores indeed, like those of lead, many ores of silver, and some others, have regular forms, and are in some manner crystallized; but this regularity of form is not so universal and so conspicuous in ores as in pyrites. The lustre of pyrites seems to be caused by its hardness, and the regularity of its form by the quantity of mineralizing substances which it contains.

By all these marks we may easily, and without analysis, distinguish pyrites from true ores. When we see a mineral that is heavy, possessed of metallic lustre, and

of any regular form, the mass of which appears evidently to be entire, that is, not to have been a fragment of another mass, and which is so hard as to be capable of striking sparks from steel, we may be assured that such a mineral is a pyrite, and not an ore.

The class of pyrites is very numerous, various, and extensive. They differ one from another in the nature and proportions of their component parts, in their forms, and in their colours. The forms of these minerals are exceedingly various. No solid, regular or irregular, can easily be conceived, that is not perfectly imitated by some kind of pyrite. They are spherical, oval, cylindrical, pyramidal, prismatical, cubic; they are solids with 5, 6, 7, 8, 9, 10, &c. sides. The surface of some is angular, and consists of many bases of small pyramids; while their substance is composed of these pyramids, the points of which all unite in the centre of the mass.

Pyritous minerals differ also in their component substances. Some of them are called sulphureous, martial, cupreous, arsenical, as one or other of these substances predominate. We must observe with Henckel, whose authority is very great in this subject, that in general all pyrites are martial; as ferruginous earth is the essential and fundamental part of every pyrite. This earth is united with an unmetallic earth, with sulphur or arsenic, or with both these matters; in which case, the sulphur always predominates over the arsenic, as Henckel observes. He considers these as the only essential principles of pyrites; and believes that all the other matters, metallic or unmetallic, which are found in it, are only accidental; amongst which he even includes copper, although so much of it exists in some kinds of pyrites, that these are treated as ores of copper, and sometimes contain even 50 lb. of copper each quintal. Many other metals, even gold and silver, are sometimes combined in pyrites; but these are less frequent, and the precious metals always in very small quantities; they are therefore justly to be considered as accidental to pyrites. The different substances composing pyrites sensibly affect its colours. Henckel distinguishes them in general into three colours, white, yellowish, or a pale yellow, and yellow. He informs us, that these three colours are often so blended one with another, that they cannot be easily distinguished unless when compared together.

The white pyrites contain most arsenic, and are similar to cobalt and other minerals abounding in arsenic. The Germans call them misspikl, or misspil. Iron and arsenic form the greatest part of this pyrite. As arsenic has the property of whitening copper; some pyritous minerals almost white, like that of Chemnitz in Misnia, are found to contain 40 pounds of copper per quintal, and which are so much whitened by the arsenic, that they are very like white pyrites. But Henckel observes, that these pyritous matters are very rare, and are never so white as the true white pyrites, which is only ferruginous and arsenical.

Yellowish pyrites is chiefly composed of sulphur and iron. Very little copper and arsenic are mixed with any pyrites of this colour, and most of them contain none of these two metallic substances. This is the most common kind of pyrites: it is to be found almost every where. Its forms are chiefly round, spherical, oval, flattened, cylindrical; and it is composed internally of needles.

Of Pyrites. needles or radii, which unite in the centre, or in the axis of the solid.

Yellow pyrites receives its colour from the copper and sulphur which enter into its composition. Its colour, however, is inclined to a green; but is sufficiently yellow to distinguish it from the other two kinds of pyrites, particularly when they are compared together. To make this comparison well, the pyrites must be broken, and the internal surfaces must be placed near each other. The reason of this precaution is, that the colour of minerals is altered by exposure to the air.

Persons accustomed to these minerals can easily distinguish them. The chief difficulty is, to distinguish white pyrites from cobalt and other minerals; which also contain some copper and much arsenic.

Hence then we see, that arsenic is the cause of whiteness in pyrites, and is contained in every pyrites of that colour; that copper is the principal cause of the yellow colour of pyrites; and that every pyrites which is evidently yellow contains copper; that sulphur and iron produce a pale-yellow colour, which is also produced by copper and arsenic; hence some difficulty may arise in distinguishing pyrites by its colours. We may also observe, that sulphur and arsenic, without any other substance, form a yellow compound, as we see from the example of orpiment or yellow arsenic. Thus, although the colours of the pyrites enable us to distinguish its different kinds, and to know their nature at first sight, particularly when we have been accustomed to observe them; yet we cannot be entirely certain concerning the true nature of these minerals, and even of all minerals in general; that is, to know precisely the kinds and proportions of their component substances, but by chemical analysis and decomposition.

Besides the above-mentioned matters which compose pyrites, it also contains a considerable quantity of unmetallic earth; that is, an earth which cannot by any process be reduced to metal. Henckel, Cramer, and all those who have examined this matter, mention this earth, and prove its existence.

We ought to observe, that this earth is combined with the other principles of the pyrites, and not merely interposed betwixt its parts. It must therefore be distinguished from other earthy and stony matters mixed accidentally with pyrites, and which do not make a part of the pyrites, since they may be separated by mechanical means, and without decomposing that mineral: but the earth of which we now treat is intimately united with the other constituent parts of the pyrites, is even a constituent part of pyrites, and essential to the existence of this mineral, and cannot be separated but by a total decomposition of it.

According to Henckel, this unmetallic earth abounds much in the white pyrites, since he found from the analyses which he made, that the iron, which is the only metal existing in these pyrites, is only about $\backslash frac\{1\}\{2\}$th part of the fixed substance that remains after the arsenic has been expelled by torrefaction or sublimation.

A much larger quantity of iron is in the pale-yellow pyrites, according to Henckel. The proportion of iron is generally about 12 pounds to a quintal of pyrites, and sometimes 50 or 60 pounds: this is therefore called martial pyrites. It contains about

one-fourth of its weight of sulphur, and the rest is Of Pyrites. unmetallic earth.

The quantity of unmetallic earth contained in the yellow or cupreous pyrites, which are also martial, since, as we have observed, iron is an essential part of every pyrites, has not yet been determined. They probably contain some of that earth, though perhaps less of it than the others.

The nature of this unmetallic earth of pyrites has not been well examined. Henckel thinks that it is an earth disposed already by nature to metallification, but not sufficiently elaborated to be considered as a metallic earth. This opinion is not improbable; but as alum may be obtained from many pyrites, may we not suspect that this unmetallic earth is of the nature of the basis of alum or argillaceous earth? Perhaps also this earth is different in different kinds of pyrites. The subject deserves to be well examined.

Although pyrites are not so valuable as true ores, because in general it contains less metal, and but exceedingly little of the precious metals; and because its metallic contents are so difficult to be extracted, that, excepting cupreous pyrites, which is called pyritous copper ore, it is not worked for the sake of the contained metal; yet it is applied to other purposes, and furnishes us with many useful substances; for from it we obtain all our green and blue vitriols, much sulphur, arsenic, and orpiment. See the principal processes by which these substances are extracted from pyrites, under the section SMELTING OF ORES.

As all pyrites contain iron, and most of them contain also sulphur; as the pyrites most frequently found contains only these two substances with the unmetallic earth; and as iron and sulphur have a singular action upon each other when they are well mixed together and moistened; hence many kinds of pyrites, particularly those which contain only the principles now mentioned, sustain a singular alteration, and even a total decomposition, when exposed during a certain time to the combined action of air and water. The moisture gradually penetrates them, divides and attenuates their parts; the acid of the sulphur particularly attacks the martial earth, and also the unmetallic earth; its inflammable principle is separated from it, and is dissipated. While these alterations happen, the pyrites changes its nature. The acid of the sulphur which is decomposed, forms with the fixed principles of the pyrites, vitriolic, aluminous, and selenitic salts; so that a pyrites, which was once a shining, compact, very hard mineral, becomes in a certain time a greyish, saline, powdery mass, the taste of which is saline, austere, and styptic.

Lastly, if this mass be lixiviated with water, crystals of vitriol, and sometimes of alum, according to the nature of the pyrites employed, may be obtained by evaporation and crystallization.

This alteration and spontaneous decomposition of pyrites, is called efflorescence and vitriolization; because the pyrites become covered with a saline powder, and because vitriol is always formed. This vitriolization is more or less quickly accomplished in pyrites according to its nature. It is a kind of fermentation excited by moisture amongst the constituent parts of these minerals; and it is so violent in those which are most disposed

Of Pyrites, posed to it, that is, in the pale yellow pyrites, which contain chiefly sulphur and iron, that when the quantity of these is considerable, not only a sulphureous vapour and heat may be perceived, but also the whole kindles and burns intensely. The same phenomena are observable, and the same results are formed, by mixing well together, and moistening a large quantity of filings of iron and powdered sulphur; which experiment Lemeri has made, to explain the causes of subterranean fires and volcanoes.

We cannot doubt that, as the earth contains very large masses of pyrites of this kind, they must undergo the same changes when air and moisture penetrate the cavities containing them; and the best natural philosophers agree, that very probably this surprising decomposition of pyrites is the cause of subterranean fires, of volcanoes, and of mineral waters, vitriolic, aluminous, sulphureous, hot and cold.

No other pyrites is subject to this spontaneous decomposition when exposed to humid air, but that which is both martial and sulphureous; that is, the pale-yellow pyrites. The arsenical pyrites, or that which contains little or no sulphur, is not changed by exposure to air. This latter kind is harder, heavier, and more compact, than the former. The pyrites which is angular and regularly shaped, is chiefly of this kind. Mr Wallerius, in his Mineralogy, proposes to distinguish this kind of pyrites by the name of marcasite. When cut, it may be polished so well as to give a lustre almost equal to that of diamonds, but without refracting or decomposing the light; for it is perfectly opaque. It has been employed some years past in the manufacture of toys, as of buckles, necklaces, &c. and is called in commerce marcasite.

We cannot, however, concur with Mr Macquer (from whom the above is taken), in thinking that there is sufficient reason for considering the minerals called pyrites, as a distinct class of substances from ores. They have indeed no mark by which they can certainly and constantly be distinguished from these. The hardness or property of striking ignited sparks from steel is not common to all the substances generally called pyrites; for we find some of these enumerated by mineralogists which have not that property. Wallerius even mentions a pyrites which contains no iron, altho' that metal is thought by Henckel to be essential to pyrites. The distinction of pyrites from ores has been chiefly introduced by miners; because the greatest part of the former minerals contain so little metal, and so much of the mineralising substances, sulphur, or arsenic, that they are seldom smelted. Nevertheless, some kinds of pyrites are found which contain so much copper, that they are smelted with great profit. Accordingly, some later mineralogists consider the cupreous yellow pyrites as an ore of copper, the pale-yellow martial pyrites as an ore of iron; and the white arsenical pyrites as an ore of arsenic. See Ores of Copper, Iron, and of Arsenic, below.

SECT. IV. Assaying of Ores in general.

ESSAYS are chemical operations made in small, to determine the quantity of metal or other matter which is contained in minerals; or to discover the value or

purity of any mass of gold or silver. The former kind Assaying of Ores is the subject of the present section; the latter is treated under the word ESSAYS, in the order of the alphabet.

Before assays of ores can be well made, a preliminary knowledge of the nature of the several metallic minerals ought to be attained. Each metal has its proper and improper ores, which have peculiar characters and appearances: hence persons accustomed to see them, know pretty nearly by the appearance, weight, and other obvious qualities, what metal is contained in a mineral. A good assayer ought to be very intelligent in this matter, that he may at once know what the proper operations are which are requisite to the assay of any given mineral.

As metals are very unequally distributed in their ores, we should be apt to make false and deceitful assays, if we did not use all possible precautions that the proportionable quantity of metal produced by an assay shall be nearly the medium contained in the whole ore. This is effected by taking pieces of the mineral from the several veins of the mine if there be several, or from different places of the same vein. All these minerals are to be shaken together with their matrixes. The whole is to be well mixed together, and a convenient quantity of this mixture is to be taken for the assay. This is called the lotting of the ore.

As assays, particularly the first, are generally made in small, assayers have very small weights corresponding to the weights used in the great; that is, to the quintal or hundred pounds weight, to pounds, ounces, drams, &c. The assay quintal and its subdivisions vary according to the difference of weights in different countries; and this occasions some confusion when these weights are to be adjusted to each other. Tables of these weights are found in treatises of assaying; and particularly in that written by Schlutter, and translated and rendered more complete by Hellot, which contains all the details necessary for the subject.

The custom is to take, for the assay quintal, a real weight of a gros, or dram, which in France is equal to 72 grains; but as the whole dram represents 100 pounds, each grain represents a pound and a fraction of a pound; and hence some difficulty and confusion arise in making the subdivisions. A better method is that of Mr Hellot, which is to make the fictitious or assay quintal equal to 100 real grains, and then each grain represents a real pound. This assay quintal is sufficiently exact for ores of lead, tin, copper, iron, antimony, bismuth, and mercury. But for ores of silver and gold, another representation is convenient: for these metals, as Mr Hellot says, are generally in so small quantity, that the button or small piece of metal obtained in the assay could not be accurately weighed if 100 real grains were made to represent a quintal; and the difficulty of separating the gold from so small a quantity would be still greater. These motives have induced Mr Hellot to use for these ores a fictitious quintal 16 times bigger; that is, equal to 1600 real grains, which represent 1600 ounces; that is, 100 lb. or quintal. The ounce being represented by a grain, its several subdivisions must be represented by fractions

of a grain. Thus 12 grains of the fictitious quintal correspond with $\backslash frac\{1\}\{12\}$ of a real grain ($z$); and this latter quantity may be accurately weighed in assay-balances; which when well made are sensible to a much less weight. See (Essay)-BALANCE.

When a quintal of an ore to be assayed has been weighed, and lotted, as we described above, it is to be roasted in a test under a muffle. It is to be washed, if necessary; and, in short, the same operations are to be made in small which are usually done in great. Additions also are to be made, and in proper proportions, according to the peculiar nature of the ore. The fluxes generally mixed with the assays in ore are three, four, or five parts of black flux; one, two, or three parts of calcined borax; and one half of that quantity of de-crepitated common salt. The more refractory the ore is, the more necessary is the addition of these fluxes: then the whole mixture is to be fused either in a forge or in a melting or assay furnace.

To make assays well, all possible attention and accuracy are to be employed. This object cannot be too much attended to; for the least inaccuracy in weighing, or loss of the smallest quantity of matter, might cause errors, so much greater as the disproportion betwixt the weights employed and those represented is greater. The most minute accuracy therefore is necessary in these operations. For instance, the assay-balances ought to be small, and exceedingly just. The ore ought not to be weighed till it has been reduced to gross powder fit for roasting; because some of it is always lost in this pulverization. When the ore is roasted, it ought to be covered with an inverted test; because most ores are apt to crackle and disperse when first heated. To make the fusion good and complete, the precise degree of fire which is requisite ought to be employed; and when it is finished, the crucible ought to be struck two or three times with some instrument, to facilitate the disengagement of the parts of the regulus from the scoria, and to occasion their descent and union into one button of metal. The crucible ought not to be broken, nor its contents examined, till it is perfectly cold.

Upon breaking the crucible, we may know that the fusion has been good, if the scoria be neat, compact, and equal; if it has not overflowed or penetrated the crucible; if it contain no metallic grains; and if its surface be smooth, and hollowed in the middle. The regulus or button ought to be well collected, without holes or bubbles, and to have a neat convex surface; it is then to be separated from the scoria, well scraped and cleaned; and, lastly, is to be weighed. If the ope-

ration has been well made, its weight shows the quantity of metal which every real quintal of ore will yield in the great. If the perfect success of this assay be in any respect doubtful, it ought to be repeated; but the best method at all times is, to make several assays of the same ore. Some small differences are always found, however well the assays may have been made. By taking the medium of the results of the several operations, we may approach as nearly as possible the true product of the ore.

Lastly, as mines are not worked, nor founderies established (which cannot be done without considerable expence), till the ore has been assayed, 10 or 12 real pounds of the ore ought to be previously assayed; and assayers ought to be furnished with necessary furnaces and instruments for these larger assays.

In Part II. to the several articles of the ores of metals, we shall add the most approved methods of assaying these ores. We shall here only further observe in general, that the methods commonly practised for assaying ores of imperfect metals, and semimetals especially, are insufficient to procure the whole quantity of metal contained in ores, or even so much as is obtained in the smelting of large quantities of ores; and that therefore the result of assays is not to be considered as the precise quantity contained in an ore, but generally only as an inaccurate approximation to that quantity. M. Gellert ascribes one cause of the want of success of these operations to the alkaline salts employed as fluxes to the ores, by which most metallic calces are partially soluble, but more especially so when any of the sulphur of the ore remains; which, by uniting with these salts, forms a hepar of sulphur which is the most powerful of all solvents. He proposes therefore to omit the black flux, and other alkaline salts, and to add nothing to the ore but powder of charcoal and some fusible glass. This method, he says, he learned from Mr Cramer, and has himself used with much success in the assays of iron and copper: but finding that other imperfect metallic substances could not sustain the heat necessary to effect the fusion and vitrification of the unmetallic parts of the ore without being partly dissipated, he found it necessary to add in the assays of these latter metallic matters some borax, by which the fusion might be completed with less heat. As we consider this as a considerable improvement in the art of assaying ores, we shall, to the articles of the several ores, add not only the processes commonly prescribed, but all those of Mr Gellert, according to the method here mentioned.

P A R T II.

Containing a summary Description of the principal ORES of each METAL, and the Methods of Essaying them.

SECT. I. Ores of Gold.

§ 1. PROPERLY speaking, no ores of gold exist: for as this metal cannot be allayed with arsenic, nor with sulphur, it is never found directly mi-
N^o 211.

neralised by these substances, as the other metals are. In the second place, if it be mineralised indirectly by the union it contracts with other metals naturally combined with sulphur and arsenic, so small a quantity of it only is found in these ores, that they

Ores of Gold. they scarcely even deserve the name of improper ores of gold.

Hence gold is found either in its natural state, of a certain degree of purity, possessed of all its properties; or engaged with some other metals in certain minerals.

The gold which is found alone is called native or virgin gold. This is generally incrustated, and fixed in different kinds of stones, principally in flints and quartz. Mr Cramer says, that the yellow brilliant spots of the blue stone called lapis lazuli, are native gold; but these are very small.

Gold is also found in fat and muddy earths; and Mr Cramer affirms, that scarcely any sand can be found which does not contain gold; but he acknowledges, at the same time, that the quantity is too small to compensate for the expence of obtaining it.

Lastly, the largest quantity of native gold is to be found in the sands of some rivers. It is chiefly collected in hollows at the bottom of these rivers, and at their several bendings. The gold is collected in these places by a natural operation, similar to that of washing of ores.

A considerable quantity of gold is in the sands of several rivers in France: so that persons who collect it find enough to compensate their trouble. Mr Reaumur, in a memoir that he gave in the year 1718 concerning the rivers of France which contain gold, enumerates ten of them; namely, the Rhine, the Rhone, the Doux, the Ceze, and the Gardon; the Arriege; the Garonne; two streams which flow into the Arriege, called Ferret and Benagues; lastly, the Salat, the source of which is in the Pyrenean mountains.

The Ceze is the river which furnishes the largest quantity of gold at certain times. Mr Reaumur observes, that its particles are larger than those of the Rhine and of the Rhone; and says, that in some days a peasant will find gold to the value of a pistole, and in others will scarcely find any.

The native gold found in rivers or elsewhere is never perfectly pure, or of 24 karats. It always contains a certain quantity of alloy, which is generally silver. The gold of the French rivers, according to Mr Reaumur's trials, was found to be from 18 to 22 karats, that of the Ceze being the lowest, and that of the Arriege being the purest.

Although gold, however, as above observed from Macquer, cannot be directly dissolved by sulphur, yet it probably may be mineralised by the intervention of other metallic matters. Thus, although no proper ore of gold exists, yet it is found in several mineral substances, in which it is always accompanied, as Cramer affirms, with a much larger quantity of silver; to which latter metal that author attributes its mineralised state. The minerals containing gold are blend, cupreous and arsenical pyrites, ore of antimony, cinabar, white ore of arsenic, vitreous and other silver ores, and the lead-ore called galena.

Gold is more frequently imbedded in quartz than in any other matrix, but it is also found in limestone and in hornblend. Gold mines are in general very precarious, as they do not form regular veins, nor is the gold uniformly distributed through a matrix.

Becher and Cramer think, that no sand is entirely free from gold. The yellow, red, black, and violet-coloured ferruginous sands, are said to contain molt gold. Mr Hellot relates, that in 11 assays of one kind of sand, from a quintal, or 921,600 grains, were obtained each time from 848 to 844 grains of noble metal, exclusive of the gold which remained in the scoria; and that of the metal thus obtained two thirds were gold, and the remaining third was silver. He says, that parcels of sand taken up at very small distances from each other contained very unequal proportions of gold.

The gold found in sands is generally less pure than that which is imbedded in a solid matrix. Reaumur says, that a piece of gold, weighing 448 ounces, was shown to the Royal Academy at Paris, which was found upon assay to have different fineness in different parts of the mass.

§ 2. Ores and earths containing gold may be assayed by the methods directed for the extraction of gold from large quantities of these auriferous matters, (see Part III.): or they may in general be assayed by being fused in a cupel or test, placed under the muffle of an assay-furnace, or in a crucible placed in an air furnace, with eight or ten times their quantity of lead if they be easily fusible, and with a larger quantity of lead if they be difficultly fusible; and by scorifying the earthy matters, while the lead becomes impregnated with the noble metals. These operations are entirely similar to those employed for the separation of silver from its ores by precipitation with lead; a detail of which see subjoined under the section ORES OF SILVER, [Processes I. III. IV. V. VI.]. These metals are afterwards to be separated from the lead by cupellation, in the manner directed in the article ESSAY (of the value of silver and of gold). The gold is then to be separated from the silver by the processes described in the article PARTING.

The quantity of lead to be added to the ore in this assay must be such as renders the scoria very thin, that the whole gold may be imbibed by the lead. Some iron ores containing gold cannot be reduced into a scoria sufficiently thin with 16 times their quantity of lead, unless the heat be at the same time considerably increased. When the ore is exceedingly refractory, the scorification ought to be promoted by adding to it four times its quantity of tartar, twice its quantity of nitre, and four times its quantity of litharge. This mixture is to be put into a good assay-crucible, and covered with the sea-salt. The crucible is to be set in a forge-hearth, and exposed gradually to heat, till the scoria has acquired sufficient fluidity, and the lead has imbibed the noble metal.

See the methods which have been used for assaying auriferous sands, under Part III.

SECT. II. Ores of Platina.

PLATINA is very rare, and has been but lately discovered. As, like gold, it cannot be alloyed with sulphur or with arsenic, probably no ore, properly so called, exists of this metal. Accordingly in the only mines of platina which we know, namely, the gold mines of Santafe near Carthagena, the platina is found native like the gold, and in its metallic state.

§ 1. NEXT to gold, silver is the metal most frequently found in its metallic state, that is, not mineralised by sulphur or by arsenic. This silver, called also native or virgin, generally affects some regular form, and consists of filaments or vegetations of various figures. It is found in form of plates, of fibres, or of grains, or crystallized. It lies generally in quartz, flint, spar, slate, cobalt, and in silver-ores. It is sometimes enveloped in a thin stony crust. It is generally alloyed with some gold: but silver, like all the other metals, is much more frequently found mineralised by sulphur and by arsenic.

Three principal proper ores of silver are known, which are very rich, but very rare. These are:

1. The vitreous silver ore. This ore has no determinate figure, and has nearly the colour, softness, and fusibility of lead. It is very heavy, and contains three quarters of its weight of pure silver. In this ore the silver is mineralised by sulphur alone. Some expert artists imitate it very well by combining sulphur with silver by fusion in a crucible.

This ore, according to Cronstedt, is either in form of plates or of fibres, or is crystallized, or has no determinate figure. It may be imitated by adding about five parts of sulphur to one part of melted silver; in which operation most of the sulphur is consumed; or it may be imitated by exposing a plate of silver red-hot to the fumes of burning sulphur.

2. The horny or corneous silver ore. This ore is so called from its colour and semitransparency, by which it resembles horn or colophony. When suddenly heated, it crackles, as almost all ores do, and melts with a gentle heat. Two-thirds of it are silver, which is mineralised by sulphur and arsenic. This ore is very rare. Wallerius says, after Woodward, that it is found at Johanna-Georgen-Stadt in Saxony.

Corneous ore has various colours; white, pearly, brown, yellow, greenish, or reddish. It is foliated and semitransparent. It is somewhat ductile, and fusible with the flame of a candle. When heated, it emits, as Wallerius says, a sulphureous and blue flame, and, according to Cramer, also a very small quantity of an arsenical fume. Wallerius says, that it contains two-thirds of silver, with a considerable quantity of sulphur, and a small quantity of arsenic. Lehman thinks that it is silver united with a little arsenic. But Mr Cronstedt says, that it is a luna cornea, or silver combined with marine acid; and that it is incapable of being decomposed but by substances which can unite with that acid. This latter opinion seems to be the most probable; as the ore, according to its description, is similar to luna cornea, and as it cannot be imitated by any mixture of sulphur and of arsenic with silver. The blue flame, and the smell slightly arsenical, which are emitted from heated corneous ore, are also observable from every combination of marine acid with a substance containing phlogiston.

3. Red silver ore, called also rosiclare. Its colour is more or less red; it is sometimes crystallized, very heavy, and is fusible like the above-mentioned ore. In this ore the silver is mineralised by arsenic and by

sulphur, but chiefly by the former. It also contains a little iron, and furnishes two-thirds of its weight of silver. Its red colour may proceed either from the iron it contains; or from the mixture of arsenic and sulphur; or, lastly, from the particular manner in which the arsenic is united with the silver, an example of which we have in the red precipitate of silver made by the neutral arsenical salt.

Red silver ore is either plated or solid, or crystallized, and frequently semitransparent. Its colour is various, from a dark grey to a deep red, according to the proportions of the two mineralising substances. It crackles and breaks in the fire, exhales an arsenical fume, and is readily fused. It is found generally in quartz, spar, crystal, hornblend.

Besides the three silver ores above described, the following ores contain silver mixed with other metals.

1. Grey silver ore. This contains copper and silver mineralised by arsenic and sulphur, and generally more of the former than of the latter metal; but as it is valued chiefly for the silver, it has been generally enumerated amongst silver ores.

2. White silver ore is an arsenical pyrites containing silver.

3. Black silver ore contains sulphur, arsenic, copper, iron, sometimes lead, and about a fourth part of silver, according to Wallerius.

4. Plumose silver ore is white or black, striated like plumb-alum, or like ore of antimony. It is silver mineralised by sulphur, arsenic, and antimony.

5. Pech-blend. In this blend silver, gold, and zinc, are mineralised by sulphur, probably by intervention of iron, by which the gold and zinc are rendered capable of uniting with the sulphur.

6. Silver is frequently found in galena; and sometimes in martial pyrites; in the red ore of arsenic; in various ores of copper, lead, tin, iron, and especially cobalt; in blends; in yellow or red earths; in black and blue basalt; and also in strata of stones which do not appear externally to contain any mineral substance.

7. Liquid silver ore or gubr of silver, is a grey or whitish liquid mass, which contains, as Wallerius says, either native silver, or some fluid substance capable of producing it. Mr Cronstedt mentions, in the Swedish Memoirs, a water flowing through a mine in Norway containing silver. Another instance is also mentioned of a silver gubr, in the Att. Brad. Upsal. 1720.

8. Mr Von Jull 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 assayed 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 assayed by the following processes, which are copied from Dr Mortimer's English

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

“Then have at hand the decimastral 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 through 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 assay-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 smoke 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 scoria. 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 scoria 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 dull or rough with grains interspersed here and there; it is a sign that the ore is not entirely turned into scoria. In this case, you must with a hammer strike off what is adherent to the hook, pulverize it, and with a laddle 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 above-mentioned 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 scoria 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 scoria, and received by the lead.

“When the scorification lasts longer than we mentioned, the lead at last turns to scoria 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 resist to the strength of the scoria long enough; so that the whole scorification may be brought to an end; which has afterwards this inconveniency, 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 scoria 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 glass or scoria: but when arsenic is predominant in the ore, the plumbeous part turns immediately into a very penetrating and very fusible glass, having a dissolving efficacy, unless the arsenic lies hidden in a white pyrites or cobalt. For this reason, the fixed part of the ore, which is no silver, is dissolved by that glass, melts, and assumes the form of scoria. 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 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 upon the absence of stones, pyrites, &c. it is easy to see, that there are an infinite number of degrees of flexibility 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 scorification 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 in their nature refractory, being eroded during their scorification, 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 unscorified 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 scorification of these earthy 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 docimal 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 scorification 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 scorification 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 scorias themselves which are already subduced 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 scorification 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 scorias that grow clammy retain something of the metal; which if you suspect, pound the scorias 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 difficultly 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 calces: if you pour carelessly 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, glass 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 glass of lead mixed with the ore: but if you think that your glass of lead is not sufficiently fusible, you may add to it litharge melted first, and then pounded into a fine powder.

"As this scorification 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 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 cupelling 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 cupelling, 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"

“Break your ore into a rough powder, and put a centner of it into the test: put upon this another test 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-test; 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 test, 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 subtle powder, and grind it together with an equal weight of glass of lead; and, finally, scorify the whole collected ore in the same test 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 dissolved from it without a considerable destruction of the lead. The white arsenical pyrites turn also a great quantity of lead into glass, 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 subtle 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 cappel under the muffle; roast it well first, and then put into it sixteen 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 up in, and diminish the fire immediately, in the same manner as if you would make a scorification in a test, but in a lesser time. The small paper, which turns presently to ashes, goes off itself, and does not sensibly increase the mass of the scorias. The ore proceeding therefrom is cast on the border, and turns to scorias very soon. Increase the fire again immediately, and, at the same time, put another portion of the ore into the cappel, 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 cappel. If you deduct from it the bead 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 cappels.—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 cappel 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 their dissolution by litharge; and which being on this account thrown on the border, are not sufficiently dissolved; because the litharge fleas away soon into the cappel. 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 as much. Add besides glass gall and common salt, both very dry, and enough, that when the whole is melted, the salts may swim at top at the height of about half an inch.

“Put the crucible thus loaded into a wind-furnace; shut it close with a tile; put coals round it, but not higher than the upper border of the crucible. Then light them with burning coals, and increase the fire till the whole melts very thin, which will be done by a middling fire, maintained always equal, and never greater; leave it thus for about one quarter of an hour, that the scorification may be perfectly made. Take off the tile and stir the mass with an iron wire, and a little after pour it out into the mould. When the regulus is cleaned from scorias, try it in a test by coppelling it.

“Remarks. The scorification of any ore whatever, or of any body fetched out of ores, may indeed be

be made by this apparatus, as well as in a test under a muffle: but it serves chiefly to the end that a greater quantity of metal may be melted from it with profit. For you may put many common pounds of it at one single time into the crucible; but then you need not observe the proportion of lead prescribed in the foregoing process; nay, a quantity of lead two or three times less is sufficient, according to the different qualities of the object. But the mafs will certainly be spilt, unless you choose a very good crucible; for there is no vessel charged with litharge that can bear a strong fire having a draught of wind, without giving way through it to the litharge.

"You add glass-gall and common salt, that they may forward the scoriification, by swimming at top; for the refractory scoria rejected by the litharge, and adhering between this and the salts that swim at top, is soon brought to a flux, and the precipitation of the silver is thereby accelerated. They also hinder in a manner a small burning coal fallen into the crucible, from setting the litharge a boiling, which troubles the operation; for the litharge or glass of lead, especially that which is made without any addition, so soon as the phlogiston gets into it, rises into a foamy mafs, consisting of a multitude of small bubbles very difficult to be confined, unless the phlogiston be entirely consumed, and the litharge reduced to lead, which sometimes rises above the border of the vessel."

The corncoat 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-Index.

P R O C E S S VII.

Silver and gold may be extracted from their ores by mercury.

A new method of extracting the precious metals by means of amalgamation with mercury has lately been introduced into Germany. The attraction between these has indeed been known from the most remote antiquity: Vitruvius informs us, that by this means gold might be recovered from embroidery and old cloaths; and Pliny mentions the gilding of bras and other metals by the same means. From time immemorial mercury has been made use of in the streaming for gold, in order to purify and collect together the gold dust which is dispersed in the sands; and almost all nations who practise this use the same process. The gold sand, after being washed, is triturated with quicksilver, and the superfluous metal separated by draining through leather. By the miners it was used in a similar manner; the stones containing gold being first pounded and then triturated in mills along with the mercury. But it was soon found, that in these mills there was a large quantity left behind in the residuum, so that it was necessary to subject what was left to the action of fire; on which account the mills were deemed unnecessary, and are now almost every where disused. The process of extracting gold and silver by amalgamation, however, was looked upon to be essentially deficient, by reason of an opinion which prevailed among the chemists, that mercury could not dissolve either of these metals except in their pure and perfect state; whence it was supposed, that a great quantity

which fire could have extracted was left by the mercury. This opinion was supported by the most celebrated metallurgists, as Schlutter, Gellert, Wallerius, and Kramer; whence it became generally believed, that amalgamation would never answer in great operations. But of late Baron Inigo Born has not only demonstrated that this can be done to great advantage, but has actually introduced it, notwithstanding that some difficulties were thrown in his way. The following is an account of the methods which have been practised for separating gold and silver from their ores by means of quicksilver.

This process was introduced into some of the mines of Mexico in 1566 by Don Pedro Fernandez de Velasco, and in 1571 into some of those of Peru by the same person; and from thence it quickly spread thro' all the mines in the south and north-east parts of America, inasmuch that it is almost the only method used in that part of the world for extracting these metals. The richer ores, however, are purified by fusion with lead; and our author informs us, that formerly the poorer kinds of ores were certainly thrown away, and when the method of amalgamation was introduced into Peru, the old barrows were searched for the ores which had been rejected as useless, but were now put to the quicksilver.

In the year 1588, Don Juan de Corduba, a Spaniard, applied to the court of Vienna, proposing to extract silver from its ores, whether poor or rich, by mercury, and in a short space of time. He made some experiments upon different kinds of ore, which on a small scale succeeded very well, but on attempting it with 20 quintals of it he failed; and as Lazarus Erker, who was employed to give in a report concerning it, disapproved of the method, it was not pursued any farther. The reasons alleged in Baron Born's book for this failure are, that he did not calcine his ore; that he did not use any salt; and that the weather was too cold; though this last circumstance might have been remedied had Corduba attended to it.

Another Latin and anonymous account of the mode of amalgamation is preserved among the records of the aulic chamber. It is directed to the emperor, but the year in which it was written is not mentioned. According to the account given by the author of this paper, he had examined the mines of Guatemala in New Spain, and made some useful regulations for them. He directs the ore to be calcined in furnaces like lime-kilns, the fire being kept up according to the nature of the ores, after which they are to be reduced to powder in mills or stamps. The pulverised matter is then passed through fine iron sieves, and put into earthen or copper vessels by 10 or 20 quintals at a time; more or less salt being mixed with it according to circumstances. The light-coloured ore requires 50 lb. to every thousand, and the darker somewhat more. To this mixture are to be added five pounds of dry tartar, two pounds of pulverized horn, and three pounds of brick-dust. Some kinds of ores require but a small quantity of these additions.

After the mixtures are put into the boilers, as much water is added as will make the whole of the consistency of pale moderately thick; the vessels must be exposed to sunshine, or kept in a place warmed artificially, adding more water when the matter begins to dry; and it must

must be stirred up three or four times a-day. At the expiration of three or four days, various colours appear upon the surface. After this 15 lb. of brimstone is to be added to every thousand pounds of ore, and the whole worked over again; but this addition is by the baron considered as quite superfluous. Lastly, 100 lb. or less of quicksilver is added, according to the nature of the ore; the whole mass is carefully worked over, and left at rest for 10 hours. A fire must next be kindled under the boiler, and the matter it contains triturated or stirred for two days together; keeping it always sufficiently diluted by a proportionable quantity of water. It is, lastly, allowed to rest for 12 hours, and then dried.

When this operation is successfully performed, if the ores be rich, particles of amalgam will be seen in it: these are collected, washed out, and kept for further use, the leavings being carried to a place fit for washing over. This place ought to be on the slope of an hill, where a kind of pit is dug out and lined with brick and mortar, and ought to be large enough to contain 25 quintals. A stream of water is then made to run upon it, and the matter stirred without intermission. The superfluous water runs over the rim of the pit, and carries off the lighter stony and earthy particles, the heavy amalgam remaining at bottom. This is then to be mixed with the small clots already mentioned, which were taken out of the mass originally, and pressed through a cloth made of hemp or coarse linen. The quicksilver, which comes through clean, is kept for farther use; the remainder distilled off in proper vessels, and the remaining silver melted into ingots. By this method it is said that even very poor ores are worked to advantage, the expence being very moderate.

The following method of extracting gold from its ores is very much recommended by our author: "The auriferous sand, which contains gold grains and gold-dust, is concentrated by washing; and without any calcination goes to the above mentioned washing-pit, which for this purpose need not be so large. On its upper part is fixed a square launder, about 12 feet long, covered in the bottom with a woollen cloth, in order to retain any part of the gold-dust which may be carried over with the water and stuff gently stirred in the pit. When the water carries off no more mud, but runs clear, the farther supply is to be stopped; the water in the pit is pumped or taken out with buckets; the coarser sand in the bottom is separated or scraped off by hands; and the finer heaviest sand at the bottom is mixed with quicksilver. Then it is squeezed through a piece of cloth; the quicksilver comes off without any gold, which separated from the sand remains as an amalgam, and is pure after the remaining quicksilver has been evaporated. The sand and heavier dust remaining on the launder is washed and treated in the same manner.

"The auriferous ores and loadstones, however, which rise from different mines, are calcined like silver ores, more or less as the nature of their matrixes will direct. Then they are ground and sifted; and the auriferous stuff, thus prepared, is put into heaps, exposed to the sunshine, and worked and turned about for three or four days. It requires no salt. Afterwards

sulphur, and at last quicksilver, are added and mixed with it. There is no occasion for fire under the vessel in which it is triturated, except in winter; and two days after, though not dried, it is immediately carried to the washing-pit, and treated like the amalgam of silver.

"This method of extracting gold and silver is so certain and safe, that when other methods of amalgamation extract only one ounce of gold and silver, this produces three or four from the poorest ores in a shorter time and with less expence."

P. Joseph Acollatells us, that at Potosi 6000 or 7000 quintals of quicksilver are annually consumed in the dressing of the ore, not to mention what is recovered from the leavings of the first washing. These leavings, called lamas, are burnt in particular furnaces in order to extract the remaining quicksilver; and there are upwards of 50 such furnaces near Potosi and Tarapaja. The ore refined there amounts, according to the best information, to the immense quantity of 300,000 quintals. Only about 2000 quintals of the quicksilver are recovered, which shows a loss of about two pounds of quicksilver on every quintal of ore. The ores are of different natures, and in proportion to the silver they contain require more or less quicksilver. That which contains most, requires naturally the greatest quantity of quicksilver; though some of the workmen pretend that there is a kind which contains very little silver, and yet requires a great deal of mercury: but whether this be owing to the ignorance of the workmen, or to the mercury being absorbed by some other matter, is not generally known. The ore is first pulverised in mills, and then passed through iron or brass sieves. The mills will grind, when properly regulated, 30 quintals in the space of 24 hours. The pulverised matter is put into heaps in the open air, and salt is mixed with it in the proportion of 5 to 50 quintals of the ore, in order to macerate and cleanse it of its impurities, that the quicksilver may the more readily amalgamate with the metal. Upon these heaps, and while they are stirring, the quicksilver is pressed through a cloth. Before the invention of fire-places, the ore was repeatedly kneaded with quicksilver in wooden troughs, and formed into large round masses, which were left in that form for two days; after which they were worked again, until the metals appeared to be embodied together, which took from 9 to 20 days; but it was afterwards found that heat assisted the operation so far, that by means of proper ovens the same might be accomplished in five or six days. When the quicksilver has taken up the silver, and wholly separated it from its matrix the lead and the copper, the ovens are opened, the matter is taken out, and the quicksilver expelled and recovered in the following manner. The mixture is put into water-troughs, and stirred therein by means of mills and water-wheels, by which the earthy and extraneous particles are washed away, and the amalgam settles at the bottom. The sediment looks like sand. It is further washed over in flat plates, and perfectly cleansed; what goes off with the water is collected for further use under the name of relater. When the amalgam is become clean and bright by this method, it is put into a cloth and squeezed out. The uncombined quicksilver

silver runs off, and the remaining body of amalgam contains five parts of quicksilver and one of solid metal. It is made into masses named pinnas, having the form of a sugar loaf, hollow within, and weighing about 100 pounds. They are exposed to a strong fire in order to expel the quicksilver, after being put into pots covered with earthen heads. The silver still appears in the form of amalgam, but is reduced to one sixth of the former weight. Its texture is spongy, and the quality of the metal so fine, that the silversmiths cannot work it, neither can it be formed into coin, without an alloy. Baron Born observes, however, that it is only cold amalgamation which produces silver of such uncommon fineness; by hot amalgamation it is generally alloyed with copper, which cannot be parted from it without cupellation.

The most circumstantial account of the amalgamation of silver ore is that of Alonzo Barba. He divides the ores into two classes: 1. those which are best treated by fire and fusion; and, 2. such as are most fit for amalgamation. Those called pacos and tacana, may be amalgamated; but that none of their richer contents may be lost, it will be best to combine them with lead, and proceed by cupellation. The former of these ores has no lustre or brightness. It is said to be of a reddish-yellow, soft and friable; seldom rich in silver, and mostly valuable on account of its being easily got from the mine. Tacana is a rich silver ore, of a black colour, sometimes of a grey or of an ash-colour; or a brown, rich, silvery earth. 3. The plomo is too rich for pulverization and amalgamation, and is therefore simply melted down with the tacana. This seems to be the same with the horn-silver ore; and is described as almost entirely consisting of native silver, of a black, grey, or greenish-white colour. Barba says that they found at Potosi some plomo of a cinnamon colour, which they had not seen any where else; but Baron Born thinks that here he has mistaken the red silver ore for another species. Frezier asserts, that in what he calls the plomo romco, the native silver appears upon rubbing or scratching it, and that it gives white and very pure silver by simple fusion without any amalgamation. In the imperial cabinet at Vienna, there is a specimen weighing about a pound, of black horn silver ore from Potosi, on the polished surface of which the virgin silver appears very plainly. 4. The machacado (virgin silver or gold grown in the matrix in the form of wire or hair), is amalgated in the mortar. 5. The foroches (lead ores containing silver), are melted along with the rositer and conchiso, two kinds of red silver ore. 6. The negrillos (grey copper and white silver ore) may be refined by amalgamation, though they are more fit for fire.

Besides this classification into such as are fit for fire, and those for amalgamation, the ores require further to be sorted into such as require the addition of particular substances for their amalgamation. Vitriol is generally hurtful, especially when salt is added to the vitriolic ores; and it requires the addition of iron, tin, lead, and lime, in order to counteract its effects; but in some cases it is of service, and promotes amalgamation. The calcination of vitriolic ores is of no service, but rather the contrary, as it disengages the vitriol, and brings on a vitriolic efflorescence. It may, however, be separated by washing till the water comes

off tasteless and sweet. The amalgamation is disturbed by sulphur, bitumen, and antimony, only by the smoothness and needle-like figure of the particles, which reduce the quicksilver to a kind of dust. The ores mixed with these always run into reguli, and must therefore be put into a strong calcining fire; if melted without calcination, they would run entirely into dross and scoria.

The finer the ores are pounded so much the better; and after putting the powder thro' a fine sieve, the coarser part goes again to the mill: they ought to be previously burnt, in order to assist the operation of grinding. The best method of obtaining fine powder is by washing over; but as this is very apt to pack and turn clammy, it ought to be mixed with sand.

The ores are known to be sufficiently calcined by their change of colour and loss of brightness. Barba tells us, that all bright ores must be calcined, but with great care, that no vitriol may be disengaged, as that proves injurious to the amalgamation; but Baron Born says, that one of the greatest objects in the calcination of the Hungarian ores is to decompose the sulphur into vitriol, as promoting the decomposition of the salt. The amalgamation is likewise promoted by burning and calcination, in as far as it promotes the pulverization of the ore, and assists the action of the quicksilver; but it is chiefly useful in the black and grey silver ores. It can only be determined by circumstances whether it be better to pulverize the ores before or after calcination. Their value is best known by pounding them previous to calcination. The stuff must be constantly stirred during the time it is calcining, and some powder taken from the mass to be tried with quicksilver and salt. The thickening of the quicksilver, and the grain of the stuff, show what additions are necessary, or whether the calcination be completed or not. When ores are calcined in lumps, the fire does not act equally upon all their parts; though this method is attended with the advantage of losing much less dust, as well as saving the expence of stamps and mills.

Ores cannot be calcined in reverberatory furnaces, as the heat would run it together, and part of the metals themselves would be carried off by the strong current of air and the violent smoke. Barba recommends a furnace of an oblong square figure, with three vaults over each other; the fire is put into the lowermost, and the ore into the two upper ones. The heat circulates by means of lateral openings in the walls, and is let out on the back without a flue. The heat is graduated by registers and dampers on the outside.—Whatever kind of furnace, however, is used, some of the ore will have clotted, and must therefore be ground to a fine powder; but to prevent as much as possible these inconveniences, the hard ores ought to be calcined before they go to the mill, and the soft ones after, but with proper additions. The iron ores, which resist the fire longer, are calcined with an addition of sulphur, or of sulphureous and antimonial matter, proportioned to the iron they contain; but sulphureous and antimonial ores require to be calcined with the scoria of iron. Arsenical ores, or those mixed with orpiment and sandarac, are calcined with lead glance; and those mixed with white or black bitumen, must be calcined with iron scoria or pounded limestone.

Amalgamation of Gold and Silver Ores. The impurities of ores, and the additions proper to be made to them, are determined by pounding them coarsely, and throwing them upon a heated plate of iron. If the smoke be white or black, it shows a mixture of bitumen of these colours; if yellow, it shows orpiment; if red, sandarach; if greenish-yellow, sulphur.

Salt ought not to be used in the calcination of ores, as it would calcine the silver; and the duration of the calcining must be determined by the change of colour which the ores undergo by calcination by themselves, and the brightness they assume by trituration with quicksilver. It is also a mark of sufficient calcination when antimonial and sulphureous ores no longer send out a disagreeable smoke; if the thick and black smoke of bituminous ores become white; and if the silver in the stuff appears in white glittering sparks. Vitriolic ores may also be calcined in the same manner; but they require a longer time with the addition of alum and salt: they, however, require no farther addition in the subsequent operations; and in the course of four days all their silver will be taken up by the quicksilver. Less quicksilver will also be lost; for as there is no occasion for the frequent turning and working of the heap, a very small part of it only can be turned into useless dust. Vitriolic ores ought always to be well washed with water before they are calcined; and if there is still a suspicion of their being vitriolic, they must be tried by quicksilver: if it takes a lead colour, the stuff must be washed till iron put into it no longer takes a copper colour. The lixivium is kept as an useful addition to some ores.

Amalgamation, according to Alonso Barba's method, is performed in three ways, viz. in heaps or caxons, in the boiler, and in mortars.

1. In heaps. Before the operation takes place in the large way, an essay is made of three or four pounds of the fine sifted powder taken from the general quantity; and according to the produce of this he calculates that of the whole. He tries it also with quicksilver, to know perfectly the method he is to follow, and the additions that are to be made. In this essay the following method is adopted: 1. The matter is elixated, to extract the vitriol if there be any. 2. One pound of the lixiviated matter is tried with quicksilver and salt, carefully observing the colour and its change. If the quicksilver assumes the appearance of silver filings, and these quicksilver flakes become thinner and thinner, it proves that the amalgamation goes on successfully, and that there is no occasion for any addition. The whole is stirred from time to time, till the quicksilver seems to diminish, and recover its natural form, but without dividing into small globules; after which the matter is to be washed, as all the silver is by that time completely taken up. The ores of Verenguela de Pacajes are treated only with quicksilver and salt, and yet yield their full produce.

When the ore turns black, iron is added; when of a light lead-colour, tin; if a dark lead-colour, lead; and if of a yellowish or gold-colour, lime. The three first of these are styled by Baron Born, "very idle and useless additions."—The ore frequently divides into small and powdery globules, in consequence of the hardness of the minerals, or from too much stir-

ring; but this may be prevented by calcination before it is reduced to powder, or by less stirring. In a great many operations, however, this quicksilver dust can scarcely be avoided. It serves the workmen as an index of the progress they have made, or sometimes as a direction how to operate; and has different names according to the cause by which it is produced; as quicksilver dust, the dust of addition, and silver dust. The first of these arises simply from too great division, and is white without any quickness, scarcely moving when the matter is stirred with water: it sticks somewhat to the bottom, and runs into globules when broken between the fingers. The second is produced by the amalgam of lead and tin; and, when pressed between the fingers, unites with the quicksilver which had begun to combine with the silver. The third comes from the amalgam of silver: it sinks towards the coarser stuff on the bottom, and floats about in flakes of different sizes; turning into an amalgam when rubbed or pressed between the fingers. All of these are produced chiefly when there are lead, marcasite, and iron ores in the mixture; or by vitriol of copper, which is particularly productive of this minute division of the quicksilver. They are produced also by too plentiful an addition of salt, which thickens the water, and prevents the descent of the particles of quicksilver.

According to the produce of the essay the large heap is regulated. It is first wetted with water, and mixed with the due proportion of salt; but at the beginning only one third of the quicksilver and one half of the lead and tin are added. It is turned over once every day during the two first days, because the quicksilver being then uncombined would be apt to be driven off in small globules, and a great waste occasioned. The heap is likewise too much cooled by the addition of too much quicksilver at once; so that it is better to put it gradually to the other matters. The lead and tin are always thrown into the heap along with the quicksilver; but too much of either is hurtful, by deadening the quicksilver, and preventing the amalgamation. All these additions, however, must vary according to circumstances; observing that the quantities added must always be less and less in proportion as the amalgam advances to perfection. The matter should be kept rather dry than otherwise, and two parts of amalgam be in the heap to one of fluid quicksilver. Too great an abundance of this fluid mass is very detrimental, on account of the quantity of quicksilver dust which it occasions; and if the other ingredients are accidentally washed, the dust of addition will be changed into quicksilver dust; which having very little weight, will be poured off along with the water. But when lime is added, the whole must be mixed at once, and the entire heap turned over two or three days, till the quicksilver be added. Too much lime prevents the union of the two metals, and is an inconvenience which cannot be remedied.

The heaps are frequently turned and worked over after the first two days, which is attended with several advantages; as that the quicksilver is thus heated, more thoroughly mixed with the matter, and the silver is purified by the frequent rubbing. The heaps, however, are subject to various accidents, owing to

the difference between the various kinds of ores, which cannot always be exactly known. When the quicksilver is deadened by too large an addition of lead, iron, tin, or lime, it loses its oval form, and assumes a vermicular one: if shaken in a glass, or other vessel, without water, it adheres to the sides in threads, and is unfit for taking up the silver. The best remedy is vitriol of copper, or the lixivium of vitriolic ores already mentioned: or powder of copper may be thrown into the heap. All additions of this kind, however, must be made very cautiously, and in consequence of experiments made by small assays, which determine the quantity of materials to be used. When the heaps have too much vitriol, without any correcting ingredient, the quicksilver has a leaden colour, and the smaller particles assume a spherical form. Iron might be added to absorb the too great quantity of vitriolic acid; but there is no certain rule for the proportion to be added, so that it must be determined by experiment.

When the quicksilver appears, on turning the heap, like a bunch of grapes, this shows an excess of salt, which prevents the quicksilver from combining with the silver: it is to be remedied by the addition of some coarse stuff which cleanses the fluid. Some add ashes; but the best and most natural remedy is alum, which is found at Potosi in abundance, and whitens the silver. If the heap be not turned equally, or the quicksilver added at a proper time, or if the silver do not unite with it, some of the silver will appear in a dry form, and lie on the coarser stuff like a cobweb; and if not skimmed off in time, will be carried away by the washing water. To collect this dry silver, and the finest quicksilver dust, some silver amalgama is pressed upon it through a chamois skin; and the whole is once more turned and worked over. The frequent turning, the heat of the climate and season, as well as the fermentation produced in the heap by the vitriol and other additions, all promote the amalgamation; but cold, neglect of stirring, and the quicksilver assuming a lead-colour, are against it. It is, however, very difficult to determine the maturity of the heap, when all the silver is taken up, and the matter may go to the washing; though great inconveniences attend an ignorance in this respect. If washed too soon, some silver is left in the leavings; and if worked too long, there is a loss of quicksilver as well as time and labour. The difficulties attending the knowledge of this important point, are by our author enumerated as follow: "The heap may appear not to require any additional quicksilver; the silver dust may appear to be completely collected; that of quicksilver may begin to make its appearance; the amalgama may begin to appear pure, and to show a gold-colour; and yet silver may remain in the leavings. The most infallible test of the maturity of the heap, is the assay of the triturated stuff by fire. If no silver is produced thereby, then so much quicksilver is thrown into the heap, that it may contain three parts of amalgama to two of silver, or at least one part of quicksilver to two of amalgama. By this additional fresh quicksilver, all the dust of quicksilver, and the dry and uncombined quicksilver, are perfectly collected; the amalgam is the heavier for it, and sinks the more readily to the bottom when brought to the washing-tub.—

Some clean quicksilver is also put into the bottom of this tub; the inside of which must be lined with iron plate well cleaned, and rubbed with quicksilver;" (though this last operation seems to be quite superfluous, as mercury will not in the least unite with iron by rubbing.) "The stuff brought into the tub must be diluted with a great quantity of water, and be stirred round with a pestle lined with iron-plate in such a manner that it may turn round six times one way and six times the other, always touching the bottom; the unconnected bodies of quicksilver and amalgam are thereby to meet, to combine, and to fall to the bottom. To recover the salt which had been mixed with the heap, the water must be evaporated;" but the Baron observes, that at Shemnitz no salt is recoverable from the lixivium; and if any be recovered by the Spaniards, it only shows that they add too much, and that part of the remainder is undecomposed by the vitriolic acid. The quicksilver is separated from the amalgama much in the same way as already described.

2. Amalgamation by boiling, was accidentally discovered by Barba, in an attempt to fix quicksilver.—On mixing silver ore finely powdered with quicksilver, and boiling it with water in a copper vessel, he found that the metals readily united; and thus having discovered a shorter method of amalgamation, he gradually improved and introduced it into practice in Peru. In this operation the boilers must be of copper, earthen or other vessels being found not to answer: the copper also must be pure, because the quicksilver would dissolve the metals with which it is alloyed. They must be in the shape of inverted cones, and flat-bottomed. The under part has a rim of six or eight inches high and half an inch broad, all beat of one piece. Other copper plates are fixed in the inside with copper nails; and care must be taken that it be water-tight, that no quicksilver may run off; and for the better security, the inside of the boiler may be lined with lime and ox-blood. The boilers may be of any magnitude; their upper parts being surrounded with iron rings with strong handles, into which a cross board is wedged. In the middle of this board is a hole for the spindle to move in. The spindle is of light wood, and moves on a brass pivot in the bottom. It has four wooden wings, with three or four perpendicular bars, also of wood; the farthest from the spindle being the shortest; the nearest so long as to sweep the bottom. It is turned by a moveable handle on the upper end.

These boilers are put into an oblong furnace, capable of holding 10 of them; the fire-place being in the middle, and the flame and smoke passing under the boilers, and going out on both ends of the furnace by two chimnies. The fire being lighted, first the water, then the fine stuff, and at last the quicksilver, is put in; observing always that the bottom be fully covered with quicksilver. The water must always be kept boiling, otherwise the operation may be interrupted or become tedious: on account of the evaporation, the boilers must be supplied with a quantity of water, in small quantities at a time, that the boiling be not checked. The stuff must be proportioned to the size of the boiler: if too little be put in, the amalgamation goes on too slowly; while too much would

Amalgamation of Gold and Silver Ores. not allow the mass to be thick enough, or to boil with sufficient freedom. Some of the amalgam is to be taken out from time to time with a long laddle, and the progress of the operation is judged of by the colour. The assay of the stuff determines whether all the silver be taken out of it in this manner. Some quicksilver is then thrown upon the surface of a sample of the boiled stuff, and worked round with it in a vessel two or three times. If the quicksilver rises and takes up some of the stuff, some silver remains; if not, the whole is taken up. Then the fire is stopped, the spindle is taken out, and the water and stuff let off. The coarser matter on the quicksilver may at all events be washed in cold water, and go once more to the mill. Almost the whole of the silver amalgama lies upon the surface of the quicksilver, immediately under the stuff, sometimes four or five fingers thick; the fire under the boilers preventing the silver from uniting with the quicksilver in the bottom. This metal, when poured off, must be pressed and treated in the usual manner.

The advantages attending this method are, that the heat promotes the union of the metals, while the boiling of the water and stirring of the mixture with the spindle bring them more frequently in contact with each other in a quarter of an hour, than they would be in several days in the common method; by which means the whole process is finished in about 24 hours. Less quicksilver is also lost by it; for being always covered with water, it cannot evaporate; and in well managed and successful operations, no quicksilver dust is produced: but the greatest recommendation is, that it is not attended with any loss of silver, so that even the poorest ores will yield all that they contain. Barba looks upon the profit of this method above the other to amount to 25 dollars for every heap of 50 quintals; even making allowance for the coals. The only objections are, that both silver and copper are apt to be lost by the corrosion of the copper-boilers: but if the copper be pure, there is no great reason to be apprehensive of any thing of this kind; or, at all events, the bottom of the boiler, which is constantly exposed to the action of the quicksilver, may be secured by a copper ring three or four inches high; and the bottom itself may be secured in the same manner; so that when corroded they may be changed for new ones: or the boilers may be paved or lined with varnishes or mortars of different kinds; which will as effectually prevent any loss. While the whole is boiling, the quicksilver violently seizes on the other metal; by which means the amalgam is filled with many heterogeneous particles. These are separated by washing in quicksilver, on the surface of which they swim like scoria, and may easily be taken off, till the quicksilver shows its usual brightness; and as this cannot be done without taking off some of the metals also, the scum may be reserved for the next operation. The advantage of amalgamation by boiling chiefly appears in this, that heaps, in which by too large additions, the quicksilver has been totally dissolved so as to disappear, may be easily cured by boiling them, in iron or copper vessels with bits of iron; for then the quicksilver appears again in its proper metallic form and brightness.

3. Amalgamation in mortars. It is difficult to pro-

Amalgamation of Gold and Silver Ores. cure the full produce from ores which contain native gold and silver either in the form of hair or wire, or in larger lumps and nodules. These cannot be completely pounded, nor can they be amalgamated; for the mercury will not dissolve the large particles of gold and silver; and when they are treated by fire, the stubborn nature of their matrices occasions a great loss of metal. The following method of treating them in a mortar was discovered by a Franciscan friar.

A round conical hole is cut in a hard stone, half a foot in diameter at top, of an equal depth, and sloping into a truncated, or rather obtuse and nearly flat bottom, of about four inches in diameter. Some quicksilver is poured into it, together with a proportional quantity of small bits of the native metal or ore; after which they are triturated with an iron pestle. By this violent trituration, the gold and silver combine with the quicksilver; and the finer, lighter stuff of red silver ore and other silver calces, which are generally found with native silver, runs off by means of a small launder and current of water. It is not, however, suffered to run away, but is left to settle for common amalgamation.

Mortars of the dimensions above described being too small for any considerable quantity of ore, Barba proposes to substitute in their place larger stones of a concave figure, with vertical grinders, as in oil-mills; or common horizontal and parallel grinders of the grist-mill. The ore and quicksilver are put between these stones, with a small stream of water; which, running off, will carry away the lighter stuff, whilst the gold and silver will remain at the bottom, taken up by the quicksilver.

There are several other methods of amalgamation described in Baron Born's work, as practised by the Spaniards of South America: but as all of them agree in the most material circumstances with those already mentioned, we shall only farther take notice of that invented by the Baron himself, and by him lately introduced at Schemnitz in Lower Hungary.

This method is very pompously related, and at great length, in his work on the subject. His theory contains the following particulars:

1. Quicksilver has a tendency to unite with other metals and femimetals, and to quicken or animate them according to certain laws of affinity which are determined by experience.

2. It unites with gold, silver, copper, tin, lead, bismuth, and zinc, without heat; but with other metals and femimetals it will not unite but in a state of fusion. It unites with tin and bismuth more easily than with gold and silver; and with these more readily than with copper.

3. The union of quicksilver with other metals is promoted by heat.

4. This union is also greatly promoted by mechanical comminution.

5. No amalgamation, or only a very slow and partial one, will take place, if the surface of the quicksilver or metallic particles be covered with a coat of heterogeneous matter; which happens chiefly in the amalgamation of ores where the fine particles of the metal are involved in sulphur and arsenic.

6. Hence it is necessary to free the noble metals

from the stony matter which surrounds them, and to reduce the baser ones from their calciform to a metallic state, before they can be amalgamated with success.

7. Particles of gold and silver may be freed from the stony matters which involve them by trituration; and from sulphur and arsenic, by calcination.

8. In calcination, some part of the sulphur is destroyed, and vitriolic acid disengaged; which, combining with the earthy matters contained in the ore, as well as the calces of the baser metals mixed with it, still leave the gold and silver involved: whence it is necessary to employ such chemical agents as will free the particles of these metals from their heterogeneous coat, and keep their surface as well as that of the quicksilver clean, without acting either upon the gold or silver. These agents are principally the mineral acids, which act variously according to their different natures. The marine acid is most efficacious for gold or silver ores; but it would be exceedingly expensive to use it in its proper form, so that it is necessary to take some method of expelling it extemporaneously from common salt by means of oil of vitriol.

9. The calcined ore, when pulverised, must be wetted with water, for the purpose of dissolving the disengaged vitriolic acid and the earthy and metallic neutral salts, which are produced by it in proportion to the sulphur contained in the ore. Vitriol is produced by calcination only in this proportion; and hence if the ore does not naturally contain a sufficiency of sulphur to produce vitriol for the purpose of decomposition, it will be necessary to add something of this kind. Vitriol of copper or of iron will answer, but the former is preferable. If, therefore, the pulverised ore, which has once gone through the process of amalgamation, should still appear to contain gold or silver, mix it with some additional vitriol and common salt; leave it for some time to macerate by itself; and, at a second trituration with quicksilver, a considerable quantity of silver will be found in the amalgama which had not been extracted in the first, though common salt had been used in it. Thus the common salt may be decomposed in the wet way.

10. To decompose the common salt in the dry way, the ore must be properly stamped and sifted, and the mixtures made up with a proportional quantity of pulverised common or rock salt, and then undergo an adequate calcination in an open fire. Thus the common salt will be decomposed according to the nature of the mixture; either by the vitriolic acid produced by the decomposition of the sulphur, or otherwise.—The muriatic acid, thus disengaged, dissolves the heterogeneous particles in which the metals are involved, and allows the quicksilver to act upon them much more effectually than it could have been enabled to do by any mechanical comminution; and this the more so as it takes up even those particles of dephlogisticated iron upon which the other acids are incapable of acting.

11. The calcination and corrosion of the baser metals is indispensably necessary, especially in a natural combination of gold and copper; for the affinity of these two is so strong, that unless the latter be perfectly calcined, or otherwise removed, very little of the

gold can be extracted. The separation will also be promoted by the addition of sulphureous substances.

From these considerations, the Baron lays down the following rules concerning amalgamation.

"1. The ores and mixtures previous to their amalgamation must be mechanically comminuted, and reduced to a fine powder, by stamping, grinding, and sifting, that the surfaces of the particles, and their points of contact, may be increased and multiplied.

"2. This powder must be calcined, that, besides the pure particles of the nobler metals, those which are disguised in the ore may be disengaged and laid bare by desulphuration and calcination.

"3. If before its calcination no common salt was added, it must be added afterwards; then it must be triturated with a proportionate quantity of quicksilver and water, long enough, and in such a manner, that the quicksilver, by an uninterrupted motion of the whole mass, may come into repeated contact with the disengaged gold and silver particles, and take them up.

"4. As much depends on the just-mentioned proportions, the inspector, director, or master of the work, must be well acquainted with the elective attraction of bodies, that forming a just idea of, and judgment on, their different mechanical or chemical decomposition and combination, he may remedy and remove such unoward difficulties and impediments in the process as may, and will sometimes, prevent its full success."

The various steps by which the metals are extracted from their ores, according to the Baron's method, are, 1. Stamping, grinding, and sifting. 2. Calcination; after which the grinding and sifting must be repeated. 3. Trituration. 4. Washing of the residuum. 5. Elutriation of the amalgama. 6. Heating of the same. 7. Distillation of the quicksilver pressed from the amalgam. 8. Refining of the heated amalgam. 9. Extracting from the residua such parts of the noble metals as may still be contained in them.

1. Stamping, grinding, and sifting. The Baron recommends dry-stamps and mills for this purpose; as wet-stamps, he says, "would bring on great loss of silver, and expensive contrivances to prevent or recover it." On the other hand, E. Raspe, the translator of his work, says, that "late experiments have proved so much in favour of the wet-stamps, that they have actually been adopted as great improvements."

The contents of the ores are accurately investigated by assays before any thing is done in the large way. The ores are delivered to the respective mills; the smaller ores are passed over a brass sieve, the meshes of which are about one-tenth of an inch wide, that the finer particles may be separated and not sent to the stamps, which would occasion some waste, especially in the dry way. The finer sand is sent directly to the mill, and the big lumps to the stamp. Each box, or set of stamps, has three stamp-heads, weighing 40 or 54 pounds, the sole being of cast-iron. The matter is every now and then wetted with water to prevent the finer parts from flying off. When the ore is sufficiently beat in the stamps, it is afterwards sifted, and the coarse part returned to the stamp. When the coarsest part is reduced in this manner to the size of coarse sand, it is sent to the mill; the running stone of which

Amalgamation of Gold and Silver Ores.

which must be kept close in a box, and nothing left open but the admission-funnel. The millstones are a kind of porphyry, and the sieves of brass-wire.

2. Calcination. The ore being reduced to a sufficient degree of fineness, is next carried to the calcining furnace; previous to which it is again to be tried by assay, and to have the proper additions according to its nature. When the furnace is properly heated, the whole quantity of ore destined to one furnace, about 30 quintals, is brought up to the top by wheel-barrows; and being spread as even as may be, the proper quantity of salt and lime is fitted over it, and the whole turned with crooks and rakes till it be perfectly mixed. The calcination is then performed in the following manner: The back-door being carefully shut, eight hundred weight of the matter, prepared as already mentioned, is let down through a funnel upon the upper hearth. Here it is again to be spread and allowed to dry before it is put down on the lower hearth; and as soon as this is done, another quantity is put upon the upper hearth, that the two operations may regularly succeed each other.

Our author describes at great length all the minutiae of this operation: but, as he justly observes, "Experience and practice are, and must be, the best teachers; for there are many things which must be attended to, and which words and descriptions will hardly make intelligible." We shall therefore only observe, that the calcining furnace must be kept heated day and night: but while the ore is shovelled down from the upper to the lower hearth, the fire must be kept very moderate; and during the calcination it will be necessary to keep the matter constantly turning with iron rakes, the combs or teeth of which are from four to eight inches long.

The grinding and sifting after calcination is only necessary when the matter has run into hard indissoluble clots during the operation; and is performed in a grinding and sifting mill, which turns by water; but which it is unnecessary here to describe, as every possessor of mines would choose such mechanical contrivances as best suit his purpose.

3. Trituration, boiling, and amalgamation. After the ores have been properly calcined and pounded, the success of the amalgamation depends mostly on the proportions of quicksilver and water which are added to the stuff, and the construction of the stirring apparatus by which the whole is kept in constant motion and mutual contact. The lighter the stuff, the more voluminous and bulky it will prove, and consequently the gold and silver will be the more dispersed: in which case the quantity of quicksilver must be proportioned to the mass, that notwithstanding its constant gravitation towards the bottom it may the more frequently come into contact with the gold and silver. It acts in proportion to its bulk and surface. A larger quantity is therefore advisable, as it not only forms a larger surface on the bottom of the vessel, but comes likewise into contact with the gold and silver more frequently; nor is there any greater loss of quicksilver to be apprehended on that account. A larger proportion of fluid metal is in particular necessary when the matter is mixed with lead or antimony: for, by taking up the lead, it becomes proportionably less active and fit for the reception of gold and silver; and turning greasy

by the antimony, it must in the former case leave rich residua, and in the latter bring on greater loss. It is also determined by experience, that the excess of quicksilver never does any hurt, while too small a quantity never fails to be disadvantageous.

With regard to the construction of the boilers, it is needless to be particular, as those recommended by Alonso Barba seem to be very adequate to the purpose. Heat is required; but it is not necessary that the matter should boil, a moderate fire being sufficient for making the metals unite. Nor is there occasion for more water than what will make the matter liquid. The stirring apparatus is put in motion by the crank of a water wheel, and a horizontal rack with cogs; which, being properly fixed in a groove by cross-bars, slides forward and backward on brass rollers and casters. The cogs of this rack catch into those of the perpendicular trundle and spindle of the stirrers, which turn round twice by three and an half feet motion of the sliding rack. The whole moves quicker or slower in proportion to the box of water thrown upon the wheel; and the quicker motion of the rack produces of course a quicker turn and better trituration. The stirrers must be circular segments corresponding with the sides and bottom of the boiler, otherwise their motion is irregular and unsatisfactory. The time of trituration, as depending on the nature of the ore, must be determined by experience.

4. The washing of the triturated levings or residuum is performed in large tubs, and requires no particular description, farther than that it be continued till all the soluble matter be got out; and for this purpose there must be a contrivance for stirring the matter all the time it is washing.

5. Eliquation of the quicksilver and amalgam. Formerly this was performed in bags made of deer-skins, strongly compressed with engines for the purpose; but this being found too expensive, it is now done by small quantities at a time, and pressed only by the hand till the ball of amalgam yields no more quicksilver. A small quantity always remains in the quicksilver which passes through; and this quantity is the greater in proportion to the warmth of the amalgam when pressed.

6. The distillation of the amalgam is performed per descensum in large iron pots. The undermost stands upright to its middle in a stream of cold running water which passes under the hearth; the upper part hardly appearing two inches above it. The amalgam, made up into balls, is placed in iron cullenders fixed upon a tripod set in the bottom of the lower pot, and covered in the inside with a coarse cloth. The upper pot is inverted on the lower one; and the juncture being luted, the fire is put all round the outer one, and the heat passing through to the amalgam quickly liquifies it, and raises the quicksilver in vapour, which condenses in the under pot continually kept cool by the stream of water. The upper pot is kept in a strong red heat for five or six hours; by which means the cloth is entirely converted into tinder, so that the cullenders must afterwards be cleaned with a brass brush.

The other operations contain nothing particular but what may be easily understood from what has been already delivered.

is known which does not contain a considerable quantity of arsenic. Effaying of
Ores of
Copper.

§ 1. Copper is found under ground 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 verdigrise, of precipitates. Such are the minerals called filmy copper ores, and several white and green earths. These matters are only copper almost pure and but little mineralised, 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 matrices (c). 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 almost 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 ochrey 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 verdigrise, 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 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. Hencel and Cramer remark, that no proper ore of copper

§ 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.

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

“ Mix one, or, if you have small weights, two decimistical 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 scorias 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 filthiness.

A soft, dusty, and very black scoria, is a sign of a fire not sufficiently strong. Small neat grains of copper

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

(b) Calciform ores are either pure calces of copper, or are mixed with heterogeneous matters. 1. The pure are loose friable ochre, called cerulium 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 malachite; and with quartz, a red ore.

(c) Copper is mineralised, 1. By sulphur, forming the grey copper ore, improperly called vitreous (minera cupri vitrea Wallerii). 2. By sulphurated iron, forming the hepatic copper ore (minera cupri hepatica Wallerii) of a brown yellow colour. It is a kind of cupreous pyrites, and is called by Cronstedt minera cupri pyritacea. Sometimes it is of a blackish grey colour, and is then called pyrites cupri grisea (minera cupri grisea Wallerii); sometimes of a reddish yellow, and tarnished with blue irises on its surface, when it is called minera cupri laevurea; when of a yellowish green colour, it is the pyrites cupri flavo-viridescens (cuprum sulphure et ferro mineralisatum Wallerii); and when of a pale yellow colour, it is the pyrites cupri pallide flavus. Most of the above pyritaceous ores contain also some arsenic, but their sulphur is predominant. 3. Copper mineralised by sulphur, iron, and arsenic. White copper ore (Minera cupri alba Wallerii). This ore contains also some silver. 4. Copper dissolved by vitriolic acid. Native blue vitriol. 5. Copper mixed 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 kopper nickel.

Essaying of Ores of Copper. Oper reduced but not precipitated, and adhering still to scorias, 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 hepar, from which the metal would not precipitate). "But especially the green and azure-coloured ores, and the aruleum 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 femimetal 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 sandver to them. This done, add four times as much of the black flux with respect to the ore; for by this means, the fertile 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 scorias, 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 (d) 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 pyritose, sulphureous, arsenical, femimetallic, copper ore.

"BREAK two decimal centners of the ore to a coarse powder, put them into a test covered with a tile, and place them under the muffle of a decimal furnace. But the fire must be so gentle, that the muffle 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 muffle, 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 colligation. 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,

(d) Mr Cramer still means the calciform ores only, and not the mineralised ores of copper.

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 ferreous 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 show.

“ 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 muffle, 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.

P R O C E S S 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, though 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.

P R O C E S S VI.

To reduce black copper into pure copper by scorfication.

“ SEPARATE a specimen of your black copper, of the weight of two small docimalical 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 lute 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 docimalical 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 scorias will be produced, that will gather at the circumference. All the heterogeneous matters being at last partly dissipated, and partly turned to scorias, 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 1/5th 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,

Essaying of Ores of Copper. 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 un-metallic 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 scorias: 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 do-cimistical centners of the scoria, if it be charged with sulphur, be beat to a subtile 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."

P R O C E S S VII.

The following process is translated from Mr Gellert's Elements of Essaying, and describes a new method of essaying ores, concerning which, see the section Of Essaying in general, p. 338. col. 2.

To essay 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 decrepitated sea-salt: 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 brisk 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.

VOL. XI. PART II.

Essaying of Ores of Copper. 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 pound of antimony, or of its regulus, may be added in the essay; as these substances more readily unite with iron than with copper, and therefore disengage the latter metal from the former.

P R O C E S S VIII.

To essay 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 roasting and fusions. These, and indeed any copper-ores, may be essayed by humid solution, or by menstruum.

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 essayed by humid solution in the following manner:

Roast the mineralised ores in the manner directed in Process IV. and pulverise 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 essay 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 so effectual as the preceding.

PROCESS IX.

Dr. Fordyce's method of effusing 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 shows 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 a luminous 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 CHARMISTY passim.

SECT. V. Ores of Lead.

6. LEAD is seldom found native (e) and malleable. Neither, says Mr. Macquer (r), 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 mineralised.

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

6. 2. Lead ores may be effused, 1. By means of the black flux, in the man. or 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 sulphureous 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

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

(r) 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 nitrosa, 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 spatum 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 mineralised, 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 distinguished from the former by yielding a black flag when scorified, whereas the former yields a yellow flag. 3. With sulphurated antimony and silver. Plumbum silbium Linnæi. Its colour is similar to that of galena, and its texture is striated. 4. With sulphur and arsenic. This ore is soft, almost malleable, like lead. From this ore lead may be melted by the flame of a candle.

Ores of Tin
Ores of Tin densely 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 assay 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 pulverised, 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 assayed, as large quantities of it are smelted, without previous roasting, and without addition, merely by fusion during a certain time. For this purpose nothing more is requisite than to keep the ore melted in a crucible with a moderate heat, till all the sulphur is destroyed, and the metal be collected. To prevent the destruction of any part of the metal after it is separated from the sulphur, some charcoal dust may be thrown over the ore, when put into the crucible; but if the galena be mixed with pyrites, especially arsenical pyrites, it requires much roasting and saline fluxes.

SECT. VI. Tin Ores.

§ 1. TIN is very seldom found pure, but almost always mineralised, 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, ex-

cepting black-lead, which appears to be tin mineralised by sulphur and iron.

The calciform ores of tin are, 1. Tin-stone, 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-stone seems to consist of attrited tin-grains. This ore is calc of tin united with calc of arsenic, and frequently with calc of iron. 2. Garnets are said to contain calc of tin united with calc of iron. 3. Manganese is said also to contain tin.

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

1. Tin-ore, on account of its greater gravity, admits better of being separated, by clutriation 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 require 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 heat, would change another part of it into ashes, and would vitiate the remaining tin. 5. The assay 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 assayed in the following manner:

"Mix a quintal of tin-ore, washed, pulverised, and twice roasted, with half a quintal of calcined borax, and half a quintal of pulverised 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 attractable by a magnet. The ore mentioned by Cramer is found vitrified: with moderate blows the scorias 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 calc; 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 mineralised 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 attractable 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 peas, of beans, of co-unioner seeds, of pepper-corns, of cinnamon, &c. which Mr Cramer treats as ridiculous trifles.

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

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 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 glass, or of the like sterile unsulphureous scorias, and add sand 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 gross 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 be never 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

Essaying of Ores of Iron 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 a 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 sulphureous 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 reguline 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 semimetallic look; which proceeds undoubtedly from a mixture of a small quantity of some other metal or semimetal."

P R O C E S S 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 glass, 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 glass; 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 a 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 glass. This change may be effected by adding some substance capable of dissolving these matters; that is, of converting them into a scoria or glass, 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 assays, where an alkaline salt is used, little or no regulus of iron is obtained. Now, glass acts upon and dissolves earths and stones; but not, or very little, iron: consequently glass is the best flux for such assays, 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 pulverised, 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."

§ 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 Montpellier, in Tuscany, and in other places.

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

Mercury is never mineralised 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 mineralised 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 opaque red colour to glass 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:

To separate mercury out of an unsulphureous ore by distillation.

“TAKE a lump of the pulverised 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.”

To revive mercury from a sulphureous cinnabar-ore.

“BEAT your ore extremely fine, and mix it exactly with an equal portion of iron-silings, not rusty;

proceed to distil 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 pulverised 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.”

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, 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 Swab, 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 semimetal is also found in ores of other metallic substances, as in the plumose silver-ore, and in the silicated lead-ore.

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

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 hearth, 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

Essaying 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."

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."

To reduce a calx of antimony into a semimetallic 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 saline scoria."

The methods of calcining antimony by means of nitre, are described under CHEMISTRY, n^o 1252—1263; 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.

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

An ore 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.

"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 semimetal is destructible and volatile, you must as quick as possible apply it to 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 assayed by fusing a quintal of pulverised ore with half a quintal of calcined borax and half a quintal of pulverised glass, in order to vitrify the adherent earths and stones which envelope the bismuth. But probably the heat requisite for this vitrification would volatilise part of the bismuth.

If the ore be of the kinds above described, mineralised 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.

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 semimetal called regulus of cobalt, the calx of which becomes blue by vitrification. This regulus is mineralised 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 semimetal 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 smalt, and the sympathetic ink. The red efflorescence is also a mark by which true cobalt is distinguishable from the false:

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 mineralised 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 vireous 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 cupreous 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 essay 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 calamite, 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.

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

Zinc is mineralised, 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 mineralised 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 es-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

Ores of Ar-
fenic.

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 dissipated, 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 testaceous texture, it has been improperly called testaceous cobalt, in German feberhencobalt. 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 mispickel. 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 subtle 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 Resazus of Arsenic.

P A R T III.

S M E L T I N G O F O R E S.

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.

VOL. XI. Part II.

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 Schlatter, 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 sul-

phur, &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 distil in vessels, which must be close, to prevent its burning.

Sulphur is extracted from pyrites at a work at Schwartzember, 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 pipe, pierced with a small hole to give air to the sulphur. The other end of the tube is exactly closed. A moderate fire is made with wood, and in eight hours the sulphur of the pyrites is found to have passed into the receivers.

The residuum of the pyrites, after 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 luted 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 moderately 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 expelling 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 smelting furnace are thrown down the channel, by which means the shrubs and wood placed below for that purpose are kindled, and the fire is from them communicated to all the wood of the pile, which continues burning till the third day. At that time the sulphur of the mineral becomes capable of burning spontaneously, and of continuing the fire after the wood is consumed.

When this roasting has been continued 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 Sander, 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 mineralised 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 every-where 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 every-where 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 pro-

cured which yields sulphur. From these cavities vapours exhale, and issue out with noise, and which are nothing else than sulphur subliming 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 under ground; 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 these walls there is a space of 15 or 18 inches; 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

Smelting of whose narrower end is placed below, and because the Ores in ge-
neral. hoops of the tub are so fastened that they may be occa-
sionally loosened. The mass of sulphur is then car-
ried to the buildings mentioned before, where it is re-
melted for its purification, and cast into rolls, such as
we receive it.

Extraction of VITRIOL from pyrites. See CHEMIS-
TRY.

Extraction of ALUM from pyritous substances and
from aluminous earths. See CHEMISTRY.

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 in-
tention of all the operations upon these compound bod-
ies 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 opera-
tions.

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 inti-
mately mixed with the ore, this must necessarily be
broken and divided into small particles. This opera-
tion is performed by a machine which moves pestles,
called bocords or stampers. 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 neces-
sary to begin by roasting it, in order to deprive it of
the greatest part of its sulphur.

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

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 be-
twixt 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 sulphu-
reous, the metal which it contains cannot have its me-
tallic 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 fu-
sion.

We may here observe upon the subject of washing
and roasting of ores, that as arsenic is heavier than sul-
phur, and has nearly the weight of metals, the ores in
which it prevails are generally very heavy, and conse-
quently 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 semimetals, such as antimony and zinc.
These are almost untractable, and are therefore neglect-
ed. They are called minera rapaces, "rapacious
ores."

When the metal has been freed as much as is pos-
sible from foreign matters by these preliminary opera-
tions, 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 sub-
stances from the ores and minerals containing them,
some operations previous to the fusion or smelting of
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 instru-
ments, and by washing with water. 2. Their divi-
sion or reduction into smaller parts by contusion and
trituration, that by another washing with water they
may be more perfectly cleansed from extraneous mat-
ters, and rendered fitter for the subsequent operations,
calcination or roasting, and fusion. 3. Roasting or cal-
cination; the uses of which operation are, to expel the
volatile, useless, or noxious substances, as water, vitrio-
lic acid, sulphur, and arsenic; to render the ore more
friable, and fitter for the subsequent contusion and fu-
sion; and, lastly, to calcine and destroy the viler me-
tals, 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 fri-
able and pulverable, to allow the separation of the me-
tallic particles.

Roasting is unnecessary for native metals; for some
of the richer gold and silver-ores; for some lead-ores,
the.

Roasting of 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 so compactly, as to prevent the passage of the air and flame. 2. The larger pieces must be placed at the bottom of the pile, where the greatest heat is. 3. The heat must be gradually applied, that the sulphur may not be melted, which would greatly retard its expulsion; and that the spars, fluors, and stones, 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 coals. 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 dissipated, and the ore is reduced to a state intermediate betwixt that of ore and of metal. It is then called a matt (lapis sulphureo-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 eliquation. 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 earths, fluors or vitreous spars, quartz, and sand, fusible stones, as slates, 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 felspar. 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 hepar 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 previously well expelled.

Fluors or fusible spars facilitate the fusion of most metallic minerals, and also of calcareous and argillaceous earths, of slates, asbestos, and some other unfusible stones, but not of silicious 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 slates, basaltes, 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 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 sulphureous compounds called matts, that the

ores,

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 mineralised 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, cupreous, 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. 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 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 of 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 glafs 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 Schlutter, the smelting of the ore of Rammelsberg, 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 roasting, it is melted, in the Lower Hartz in Saxony, in a particular kind of furnace, called a furnace for smelting upon a hollow or casse. 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 casse, 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 braque. 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 casse; 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 Rammelsberg ore (the schorben is a measure whose contents are

Smelting of Ores of Silver. 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, Cologne 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 dross of lead, impure litharge, 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 casse, 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 Gossar, whose basis was zinc: which proves that this ore contains also a certain quantity of this femimetal. 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 cadmia 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 in-

ternally, 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 an 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-plate, 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 femimetal 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 casse with the lead and silver, because, being a volatile femimetal, 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 cadmia of zinc, or the cadmia of furnaces, is obtained. This ore is composed of sulphureous and ferruginous pyrites, of true lead-

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 in fusion, behind the chemise or fore-part of the furnace, which is, as has been said, a kind of schistus or slate, called by the workmen steel-stone. But the part of this semimetal which falls in the middle of the furnace, near the middle-wall, or towards the sides, being exposed to the greatest heat of the fire, is there burnt; and its smoke or flowers attaching itself on all sides to the walls of the furnace, undergo there a semifusion, which renders this matter so hard and so thick, that it must be taken away after every fourth fusion, or, at most, after every sixth fusion. That which is found attached to the highest part of the furnace is the best and purest. The rest is altered by a mixture of a portion of lead which it has carried up with it; and which, from its great weight and fixity, has hindered the zinc from rising so high as it would have done alone. Therefore, with this kind of impure cadmia, ductile brass cannot be made.

Almost all the zinc we have, as well as the cadmia of the furnaces, is obtained from the Ramelsberg ore by the process described, and consequently is not the produce of a pure ore of zinc or lapis calaminaris, which is never fused for that purpose. Before Mr Margraaf, although it was well known that this ore contained zinc, and that it was employed for the making of brass, a convenient process for extracting zinc from it was not known; because, when treated by fusion with fluxes, like other ores, it does not yield any zinc: which proceeds partly from the refractory quality of the earth contained in the calamine, that cannot be fused without a very violent fire; and also from the volatility and combustibility of the zinc, which for this reason cannot be collected at the bottom of a crucible, as a regulus under a scoria, like most metals.

M. Margraaf has remedied these inconveniences by distilling lapis calaminaris, mixed with charcoal, in a retort, to which is joined a receiver containing some water, and consequently in close vessels, where the zinc, by the help of a very strong fire indeed, is sublimed in its metallic form without burning. He also by the same method reduced into zinc the flowers of zinc, or pompholix, cadmia of the furnaces, tutty, which is also a kind of cadmia; in a word, all matters capable of producing zinc by combination with phlogiston.— But it is evident that such operations as these are rather fit to supply proofs for chemical theory, than to be put in practice for works in great. M. Margraaf has observed, that the zinc which he obtained by this process was less brittle than what is obtained from the fusion of ores; which may proceed from its greater purity, or from its better combination with phlogiston.

Zinc is obtained, not only in the method used at Goslar above described; but is also extracted in great works, from lapis calaminaris and calcined blend, by a distillation similar to that by which M. Margraaf has

effayed ores of zinc. The first work of that kind was erected in Sweden by Mr Von Swab, in the year 1738. The ore employed was a kind of blend; this ore, when calcined, powdered, and mixed with charcoal, was put into iron or stone retorts, and the zinc was obtained by distillation. In Bristol a work is established in which zinc is obtained by distillation by descent.

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 insert elsewhere, because of the necessary relation it has with the smelting of the Ramelsberg 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 effay, or in small, 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 Ramelsberg 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-hole, 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 test, is disposed. This test 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 test is well prepared and dried, all the work is put at once upon the cold test, 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 test may have time to dry; 2. Because the work of the Ramelsberg 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-waste. 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-waste.

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 popillens. 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 test towards a channel, called the litharge-way, through which

Various processes for extracting Silver. 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 and reduced into lead. 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 merks 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-dross. 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

VOL. XI. Part II.

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 revived 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 scorifying 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 mafs of copper and silver with a quantity of lead, and applying such a heat as shall be just sufficient to make the lead eliquate 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 cast or filed iron be thrown into the liquid mafs, 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 Adelsors 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 cast 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 Silvers, and REFINING.

SECT. IV. 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 Ramellerg, is performed in furnaces not essentially different

ferent 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 basons, 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 bason composed of heavy brasque, which is a mixture of charcoal-powder and clay. In the front of the furnace, and at the bottom of the chemise, 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 basons made of earth, scoria, sand, &c. There the metal is separated from the scoria, by making it flow from these basons 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 basons, 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 foundery: on one side is the fire-place, under which is an ash-hole hollowed in the earth; on the other side is a bason 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 bason, 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 mineralised, not only by sulphur and arsenic, but also by semimetals 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 unmalleable, 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 expence 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

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 assay-iron, the polished end of which being dip in melted copper, shows that this metal is pure when the copper adhering to the iron falls off as soon as it is dip 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 beom 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 of 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 roasting 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 assay 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 sulphureous 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 stones, 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 $\backslash frac\{1\}\{10\}$th to $\backslash frac\{1\}\{4\}$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 sciorification, with addition of lead, seems to be the best method for the last purification of copper.

SECT. V. 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 smelting of ores of iron, for the forging of that metal, and for the conversion of it into steel: but we do not find that he or any other author have, by experiments and discoveries, contributed much to the illustration or to the improvement of this part of metallurgy, unless, perhaps, we except those of 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 farther 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 lime-stone.

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 sulphureous acid, till these be first extricated from the ore, and does therefore only prevent the dissipation of these volatile matters; and, secondly, that the sulphur thus united with the quicklime forms a hepar 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 smelting 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. When 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 scow, 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 smelted 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

Manufacturing of Iron. 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. 2. Those which are mixed with some very refractory substance. Some of these refractory ores contain arsenic; but as this substance facilitates the fusion of ores, 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 calciform 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 metallisation; and since we know, that in every calcination and subsequent reduction of a given quantity of any 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 difficulty 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 difficulty 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 of 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 those earths, but by uniting with that part of the ore which is most perfectly calcined, and least disposed to metallisation; 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 unmetallised 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 hepar 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 coaks, 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 coaks for producing

ducing 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 darker-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 smelted 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 spongy. The drops falling from this smelted 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 also be 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 concoction 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 of 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 the 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 this 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,

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 basin placed for its reception. When the furnace is heated sufficiently, the workmen begin to throw into it alternate charges 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 stopped; 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 disuse 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 Courtivron thinks; or on some other cause, not observed.

The iron thus produced by smelting 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 causes 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 matters, 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 metallized, and also of some unmetallized 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 luted with clay. This tube is a kind of case 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 ap-
proaches

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, tho' 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 unfusible 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 finds 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 coction, 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 coction, 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 coction 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 stopped, 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 coction 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 pass 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 cleansed 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 fold.

In some forges, the iron is fused only once, and in others it suffers three fusions, by which it is said to be rendered

Manufacturing of Iron. rendered very pure. Where only one fusion is practiced, 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 considerably 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 $\backslash frac\{1\}\{4\}$ 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 so 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 semimetals would render the iron brittle both when hot and when cold. Cramer and other authors impute this vicious quality to a mixture of 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 smelting; 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. VI. 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 cleansed 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 state. 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 calcined. 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. VII. Smelting of Ores of Lead.

Ores of lead are either pure, that is, containing no mixture of other metal; or they are mixed with silver, copper, or pyrites. The methods of treating ores of lead containing silver and copper, are described in the sections of Smelting of Ores of Silver and of Copper; and in the former of these an instance is given of the method of smelting the ore of Ramelsberg, 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 smelted in furnaces, and by operations similar to those used at Ramelsberg, 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 basin placed for its reception. The ore which is thus roasted is heat into smaller pieces, and exposed to a second operation similar to the former, by which more metal is eliquated; and the remaining ore is afterwards ground, washed, and smelted, 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 roasted ore. This method requires a very large quantity of wood.

2. In England, lead ores are smelted either upon 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 metal. 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 cistern. But immediately before the lead is allowed to flow out of the furnace, the workmen throw upon the liquid mass a quantity of slacked quicklime, which renders the scoria so thick and tenacious, that it may be drawn out of the furnace by rakes. Schlutter mentions this addition of quicklime in the smelting of lead ores in England, but thinks that it is intended to facilitate 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. VIII. Of the Smelting of Ores of Semi-metals.

ANTIMONY is obtained by a kind of eliquation from the minerals containing it, as is described in the article ANTIMONY; and the regulus of antimony is procured from antimony, by the processes described in the same article, and in the article REGULUS of Antimony.

Arsenic, saffre, and bismuth, are obtained generally from one ore, namely, that called esbalt. The arsenic of the ore is separated by roasting, and adheres to the internal surface of a chimney, which is extended horizontally about 200 or 300 feet in length, and in the sides of which are several doors, by means of which the arsenic, when the operation is finished, may be swept out and collected. These chimneys are generally bent in a zig-zag direction, that they may better retard and stop the arsenical flowers. These flowers are of various colours, white, grey, red, yellow, according to the quantity of sulphur or other impurity with which they happen to be mixed. They are afterwards purified by repeated sublimations; while some alkaline or other substances are added to detain the sulphur, and to assist the purification.

In the same roasting of the ore by which the arsenic is expelled, the bismuth, or at least the greatest part of this semimetal which is contained in the ore, being very fusible, and having no disposition to unite with the regulus of cobalt, which remains in the ore, is separated by eliquation.

The remaining part of the roasted ore consists chiefly of calx of regulus of cobalt, which not being volatile, as the arsenic is, nor so easily fusible as bismuth is, has been neither volatilized nor melted. It contains also some bismuth, and a small quantity of arsenic, together

Smelting of Ores of Semi-metals. Smelting of Ores of Semi-metals. together with any silver or other fixed metal which happened to be contained in the ore. This roasted ore being reduced to a fine powder, and mixed with three or four times its weight of fine sand, is the powder called

See Zaffre. Zaffre or zaffre. Or the roasted ore is sometimes fused with about thrice its quantity of pure sand and as much pure pot-ash, by which a blue glass, called smalt, is produced; and a metallic mass, called speiss, is collected at the bottom of the vessel in which the matters are fused. The metallic mass or speiss is composed of very different substances, according to the contents of the ore and the methods of treating it. The matters which it contains at different times are, nickel, regulus of cobalt, bismuth, arsenic, sulphur, copper, and silver.

Bismuth is seldom procured from any other ores but that of cobalt. It might, however, be extracted from its proper ores, if a sufficient quantity of these were found, by the same method by which it is obtained from cobalt, namely, by eliquation.

Mercury, when native, and enveloped in much earthy or other matter, from which it cannot be separated merely by washing, is distilled either by ascent or by descent. When it is mineralised by sulphur, that is, when it is contained in cinnabar, some intermediate substance, as quicklime or iron, must be added in the distillation, to disengage it from the sulphur.

The rich ore of Almaden in Spain is a cinnabar, with which a calcareous stone happens to be so blended, that no addition is required to disengage the mercury from the sulphur. The distillation is there performed in a furnace consisting of two cavities, one of which is placed above another. The lower cavity is the fire-place, and contains the fuel, resting upon a

grate, through the bars of which the air enters, maintains the fire, and passes into a chimney, placed at one side of the fire-place immediately above the door thro' which fuel is to be introduced. The roof of this fire-place, which is vaulted and pierced with several holes, is also the floor of the upper cavity. Into this upper cavity, the mineral from which mercury is to be distilled is introduced, through a door in one of the sides of the furnace. In the opposite wall of this cavity are eight openings, all at the same height. To each of these openings is adapted a file of aludels connected and luted together, extending 60 feet in length. These aludels, which are earthen vessels open at each end, and wider in the middle than at either extremity, are supported upon an inclined terrace; and the aludel of each file, that is most distant from the furnace, terminates in a chamber built of bricks, which has two doors and two chimneys.

When the upper cavity is filled sufficiently with the mineral, a fire is made below, which is continued during 12 or 14 hours. The heat is communicated thro' the holes of the vaulted roof of the fire-place to the mineral in the upper cavity, by which means the mercury is volatilised, and its vapour passes into the aludels, where much of it is condensed, and the rest is discharged into the brick-chamber, in which it circulates till it also is condensed. If any air or smoke passes through the aludels along with the vapour of the mercury, they escape through the two chimneys of the chamber. Three days after the operation, when the apparatus is sufficiently cooled, the aludels are unluted, the doors of the chamber are opened, and the mercury is collected.

Metamorphosis, Metaphor. METAMORPHOSIS, in general, denotes the changing of something into a different form; in which sense it includes the transformation of insects, as well as the mythological changes related by the ancient poets.

Mythological metamorphoses were held to be of two kinds, apparent and real: thus, that of Jupiter into a bull, was only apparent; whereas that of Lycan into a wolf, was supposed to be real.

Most of the ancient metamorphoses include some allegorical meaning, relating either to physics or morality: some authors are even of opinion that a great part of the ancient philosophy is couched under them; and Lord Bacon and Dr Hook have attempted to unriddle several of them.