the natural process by which metals are formed in the bowels of the earth. See Metallurgy, sect. i.

METALS. See Metallurgy; and Chemistry, no 43, 140, 192, 236, 278, 332, 348.

Metal, in heraldry. There are two metals used in heraldry, by way of colours, viz. gold and silver, in blazon called or and argent.

In the common painting of arms these metals are represented by white and yellow, which are the natural colours of those metals. In engraving, gold is expressed by dotting the coat, &c. all over; and silver, by leaving it quite blank.

It is a general rule in heraldry, never to place metal upon metal, nor colour upon colour: so that if the field be of one of the metals, the bearing must be of some colour; and if the field be of any colour, the bearing must be of one of the metals.

METALLURGY

Metallurgy, according to Boerhaave, comprehends the whole art of working metals, from the glebe or ore, to the utensil; in which fusing, effaying, 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 Effaying; and the larger, or Smelting. But a particular description of the ores themselves seemed likewise necessary to be given; and to this place, too, we have referred a general account of metals, metallization, mines, and ores, as a proper introduction to the subject. Hence the following division into three parts. The first treating, 1. Of metals and metallization. 2. Of mines and ores in general. 3. Of the pyrites. 4. Of the effaying of ores in general. The second, Of the particular ores, and the methods of effaying 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. Sect. I. Of Metals and Metallization.

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 a 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 reflexion 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 general, 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 inability 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 disposesthe 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, sect. iv. With acids, they form a kind of neutral salts, which 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 earthy and saline alkalies.

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

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 obstructions 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 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 abovementioned 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, ened, 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, platinum.

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 five; regulus of antimony, bismuth, zinc, regulus of cobalt, and regulus of arsenic.

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 perfect 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, 13 metallic substances; two of which only were unknown to the ancients, namely, platinum and regulus of cobalt. We have reason to wonder that these two metallic bodies, and particularly platinum, which is a perfect metal, should have remained unknown till lately.

This may give us cause to hope, that if natural history and chemistry be carefully cultivated, as they have been since the renovation of the sciences, we may still make essential discoveries in this way. Mr Cronstedt has given, in the Swedish Memoirs, a description of a metallic matter, which, as he says, appears to be a new femimetal distinct from the others. In that case, this would be the fourteenth metallic matter known, and the third lately discovered: but as, since the Memoir of Mr Cronstedt, this new femimetal has not been examined by chemists, it is yet but little known; and therefore further experiments seem requisite to decide whether it ought to be admitted as a new femimetal (A).

As chemists can only know 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 platinum, all the other metallic matters are susceptible of decomposition and of recomposition, at least to a certain degree; and the experiments of this kind made by chemists, and chiefly by the modern chemists, have thrown much light on this important 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 confluence, 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 alloyed 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.

We must acknowledge, however, that these considerations would only have furnished concerning the existence of the inflammable principle in metals, but a simple probability, very far from the complete proof we now have: but the combustibility of all metals capable of decomposition by this method, and of the subsequent reduction, with all their properties, by the reunion of the inflammable principle, furnishes the clearest and the most satisfactory demonstration that we have in chemistry. We shall now mention what is known upon this subject, and the consequences necessarily resulting.

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.

Also the imperfect metals detonate with nitre, when all the circumstances which that detonation requires are united*. Their phlogiston is consumed by this method much 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 alkaliified by these metallic detonations exactly in the same manner as in its detonation by coals.

Lastly,

(A) See Nickel. Mr Justi pretends that he has discovered a new metallic substance contained in yellow mica. This, he says, was of a blackish grey colour; but when mixed with gold heightened the lustre, without destroying the malleability of that metal, though itself is brittle. Lastly, imperfect metals being treated with acids which have an affinity with phlogiston, that is, with the vitriolic and nitrous acids, are deprived also 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 furnishing sulphur with that acid.

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

If the inflammable matter which flows itself to 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, no 44, 45.

We must observe concerning the decomposition of metals, 1. That when only a small quantity of inflammable principle is taken from metals, a small quantity only of calx is formed, and the remaining part continues in the metallic state: hence, as the portion of calcined metal can no longer remain united with the undestroyed metal, 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 semimetallics.

2. The imperfect metals are not all equally easily and completely calcinable. In general, as much of their phlogiston may be easily taken from them, as is sufficient to deprive them of their metallic properties; but the remaining portion of their phlogiston cannot be so easily driven from them. 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.

Vol. VII.

When metallic earths have lost but little of their phlogiston, and are exposed to strong fire, they melt, and are reduced to compact masses, still heavy and opake, although much less so than the metals, and always brittle and absolutely unworkable. 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 semimetals 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 characterized.

These are the principal changes which metals suffer by losing their phlogiston. 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 phlogiston 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 raised; 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. See Reduction.

We cannot doubt that this wonderful transformation of an earthy substance into a metal, is solely caused by the phlogiston 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 phlogiston. Secondly, The nature of the substance which is to furnish phlogiston is quite indifferent, because this principle is the same in all bodies containing it. Thirdly, If, after 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.

The facts related concerning the decomposition and the recomposition of metals prove incontrovertibly, 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. 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 convinced of this opinion; and 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 from the other metals, silver, mercury, and lead; 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 only 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. The reflections we shall add upon this subject will be sufficient demonstration to every sensible person, that great knowledge is requisite in that science, to attempt with any hopes of success the production even of the most imperfect semimetal. Even if we were certain that it depends only on the intimate combination of the inflammable principle with a matter simply earthly, we should labour by chance, and without any reasonable expectation of success, if we were to attempt that combination without having more knowledge than we now possess, concerning the true nature of the earthly principle which enters into the composition of metals; for we must acknowledge that chemistry has made but little progress in this matter.

Metallic substances, although they resemble each other by the general properties mentioned in the beginning of this article, differ nevertheless from each other very evidently by the properties peculiar to each. Do these differences proceed from the different proportions, and from the more or less intimate connection of the inflammable principle with the earthly 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, 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, to reduce 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 by the methods known in chemistry, 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.

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 calxes, 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 do only obtain metal that was already formed. Every earth and sand, as the intelligent and judicious Cramer observes, contain some particles of gold. Clays do not commonly contain iron ready formed; but all of them contain a ferruginous earth, naturally disposed to metallification. 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 earthly 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 velleity 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 shews, 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 difficultly 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, the water 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; and even now many persons, who talk of chemistry without understanding it, speak of the oil or fat of metals; expressions, which do not sound well to genuine chemists. 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 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 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 proportional 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, and from the disposition of their pores. Phlogiston also appears to communicate ductility to most of the bodies containing it; as we see in sulphur, and in unctuous bodies, as resins, wax, &c., all which are more or less ductile, at least when heated to a certain degree. Lastly, 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. In general, if we reflect on the essential properties of the earthy and inflammable principles, we shall easily perceive that these properties, being combined and modified by each other, ought to produce the properties of metals.

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, according to Mr Macquer, beginning always with that metal in which the property is most considerable.

1. Specific gravity or density. Gold, platina, 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, 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 effectual. 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, as Messrs Macquer and Beaumé have determined.

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. Of Ores. 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 earthly substances, of different natures, and more or less divided.

These different matters united together form masses which are compact, heavy, brittle, and frequently polished 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 diversely coloured, 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 earthly 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 its 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 calxes 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 cornuous 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 sedative 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 Jutti pretends to have discovered.

Henneclet, 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 shewn, and that sulphur is incapable of dissolving unmetallic earths, and even the calxes of all metallic substances, excepting those of lead, bismuth, and nickel.

Having thus defined and distinguished the several general classes of ores, we proceed to show how they are lodged, and where they are found.

Metals and metalliferous ores are found in various places.

I. They are found 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. They are found dissolved in water: such are the vitriolic waters containing iron, copper, or zinc.

III. They are found 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. They are found 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 infused in stones and earths, formed 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 flowers, 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.

9. Lastly, and chiefly, metals and ores are found in oblong tracts, forming masses called veins, which lie in the stony strata composing mountains.

The direction of veins greatly varies; some being straight, and others curved. Their position also respecting the horizon is very various; some being perpendicular, some horizontal, and the rest being of the intermediate degrees of declivity.

The dimensions, the quality, and the quantity of contents, and many other circumstances of veins, are also very various. Miners distinguish the several kinds of veins by names expressive of their differences. Thus veins are said to be deep; perpendicular; horizontal, or hanging, or dilated; rich; poor; morning, noon, evening, and night veins, by which their direction towards that point of the compass where the sun is at any of these divisions of the natural day, is signified.

The stratum of earth or stone lying above a vein is called its roof: and the stratum under the vein is called its floor.

Some parts of veins are considerably thicker than others. Small veins frequently branch out from large veins, and sometimes their branches return into the trunk from which they issued. These veins from which many smaller veins depart, have been observed to be generally rich.

Veins are terminated variously: 1. By a gradual diminution, as if they had been compressed, while yet soft, by superincumbent weight; or by splitting and dividing into several smaller veins. Or, 2. They are terminated abruptly, together with their proper strata in which they lie. This abrupt termination of veins and strata is occasioned by their being crossed by new strata running transversely to the direction of the former; or by perpendicular fissures through the strata; which fissures are frequently filled with alluvial matters, or with water, or are empty. These perpendicular fissures seem to have been occasioned by some rupture or derangement of the stratum through which the vein passes, by which one part of it has been raised or depressed, or removed aside from the other, probably by earthquakes. Where the veins are terminated abruptly, it does not cease, but is only broken and disjoined; and is often recovered by searching in the analogous parts of the opposite side of the deranged stratum. A principal part of the art of miners consists in discovering the modes of these derangements from external marks, that they may know where to search for the disjoined vein.

The contents of veins are metals and metalliferous minerals; as, the several kinds of ores, pyrites, blends, guhrs, vitriols; the several kinds of fluors, spars, quartz, horn-blend, in which the ores are generally embedded, or enveloped, and to which therefore the name matrix of the ore is applied; talcites; crystallizations of these metalliferous and stony substances encrusting the small cavities of the circumjacent rock; and lastly, water, which flows or drops through crevices in that rock.

In a vein, ores are found sometimes attached to the rock or stratum through which the vein runs, but more frequently to a matrix which adheres to the rock; and sometimes both these kinds of adhesion occur in the same vein at different places. Frequently between the matrix and the rock, is interposed a thin crust of stone or of earth, called by authors the fimbria of the ore.

The matrix or the stone in which the ore lies enveloped is of various kinds in different veins. And some kinds of stone seem better adapted than others to give reception to any ore, or to the ores of particular metals. Thus quartz, spar, fluors, and hornblend, give reception to all ores and metals; but slates, chiefly to copper and silver, and never to tin; calcareous and sparry matrixes, to lead, silver, and tin; and mica to iron.

Veins lie in strata of different kinds of stone; but more frequently in some kinds of stone than in others. Thus of the simple or uncompounded stones which compose strata, the following are metalliferous: Calcareous stones; flinty sand-stone (cos fissilis arenosus Wallerii); feldspar (fpatum pyramicum five scintillans); quartz; sometimes jasper; frequently slates; and chiefly micaceous or talc stones; and hornblend, (lapis cornicus Wallerii; bolus indurata particulis squamosis Cronfeldtii). No veins have been found in gypseous or in siliceous strata, although cherts and flints frequently contain metallic particles, and some instances have been observed of ores of silver and of tin in alabaster. Of compound stones, those are said to be chiefly metalliferous which consist of particles of hornblend. Veins have also been found in the red granite; but seldom, if ever, in any other granite, or in porphyry. In general, veins are more frequently found in soft, sifiable, and friable strata, than in those which are compact and hard.

A vein sometimes passes from one stratum into the inferior contiguous stratum. Sometimes even the veins of one stratum do not correspond with those of an inferior stratum, the contiguity of which with the former is interrupted by a mass of different matter thro' which the veins do not pass, that they seem originally to have been continued from one stratum to the other. Thus in the mines of Derbyshire, where the veins lie in strata of limestone, the contiguity of which strata with each other is interrupted in some places by a blue marle or clay, and in other places by a compound stone called toadstone; the veins of one stratum frequently correspond with the veins of the inferior stratum of limestone, but are never continued through the interposed clay or toadstone. But we must observe, that these interposed masses, the blue marle, clay, and toadstone, have not the uniform thickness Formation observable in regular strata, but are (especially the Mines, toadstone) in some places a few feet in depth, and in others some hundreds of yards. The above disposition seems to indicate, that these several strata of limestone have been originally contiguous; that the veins now disjointed have been once continued; that these strata of limestone have been afterwards separated by some violent cause, probably by the same earthquakes which have in a singular manner shattered the strata of this mountainous country; that the interstices thus formed between the separated strata have been filled with such matters as the waters could infilluate, probably with the mixed comminuted ruins of shattered strata; or with the lava of neighbouring volcanoes, of which many vestiges remain.

To the above historical sketch of mines, we shall add some conjectural remarks concerning their formation.

Those ores which are found under water (I.), upon the surface of the earth (III.), in fissures of mountains and subterraneous cavities, accumulated, but not accreted to the contiguous rocks, (IV. 4.), seem from their loose, unconnected, broken appearances, to have been conveyed by alluvion.

All martial ochres have probably been separated from vitriolic ferruginous waters (II.) either spontaneously or by calcareous earth; and these waters seem to have acquired their metallic contents by dissolving the vitriol which is produced by the spontaneous decomposition of martial pyrites. The ochres of copper, zinc, and perhaps of several other metals, have probably been precipitated from vitriolic waters by some substance, as calcareous earth, more disposed to combine with acids; and these vitriolic waters have probably been rendered metalliferous, by dissolving the vitriols produced by a combustion of cupreous pyrites and of the ore of zinc called blend; for these minerals are not, as martial pyrites is, susceptible of decomposition spontaneously, that is, by air and moisture.

The metalliferous nodules and spots (IV. 1.) seem to have been infixed in stones while they were yet soft. Perhaps the metalliferous and lapidaceous particles were at once dissolved and suspended in the same aqueous menstruum, and during their concretion crystallized distinctly, as different salts do when dissolved in the same fluid.

The earths and stones uniformly coloured by metals (IV. 2.) were also probably in a soft state while they received these tinges. The opake-coloured stones seem to have received their colour from metallic calxes mixed and diffused through the soft lapidaceous substance; and the transparent-coloured stones have probably received their colours from vitriolic salts, or from metallic particles dissolved in the same water which softened or liquefied the stony substance; which metallic salts and particles were so much diffused, that they could not be distinctly crystallized. That all stones have been once liquid and dissolved in water, appears probable not only from their regular crystallized forms, but also the solubility of some stones, as of gypseous and calcareous earths, in water; and from the water which we know is contained in the hardest marbles, as well as in alabasters; to which water these stones owe the crystallization of their particles.

The veins called cumulated (IV. 5.), and the entire metalliferous mountains (IV. 6.), are believed by Wallerius to be analogous to the nodules (IV. 1.). These metalliferous substances seem to have been originally formed or concreted in the places where they are found.

The metalliferous strata (IV. 3.) have probably been infilled between the lapidaceous strata, after the separation of these from each other by some violent cause; in the same manner in which we supposed that the clay and toadstone have been infilled between the several strata of lime-stone in Derbyshire. The matters thus infilled may have been either fluid, which would afterwards crystallize and form entire regular masses; or they may have been the ruins of shattered strata and veins brought by waters, and there deposited; in which case they will appear broken and irregular. The metalliferous strata, although frequently confounded with the horizontal or dilated veins, may be distinguished, according to Wallerius, from these by the following properties: 1. They are generally thinner and much broader than the veins called dilated. 2. They are seldom found at a greater depth than 100 perches, and generally in the neighbourhood of veins from which they probably have received their contents. 3. From their want of the thin encrustations called fimbriae; which, we observed, are frequently interposed betwixt the rock and the ore or its matrix; and from their want of the other properties of veins.

But in veins properly so called, the strongest marks exist of ores having been there concreted, and not carried thither and deposited in their present state. Their regular, unbroken appearance; their accretion to the contiguous rock, either immediately, or by intervention of a matrix; the regular appearance of this matrix enveloping the ore; the frequent crystallization of the ore, and of the other contents of the vein, indicate that ores, as well as the other solid contents, have been there concreted from a fluid to a solid state.

Most authors believe that veins, and the perpendicular clefts in the stony strata of mountains, called fissures, have been produced by the same cause; or rather, they consider veins only as fissures filled with metalliferous matters. They further believe, that fissures have been occasioned by the exsiccation of strata, while these were passing from a fluid to a solid state. Wallerius thinks, that fissures have been formed from exsiccation; but that veins were channels made through the strata, while yet soft and fluid, by water, or by the more fluid parts of the strata penetrating and forcing a passage through the more solid parts. He thinks, that these fluid parts conveyed thither their metalliferous and stony contents, which were there coagulated or concreted. He supports his opinion by observing, that all the veins of the same stratum generally run parallel to each other; that they frequently bend in their course; that the same vein is sometimes contracted, and sometimes dilated; that veins are frequently terminated by being split, or divided into inferior veins; that veins are frequently wider at bottom than at top, whereas fissures are always widest at top, and are very narrow below; all which appearances, he thinks, could not have been produced by exsiccation. From these reasons, Formation sons, fissures appear to have had a different, and, from the disjunction and rupture of veins crossed by fissures, they seem to have had a later origin than veins. Whether fissures could have been produced by the very gradual efflorescence of these large masses of strongly coherent matter; or whether they have been produced by the same violent causes, namely, earthquakes, by which the strata in which fissures are generally found have been broken and deranged, and by which metalliferous mountains themselves have been formed, or their strata raised above their original level, as some authors have with great probability conjectured, we do not pretend to determine.

Veins are seldom, if ever, found but in mountains. The reason of which may not improbably be, that in metalliferous mountains we have access to the more ancient strata of the earth, which in plains are covered with so many deposited, alluvial, and other later strata, that we can seldom, if ever, reach the former. That these mountains consist of strata which have been originally lower than the upper strata of adjacent plains, appears from an observation which has been made, that the strata of mountainous countries dip with more or less declivity as they approach the plains, till they gradually sink under the several strata of those plains, and are at last immersed beyond the reach of miners. This leading fact in the natural history of the earth has been observed by a sagacious philosopher, Mr Mitchell, in his Conjectures concerning Earthquakes, Phil. Trans. 1760.

That the inferior strata of the earth contain large quantities of pyritous, sulphurous, and metalliferous matters, appears, 1. From the subterranean fires in those inferior strata, which produce volcanoes, and probably earthquakes, as Mr Mitchell ingeniously conjectures. 2. From the observation, that all kinds of mountains are not equally metalliferous; but that veins especially are only found in those mountains which, being composed of very ancient strata, are called primordial, which form the chains and extensive ridges on the surface of the earth, which direct the course of the waters, and which consist of certain strata, the thickness of each of which, its generic qualities, and its position relatively to the other strata, are, in different parts of the chain of mountains where that stratum is found, nearly uniform and alike, notwithstanding that the numbers and the inclinations of the strata composing contiguous mountains, or even different parts of the same mountain, are often very various; and therefore that veins are seldom, if ever, found in the mountains called by authors diluvial and temporary, which are single, or detached, which consist not of strata uniformly disposed, but of alluvial masses, in which fragments of ores may be sometimes, but veins never, found. Nevertheless, single and seemingly detached mountains, in small islands, have sometimes been found to be metalliferous. But we must observe, that these mountains consist of uniform strata; that islands themselves, especially small islands, may be considered as eminent parts of submarine ranges of mountains, and that the mountains of such islands may be considered as apices or tops only of inferior mountains.

Those mountains are said to be most metalliferous which have a gentle ascent, a moderate height, and a broad basis, the strata of which are nearly horizontal, and not much broken and disjoined. In these mountains at least the veins are less interrupted, more extended, and consequently more valuable to miners, than the veins in lofty, craggy, irregular, and shattered mountains.

Authors dispute concerning the time in which ores have been formed; some referring it to the creation of the world, or to the first subsequent ages; and others believing that they have been gradually from all times, and are now daily, formed. From the accretion of ores and of their matrices to their proper rocks, and from the insertion of metalliferous nodules and strata in the hardest stones, we are inclined to believe that the matter of these veins and nodules are nearly coeval with the rocks and stones in which they are enveloped. Nevertheless, we cannot doubt that small quantities at least of ores are still daily formed in veins, fissures, and other subterranean cavities. Several well-attested instances confirming this opinion are adduced by authors: Cronstedt mentions an incrustation of silver-ore that was found adhering to a thin coat of lamp-black or of foot, with which the smoke of a torch had foiled a rock in a mine at Koningsberg in Norway; and that this incrustation of silver-ore had been formed by a metalliferous water passing over the rock. Lehman affirms, that he possesses some silver-ore attached to the step of a ladder found in a mine in Hartz, which had been abandoned 200 years ago; and that several steps of ladders similarly incrusted had been found. Many other instances are mentioned by authors, of galena, pyrites, silver-ores, and other metalliferous substances, having been found adhering to wood, to fossil-coal, to stalactitical incrustations, to oyster-shells, and other recent substances. From these, and from similar instances, it is probable, that not only ochres and fragments of ores may, with other alluvial matters, be now daily deposited, but also that small quantities of mineralized ores are recently formed; although many histories mentioned by Becher, Barba, Henckel, and other authors, of the entire renovation of exhausted veins, and especially those of the growth and vegetation of metals and of ores, appear to be at least doubtful.

Various opinions have been published concerning the formation of mineralized ores. According to some, these ores were formed by congelation of the fluid masses found in mines, called Guhr. Other authors believe, that ores have been formed by the condensation of certain mineral, metallic, sulphureous, and arsenical vapours, with which they suppose that mines abound. Some have even affirmed, that they have seen this vapour condense, and become in a few days changed into gold, silver, and other metallic matters. It has been above observed, that from several appearances which occur in veins, there is great reason to believe, that ores have not been carried thither and deposited in their present state, but have been there concreted and crystallized; that is, changed from a fluid to a solid state. But the fluidity of the metalliferous matters at the time of their entrance into veins, may have been occasioned either by their having been dissolved in water, if they were capable of such solution, or by their having been raised in form of vapour by subterranean fires. For the disposition to crystallize is Of Pyrites, is acquired by every homogeneous substance that is fluid, whether it has received its fluidity by being melted by fire, or by being dissolved in a liquid menstruum, or by being reduced to the state of vapour. Thus crystals of sulphur have been observed to be daily formed by the sulphureous vapours which exhale in the neighbourhood of volcanoes. The volatility of the two mineralising substances sulphur and arsenic, and the power which volatile bodies possess of elevating a certain portion of any fixed matter which happens to be united with them, render it probable, that the greatest part at least of mineralised ores have been formed of vapours exhaled from subterranean fires, through the cracks in the intervening strata occasioned by those earthquakes which have, in a singular manner, broke and deranged the strata of metalliciferous countries, and which, as has been above remarked, have been probably occasioned by, at least have certainly been always accompanied with, subterranean fires.

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 firearms, as we now use flints; hence it was called carbuncle-stone. It is still named by some marcasite. Perhaps no other kind of natural body has received so many names. Persons curious to known 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 pyrites, 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 pyrites. 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 faces 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, cuprous, 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 pyrites. 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 50lb. 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 mispickel or misfilt. Iron and Of Pyrites, and arsenic form the greatest part of this pyrites. 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 everywhere. Its forms are chiefly round, spherical, oval, flattened, cylindrical; and it is composed internally of 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 between 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 1/5th 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 twelve pounds to a quintal of pyrites, and sometimes 50 or 60 pounds: this is therefore called martial pyrites. It contains about 1/3 of its weight of sulphur, and the rest is unmetallic earth.

The quantity of unmetallic earth contained in the yellow or cuprous 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 metallization, 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 is 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 pyrite 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, soft, line, Of Pyrites, line, powdery mass, the taste of which is saline, astringent, 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 vitrification; because the pyrites become covered with a saline powder, and because vitriol is always formed. This vitrification 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 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 Lemer 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 opake. 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, although 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 mineralizing 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 cuprous 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, infra.

Sect. IV. Effaying 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 is the subject of the present section; the latter is treated under the word Essays, in the order of the alphabet.

Before essays 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 effayer ought to be very intelligent in this matter, that he may at once know what the proper operations are which are requisite to the effay of any given mineral.

As metals are very unequally distributed in their ores, we should be apt to make false and deceitful essays, if we did not use all possible precautions that the proportionable quantity of metal produced by an effay 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 shook 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 effay. This is called the lotting of the ore.

As essays, particularly the first, are generally made in small, effayers 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 effay 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 effaying; 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 effay 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 effay quintal equal to 100 real grains, and then each grain represents a real pound. This effay 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... Effaying of obtained in the effay 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, 100lb. 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 \( \frac{1}{16} \) of a real grain (a); and this latter quantity may be accurately weighed in effay-balances, which when well made are sensible to a much less weight. See (Effay) Balance.

When a quintal of an ore to be effayed 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 ore in effays are three, four, or five parts of black flux; one, two, or three parts of calcined borax; and one half of that quantity of decrepitated 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 effay furnace.

To make effays 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 between the weights employed and those represented is greater. The most minute accuracy therefore is necessary in these operations. For instance, the effay-balances ought to be small, and exceedingly just. The ore ought not to be weighed till it has been reduced to grofs 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 operation has been well made, its weight shews the quantity of metal which every real quintal of ore will yield in the great. If the perfect success of this effay be in any respect doubtful, it ought to be repeated; but the best method at all times is, to make several effays of the same ore. Some small differences are always found, however well the effays 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 expense), till the ore has been effayed, ten or twelve real pounds of the ore ought to be previously effayed; and effayers ought to be furnished with necessary furnaces and instruments for these larger effays.

In Part II., to the several articles of the ores of metals, we shall add the most approved methods of effaying these ores. We shall here only further observe in general, that the methods commonly practised for effaying ores of imperfect metals, and femimetals 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 effays 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 calxes are partially soluble, but more especially so when any of the sulphur of the ore remains; which, by uniting with these salts, forms a heap 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 effays 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 effays 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 effaying 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) The pounds, of which 100 is here supposed to make a quintal, are called Paris pounds, one of which contains 1269 Troy grains. Sect. I. Ores of Gold.

§ 1. Properly speaking, no ores of gold exist; for as this metal cannot be alloyed with arsenic, nor with sulphur, it is never found directly mineralised 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 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 expense 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 sand 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 Céze, and the Gardon; the Arriège; the Garonne; two streams which flow into the Arriège, called Ferriet and Benagues; lastly, the Salat, the source of which is in the Pyrenean mountains.

The Céze 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 twenty-four carats. 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 eighteen to twenty-two carats, that of the Céze being the lowest, and that of the Arriège 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, cuprous 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 hornblende. 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 most gold. Mr Hellot relates, that in eleven essays 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, weighting 448 ounces, was shown to the Royal Academy at Paris, which was found upon essay to have different finenesses in different parts of the mass.

§ 2. Ores and earths containing gold may be essayed 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 essayed by being fused in a cupel or teft, placed under the muffle of an essay-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 joined 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 essay 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 Platina and into a scoria sufficiently thin with sixteen 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 in a good essay-crucible, and covered with the sea-falt. 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 allayed 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 Cartagena, the platina is found native like the gold, and in its metallic state.

Sect. III. Ores of Silver.

§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 allayed 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. This ore, being suddenly heated, 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 Johaun-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 rosficlaire. Its colour is more or less red; it is sometimes crystallized, very heavy, and is fusible like the above-mentioned ores. 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 crystalized, 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 plum-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 balsaltes; 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 Swe- Part II.