OBSERVATIONS ON THE NATURE OF PLATINA.
WE have already seen, that of all the Mineral substances which I subjected to trial it was not the most dense, but the least fusible, which required the longest time to receive and lose heat. Iron and emery, which are the most difficult matters to fuse, are, at the same time, those that heat and cool the slowest. There is nothing except platina that is accessible to heat, which retains it longer than iron. This mineral, (which has not long been publicly mentioned) appears, however, to be more difficult to fuse; the fire of the best furnaces is not fierce enough to produce that effect, nor even to agglutinate the small grains, which are all angular, hard, and similar in form to the thick scale of iron, but of a yellowish colour; and although we can fuse them without any addition, and reduce them into a mass by a mirror, platina seems to require more heat than the ore and scales of ironwhich we easily fuse in our forge furnaces. In other respects, the density of platina being much greater than that of iron, the two quantities of density and non-fusibility unite here to render this matter the least accessible to the progress of heat. I presume, therefore, that platina would have been at the head of my table if I had put it to the experiment; but I was not able to procure a globe of it of an inch diameter, it being only found in grains[C]; and that which is in the mass is not pure, it being necessary, in order to fuse it, to mix it with other matters, which alter its nature. The Comte de Billarderie d’Angivilliers, who often attended my experiments, led me to examine this rare metallic substance, not yet sufficiently known. Chemists who have employed their time in platina, have looked upon it as a new, perfect, proper, and particular metal, different from all the rest: they have asserted, that its specific weight was nearly equal to that of gold; but that it essentially differed in other respects from gold, having neither ductility nor fusibility. I own I am of a quite contrary opinion; because a matter which has neither ductility nor fusibility, cannot rank in the number ofmetals, whose essential and common properties are to be ductile and fusible. Neither, after a very careful examination, did platina appear to me a new metal different from every other, but rather an alloy of iron and gold formed by Nature, in which the quantity of gold predominated over the iron; and I founded this opinion on the following facts:
[C]I have been assured, however, by a person of the first respectability, that platina is sometimes found in masses, and that he himself saw a piece that weighed twenty pounds, pure as it was extracted from the mine.
[C]I have been assured, however, by a person of the first respectability, that platina is sometimes found in masses, and that he himself saw a piece that weighed twenty pounds, pure as it was extracted from the mine.
Of 8 ounces 85 grains of platina, furnished me by Comte d’Angivilliers, which I presented to a strong loadstone, there remained only 1 ounce, 1 dram, and 98 grains, all the rest was taken away by the loadstone; therefore, nearly six-sevenths of the whole was attracted by the loadstone, which is so considerable a quantity, that it is impossible to suppose that iron is not contained in the intimate substance of platina, but that it is even there in a very great quantity. I am convinced it contains much more, for if I had not been weary of these experiments, which took me up several days, I should have attracted a great part of the remainder of the 8 ounces by my loadstone, for to the last it continued to draw some grains one by one, and sometimes two. There is, therefore, much iron in platina, and it is not simply mixed with it, as with a foreign matter, but intimately united and making part of its substance; or, if this is denied, it must be supposed, that there exists a second matter in Nature which like iron may be attracted by the loadstone.
All the platina I have had an opportunity of examining, has appeared to be mixed with two different matters, the one black, and very attractable by the loadstone; the other in larger grains, of a pale yellow, and much less magnetic than the first. Between these two matters, which are the two extremes, are found all the intermediate links, whether with respect to magnetism, colour, or size of the grains. The most magnetic, which are at the same time the blackest and smallest, reduce easily into powder by a very slight friction, and leave on white paper the same marks as lead. Seven leaves of paper which were successively made use of to expose the platina to the action of the loadstone, were blackened over the whole extent occupied by it; the last left less than the first, in proportion as the grains which remained were less black and magnetic; the largest grains, which are yellow, and least magnetic, instead of crumbling into powder like the small black grains, are very hard, and resist all trituration; nevertheless, they are susceptible of extension in an agate mortar, under the reiterated strokes of a pestle of the same matter, and I flattened and extended many grains to the double or treble extent of their surface: this part of platina, therefore, has a certain degree of malleability, and ductility, whereas the black part appears to be neither malleable nor ductile. The intermediate grains participate of the qualities of the two extremes: they are brittle and hard, they break or extend under the strokes of the pestle, and afford a little powder not so black as the first.
Having collected this black powder and the most magnetic grains that the loadstone at first attracted, I discovered that the whole was iron, but in a different state from common iron. The latter reduced into powder and filings contracts moisture, and rusts very readily; in proportion as the rust increases, it becomes less magnetic, and absolutely loses this magnetical quality when entirely and intimately rusted; whereas this iron powder, or ferruginous sand found in the platina, is inaccessible to rust, how long soever it may be exposed to the air and humidity; it is also more infusible and much less dissoluble than common iron; but is, nevertheless, an iron which appears to differ only from common iron by a greater purity. This sand is, in fact, iron divested of all the combustible matter and all terrene parts which are found in common iron,and even in steel. It appears endowed and covered with a vitreous varnish which defends it from all injury. What is very remarkable, this pure iron sand does not exclusively belong to the platina ore; for I have found it, although always in small quantities, in many parts where the iron ore has been dug, and which consumed in my forges. As I submitted to several trials all the ores I had, before I used them in my experiments, I was surprised to find in some of them, which were in grains, particles of iron, somewhat rounded and shining, like the filings of iron, and perfectly resembling the ferruginous sand of the platina; they were all as magnetic, all as little fusible, and all as difficult of solution. Such was the result of the comparison I made on the sand of platina, and of the sand found in both my iron ores, at the depth of three feet, in earths where water easily penetrated. I was puzzled to conceive whence these particles of iron could proceed, how they had been defended against rust for the ages they were exposed to the humidity of the earth, and how this very magnetical iron had been produced in veins of mines, which had not the smallest degree of that quality. I called experience to my aid, and became at length satisfied upon these points. I waswell convinced that none of our iron ores in grain were tractable by the loadstone, and well persuaded that all iron ores, which are magnetical, have acquired that property only by the action of fire: that the mines of the north, which are so magnetical as to be sought after by the compass, must owe their origin to fire, and are formed by the means, or the intermedium of water; from which I was induced to suppose that this ferruginous and magnetic sand, that I found in a small quantity in my iron mines, must owe its origin to fire, and having examined the place I was confirmed in this idea. This magnetical sand is found in a wood, where, from time immemorial, they have made, and still continue to make, coal furnaces. It is likewise more than probable that there were formerly considerable fires here. Coal and burnt wood produce iron dross, which includes the most fixed parts of iron that vegetables contain; it is this fixed iron which forms the sand here spoken of, when the dross is decomposed by the action of the air, sun, and rain, for then these pure iron particles, which are not subject to rust, nor to any other kind of alteration, suffer themselves to be carried away by the water, and penetrate with it some feet deep into the earth. What I hereadvance may be verified by grinding the dross well burnt, and there will be found a small quantity of this pure iron, which, having resisted the action of the fire, equally resists that of the solvents, and does not rust at all.
Being satisfied on this head, and having sufficiently compared the sand and dross taken from the iron ores with that of the platina, so as to have no doubt of their identity, it was not long before I was led to conclude, considering the specific gravity of platina, that if this pure iron sand, (proceeding from the decomposition of dross) instead of being in an iron mine, was found near to a gold one, it might, by uniting with that metal, form an alloy which would be absolutely of the same nature as platina. Gold and iron have a great affinity; and it is well-known that most iron mines contain a small quantity of gold; it is also known how to give to gold the tint, colour, and even the brittleness of iron, by fusing them together. This iron-coloured gold is used on different golden jewels to vary the colours; and this gold mixed with iron is more or less grey, and more or less tempered, according to the quantity of iron which enters the mixture. I have seen it of a tint absolutely like the colour of platina; and having enquiredof a goldsmith the proportion of gold and iron therein, he informed me, that in a piece of 24 carats, there were no more than 18 gold, consequently a fourth part was iron, which is nearly the proportion found in the natural platina, if we judge of it by the specific weight; and this gold made with iron is harder and specifically less weighty than pure gold. All these agreements and common qualities with platina, have persuaded me, that this pretended metal is, in fact, only an alloy of gold and iron, and not a particular substance, a new and perfect metal different from every other, as chemists have supposed.
It is well known that alloy makes all metals brittle, and that when there is a penetration, that is, an augmentation in the specific gravity, the alloy is so much the more tempered as the penetration is the greater, and the mixture becomes the more intimate, as is perceived in the alloy calledbell-metal, although it be composed of two very ductile metals. Now nothing is more tempered, nor heavier than platina, which alone ought to make us conclude that it is only an alloy made by Nature, a mixture of iron and gold, owing in part its specific gravity to this last, and, perhaps, also, in a great part, to the penetration of the two matters of which it is composed.
As this matter, heated alone and without any addition, is very difficult to reduce into a mass, as by the fire of a burning mirror we can obtain only very small masses, and as the hydrostatical experiments made on small volumes are so defective, that we cannot conclude any thing therefrom, it appears to me that the chemists have been deceived in their estimation of the specific gravity of this mineral. I put some powder of gold in a little quill, which I weighed very exactly; I put in the same quill an equal volume of platina, and it weighed nearly a tenth less; but this gold powder was much too fine in comparison of the platina. M. Tillet, who besides a profound knowledge of metals, possessed the talent of making experiments with the greatest precision, repeated, at my request, this experiment upon the specific weight of the platina, compared to pure gold; for this purpose, he, like me, made use of a quill, and cut gold of 24 carats, reduced as much as possible to the size of the grains of platina, and he found, by eight experiments, that the weight of platina differed from that of pure gold very near a fifteenth? but we both observed that the grains of gold had much sharper angles than the platina: all the angles of the latter were blunt, and even soft, whereas the grains of this gold had sharpand cutting angles, so that they could not adjust themselves, nor heap one on the other as easily as those of platina. The gold powder I had before made use of was such as is found in river sand, whose grains adjust themselves much better one against the other, and I found a about a tenth difference between the specific weight of those and platina; nevertheless, those are not pure gold, more than two or three carats being often wanting, which must diminish the specific weight in the same relation. Thus we have thought we might maintain, from the result of my experiments, that platina in grains, and such as Nature produces it, is, at least, an eleventh, or twelfth, lighter than gold. There is every reason to presume that the error on the density of platina, proceeded from its not having been weighed in its natural state, but only after it had been reduced into a mass; and as this fusion cannot be made but by the addition of other matters, and a very fierce fire, it is no longer pure platina, but a composition in which fusing matters are entered, and from which fire has taken the lightest parts.
Platina, therefore, instead of being of a density almost equal to that of pure gold, as has been asserted, is only a density between that of goldand iron, and only nearer this first metal than the last. For supposing that the cube foot of gold weighed 1326lb and that of iron 280, that of platina in grains will be found to weigh about 1194lb. which supposes more than3/4of gold to1/4of iron in this alloy, if there is no penetration; but as we extract6/7by the loadstone, it might be thought, that there is more than1/4iron therein: especially as by continuing this experiment, I am persuaded, we should be able, with a strong loadstone to bring away all the platina even to the last grain. Nevertheless, we must not conclude that iron is contained therein in so great a quantity; for when it is mixed by the fusion with gold, the mass which results from this alloy is attractable by the loadstone, although the iron is in no great quantity therein. M. Baume had a piece of this alloy weighing 66 grains, in which was only entered 6 grains, that is,1/11of iron, and this button was easily taken up by the loadstone. Hence the platina might possibly contain only1/11iron, or16/11gold, and yet be attracted entirely by the loadstone; and this perfectly agrees with the specific weight which is1/12less than gold.
But what makes me presume, that platina contains more than1/11of iron, or16/11of gold,is, that the alloy from this proportion is still of the gold colour, and much yellower than the highest coloured platina, and that1/4iron, or3/4gold is requisite for the alloy to be precisely of the natural colour of platina. I am, therefore, greatly inclined to think that there might possibly be this quantity of1/4iron in platina. We were assured by many experiments, that the sand of this pure iron which contained platina, is heavier than the filings of common iron. Thus, this cause, added to the effect of penetration, is sufficient for the reason of this great quantity of iron contained under the small volume indicated by the specific weight of platina.
On the whole, it is very possible that I may be deceived in some of the consequences which I have drawn from my observations on this metallic substance: for I have not been able to make so profound an examination as I could wish; and what I say is only what I have observed, which may perhaps serve as a stimulus to other and better researches.
Chance led me to tell my ideas to Conte de Milly, who declared himself nearly of my opinion. I gave him the preceding remarks to inspect, and two days after he favoured mewith the following observations, and which he has permitted me to publish.
“I weighed exactly thirty-six grains of platina; I laid them on a sheet of white paper that I might observe them the better with a magnifying glass: I perceived three different substances; the first had the metallic lustre, and was the most abundant; the second, drawing a little on the black, very nearly resembled a ferruginous metallic matter, which could undergo a considerable degree of fire, such as the scoria of iron, vulgarly calledmachefer: the third less abundant than the two first, i. e. sand, where the yellow, or topaz colour, is the most predominant. Each grain of sand, considered separate, offered to the sight regular chrystals of different colours. I remarked some in an hexagon form, terminating in pyramids like rock chrystal; and this sand seems to be no other than adetritusof chrystal, or quartz of different colours.
“I resolved on separating, as exactly as possible, these different substances, by means of the loadstone, and to put aside the parts most attractable by the loadstone, from those which were less, and both from those which were not so at all; then to examine each substance particularly, and to submit them to different chemical and mechanical heats.
“I separated these parts of the platina which were briskly attracted at the distance of two or three lines; that is to say, without the contact of the loadstone; and for this experiment I made use of a good fictious magnet; I afterwards touched the metal with this magnet, and carried off all that would yield to the magnetical force. Being scarcely any longer attractable, I weighed what remained, and which I shall call No. 4; it was twenty-four grains; No. 1, which was the most sensible to the magnet, weighed four grains; No. 2 weighed the same; and No. 3, five grains
“No. 1, examined by the magnifying glass, presented only a mixture of metallic parts, a white sand bordering on the greyish, flat and round, or black vitriform sand, resembling pounded scoria, in which very rusty parts are perceptible: in short, such as the scoria of iron presents after having been exposed to moisture.
“No. 2 presented nearly the same, excepting that the metallic parts predominated, and that there were very few rusty particles.
“No. 3 was the same, but the metallic parts were more voluminous; they resembled melted metal which had been thrown into water to be granulated; they were flat, and of all sorts of figures, rounded on the corners.
“No. 4, which had not been carried off by the magnet (but some parts of which still afforded marks of sensibility to magnetism, when the magnet was moved under the paper where they were in), was a mixture of sand, metallic parts, and real scoria, friable between the fingers, and which blackened in the same manner as common scoria. The sand seemed to be composed of small rock, topaz, and cornelian chrystals. I broke some on a steel, and the powder was like varnish, reduced into powder; I did the same to the scoria; it broke with the greatest facility, and presented a black powder which blackened the paper like the common.
“The metallic parts of this last (No. 4) appeared more ductile under the hammer than those of No. 1, which made me imagine they contained less iron than the first: from whence it follows, that platina may possibly be no more than a mixture of iron and gold made by Nature, or perhaps by the hands of men.
“I endeavoured to examine, by every possible means, the nature of platina: to assure myself of the presence of iron of platina by chemical means, I took No. 1, which was very attractable by the magnet, and No. 4, which was not; I sprinkled them with fuming spirit of nitre; I immediately observed it with the microscope, but perceived no effervescence:I added distilled water thereon, and it still made no motion, but the metallic parts acquired new brilliancy, like silver: I let this mixture rest for five or six minutes, and having still added water, I threw some drops of alkaline liquor saturated with the colouring matter of Prussian blue, and very fine Prussian blue was afforded me on the first.
“No. 4, treated in the same manner, gave the same result. There are two things very singular to remark in these experiments; first, that it passes current among chemists who have treated on the platina, that aquafortis, or spirit of nitre, has no action on it. Yet, as I have just observed, it dissolves it sufficiently, though without effervescence, to afford Prussian blue, when we add the alkaline liquor phlogisticated and saturated with the colouring matter, which, as is known, participates iron into Prussian blue.
“Secondly, Platina, which is not sensible to the magnet, does not contain less iron, since spirits of nitre dissolves it enough, and without effervescence, to make Prussian blue. Whence it follows, that this substance, which modern chemists, perhaps too greedy of the marvellous, and too willing to give something novel, have considered as a ninth metal, may possibly be only a mixture of gold and iron.
“Without doubt there still require many experiments to determine how this mixture has taken place, if it be the work of Nature or the effects of some volcano, or simply the produce of the Spaniards’ labours in the New World to acquire gold in the mines of Peru.
“If we rub platina on white linen it blackens it like common scoria, which made me suspect that it was the parts of iron reduced into scoria which are found in this platina, and give it this colour, and which seem, in this state, only to have undergone the action of a violent fire. Besides, having a second time examined platina with my lens, I perceived therein different globules of liquid mercury, which made me suppose that platina might be the produce of the hands of man, in the following manner:—Platina, as I have been told, is taken out of the oldest mines in Peru, which the Spaniards explored after the conquest of the New World. In those dark times only two methods were known of extracting gold from the sands which contained it; first, by an amalgama with mercury; secondly, by drying it. The golden sand was triturated with quicksilver, and when that was judged to be loaded with the greatest part of the gold, the sand was thrown away, which was namedcrasse, as useless and of no value.
“The other method was adopted with as little judgment; to extract it they began by mineralising auriferous metals by means of sulphur, which has no action on gold, the specific weight being greater than that of other metals: but to facilitate its precipitation iron was added, which loaded itself with the superabundant sulphur, and this method is still followed. The force of fire vitrifies one part of the iron, the other combines itself with a small portion of the gold, or even silver, which mixes with the scoria, from whence it cannot be drawn but by strong fusions, and being well instructed in the suitable intermediums which are made use of. Chemistry, which is now arrived to great perfection, affords, in fact, means to extract the greatest part of this gold and silver: but at the time when the Spaniards explored the mines of Peru, they were, doubtless, ignorant of the art of mining with the greatest profit; besides, they had such great riches at their disposal that they, probably, neglected the means which would have cost them trouble, care, and time; there is much reason therefore to conclude that they contented themselves with a first fusion, and threw away the scoria as useless, as well as the sand which had escaped the quicksilver, and perhaps they made a mere heap of these two mixtures, which they regarded as of no value.
“These scoria contained gold and silver, iron under different states, and that in different proportions unknown to us, but which, perhaps, are those that gave origin to the platina. The globules of quicksilver which I observed, and those of gold which I distinctly saw, with the assistance of a good lens, in the platina I had in my hands, have given birth to the ideas which I have written on the origin of this mineral; but I only give them as hazardous conjectures. To acquire some certainty we must know precisely where the platina mines are situated, and examine if they have been anciently explored, whether it be extracted from a new soil, or if the mines be only rubbish, and to what depth they are found; and, lastly, if they have any appearance of being placed by the hands of man there or not, which alone can verify or destroy the conjectures I have advanced.”[D]
[D]Baron Siekengen, minister of the elector Palatine, told M. de Milly, that he had then in his possession two memoirs which had been given to him by M. Kellner, chemist and metallurgist in the service of the Prince of Birckenfeld, at Manheim, and which offered to the court of Spain to return nearly as much gold as they would send him platina.
[D]Baron Siekengen, minister of the elector Palatine, told M. de Milly, that he had then in his possession two memoirs which had been given to him by M. Kellner, chemist and metallurgist in the service of the Prince of Birckenfeld, at Manheim, and which offered to the court of Spain to return nearly as much gold as they would send him platina.
These observations of Comte de Milly confirm mine in almost every point. Nature is the same, and presents herself always the same to those who know how to observe her: thus wemust not be surprized that, without any communication, we observed the same things, and deduced the same consequence therefrom; that platina is not a new metal, different from every other, but a mixture of iron and gold. To reconcile his observations still more with mine, and to enlighten, at the same time, the doubts which remain on the origin and formation of platina, I have thought it necessary to add the following remarks:
1. The Comte de Milly distinguishes three kinds of matters in platina, namely, two, metallic, and the third, non-metallic, of a chrystalline form and substance. He observed, as well as I, that one of the metallic matters is very attractable by the magnet, and the other but little, or not at all. I mentioned these two matters as well as he, but I did not speak of the third, which is not metallic, because there was none, or very little, on the platina on which I made my observations. It is possible that the platina which the Comte made use of was not so pure as mine, which, I observed with the greatest care, and in which I saw only some small transparent globules, like white melted glass, which were united to the particles of platina, or ferruginous sand, and which were carried any where by the magnet.These transparent globules were very few, and in eight ounces of platina which I narrowly inspected with a very strong lens, I never perceived regular crystals. It rather appeared to me that all the transparent particles were globulous, like melted glass, and all attached to metallic parts; nevertheless, as I did not in the least doubt the veracity of the Comte de Milly’s observation, who observed chrystalline particles of a regular form, and in a great number, in his platina, I thought I ought not to confine myself solely to the examination of that platina of which I have spoken; and finding some in the king’s cabinet, M. Daubenton and I examined it together: this appeared to be much less pure than that we had before made our experiments on; and in it we remarked a great number of small prismatic and transparent crystals, some of a ruby colour, others of a topaz, and others perfectly white, which convinced us of the correctness of the Comte de Milly in his observations; but this only proves that there are some mines of platina much more pure than others, and that in those which are the most so, none of these foreign bodies are found. M. Daubenton also remarked some grains flat at bottom and rough at top, like melted metal cooled on a plain, and Ivery distinctly saw one of these hemispherical grains, which might indicate that platina is a matter that has been melted by the fire; but it is very singular, that in this matter, if melted by fire, small crystals, topaz, and rubies, are found; and I know not whether we ought not to suspect fraud in those who supplied this platina, who, to increase the quantity, mixed it with these crystalline sands, for I never met with these crystals but in one half pound of platina given me by the Comte de Angilliviers.
2. I, as well as Comte de Milly, found gold sand in platina; it is readily discovered by its colour, and because it is not magnetical; but I own that I never perceived the globules of mercury which he states to have done; yet I do not mean therefore to deny their existence, only that it appears to me that the sand of gold meeting with the globules of mercury, in the same matter, they might be soon amalgamated, and not retain the colour of gold, which I have remarked in all the gold sand that I could find in half a pound of platina; besides, the transparent globules, which I have just spoken of, resemble greatly the globules of live and shining mercury, insomuch that at the first glance it is easy to be deceived in them.
3. There were by no means so many tarnished and rusty parts in my first platina as in that of Comte de Milly’s, nor was it properly a rust which covered the surface of those ferruginous particles, but a black substance produced by fire, and perfectly similar to that which covers the surface of burnt iron. But my second platina, that which I had from the royal cabinet, had a mixture of some ferruginous parts, which under the hammer were reduced into a yellow powder, and had all the characters of rust. This platina therefore of the royal cabinet, and that of Comte de Milly, resembling in every respect, it is probable that they proceeded from the same part, and by the same road. I even suspect that both had been sophisticated and mixed nearly one half with foreign crystalline and ferruginous rusty matters, which are not to be met with in the natural platina.
4. The production of Prussian blue by platina appears evidently to prove the presence of iron in those parts even of this mineral which are the least attractable to the magnet, and at the same time confirms what I have advanced on the intimate mixture of iron in its substance. The flowing of platina by spirits of nitre, also proves that although it has no sensible effervescence, this acid attracts the platina in an evidentmanner; and the authors who have asserted the contrary, have followed their common track, which consists in looking on all actions as null which do not produce an effervescence. These second experiments of the Comte de Milly would appear to me very important, if they succeeded always alike.
5. We must however admit that many essential points of information are wanting to pronounce affirmatively on the origin of platina. We know nothing of the natural history of his mineral, and we cannot too greatly exhort those who are able to examine it on the spot, to make known their observations; and until that is done we must confine ourselves to conjectures, some of which appear only more probable than others. For example, I do not imagine platina to be the work of man. The Mexicans and Peruvians knew how to cast and work gold before the arrival of the Spaniards, and they were not acquainted with iron, which nevertheless they must have employed in a great quantity. The Spaniards themselves did not establish furnaces in this country when they first inhabited it to fuse iron. There is, therefore, every reason to conclude, that they did not make use of the filings of iron for the separation of gold, at least in the beginningof their labours, which does not go above two centuries and a half back; a time much too short for so plentiful a production as platina, which is found in large quantities in many places.
Besides, when gold is mixed with iron, by fusing them together, we may always, by a chemical process, separate them, and extract the gold: whereas, hitherto, chemists have not been able to make this separation in platina, nor determine the quantity of gold contained in this mineral. This seems to prove, that gold is united with it in a more intimate manner than the common alloy, and that iron is also in it, in a different state from that of common iron. Platina, therefore, appears to me to be the production of nature, and I am greatly inclined to think, that it owes its first origin to the fire of volcanos. Burnt iron, intimately united with gold by sublimation, or fusion, may have produced this mineral, which having been at first formed by the action of the fiercest fire, will afterwards have felt the impression of water, and reiterated frictions, which have given it the form of blunt angles. But water alone might have produced platina; for supposing gold and iron divided as much as possible by the humid mode, their molecules,by uniting, will have formed the grains which compose it, and which from the heaviest to the lightest contain gold and iron; the proposition of the chemist who offers to rendernearlyas much gold as they shall furnish him with platina, seems to indicate, that there is, in fact, only1/11of iron to10/11of gold in this mineral, or possibly less. But thenearlyof this chemist is perhaps a fifth, or fourth, and indeed, if he could realize his promise to a fourth, it would be doing a great deal, and no vain boast.
Being at Dijon the summer of 1773, the Academy of Sciences and Belles Letters, of which I have the honour to be a member, expressed a desire of hearing my observations on platina; and having complied, M. de Morveau resolved to make some experiments on this mineral; for which purpose I gave him a portion of that which I had attracted by the loadstone, and also some which I had found insensible to magnetism, requesting him to expose it to the strongest fire he could possibly make. Some time after, he sent me the following experiments, which he was pleased to subjoin to mine.
“Monsieur the Comte de Buffon, in a journey to Dijon, in the summer of 1773, having caused me to remark in half a drachm of platina, which M. de Baume had sent him in 1768, grains in form of buttons, others flatter, and some black and scaly; and having separated by the loadstone those which are attractable from those which appeared not so, I tried to form Prussian blue with both. I sprinkled the fuming nitrous acid on the non-attractable parts, which weighed 21/2grains. Six hours after I put distilled water on the acid, and sprinkled alkaline liquor, saturated with a colouring matter; however there was not a single atom of blue, the platina had only a little more brightness. I alike sprinkled the fuming acid on the remaining platina, part of which was attractable, the same Prussian alkali precipitated a blue feculency, which covered the bottom of a pretty large bason. The platina, after this operation, shewed like the first. I washed and dried it, and found it had not lost1/4of a grain, or1/138part; having examined it in this state I perceived a grain of beautiful yellow, which was pure gold.
“M. de Fourcy had lately told the world, that the dissolution of gold was thrown down in a blue precipitate by the Prussian alkali, and had placed this circumstance in a table of affinity; I was tempted to repeat this experiment, and sprinkled, in consequence, the phlogisticated alkaline liquor in the dissolution of gold, but the colour of this dissolution did not change, which made me suspect that the dissolution of gold made use of by M. de Fourcy might possibly not have been so pure.
“At the same time the Comte de Buffon having given me a sufficient quantity of platina to make further assays, I undertook to separate it from all foreign bodies by a good front; and I have here subjoined the processes and their results.
EXPERIMENTS.
“I. Having put a drachm of platina, in a cupel, into a furnace, I kept up the fire two hours, when the covers sunk down, the supporters having run, nevertheless the platina was only agglutinated; it stuck to the cupel, and had left spots of a rusty colour. The platina was then tarnished, even a little black, and had only augmented a quarter of a grain in weight; a quantity very small in comparison with that which other chemists have observed. What surprised me still more was, that this drachm of platina, as well as that I used for other experiments, had been successively carried away by the loadstone, and made a portion of6/7of eight ounces, of which the Comte de Buffon has before spoken.
“II. Half a drachm of the same platina, exposed to the same fire in a cupel, was also agglutinated; I adhered to the cupel, on which it had left spots of a rusty colour; the augmentation of weight was found to be nearly in the same proportion, and the surface as black.
“III. I put this half drachm into a new cupel, but instead of a cover I placed over it a leaden crucible. This I kept in the most extreme heat for four hours; when it was cooled I found the crucible soldered to the support, and having broken it I perceived that nothing had penetrated into the internal part of the crucible, which appeared to be only more glossy than before. The cupel had preserved its form and position; it was a little cracked, but not enough to admit of any penetration; the platina was also not adherent to it, though agglutinated, but in a much more intimate manner than in the first experiments; the grains were less angular, the colour more clear, and the brilliancy more metallic. But what was the most remarkable during the operation, there issued from its surface, probably in the first moments of its refrigeration, three dropsof water, one of which, that arose perfectly spherical, was carried up on a small pedicle of the vitreous and transparent matter. It was of an uniform colour, with a slight tint of red, which did not deprive it of any transparency; the smallest of the other two drops had likewise a pedicle, and the other none, but was only attached to the platina by its external surface.
“IV. I endeavoured to assay the platina, and for that intent put a drachm of the grains taken up by the loadstone into a cupel, with two drachms of lead. After having kept up a very strong fire for two hours, I found an adherent button, covered with a yellowish and spungeous crust of two drachms twelve grains weight, which announces that the platina had retained one drachm twelve grains of lead. I put this button into another cupel in the same furnace, observing to turn it, by which it only lost twelve grains in two hours; its colour and form were very little changed. The same piece of platina was put into Macquer’s furnace, and a fire kept up for three hours, when I was obliged to take it out, because the bricks began to run. The platina was become more metallic, but it, nevertheless, adhered to the cupel, and this time it lost 34 grains. I threw it into the fuming nitrous acid to assay it,and there arising a little effervescence, I added distilled water thereon. The platina lost two grains, and I remarked some small holes, like those which its flying off might occasion.
“There then remained only 22 grains of lead in the platina. I began to form a hope of vitrifying this remaining portion of lead, for which purpose I put the same piece of platina into a new cupel, and by the care I took for the admission of air, and other precautions, the activity of the fire was so greatly augmented that it required a supply every eleven minutes; to this degree of heat we kept for four hours, and then permitted it to cool.
“I perceived the next morning that the leaden crucible had resisted, and that the supporters were only glazed by the cinders. I found a piece in the cupel, not adhering, of a uniform colour, approaching more the colour of tin than any other metal, but only a little ragged. It weighed exactly one drachm. All, therefore, announced that this platina had endured an absolute fusion, and that it was perfectly pure, for if we suppose it still contained lead, we must then admit that it had lost exactly as much of its substance as it had gained of foreign matter; and such a precision cannot be the effect of pure chance.
“I passed several days with M. Buffon, whose company has the same charms as his style, and whose conversation is as complete as his books: I took a pleasure in presenting him with the production of our essays; we examined them together, and observed, First, that the drachm of platina, agglutinated by these experiments, was not attractable by the loadstone; that, nevertheless, the magnetical bar had an action on the grains that were loosened from it.
“2. The half drachm of the third experiment was not only attractable in the mass, but the grains of gold separated therefrom did not themselves give any signs of magnetism.
“3. The platina of the fourth experiment was absolutely insensible to the loadstone.
“4. The specific weight of this piece was determined by a good hydrostatical balance, and being, for the greater certainty, compared to coined and to other very pure gold, used by M. Buffon in his experiments, their density was found, with water, in which they were plunged,
“5. This piece of platina was put uponsteel to try its ductability; it supported the hammer very well for a few strokes; its surface became flat and even, a little smooth in the parts which were struck, but it split soon after, and nearly a sixth part separated. The fracture presented many cavities, some of which had the whiteness and brilliancy of silver, and in others we remarked several points like chrystalization; the tops of these points examined with the lens, was a globule absolutely similar to that of the third experiment. All the other parts of this piece of platina were compact, the grain finer and closer than the best brass, which it resembled in colour. We offered several of these pieces to the loadstone, but not one was attracted thereby. We powdered them again in an agate mortar, and then remarked that the magnetical bar raised up some of the smallest every time they are placed under it.
“This new appearance of magnetism was so much the more surprising, as the grains were detached from the agglutinated mass of the second experiment, which seemed to have lost all sensibility at the approach and contact of the loadstone. In consequence we again took some of these grains, which were alike powdered, and soon perceived the smallest parts sensibly attach themselves to the magnetic bar. It is impossibleto attribute this effect to the smoothness of the bar, or to any other cause foreign to magnetism. A piece of smooth iron, applied in the same manner on the parts of this platina did not raise up a single grain.
“By these experiments, and the observations which have arisen therefrom, we may judge of the difficulty of determining the nature of platina. It is very certain that it contains some parts which are verifiable even without the addition of a fierce fire; it is also certain that all platina contains iron and attractable parts; but if the Prussian alkali never affords blue but with the grains which the loadstone attracts, we should conclude, that those which resist it are pure platina, which of itself has no magnetical virtue, and of which iron does not make an essential part. We must suppose that a sufficient fusion, or perfect cupellation, might decide the question; at least, these operations appear to have, in fact, deprived it of every magnetic virtue, by separating it from all foreign bodies; but the last observation proves, in an incontrovertible manner, that this magnetic property was, in reality, only weakened, and perhaps masked or buried, since it reappeared when it was ground.”
From these experiments of M. de Morveau there results, 1. That we may expect to meetplatina without addition, by applying the fire of it several times successively, because the best crucibles might not resist the action of so fierce a fire during the whole time that the complete operation would require.
2. That by melting it with lead, and assaying them several times, we should in the end vitrify all the lead and the platina; and that this experiment would be able to purge it from a part of the foreign matters it contains.
3. That by melting without any addition, it seems to purge itself partly into the vitrescible matters it includes, since it emits to its surface small drops of glass, which form pretty considerable masses, and which we can easily separate after refrigeration.
4. That by making experiments on Prussian blue with the grains of platina, which appeared to be most insensible to the loadstone, we were not always certain of obtaining it; a circumstance which never fails with grains that have more or less sensibility to magnetism.
5. It appears that neither fusion nor cupellation can destroy all the iron with which platina is intimately penetrated; the pieces melted or assayed, appeared, in reality, equally insensible to the action of the loadstone; but having pounded them in a mortar, we found magneticalparts; so much the more abundant as the platina was reduced to a fine powder. The first piece, whose grains were only agglutinated, being ground, rendered many more magnetical parts than the second and third, the grains of which had undergone a stronger fusion; but, nevertheless, being both ground, they furnished magnetical parts; insomuch that it cannot be doubted that there is iron in platina, after it has undergone the fiercest efforts of fire, and the devouring actions of the heat in the cupel. This demonstrates, that this mineral is really an intimate mixture of gold and iron, which hitherto has not been able to separate.
6. I made another observation with M. Morveau on melted, and afterwards on ground platina; namely, that it takes in grinding precisely the same form as it had before it had been melted; all the grains of this melted and ground platina are similar to those of the natural, as well in form as variety of size; and they appear to differ only because the smallest alone suffer themselves to be raised by the loadstone, and in so much the less quantity as the platina has endured the fire. This seems also to prove, that, although the fire has been strong enough not only to burn and vitrify, but even to drive off a part of the iron with other vitresciblematter which it contains; the fusion, nevertheless, is not so complete as that of other perfect metals, since, in grinding, it retakes the same figure as it had before fusion.