s a metallic substance lately discovered. The name, which has an allusion to its colour, is a diminutive of plate, and signifies "little silver." From its great specific gravity, and other resemblances which Platina; it has to gold, it has been called or blanc, or white gold; from its refractory nature, diabolus metallorum; from some doubts entertained of its character as a metal, juan blanco, white jack, white rogue, or white mock metal. It has also received the appellation of the eighth metal; and, probably from some district which affords it, has gotten the name of platina del Pinto.

The first in Europe who mentioned it by its present name was Don Antonio Ulloa, a Spanish mathematician, who in 1735 accompanied the French academicians that were sent by their sovereign to determine the figure of the earth by measuring a degree of the meridian in Peru. In the relation of his voyage, which was published at Madrid in 1748, he says, that the golden mines in the territory of Choco had been abandoned on account of platina; which he represents as a hard stone not easily broken by a blow on the anvil, which could not be subdued by calcination, and from which the gold could not be extracted without much labour, much expense, and great difficulty.

The particular places of Choco where it is found are Novita and Citara; but in what quantity it is there to be met with is not ascertained. The miners, discovering at an early period that it was a metal, had begun to employ it in adulterating their gold; and the court of Spain, it is said, dreading the consequences, took measures not only to prevent its exportation, but partly to conceal the knowledge of it from the world. It is reported in the Chemical Annals for July 1792, that when the gold is brought from Choco to be coined in the two mints of Santa-fe, in that of Bogota and Popayan, the gold undergoes a new examination, the platina that remains is carefully separated, and being given to officers appointed by the king; they, as soon as a certain quantity is collected, carry it away, and before witnesses throw it into the river Bogota, at two leagues distance from Santa-fe, or into the Cauca, about one league distant from Popayan.

In the Physical Journals for November 1785 we are told, that the primitive mines which produced it have not yet been discovered in any part of the globe, and that those which furnish it at present are of the secondary kind, being strata of loose earth washed down from the higher grounds. In these strata the particles are reported to be from the size of a millet seed to that of a pea. The author of the account says, that he had some pieces which weighed from 15 to 20 grains; and adds, that on trying some of them between steel rollers in the presence of Messrs Darcey and Tillet at Paris, they were perfectly laminated. He says also, that a native piece of platina was found nearly of a square figure, and almost as large as a pigeon's egg, which was deposited in the Royal Society of Bilcay. M. de Buffon, however, says expressly, that "a person of credit had assured him that platina is sometimes found in large masses; and that he had seen a lump of it weighing no less than 20 lb. which had not been melted, but taken in that state out of the mine." As to the small particles, they are of a whiter colour than iron, with a smooth surface. Their figure is generally of an oblong form, very flat, rounded in the edge, and has been ascribed to the hammering of the mills in which the gold is amalgamated.

The heterogeneous substances with which the platina is generally mixed are particles of gold, grains of quartz or crystal, some sand of a brownish hue, and some dust of a dark colour obedient to the magnet, and which seems to be fragments of other irregular dark-coloured particles, which resemble pieces of emery or loadstone. Dr Ingenhouz, however, says, that every particle even of some fine platina which he examined obeyed the magnet more or less, excepting some that were transparent and stony; and that these were all magnets in themselves, or that each of these particles had two poles, which he could change at pleasure by magnetic bars. In about 72 pounds weight of platina which was brought from Spanish America, M. Magellan found not only a large quantity of ferruginous sand, but many pieces of vegetable stalks, a number of seeds, and some very small red crystals like rubies. These crystals being sent to M. Achard of Berlin, he tried them as far as their minute-ness and small quantity would permit, and at last concluded that they really were rubies. As for the mercurial globules which are sometimes intermixed with the particles of platina, they are entirely foreign to its mines. They are now generally thought to be part of the mercury that has been employed in amalgamation; and which could not be brought from a place less distant than Guancavelica, about 900 miles from the province of Choco where the platina is found.

This metal, though not under its present name, which was first mentioned by Don Ulloa, has perhaps been known in Europe since 1741. At that period Charles Wood found in Jamaica some platina which was brought from Cartagena. He even made some chemical trials of it. Among others, he attempted to cupel it; and observes, in the account which he gave of it in 1749, that the Spaniards had a method of casting it into different sorts of toys, which are common enough in the Spanish West Indies. It was probably, too, imported into Spain soon after its discovery in America. It is said that Rudenschloel carried some of it from Spain to Stockholm in 1745; and the first important set of experiments that appeared on the subject were those of Scheffer, one of the members of the Swedish Academy. They were published in 1752; and gave this information, that platina is easily fusible with arsenic, but when alone remains unchanged by the most violent heat of the furnace. Two years after Dr Lewis published some papers concerning this metal in the Royal Philosophical Transactions of London. This eminent chemist, in the course of his experiments, had examined it both in the dry and the wet way; discovered a number of its relative affinities; mixed it in different proportions with different metals; and had fused it with arsenic, though he did not afterwards attempt to separate them.

In 1757 Margraaf published several very interesting observations about the method of separating it from the iron which always accompanies it.

In 1758 and 1763 Macquer and Beaumé made upon it a considerable number of experiments together, and finally formed it at last a concave mirror.

And it was in 1780 that the Journaux de Physique gave an account of the labours of Bergman on the same subject.

The platina of which the toys were made in the Spanish West Indies was found by Dr Lewis to be always—mixed with some other metals. What these particular mixtures were is not well known; but many of the alloys formed by Dr Lewis himself have promised to be both... both ornamental and useful. He found that platina, which is \( \frac{1}{2} \) of the whole mass, will render gold no paler than a guinea, which contains only \( \frac{1}{2} \) of silver. He found that copper was much improved by allaying it with platina in certain proportions; and that equal parts of platina and brass formed a compound not subject to tarnish, and which might be employed with great advantage for the speculums of telescopes.

Besides allaying it with the different metals, it was an object equally interesting to the chemists and society that platina should be obtained pure and unmixed; and that means should be contrived to render it fusible, malleable, and ductile. We are now to see what the chemists have done to accomplish these ends. They readily saw that it would be necessary, in the first place, to bring it to a state of ultimate division, and that this should be tried in one or other of these two ways; by dissolving it in acids, or by fusing it along with some other metal; for by itself it had hitherto proved absolutely unfusible, except when exposed to the focus of a large burning glass, or the kindled stream of depoliticated or vital air. Among the methods which they employed to separate it from gold, the principal were the following: The first was by uniting the mixture of platina and gold with mercury, and grinding the amalgam for a considerable time with water; in which process the platina was gradually thrown out, and the gold retained by the quicksilver. Another method was by mixing a few drops of a solution of platina with above a hundred times the quantity of a solution of gold, and gradually adding a pure fixed alkaline salt as long as it occasioned any effervescence or precipitation. The remaining liquor in this case was yellow, that it has been judged the platina would dissolve itself, though its proportion had been less than a thousandth part of that of gold. A third mode of separating platina and gold was that of precipitation, by means of mineral fixed alkali; for when this alkali is mixed with a solution of gold containing platina, the gold alone is precipitated, and all the platina remains dissolved. Another method was by precipitation of the platina with sal ammoniac. For this purpose, to a solution of the metal in aqua regia a small quantity of the solution of sal ammoniac in water was added; and if the gold contained any platina, the liquor instantly grew turbid, and a fine yellow or reddish precipitate quickly fell to the bottom; if the gold was pure, no precipitation or change of transparency ensued. The fifth method of separation was by means of inflammable liquors. The compound to be examined was dissolved in aqua regia; the solution mingled with twice its quantity or more of rectified spirit of wine, and the mixture suffered to stand for some days in a glass slightly covered, the gold rose to the surface, leaving the platina dissolved. Otherwise, to the solution of the metal in aqua regia about half its quantity of any colourless essential oil was added: the two were shaken well together, and suffered to rest; upon which the oil rose immediately to the surface, carrying the gold with it, and leaving the platina dissolved in the acid under it. Or, the gold was taken up still more readily and more perfectly by ether, or the ethereal spirit of wine. But, after all, the most effectual and advantageous method of separating platina from gold was founded on a property which gold has, and not platina, of being capable of precipitation from aqua regia by martial vitriol; and upon a property which platina has, and not gold, of being capable of precipitation from aqua regia by sal ammoniac. When therefore we would discover if gold be allayed with platina, let it be dissolved in aqua regia; and to this solution, which will contain both metals, let some sal ammoniac dissolved in water be added; upon which the platina will be precipitated in form of a brick-coloured sediment. If, on the other side, we would know if platina contain any gold, let this platina be dissolved in aqua regia, and to the solution add a solution of martial vitriol in water; upon which the liquor will become turbid, and the gold will form a precipitate which may be easily separated by decanting and filtrating the liquor. This property which platina possesses of being precipitated by martial vitriol was first discovered by M. Scheffer.

With respect to the iron contained among the platina, M. de Buffon separated, by means of a magnet, five parts out of seven of a parcel of platina. He distinguished two different matters in platina; of which one was black, friable, and attractive by magnets; and the other consisted of larger grains, was of a livid white or yellowish colour, much less attractive, and was extensible. Between these two different matters were many intermediate particles, some partaking more of the former, and some of the latter. He thought that the black matter was chiefly iron; and says, that he had observed a similar black powder in many ores of iron.

M. Morveau found, that a Prussian blue could be obtained from the black part of the platina, by pouring upon it spirit of nitre, and afterwards adding to the solution diluted some phlogisticated alkali; and that the particles of platina which could not be attracted by magnets, did not by this method show any sign of their containing iron.

But the most important discovery concerning the separation of platina from other metals was a method of melting it, by which it became a perfect metal, malleable, and denser than gold. It was in 1773 and 1774 that M. de Lisle effected this, by dissolving crude platina in aqua regia, precipitating it from the acid menstruum by sal ammoniac, and by fusing this precipitate, without addition, in a double crucible, exposed to the intense heat of a forge-fire excited by double bellows. M. Morveau has repeated the experiment, and found that he could melt the precipitate with several fluxes; he found likewise that by means of white glass, borax, and charcoal, he could melt even crude platina, and could alloy together platina and steel in various proportions.

M. de Sieckengen was the inventor of another method: he dissolved his platina in aqua regia, and precipitated the iron by the prussiate of potash. In evaporating this liquor he obtained small octahedral crystals of the colour of rubies; which, being exposed to a strong heat, yielded a metal which bore easily the stroke of the hammer, which could be readily drawn into wire, and was extremely malleable.

In attempting to refine platina by the dry way, cupellation was a method to which the chemists early had recourse; but, notwithstanding their utmost endeavours, it has not been attended with all the success which could have been wished. It was found that the scorching proceeded as well at the beginning of the operation, as when gold and silver are cupelled: but the cupellation afterwards became more and more difficult; because, as the quantity of lead diminished, the matter became less and less fusible, and at last ceased to be fluid, notwith- standing the most violent heat; and also because, when the quantity of platina was greater than that of the lead, this latter metal was protected, and not converted into litharge. Hence the regulus obtained was always dark- coloured, rough, adhering to the cupel, brittle, and weighing more than the platina originally employed, from the lead which remained united with it. M. de Mac- quer and Beaumé appear nevertheless to have carried this experiment further; they kept the matter exposed to a violent fire during a longer time; that is, about 50 hours successively; and therefore, although their platina was tarnished and rough on its surface, it was internally white and shining, easily separable from the cupel, and a little diminished in weight; a certain proof that no lead remained in it. This platina was also ductile, and capable of extension under the hammer.

Cupellation, therefore, though not the best, is at least a certain method of applying platina to use, and of form- ing it into utensils.

What has been thought a preferable method, is first to fuse the platina with arsenic, and afterwards dissipate this last metal by a strong heat: by this means Achard and Rochon were able to obtain a pure platina; of which the former made some small crucibles, and the latter, by alloying it with copper and tin, some large mirrors for reflecting telescopes.

Jeanety of Paris has gone still farther: besides snuff- boxes, watch-chains, and a coffee-pot of platina prepared by this artifit, the world has seen a lens weighing six pounds, a ball weighing nine, and two bars 19 feet long, and weighing no less than 11 pounds each. This gentle- man has the merit of being the first who wrought this metal in the great way. The method he employ- ed was far from being new; it had been suggested by Scheffer, by Willis, by Margraff, and was afterwards practised by Achard, Moreau, and a great many others, but who always prepared it in very small quantities. In the Chemical Annals for July 1792, the following ac- count of it is given by himself.

The platina is first pounded in water, to disengage it from the ferruginous and other heterogeneous particles that are mixed with it. "This being done, I take (says he) one pound and a half of platina, two pounds of white arsenic in powder, and one pound of purified potash. I mix the whole: I put a crucible in the fire capable of containing about 20 pounds; when my furnace and crucible are well heated, I throw into the crucible one third of the mixture, and apply a good heat; I then add a second quantity and a third, and so on, always ta- king care at every time to mix the whole with a rod of platina. I give now a considerable force to the fire; and when I am certain that the whole is completely in a state of fusion, I withdraw my crucible and leave it to cool. After breaking it, I find a button that is well formed and attractable by the magnet. I bruise this button into small pieces, and fuse it a second time in the same manner; if this second fusion, which it generally is, be not sufficient to effect the separation of the iron from the platina, I fuse it a third time; but if I be obliged to do it a third time, I always put two buttons together, to save at once a crucible and charcoal.

This first operation, being finished, I take a crucible with a flat bottom and of a circumference to give to the button about three inches and a quarter in diameter. I make this crucible red hot, and throw into it: one pound and a half of the platina which has been already fused with the arsenic after it was broken into small pieces; to this I add a quantity of arsenic of the same weight, and about half a pound of refined potash. I give to the fire a considerable force; and when I am certain that the whole is completely in a state of fusion, I withdraw my crucible and leave it to cool, taking care always to place it horizontally, that the button may be of an equ- al thickness. After breaking the crucible, I find a but- ton clear and honourable, and weighing commonly about 1 pound and 11 ounces. I have remarked, that in pro- portion to the quantity of arsenic combined with the platina, the purification always succeeds with the more or less promptness and ease; and the greater the propor- tion so much the better. In this state I put my button into a furnace under a muffle, which ought not to be higher than the edge of the button lying on its flat side, and inclining a little to the walls of the muffle. In this manner I place three buttons on each side of the muffle, and apply fire to my furnace, that the muffle may be equally heated throughout: as soon as the buttons be- gin to evaporate I shut the doors of my furnace, that the heat may be kept up to the same degree; this ought always to be carefully attended to even to the end of the operation, for even a temporary excess of heat might spoil the whole of my past operations and render them abortive. I cause my buttons to volatilize during six hours, always taking care to change their situation, that every part may receive an equal portion of heat. I then put them in common oil, and for a like time keep them in a fire sufficient to dissipate the oil in smoke. I continue this operation as long as the button emits vapours; and when the evaporation has ceased I push the fire as far as it will go by means of the oil. These arsenical vapours have a bright shining metallic appear- ance, which I never can obtain any other way, and with- out which I have never been able to render platina per- fectly malleable.

"If these steps which are here pointed out be proper- ly followed, the operation lasts only eight days. My buttons are then thrown into the nitrous acid, and af- terwards boiled in distilled water, till no part of the acid remains with them: I now heap them together one above another, apply the strongest possible heat, and beat them with a hammer, taking always care at the first heat to make them red hot in the crucible, that no foreign bo- dies may mix with them, as before this compression they are only so many spongy masses. I afterwards heat them in a naked state (les chauffe à nu); and bringing them to a square form, I hammer them on all sides for a shorter or longer time according to their bulk."

Such is the process observed by Jeanety in fusing pla- tina; but he thinks that the working of this metal is susceptible of still greater improvement. In 1788 it was accordingly proposed by some of the French che- mists to fuse platina by mixing it with charcoal and phosphoric glass, and afterwards to expose the phos- phure of platina to a heat sufficient to volatilize and dis- sipate the phosphorus. This method succeeded remarkably well with M. Pelletier; but, besides being tedious, it is difficult to separate the last portions of the phosphorus; and as these operations are always costly, there are few artists artists who are willing to undertake them. M. de Morveau has also fused platinum with his vitreous flux, made of pounded glass, borax, and charcoal; and Beaumé has advised to fuse it with a slight addition of lead, bismuth, antimony, or arsenic, and by keeping the alloy in the fire a long time to dissipate the metals which have facilitated the fusion. Platinum may likewise be fused with a metal soluble in an acid; the mixture being pulverized, the alloyed metal may be dissolved, and the powder of platinum may then be fused with the flux of De Morveau; or, instead of using a fusible metal, a calcinable metal may be employed, and heated as before.

The colour of platinum, when properly refined, is something between that of iron and silver; it has no smell, and is the heaviest body yet known in nature. According to Mr. Kirwan its specific gravity is to that of water as 23 to 1. It may likewise be said to be the most durable of all the metals: it is harder than iron; it undergoes no alteration in the air, and fire alone does not even appear to possess the power of changing it; for which reason it forms the basis of all crucibles that have yet been invented. It resists the action of acids, alkalis, and sulphurs; it may be rolled into plates as fine as leaves of gold which are used in gilding; it is likewise extremely ductile; and Dr Withering tells us, that a wire of platinum is stronger than a wire of gold or of silver of the same thickness; it is preferable to gold by the property which it has of soldering or welding without mixture; and it unites, says Chaptal, two qualities never before found in one and the same substance. When formed into a mirror, it reflects but one image, at the same time that it is as unchangeable as a mirror of glass.

As those motives which at first prepossessed the court of Spain against this metal no longer exist, it is to be hoped that the decree which was passed against it will soon be revoked, and that the Spanish monarch will neither despise so rich a treasure as his mines of platinum nor refuse to the world the numerous advantages that may be derived from a substance that promises to be of so much importance in commerce and the arts.