The whole of the platinum which has been brought to Europe, has been previously subjected to the process of amalgamation in South America; and hence it happens that a.small quantity of mercury remains in it In treating the ores, therefore, the first object is to separate the mercury by means of heat, either in an open ladle, or in an earthy retort; the platinum remaining after the mercury is thus driven off, appears much yellower, because the particles of gold dispersed through it exhibit their peculiar colour. Proust's method of analysis is, first, to separate the sand with which the grains of platinum are mixed, by exposing them to a blast of air. By heat he evaporates the mercury, which still adheres to them, and then picks out the grains of gold, which are always mixed with platinum, and which are thus rendered visible. The ore is then dissolved in an acid composed of one part of nitre, and three parts of muriatic acid; a black powder remains: this powder, when roasted, gives out phosphorus and sulphur.
After the separation of the gold, nitro-muriatic acid being poured on the remaining mas3 will dissolve it, with the exception of a small quantity of black matter, which was formerly mistaken for plumbago, but is now proved to be a compound of osmium and iridium, two of the four new metallic bodies, which were discovered a few years ago by Mr. Tennant. These two metals Dr. Wollaston has since shown to exist also in the crude platinum ore. united together in the form of distinct minute crystals, and dispersed through the other grains, from which they can be distinguished and picked out without difficulty. Muriate of ammonia being now added to the solution, the platinum is precipitated in the form of a yellowish powder, which is a compound of muriatic acid, ammonia, and platinum: the remaining solution, after the platinum has been separated from it, still contains, besides iron, minute quantities of various other substances, amongst which the two other metallic bodies, palladium and rhodium, were discovered by Dr. Wollaston. Having now brought the platinum to the state of salt, the next object is to restore it, thus purified, to its metallic state, and to consolidate it into a malleable mass; this, from the great infusibility of platinum, has long been a matter of considerable difficulty and labour.
It had been long discovered that arsenic readily united with platinum, and formed with it an alloy of great fusibility; an alloy, therefore, was made of crude platinum and arsenic; and the latter metal, being easily volatilized, was driven off by heat, whilst the iron, being oxidated during the process, was also separated from the mass; so that the platinum was left in an impure but malleable state.