ARTICLE VI.

On the Existence of Chrome in the Ore of Platina.

SIR,

(To the Editor of the Annals of Philosophy.)

THE chemical history of platina must be considered to be as yet by no means complete. The last statement, with respect to the composition of its oxide, with which I am acquainted, is that of Mr. Cooper in No. 5, of the Royal Institution Journal, which differs widely from the statement of Berzelius. This has again been controverted, in a paper inserted in the Annals for November, 1821, the writer of which asserts, that the black powder, called oxide by Mr. Cooper, is in fact in the metallic state. This is a subject deserving of further investigation; * I am, therefore, desirous of learning (and, perhaps, some of your correspondents would inform me), whether the experiments of Berzelius are detailed in any English work? But the point to which I now wish to call your attention, is the existence of chrome in the ore of platina, a fact originally pointed out by Vauquelin, but upon which Tennant, by stating that he was unable to discover any, has thrown some doubt. An experiment which I have lately made completely verifies Vauquelin's statement, and at the same time seems to point out the reason why Tennant obtained no chrome, viz. that he operated only on the picked metallic grains of platina; while Vauquelin probably employed the crude ore, containing a quantity of black irony sand, in which the chrome is found.

In order to detect the presence of chrome, it is sufficient to separate the black sand by means of the magnet, and to expose it to a strong heat with carbonate of potash: chromate of potash is found in the crucible. To prove its nature, it was dissolved, neutralized, and tested with acetate of lead, when a yellow precipitate fell down: this precipitate being treated with muriatic acid, was resolved into a white salt and an orange liquid, which, after some boiling, turned green. Another portion of the precipitate, being properly fluxed, and exposed to a dull red heat, yielded the peculiar orange-enamel characteristic of chromate of lead: no doubt, therefore, could remain as to the nature of the substance. I am, Sir, your most obedient servant,

C. C.

I have repeated Mr. Cooper's process, which is to precipitate platina by nitrate of mercury, and to expel the calomel by heat; but as oxide of platina is decomposable at a heat below redness, I consider it impossible to stop the heat at the exact point, when all the mercurial salt is expelled, and all the oxygen of the platina retained, and, therefore, that the method can afford no satisfactory results.