198 Existence of Chrome in the Ore ofFlatina, [Sept. 



Article VI. 



On the Existence of Chrome in the Ore of Platina, 



(To the Editor of the Annals of Philosophy,) 

 SIR, 



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 pow- 

 der, called oxide by Mr. Cooper, is in fact in the metallic state. 

 This is a subject deserving of further investigation ; * I am, there- 

 fore, desirous of learning (and, perhaps, some of your corres- 

 pondents would inform me), whether the experiments of Berze- 

 lius 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 1 have 

 lately made completely verifies Vauquehn'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 polash : chromate of potash 

 is found in the crucible. To prove its nature, it was dissolved, 

 neutrahzed, and tested with acetate of lead, when a yellow pre- 

 cipitate 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 preci- 

 pitate, 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. 



• 1 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. 



