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XX. Extract from a Memoir on Platina, ly FotJiiCROY 

 and VAuauELiN*. 



W e shall not follow the authors of this memoir in all the 

 details of their experiments, because they are too numerous; 

 and as it would be impossible to give a clear account of 

 them in a short extract, we shall attend only to the most 

 interesting points, and those which exhibit new results. 



To ascertain the influence which the foreign substances 

 that accompany platina in its ore have in operations on a 

 grand scale with this metal, the authors first separated and 

 then carefully examined them. It results from this first 

 labour, that the sand of platina contains iron, copper, tita- 

 nium, chrome and silex, forming together different combi- 

 nations, the state and manner of which the authors have 

 explained from analogies known in the mineral kingdom. 



They then treated platina thus freed from foreign bodies 

 with nitro-muriatic acid, in order to obtain it in solution ; 

 but they observed, as Mr. Proust and several other chemists 

 did, that there remained a small quantity of black pow- 

 der, formed by brilliant laminae, soft to the touch, which 

 blackened paper like plumbago, and on which the nitro- 

 muriatic acid had scarcely any action. 



This black matter having particularly engaged their atten- 

 tion, they subjected it to a great number of experiments 

 after they had obtained a sufficient quantity of it : as acids 

 could be of no use to them in the examination of this sub- 

 stance, to make known its nature^ they employed alkalies. 

 Four parts of caustic potash, and one part of the black 

 powder, were fused and calcined together in a platina cru- 

 cible for an hour : the mass, which had then a very rich 

 green colour, was diluted in water, to which it communi- 

 cated the same tint. 



When the green liquor was separated, and the residuum, 

 which was also green, had been washed, they saturated the 

 excess of alkali which the liquor contained, and exposed it 

 to heat. By these means the green matter was separated 

 under the form of flakes, and the liquor . retained only a 

 reddish yellow colour. The green flakes were united to the 

 residuum not dissolved by the potash, and the yellow liquor 

 was subjected to different tests, by the help of which they 

 found that it contained chromic acid. 



The residuum treated with concentrated muriatic acid was 



* From the Annates dc Chimie, No. 143. 



Vol. 19. No. 74. July 1804. K in 



