1 18 Memoir on Platina* 



in a great measure dissolved, and gave a liquor of a beau- 

 tiful green colour; but there still remained a portion of the 

 black powder which had not been attackedby the potash, 

 and on which the muriatic acid had exercised no action. 

 On repeating this operation several times in succession with 

 potash and muriatic acid, they decomposed it entirely, and 

 obtained the whole chromic acid in the alkali, and the green 

 matter in the acid. 



It was then necessary to examine the green matter dis- 

 solved in the muriatic acid. For this purpose the authors 

 began by evaporating the solution, in order to separate the 

 excess of acid; but they were much surprised to find, at the 

 moment when the liquor entered into ebullition, that its 

 green colour was changed into a beautiful red. When the 

 greater part of the superabundant acid was volatilized, they 

 tried the rest by the following means. 



1st, Alkalies precipitated from it a brownish red matter. 

 2d, A small piece of the sulphate of iron made it immedi- 

 ately lose its red colour, and gave it a green tint, whick 

 in the course of time acquired more intensity. 3d, Prus- 

 siate of potash formed in it a green precipitate, which be- 

 came blueish in the air. 4th, Infusion of gall nuts pro- 

 duced a blackish brown precipitate. 5th, A solution of 

 muriate of ammonia did not form a precipitate, as it does 

 in a solution of platina. 6th, A solution of tin put into 

 this solution, diluted with water, did not become red like 

 solution of platina mixed with the same re-agent. 7th, 

 This liquor mixed with a solution of pure platina, which 

 was precipitated yellow by sal-ammoniac, gave it the pro- 

 perty of being precipitated of a very dark red colour by the 

 same salt. 



This last experiment made Fourcroy and Vauquelin 

 "suspect that this might be the same substance which causes 

 that diversity of colour which the precipitates of platina 

 formed by sal-ammoniac assume ; and this opinion they 

 placed beyond all doubt by processes which we shall here 

 mention. Hitherto every thing announced to them, that 

 the black powder which remains after the solution of the 

 platina contained together with chrome a new metal; but 

 to be convinced of this fact it was necessary to obtain it se- 

 parately, and in the metallic state. 



For this purpose, as the above trials had indicated to them 

 the presence also of a small quantity of iron, they evapo- 

 rated "to dryness the muriatic solution before mentioned, 

 and then treated the residuum with alcohol : the latter dis- 

 solved the muriate of iron, and left a red powder in which 



the 



