392 Intelligence and Miscellaneous Articles. 



ANALYSIS OF THE PURPLE POWDER OF CASSIUS. BY M. FIGUIER. 



In our last Number we gave the author's mode of preparing this 

 compound ; we shall now state his analysis of it. 



The author remarks, that this substance has engaged the atten- 

 tion of numerous chemists, several of whom he names, and he consi- 

 ders that its composition is still not well understood ; and he ob- 

 serves, that it has been regarded, — 1st, as a mixture, or true combina- 

 tion of gold and stannic acid ; 2nd, as a mixture of oxide of gold, or 

 of metallic gold and peroxide of tin ; 3rd, as a compound of prot- 

 oxide of tin and hypothetical binoxide of gold, and afterwards as a 

 compound of protoxide of gold and a peculiar oxide of tin, St^ O^ ; 

 4th, as a mixture of subdeutochloride of tin and metallic gold ; 5th, 

 as a stannate of an unknown oxide of gold ; 6th, as a double stan- 

 nate of binoxide of gold and of protoxide of tin ; 7th, as a double 

 stannate of protoxide of gold and protoxide of tin. 



M. Figuier states, that from the results of his experiments he con- 

 siders that the purple of Cassius is a perfectly definite compound of 

 peroxide of tin and protoxide of gold ; the clearest proof which can 

 be given of the fact is, that the purple is formed in a direct manner 

 by the admixture of stannic acid and protoxide of gold ; to make this 

 experiment, it is merely requisite to boil protoxide of gold in a solu- 

 tion of stannate of potash obtained by dissolving in potash stannic 

 acid derived from the action of nitric acid on tin. The ])urple sepa- 

 rates in the state of a flocky precipitate, ditterent however, though but 

 slightly, in its colour from the protoxide employed ; analysis shows 

 that the compound is similarly constituted to the purple of Cassius. 



Other facts lead to the same conclusion. The purple of Cassius, 

 treated with hydrochloric acid, yields a solution of ])ichloride of tin 

 without any trace of protochloride ; boiling potash also takes stannic 

 acid from the purple powder, which may be proved by saturating the 

 alkali; these facts prove then, that stannic acid exists in the purple. 



The existence of protoxide of gold in this compound is unques- 

 tionable, for the purple of Cassius, and the protoxide of gold, when 

 dried, have exactly the same colour; added to which, when hydro- 

 chloric acid is made to react on the purple, the residue of the action 

 consists entirely of gold, which is what would be expected in this 

 Qase, for the hydrochloric acid decomposes the protoxide of gold, 

 forming water and leaving metallic gold. 



Adopting M. Fremy's opinion, that three equivalents of stannic 

 acid alM'ays enter into the composition of a neutral stannate, M. Fi- 

 guier gives the following as the formula and composition of the purple 

 powder of Cassius, the results arrived at being obtained by ditterent 

 methods : — 



3(StO0A^O-t-4HO, or 



Three equivalents of stannic acid .... 

 One . . . protoxide of gold 



Four ... water 



5841 100- 100- 

 M. Figuier remarks, that this view of the constitution of the purple 



