T II K 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



DECEMBER 1837. 



LXVIII. On the Action of Chromic Acid upon Silver, and its 

 Combinations with the Oxide of that Metal, By R. Wa- 

 zington, Esq.* 



"IIlTHEN liquid sulphuric acid is added to a solution of the 

 7 bichromate of potass and a plate of silver immersed, 

 or the mixed solutions poured into a silver capsule, an imme- 

 diate chemical action takes place, and the whole surface of 

 the metal becomes covered with a scarlet-coloured precipitate, 

 which in a very short time assumes a crystalline structure, 

 and is changed to a dark crimson ; this salt is the bichromate of 

 silver, as will be demonstrated by analysis in a subsequent part 

 of this paper. The precipitate should be removed at intervals 

 to facilitate the progress of the action, as it would otherwise 

 form a coating over the surface of the silver and prevent the 

 acid from acting with its full energy. During this operation 

 the colour of the supernatant liquid becomes much deeper, 

 until the orange red tint of the original solution has become of 

 a dark mahogany hue, and it then passes gradually into a deep 

 green. This solution yields by evaporation one or two s uts 

 that will be hereafter described, and a large quantity of very 

 fine octohedral crystals of the double sulphate of the prot- 

 oxide of chromium and potass, or chrome alum. 



Now to account for these phenomena, it must be evident 

 both from the nature of the materials employed, and also of 

 the compounds arising from their action, that the silver must 

 become oxidized (this being necessary before any combination 

 can take place between it and the chromic acid) at the ex- 



* Communicated by the Author. 

 Third Series. Vol. 11. No. 70. Dec. 1837. 3 R 



