628 Foreign and Miscellaneous Intelligence. 



absorption of the metal by the cupel, especially towards the close of 

 the operation *. 



17. ROBIQUET ON A NEW METALLIC DYE. 



A stuff dyed of a clear bluish-grey colour was taken to M. Robiquet 

 as able to stand the action of every agent without change of tint, a 

 character which M. Robiquet ascertained it to deserve. Concluding 

 that it was metallic, it was also concluded that it must be chloride of 

 silver, from its colour and characters ; on boiling the cloth in am- 

 monia, however, no silver, or chloride of silver, was dissolved, the 

 colour, indeed, became brighter. On incinerating the substance and 

 digesting the ashes in ammonia, and then in nitric acid, both solvents 

 dissolved silver, the first having taken up muriate of silver, and the 

 latter having dissolved the metal. 



As it was not likely that any chloride would be decomposed and 

 brought into the metallic state by incineration, it was supposed that 

 the silver had been applied at first as a nitrate and then converted 

 into a chloride; the parts which had penetrated deepest having escaped 

 the converting action. Imitations of the dye were therefore made 

 by dipping the cloth first into solution of nitrate of silver, then drying 

 it, immersing it in a solution of a muriate or of chloride of lime, and 

 immediately upon withdrawing it, exposing it to light ; the colour was 

 at once developed, and the success was perfect. By using different 

 strengths of solution of silver, different tints were obtained. 



Upon trying the application in a large way, a curious cause of 

 failure occurred. Unless the whole be exposed to the light at once, 

 the colour is not uniform ; the parts exposed at different times are 

 dissimilar, and hence cloudiness is produced. This may be obviated 

 in some situations, but not in others, where space is limited. 



In printed goods it is supposed that some good applications of 

 this idea may be madet. 



18. PURPLE PRECIPITATE OP SILVER, GOLD, &c. &c. 



Fischer has shewn that protosalt of tin yields with solutions of 

 silver, platina, palladium, and tellurium, precipitates similar to those 

 produced with solution of gold. Frick has shewn that the silver 

 precipitate may be prepared of great purity, by using a very pure 

 protonitrate of tin, and after adding it to the solution of silver, 

 adding also dilute sulphuric acid. The addition is supposed to pre- 

 vent the further oxidation of the tin by the free nitric acid, and so 

 alter the precipitate. The protonitrate of tin is to be prepared by 

 decomposing the protomuriate by nitrate of lead. In the purple 

 precipitate of silver, the combination is as strong as in Cassius' 

 purple ; the substance is not decomposed either by muriatic acid or 

 ammonia. 



Ann. de China., xlv. p. 221, f Jour, de Pharm., 1831, p. 162. 



