Prof. R. Bunsen on Rhodium. 253 



are to be heated or boiled again, it is well to rinse out the flask 

 in which the solution is to be kept fluid with the acid of the 

 salt, such as a little strong acetic acid for an acetate, nitric 

 acid for a nitrate, and so on. For ammoniacal salts, a little 

 solution of ammonia should be used. In this way, not only 

 is the surface cleaned in the best manner, but any loss of 

 acid or of ammonia during the heating is compensated. The 

 flame of a spirit-lamp may often be used in cleaning such sur- 

 faces as those of platinum wire and foil, or of a glass rod, &c. 



Highgate, N. 

 September 3, 1868. 



XXXIII. On Rhodium. By R. Bunsen*. 



[With a Plate.] 



N working platinum ores on a manufacturing-scale, three 

 products are obtained, which are principally used for the 

 preparation of the other metals occurring along with platinum. 

 These are : — 



(1) The residues which remain after extracting the ores with 

 aqua regia; they are rich in osmium and iridium, and are there- 

 fore especially fitted for the preparation of these metals. 



(2) Osmium-indium, which is obtained from these first residues 

 by lixiviation, and which serves best for the preparation of ru- 

 thenium. 



(3) The residues of the mother-liquors, which have been re- 

 duced by iron from the aqua-regia solution from which the pla- 

 tinum has been removed; being especially rich in palladium 

 and rhodium, they are most conveniently used for obtaining 

 these metals. 



The following investigation was made with a material of this 

 kind, which was supplied to me with the utmost liberality from 

 the Imperial Mint in Petersburg. A kilogramme was used for 

 each operation. These Petersburg residues contain all the pla- 

 tinum-metals with the exception of osmium, and are especially 

 interesting owing to the large quantity of rhodium they contain. 

 Claus, who worked on this subject, has endeavoured, if not to 

 eliminate, at any rate to diminish the great difficulties incident 

 to their preparation. The method he adopted, however, is ex- 

 tremely tedious^ and scarcely practicable without sacrificing a 

 great part of the valuable platinum- metals which accompany 

 rhodium. In separating rhodium from iridium he used Wol- 

 laston's original process, which is based on the solubility, in 

 chloride of ammonium, of the ammonium and potassium double 



* Translated from Liebig's Annalen, June 1868. 



