PLATINUM KESIDUES. 121 



The ruthenium is combined with the iridium. They 

 are separated, as already stated, by fusing with caustic 

 and chlorate of potassa. 



The rhodium is contained in the remaining solution 

 of chloride of ammonium. It is heated with a large 

 excess of nitric acid, evaporated to a small quantity, 

 placed in a weighed porcelain crucible, evaporated to 

 dryness, and the salt, heated to redness, is reduced by 

 conducting a stream of hydrogen upon it. 



The iron, copper, baryta, and alumina (the last from 

 the peroxide of barium) are separated by alternate 

 treatment with hydrochloric and nitric acids. 



The solution is neutralized with carbonate of soda, 

 and the palladium precipitated by a solution of cyanide 

 of mercury. The yellowish-white cyanide of palla- 

 dium having settled, it is filtered off, washed, and ig- 

 nited, when metallic palladium is left behind. 



The filtered solution is boiled with hydrochloric acid 

 until it has assumed a red tint, and the hydrated oxide 

 of rhodium is then precipitated by caustic potassa. By 

 ignition in hydrogen it is reduced to the metallic state. 



From the solution which contains the rhodium and 

 palladium both metals may also be precipitated by 

 pure zinc, with the addition of hydrochloric acid, the 

 precipitate washed, and the palladium extracted by 

 nitric acid, in which the rhodium is insoluble. 



If the rhodium be not reduced by formic acid, the 

 solution obtained with bisulphate of potassa might also 

 be mixed with formate of soda and boiled, when pal- 

 ladium is separated in the metallic state. If both be 

 reduced, the palladium could be extracted from the 

 mixture by means of nitric acid. 



II. PLATINUM-RESIDUES. 



There are two kinds. The kind A is that which 

 remains insoluble when large quantities of platinum 



