254 Prof. It. Bunscn on Rhodium. 



salts of scsquichloride of rhodium. The circumstance that, as 

 I have found, the bichloride of potassium and iridium is dissolved 

 to a considerable extent by a solution of sal-ammoniac, or chloride 

 of potassium saturated with rhodium-salt, must excite a reason- 

 able doubt whether the metal thus prepared, and which has 

 hitherto been regarded as the purest rhodium, and to which 

 Claus, like Berzelius, assigned the atomic weight 52, does not 

 contain considerable quantities of iridium. Hence it seemed ne- 

 cessary to forsake the old way and attempt a more exact method, 

 so as to settle the doubts which the various and frequently dis- 

 cordant statements about rhodium still leave. 



1. Separation of Platinum and Palladium. 



The separation from platinum and palladium of rhodium, iri- 

 dium, and ruthenium, which are insoluble in aqua regia, by di- 

 gestion with this mixture, does not succeed with the residues in 

 question; for a considerable portion of the latter metals is pre- 

 sent partly in a finely divided state, partly in the form of hy- 

 d rated scsquioxides, and consequently is dissolved in large 

 quantities with the former metals — apart from the circumstance 

 that the residue is filtered with extreme difficulty. But it is easy 

 to extract platinum and palladium almost completely from the 

 other metals by mixing the original material with one-third to 

 one-half its weight of sal-ammoniac and heating the mixture 

 gently in a Hessian crucible until the sal-ammoniac is completely 

 volatilized and only vapours of chloride of iron are seen ; the 

 residue is then heated in a large porcelain dish with two to three 

 times its weight of crude commercial nitric acid, and evaporated 

 to the consistence of syrup. By ignition with sal-ammoniac, the 

 metals not belonging to the platinum group arc partially con- 

 verted into chlorides; iridium, rhodium, and ruthenium are 

 rendered insoluble, and the gelatinous silica present in the 

 original material transformed into a pulverulent condition^ so 

 that it can be readily filtered. The chlorides formed from the 

 sal-ammoniac yield, when digested with nitric acid, just as much 

 hydrochloric acid as is sufficient for dissolving the platinum as 

 bichloride; at the same time the copper and iron present reduce 

 the palladium dissolved in nitric acid to such an extent that it is 

 contained in the solution, not as bichloride, but as monochloride, 

 which is not precipitated by chloride of potassium. Hence the 

 mass, after treatment with nitric acid, need only be digested with 

 water, filtered, and saturated with chloride of potassium, to ob- 

 tain at once the greater part of the platinum as very pure bright 

 yellow potassiochloride of platinum. This is washed with chlo- 

 ride of potassium and then with spirit, and the latter must not 

 be mixed with the solution. The platinum precipitate weighed 



