354 W. Gibbs on the Platinum metals. 



The undissolved mass, which consists chiefly of the impurities 

 of the ore, when these have not been removed before the process 

 of oxydation, is then to be thrown upon a filter and washed with 

 boilins: water until the washings are colorless. By keeping the 

 solutio'n somewhat alkaline the whole of the iron remains upon 

 the filter as sesqaioxyd Avith the other impurities. The filtrate 

 contains iridium and rhodium as scsqnichlorids, ruthenium partly 

 as bichlorid and partly as protochloiid, platinum as bichlorid. 

 When the operations* already mentioned have been well per- 

 formed, no determinable quantities of osmium and palladium 

 are present. On cooling the greater part of tlie platinum is de- 

 posited as PtCl3,KCl, mixed with a little of the corresponding 

 iridium salt, and is to be separated by pouring otf the olive-green 

 supernatant liquid. The quantity of the alkaline nitrite to be 

 added in this process need not exceed half of the weight of the 

 mass of double chlorids, but with a little experience it will be 

 found unnecessary to weigh the nitrite added, the process of 

 the reduction of the iridum salt, IrCUKCl, being evident to 

 the eye. 



To the filtrate a solution of nitrite of soda is to be added and 

 the whole boiled until the liquid assumes a clear orange color. 

 Nitrite of soda should be used in this process because the result- 

 ing double nitrite of iridium and soda is easily decomposed by 

 boiling with chlorhydric acid, which is not the case with the 

 potash salt. When" nitrite of potash is used a small quantity ot 

 the white insoluble double salt already mentioned is usually 

 formed and renders the solution turbid. 



To the clear yellow or orange-yellow boiling solution sulplud 

 of sodium is to be added until a portion of the dark brown pre- 

 cipitate of the sulphids of ruthenium, rhodium and platinum is 

 dissolved with a brown-yellow color, and an excess of the alka- 

 line sulphid is consequently present. The liquid is then to be 

 allowed to cool and treated with dilute chlorhydric acid uiitu a 

 distinctly acid reaction is produced. In this manner the wlioic 

 of the platinum, ruthenium and rhodium present in the solution 

 are thrown down as insoluble sulphids. After complete subsi- 

 dence the sulphids are to be thrown on a double filter and thor- 

 oughly and continuously washed with boiling water. When tHe 

 operation is ciirefullv performed the filtrate and washings con- 

 tain only iridium. It is best to neutralize this solution witij 

 carbonate of soda, boil a second time with a little additional 

 nitrite of soda and treat as before with sulphid of sodium and 

 chlorhydric acid. In this manner very small additional quanti- 

 ties of the sulphids of platinum, ruthenium and rhodium va&y 

 sometimes be separated. 



