W. Gibhs on the Platinum metals. 345 



present, it is better, after adding the alkaline carbonate and nitrite, 

 to evaporate the whole to perfect dryness on a water-bath and 

 treat the dry and powdered mass with a small quantity of abso- 

 lute alcohol. The alcoholic solution is then to be filtered off, 

 and tested directly with sulphid of ammonium. In this mi 

 the smallest trace of ruthenium may be detected, even in the 

 presence of very large quantities of the other platinum metals 

 A solution of the double nitrite of ruthenium and potassium ii 

 completely precipitated by a long continued current of sulphy 

 dric acid gas. Sulphid of ammonium also precipitates the solu 

 tion after a short time, but when added in excess redissolves the 

 dark chocohite-brown precipitate. The addition of a slight ex- 

 cess of dilute chlorhydric acid then completely precipitates the 

 sulphid of ruthenium. 



Ir{dium,-~\Y \ien a solution of nitrite of potash or soda is 

 added to one of chloro-iridate of potassium or ammonium, 

 the color of the solution instantly changes to olive-green, the 

 iridium being reduced from bichlorid to sesquichlorid. The 

 reduction takes place most rapidly in a hot solution, in which 

 It IS almost instantaneous. When the solution cools, the new 

 double chlorid usually crystallizes. An alkaline nitrite is 

 afar more elegant and convenient reducing agent for the sepa- 

 ration of iridium from platinum than either sulphuretted hydro- 

 gen, sulphurous acid or cyanid of potassium. The reduction in 

 question is expressed by the equation, 



2(IrCl2.KC!)4-KO, NOg^Ir^CIg, SKCl+NO^ 



A very different result is however produced when an excess 

 of nitrite of potash is added to a solution containing either of 

 thechlorids of iridium, and the solution is boiled for a few min- 

 ''-s or even allowed to evaporate spontaneously. The olive- 

 liquid becomes yellow and contains the whole of the 

 1 in the form of a double salt which is soluble in water 

 -"'luble in alcohol. 



'•■11 however the solution is boiled, an excess of the alkahne 

 ; ■''-^ being present, part of the iridium is thrown down as a 

 |- -ivy snow-white powder, which is insoluble in cold water; hot 

 ^vater dissolves it in small proportion; the solution however 

 'peedily becomes milky and remains so for a long time. Chlor- 

 ^^'.'^ric acid even on boiling exerts but little action upon it. 

 -^itro-muriatic acid with the aid of heat gradually yields a solu- 

 ^^01^ containing bichlorid of iridium. The insolubility of this 

 '^^fnpound in water and acids is very remarkable, the similar 

 salts of the other platinum metals being nearly all readily soluble 

 ^'ther in water or in dilute acids. Nitrite of soda under the 

 same circumstances forms with iridium a soluble orange-yellow 

 ^^^t. The two soluble double nitrites of iridium and potassium 

 ^^ sodium give no precipitate with alkaline sulphids even on 



