3 52 IF. Gihhs on the Platinum metals. 



It may happen that the precipitated sulphid of ruthenium 

 contains 'traces of iridium. This can only arise from imperfect 

 washing or want of proper care in precipitating with sulphid of 

 sodium. In this case the washings from the chloro-ruthenate of 

 ammonium are yellow and contain sulphate of iridium, probably 

 Ir^Og, 3SO3. The quantity of iridium in such cases is too small 

 to be worth the trouble of separate treatment. 



When a solution contains iridium and ruthenium in the form of 

 bichlorids, the ruthenium may be easily and completely separated 

 by boiling the solution with nitrite of potash in excess, adding 

 at the same time enough carbonate of potash to give an alkalme 

 reaction, evaporating to dryness and dissolving out the double 

 nitrite of ruthenium and potassium by means of absolute alcohol, 

 in the manner recommended for the separation of ruthenium 

 from platinum. The undissolved mass in this case contains the 

 two double nitrites of iridium and potassium. By adding a strong 

 solution of chlorid of ammonium, evaporating to dryness, igni- 

 ting the dry mass in a porcelain crucible, and dissolving out the 

 soluble salts, metallic iridium remains in a state of purity. This 

 method may be used for the quantitative separation of indium 

 from ruthenium, but when the object is simply to prepare both 

 metals in a state of chemical purity I prefer the separation by- 

 means of sulphid of sodium. 



Iridium from rhodium. — Iridium may be approximately sepa- 

 rated from rhodium by the process recommended by Claus, whicU 

 consists in taking advantage of the solubility of the double chlo- 

 rid of rhodium and ammonium, Rh,Cl3,3NH,Cl, in moderately 

 strong solutions of chlorid of ammonium in which chloro-indate 

 of ammonium is nearly insoluble. This method is difficult ot 

 application when the quantity of rhodium is small, and is at best 

 tedious and unsatisfactory. A better method is that given above 

 for the separation of iridium from ruthenium. The mixed soJa- 

 tions of iridium and rhodium are to be treated as above men- 

 tioned with nitrite of soda, the rhodium precipitated by sulpha 

 of sodium in slight excess, the liquid rendered slightly acid, H; 



tered and the dark brown sulphid of rhodii " '^'" 



The filtrate is perfectly i 



the manner already described. 



oxydized in the same manner as the sulphid of rutheniuui .— 



converted into the double chlorid of rhodium and ammonium, 



Rh„Cl3,3NH,Cl, which is insoluble in a cold saturated solution 



of sal-ammoniac, in which it may be washed once or twice t 



remove alkaline salts and any traces of iridium which "^^J^ 



present as sulphate. The rhodium salt is then to be purified oy 



crystallization, or converted into the chlorid of Claus's rbodmm- 



ammonia base by evaporation on a water-bath with a solution 01 



ammonia. The sulphate of iridium, Ir, 3 ,3S0 3 , does not give 



vn sulphid of rhodium thoroughly washed. 

 ' free from rhodium and is to be treated m 

 scribed. The sulphid of rhodium is to be 



