IRIDOSM1NE AND PLATINUM RESIDUES. 119 



heating in the oxyhydrogen flame, the indium contain- 

 ing ruthenium and rhodium will be fused. 



The pulverulent iridosmine is easily separated by 

 fusing in a silver crucible with caustic potassa and 

 chlorate of potassa. It is heated carefully in the be- 

 ginning on account of the frothing, but finally to red- 

 ness. The mass is treated with water^ until dissolved, 

 and then left in a high closed vessel until it has settled 

 clear. The deep yellow solution of osmiate and ru- 

 theniate of potassa are drawn off clear by means of a 

 syphon, and the black residue, consisting of oxides of 

 rhodium and iridium treated again in the same manner 

 with M^ater. From the yellow solution ruthenium is 

 precipitated as a black oxide by carefully neutralizing 

 with nitric acid. It is reduced by means of hydrogen. 



The solution containing osmium is made alkaline 

 with potassa, alcohol added and heated, whereby the 

 osmium is precipitated as a black oxide containing 

 potassa. It is ignited in hydrogen and the potassa 

 removed by water. 



The oxide of iridium is reduced by heating in hydro- 

 gen, washed, intimately mixed with an equal weight 

 of fused chloride of sodium, and gently ignited in a 

 current of chlorine, until the gas passes off unabsorbed 

 in excess. The resulting double chloride is dissolved in 

 water, the solution concentrated and mixed with an ex- 

 cess of a hot saturated solution of chloride of potassium, 

 when the iridium is precipitated as a black crystalline 

 double chloride. It is then washed with a saturated 

 solution of chloride of potassium. (It may also con- 

 tain some of the ruthenium salt precipitated at the 

 same time. In order to extract this the metal is fused 

 with caustic and chlorate of potassa.) 



The solution which contains the rhodium and the 

 ruthenium is concentrated, formate of soda added and 

 boiled, when all the rhodium is precipitated. The 



