Obtaining Iridium and Osmium from the Platinum residue. 373 



i 

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The greater part of the osmic acid, is likewise deposited in a 

 beautiful crystallization in the balloon. In order to preserve it as such, 

 the balloon is gently warmed and it is suffered to flow into a close- 

 ly shutting vial or into a tube which may be closed by the blowpipe. 

 But the greatest precaution must be observed by this operation, for 

 there is probably no substance which highly diluted with air is more 

 capable of violently and dangerously affecting the eyes and lungs than 

 osmic acid. Nothing is easier than repeatedly to crystallize this most 

 curious substance. If the vessel containing it be placed in a window 

 or in such a manner that one side is cooler than the other, it sublimes 

 like camphor, from one part to another, sometimes in well formed 

 and often very long crystals. 



To the ammonia, which is colored yellow from the absorption of 

 more or less osmic acid, muriate of ammonia and carbonate of soda 

 are added, the whole evaporated to dryness and heated at a low red 

 heat in a retort. The acid is by this means reduced to the metallic 

 state, and upon treating with water remains as a black powder. It is 

 washed and dried. The osmic acid in the balloon may be reduced in 

 the same manner after solution in ammonia. 



The content of the large tube is somewhat caked together (agglu- 

 tinated). By placing this tube in a large cylinder of waier, the mass 

 is easily loosened and the soluble parts extracted. A deep brown 

 solution is obtained of a double salt of iridium. It smells faintly of 

 osmic acid arising from decomposing chloride of osmium. The solu- 

 tion is decanted from the remainder, which consists principally of 

 titanate and chromate of iron and in which may be observed the 

 larger leaves of osmium-iridium. The decanted fluid may be sub- 

 jected to distillation to obtain more osmic acid, the receiver contain- 

 ing ammonia. When one half the liquid has passed over, the ope- 

 ration is terminated and the remainder filtered. 



It is now placed over the fire in an evaporating dish and during its 

 vaporization, carbonate of soda is gradually added until it is in excess, by 

 which a precipitate, at first brown but at length blue-black, is formed. 

 The dried black mass is gently ignited in a Hessian crucible and 

 after cooling, heated with water. A coal-black powder remains con- 

 sisting chiefly of the deutoxide of iridium (i r ). It is washed and dri- 

 ed. The solution is thrown away, since in addition to common salt 

 and carbonate of soda, it contains merely, an alkaline chromate 

 producing its yellow color. 





