IRIDIUM. 



325 



These figures serve to fix the place of osmium below iridium in the 

 periodic classification of the elements, but are not concordant enough to 

 be fully satisfactory. More determinations are evidently needed. 



IRIDIUM. 



The only early determination of the atomic weight of iridium was 

 made by Berzelius * who analyzed jootassium iridichloride by the same 

 method employed with the platinum and the osmium salts. The result 

 found from a single analysis was not far from Ir = 196.7. This is now 

 known to be too high. I have not, therefore, thought it worth while to 

 recalculate Berzelius' figures, but give his estimation as it is stated in 

 Roscoe and Scho'rlemmer's " Treatise on Chemistry." 



In 1878 the matter was taken up by Seubert,t who had at his disposal 

 150 grammes of pure iridium. From this he prepared the iridichlorides 

 of ammonium and potassium (NH J JrClg and KJrClg, which salts were 

 made the basis of his determinations. The potassium salt was dried by 

 gentle heating in a stream of dry chlorine. 



Upon ignition of the ammonium salt in hydrogen, metallic iridium 

 was left behind in white coherent laminae. The results obtained were as 

 follows : 



Am-JrCl^. Ir. Per cent. Ir. 



1-3164 .5755 43725 



1. 7122 .7490 43-745 



1.2657 .5536 43 



1.3676 .5980 43 



2.6496 I. 1586 43 



2.8576 1.24S9 43 



2.9088 1.2724 43 



739 

 726 



739 

 70s 

 742 



Mean, 43-732, ± .0035 



The potassium salt was also analyzed by decomposition in hydrogen 

 with special precautions. In the residue the iridium and the potassium 

 chloride were separated after the usual method, and both were estimated. 

 Eight analyses gave the following weights : 



* Poggend. Annalen, 13. 435. 1828. 



tBer. Deutsch. Chem. Gesell., ir, 1767. 1S7S. 



