254 THE ATOMIC WEIGHTS. 



K = 39, N = 14, Ag = 108, and CI = 35.5, give nearly 



Pt = 195, namely : 



194.906 



194-933 

 194-955 



The general mean of all, if = 16, giv.es Pt == 194.867. 

 Hence, for all practical calculations, the value 195 may be 

 safely employed. 



OSMIUM. 



The atomic weight of this metal has been determined by 

 Berzelius and by Fremy. 



Berzelius* analyzed potassium osmichloride, igniting it 

 in hydrogen like the corresponding platinum salt. 1.3165 

 grammes lost .3805 of chlorine, and the residue consisted of 

 .401 grm. of potassium chloride, Avith .535 grm. of osmium. 

 Calculating only from the ratio between the Os and the KCl, 

 we have, Os = 198.494 ; or, if = 16, Os -- 198.951. 



Fremy's determination f is based upon the composition of 

 osmium tetroxide. No details as to weighings or methods 

 are given ; barely the final result is stated. This, if = 

 15.9633, is Os = 199.190. If = 16, Os = 199.648. 



Berzelius' work is evidently entitled to preference, althougli 

 neither determination is in any sense equal to the present 

 requirements of chemical science. The values given are 

 doubtless several units too high. 



IRIDIUM. 



The only early determination of the atomic weight of 

 iridium was made by Berzelius,| who analyzed potassium 

 iridichloride by the same method employed with the plati- 

 num and the osmium salts. The result found from a single 



* Poggend. Annal., 13, 530. 1828. 



t Compt. ReiuL, 19, 46S. Journ. fiir Prakt. Chem., 2,T), 410. 1844. 



■t Poggend. Annal., 13, 435. i8.:8. 



