PLATINUM. 327 



And the six independent values for the atomic weight of iridium be- 

 come — 



From (i) It = 191.935, d= .0300 



From (2) "=: 191.51 1, ± .0221 



From (3) . . " r= 191.604, d= .0485 



From (4) . . . " = 191. 641, ±z .0622 



From (5) " = 191.833, ± .0641 



From (6) " =z 191.695, it .0966 



General mean Ir ^ 191.664, ± .0154 



If 0=16, Ir= 193.125. 



PLATINUM. 



The earliest work upon the atomic weight of this metal was done by 

 Berzelius * who reduced platinous chloride and found it to contain 73.3 

 per cent, of platinum. Hence Pt = 193.155. In a later investigation f 

 he studied potassium chloroplatinate, K^PtClg. 6.9S1 parts of this salt, 

 ignited in hydrogen, lost 2.024 of chlorine. The residue consisted of 

 2.822 platinum and 2.135 potassium chloride. From these data we may 

 calculate the atomic weight of platinum in four ways : 



1. From loss of CI upon ignition Pt ^ 196.637 



2. From weight of Pt in residue " ^ 195.897 



3. From weight of KCl in residue " ^ 195.384 



4. From ratio between KCl and Pt " r= 195.690 



The last of these values is undoubtedly the best, for it is not affected 

 by errors due to the possible presence of moisture in the salt analyzed. 



The work done by Andrews % is even less satisfactory than the foregoing, 

 partly for the reason that its full details seem never to have been pub- 

 lished. Andrews dried potassium chloroplatinate at 105°, and then 

 decomposed it by means of zinc and water. The excess of zinc having 

 been dissolved by treatment with acetic and nitric acids, the platinum 

 was collected upon a filter and weighed, while the chlorine in the filtrate 

 was estimated by Pelouze's method. Three determinations gave as fol- 

 lows for tlie atomic weight of platinum : 



197.86 

 197.68 

 198.12 



Mean, 197. 8S7 



Unfortunately, Andrews does not state how his calculations were made. 



*Poggend. Annalen, S, 177. 1826. 



tPoggend. Annalen, 13, 46S. 1828. 



I British Assoc. Report, 1S52. Chera. Gazette, 10, 



