ATOMIC WEIGHTS 473 



PLATINUM. 



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

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

 per cent, of platinum. Hence Pt = 194.69. In a later investigation,' 

 he studied potassium chloroplatinate, KoPtClp. 6.981 parts of this salt, 

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

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

 calculate the atomic weight of platinum, in four ways : 



1. From loss of CI upon ignition Pt = 198.25 



2. From weight of Pt in residue " = 197.42 



3. From weight of KCl in residue " = 196.63 



4. From ratio between KCl and Pt " = 197.10 



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 fore- 

 going, partly for the reason that its full details seem never to have been 

 published. 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 the atomic weight of platinum : 



197.86 

 197.68 

 198.12 



Mean, 197.887 



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



In 1881 Seubert * published his determinations, basing them upon 

 very pure chloroplatinates of potassium and ammonium. The ammonium 

 salt, (]SrH4)oPtCl6, was analyzed by heating in a stream of hydrogen, 

 expelling that gas by a current of carbon dioxide, and weighing the 

 residual metal. In three experiments the hydrochloric acid formed 

 during such a reduction was collected in an absorption apparatus, and 



^ Poggend. Annalen, 8, 177. 1826. 



- Poggend. Annalen, 13, 468. 1828. 



■■! British Assoc. Report, 1852. , 



•1 Ber. Deutsch. chem. Gesell. , 14, S65. 



