250 . THE ATOMIC WEIGHTS. 



value very near that obtained most recently by Seubert. In 

 his later investigations, Berzelius * studied the potassium 

 chloroplatinate, K2PtCl6. G.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. From 

 these data we may calculate the atomic weight of platinum 

 in four ways : 



1st. From loss of CI upon ignition Pt = 197.722 



2d. " weight of Pt in residue " =196.942 



3d. " " KCl " " =-196.215 



4th. " ratio between KCl and Pt " =196.652 



The last of these values is undoubtedly the most reliable, 

 since it involves no errors due to the possible presence of 

 moisture in the salt analyzed. If ^ IG, the value be- 

 comes Pt = 197.104. 



The work clone by Andrews! is even less satisfactoiy than 

 the foregoing, for the reason that its full details seem never 

 to have been published. AndreAvs dried potassium chloro- 

 platinate 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 follows for the atomic weight of 

 platinum : 



197.86 



197.68 



198.12 



Mean, 197.887 



If we assume that these values were calculated with K = 

 39 and CI = 35.5, the mean, corrected by our later figures 

 for these elements, becomes Pt ^= 197.382. If O ^= 16, this 

 becomes Pt = 197.836. Unfortunately, Andrews does not, 

 in his brief note upon the subject, indicate the manner by 

 which his calculations were made. 



* Poggend. Annal., 13, 46S. 1828. 



f Bntibli Association Rejort, 1852. Chem. Gazette, 10, 380. 



