THE ATOMIC WEIGHT OF POTASSIUM. 43 



THE ATOMIC WEIGHT OF POTASSIUM. 



The preceding paper and the present one together yield four ratios 

 determined with modern precision, which together fix the atomic weight 

 of potassium as definitely as could be expected. The respective values are 

 as follows: 



From the ratio of argentic to potassic chloride K = 39. 11 34 



From the ratio of metallic silver to potassic chloride .... K = 39. 1145 



From the ratio of argentic to potassic bromide K = 39. 11 35 



From the ratio of metallic silver to potassic bromide .... K = 39. 11 43 



Average atomic weight of potassium, if Ag= 107.930 . . . K = 39. 11 39 



These figures are interesting and significant. The maximum departure 

 from the mean is only 1 part in 70,000, and such differences as exist in the 

 figures are explicable. It is likely that the slightly lower value given by 

 the first member of each pair of series was due to a trace of occlusion of 

 potassic nitrate by each of the precipitates a circumstance which can not 

 be absolutely prevented. Therefore the higher values, averaging 39.1144, 

 are more probable. The differences are, however, wholly negligible at 

 present. 



In this connection it is interesting to note that Clarke in 1897, from a 

 miscellaneous collection of partly uncertain results obtained by others, 

 decided upon the almost identical value, 39.112, 1 although at the same time 

 from similar results he obtained values much too low for chlorine and 

 iodine, somewhat too low for bromine, and much too high for sodium. 



The very close mutual agreement of the new results obtained from two 

 different compounds is a satisfactory verification of the relative values 

 yielded by the recent work on the atomic weights of chlorine and bromine. 2 

 The value of chlorine found from the work on potassium chloride was 

 35.475 ; and that of bromine from the present work is 79.954. The ratio 

 of chlorine to bromine is thus found to be 0.44369, whereas the ratio com- 

 puted from the work of Richards and Wells and of Baxter is 0.44367. 



Against such an accumulation of concordant data as that just presented, 

 the older figures can have no important weight. Whatever may have been 

 the cause of the irregularity and internal inconsistency of Stas's results 

 with potassic chloride and bromide, there seems to be little reason to 

 doubt that the outcome of the present investigation, 39.114, really repre- 

 sents the atomic weight of potassium. 



It is needless to point out that this change in the atomic weight of potas- 

 sium will affect many other atomic weights. 



Recalculations, p. 57. 



2 Richards and Wells, loc. cit; Richards, Trans. Amer. Phil. Soc., 43, 116 (1901) ; 

 Baxter, loc. cit. 



