EFFECT OF NEW ATOMIC WEIGHTS. 67 



THE NEW ATOMIC WEIGHTS OF SODIUM AND CHLORINE AND 

 THEIR EFFECT ON OTHER ATOMIC WEIGHTS. 



From the preceding description of the syntheses of argentic 

 chloride, it is clear that 100.000 grams of the purest metal yields 

 132.867 grams of chloride. If then the atomic weight of silver is 

 taken as 107.920* (a convenient value to assume for preliminary 

 calculation), the molecular weight of argentic chloride becomes by 

 simple proportion 143.393, and by difference the atomic weight of 

 chlorine becomes 35.470^ This value is about 0.05 per cent greater 

 than the value announced by Stas ; and the change produces a serious 

 effect on a number of atomic weights. It is, of course, impossible to 

 be perfectly certain of the accuracy of the new value, because it may 

 contain concealed within it some entirely unsuspected source of error, 

 but at least it is free from the real mistakes in the earlier work. It 

 was reasonably certain that at least ten more syntheses would be 

 needed to affect the value one unit in the third decimal place, if the 

 further results varied no more widely than those recorded above in the 

 final series. Hence it seems unlikely that chlorine is above 35.471 or 

 below 35.469 if silver is taken as 107.920. 



What, now, is the effect of this new value upon the atomic weight 

 of sodium? In the table given upon page 44 it is shown that 100.000 

 grams of argentic chloride could be obtained from 40.780 grams of 

 sodic chloride. If now argentic chloride is taken as 143.390, sodic 

 chloride becomes 58.474, and by subtracting the new value for chlorine, 

 23.004 is obtained as the new value for sodium. 



This is not, however, the only value for sodium which may be 

 calculated from our results. On page 52 has been given a table show- 

 ing the results of ten experiments on the comparison of sodic chloride 

 with silver direct, and on page 56 the results of two more. These deter- 

 minations were made before we had discovered the best method of 

 obtaining pure silver ; but the trace of impurity is allowed for in those 

 tables, and it is safe to conclude that 100.000 parts of the purest silver 

 are equivalent to 54.185 parts of sodic chloride. If, then, silver is 

 taken as 107.920 and chlorine as 35.470, sodium becomes 23.007. 



Thus two entirely independent values, calculated from two entirely 

 separate series of experiments, yield respectively the values 23.004 and 

 23.007 for the atomic weight of sodium. Of these two, the latter is 



*F. W. Clarke has for a long time accepted this value, and it is now assumed 

 because it is probably nearer the true value than 107.93. 



tin this connection it should be pointed out that Leduc called attention to 

 the fact that if Stas's silver really contained as much oxygen as Dumas said it 

 must, chlorine would become 35.47. Compt. Rend. (1901). 



