RICHARDS. — THE ATOMIC WEIGHT OP STRONTIUM. 607 



It must be borne in mind that the standard Ag = 107.930 is probably 

 not precise, if oxygen is taken as 16.000. The recent work just cited 

 has shown that the silver of Stas must have contained weighable traces 

 of impurity, and therefore that silver must have a lower atomic weight 

 than 107.93. Because, however, the exact value is still uncertain, the 

 value 107.930 is still retained, in order to avoid an additional shift from 

 one arbitrary standard to another. An alteration in the assumed value 

 for silver affects that for strontium in direct proportion, and may there- 

 fore be applied at any time. 



Summary. 



In this paper are detailed four determinations of the atomic weight of 

 strontium, by comparison of strontic chloride with silver. Calculated 

 upon the basis of the old incorrect value for chlorine, these results yield 

 a value higher than that obtained from strontic bromide ; but on the 

 basis of the new value for chlorine 35.473 (silver being assumed as 

 107.930) the two different series yield almost identical results. Accord- 

 ingly the new value for chlorine is confirmed by this investigation. The 

 atomic weight of strontium is thus found as follows (Ag = 107.930). 



From SrBr.; 8r = 87.663 

 From SrCl^; Qr = 87.661 

 Average Sr = 87.662 



