186 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



The atomic weights used in reducing tliese ratios are : 



Ag = 107.880, ± .00029 Br = 79.9197, ± .0003 



CI = 35.4584, ± .0002 S = 32.0667, ± .00075 



H=: 1.00779, ± .00001 



Hence, 



From ratio 3 Sr = 86.899, ± .0811 



" 2 87.366, ± .0178 



" 4 87.614, ± .0026 



" 1 87.616, ± .0018 



" 5 87.621, ± .0024 



General mean, Sr = 87.616, ± .0013 



Ratios 2 and 3 evidently count for nothing in this combination. 

 final value for strontium is practically that of Richards alone. 



The 



Addendum. Since the manuscript of this volume went to the printer, 

 Sir Edward Thorpe has kindly sent me, in advance of publication, the 

 work of Thorpe and Francis ^ on the atomic weight of strontium. Six 

 ratios were measured, involving the chloride, bromide, and sulphate of 

 strontium, all with vacuum weights, and with every known precaution 

 to ensure accuracy. For details the published memoir must be con- 

 sulted. 



First. The ratio 2Ag : SrBr, : 



8rBr.,.. 



1.77884 



1.86109 



1.85254 



1.73801 



1.85787 



1.70563 



.0040 



Hence Sr=: 87.644. 



Second. The ratio 2AgBr : SrBr„ : 



SrBr^. AgBr. 



1.80112 2.82438 



1.85261 2.81155 



1.73807 2.63762 



1.85798 2.81999 



1.70571 2.58806 



Ratio. 



65.895 

 65.893 

 65.895 

 65.886 

 65.892 



Hence Sr = 87.651. 



Mean, 65.892, ± .0011 



1 Proc. Roy. Soc, S3A, 277. 1910. 



