BICHARDS. — ATOMIC WEIGHT OF STRONTIUM. 



369 



XIV. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLIiGE. 



A REVISION OF THE ATOMIC WEIGHT OF 



STRONTIUM. 



FIRST PAPER: THE ANALYSIS OF STRONTIC BROMII)E. 



By Theodore William Richards. 



Presented June 9, 1894. 

 « 



Table of Contents. 



Earlier Work 364 



Properties of Strontic Bromide . . 373 



Preparation of Materials .... 375 



Method of Analysis 380 



PAGE 



Ratio of Silver to Strontic Bromide . 384 

 Ratio of Argentic to Strontic Bromide 388 

 Final Averages 389 



Earlier Work. 



A GLANCE at published results shows that the atomic weight of 

 stroutiuin has not been investigated for thirty-five years. The early 

 determinations, good enough for their time, show variations which 

 render them quite unsatisfactory to-day ; and the case is parallel in 

 every respect to that of barium, which has formed the subject of two 

 recent papers.* 



The oldest experiments of any note upon the atomic weight of stron- 

 tium are those of Stromeyer,t who measured, in 1816, the gas evolved 

 from strontic carbonate upon its decomposition by an acid. The 

 result, which is only of interest historically, gives Sr = 87.3, if a litre 

 of carbon dioxide weighs 1.977 grams under normal conditions. 



At about the saine time Rose t found that 181.25 parts of argentic 

 chloride could be obtained from a hundred parts of strontic chloride, — 

 data which indicated Sr = 87.31. Twenty-seven years afterward, in 



* These Proceedings, XXVIII. 1 ; XXIX. 55. 



t Schweig. J., XIX. 228 ; Meyer u. K. Seubert's Atomgewichte, p. 123. 

 } Poggendorff's Annalen, VIII. 189. 

 VOL. XXX. (n. s. XXII.) 24 



