PROCEEDINGS 



OF THE 



AMERICAN ACADEMY 



OF 



ARTS AND SCIENCES. 



VOL. XXVIII. 

 PAPERS READ BEFORE THE ACADEMY. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF BARIUM. 

 FIRST PAPER: THE ANALYSIS OF BARIC BROMIDE. 



By Theodore William Richards. 



Presented January 11, 1803. 



Table of Contents. 



PAGE 



Introduction 1 



Balance and Weights 5 



Spectroscopic Detection of Calcium, 



Strontium, and Barium .... 7 



Choice of Material 9 



Properties of Baric Bromide . . 

 Preparation of Materials . . . 

 Method of Analysis . . . . 



Data and Results 



The Atomic Weight of Barium 



PAOl 

 11 

 10 



23 

 36 

 80 



Introduction. 

 In the course of a recent determination of the atomic weighl of 

 copper,* there was an attempt made to determine (the ratio of cupric 

 to baric sulphate; hut in the discussion of the result it became 

 evident that the ordinary method of precipitation was far too crude 

 for the desired purpose. Moreover, even had there not been pos- 

 sible errors of a serious nature in the method, the atomic weigh! "f 

 barium was evidently too uncertain to form the basis of any accu- 

 rate comparison. Hence this attempt was at the ti given op, 



* These Proceedings, Vol. XXVI. p. 2 

 vol. xxvni. (n. s. xx.) 1 



