CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF 



CAESIUM. 



By Theodore William Richards and Ebenezer Henry Archibald. 



Presented December 8, 1902. Received November 3, 1902. 



CONTENTS. 



Page 



I. Introduction 443 



II. Review of Earlier Determinations 444 



III. The Analysis of Caesic Chloride 446 



(a) Preparation of Materials 446 



(b) Method of Analysis 451 



(c) Results of Analysis 455 



IV. The Analysis of Potassic Chloride 456 



V. The Quantitative Decomposition of Nitrates 458 



VI. The Analysis of Potassic Nitrate 462 



VII. The Analysis of Caesic Nitrate 463 



VIII. The Analysis of Caesic Bromide 464 



IX. The Atomic Weights of Caesium, Potassium, and Nitrogen .... 467 



X. Summary 469 



I. Introduction. 



Several considerations led to the renewed investigation of the atomic 

 weight of caesium. Forming as it does the highest known member of 

 an important and well-marked series, this metal might furnish data for 

 the discovery of the long-sought mathematical relationship between the 

 atomic weights ; moreover, its study might also lead to the discovery of 

 a yet higher member filling the supposedly vacant place in the classified 

 system. In case both of these somewhat illusory hopes remained unful- 

 filled, there would yet be obtained data concerning an important constant 

 of nature whose value possessed previously an undesirably large possible 

 error. Moreover, the highly electropositive nature of caesium and its 

 univalence combined to promise the probability of definite results from 



