CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OP^ COBALT. 



THIRD PAPER: — THE ANALYSIS OF COBALTOUS 

 CHLORIDE AND OXIDE. 



By Theodore William Richards and Gregory Paul Baxter. 



Received June 24, 1899. 



The two preceding papers,* describing the earlier part of this investi- 

 gation, were concerned with the complete analysis of cobaltous bromide. 

 Both the cobalt and the bromine in this compound, as well as the trace 

 of inevitable impurity, were determined with care, and the consistent 

 verdict of all the results pointed toward a value between 58.99 and 59.00 

 for the number soujjht. The danger of the existence of an unknown 

 error in a result thus obtained from a single compound is too well known 

 to need emphasis ; and with this danger in mind we sought to obtain 

 support from wholly different data. The present paper describes two 

 series of determinations, which, while less satisfactory than the work with 

 the bromide, are nevertheless of corroborative value, and moreover serve 

 to point out some of the pitfalls which ensnared the earlier experimenters. 



I. The Reduction of Cobaltous Chloride. 



Cobaltous chloride was chosen first as the basis of the confirmatory 

 work, both on account of the ease with which it can be prepared, and 

 because it can be heated to a much higher temperature than the bromide 

 without danger of vaporization. These circumstances allow greater 

 surety both in drying and in reducing. 



Owing to the comparatively slight volatility of cobaltous chloride and 

 to the dilHcult}' of obtaining chlorine in a sufficiently pure state, we made 

 no attempt to purify the salt by sublimation. The preparation of 

 cobaltous chloride in aqueous solution was inadmissible on account of the 

 certain presence of oxide in the dried and ignited substance under these 



* These Proceedings, XXXIIL 113 (1897), XXXIV. 351 (1898). 



