CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF NICKEL. 



SECOND PAPER. — THE DETERMINATION OF THE NICKEL IN 

 NICKELOUS BROMIDE. 



By Theodore William Richards axd Allerton Seward Cushman. 



Presented October 12, 1S98. Received December 29, 1S98. 



In a recently published investigation upon the atomic weight of nickel 

 we gave three series of results, depending upon the ratios of silver and of 

 argentic bromide to nickelous bromide.* These led us to the conclusion 

 that the atomic weight in question could not be far from 58.09 if oxygen is 

 16.000. Since however no single method is ever convincing, and since the 

 results above mentioned did not represent all that might be done even with 

 one method, it was evidently advisable to pursue the matter to a more defi- 

 nite conclusion. Accordingly, we determined to continue the work with a 

 twofold object in view: first, to study further the preparation of pure 

 material, and secondly, to complete the analysis of nickel bromide in such 

 a way as to determine directly the amount of nickel as well as the amount 

 of bromine in the salt. No surer test of a quantitative result than such 

 a complete analysis is known. The careful study of all the conditions 

 and results has led us to the conclusion that the preparation of pure 

 nickelous bromide is an unusually difficult problem ; but the problem has 

 been so nearly solved that we know exactly the precautions and correc- 

 tions necessary to make this substance serve as an accurate basis for the 

 determination of the atomic mass of nickel. In the light of this later 

 knowledge we find that the results of the last paper need a slight cor- 

 rection, but it is satisfactory to note that the change amounts to not 

 much over one unit in the second decimal place of the atomic weight. 



While carrying out the work, we had continually in mind the various 

 controversies which have arisen over the atomic weights of nickel and 



* These Proceedings, XXXHI 97. 



