432 PROCEEDINGS OF THE AMERICAN ACADEMY. 



independently of any assumption except the atomic weight of oxygen 

 from the following equations : 



= 0.650333 



2Ag + Cr + 64 

 2Ag 



= 0.499692 



2Ag +2Cr + 112 



to be 52.074 and 107.941 respectively. However interesting these 

 results may be, they have little real significance, since an error of five 

 thousandths of a per cent in either ratio causes an error of over one 

 tenth of a unit in the atomic weights of both silver and chromium. 



The most important results of this research are as follows : 



1. Pure silver dichromate was prepared. 



2. It is shown that silver dichromate cannot be completely dried 

 without decomposition. 



3. It is shown that silver dichromate when crystallized from nitric 

 acid retains traces of the nitric acid. 



4. The proportion of moisture and nitric acid in silver dichromate 

 treated in definite fashions was determined. 



5. The specific gravity of silver dichromate is found to be 4.770 at 

 25° C. referred to water at 4° C. 



6. The per cent of silver in silver dichromate is found to be 49.9692. 



7. With several assumed values for the atomic weight of silver 

 referred to oxygen 16.000, the atomic weight of chromium is found to 

 have the following values : 



If Ag= 107.93 Cr = 52.06 



IfAg= 107.88 Cr = 52.01 



If Ag= 107.85 Cr = 51.98 



8. If these results are averaged with those previously found by 

 Baxter, Mueller, and Hines, the atomic weight of chromium is found 

 to be as follows : 



If Ag= 107.93 Cr = 52.06 



If Ag =-107.88 Cr= 52.01 



If Ag = 107.85 Cr = 51.98 



"We are greatly indebted to the Carnegie Institution at Washington 



for generous pecuniary assistance in pursuing this investigation ; also 



to the Cyrus M. Warren Fund for Research in Harvard University 



for many pieces of platinum apparatus. 



Cambridge, Mass., 



December 10, 1908. 



