368 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



from the ratio between the weight of nitrogen and that of uranous oxide 

 contained in crystallized nranyl nitrate. Uranyl nitrate was purified by 

 repeated crystallization. A quantity of the pure nitrate, the weight of 

 which need not be known, was put into a boat, and the boat surrounded 

 by a section of platinum tube, to prevent loss of material. The whole 

 >\'as placed in a combustion tube between spirals of reduced copper. 

 One end of the combustion tube was connected with a carbon dioxide 

 generator, and the other with an absorption apparatus containing a con- 

 centrated solution of potash. 



After sweeping the air out of the apparatus with a current of carbon 

 dioxide, the nitrate was heated so long as evolution of nitrogen occurred, 

 the temperature being finally raised to red heat. The reduced copper 

 was kept at red heat throughout the operation. When it was certain 

 that no more nitrogen was evolved, the green oxide remaining in the 

 boat was reduced by hydrogen to uranous oxide and weighed. The 

 nitrogen was transferred to a measuring tube reading to tenths of a 

 cubic centimeter. From the ratio of the weight of this volume of 

 nitrogen to the weight of the oxide, the atomic weight is calculated. 



The following are the results of the eight determinations given : — 



Atomic Weight of Uranium. 

 N = 14.04 



Volume of nitrogen, 15.25 cc. 

 Atomic wt. of uranium, 239.3 



33.5 

 239.4 



38.0 

 239.6 



52.5 

 239.5 



81.25 

 239.4 



125.0 

 239.5 



151.2 

 239.4 



165.0 

 239.4 



Average 239.4 



This method has the merit of simplicity, and does not involve the 

 weight of the crystallized salt. There are, however, several sources of 

 possible constant error that have not been taken into account. When 

 crystallized uranium nitrate is heated, it first melts in its water of crystal- 

 lization. As in all similar cases, it requires the very greatest care to 

 prevent spattering while the crystal water is being driven off. It was 

 undoubtedly as a precaution against loss of material in this way that 

 Aloy used his j^latinum tube. By the time the crystal water is expelled, 

 the fused mass has hardened into a solid cake, changing in color from 

 yellow to orange, and finally to the green of urano-uranic oxide, UsOg. 



This method of preparing the green oxide from pure uranyl nitrate 



