McCoy an 



cl Ash 



man — TJrano- 



Table I. 



Ur 



anic 



Oxide. 



ration of Heating. 





Temperature. 





Weight of Oxide 



60 min. 





560° C. 







3-698 



35 





600 







3-697 



75 





600 to 700 







3-693 



523 



Reduced to TJ0 2 in hydrogen, over Bunsen flame (3-554) 

 The dioxide was reheated, in air, in the muffle. 



30 700° 3-691 



And reduced to TJ0 2 , as before (3-552) 



and again heated in the air, in the muffle: 



30 570° 3*690 



This experiment was repeated several times with perfectly similar 

 results. 



reached, the TJ 3 O s was reduced to U0 2 by the usual analytical 

 method, heating over a Bunsen flame in a stream of hydrogen. 

 The reduced oxide was again heated in air in the muffle. It 

 absorbed oxygen rapidly and changed to U 3 8 . Table I gives 

 the details of the experiment. 



The reduction of an oxide of uranium to U0 2 and weighing 

 in that form is a standard analytical method. Therefore the 

 composition of the product obtained by the reduction may be 

 considered as known. The mean weight of the U0 2 , 3'553 g., 

 corresponds to 3*693 g. of U 3 8 . The fact that the product 

 formed in air at 700° has the same composition whether formed 

 by the decomposition of the trioxicle or by the oxidation of 

 the dioxide shows that this temperature is below that at which 

 the U 3 8 can lose oxygen in contact with the air. There is, 

 therefore, no danger that heating for any length of time will 

 decompose U 3 8 at 700°. 



]Sme portions of U 3 8 were prepared from samples A, B and 

 C, and made into ten standard Alms. Films nine and ten were 

 made from the oxide prepared from sample A as shown in 

 Table I. The TJ 3 8 for him thirteen was made as follows : A 

 portion of sample C was heated in the muffle, in air, for thirty 

 minutes at 700° ; weight 1*2134 g. This was then reduced by 

 hydrogen and again heated' in the muffle, in air, for thirty 

 minutes, at 700° ; weight 1*2 133 g». Each of the remaining 

 seven portions of U 3 8 was prepared separately by heating the 

 corresponding sample for forty to sixty minutes, in air, in 

 the electric muffle, at 700°. 



The method of preparation of films for activity measurements 

 has previously been described in detail.* Seven films, Nos. 9 

 to 19 inclusive, were made in circular tin dishes 7*15 cm in 

 diameter, with rims 0*8 cm high ; films 23, 24 and 25 were made 

 on flat copper plates, 7*00 cm in diameter. 



* McCoy. J. Amer. Chem. Soc, xxvii, 391, 1905 ; Phil. Mag., xi, 176, 1906 ; 

 McCoy and Ross, J. Amer. Chem. Soc, xxix, 1698, 1907. 



