132 FLUORESCENCE OF THE URANYL SALTS. 



acid, since when this was done no reaction occurred between the oxide 

 and the nitric anhydride. 



At temperatures above 30 C. the N 2 2 reacts with the mixture of 

 UOg and H 2 UO 4 to form uranyl nitrate, presumably anhydrous, and a 

 considerable amount of HNO 3 . To free the specimen from acid, the 

 tube containing it was placed in a freezing mixture until the N 2 0s was 

 frozen, when the HN0 3 , which still remained a liquid, was poured off. 

 This process was repeated several times. While the amount of water 

 remaining after this treatment must have been extremely small, we 

 cannot feel certain that all traces were removed, and it is possible, 

 therefore, that the nitrate formed may have consisted in part of the 

 monohydrate. No fluorescence bands belonging to the other hydrates 

 could be observed. The method of preparation was varied by changing 

 the temperature at which the reaction was allowed to occur, and by 

 heating the salt, after it had been formed, to different temperatures 

 and for different periods. 



The fluorescence spectra of the different preparations differed widely. 

 In one case the spectrum was found to consist of 3 narrow bands only, 

 but in all other cases bands were observed which remained broad 

 (about 100 A. u.) even at the temperature of liquid air. These bands 

 were spaced with a constant-frequency interval of approximately 88 

 to 89. It seems probable that these broad bands were due to the 

 solution of the anhydrous salt in nitric acid. To test this point a 

 specimen was prepared under conditions which made certain the 

 presence of a considerable excess of nitric acid. The fluorescence 

 spectrum contained two series of broad bands, the central band of the 

 stronger series lying at 1/X = 1,939.0 and that of a weaker series at 

 1/X = 1,920.0. The specimen was then gently heated and the nitric 

 acid driven off was condensed in a connecting-tube. After this process 

 had continued for a short time, several series of narrow bands or lines 

 appeared in the fluorescence spectrum (at 186 C). As this pro- 

 cedure was repeated, the line spectrum became more prominent and the 

 broad bands fainter. In one instance the specimen was heated nearly 

 to decomposition in fact, part of the salt was undoubtedly decom- 

 posed and in this case the very faint fluorescence spectrum consisted 

 of three narrow bands only. The same three bands were observed in 

 the case of most of the specimens that were prepared in the attempt to 

 remove the water of crystallization, although in other cases they were 

 accompanied by other lines or broad bands. It seems probable that 

 these three bands constitute the brightest part of the fluorescence 

 spectrum of the anhydrous salt, and that the additional lines and bands 

 that were observed in some specimens are due to traces of the mono- 

 hydrate or to a solution of the nitrate in HNO 3 . The three bands 

 formed a series with the interval 88.5, the central band lying at 

 1/X= 1,902.0. 



