64 



FLUORESCENCE OF THE URANYL SALTS. 



As will appear in the course of the subsequent consideration of 

 individual series, the tendency of the group intervals of the csesium 

 salt to diminish toward the violet is not, as might seem at first sight, 

 an indication that the groups are made up of series having a diminish- 

 ing interval. As regards the other salts, it will be noted that the dis- 

 tance between groups is essentially constant. 



TABLE 19. Distances between fluorescence groups. 



DISTRIBUTION OF BANDS WITHIN THE GROUPS. 



While to the eye the fluorescence spectra under consideration present 

 the appearance of evenly spaced bands varying periodically in intensity 

 so as to form the groups, this is not strictly the case, as may readily be 

 shown by subtracting neighboring values in table 29. The average 

 distances thus obtained are given, for convenience, in table 20. 



The greatest departures from uniformity of distribution occur in the 

 spectra of the rubidium chloride and the cesium chloride. 



TABLE 20. Average distances between neighboring bands in the fluorescence spectrum at +20 C. 



In the rubidium spectrum, bands A and E are crowded together, 

 the average interval being 12.75, and in the csesium spectrum D and C 

 are similarly crowded. It will be noted that the average distance 

 between A and E is less for the four chlorides than any of the corre- 

 sponding distances between other bands. 



The arrangement of the bands within the group in the four salts is 

 conveniently compared by means of the diagram in figure 54, in which 



