76 



FLUORESCENCE OF THE URANYL SALTS. 



A search by similar methods failed to reveal any bands of class (1), 

 mentioned above, in the spectra of the crystals when cooled to the 

 temperature of liquid air. No selective absorption could be detected 

 beyond the violet end of group 6, 1/X 1940, and while a considerable 

 number of new absorption bands were detected, nearly all of these 

 (see table 26) were found to be members of series already recognized. 

 The exceptions, two each in the spectra of the ammonium, rubidium, 

 and caesium double chlorides, do not appear to be related to the fluores- 

 cence. Coincidences between fluorescence and absorption are of the 

 sort already established as characteristic of the reversing region. 



TABLE 27. Average intervals of absorption series at -\-20 C. 



The failure to find the bands in groups 5 and 6 is not surprising. 

 They are sufficiently difficult objects at +20, where two or more 

 components are blended into a broader band. The existence of these 

 components at 185 may be regarded as probable, but they were 

 invisible under the conditions which we have thus far been able to 

 obtain. 



The absorption spectra of the double chlorides do not exhibit the 

 same remarkable approach to identity of structure and regularity of 

 arrangement manifested in the fluorescence spectra. Upon analysis, 

 however, they are all found to consist of series having intervals of 

 approximately 70 frequency units. As may be seen from table 27, 

 this interval for a given series is very nearly the same for all four salts. 

 The average interval for all the series of a given salt is constant within 

 the errors of observation. These averages are based on the values in 

 table 33 at the end of this chapter. 



The absorption bands, unlike those of the fluorescence spectrum, do 

 not appear to fall into a succession of strictly homologous groups, but 

 this is because some series disappear, while others increase in strength 



