148 



FLUORESCENCE OF THE URANYL SALTS. 



URANYL ACCTATE 



purpose group 7, which is in the brightest part of the spectrum and is 

 free from the complications due to the overlapping of fluorescence and 

 absorption in the reversing region, is most favorable. In figure 82 

 the spectral region of this group is plotted for the anhydrous and 

 crystalline forms of the single acetate to depict the remarkable dis- 

 placements brought about by the presence of water of crystallization 

 and the consequent modifi- 

 cation of crystal structure. 

 The effect is very similar, 

 both as regards the direction 

 of the shift of the groups and 

 the amount of shift, to that 

 already described in the case 

 of the nitrates. (Compare 

 fig. 78 in Chapter VII.) 



In both instances it is not 

 the transfer of the groups 

 toward the blue without 



change in their structure that p 82 



occurs, but something much 



less obvious. In fact, it is not possible to identify any of the bands 

 in the spectra of the hydrated form with those belonging to the an- 

 hydrous salt. 



To produce this change in the spectrum it is only necessary to add 

 a drop of water to a small portion of the anhydrous powder and to 

 compare the fluorescence of the dry and moistened substance when 

 excited in the usual way at 185. 



FREQUENCY INTERVALS OF THE SINGLE ACETATES. 



The frequencies and frequency intervals of the series occurring in 

 the spectra of the two forms of the single acetates are given in tables 

 56 and 57, from which it will be seen that the two forms of the acetate 



TABLE 56. Uranyl acetate (anhydrous). 



1900 



1950 



