FLUORESCENCE AND ABSORPTION OF THE URANYL SALTS. 23 



A more detailed use of the instrument, working with narrow slits and 

 making settings at closer intervals, will often bring out the complexity 

 of single bands, where the overlapping of the components is such as to 

 conceal the structure Figures 14, 15, 16, and 17 give the results of 

 such a study by Miss Wick. The existence of numerous partly sub- 



.48 



.50 



.5. 



20JOO 



19(30 



20 



FIG. 12. FIG. 13. 



Showing the relative intensities of the brightest fluorescence bands of uranyl 

 nitrate (fig. 13) and uranyl potassium sulphate (fig. 14). 



merged crests is apparent in the curves, corresponding to the com- 

 plexity of structure which these bands show when the substance is 

 excited at the temperature of liquid air. The vertical lines indicate 

 the position of the bands, as observed at low temperatures by methods 

 to be described in subsequent chapters. 

 That these lines in general do not co- 

 incide with the positions of the crests 

 might seem to indicate that there is no 

 definite relation between the spectra at 

 the two temperatures or that the accu- 

 racy of the curves is in doubt; but the 

 discrepancies are quite in accordance 

 with the results obtained by the detailed 

 study of the spectra of the double 

 chlorides (Chapter V), where the spectra 

 are sufficiently resolved at +20 C. to 

 enable us to trace the changes on cool- 

 ing, measure the definite shifts, and dis- 

 cover the remarkable mechanism of the 

 process of resolution. 



15 



10 



.49 



J I 



1 



.50 .51 // 



FIG. 14. 



