FLUORESCENCE AND ABSORPTION OF THE URANYL SALTS. 21 



In certain cases the resolution of the bands is such that the brightness 

 of two crests can be determined and two overlapping envelopes drawn, 

 as in figure 10, which pertains to the spectrum of U02S0 4 +3H 2 O. The 

 relative brightness of the two crests is seen to vary slightly from band 

 to band. 



.55/4 



18|00 



19100 



20100 



i slop 



I9JOO 



20JOO 



FIG. 7. 



FIG. 8. 



The changes in the position of the crests in the case of the sulphates, 

 nitrates, and acetates is illustrated in figure 11, in which a typical curve 

 from each family of salts is given. 



While these measurements by Dr. Wick do not include all the spectra 

 for which such determinations are possible, they suffice to demonstrate 

 the essential uniformity of type of the envelopes and to show that 

 within a given family, such as the double sulphates or the nitrates, the 

 crests occupy the same region in the spectrum. It will be seen, when 

 we come to the consideration of the detailed structure of these fluores- 

 cence spectra, that there is a slight but definite shift of all the bands 

 with molecular weight. 



Spectrophotometric measurements of single unresolved bands, prac- 

 ticable with accuracy only in the case of some of the brightest, show the 



