FLUORESCENCE AND ABSORPTION OF THE URANYL SALTS. 35 



forces of the system. In fact, the presence of water so intimately 

 associated with the salt molecule would probably increase the effective 

 dielectric constant of the region in which the vibrations occur, and 

 would thus cause a decrease in frequency quite independent of any 

 effect due to increase in mass. 



It has been shown by Deusen 1 and by Jones and Strong 2 that the 

 absorption spectrum of the crystallized nitrate is nearly coincident with 

 the absorption spectrum of the aqueous solution. In many cases no 

 difference can be detected in the 

 wave-length of the band in solu- 

 tion and in the solid crystal. In 

 the case of other bands, however, 

 the difference appears to be too 

 great to be accidental. It seems 

 not unlikely that the absorption 

 spectrum contains several series 

 of bands, some of which occupy 

 almost identically the same po- 

 sitions for the solution as for the 

 solid salt. We must assume, therefore, that at least a part of the 

 dissolved salt has the same molecular structure as the solid crystals. 



In the case of the uranyl sulphate studied by us the phenomena are 

 more complicated. As has already been shown, the luminescence 

 spectrum of this salt, even at ordinary temperatures, contains two 

 series of bands, which for convenience we shall designate the a and (3 

 series respectively. The a bands are by far the stronger and 6 of these 

 could be observed. Of the relatively weak bands only 3 could be 

 seen. In the absorption spectrum of the solid salt 2 series of bands 

 were also found (see fig. 21) which we shall call the a' and /3' bands. 

 Two of the a' bands corresponded in position with two of the a bands 

 of luminescence, while one band of the /3' series corresponded with one 

 of the |8 bands. The wave-lengths are given in table 14 and are shown 

 graphically in figure 23. It is a remarkable fact that while the a bands 



.54 



.58 



.46 .50 



FIG. 23. Position of fluorescence and absorption 

 bands of uranyl sulphate. 



TABLE 14. Uranyl sulphate fluorescence and absorption bands. 



Fluorescence: 



Crystals Principal series (a) 4763 4929 5148 



Crystals Secondary series OS) 4894 5098 



Dehydrated salt (7) 4843 5049 



Concentrated solution 4928 5145 



Absorption : 



Crystals a' series 4595 4755 4925 



Crystals 0' series 4555 4720 4880 



Concentrated solution.. 4718 4887 



5659 



5395 



5340 



5285 5538 



5387 



5095 



5925 



1 Annalen der Physik, 43, p. 1128. 1898. 



2 American Chemical Journal, vol. XLIII, p. 37, 1910. See also Vogel, Spectralanalyse, p. 270, 

 1889. 



