176 



FLUORESCENCE OF THE URANYL SALTS. 



TABLE 105. Average frequency intervals in the fluorescence spectra of the sulphates. 



wave-length being much stronger in the bands toward the red and 

 dying away gradually in subsequent bands as we approach the blue, 

 while the other component steadily increases, will give the effect of an 

 increased frequency interval for the series. The increase might easily 

 be of the general order observed in this case. 



There is also always the possibility of the presence of a trace of 

 another uranyl compound which would yield additional series. Such 

 cases, for example, are not uncommon in the study of the acetates, 

 where an admixture of the single acetate occurs. 



ABSORPTION SPECTRA. 



The difficulties in obtaining a complete record of the absorption 

 bands of the uranyl sulphates are similar to those described in the 

 preceding chapters. The transmission, like that of the other uranyl 

 salts, ranges progressively from almost complete transparency in the 

 red, yellow, and green to a high degree of opacity in the ultra-violet. 



Large, clear crystals of the sulphates are not obtainable and there- 

 fore it is not possible to use very thick layers and thus to follow the 

 selective absorption far beyond the reversing region toward the red, 

 as has been done in the case of the chlorides. 1 The bands which we 

 were able to locate lie approximately between 2,000 and 2,600 fre- 

 quency units. They belong almost exclusively to the system having 



1 H. L. Howes. Physical Review (2), xi, p. 66. 1918. 



