IX. THE SULPHATES. 



Uranyl sulphate (U0 2 S0 4 .3H 2 0) and the double uranyl sulphates 

 of the alkaline metals are among the most brilliant of known fluores- 

 cent substances. Their spectra are characterized by an unusual com- 

 plexity of narrow bands brought out by cooling to the temperature of 

 liquid air. The group structure is by no means so obviously uniform 

 as in the case of the compounds already considered, nor is there the 

 marked similarity between the spectra of the double sulphates which 

 has been noted in the discussion of the fluorescence and absorption of 

 the chlorides, nitrates, and acetates. There are, however, certain 

 characteristics common to all the sulphates thus far examined; i. e.: 



(1) Fluorescence at 185 vanishes with the group 7 (frequency 

 2000 to 2070), which is the reversing region for this family of salts, 

 and the eighth group lies entirely within the absorption region. 



1 



II 



NH 4 



I I I I 



II 



NH* 



No. 



ii 



II 



_u 



jli 



Rb 



1 



Ca 



I 



, 



1 1 I 



II 



Na 



11 



l_l 



Rb 



Ca 



1 



I I 



II 



n 



lin 



i 



i 



FIG. 88. 



FIG. 89. 



(2) Absorption of the type having the usual 70 frequency interval 

 extends without change of interval into group 7. In discussing the 

 acetates, what we have called the heads of the prominent absorption 

 series lie in the region between 2040 and 2060 instead of at about 

 2170, as in the spectra of the acetates. 



169 



