120 



FLUORESCENCE OF THE URANYL SALTS. 



The same drift occurs quite systematically throughout the entire 

 fluorescence and absorption spectrum, as may be seen from figure 76. 

 In this chart such of the fluorescence and absorption series as are 

 present in all four salts at +20 are plotted on the frequency scale. 

 The solid lines represent observed fluorescence bands; the dotted lines 

 represent observed absorption bands; no hypothetical values are 

 indicated. The order of the salts is the same as in table 39 and follows 



TABLE 39. 



that given by A. E. Tutton in his Treatise on Crystalline Structure and 

 Chemical Constitution (London, 1916). He found for both single and 

 double salts of the alkali metals that several of their optical properties, 

 such as refractive index, etc., follow the order of the molecular weights, 

 but that in the ammonium salts the NH 4 radical often acts as if it were 

 much heavier than the combined weights of its components would 

 indicate, so that its position is quite close to rubidium and sometimes 

 on the side toward caesium. It will be observed that there are several 

 examples of this in figure 76, particularly in the case of the C g series. 



SUMMARY. 



(1) The four double chlorides, uranyl ammonium chloride, uranyl 

 potassium chloride, uranyl rubidium chloride, and uranyl caesium chlo- 

 ride, crystallize in the triclinic system. The crystals are pleochroic 

 and their fluorescence spectra and absorption spectra are polarized. 



(2) The spectra differ from those of other uranyl compounds thus 

 far examined in that both in the fluorescence and absorption regions 

 each band is resolved at +20 C. into a group of five bands forming 

 homologous series of constant frequency interval. 



(3) The structure of the fluorescence spectrum is essentially the 

 same in the different salts, the spacing of the bands of each group 

 repeating itself in the successive groups, excepting in the reversing 

 region, the appearance of which is modified by the overlapping of 

 fluorescence and absorption. 



(4) Each of the five bands which constitute a group is a doublet, the 

 two components of which are polarized at right angles to one another. 



(5) The frequency interval is the same or nearly the same for each 

 series in a given salt. 



