66 



FLUORESCENCE OF THE URANYL SALTS. 



At the same time, while not obviously systematic, the variations 

 in these values are considerably larger than those resulting from the 

 measurement of the interval of any given series, taken by itself, which 

 should not exceed, at most, 0.2. 



TABLE 21. Average intervals at -{-20 C. for the four double chlorides. 



These seeming discrepancies are not to be considered as wholly 

 accidental, but as being due to the fact that the bands are complex, 

 and variously so, as will appear from the study of these spectra at low 

 temperatures. 



While he determinations thus 

 far described may be regarded as 

 indecisive as to small differences 

 of interval between the various 

 series and salts, excepting as 

 noted above, the influence of 

 molecular weight upon the posi- 

 tion of bands in the spectrum is 

 unmistakable. 



In tables 29 and 30 (at end of 

 chapter) the almost universal 

 and fairly regular increase in the 

 frequency of each band as we 

 pass from potassium to csesium is 

 sufficiently evident. In figure 

 55 this general shift, which is 

 present in all the groups and 

 affects all series, can be seen at 

 a glance. Almost the only re- 

 versed shifts occur in the case of 

 those bands of the csesium spec- 

 trum which show anomolous plac- 

 ing in the spectral groups. 



In table 19, where the groups 

 are units, the accidental errors 

 pertaining to individual bands are submerged in the processes of aver- 

 aging and the shift with molecular weight appears as a still more 



FIG. 55. 



