THE SULPHATES. 



179 



TABLE 107. Average frequency intervals for the six sulphates. 



UO 2 SO 4 69.6 



(NH 4 )2U0 2 (SO4)2 70.3 



Na 2 UO 2 (SO 4 ) 2 71 .3 



K 2 UO 2 (SO 4 ) 2 70.3 



RB 2 UO 2 (SO 4 ) 2 69.8 



Cs..UO 2 (SO 4 ) 2 70.4 



As is frequently the case in these absorption spectra, one or more 

 bands of a given series are commonly missing or at least not discerni- 

 ble in the negatives. On the other hand, nearly all the bands are 

 found to be members of a series which is definitely related to a fluores- 

 cence series and has the proper frequency interval. The occasional 

 isolated bands, moreover, are so located that they may be definitely 

 associated with a fluorescence series and may reasonably be classed as the 

 sole visible member of an absorption series the remainder of which 

 fails to appear in our photographs. 



These show no systematic departure from the general average (70.3) 

 for the entire group. Lying as they do within one frequency unit of 

 the average, we may fairly conclude that within the errors of observa- 

 tion, which are rather large on account of the lack of definition and 

 incomplete resolution of these absorption groups, the various sulphates 

 have a common frequency interval. 



The frequency intervals of the various series of a given salt depart 

 somewhat more widely from the average for that salt, but again there 

 is no systematic variation, and it is probable that all the series would 

 be found to have the same interval, were it possible to locate the bands 

 with greater certainty. 



SUMMARY. 



(1) The fluorescence spectrum of the uranyl sulphates consists of 

 8 equidistant bands, the first and eighth of which disappear at the 

 temperature of liquid air. 



(2) The remaining bands are resolved into groups of narrow line- 

 like bands, the homologous members of which form series having 

 constant frequency intervals, ranging from 85.7 in caesium uranyl 

 sulphate to 83.0 in potassium uranyl sulphate. 



(3) The fluorescence groups are distinguished by a strong pair of 

 bands about 8 frequency units apart and 7 weak bands, some of which 

 are doublets. 



(4) There is a shift of all bands toward the violet, with increasing 

 molecular weights, of about 15 frequency units in passing from the 

 spectrum of uranyl sulphate to that of caesium uranyl sulphate. 



(5) The absorption spectra of the sulphates are made up of series of 

 bands having a frequency interval of 70.3 (general average) . 



(6) These absorption series extend into group 7 of the fluorescence 

 without break of interval . There are many reversals where fluorescence 

 and absorption overlap. The reversing region is therefore one group 

 farther toward the red than in most spectra of the uranyl compounds. 



