168 FLUORESCENCE OF THE URANYL SALTS. 



SUMMARY. 



(1) The spectra of the uranyl acetates consist of the usual equi- 

 distant fluorescence bands. 



(2) When excitation occurs at the temperature of liquid air, these 

 bands are resolved into groups the homologous members of which form 

 series of constant-frequency intervals. 



(3) There are two single acetates a finely powdered, anhydrous 

 variety and a crystalline form with 2 molecules of water of crystalliza- 

 tion, whose spectra differ widely, particularly as to the groups of 

 fluorescence bands. 



(4) Of the double acetates, those containing lithium, potassium, 

 calcium, manganese, and strontium have spectra which may be 

 regarded as essentially identical both as regards the location of the 

 principal bands and the structure of the fluorescence groups. The 

 only distinctions between their spectra are in the sharpness of reso- 

 lution and relative brightness of the various components. 



(5) The spectrum of barium uranyl acetate differs from the above 

 in that the groups are shifted, as a whole, about 5 frequency units 

 toward the red. 



(6) In the spectra of the double acetates of ammonium and rubidium, 

 band D in each group is doubled, but there is no shift of the groups. 



(7) The presence of sodium, magnesium, zinc, silver, and lead 

 modifies the group structure by the addition of bands characteristic 

 of the metal and causes slight relative displacements of the group 

 system as a whole. Otherwise the spectra resemble those mentioned 

 under (4). 



(8) The frequency interval for the fluorescence series of the double 

 acetates is probably the same for all series and for all salts, the depar- 

 tures of the general averages for the various salts being less than one 

 frequency unit from the average for all, i. e., 84.76. The same is 

 probably true of the absorption series, the general average for which 

 is 70.68. 



(9) The frequency intervals, both in the fluorescence and absorp- 

 tion spectra, are larger by more than one frequency unit for the single 

 acetates than for the double acetates. 



