PHOSPHORESCENCE SPECTRA. 



43 



out an unusual characteristic. It is usual to find two processes of 

 phosphorescence succeeding one another and represented by the two 

 straight arms of the curve DE and FG, but in all the numerous cases 

 hitherto described, excepting two to be discussed in a subsequent para- 

 graph, the later process (FG) is indicated by a curve of lesser slope. 

 In the case of this uranyl salt, however, FG trends very sharply up- 

 ward, showing a greatly accelerated decay. 



I. URANYL AMMONIUM SULPHATE. 



2.URAMYL POTASSIUM SULPHATE. 



3. URANYL NITRATE. 



4. URANYL SULPHATE. 



5. URANYL AMMONIUM CHLORIDE. 



URANYL AMMONIUM SULPHATE 



0.0 



.002 



SEC 



001 



.002 



.003 SEC. 



FIG. 33. 



FIG. 34. 



By means of these preliminary observations certain facts may be 

 regarded as established. 1 These may be summarized as follows: 



(1) There is no appreciable change of color during decay. 



(2) The decay of phosphorescence is exceedingly rapid, the intensity 

 falling to one-thousandth of its initial value within 0.0035 second. 



(3) The very complex fluorescence spectrum at 180 C. is identical 

 in structure and relative distribution of intensities with that observed 

 during the earlier and later stages of phosphorescence. 



1 Nichols, Proceedings National Academy of Sciences, vol. n, p. 328. 1916. 



