36 



FLUORESCENCE OF THE URANYL SALTS. 



are much the brighter in the luminescence spectrum, the of bands in 

 the absorption spectrum are much weaker than the (3 f bands. 



The sulphate used in this experiment was in the form of small crystals, 

 When the salt was dehydrated by being kept for about an hour in a 

 stream of warm, dry air its luminescence spectrum was found to be 

 absolutely different, each band being shifted 

 toward the violet by about 100 A. u. Brief 

 exposure to the air apparently permitted a 

 portion of the salt to return to the original 

 condition, so that the original a and/3 bands 

 could be seen as well as the 7 bands charac- 

 teristic of the dehydrated salt. In the case 

 of a thin layer of the sulphate which had 

 been dehydrated and then exposed for a 

 short time to the air, each of the lumi- 

 nescence bands was found to consist of 

 three overlapping bands, the components 

 corresponding in position to the a, /3, and 

 7 bands respectively. Spectrophotometric 

 measurements (with a rather wide slit) of 

 the brightest luminescence band and of a 

 portion of the absorption spectrum of the 

 same layer are shown in figure 24. In the 

 luminescence spectrum the (3 bands are by 

 far the most prominent, 1 while in the ab- 

 sorption spectrum the of bands are strong- 

 est and no 7' bands can be detected. The 

 results point to the existence of two dif- 

 ferent hydrated salts corresponding to the 

 a and /3 bands respectively, but further 

 study would be necessary to make possible 

 an entirely satisfactory explanation of the 

 observed phenomena. 



The concentrated aqueous solution of the sulphate showed weak fluor- 

 escence, and the three brightest bands, which could be located with 

 reasonable accuracy, were found to agree in position with three of the 

 a bands of the solid crystallized salt. In the absorption spectrum of 

 the concentrated solution it was possible to locate three well-defined 

 bands, two of which corresponded with two of the /? bands of the solid 

 salt (see fig. 25). The solution showed no trace of any fluorescence 

 corresponding to the /3 series, nor did it show any trace of absorption 

 corresponding to the a' series. 



1 The a' band appears in fig. 24 to be shifted by about 15 Angstrom units toward the violet; 

 whether this is a real shift, or whether it is due to disturbances caused by simultaneous absorp- 

 tion and luminescence we are unable to say. 



.48 



.so 



FIG. 24. Uranyl sulphate (solid), 

 showing the brightest fluo- 

 rescence band at about 0.51 n 

 and a group of absorption 

 bands at about 0.49 /i. 



