FLUORESCENCE AND ABSORPTION OF THE URANYL SALTS. 25 



curves indicates the extent to which the results agree. In the case of 

 the other salts studied, curves very similar to that of figure 18 were 

 obtained. 



TABLE 11. Relative intensity of excitation of the three brightest bands by five different lines 



in the spectrum of the mercury arc. 



*The intensities given in table 11 are not corrected for energy distribution in the acetylene flame. 



It will be noticed that the lower curve in figures 18 and 19 indicates 

 a very nearly constant ratio between the intensity of the brightest 

 band and that of the band lying next in the direction of the red. But if 

 we compare the brightest band with the band lying next to the violet 

 side we find a considerable variation in the ratio of intensities, especially 

 in the case of the double sulphate. It appears to us probable that this 

 variation is the result of a partial absorption of the luminescence by the 

 substance. The absorbing power of a given salt differs for the different 

 mercury lines used, so that in some cases the exciting light may pene- 

 trate much further into the substance than in others. It is clear that 

 those bands for which the absorption is greatest will appear relatively 

 weaker when the exciting light penetrates a considerable distance into 

 the substance, even if the relative intensity of the excitation of the 

 different bands is really the same for all wave-lengths of the exciting 



