120 



A STUDY OF THE ABSORPTION SPECTRA. 



position. Becquerel and Onnes find that the difference in the appearance 

 of the different groups of bands is the result of successive ascending changes 

 in the relative intensities of the bands in these groups. They find, when 

 crystals of double salts are used, that the spectrum depends more upon the 

 acid of the salt than upon the other base. The difference between the fre- 

 quencies of two successive homologous bands is practically constant, not 

 only for the same, but also for all series of homologous bands of the same 

 salt. The values of this constant for the various salts differ but slightly 

 from one another. 



At low temperatures the phosphorescent spectrum of uranyl compounds 

 resembles that of the channeled spectrum of nitrogen and carbon. Bec- 

 querel and Onnes consider both to have the same character. Placing the 

 phosphorescing uranyl salt in a powerful magnetic field did not produce 

 any noticeable effect upon the uranyl bands. Some of the bands become 

 arbitrarily absorption or emission bands, and at low temperatures the 

 wave-lengths are the same for both kinds of bands. Following is a table 

 giving the wave-lengths of the phosphorescent bands of various uranyl 

 salts at 80 C. 



The authors have done a little work on the phosphorescent spectra 

 of uranyl compounds. For the stimulation of the phosphorescent bands 

 either sunlight or the light from a spark has been used. The glass screens 

 previously described or a Feuss monochromatic illuminator were used 

 when only certain wave-lengths of exciting light were needed. In the case 

 of uranyl nitrate it was found that practically no phosphorescence was 

 excited unless the exciting light had a wave-length less than X 4900. For 

 all wave-lengths less than this phosphorescence was excited, but the bands 



Phosphorescent bands. 



Double sulphate of uranyl 

 and sodium 



Double sulphate of uranyl 

 and ammonium 



Uranyl sulphate 



Uranyl nitrate 



Double acetate of uranyl 

 and sodium 



r4891.5 



/491216 

 14934.7 

 (-4916.3 



5101.2 

 5125.4 

 5124.5 

 5147.8 

 5133.9 

 5160.2 

 5069.6 

 5148.6 

 5167.8 

 5184.9 

 5192.2 



522L4 



5330.0 

 5354.7 

 5355.4 

 5380.1 

 5369.4 

 5395.8 

 5301.5 

 5384.5 

 5404.5 

 5424.0 

 5431.6 



5463!5 



5578.5 

 5604.6 

 5607.4 

 5633.3 

 5626.8 

 5654.0 

 5554.6 

 5642.7 

 5663.4 

 5685.8 

 5694.6 



5881.1 

 5908.0 

 5910.1 

 5938.8 

 5832.9 



seemed the same, irrespective of the wave-length of the exciting light. It 

 seems that the energy that is absorbed by the series of uranyl absorption 

 bands is partly radiated as the energy of the phosphorescent bands. This 

 suggests a number of lines of work which we hope to carry out in the future. 

 Among these are the following: Are the phosphorescent bands of the salts 

 of uranyl affected in the same way as the uranyl absorption bands? In 

 the case of uranyl chloride can phosphorescent light be excited by the 

 bands in the region X 6000? Does light of wave-lengths between that of 

 the uranyl absorption bands excite phosphorescence? In the case of uranyl 



