8 4 



STUDIES IN LUMINESCENCE. 



probable, therefore, that Sidot blende possesses broad absorption bands 

 with maxima not far from 0.9 ju and 1.35 fx. Experiments with other phos- 

 phorescent substances having ZnS as their base will be necessary to deter- 

 mine whether the absorption that determines this effect on phosphorescence 

 is characteristic of the solvent (ZnS) or of the dissolved metal causing lumi- 

 nescence. It is interesting to note, however, that in the absorption 



26 

 24 

 22 



20 



15 



16 



+-> 14 

 C 

 (D 

 U 12 



'0 



8 



6 



4 



2 







-2 



Fig. 76. 



Effect of infra-red rays of different wave-length. Ordinates represent the percentage diminution in the 



time of decay under the influence of infra-red. 



spectrum of sphalerite (ZnS) Coblentz has found evidence of bands 

 at about 0.9^1 and 1.4 ju. While Coblentz's work does not indicate great 

 absorption at these points, it must be remembered that they fall in the 

 most intense region of the spectrum of a Nernst glower, so that the total 

 amount of energy absorbed might be very considerable. 



