DECAY OF PHOSPHORESCENCE PRODUCED BY HEATING. 



107 



on a curve to say positively that it does not exhibit double curvature at 

 high temperatures. In the cases where the powder is heated after excita- 

 tion, Balmain's paint shows a double flash under some conditions, and one 

 flash under other conditions, while Sidot blende shows one flash under all 

 conditions, unless it be admitted that there are indications of a double flash 

 in some of the Sidot-blende curves, in which case the two substances show 

 substantially the same curves. Considering the first flash only, there is 



12 



8 



B 



100 



200 300 



Fig. 115. 





I 



40O Sec. 



Effect of delay in heating. Time measured from the end of excitation. Excited 

 30 seconds at room temperature. Temperature of furnace, 338 C. 

 Curve .4, decay at room temp. 



B, waited 2 sec. after excitation before heating. 



C, waited 400 sec. after excitation before heating. 



perfect agreement between the curves of Sidot blende and Balmain's paint. 

 The action of infra-red is more marked in the case of Sidot blende, but 

 otherwise there is no marked difference. The fluorescence spectrum shows 

 two bands in the case of each substance, but there is one point of difference, 

 in that the band of shorter wave-length is more prominent in the case of 

 Balmain's paint and less prominent in the case of Sidot blende than the 

 band of longer wave-length. 



