STUDIES OF PHOSPHORESCENCE OF SHORT DURATION". 



117 



were more or less irregular. This was no doubt due to the fact that with 

 the small opening of the disk the irregularities of the spark were more pro- 

 nounced. However, on the 140-eycle current the curves were quite regular 

 and could be duplicated very closely. The curves given in Fig. 1 2 1 were 

 taken with the spark operated from the 140-cycle current. It will be noted 

 that a decrease in the time of excitation brings about a more rapid decay. 



The curves in Fig. 121 also serve to confirm the results obtained with the 

 60-cycle current; for it will be seen that they have the same general shape 

 as those given for ZnCl 2 No. 3 in Fig. 117. 



.02 .03 .04 .05 



Seconds 

 Fix. 120. 



01 02 .03 04 



Seconds 

 Fig. 121. 



Carves showing effect of heat treatment. Showing the effect of changing the time of excitation. 



Curve //, ZnCte No. i, time of excitation 0.031 sec. Curve .4. ZnCh No. 3, time of excitation 0.013 sec. 



K, " " 2, " " " 0031 sec. B, 0.024 sec- 



G, " " 3, " " " 0.031 sec. C, " 0.05S sec. 



EFFECT OF INFRA-RED ON THE INITIAL DECAY OF SIDOT BLENDE- 



The effect of infra-red on long-time phosphorescence is well known, 1 and 

 it was natural to expect that short-time phosphorescence would be affected 

 in somewhat the same way. The method of experimentation followed was 

 to allow the light from the arc to fall on the phosphorescent screen through 

 a piece of very dense ruby glass, and to compare the shape of the decay curves 

 taken with and without the infra-red. It was found, however, that none 

 of the short-time substances were affected in measurable amount. There 

 was a slight indication of some change in the shape of the later portion of 

 the decay curve, but the error in setting the spectrophotometer in this 

 region, where the light is so faint, would account for the observed change. 



While the effect of infra-red on the decay of short-time phosphorescent 

 compounds is so small that it can not be readily measured, the effect of 

 infra-red on Sidot blende is well marked. 



See Chapter V of this treatise. 



