DECAY OP PHOSPHORESCENCE PRODUCED BY HEATING. 



99 



but its effect is small, because the excitation, which is relati\ r ely a long one, 

 was not changed during a set of curves. The curves were taken in the 

 order that they are numbered. Curve I, taken at room temperature, is 

 similar to the typical decay curves shown in Fig. 99. As the temperature 

 is raised the curves pass through a series of changes. Curve 2 begins con- 

 cave upward, but changes during the decay to concave downward. Curve 

 3 is practically a straight line throughout. As the temperature is raised 

 still farther, the curves again become concave downward throughout, 

 differing not widely from the typical decay curves at room temperature. 

 Another set of curves similar to those in Fig. 100 is shown in Fig. 10 1, 

 where the length of excitation is 10 minutes. The double bending 1 is again 

 exhibited in curve 2. 



40 



80 



200 



?40 



120 160 



Seconds 

 Fig. 101. 



Decay curves at different temperatures. Excited 10 minutes. 

 Curve 1, temp, of excitation and decay, room temp. 



2. " " ' 42 C. 



3. " " " " " 74 



4. " " " " " IOI 



5. " " '* " " 124 



The effect of previous history is shown in Figs. 102 and 103. These 

 curves might readily be mistaken for curves showing the effect of varying 

 the length of excitation. Fig. 103 also shows the effect of previous history, 

 modified, however, with the effect of temperature. 



The decay of phosphorescence in the case of Balmain's paint was studied 

 some years ago by F. J. Micheli, 2 who has published decay curves of several 

 phosphorescent substances, among them Balmain's paint. For the sake of 

 comparison, several of these curves have been replotted in Figs. 105 and 106 

 with i/V-f an d time as coordinates. Fig. 105 shows the effect of varying the 

 length of excitation. 



Fig. 106 shows the effect of varying the tempera- 



When taking the runs on which Fig. 99 is based, no importance was given to the single curve which shows 

 double bending. Later, the runs on which Fig. 100 is based were made and the apparatus was rearranged 

 for study of another substance before the significance of the double bending was recognized. On looking 

 over all the curves taken on Balmain's paint, other indications of double bending were found, but none of 

 them so pronounced as those shown above. 



-Arch, des Sci. Phys. et Nat., 12, p. 5, 1901. 



