278 



NICHOLS— EFFECTS OF TEMPERATURE 



[April 22, 



might be thought that since the solvent is alcohol which freezes at 

 — 112° the shift of the band is due to the change from a liquid to a 

 solid solution, but this would not account for the changes occurring 

 in the fluorescence of anthracene nor for the very marked shift 

 towards the red observed in the case of willeniite (Fig. 14). 



^\— ^ ^3/<. 



.SS'Of^ 



Fig. 12. 



■ tfa 



'/* 



-11,0° -ao' -yo" -<iO° 0° 

 Fig. 13. 



Fluorescence of resorufin. 



In this fluorescent silicate, willemite, the band at + 20° is evi- 

 dently complex, a closely overlapping band towards the violet being 

 indicated by the slight notch or shoulder at .^ifx (Fig. 14). Upon 

 coohng to — 70° this component is suppressed and as a result the 

 violet edge of the band is greatly shifted. Whether the shifting of 

 the crest, which occurs on further cooling is altogether due to this 

 cause cannot be definitely determined from these observations. 



A very interesting example of a complex band exists in the case 

 of a phosphorescent sulphide of strontium prepared by the method 

 of Lenard and Klatt with bismuth as the active metal and a sodium 

 salt as flux. Measurements of the fluorescence spectrum made with 

 the spectrophotometer when this substance at -1- 20° is excited by 



