Fluorescence of Dyes on Wave-Lengtli of Exciting Light. 315 



Measurements were repeated several times during our 

 work, giving always the same result. 



We used light-filters, partly coloured glasses, partly 

 coloured films put between two glass plates. Some light- 

 filters were prepared by us in collodion and gelatine films 

 on glass. The curves of absorption of light-filters were 

 measured at least twice. 



Dyes. 



The fluorescing dyes were selected so that their bands of 

 absorption covered the whole region accessible to visual 

 investigation from 400 //-//, to 600 //,//,. Most careful measure- 

 ments were made with water solutions of the following 

 dyes : — 



Fluorescein (Ferrein) + KOH 9'7 . 10 



Eosin S extra C. (Bayer) 

 Ehodamin B extra (Bayer) 



1-2.10 



... 1'4 



Fig-. 2. 



10 



-6 gr- 

 cm. 3 



-5 g r - 

 cm. 3 



cm/ 



and 4-85 



-7 gr. 



Eosin S gives a rather weak fluorescence ; still it was the 

 only one whose band of absorption followed sufficiently that 

 of the Eosin studied by Nichols and Merritt. In fig. 2 are 



XI 

 U 

 11 

 10 



'0,9 

 0.8 



07' 



i 

















! 





















— 





1 











































! 











(FlU, 



Die* 



2. el 



(X- 





/ 





S\h.c 



dan 



lllV 





























* 

 » 



k 







/ 



\ 



i 



^. 







































/ 





\i 































f 





f ' 







/ 







'» 

 i 





























« 





■ 









i 



'\ 



I 



' 













0,6 

 05 



o,v 

 0,3 

 o,l 

 o,i 













'. 







\ 







J 







\ 











i 



1 











* 









: . / 







f 



\ 





\ 

















i 

 i 



1/ 



















1 



\ 



\ 







! 













s 









/ 



/ 



k 



y 









\ 



\ 











1 









t 



i 









/ 





/., 











\ 





\ 















y 



t 













■•" 



t * 











\ 



A, 



* 



f 









...-»'■* 



,..•■* 







1 



— » 



.-*r' 



.-#-' 







N 



• 









V 



1 



" --ft. 











Wfo 1H0 160 H80 MO 510 510 560 580 600 



i 



