ELECTRICAL PROPERTIES OF FLUORESCENT SOLUTIONS. 



161 



>> 60 

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o 



3 

 C 



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 a 



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CL 



>> 



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.4 .8 1.2 1.6 2.0 2.4 2.8 2.2 3.6 



Potential difference in volts at cell terminals. 

 Fig. 158. 



bridge, the condition of the cell appearing very unstable. At the three 

 voltages 1.03, 1.2 1, and 1.38 of the first of these two curves a phenomenon 

 was observed which occurred frequently throughout the experiments, at the 

 point where the effect reversed. When the cell was first exposed the gal- 

 vanometer showed an imme- 

 diate decrease of resistance, 

 followed in a few seconds, with 

 the light still on, by a large 

 increase. When the light was 

 shut off the cell showed the 

 two changes in the reverse 

 order. 



This would seem to indicate, 

 at least in this region, a com- 

 bination of two effects, one 

 growing to a maximum more 

 rapidly than the other, and 

 dying away more slowly. 



A few experiments were made 

 with fluorescein in absolute 

 alcohol, a trace of caustic soda 

 being added to produce fluo- 

 rescence. The effects obtained 

 were very similar to those 

 with the eosin, but not nearly 

 as marked. 



Rhodamin was also tried, 

 with somewhat doubtful re- 

 sults, except that the effects 

 with very low voltages were 

 fully equal to those with eosin. 



vSince there seemed to be no 

 doubt that the seat of the effect 

 was the thin film of liquid in 

 front of the electrode, and since 

 the current could not be sup- 

 posed to flow only to and from 

 this film without entering the 

 edge of the electrode, it did not 

 seem possible to account for 

 the changes in resistance ob- 

 served, except by the actual 

 creation of an electromotive 

 force at the surface of the elec- 



60 

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-> 

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3 

 TJ 



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1*- 

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-40 



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t) 



L. 

 O 

 Q. 



.4 .8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 



Potential difference in volts at cell terminals. 

 Fig- 159- 



8 1.2 l.tfo' 2.0 2.4 2B 32 3.6 



Po+ential difference in vol+s a+cell terminals 



Fig. 160. 



trode or near it, by the action of the light. So long as low voltages were 

 used, such an effect if it did exist would account for the change of resistance 

 when either anode or kathode was illuminated. For suppose the E.M.F. 

 produced to be such as to tend to make the exposed plate positive to the 

 unexposed one. Then if the exposed plate were made the kathode with 



