ELECTRICAL PROPERTIES OF FLUORESCENT SOLUTIONS. 1 63 



Dilute solutions of rhodamin were also tried with very good effects. The 

 maximum dilution thus far tested is that of one part saturated solution to 

 ten of alcohol. 



With dilute solutions of eosin, however, the effects were greatly reduced. 

 The extremely thin capillary film was found to be unnecessary, either in 

 eosin or rhodamin, though the effects produced when the electrodes were 

 more than 0.02 mm. back from the front of the cell were very small. 



Tests were made of the absorbing power of both of the substances in 

 saturated solution, and it was found that practically no light penetrated 

 to a depth of 0.02 mm. in the region of the absorption band. Thus, if the 

 effect is produced at the surface of the platinum plate itself, a film of this 

 thickness or greater would completely screen the electrode from the action 

 of the light. 



The results obtained by Goldman, whose paper is referred to on page 151, 

 agree in general with those of Dr. Hodge. 



MR. HOWE'S 1 EXPERIMENTS ON FLUORESCENT ANTHRACENE VAPOR. 



The following is an account of an attempt to determine whether fluores- 

 cence has any effect on the electrical conductivity of anthracene vapor. 

 The expectation of a change in conductivity during fluorescence is based 

 on the theory that fluorescence is a dissociation phenomenon. Although 

 the results of the experiment were negative, it being impossible to detect 

 any conductivity of the vapor either unilluminated or fluorescent, the 

 accuracy of the work was such as to set a rather definite upper limit for any 

 effect that may be present. 



Little work has been done on the conductivity of vapors as affected by 

 light. Henry 2 could find no conduction of iodine vapor due to light. On 

 the other hand, J. J. Thomson 3 states, without giving reference, that light 

 increases the conductivity of sodium vapor. Wiedemann and Schmidt, 4 in 

 their paper in which they propose the dissociation theory, say that this does 

 not call for any ionization in the case of fluorescent vapors. 



The desirability of anthracene vapor for this experiment is seen from the 

 following considerations : 



1. The vapor is strongly fluorescent. 



2. It has banded absorption and fluorescence spectra 5 lying in the region 

 320-400 nn, light of these wave-lengths being transmitted by the glass used 

 in this experiment. Stark, 6 in his work on band spectra, has concluded that 

 fluorescence and photo-electric properties are intimately associated with 

 absorption in bands shaded toward the red, and that the "carriers" of the 

 band spectra are the negative electrons, which are pulled out of their normal 

 position by the incident light, and upon their return to the position of 

 equilibrium liberate the energy of the fluorescent light. 



3. If the separation of the electron is complete, photo-electric properties 

 would be exhibited. It is thus that Stark and Steubing explain the fluores- 



'See H. E. Howe. Physical Review, xxx, p. 453. 'Wiedemann and Schmidt, Ann. der Phys., 56, 



: Henry, Proc. Camb. Soc, 9, p. 319, 1897. p. 201. 1895. 



3 Tbornson, Cond. through Gases, p. 213. 5 Elston, Astr. Jour., 25, p. 155, 1907. 



'Stark, Phys. Zeit., 8, p. 81, 1907. 



