CHAPTER X. 



ON THE ELECTRICAL PROPERTIES OF FLUORESCENT SOLUTIONS 



AND VAPORS. 



THE INFLUENCE OF FLUORESCENCE UPON ELECTRICAL CONDUCTIVITY. 



The effect of light and of Roentgen rays upon the conductivity of solutions 

 has been tested by Cunningham, 1 in the case of five solutions, one of which, 

 namely, uranyl nitrate, was fluorescent. In the experiments with light an 

 arc containing iron was used as a source, and the solutions were contained 

 in a cell having a quartz window, the object being to obtain intense ultra- 

 violet rays. Although some indication of increased conductivity was ob- 

 served, the observations were rendered so uncertain by the heating effect 

 of the rays from the arc that the author did not regard the results as 

 reliable. 



Experiments of a similar character were undertaken by Regner 2 with 

 especial precautions against the disturbances due to the heating effect of 

 the source. No change in conductivity as great as o.i per cent could 

 be detected, although the substances tested included those for which 

 Cunningham had found indications of a positive result. Several fluorescent 

 substances were tested by Regner, also with negative results. 



In a paper by Burke ;i on the change in absorption due to fluorescence, 

 mention is made of preliminary experiments upon the conductivity of 

 fluorescent substances; but the author states that difficulties were met with 

 which led him to abandon these experiments and to take up the study of 

 absorbing power instead. 



Our own experiments upon this subject were undertaken with the feeling 

 that the increase in conductivity due to fluorescence was probably very 

 small, comparable rather with the conducting power produced in gases by 

 the action of Roentgen rays than with ordinary electrolytic conductivity 

 in solutions. In attempting to detect so small an effect it seemed advisable 

 to work with solutions in which the normal conducting power was as small 

 as possible. In the case of all the substances thus far tested we have there- 

 fore used absolute alcohol as a solvent. 4 



The accurate measurement of the resistance of alcoholic solutions offers 

 considerable difficulty ; for while the conducting power is too great to permit 

 the employment of an electrometer method, such as would be used with 

 gases, it is too small to be determined with accuracy by the methods gen- 

 erally used with aqueous solutions. No benefit was to be gained in the 

 present experiments by increasing the cross-section of the liquid tested, 

 and so reducing its resistance; for if the thickness exceeded a rather small 



J. A. Cunningham, "An attempt to detect the ionization of solutions by the action of light and 

 Roentgen rays," Proc. Cambridge Philosophical Society, II, pp. 431-433. 1902. 

 -Physikalische Zeitschrift, 4, 862, 1903. 

 3 Burke, Philos. Transactions, 191A, p. 87. 

 'In the experiments of Cunningham and Regner the solvent was water. 



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