Section III, 1922 [257] Trans. R.S.C. 



The Destructiofi of the Fluorescence of Dilute Solutions hy Ultraviolet 



Light 



By Miss F. M. Cale, B.A., 

 University of Toronto 



(Read May Meeting, 1922) 



I. Introduction 



The theory of luminescence as presented by Wiedemann^ is in 

 accord with many experimental results and has been accepted by 

 scientists, generally, in some analogous form. By this theory the 

 emission of fluorescent light accompanies either the expulsion or 

 return of the ionized parts of the active centre. Fluorescence is then 

 due to a permanent ability of the molecule to absorb indefinitely light 

 of a certain wave-length and emit light of another. 



In a paper describing the examination of thin films of fluorescent 

 solutions Perrin^ has presented an extremely interesting explanation 

 of fluorescence. He has shown that an organic body is always 

 destroyed when fluorescing, and assumes the destruction to be the 

 cause of the fluorescence. The molecule does not then possess a 

 permanent ability to emit light but gives a flash at the moment of 

 transformation and is then rendered incapable of further fluorescence. 

 Since all the fluorescent substances studied by him contained one or 

 more benzene rings he has made the suggestion that the fluorescence 

 may be due to the rupture of these rings. 



Zinc sulphide has been found to be chemically changed and its 

 power to phosphoresce decreased by the light that causes phos- 

 phorescence.^ Exposure to a powerful oxidizing gas restored in part 

 the original colour and ability to phosphoresce. Exposure to j8 rays*, 

 canal rays^ and cathode rays^ has also been known to cause the 

 destruction of phosphorescence. 



IE. Wiedmann, Aiyi. d. Phys. 37, p. 177, 1889; E. Wiedemann and C. C. 

 Schmidt, Ann. d. Phys. 56, p. 177, 1895. 



2J. Perrin, Ann. d. Physique (IX) 10, pp. 133-159, Sept., Oct., 1918. 



3L. B. Loeb and L. Schmiedeskamp, Nat. Acad. Sci. Proc, Vol. 7, pp. 202-207, 

 July, 1921. 



^E. Marsden, London Proc. Roy. Soc, 83A, pp. 549-561, 1910. 



«H. Baerwald, Ann. d. Physik 37, 4, pp. 849-880, Nov., 1912; J. Bernd. Zs. 

 Physik, Leipzig, pp. 42-44, 1920. 



«Nichols and Merritt, Phys. Rev. Ithaca, 28, p. 349, 1909; Pospielow, Ann. d. 

 Phys. 45, 7, pp. 1039-1062, No. 17, 1914. 



17— C 



