Ligltt Absorption and Fluorescence . 



635 



Up to the present I have found only a few substances in 

 which more than two absorption and fluorescent maxima 

 have been measured ; but in each of these there exists a 

 constant frequency difference between these maxima. This 

 is shown very clearly in the case of the substances given 

 below. Ai, A 2 refer to absorption bands and F to fluorescent 

 maxima. The measurements are expressed in terms of 1/X, 

 and in order to convert them to oscillation frequencies they 

 must be multiplied by 3 x 10^. 







A,. 



F. 



Differences. 

 1. II. 



o-Aininocinnamic acid.. 



. 3600 



2800 



2000 



800 800 



/3-Naphthylamine 



. 3600 



3000 



2400 



600 600 



A solution of benzaldehyde in strong sulphuric acid shows 

 absorption bands at 1/X = 21 74 and 3400, the difference of 

 frequency being 1226, which is twice 613. In alcoholic 

 solution it shows two bands at 1/X 3470 and 4070, the 

 difference being 600. Clearly therefore the constant dif- 

 ference is shown here also. We should also expect to find 

 an absorption band with a value of 1/X=2787; and it is 

 interesting to note that the absorption curve of the sulphuric 

 acid solution shows a " step out " in this region, which denotes 

 that there is evidence of an absorption band about this 

 position. The measurements of 1/X=3400 and 3470 evi- 

 dently refer to the same band, the difference being due to 

 the two solvents. 



Similar constant frequency differences seem to be present 

 in several other compounds, e. g. trinitroanisole and trinitro- 

 benzene ; but more accurate measurements are necessary 

 before the fact of their existence can definitely be stated. 



It is also interesting to note that a large number of 

 compounds, for which only two maxima of absorption and 

 fluorescence are known, show a frequency difference of 400 

 or some multiple of 400. The following examples may be 

 given : — 



Phenol 



Dibenzylideneacetone 



Dianisylideneacetone 



Quinol dimethylether 



Ethyl a-Benzoylsuccinate 

 a-Naphlhol 



A,. 



A 2 . 



F. 



Differences. 



3660 





3255 



405 



3200 



2060 





3X3S0 



2800 



2000 





2X400 



3420 



2210 





3x404 



4050 



2800 





3X417 



3390 





2600 



2x395 



