Light Absorption and Fluorescence. 



633 



observations lead to the inevitable conclusion that in the 

 reaction by which the amino compound is converted into its 

 hydrochloride, it passes through an intermediate phase which 

 is formed in presence of small traces of the acid and. on the 

 addition of more acid, reacts with this acid to give the salt. 

 Here, therefore, we have evidence of the same substance 

 exhibiting two different absorption bands in different 

 solvents. 



An exactly similar phenomenon was observed in the case 

 of the sulphouation of: certain benzene compounds. In the 

 case of hydroquinone, for example, the chemistry of the 

 process is represented by the equation 



C 6 H 4 (OH) 2 + H 2 S0 4 = (S0 3 H)C 6 H 3 (OH) 2 + H 2 0. 



Tf hydroquinone is dissolved in alcohol the solution exhibits 

 a very strong absorption band in the ultra-violet. A solution 

 of hydroquinone in concentrated sulphuric acid, however, 

 exhibits an absorption band which is much nearer to the red 

 than that shown by the alcoholic solution. The acid solution 

 on standing slowly changes to a solution of the sulphonic 

 acid, and the change may be readily followed with the 

 spectroscope. Clearly, therefore, the hydroquinone in the 

 acid solution exists in an intermediate condition which 

 proceeds to form the sulphonic acid. Clearly, also, the 

 hydroqninone can show two absorption bands, one in 

 alcoholic solution and the other in sulphuric acid solution. 



In order to explain the shift of the emission spectrum lines 

 of metals when the arc is formed under pressure, Humphreys'* 

 postulated the existence of electromagnetic force fields sur- 

 rounding each atom of the metal. This conception may be 

 extended to the case of molecules. It would follow from the 

 fact that the atoms of th i different elements differ so much 

 in their chemical characteristics that their electromagnetic 

 force fields must also differ. In a molecule composed of 

 several different atoms there will exist several electromagnetic 

 force fields in close juxtaposition and differing amongst 

 themselves. There must ensue, therefore, a condensing 

 together of these force fields with the escape of energy and 

 the formation of a closed force field having a materially 

 reduced chemical reactivity. In fact the force field may be 

 so closed that the reactivity becomes immeasurably small. 

 In other cases a balance mny be left over, giving rise to 

 what chemists recognize as residual affinity. It follows 

 from this view that in order to induce chemical reactivity it 



* Astrophys. Jouru. xxiii. p. 233 (1906). 



