10 



A STUDY OF THE ABSORPTION SPECTRA. 



by the presence of neighboring atoms. The electrons of this type vibrate 

 in definite frequencies that can be changed by only infinitesimal amounts. 



ORGANIC ABSORPTION SPECTRA. THE UNIT OF THIS ABSORPTION. 



In discussions concerning the color of organic compounds it is custom- 

 ary to speak of the selective absorption as being due to certain ions or mole- 

 cules. This is probably true in the infra-red; the electric charges absorbing 

 these long wave-length radiations being probably associated with masses 

 of molecular size. But in the visible and ultra-violet portions of the spec- 

 trum the absorber invariably has a value of e/m (e the charge, and m the 

 mass) of the same magnitude as that of the electron. Drude ' has investi- 

 gated a large number of organic compounds and shows that the absorber 

 of all the shorter waves of the spectrum is the negative electron. Hous- 



toun 2 has calculated the value of e/m= 1.297 y k * for the absorption 





 bands of several organic compounds and also shows that the absorber is 



the electron. (7- is the refractive index, k the maximum value of the 



coefficient of extinction; ^ is the wave-length of maximum absorption, and 



X t is the wave-length for which the coefficient of extinction has a value 



equal to half its maximum.) The formula used is based on the present 



laws of dispersion. 



The following table is taken from Houstoun's paper. 



Throughout this monograph, then, it will be considered that the 

 absorbers are negative electrons. These electrons have certain free periods 

 corresponding to bands of selective absorption. These free periods are 

 greatly modified by the presence of certain chemical radicles, and seem to 

 be electrons that are situated either in the outer parts of the atom or between 

 two or more atoms. Stark and others call these the valency electrons and 

 consider that chemical valency is due to them. Chemical bonds and these 

 electrons will therefore be closely related. As an aid to our imagination 

 we will consider the atoms or ions as large spherical regions throughout 

 which a positive charge is uniformly distributed. These regions are some- 

 what similar to the "spheres of influence." Two atoms collide when their 

 spheres of influence touch one another. Groups of atoms comprising ions, 

 radicles, or molecules will also have spheres of influence. No ion can pene- 



1 Ann. Phys., 14, 677, 726, 936, 961 (1904). 



2 Nature, 80, 338 (1909); Proc. Roy. Soc, A, 82, 606, Sept. 18 (1909). 



