24 



THE ABSORPTION SPECTRA OF SOLUTIONS. 



In this consideration of atoms it would be expected in general that the 

 space containing the electric field of the electron would more or less envelop 

 the positive nuclei of the atoms, and that the volumes of atoms would depend 

 on their valency. This would agree very well with the assumptions of Barlow 

 and Pope. 1 These assumptions are as follows: In any chemical body the 

 relative volumes of the atoms are proportional to their valencies; in a crystal- 

 lized body the atoms are close packed; in a compound the volumes of the 

 spheres of atomic influences of atoms of the same valency may differ slightly. 

 The latter variation of the sizes of the spheres of influence (interpreted here 

 as the space filled by the electric fields of the valency electrons) may be due 

 to the different amounts of saturation, or, as Stark calls it, the lack of the 

 valency electrons. It would be interesting to know whether the energy rela- 

 tions support this view, it being expected that the greater the lack of the 

 electrons, the less the potential energy of the compound. 



Stark and Steubing 2 have investigated the fluorescence of a large number 

 of organic compounds. Most spectra are banded, and a band never runs in 

 both directions. The band consists of a tail where the smaller bands are close 

 together. From the tail the small bands may run towards the red or towards 

 the ultra-violet, getting farther and farther apart all the time. But there are 

 never small bands on both sides of the tail. The absorption of light by bands 

 running "to the red" is not accompanied by fluorescence or by any photoelec- 

 tric effects. The absorption of light in bands running towards the violet 

 (benzene bands) is accompanied by a photo-electric effect, a fluorescence of 

 the bands themselves and by a fluorescence of bands due to the connection of 

 carbonyl, ethylene, or other chromophoric groups if these be present in the 

 molecule. The addition of more chromophores to the compound shoves 

 the fluorescent bands to the red. 



Other Benzene Theories. 



There are some color changes of benzene compounds for which the general 

 theory does not seem easily to account. For instance, nitronaphthalene is 

 yellow. By introducing two nitro groups a colorless compound is obtained. 

 In order to explain phenomena of this kind Kauffmann :i assumes that the 

 introduction of groups into a benzene nucleus may change the condition of the 

 benzene ring itself. He considers that benzene may have the diagonal, the 

 Kelule, or the Dewar 4 formula. 



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II. 



III. 



1 Pope: Journ. Chem. Soc, 89, 1675 (1906); 91, 1150 (1907). Swartz: Amer. Chem. 

 Journ., 37, 638 (1907); 42, 158 (1909). 



2 Phys. Zeit., 9, 481, 661 (1908). 



3 Zeit. phys. Chem., 50, 530 (1905). Ber. d. chem. Ges., 37, 2941 (1904). 



*Ber. d. chem. Ges., 33, 1725 (1900); 34, 682 (1901); 35, 366S (1902). Zeit. phys. 

 Chem., 55, 547 (1906.) 



