420 GIBBS. 



and black in layers 0.25 centimeter thick, both by reflected and trans- 

 mitted light. 



The major reaction involved produces azophenine. benzene and am- 

 monia and can be expressed by the equation 



= KC 6 H 5 

 -NH.CJBL 



9C 6 H 5 .NH 2 = C 6 H 2 



-NH.C 6 H 5 + 4C ^+™3- 

 = N.CLH S 



While other compounds may be produced, I have not been able to isolate 

 any other products and there is much evidence to show that if any are 

 produced they are present in almost negligible quantities. 



On evaporating the aniline at 30° in a vacuum desiccator over sulphuric 

 acid; pure, perfectly formed crystals of azophenine separate as long as 

 any liquid aniline remains. 



While the theory is that it is only the absorbed rays which produce 

 chemical activity, it is equally true that all absorbed rays are not chemi- 

 cally active. The theory has been advanced that the general absorption 

 is produced by the movements of the molecules themselves and the selec- 

 tive absorption by the movements of the atoms in the molecule. Thus, 

 in certain solutions it is possible that the molecular motion will be very 

 different from that of the compound in the pure liquid or vapor states, 

 while the intramolecular vibrations will not be fundamentally altered. In 

 the cases which I have investigated, namely, phenol, aniline and methyl 

 aniline, the chemical activity induced or catalyzed by light waves is depen- 

 dent upon the presence of a labile hydrogen atom. The action of light 

 upon mono- and dimethylaniline in the presence of oxygen has not been 

 investigated. I have found that the fixation of the labile hydrogen atom 

 of phenol destroys the sensibility of the molecule to chemical change pro- 

 duced by sunlight in the presence of oxygen and that the fixation of 

 aminic hydrogen of aniline reduces the susceptibility in the case of 

 methyl aniline and probably inhibits entirely the sensibility of dimethyl- 

 aniline. 



The introduction of methyl or ethyl groups into the molecule of certain dyes 

 such as fluoresceine and eosine to produce the methyl or ethyl esters or ethers, 

 is known to increase the fastness of the dye to light. 4 Gross 5 has found that 

 the bleaching of some dyes in light was associated with the absorpton of oxygen 

 and most probably due to oxidation. Watson 6 advanced the theory that the 

 fading in light of an azo-dye is due to the oxidation of that part of the molecule 

 which contains hydroxyl- or aminogroups, and that the fastness of such a dye 

 is increased by introducing into the phenolic or arylamino-part such other groups 

 as will reduce the tendency to become oxidized. Experimental work confirms this 

 theory in part. 



•Hummel, Journ. Soc. Chem. Ind. (1892), 11, 13. 



'Ztschr. f. phys. Chem. (1901), 37, 157. 



°Proc. Chem. Soc, London (1909), 25, 224, 290. 



