COLORATION OF ANILINE: II. 427 



"* * * the difference between the persistence of the bands in the three 

 cases is very marked, * * *. The absorption curve of the dimethyl compound 

 shows also the second benzene band to a small degree with the broad band 

 characteristic of the second type, which is a further evidence that the sub- 

 stituting group has nearly been saturated. The two methyl compounds, in 

 presence of hydrochloric acid, give a very similar spectrum, as does aniline 

 hydrochloride." 



From these considerations it is to be expected that the fixation of the 

 aminic hydrogen of aniline by the methyl group will decrease the suscep- 

 tibility of the compound to the action of light. I have found that the 

 rate of coloration of aniline in the sunlight is greatest, monomethyl- 

 aniline less and dimethylaniline least, if the latter is at all susceptible. 

 Methylamine has been identified as one of the reaction products of 

 monomethylaniline. 



Variations in the rate of coloration due to the pressure in the sealed 

 tubes has also been noted, although my observations upon this point are 

 not entirely satisfactory and further experimental work will be required 

 to settle the question entirely. In atmospheres of hydrogen at pressures 

 ranging from that of the atmosphere to about 1 millimeter, aniline 

 colors more rapidly in the tubes containing the greatest pressure. Little 

 or no differences were discernible in the tubes containing methyl and 

 dimethylaniline. The differences in the coloration of the aniline tubes 

 were so marked that the experiments were repeated with the same results. 

 While the explanation of this phenomenon at this time is not clear it is 

 worthy of note that Purvis, 28 in his investigations of the absortion spectra 

 of the vapors of aniline, methjdaniline and dimethylaniline, has observed 

 that the effect of increasing the temperature and the pressure of aniline 

 vapor is a strengthening and widening of the bands with the appearance 

 of new bands on the side of the larger wave lengths and a shifting of the 

 region of complete absorption toward the red, while at constant temper- 

 ature a decrease in pressure produces a weakening, narrowing, and 

 sharpening of the bands and a shift in the region of complete absorption 

 toward the shorter wave lengths. While none of the homologues of 

 aniline show any of the bands characteristic of aniline, the same shifting 

 of the region of complete absorption on change of temperature and pres- 

 sure are noted. 



While every precaution was taken to seal pure aniline in the tubes, 

 described in the experimental part, I am not prepared to state that the 

 rate of coloration is not effected by impurities which may be derived 

 from the glass, for example iron compounds. 



Neuberg : " has converted benzoic acid into salicylic acid by exposure to sun- 

 light in the presence of ferric or ferrous sulphate. In Berlin 13 per cent was 

 converted in sixteen days while in Teneriffa, at an altitude of 2,200 meters, 



28 hoc. cit. 



-°Biochem. Ztschr. (1910), 27, 271. 



