THE CHEMICAL ACTION OF LIGHT 257 



advantage. In fact as regards the action of light, the system 

 (C 2 H 6 ) 2 + H 2 seems to be equivalent to 2C 2 H 5 OH but it is more 

 effective and rapid in its action. A striking illustration of this fact 

 is found in the case of phenanthraquinone, which is only slowly 

 affected by alcohol but is decolourised almost instantly when dis- 

 solved in moist ether on exposure to sunlight ; phenanthraquinol 

 is formed. 1 Isatin also, which is hardly changed by alcohol, 

 gives hydrisatin in ethereal solution. 2 In these cases acetalde- 

 hyde is formed, just as from alcohol itself. The action of dry 

 ether, however, is entirely different in character and gives rise to 

 synthetic changes, no aldehyde being formed (see Section VII.). 

 One of the most complex cases of reciprocal oxidation and 

 reduction is that which occurs when certain benzenoid nitro- 

 compounds are dissolved in a paraffinoid alcohol and the solutions 

 are exposed to sunlight during several months. The case of 

 nitrobenzene has been studied by Ciamician and Silber 3 with great 

 care ; from their results they conclude that the photochemical 

 reduction takes place in successive simple stages as follows : 



C 6 H 5 NO, -> [C 6 H 6 NO] -> C fi H 5 NH(OH) -> C 6 H 5 NH a 



OH.C 6 H 4 .NH, 



Aniline can always be isolated as well as />-aminophenol, 

 which, as shown by Bamberger, is undoubtedly a product of the 

 transformation of phenylhydroxylamine ; no doubt therefore the 

 latter is formed in the first instance. The fate of the alcohol 

 is uncertain ; the corresponding aldehyde can never be isolated. 

 Instead of this, quinaldine(a-methylquinoline) can be separated 

 in the case of ethylic alcohol, 2-methyl-3-ethylquinoline in the 

 case of propylic alcohol and 2-isopropyl-3-isobutylquinoline in 

 that of isoamylic alcohol. These bases are formed in larger 

 quantity than aniline itself, which is the other principal con- 

 stituent of the basic fraction of the product ; and they are the 

 condensation products obtained by heating aniline and concen- 

 trated chlorhydric acid with acetaldehyde, propionaldehyde and 

 isovaleraldehyde, respectively, during several hours, in Doebner 

 and Miller's well-known method of synthesising quinoline bases. 

 The formation of the bases is without doubt, therefore, to be 



1 Klinger, Ber. 1886, 19, 1862. 



8 Ciamician and Silber, Atti R. Accad. Lincei, 1901, 10, i. 92. 

 3 Ber. 1886, 19, 2899 ; Atti R. Accad. Lincei, 1902, 11, i. 277, 1905 ; 14, ii. 375 ; 

 Ber. 1905,38, 3813. 



