THE TROPICAL SUNLIGHT. 7 



The color change of phenol takes place much less rapidly in temperate 

 climates where measurements have been made. Richardson gives three 

 days in Clifton, England, 13 and in some instances several weeks have not 

 sufficed to produce the color. A tube of phenol and oxygen, in the dark, 

 kept at a temperature of 100° for two weeks, gave only a faint yellow color, 

 and phenol under the same conditions in the diffused light of a laboratory 

 room at Manila at a temperature of approximately 30° was not appreciably 

 colored after two months. 



The products of oxidation are quinol, quinone and catechol, all of 

 which confirm the conclusion that the change to the quinone formula is 

 markedly accelerated by the ultra-violet rays which are absorbed by 

 phenol -and point in the direction of the supposition that these rays are 

 present in greater proportion in the sunlight of the Tropics, at sea level, 

 than in more northern climates. The conclusion in regard to the labile 

 condition of one-sixth of the hydrogen in phenol would probably also be 

 found true for a large series of similar compounds, and may, possibly in 

 the future be extended so as to explain a great many chemical phenomena 

 prominent in tropical climates. 



Aniline is even more fitted than phenol for a study of the effects of 

 insolation, as the changes are brought about with greater rapidity and 

 the oxidation products are present in greater quantity. 



When perfectly pure aniline is sealed in a thin glass tube with dry air 

 and exposed to the sunlight in Manila during the months of April, May 

 and August, it darkens and assumes a decided red shade in less than ten 

 minutes. Of course, the temperature, as in the case of phenol, is also an 

 important factor. 



The products of the reaction which have been isolated are azobenzene, 2,5- 

 dianilinoquinone, 2,5-dianilinoquinoneanil, and azophenene. The oxidation is 

 therefore in all probability accompanied by one of condensation, and again it seems 

 not unreasonable to refer the rapid accomplishment of this portion of the reaction 

 to the part of the spectrum lying in the violet and beyond. 



Pure samples of aniline also became colored upon long standing in the dark. 

 Aniline, like phenol, therefore, has a portion of its hydrogen labile and probably 

 shows a similar equilibrium between the ordinarily accepted formula and the 

 quinoid structure as is presented by phenol. Its absorption spectrum also gives 

 a deep band in the violet. 



However, aniline differs from phenol in the fact that in the tropical 

 sunlight it undergoes chemical changes even in the absence of oxygen, 

 that is, when it is placed either in vacuo or in the presence of indifferent 

 gases such as hydrogen, nitrogen, or carbon dioxide. At first it is colored 

 yellow and finally it changes to a brilliant red. The work on this subject 

 is not entirely completed. However, it may be stated that no gas is 

 evolved, azophenene is the main substance formed, and ammonia is also 



"Jowrn. Soc. Chem. Ind. (1893), 12, 415. 



