428 GIBBS. 



almost twice the time was required to produce the same result. While Neuberg 

 does not account for this difference it is. possible that the heat factor may be 

 responsible. 



The glass from which the tubes were made was colorless and permeable 

 in the ultra-violet as far as A =285 fi/x which is a region beyond the limit 

 of the sun's spectrum. 



In atmospheres of carbon dioxide at various pressures the coloration 

 of aniline is in the inverse ratio to that found in hydrogen atmospheres. 

 The tubes at reduced pressure color more rapidly than those at atmos- 

 pheric pressure. The explanation of this phenomenon appears to lie in 

 the acid character of the gas which will tend to reduce the susceptibility 

 of the aniline molecule to the action of light. Carbon dioxide can not be 

 regarded as a gas indifferent to aniline, and the explanation of the 

 phenomenon can not be that it acts as a photo-chemical inhibitor in the 

 sense of the theory advanced by Chapman and MacMahon. 30 



EXPERIMENTAL. 



The aniline employed in these experiments was obtained from three 

 different sources and was purified by several different methods. 



First. — Acetanilid, purified by recrystallization, was decomposed by potassium 

 hydroxide. The aniline was distilled with steam, separated from the water by 

 extraction with ether, and fraetioned several times after the ether was expelled. 

 Portions of this aniline were further treated with acetone by the method of 

 Hantzsch and Freese 31 which is designed to remove sulphur compounds. The 

 final drying was accomplished by distillation over sodium. 



Second. Kahlbaum's aniline, from the sulphate, was purified by distillation 

 and only the middle fractions of constant boiling point were employed. Portions 

 of this aniline were further purified by the method of Hantzsch and Freese. 



Third. Nitrobenzene, made from thiophene free benzene as a starting point, 

 was reduced by tin and hydrochloric acid and the resulting aniline purified by 

 distilling in steam from potassium hydroxide solution. The aniline was extracted 

 with ether, fractionally distilled, and finally dried by distilling over sodium. 



I have not been able to observe any very great differences in the be- 

 havior in sunlight or in the compounds formed in these samples of aniline, 

 although some of the samples obtained do color more rapidly than others. 



ANILINE IN VACUO. 



Purified aniline was distilled in a small glass bulb, drawn out as shown in 

 figure 1, until the air was completely displaced and the entire apparatus filled 

 with aniline vapor. About 5 cubic centimeters of liquid aniline were then 

 condensed in the tube d. With the end of the tube / dipping under mercury, to 

 prevent the entrance of air, the tube d was removed by sealing at the points c 

 and e. 



A second tube was sealed in the same manner with the exception that the 

 tube / was attached to an air pump which was kept running during the distillation 

 of the aniline and until the tube d was sealed off. The first portions of the 



'"Journ. Chem. Soc. London (1910), 97, 845. 

 B1 Ber. d. deutschen chem. Ges. (1894), 27, 2966. 



