150 GIBBS. 



dark. The steam bath was heated for seven hours a day during six days 

 of the week. The tin-foil covering was carefully removed once a week 

 for the shortest possible length of time, to allow examination of the 

 phenol. At the end of the second week a faint reddish yellow was ob- 

 served. This color deepened constantly as time proceeded. 



The rate of combination of the phenol molecule with oxygen, and 

 consequently the formation of the color will undoubtedly be augmented 

 with a gas mixture containing a higher percentage of oxygen than 

 atmospheric air. 



It is evident from these experiments, that for the production of the 

 purest phenol, the distillation should not be conducted with access to 

 oxygen. While the temperature of the phenol is elevated it should come 

 in contact only with an indifferent gas. It is also probable that the 

 combination with oxygen goes on at all temperatures down to the ab- 

 solute zero, the temperature being an important factor of the rate. 



INFLUENCE OF T^HE ALTITUDE OF THE SUN UPON THE RATE OF 

 COLORATION. 



I believe that I have noticed a difference in the rate of coloration of 

 phenol at different seasons of the year. When the sun is directly over- . 

 head, which occurs twice a year in this latitude, there is apparently a 

 more rapid production of the red color than when it is in the far south 

 in December and January. This observation is attended by so many 

 factors that it is difficult at this time to make any positive statement. 

 A more complete series of observations and measurements extending over 

 a long period of time will be necessary before any definite results can be 

 obtained. 



It is obvious that the rays pass through a thinner layer of atmosphere 

 in reaching the surface of the earth when the sun is in the zenith and 

 therefore the ultra-violet absorption will vary at different seasons of the 

 year, and since the shorter wave lengths undergo refraction to a lesser 

 extent than the longer, a greater proportion of the shorter waves reach 

 the earth's surface when the sun is directly overhead. 



It is possible that these considerations produce different light effects 

 in the Tropics, where the sun is sometimes in the zenith, than in the 

 temperate and arctic zones where it never reaches the same condition.^^ 



The admirable observations of Cornu have sho^s^l that the limit of the 

 sun's spectrum is variable, according to the state of the atmosphere and 

 the altitude of the sun "^ and that the longest ultra-violet spectrum was 

 obtained near noon at the highest elevations."^ 



" The attempt to photograph the sun spectrum to shorter wave lengths than 

 any recorded will shortly be made in this locality by the writer. 

 "Gompt. rend. Acad. sci. (1879), 88, 1101. 

 <"Ibid. (1879), 89, 808. 



