SOIL HEAT 301 



conditions, however, as the atmosphere continuously 

 refracts, reflects, and absorbs a certain amount of this 

 radiant energy. More important still are certain inher- 

 ent qualities of the soil itself which function materially 

 in the modification of the amount, of heat absorbed. These 

 intrinsic factors are color, reflection, texture, and structure. 

 216. Effect of color on absorption of heat. (See Fig. 

 47.) — In a natural soil it is very difficult to effect a change 

 in soil color without changing the texture, structure, and 

 more particularly the constitution, of the particles. In 

 order to eliminate these disturbing factors in a study of 

 heat, a quartz sand colored with various dyes was used 

 by Bouyoucos. 1 The following data, taken at Lansing, 

 Michigan, on a clear, warm day in August, illustrate 

 the general effects of color on absorption : — 



Effect of Different Colors on Heat Absorption by 

 Quartz Sand, August 5, 1.30 p.m. 



Color . Temperature 



(Degrees Centigrade) 



Black 37.6 



Blue 36.7 



Red 35.9 



Green 34.7 



Yellow 32.6 



White 31.7 



It is quite evident that the darker the soil, the greater 

 is its absorptive power. This is because of differences 

 in reflection, a light-colored soil reflecting more of the 

 heat rays than one of a darker color. There might be a 

 question here as to the difference in radiation arising from 



1 Bouyoucos, G. J. An Investigation of Soil Temperature, 

 Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 31. 1913, 



