SOIL HEAT 



311 



tivity study, however, is the moisture content of the soil. 

 The following curve for quartz powder, taken from Pat- 

 ten's * work, illustrates its effect and shows how its influ- 

 ence may heavily override the factors already mentioned. 



FIG. 49. Effect of moisture upon the apparent specific volume, heat 

 conductivity, and diffusivity of coarse quartz powder. 



1 Patten, H. E. Heat Transfer in Soils. U. S. D. A., 

 Bur, Soils, Bui. 59, p. 30. 1909. 



