SOIL EM AT 



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. 



.61^3 



M/ 



,om 



cT J^ /S 



^O 



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. 

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



U. S. D. A.. 



