Temperature and Capillary Moisture in Soils 



165 



abstracting force. When the attractive forces of the soil for water are 

 satisfied and the thickness of the surface and capillary films is increased, 

 then greater quantities of water will be removed by the same abstracting 

 force. The smaller thermal water movement which occurs in the moist 

 and dry soil rather than in the soil of uniform moisture content is due 

 mainly to the cheesecloth which is placed between the dry and moist 



CLKDE S/LTLOAM 



EXPL^/V^r/O/y: 

 — —» — ^ Waier moi/e<^ /hsm mo/s/ so//<3/ 40 "c. fo c/ry so// 3/ O "c. 



" — - " " " « " O'c. " ■> '> "40°c. 



— — — » " » " " « 20°c. » " " " Cc. 



— .— .. « „ » .. „ » O'c. " » " "20'c. 



Fig. 9.— Curve showing the percentage of moisture moved from a moist and warm column to a dry and cold 

 column of Clyde silt loam, and from a moist and cold to a dry and warm column of Clyde silt loam. 



columns of soil. Althoi^h this cheesecloth was very thin and had wide 

 meshes, yet it prevented the two columns from forming a complete and 

 perfect contact; consequently the dry soil had to absorb water directly 

 through the cheesecloth as well as from the soil. 



Another factor which would seem to impede the rate of water move- 

 ment from a moist and warm to a dry and cold column of soil is the 

 resistance which the dry soils offer to wetting, owing to the air film 



