THE: soiiv AND WATER 



129 



and then placed them under conditions of very little evaporation 

 until they began to wilt. The moisture in the soil was then 

 determined. The hygroscopic moisture was also determined by 

 the method already indicated. A variety of soils and plants were 

 used. The following table shows the average results secured with 

 Indian corn and oats : 



It appears that hygroscopic water may be of advantage in 

 regions of hot, dry winds ; the higher the hygroscopic water, the 

 less rapidly the soil dries out and heats up. It also appears that 

 heavy fogs, such as occur in parts of California, may add to the 

 hygroscopic water of the soil, and keep the plant growing slowly 

 when rainfall is lacking. 



Capillary Moisture. This is the thin film of water surround- 

 ing the soil particles and so held between them that it cannot flow 

 off. In a clean glass tube of i mm. internal diameter, capillary 

 attraction will cause water to rise 15.3 cm; if the bore is o.i mm. 

 the water will rise 153.6 cm; if it is o.oi mm. the water will 

 rise 1536.6 cm. That is, the height to which the water is carried 

 varies inversely as the diameter of the tube. It also varies with 

 the temperature and the liquid used. 



If glass tubes be filled with various soils and the lower ends of 

 these be set in water, a great difference will be observed, both in 

 the speed and in the height to which the water rises in them. This 

 is the method used for comparing the capillarity of dried soils. 



The following table 1 exhibits the differences in the height to 

 which water rises in some soils : 



1 Meister, Jahresber. f. Agr. Chem., 1859-60, p. 42. 



