WATER CAPACITY OF SOILS 



67 



takes place when they are wetted. When soils swell on being 

 wetted, it is obvious that the quantity of water they will 

 hold when saturated must be in excess of that calculated 

 from their interstices when dry. Hilgard and Loughridge 

 regard the hydrated silicates in the California soils as having 

 a distinct influence on their capacity for holding water. 



In ordinary soils, humus is the constituent which most 

 powerfully influences the water-holding capacity. It acts in a 

 double way ; first, by increasing the volume of the interspaces 

 through its great porosity ; and second, by its absorption of 

 water due to the colloid nature of some of its constituents. 



As examples of the proportion of water held by various 

 soils when fully saturated we may quote the results obtained 

 by Meister (Jahresb. Agrik. Chem. 1859-60, 36), by Schwarz, 

 and by Hilgard and Loughridge. 



TABLE VIII 



WATER IN FULLY SATURATED SOILS (MEISTER) 



WATER IN FULLY SATURATED SOILS (SCHWARZ) 



F 2 



