THE FORMS OF SOIL WATER 



221 



149. The maximum retentive power of a soil. — An- 

 other determination has been devised by Hilgard 1 and 

 used to considerable extent by other investigators. 2 It 

 is designated as the maximum retentive power of a soil. 

 A small perforated brass cup is used, having a diameter 

 of about 5 centimeters and capable of containing a soil 

 column 1 centimeter in height. A short column is used, 

 since it is only under such conditions that a soil may re- 

 tain against gravity the greatest amount of water. Also, 

 the soil is able to expand or contract, as the case may be, 

 on the assumption of water until an equilibrium is reached. 

 A filter-paper disk is placed in the metal cup, and the soil 

 is poured in, gently jarred down, and stroked off level 

 with the top of the cup. The cup is then set in water 

 and the soil is allowed to take up its maximum moisture. 

 After draining, the weight of the wet soil plus the cup, 

 together with the weights previously obtained, will allow 

 the calculation of the total water contained by the soil. 



150. Capillary movement. — It has already been shown 

 how different thicknesses of films on two particles tend 



1 Hilgard, E. H. Soils, p. 209. 



2 This text, paragraph 181. 



New York. 1911, 



