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PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Briggs and Lapham 1 found that water rose 37.5 cm. in a dry 

 soil, while in a moist soil it rose over 165 cm. The method of 

 work was as follows : 



Two tubes of glass were provided with perforated bases, filled 

 with soil, and saturated with water by sucking it up through the 

 earth. One tube was then sealed at the base, and the other 

 inserted into a reservoir of water. At various intervals of time, 

 both tubes were weighed. If 'water rises by capillary action, the 

 tube with reservoir attached will lose water more rapidly than 

 the other one. If not, a section of the tube was removed after a 

 suitable interval, and the operation repeated. For example, with 

 one soil, no loss occurred at 180 cm. ; loss occurred at 165 cm. 

 The capillary water rose 165 cm., but did not rise 180 cm. 



The so-called capillary moisture of the soil is held as thin films 

 of water surrounding the soil particles, due to what is called "sur- 

 face tension." The surface of the film of water surrounding the 

 soil particle is in the condition of an elastic membrane exerting 

 considerable pressure and consequently holding the water firmly 

 against the soil particle. In a fully drained soil there is a condition 

 of equilibrium between the force of surface tension and the force 

 of gravity. If the film of water becomes thicker and heavier, the 

 force of gravity will gradually draw away the excess of water. 

 If the films become thinner, a force is developed which may cause 

 a flow of water from thicker neighboring films. 



Loughridge 2 studied the capillary action of soils placed in 

 copper tubes one inch in diameter and in one foot lengths, fitting 



1 Bulletin 19, Bureau of Soils. 



2 Rep. Cal. Exp. Sta., 1892-4 



