PHYSICAL INTER-RELATIONS IN SOILS 45 



water acts as a membrane holding 

 the particles of the crumbs loosely 

 together. (See Figs. 12, 17, and 18.) 

 When the pore-space in loam or 

 clay soils is filled with water, as it 

 is when gravitational or surface 

 water is present, the films of capil- 

 lary water, which may have held 

 the soil in crumbs, can no longer 



exist, and the 



particles, 



which may 



have been held 



in crumbs, 



FIG. 18. Pyramid of proceed to fall 



sandy loam held in apart an( J then 

 position by capillary 



film. It was formed to Settle to- 



by pouring a fine ge ther, as the FIG. 17. A mass of 



steady stream of the 



soil into a dish in which particles 



had been previously 



placed a small amount 



of water. As the pour- 



sand loam held n 



a 

 film (about twice the 



Set- 



to tne 

 . 



bottom of the 

 ing continued, the glags ( part 5 Q f Exp 5 p 2 30), Or 

 water climbed up the ' 



mass of soil slowly as when the pyramid collapsed 

 enough so that the ( part 2 &, Exp. 7, p. 231). Every 



tension of the film held 2 e \ 



it in place. The pour- farmer who has worked clay or 

 ing was continued till i oam so n s O r observed their be- 



the water was entirely . 



transformed into capil- havior, knows what happens when 

 lary water. The col- ^ey become saturated with water 



umn stands 2 inches 



in height. The column even tor a tew hours. JNo matter 

 retained its form in an j low excellent the condition of mel- 



open room several 



hours after being lowness may have been, they at 

 formed and illustrates once begin to puddle or pack. The 



the strength of the 



capillary film. 



j j- 



longer the saturated condition exists, 



