Capillary Movements of Soil Moisture. 163 



In the 1.0 inch tube 04285 cubic inch. 



In the .1 inch tube 004285 cubic inch. 



In the .01 inch tube .0004285 cubic inch. 



In the . 001 inch tube 00004285 cubic inch. 



193. Capillary Rise of Water in Soils. The spaces left be- 

 tween the soil grains form more or less triangular capillary 

 tubes whose cross-section, formed by four spherical grains, 

 placed as closely together as possible, is represented at the 

 left in Fig. 54; and these tubes extend in all directions 

 through a soil. 



The effective diameters of these capillary tubes are 

 somewhat nearly proportional to the diameters of the soil 

 grains so that for soils with spherical grains having the 

 closest packing, doubling the diameters of the grains would 

 also double the effective diameters of the capillary tubes 

 through which the water must be moved. 



FIG. 54. Showing the shape of cross-sections of the pore space between 



soil grains. 



Th3 area of cross section of the two capillary pores 

 shown in Fig. 54 is equal to the area of the rhombus con- 

 necting the centers of the four grains minus the area of a 

 circle having the diameter of the soil grains, so that divid- 

 ing this area by two gives the area of the section of the 

 pore. 



Where the pore has the smallest section its area is given 

 by the equation 



Area = (v/3 - |) X r 8 = .1613 r 

 where r is the radius of the soil grain. 



