122 



Physics of the Soil. 



spt 



[8.9434 10] 



where 



d = diameter of grain in c. m. 



h = length of sand column in c. m. 



s = area of cross-section of sand column in sq. c. m. 



p = pressure in c. m. of water at 20 C. 



t = time in sec. for 5,000 c. c. of air to flow through at a torn 



perature of 20 C. 



[8.9434 10] is a logarithm of a constant 

 k is a constant taken from the following table. 



FIG. 29. Showing aspirator for determining the mean effective diameter 

 of soil grains. A, aspirator bell; B, pressure gauge; C, air meter; 

 D, aspirator tube for samples. 



