62 



dition of a second set of spheres of such diameter 

 as will just fit into the pore spaces between a larger 

 set will reduce the minimum percentage of pore space 

 (that for closest packing) from 25. y5 to 6.76. A third, 

 still smaller set of spheres introduced into the pore 

 spaces between those of the second set will decrease 

 the pore space percentage to 1.76. 1 vn the other 

 hand, irregularities in the shape of the particles 

 will tend to increase the possible pore space and this 

 tendency is greatly increased by the flocculation and 

 loosening of texture which is caused and maintained 

 by the capillary water of the soil and the surface- 

 tension forces which capillary water system puts 

 into action. 



The result of this widening of limits is 

 that the pore space of actual soils may vary between 

 60 or 70 percent for soils high in organic matter to 

 10 percent for closely packed sands. The pore space 

 of ordinary cultivated soils is usually between 35 and 



1. Soyka,- Forsch. Geb. Agr. Physic 



1 (1885). 



2. I have discussed these matters elsewhere 

 in detail. See Free,- Jour. Frank. Inst. 170: 21-26 

 (1910), Studies in Soil Physics, pp. 3-8 (1912); where 

 further literature is cited. 



