Texture of Soils. 



Ill 



133. The Pore Space of Soils When the weight of a cu- 

 bic foot of dry soil is known the amount of pui-3 space or 

 space not occupied by the soil grains may be computed from 

 the specific gravity. Taking the weight of a cubic foot of 

 water at 62.42 Ibs., a cubic foot of dry soil, if there were 

 no open spaces in it, should be 



2.65 X 62.42 = 165.4 Ibs. 



With this value and the data given in (149) the pore space 

 of those soils may be calculated. Thus, for the surface 

 foot we have 



Pore space = ^^^ = 52.23 per cent. 



That is, in this soil the surface foot is more than half open 

 space. The pore space for the six feet will be as given be- 

 low: 



Thus it is seen that the unoccupied space in a soil varies 

 from more than half to less than one-third of its volume, 

 the finest grained soils having the largest pore space and 

 the sandy soils and sands the smallest. 



134. Pore Space Eetween Spherical Grains. It can be 

 shown mathematically that when a space is filled with 

 spheres all of one size and these are given the closest pos- 

 sible packing, having the arrangement shown in the 1- 

 part of Fig. 34 and in Fig. 35, the pore space must be 

 25.95 per cent. ; but when the spheres are given the closest 

 possible packing and the arrangement represented in 



