68 THE TEXTURE OF THE SOIL [chap. 



maximum and amounts to 4764 per cent, of the whole 

 volume occupied by the soil ; this proportion is the same 

 when the soil particles have a smaller diameter, as in B ; 

 as long as the spheres are uniform in size, whatever that 

 may be, and are packed as shown in the diagram, the 

 pore space will be at its maximum. The minimum pore 

 space is attained by the packing shown in C and D ; it 

 amounts to 25-95 per cent., and is again independent of 

 the size of the particles, provided they are uniform. If 

 the spheres are, however, of very different sizes, so that 

 smaller spheres lie wholly within the spaces between 

 the larger spheres, as in the arrangement shown in E, 

 the pore space may be indefinitely reduced. Per contra :, 

 if aggregates of particles exist in the soil, containing 

 both pore space between the ultimate particles and 

 between the aggregates which behave as single particles, 

 as in F, the pore space may rise much above the 

 maximum of 49 per cent. A soil in situ generally 

 possesses a pore space larger than the proportions 

 indicated above ; various causes, such as the stirring 

 due to cultivation, the decay of vegetation, etc., leave 

 definite cavities in the soil : for example, if a hole be 

 dug for any purpose in ordinary cultivated ground and 

 afterwards filled up with its own soil, it is rarely possible 

 to fill the hole completely, especially if a little pressure 

 has been used to trample down each layer. 



In ordinary soils the pore space varies from a little 

 over 50 per cent, among the stiff clays, down to 25 or 30 

 per cent, in the case of coarse sands of uniform texture. 

 The reason for the greater pore space with the finer 

 grained soils lies in the fact that the weight of the 

 small particles of clay is not sufficient to overcome the 

 friction and move the particles into the arrangement 

 giving the minimum pore space. If some small shot are 

 shaken into a graduated measure and the pore space 



