ARRANGEMENT OF SOIL PARTICLES 



89 



continue to be filled in by smaller spheres until the 

 mass is practically solid, without pores. (See Fig. 26.) 

 It is of course recognized that under field conditions 

 these ideal arrangements do not pertain, but these 

 figures illustrate the underlying factors which determine 

 differences in pore space, and, also, differences in other 

 physical properties. Soil particles are irregular in shape 

 and uneven in size. When brought very close together, 



Fig. 26. Ideal arrangements of spherical soil particles: (1) Columnar order, 

 47.64 per cent of pore space. (2) Oblique order, 2.5.95 per cent of pore space. 

 (3) Compound spheres in oblique order, 74.05 per cent of pore space. (4) Three 

 sizes of spheres with closest packing, about 5 per cent of pore space. 



as occurs in mixing in a wet condition, their molecular 

 attraction is brought into operation and, especially 

 when dry, they are held together very securely. In this 

 way the normal molecular attraction of the soil particles 

 is increased by the deposition around them of the 

 material in solution. 



Applying these principles to the soil, it is observed 

 that there may be two general arrangements of the 

 particles. (1) Each particle may be separate and free 

 from its neighbors. This is a separate-grain structure. 

 That is, each particle of soil functions separately. When 

 by proper manipulation the particles are so packed 

 together that the small particles quite completely fill in 

 the spaces between the large ones, so that a very dense 



