SOME PHYSICAL PROPERTIES OF THE SOIL 109 



to two different arrangements: (1) in columnar order, 

 with each particle touched in four points by its neighbors ; 

 and (2) the oblique, in which each particle is in contact 

 with six of its neighbors. The possible pore space in 

 the first case is 47.64 per cent, while that in the second 

 case is 25.95 per cent. The amount of this pore space 

 is uninfluenced by the size of the particles, provided they 

 are round and all of the same volume. 



FIG. 17. Ideal arrangements of spherical particles, showing, from left 

 to right, columnar, oblique, compact, and granular orders. 



To any one of practical experience it is a well-known 

 fact that the soil particles are not homogeneous as to 

 size, and neither do all the particles function as simple 

 grains, being gathered together in groups called granules, 

 or crumbs. A small particle of soil may be made up of 

 a number of very small grains. This will modify the 

 ideal condition as described above, giving two additional 

 conditions first, a mixture of spherical grains of differ- 

 ent sizes, and, secondly, a condition in which the large 

 grains are complexes made up of numerous small particles. 

 A mixture such as is presented by the first of these con- 

 ditions, in which the small grains fit in between the 

 larger ones, will result in a reduction of pore space. The 

 pore space will fall below 25.95 per cent and approach 

 zero. A real soil having such restricted pore space is 



