PHYSICAL PROPERTIES OF SOILS 



181 



cent of 74.05 per cent) ==45.17 per cent. The latter pore space, 

 45.17 per cent, is approximately that possessed by the medium and 

 fine sandy loams; while the former, 72. 58 per cent, is too high for 

 soils unless under exceptional conditions. The coarse sands which 

 approach to theoretical conditions most nearly show 33 to 35 per 

 cent of pore space. The granular condition developed in a soil in- 

 creases its pore space. 



10. Internal Area or Surface. The total surface of the soil 

 particles in a given volume or weight is called the internal area or 

 surface of the soil, and is usually expressed in square feet, or acres 

 per cubic foot. This is very important because it controls to a 

 large extent the amount of hygroscopic and capillary or film 

 moisture. A system of grades of soil particles based on the internal 

 surface would be of great value. Since the surfaces of spheres 

 vary as the squares of their radii or diameters, the internal surface 

 of a soil varies inversely as these functions. This may lie shown 

 by means of marbles as above and calculating the total surface 

 with each diameter for columnar arrangement. 



Area of Spheres in a One-inch Cubical Box with Columnar Arrangement 



The following table gives the internal area of various soils: 

 Computed Surfaces of Soil Particles in Different Kinds of Soil King s 



