THE PHYSICAL PROPERTIES OF SOILS 51 



The names gravel, sand, etc. given to the different 

 fractions in the table are quite empirical and, though in 

 common use, are not always applied in exactly the same 

 sense. It is more important to notice that in the sandy 

 soil more than 80 jper cent, of the particles are of greater 

 diameter than 0*05 m.m., in the clay soil more than 

 80 per cent, of the particles are smaller than that, 

 while in the loamy soil the particles are of intermediate 

 size. 



Number of Particles. The number of particles in a 

 given volume could be easily computed if they were 

 regular in shape, size and arrangement. Thus, if the 

 particles were cubes and were built up in a compact mass 

 without any spaces between them, one cubic decimetre 

 would contain a thousand cubic centimetres, a million 

 cubic millimetres, and so on. 



If each cube were replaced by a sphere or particle of any 

 other shape the number would remain unaltered. A cubic 

 decimetre would thus contain a thousand spheres of one 

 centimetre diameter, a million of one millimetre diameter, 

 and so on. In short, the number of spheres in a given 

 volume would be inversely proportional to the cube of the 

 diameter. 



If the spheres were as small as the particles of sand say 

 T Jo part of an inch in diameter there would be a million 

 of them in one cubic inch ; if they were as small as those 

 of clay say 5^00 part of an inch in diameter there would 

 be 125,000,000,000 in one cubic inch. 



Arrangement of the Particles. - - If spheres were 

 arranged in the manner indicated above, by substituting 

 them for cubes in a compact mass, the spaces between them 

 would be the largest possible. Any re-arrangement would 

 therefore bring them closer together, and a larger number 

 would be required to fill a given volume. 



Interspace. The amount of space occupied by a mass 



E 2 



