2 PHYSICAL CONSTITUTION OF SOIL 



volume of the mass ; with the loosest packing the interspaces 

 are 47-64 per cent, of the total volume. 



The proportion of the volume occupied by interspaces, 

 though varying so much with the mode of packing, is quite 

 independent of the size of the particles, so long as all the 

 particles are of one size. Thus, if a single spherical marble, 

 one inch in diameter, be placed in a square box having an 

 internal capacity of one cubic inch, the unoccupied space will 

 be 47*64 per cent, of a cubic inch. If the same box is now 



FlGUEE I. 



filled with one million marbles, each of T ^jth inch in diameter, 

 the packing being of the loosest description already referred 

 to, the unoccupied space will again be 47-64 per cent, of 

 a cubic inch x . In the second case the interspaces are indi- 

 vidually far smaller than in the first case, but their united 

 volume forms the same proportion of the whole. This is 

 an important fact to bear in mind. The proportion of inter- 

 spaces in a soil plainly determines both the volume of- air 

 which the soil will contain when dry, and the volume of water 

 which it will hold when fully saturated. In a coarse sand, 

 and in a fine clay, the maximum capacity for air and water 

 will be the same, if each is composed of uniform particles 

 packed in the same way. 



1 This, and several other illustrations in this chapter, are taken from 

 Professor King's very interesting book The Soil. 



