CHAPTER III 



THE PHYSICAL PEOPEETIES OF SOILS 

 THE PARTICLES 



Size of the Particles. The physical properties of soils, 

 like those of their constituents, depend very largely upon 

 the size of the particles, and, as a rule, soils are extremely 

 heterogeneous in this respect. The coarser particles- 

 stones, etc. may be separated and their size determined 

 by means of sieves with circular holes of known diameter. 

 The size of the particles in the fine earth can be estimated 

 by microscopic measurements. The proportion of stones 

 and coarse material may vary from 50 per cent, or more 

 down to zero ; from 2 to 20 per cent, is common in culti- 

 vated soils. The proportions in which the particles of 

 various sizes are mixed together in the fine earth of dif- 

 ferent soils are still more variable. All that can be said is 

 that those of coarser texture contain more of the larger and 

 those of finer texture more of the smaller particles. 

 Taking particular cases for example, the following table 

 shows the proportions in which the particles of various 

 sizes were found in the fine earth of some sandy, loamy and 

 clay soils respectively : 



