THE PHYSICAL PROPERTIES OF SOILS 



91 



purely artificial because, 

 even if the arrangement of 

 the particles has not been 

 disturbed in taking the 

 sample, the process takes 

 no account of the influence 

 of the subsoil. 



In estimating the size of 

 the particles the experiments 

 are performed upon the air- 

 dried sample. The larger 

 particles are first separated 

 by sieves. All mineral par- 

 ticles too large to pass 

 through circular holes of 

 5 m.m. diameter are classi- 

 fied as stones and what 

 passes through is called fine 

 earth. Whatever part of the 

 fine earth is retained by a 

 sieve, in which the holes are 

 of 1 m.m. diameter, must be 

 composed of particles of less 

 than 5 m.m. and greater 

 than 1 m.m. diameter. By 

 using sieves having holes of 

 different size, the coarser 

 particles can all be separated 

 and divided into groups of 

 different degrees of fineness. 



For the separation of 

 particles below 0*5 m.m. 

 diameter recourse must be 

 had to some process of 

 elutriation. Many methods 



d 



FIG. 13. 



