THE PHYSICAL PROPEKTIES OF SOILS 



93 



HYDRAULIC VALUE OF PARTICLES OF DIFFERENT SIZES. 



particles soon settle to the bottom of the vessel. The 

 liquid containing the finer particles in 

 suspension is decanted off, allowed to 

 settle for a longer period, again decanted 

 from the second sediment, and so on. 

 The separation, however, is far from 

 complete ; the first sediment still con- 

 tains particles which properly belong to 

 the second; the latter contains some 

 particles which properly belong to the 

 first and some which belong to the 

 third. To adjust these irregularities a 

 second series of operations must be 

 performed. More water is added to the 

 first sediment, stirred, allowed to settle 

 for the same time as before, then 

 decanted off and added to the second 

 sediment. The second sediment is 

 stirred with the water decanted from 

 the first ; what is deposited after stand- 

 ing for a short time is returned to the 

 first sediment and what is not deposited FIG. 14. 



