126 



SOIL PHYSICS AND MANAGEMENT 



(d) The Churn Elutriator Method of Hilgard. 3 This con- 

 sists of an apparatus as shown in figure 68. The soil in suspension is 

 placed in the hase of a cylindrical tuhe which contains a rapidly re- 

 volving stirrer. Water is forced into the base of the tuhe in 

 amounts sufficient to create an upward current just rapid enough to 

 carry out the finest particles. When these are removed the rate of 



FIG. 66. 



FIG. 67. 



FIG. 68. 



Fio. 66. Nobel's Elutriatpr. The suspended soil is placed in C and allowed to flow 



through the conical glasses 1, 2, 3, and 4, giving five different grades. 



Fio. 67. Schone's Elutriator. The water enters at G and the grades are collected at A". 

 Fio. 68. Hilgard's Churn Elutriator. 



the current is increased and another grade is carried out. A screen 

 between the stirrer and the separating chamber prevents the agita- 

 tion of water in this chamber. In this way all separations except the 

 finest particles are made. Particles of clay less than 0.0023 mm. 

 must be separated by subsidence. This is done by allowing the 

 larger particles to subside for 24 hours and then decanting the clay. 



