MINERAL CONSTITUENTS 



127 



(e) Centrifugal Method. 4 The centrifugal method lias been 

 perfected by the Bureau of Soils and is now used more extensively 

 in this country than any other. The machine for this purpose is 

 shown in figure GO. It consists of a centrifuge suspended from the 



FIG. 09. Machine for centrifugal analysis of soils. Bureau of Soils, U. S. D. A. 



Fio. 70. Voder's Centrifugal Elutriator. 



shaft of an electric motor. The sample to he analy/ed is detloceu- 

 lated by shaking with water containing a few drops of ammonia. 

 This requires from two to thirty hours. The clay and silt are sepa- 

 rated from the sands by subsidence and dccantation or bv sieves. 



