THE SOIL PARTICLE 98 



same width as for tlie finer particles. The graduation of 

 the cylinder and its diameter are the same as described 

 above. 



A 20-gram sample of soil is used with this apparatus, 

 and defiocculation is brought about by means of a stiff 

 brush. The sample is reduced to a paste in a porcelain 

 dish, and then, by alternate working with the brush 

 and decanting, all the particles are thrown into separate 

 suspension. A deflocculating chemical is used in humus 

 soils, in order to hasten the process and counteract the 

 effect of the organic matter. As in the beaker method, 

 the size of the various grades of separation may be varied 

 according to the will of the operator. 



70. Centrifugal soil analysis. — Of the centrifugal 

 methods used in mechanical analysis, that employed by 

 the United States Bureau of Soils ^ is the most successful. 

 A 5-gram sample of well-pulverized soil is put into a 

 shaker bottle of about 250 cubic centimeters capacity 

 (see Fig. 15). This bottle is filled about two-thirds 

 full of water, so that in shaking the disintegrating force 

 of the liquid may be utilized. A few drops of ammonia 

 are added, to dissolve the organic matter and to make 

 defiocculation easier. The sample is then agitated in 

 the bottle imtil disintegration is complete. This period 

 ranges from five to twenty hours, depending on the 

 sample. 



The separation of the silt and the clay from the sands 

 is made in the shaker bottle by simple subsidence, the 

 time for decantation being determined by a microscopic 

 examination of a drop of the suspension. The silt and 



1 Fletcher, C. C, and Bryan, H. Modifications of the 

 Method of Soil Analysis. U. S. D. A., Bur. Soils, Bui- 84* 

 1912. 



