SOME PHYSICAL PROPERTIES OF THE SOIL 119 



in order that the weight in grams of a single soil grain 

 may be obtained. A calculation by this method of the 

 number of particles in a sandy loam is given below : 



A very great error is introduced by this method, es- 

 pecially in assuming that the average size of particles 

 for the clay separate is .0025 millimeter. As the clay 

 particles may become molecular complexes and conse- 

 quently are very, very small, it stands to reason that 

 such an assumption is far from correct. Nevertheless, 

 it gives a very good idea as to the immense number of 

 grains that we have to deal with, even in the coarsest of 

 soils. A few figures as to the approximate number of 

 particles in various average soil classes of the United 

 States, 1 as reported by the Bureau of Soils, are given 

 below : 



1 For mechanical analysis of the classes, see Chapter VI, p. 104. 



