SOMJE PHYSICAL PROPJERTmS OF TBB 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 : — 









1 



fe ■< fe fe 



APPKOXIM.1TE 



Sepieates 



Limits 



Number of Parti- 

 cles TO THE Gram 

 OP Each Separate 



o ^ S ^ o 



S ?J ^ "< 



Number op 



Particles in one 



Gram op Sandy 



Loam 



Fine grav- 











el . . 



2-1 mm. 



209 



1 



2 



Coarse 











sand . 



1-.5 mm. 



1,670 



4 



67 



Medium 











sand . 



.5-.25 mm. 



13,410 



25 



3,352 



Fine 











sand . 



.25-. 10 mm. 



131,900 



35 



46,165 



Very fine 











sand 



.10-.05 mm. 



1,676,500 



20 



335,300 



Silt . . 



05-.005 mm. 



35,934,000 



10 



3,593,400 



Clay. 



below .005 mm 



45,632,000,000 



5 



2,281,600,000 





2,285,578,286 



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

 pecially in assummg 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,^ as reported by the Bureau of Soils, are given 

 below : — 



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



