THE SOIL PARTICLE 



67 



in texture may be made on a small scale by mixing two soils, 

 but this is not practicable in the field. 



38. Separation and classification of soil panicles.— In 

 order that the particles of soil, varying so tremendously in 

 size as they do, may be studied successfully, they must be 

 separated into groups according to their diameters. The va- 

 rious groups are spoken of as soil separates Such a grouping 

 is of course arbitrary, and must meet certain theoretical as 

 well as practical requirements. It must be simple, short, and 

 capable of expressing in a practical way the physical char- 

 acter of the soil- Moreover, it must lend itself to the actual 

 separation and percentage evaluation of each group. This 

 analytical procedure is called a mechanical analysis. 



With the large number of different methods of mechanical 

 soil analyses, there has arisen considerable variation in tex- 

 tural groupings expressed in diameter of particles. This 

 would naturally occur because of the differences in degree of 

 refinement, which the various methods of separation allow, 

 and also because of the uses which the investigators wished to 



Table XI 



THE NAMES AND BANGES IN SIZE OF SOIL PAETICLES AS ESTAB- 

 LISHED BY THE BUREAU OP SOILS CLASSIFICATION^ 



Separate 



Size in 

 Millimeters 



Fine Sandy 

 Loam 



Ct,at 



1. Fine Gravel. . 



2. Coarse Sand. 



3. Medium Sand. . 



4. Fine Sand 



5. Very Fine Sand 



6. Silt 



7. Clay 



m.m. 

 2 1 

 1 .5 



.5 .25 

 .25 .10 

 .10 .05 

 .05 .005 

 .005 and below 



% 

 1 



2 

 3 



22 

 35 

 27 

 10 



1 



2 

 2 

 6 



7 

 39 

 43 







* Briggs, L. J., et at, The Centrifugal Method of Soil Analysis; U. S. 

 Dept. Agr,, Bur. Soils, Bui. 24, 1904. 



