PHYSICAL PROPERTIES OF SOILS 13 



Millimeters. Inches. 



Medium sand 0.5 to 0.25 0.02 to 0.01 



Fine sand 0.25 too. 1 0.01 to 0.004 



Verv fine sand o. 1 to 0.05 0.004 to 0.002 



Silt 0.05 to 0.01 0.002 to 0.0004 



Fine silt o.or to 0.005 0.0004 to 0.0002 



Clay 0.005 and less 0.0002 and less 



Soils are mechanical mixtures of various sized par- 

 ticles. In most soils there is a predominance of one 

 grade, as clay in heavy clay soils, and medium sand 

 in sandy soils. No soil, however, is composed entirely 

 of one grade. The clay particles are exceedingly 

 small ; it would take 5000 of the larger ones, if laid 

 in a line with the edges touching, to measure an inch, • 

 while it would take but 50 of the larger medium sand 

 particles to measure an inch. 



5. Clay. — The term clay used physically denotes 

 those soil particles less than 0.005 mm - (0.0002 inch) 

 in diameter, without regard to chemical composition. 

 As used in a physical sense clay may be silica, feld- 

 spar, limestone, mica, kaolin, or any other rock or 

 mineral which has been pulverized until the particles 

 are less than 0.005 mm. in diameter. Chemically, 

 however, the term clay is restricted to one material, 

 as will be explained in another part of the work. 

 The physical properties of clay are well known. It 

 has the power of absorbing a large amount of water, 

 and will remain suspended in water for a long time. 

 The roiled appearance of many streams and lakes is 



