34 



SOILS AND FERTILIZERS 



up of particles of various sizes, but the proportion of the 

 large, medium or small particles determines the class to 

 which it belongs. The following table published by Whitney 

 will show what percentages of soil separates are contained 

 in an average sample of each of the soil classes. 



There must be a certain amount of variation in the per- 

 centages of the separates that go to make up a soil class. 

 In order to determine the class to which a soil belongs 

 when its mechanical analysis is known, the diagram in Fig. 

 4 may be used. If, for instance, a soil contains 40 percent 

 of silt and 15 percent of clay, lines are drawn from the point 

 marked 40 percent silt and 15 percent clay, the lines being 

 parallel to the sides of the right angle formed at 0. It will 

 be found that these lines intersect in the space marked 

 loam, which is the class to which the soil belongs. If a soil 

 has 20 percent silt and 10 percent clay, the intersection of the 

 lines drawn from these points falls in the space marked sandy 

 loam, and the soil belongs to that class.. 



