FUNDAMENTALS OF AGRICULTURE. 



Per Cent 



Coarse sand. 



Clay. 



/./<> 



7.7* 



2-1 



1-.5 



.6-.S5 



.25-.1 



J-.05 



".O5-.01 



.01-.005 .006^0001 



Diameter of the grains in mi/timefers. 



MECHANICAL ANALYSIS OF A SANDY SOIL. 



Mechanical Composition and Texture. The me- 

 chanical composition of soils is of great importance 

 because it determines many of their physical properties. 

 The granulation of the soil or clustering due to the 

 aggregation of these soil grains is largely caused by 

 films of water surrounding several grains and holding 

 them together in small aggregates or clusters. These 

 in turn are held together where they come in contact with 

 each other by the same films so that the aggregation of 

 these clusters into lumps is the result of the surface ten- 

 sion of the films of water surrounding the soil grains. 

 Now if we compare equal volumes of coarse and fine 

 soils, we will see at once that there is a much larger 

 area of surface in the fine soil than in the coarse soil. 

 There is, therefore, a much greater tendency of the 

 fine soils to adhere as a result of this surface tension 

 of the soil films. We can understand, therefore, why 

 it is that the clay soils have a much more marked ten- 



