CHAPTER II 



THE MECHANICAL ANALYSIS OF SOILS 



Nature of Soil Constituents : Sand, Clay, Chalk, and Humus 

 Methods of Sampling Soils Methods for the Mechanical 

 Analysis of a Soil Interpretation of Results. 



It has already been indicated that as soils are derived 

 from the waste of rocks, they consist of a mass of 

 particles of various minerals and of all sizes, together 

 with a certain amount of humus of vegetable origin, 

 and that they may be roughly classified according to 

 the predominance of the coarse-grained particles called 

 "sand," or the very fine material known as "clay." 



The mechanical analysis of a soil consists in pushing 

 this rough " eye and hand " classification a stage further 

 into the region of exact measurement, and in deter- 

 mining the minute physical structure of the soil by 

 estimating the proportions in which particles of various 

 sizes are mixed together in the soil. Upon the physical 

 structure of the soil so determined, or as we shall 

 practically term it, the texture, depend some of its 

 most important features, particularly its behaviour with 

 regard to the supply of water to crops and its amena- 

 bility to cultivation. 



In the first place, it will be necessary to discuss a 

 little more thoroughly the nature of the four substances 

 to which the texture of the soil has been referred the 

 sand, clay, chalk, and humus of which the first two 



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