KINDS OF SOILS. 147 



mechanical ingredients, or from other liighly obvious 

 qualities. 



The distinctions thus established, tliough very vague 

 scientifically considered, are extremely useful for practical 

 purposes, and the grounds upon which they rest deserve 

 to be carefully reviewed for tlie purpose of api)reciating 

 their deficiencies and giving greater jirecision to the terms 

 employed to define them. 



The farmer, speaking of soils, defines them as gravelly^ 

 sandy^ doyey^ loamy, calcareous, peaty, oehreous, etc. 



Mechanical Analysis of the Soil. — Befoie noticing 

 these various distinctions in detail, we may appro] >riately 

 Btudy the methods which are employed fi)r separating the 

 mechanical ingredients of a soil. It is evident that the 

 epithet sandy, for example, should not be applied to a soil 

 unless sand be the predominating ingredient ; and in or- 

 der to apply the term with strict correctness, as well as to 

 know how a soil is constituted as regards its mechanical 

 elements, it is necessary to isolate its parts and determine 

 their relative quantity. 



Boulders, stones, and pebbles, are of little present or 

 immediate value in the soil by way of feeding the plant. 

 This function is performed by the finvr and especially by 

 the finest particles. JMechanical analysis serves therefore 

 to compare together difierent soils, and to give useful in- 

 dications of fertility. Simple inspection aided by the feel 

 enables one to judge, perhaps, with sufficient accuracy for 

 all ordinary jjractical purposes ; but in any serious attempt 

 to define a soil precisely, for the purposes of science, its 

 mechanical analysis must be made with care. 



Mechanical separation is effected by sifting and wash- 

 ing. Sifting serves only to remove the stones and coarse 

 sand. By placing the soil i:i a glass cylinder, adding wa- 

 ter, and vigorously agitating for a few moments, then 

 letting the whole come to rest, there remains suspended 

 in the water a greater or less quantity of matter iu a stJ»*<i 



