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SOIL STRUCTURE 193 



127. Addition of lime. — One of the important effects 

 of lime is in its flocculating action. This agglomeration, 

 as already explained under colloids, is the drawing to- 

 gether of the finer particles of a soil mass into granules. 

 When caustic lime is mixed with water containing fine 

 particles in suspension, there is almost immediately a 

 change in the arrangement of the particles. They appear 

 first to draw together in light, fluffy groups, or floc- 

 cules, which then rapidly settle to the bottom so that 

 the supernatant liquid is left clear or nearly so. This 

 phenomenon is termed flocculation, because of the 

 groups of particles. It is not an action limited to 

 caustic lime alone, however, but because of the useful- 

 ness of this compound in other ways, and because of 

 its very strong action, it is ordinarily used on soils. 

 This flocculating tendency when caustic lime is added 

 goes on in the soil as well as with suspensions, although 

 more slowly. In general the lime serves to satisfy the 

 adsorptive capacity of the colloidal material, and by 

 throwing down these colloids develops lines of weakness. 

 The cohesive power of the soil is thus localized and 

 granulation must necessarily occur. 



The various forms of lime differ in their granulating 

 capacities, calcium oxide and calcium hydrate being very 

 active while calcium carbonate is relatively inactive in 

 this regard. For this reason, if flocculation effects are 

 desired, the oxide or hydrate combinations are added. 

 The relative influences of lime on puddled clay as measured 

 by penetration is shown in the following table ; * the soil 

 was dried once and the untreated soil was used as 100 

 per cent : — 



• » Fippin, E. O. Some Causes of Soil Granulation. Trans, 

 Amer. Soc. Agron., Vol. 2, pp. 106-121. 1910. 

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