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The oscillation is due to the collision of colloidal

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The oscillation is due to the collision of colloidal particles or molecules with those of theliquid in which they are suspended.57
Fundamentals of Soil ScienceSoil colloidal particles with those of water in which they are suspended are always in aconstant state of motion called Brownian movement. The smaller the particle, the more rapidis its movement.11. Non permeability:Colloids, as opposed to crystalloids, are unable to pass through a semi-permeablemembrane.Even though the colloidal particles are extremely small, they are bigger than molecules ofcrystalloid dissolved in water.The membrane allows the passage of water and of the dissolved substance through its pores,but retains the colloidal particles.Classification of Soil ColloidsSoil colloids can be broadly classified in two types, depending on the nature of the linkages present andthe types of compound formed.These are:i) Inorganic colloidsii) Organic colloids.Both inorganic and organic colloids are intimately mixed with other soil solids. Thus, the bulk of the soilsolids are essentially inert and the majority of the soil's physical and chemical character is a result of thecolloids present.Inorganic soil colloids:Layer aluminosilicates which consist of thin layers of repeated structural units. These are thedominant clay minerals in temperate regions.Amorphous aluminosilicates that form from volcanic ashAl and Fe oxides which may be crystalline or amorphous. These are common in subtropicaland tropical regions.Organic colloids:Include highly decomposed organic matter generally called humus.Organic colloids are more reactive chemically and generally have a greater influence on soilproperties per unit weight than the inorganic colloids.The negative charges of humus are associated with partially dissociated enolic (-OH),carboxyl (-COOH), and phenolic groups; these groups in turn are associated with centralunits of varying size and complexity.The complex humus colloid is composed of C,H and O rather than Al, Si and O like thesilicate clays.Humus is amorphous and its chemical and physical characteristics are not well defined. Theorganic colloidal particles vary in size, but they may be at least as small as the silicate clayparticles.They are not stable as clay and thus more dynamic, being formed and destroyed morerapidly than clay.58
Fundamentals of Soil ScienceLayer Aluminosilicates:The most important silicate clays are known as phyllosilicate (Gr. Phullon, leaf) because oftheir leaf or plate like structure.Two types of structural units are basic in the layer lattice structure of most clay minerals thatare tetrahedral and octahedral unit.Silica tetrahedron:The tetrahedral unit is SiO4in which silicon ion is equidistant from the four oxygen anions(Fig.1). It is called silica tetrahedron because of its four sided configuration.

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