MOVEMENT AND EQUILIBRIUM OF WATER IN HETEROGENEOUS SYSTEMS WITH SPECIAL REFERENCE TO SOILS

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Abstract
The total potential concept, which was developed in an earlier paper (7), had been applied to the movement and equilibrium of water in heterogeneous systems such as soil. A general equation was developed, showing the change in the total potential of a constituent during any process to be due to changes in the positional potential energy of the constituent and to changes in concentration, also, to changes in pressure and in temperature occurring in that process. The presence of gravitational, electrostatic, and Van der Waals force fields in the system was considered to be responsible for the positional potential energy of the water in the soil. The hypothesis was made that the rate of movement of the water in the soil is directly proportional to the driving force, which was regarded as equal to the negative gradient of the total potential of the water. On the basis of this hypothesis and the general equation for the total potential, an equation for the velocity of water in a heterogeneous system was developed. As a special case, the latter equation yielded Darcy''s law. Integration of the general equation produced a second general equation expressing the equilibrium pressure difference between any 2 phases as a function of the concentration ratio and positional potential energy difference for any constituent distributed between the two phases. The capillary rise and Van''t Hoff''s law emerged as special cases. The general equation was applied to the water in the interfacial region of a clay particle, with the result that the hydrostatic pressure was shown to be greater in the micellar solution than in the intermicellar solution, the magnitude of the difference depending on the salt concentration in the intermicellar solution, the electrostatic potential in the micellar solution, and the distance from the particle. Simplification of the equation resulted in an equation for equilibrium osmotic pressure differences originally due to Langmuir.

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