Movement and Equilibrium of Water in Heterogeneous Systems With Special Reference to Soils

A Thermodynamic Study of Water in Heterogeneous Systems Was Conducted to Obtain an Equation to Present a Unified Picture of the Thermodynamics of Soil Moisture. A Thermodynamic Function, the Total Potential, Which Was Shown to Be Equivalent to the Partial Molar Free Energy and Which Was Applied to the Movement and Equilibriums of Constituents in Heterogeneous Systems Was Used. 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, Pressure and 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 THW Water. An Equation for the Velocity of Water in a Heterogeneous System Was Developed on the Basis of This Hypothesis and the General Equation for the Total Potential. This Equation Yielded Darcy's Law. Integration of the General Equation Produced a Second General Equation Expressing the Equilibrium Pressure Difference Between Any Two 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 the 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 Resulted in an Equation for Equilibrium Osmotic Pressure Differences Originally Due to Langmuir.