Thermodynamics of soil moisture

Abstract does not appear. First page follows. Introduction The worker who attempts to study the basic principles of thermodynamics with reference to soil moisture has considerable difficulty because both the nomenclature and the method of treatment in existing literature vary greatly. Writers on thermodynamics have usually had in mind specific purposes quite foreign to soil-moisture studies; their conclusions and equations, being adapted to some other particular field, are not easily applied to soil moisture. This paper aims to eliminate at least part of the difficulty and also to make certain helpful original applications. It applies the well-grounded principles of thermodynamics to a study of the soil-moisture system. The first part includes, for the convenience of the reader, some material that can be found scattered in numerous published reports and books. Such material, it is hoped, is here presented in such a way as to be more readily available. Probably the most useful thermodynamic function, as far as the student of soil moisture is concerned, is free energy. The following treatment has been built, accordingly, around that function. The chief purpose of this paper, aside from the presentation of the basic thermodynamic principles, is to develop quantitative expressions for the dependence of the free energy of soil moisture on such factors as the adsorptive force field that surrounds a soil particle, the hydrostatic pressure on the soil moisture, the dissolved material present, and the temperature. In mathematical treatments of physical systems, the inexperienced student cannot always distinguish clearly between the parts that result from pure mathematical manipulation and the parts that can be deduced, either directly or indirectly, from experimental measurements.