The relation between the vapour pressure and water content of soils

Abstract

Much of the modern work on the physical properties of soil has been interpreted on a colloidal basis and more recently this hypothesis has been extended by the thermodynamical studies of Wilsdon and also by the investigations of two of us on an indirect measurement of the vapour pressure of capillary systems. There is evidence that the colloidal portion of the soil can be regarded as possessing a reticulate structure, possibly analogous to that shown by Zsigmondy to exist in silica gels. The pore space in soils is therefore an assemblage of voids and irregular capillaries ranging from ultramicroscopic dimensions in the colloidal portions to the macroscopic interstices between adjacent compound particles and the larger mineral fragments. Whereas in studies of evaporation and movement of water the total intersticial space is operative, the vapour pressure of soils at different moisture contents is very largely controlled by the minute pores associated with the colloidal portion and the larger voids have comparatively little influence. Vapour pressure measurements therefore afford a promising line of attack on the physical relations between the colloidal soil material and water, especially when the measurements are made on soils subjected to a variety of preliminary treatments, known to have a considerable effect on other physical properties. The effect of successive wetting and drying, heating and addition of salts are of especial interest in this connection.

Interrelationships Between Flux, Membrane Properties, and Soil Water Transport in a Subsurface Pervaporation Irrigation System

“…Only in extremely dry soil conditions (desert/arid) will the bulk connectivity of water in the liquid phase break down, which would promote water transport in the vapor phase across the soil even if to a lesser extent when compared with water transport in the liquid phase (Churaev et al, 2000). Water vapor flows in soil due to the soil water content variations are miniscule because the vapor pressure in most soils approaches the saturated vapor pressure at soil water contents greater than the residual water content of the soil (Puri et al, 1925). For example, in sand, the equilibrium humidity is greater than 99.5% even at a suction pressure of 600 MPa (Hillel, 1998).…”

A soil‐water retention function that includes the hyper‐dry region through the BET adsorption isotherm

“…Whereas in the wet range the SWR curve is the expression of capillary forces, in the dry range, adsorption dominates the relationship between water content and the forces that hold this water in its condensed state. Water adsorption onto soils has been studied by different authors [ Puri et al , 1925; Orchiston , 1952; Chiou and Shoup , 1985; Valsaraj and Thibodeaux , 1988; Rhue et al , 1989; Pennell et al , 1992; Amali et al , 1994; Ruiz et al , 1998; Chen et al , 2000a; de Seze et al , 2000] and it has been shown that it can be described by the conventional BET isotherm [ Valsaraj , 1995]. This adsorption isotherm is written here as where is a pseudo‐volumetric water content at monolayer capacity.…”

Laboratory Studies on the Moisture Relations of Limonius (Coleoptera: Elaterida)

“…The absorption isotherms of the various types of solids given by Puri, Crowther, and Keen ( 1925) are instruc-tive from several point of view. These curves show the typical S-shape displayed by many hygroscopic materials, they indicate that if a soil is dried larger amounts of water have to be removed to shift the equilibrium humidity, for instance from 99 to 90 per cent, whereas with further water loss small differences in moisture content cause a rapid drop in humidity.…”