The degree of soil water content is defined by the fraction, by mass or weight, of pore water relative to the total dry soil solid particles, usually expressed as a percentage. In practice, soil water content is measured by heating a wet soil sample at 105 – 110oC to a constant mass. The weight loss by heating is assumed to be the weight of water, and the residual weight is the weight of dry soil solids.
Syn., moisture content
Cf., water saturation, degree of;
H2O molecules attracted to internal or external surfaces of a phyllosilicate, or other material, and adhered to these surfaces in thicknesses of one or more molecules. The term “water” (rather than “H2O”) is not precisely used here because “water” is a (liquid) phase. Elevated temperatures, typically 110oC for 12 hours, can desorb the adhered H2O. However, for phyllosilicates, a temperature of 110oC may not liberate all the adsorbed water molecules present, and temperatures of as high as 300oC (in special cases, even higher) may be needed for some vermiculites and smectites.
Syn. absorbed water
Cf., water, structural
The degree of water saturation is the ratio of pore water volume to the total void volume, usually expressed as a percentage. In soil science, values may range from 0 % for a dry soil to 100% for a soil with its void fully occupied by water. Water saturation of a soil refers to the latter.
See also water content
H2O adsorbed by soil that is equilibrated with the atmosphere to which it is exposed at a given temperature and relative humidity, usually 25oC at 98 % relative humidity.
Water (or more precisely, H2O molecules) adsorbed between the (1:1 or 2:1) layers of a phyllosilicate. The use of “water” is a misnomer because the interlayer H2O is not equivalent to bulk water (i.e., a phase, a liquid), which involves randomly oriented H2O. Instead, the interlayer H2O is affected structurally by the adjacent 1:1 or 2:1 layers and by the cations present in the interlayer.
Cf., water, adsorbed
Water (more precisely, H2O or OH molecules) that is directly bound to cations at crystallographic sites in a crystal structure. This H2O or OH is capable of being driven off at elevated temperature, generally by heating to 1000oC. For phyllosilicates, structurally bound “water” is in the form of hydroxyl (OH) groups coordinated to cations, and the high temperature is required to promote dehydroxylation. Fluorine and certain other anions may be driven off at these temperatures also. However, hydrates, such as gypsum (CaSO4 .2H2O), have structural water coordinated to cations as H2O (e.g., water of hydration) that is liberated by heating to relatively low values, 65 – 95oC.
Syn. combined water, molecular water, structurally bound water, water of crystallization, water of hydration. “Lattice water” is also used, but is not recommended because a “lattice” refers to a collection of identipoints, see “lattice”.
Cf., water, adsorbed
Water molecules adsorbed within the cavities/tunnels of the zeolite framework structure, commonly removed by heating at 350 to 400oC for about 12 hours. “Zeolitic water” was a term used by early workers to describe interlayer water of phyllosilicates. However, the analogy is imperfect (and not in use anymore) because the number of interlayer water molecules affects the layer-to-layer spacing of a phyllosilicate, whereas the shape and size of zeolitic tunnels are not significantly affected by the number of H2O molecules present.
Cf., water, structural; water, adsorbed
The physical (mechanical) and/or chemical breakdown of rock, sediment, and soil in place under the influence of the hydrosphere and/or atmosphere. Biota may influence or control physical or chemical weathering.
See physical weathering, chemical weathering.
Cf., erosion
See hydrotalcite group.
An industrial or commercial term, originally used to designate the high quality sodium bentonite from Wyoming, USA. This material exhibits characteristics of high water adsorption, dilation, viscosification and dry sand binding strength. Usage of the term has since broadened to include any bentonite having performance characteristics equal to that of high quality sodium bentonite from Wyoming. Whereas the term “Western Bentonite”, and its synonyms, continue to have meaning in the industrial and commercial realm, they are scientifically obsolete and should not be used in that context.
Syn: Wyoming Bentonite, Wyoming Sodium Bentonite, Wyoming-Type Bentonite