Remarks and observations on imbibitional soil moisture

Abstract

It has been shown in earlier papers that the water present in soils is held in two ways: as capillary or interstitial water present as water wedges between the soil grains and as imbibitional or “gel” water which is associated in some way other than interstitially with the clay particles and with the colloidal coating of the soil grains. Imbibitional water is the cause of the swelling in water of soil and other colloidal (gel) systems such as cotton, wool, gelatin.The nature of the imbibitional process is discussed and it is suggested that with clay, wool and soil imbibition may be due to the attainment of a Donnan equilibrium as is the case with gelatin. Experiments are quoted and discussed in support of this suggestion; and in particular it is pointed out that such swollen colloids appear to behave as perfectly elastic solids when under compression. This is not the case with sand and water nor with soil, wool or cotton in xylol, i.e. when no swelling occurs.Imbibition may be a factor in the movement of soil water, in addition to capillarity, and it is shown that such a factor is quite consistent with the general mathematical treatment of the movement of soil water as developed by Gardner and others.[It is realised that the point of view outlined above rests, as far as soil is concerned, on a very slender experimental basis, but it appears to be of sufficient interest to merit further investigation. The writer, however, has neither facilities nor opportunity for developing the matter further and this paper is published in its present form in the hope that it may prove of some interest to other workers more directly connected with soil research.]