Some moisture relations of colloids. II.—Further observations on the evaporation of water from clay and wool

Abstract

In two earlier paper, the results of a study of the rate of evaporation of water from soil, sand and a wool fabric were described and discussed. It was shown that, when the rate of evaporation is plotted against the water content (on a dry weight basis), the curve obtained is made up of three straight lines cutting one another sharply, so that there are points on the curve at which there are sudden changes of direction. The factors determining the shape of the curve were discussed and it was suggested that variable temperature of the drying mass, and two others, due to capillarity, viz., the diminishing rate of movement of water from the interior of the material to the surface as the larger capillary spaces become empty, or as the water wedges between the soil grains get progressively smaller. It was shown that, with the materials mentioned above, the first sloping portion of the rate curves could be accurately expressed by the equation – dw / dt – A = kw in which A is the intercept cut off from the vertical axis when the curve is extrapolated to W = 0. With wool, the curve, on extrapolation, passed through the origin, in which case A = 0.