In three earlier papers the results of a study of the rate of evaporation of water from wool, sand, kaolin, ball clay and various kinds of soil were described and discussed. The method of investigation consisted in exposing moist material over sulphuric acid in a closed vessel at a constant temperature, the apparatus being so constructed that the “drying” material could be weighed at frequent intervals without removing it from the drying vessel or in any way disturbing the drying conditions. In this way the percentage moisture content could be calculated each time the material was weighted, and curves were constructed by plotting on a large scale percentage water contents against time of drying. These experimental time curves were straight lines down to a certain ceritical moisture content which varied with different materials; below this point curvature commenced, slight at first but increasing later and diminishing again until the curve became almost straight at the extreme “dry” end of the curve. At the same time no sharp discontinuity could be detected by visual examination of the graphs. By measuring the tangents at different points along the curve values were obtained for the instantaneous rates of evaporation at different water contents under the particular drying conditions (on a dry weight basis) the rate curves obtained, although of a relatively simple type, showed distinct and well marked discontinuities varying in number from two to four according to type of material dealt with. Each section of the rate curve was expressible by a simple type of equation. The factors determining the shape of the curves were discussed and this discussion was elaborated and extended in two subsequent papers. The experimental side of this work is being rapidly developed and it is hoped that two further communications will be issued shortly that will carry the matter a stage further, while, at the same time, supporting in every way the conclusions already ready. Recently, however, a paper has appeared in this Journal by W. A. Davis and J. V. Eyre entitled “The Discontinuity of the Hydration Process,” in which some of the writer’s main conclusions are controverted. These authors studied the “hydration” and “dehydration” of calcium sulphate and copper sulphate at two different humidities, and also flax fibres (natural, bleached and extracted), flax and ramie yarns and cotton wool, and found that “hydration” “took place in a series of discontinuous steps, the change n rate occurring at frequent intervals. Moreover, action was found to occur along a series of simple curves, generally either parabolic or linear....” and each curve consisted of a considerable number of segments, the discontinuities between which were sharp and visible on even casual visual inspection of small scale curves. All experimental and other details given in the paper relate to the “hydration” process only, and therefore do not necessarily have any bearing on the writer’s work, but, without giving any details, Davis and Eyre state that precisely similar curves were obtained for the rate “dehydration,” or, as the writer prefers to call it, drying of these materials. This is definitely at variance with the writer’s experimental results, and the authors say (p. 537) that “his (
i. e.
, the writer’s) observations did not lead him to notice that the change is discontinuous, but he arrives at the conclusion that there is a change of rate by subjecting his curves to mathematical analysis. In this respect his conclusion is in agreement with ours, and his failure to obtain direct evidence may be attributed to the fact that his observations were not made at sufficiently frequent intervals.”
Design of an Artificial Intelligence of Things Based Indoor Planting Model for Mentha Spicata
