[21] Williams (Forsch. Agr. Phys. Vol. 18, p. 225 ff.) claims that the diameter of the minutest clay particles is one-thousandth of a millimeter, their form being that of scales showing continual (Brownian) motion in water. He maintains that the plasticity of clay is due to this minute size, and this view has gained wide acceptance in late works on the subject. But this assumption cannot be maintained in the face of the fact that nothing like the adhesive plasticity of clay can be attained even by the finest powders of other substances, least of all by those having the closest mineralogical resemblance to kaolinite, such as graphite and talc. Above all, the most persistent trituration with water utterly falls to restore plasticity to clay once baked so as to expel its water of hydration, although the fineness of the particles is thereby not only not diminished, but actually increased, by contraction in heating. No powders however fine can replace the functions of clay in soils, viz. the maintenance of floccules, and tilth dependent thereupon; and they distinctly impair the plasticity of clay. The fine “slickens” of quartz mills merely render soils containing them more close and impervious, and more difficult to flocculate. Even gelatinous masses like hydrated ferric and aluminic oxids fail to replace clay in its adhesive functions.
[22] Rep. Conn. Agr. Expt. Stn., 1886, 1887.
[23] And soda.
[24] This fact emphasizes the impossibility of explaining the plasticity and adhesiveness of clay simply as a function of fineness of grain.
[25] The figure given of this elutriator in Bulletin No. 24, on physical soil analysis, published by the U. S. Bureau of Soils, shows as the receiver a bottle entirely too low to insure the complete retention of the sediments by settling. The receiving bottle should not be less than twelve inches high and five inches wide.
[26] Convenient stands for this purpose, used by the writer since 1872, may be cut from L-shaped moldings of wood, such as can be readily ordered from any planing mill. The vials can be cemented, wired or tied.
[27] Bauxite is not only the most abundant of the three hydrates of alumina known to occur naturally, but also stands nearly midway between the two others in its water content, viz., a little over 25%; that of diaspore being nearly 15%, gibbsite about 35%.
[28] The Mechanical Composition of Wind Deposits, Bull. No. 1, Augustana Library Publications; 1898.
[29] This remarkable soil seems to have been derived from the finest “slickens” of the hydraulic gold mines.
[30] King, Physics of Agriculture, p. 116, ff.