イ草染土に関する研究 (第3報)染土の化学的性質,とくに明石染土の組成特徴について

The sendos having been put to practical use in Okayama, Hiroshima and Fukuoka may be divided by their colors into two groups, the greyish and brownish ones. Akashi and Awaji sendos belong to the former and Hiroshima, Kyushu and most of Okayama sendos to the latter. The chemical composition of sendo samples, with special reference to its effects on physical behavior of sendo in mud water and on color of dried rush were studied by the authors. The results obtained are to be summarized as follows: 1)The sendos in water suspension showed reactions within the range pH 5.2 to 9.3. Hiroshima sendos are weak acid, while the others are neutral or slightly alkaline. In most of sendos, the content of soluble salts is very low, while a considerable amount of salts, mostly of calcium sulfate, is contained in Kyu-Akashi sendo. 2)The content of humus and Fe++ in the greyish group is comparatively high, while that in the brownish group is low. The content of HCL-soluble Fe2O3 in the brownish group increases in the following order: coarse sendo＜clayey sendo＜Kyushu sendo, and that in the greyish group is nearly the same as Kyushu sendo. In the greyish group, the amount of MgO is larger than CaO, while the former is less than the latter in the brownish group. 3)It is found that the base exchange capacity of sendo is closely related to the content of clay, namely, that of clayey sendos are higher than that of coarse sendos. In general, the content of exchangeable cation decreases according to the following order excepting a few samples: Ca＞Mg＞Na＞K. 4)A fairly large amount of oxidizable sulfur is found in Kyu-Akashi sendo and the pH value of soil become extremely acid after oxidation with H2O2, while the content of oxidizable sulfur in Shin-Akashi sendo is much less than in the former. On the contrary, oxidizable sulfur is not found at all in the brownish group. 5)It has been experienced that readiness of changing color is a single, serious drawback of Kyu-Akashi sendo. It is shown that the discoloration is due mainly to the oxidation of Fe++, especially of iron sulfide in Kyu-Akashi sendo. It is concluded that sufficient drying of sendo is an effective measure for preserving the characteristic bluish grey color of Kyu-Akashi sendo, and it is necessary to keep the original color.