Abstract
There have been reported many classical chemical investigations on colloidal clay materials in the volcanic ash soils in Japan. It has been proved that the main constituent of clay fraction was allophane. In the present study, the inorganic colloidal fractions (<2μ) were separated from soils, taken from each horizon of soil profile at Taisho in Tokachi. Chemical and physical studies were carried out on these samples.Generaly, Al_20_3 was proved to be much as one of the principal materials throughout all samples, so the Si0_2/Al_20_3 ratio by the total analysis was small (1.6〜4.0). Moreover, the Si0_2/Al_20_3 ratios by TAMM's Reagent was low (0.5〜0.7) in surface soil and high (1.9) in lower soils. Total Al_20_3 and also the Al_20_3 insoluble in TAMM's Reagent were much in lower soils. The latter was estimated as the combined Al_20_3. So the degree of the presence of free or soluble Al_20_3 was greater in upper soils and smaller in lower soils. From the Differential Thermal Analysis curves of soil colloids from lower parts of profile, the presence of gibbsite was observed. Electron microscopic photographs of surface samples showed many needle crystalls of hydrated halloysite. The lines of X-ray diagram showed the presence of hydrated halloysite, gibbsite, allophane, goethite and boehmite. It was conclude that the principal constituent colloidal materials of these volcanic ash soils were hydrated sesquioxide, 1 : 1 latice clay material and allophane.
