DETERMINATION OF ALLOPHANE AND AMORPHOUS INORGANIC MATTER IN CLAY FRACTION OF SOILS : II. Soil Clay Fractions

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The quantitative determination of allophane and amorphous inorganic matter in the clay fractions of volcanic ash soils was examined by means of five methods. An outline of the results is as follows : An alternate dissolution with 8 N HCl for 30 min and warmed 0.5 N NaOH for 5 min according to the method of SEGALEN (8) was suited for the purpose. The coexistence of gibbsite did not strongly influence the determination of allophane and amorphous matter, but goethite and hematite in soils behaved just as amorphous matter in this method. A method based on the weight loss with heating at 200℃, which is newly proposed in this study, was statistically analyzed in the clay fractions of soils and the allophane-halloysite mixture samples, compared with the result of the method by means of the alternate dissolution with HCl and NaOH. It was clarified that the method based on the weight loss with heating at 200℃ could be applied to a determination of allophane and amorphous matter, i.e., a high linearcorrelation was established between the weight loss with heating and the contents of allophane and amorphous matter obtained from the alternate dissolution with HCl and NaOH. Three other methods; a dissolution with boiled 0.5 N NaOH for 2.5 min, an extraction with acid ammonium-oxalate solution, and cation-exchange capacity delta value of allophane. These were not so good as the two first mentioned above.
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