According to the recent several publications, there seem to exist three principal clay minerals ; namely, montmorillonite, kaolinite and illite.Of the former two, many investigations, for various objects, have been made so often that they have shown already physical and chemical natures of those clay minerals to a certain admirable extent.But, of the latter one, there still remain many problems in relation to ascertaining its composition and also nature. Author, cn this occasion, made an experiment for the object of determining the amount of illite in the clays from arable soils, in the following way with a hope, if possible, of giving a certain idea to those who are willing to determine the amount of this clay mineral-illite. After the rational method the clay fractions (<0.002mm) were got from the soils (see Table 2).Of these clay fractions (free from humus) K_2O was determined by the fusion method by the use of Calcium carbonate and Ammonium chloride as in the Table 3.The amount of illite was counted by the authors from the above amount of K_2O after the assumption that illite has its K_2O to such an amount as about 6% in general (see Table 1). After the results of analyses (refer to Table 3) the following conclusions were got. 1)Illite seems to be contained more in the clays from soils of ground water soil type (refer to soils, 55.56.57.5&6) than in those of forest type & etc (refer to soils, 31.32.33.34.35.36&37). 2) In the clays of the soils from granite as well as andesite, illite was determined more than those from other origins ; and among these two kinds of rocks, Illite was observed to be much in the former. 3)Of the clays of ground water soil types, the clays of River Sagami Region (soils.55.56.57) have more Illite than those of River Sakao Region (soils.5.6) The above inclination is probably due to the difference of the rocks which cover the area occupied by the rivers.The area, occupied by River Sagami and its tributaries, is understood to be of more granitic than that of River Sakao, (refer to 2)).
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