The author determined the silicate content of the thermal water of Hisui-no-Yu, Misasa, Tottori Prefecture, Japan, at varying times after flowing out, and obtained the following results: 1) The change in the silicate content after flowing out is at first remarkable. 2) The velocity of the changes in the silicate content has a tendency to be faster in the sample that is kept in the vessel with a wide water surface than in the one that has a smaller surface.

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