We compared two analytical values for sulfur species in water samples of Yugama, a crater lake of the Kusatsu-Shirane volcano, collected between +300 and +33/. One analytical method was ion chromatograph, by which concentrations of the sulfate ion (SO. , ΐ ) were determined. The other was gravimetric analysis preceded by oxidation of the samples, by which total concentrations of sulfur species (T-SO. , ΐ ) were determined. The concentration di#erences between the two were in good accordance

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... the total concentration of poly-thionates reported by Takano and Watanuki (+33*) through the whole period studied. This suggested that the concentration di#erence between SO. ,ΐ and T-SO. , ΐ can be used to estimate the concentrations of dissolved poly-thionates. In this way we can grasp very easily the secular change of the total concentration of poly-thionates without any special analytical conditions and/or instruments.