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The author obtained three kinds of humic acid from the soil of suburbs in the Wonju city, sediments of Wonju stream and Maeji reservoir in 29 April 1986. The yield of each humic acid was 7.23 g, 3.35 g and 4.61 g per sample 200 g. In the physicochemical characters, the COD varied from 65.9 ppm to 54.9 ppm and BOD showed 6.7～15.9 ppm, but the standard humic acid was COD 58.9 ppm and BOD 6.5 ppm in 0.01 % solution. Doses of the humic acids for 20% methemoglobin formation are as follows; 0.303 mg/m in St. A humic acid, 0.602 mg/m in St. B humic acid, 0.84 mg/m in St. C humic acid and 0.105 mg/m in standard humic acid.
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