The method of water sample preservation used by Gad-Andresen is not suitable for nitrite or nitrate estimation. 2. Using Buch's method it has been shown that the variation in nitrite during the summer is from less than 0-001 mg. to about 0-01 mg. per litre and that the deeper water layers have more than the surface layers.
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A. P. Orr (1926) studied this question.
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