Gilcreas (1935) describes a method for the approximate colorimetric determination of dissolved oxygen with 2-4-diaminophenol dihydrochloride, using a concentrated solution of this substance and a mixture of cobalt chloride and potassium dichro-mate solutions for colour comparison. The colour formed is described as a combination of red and yellow, which varies with the concentration of oxygen, but is not directly proportional to the oxygen content. It is intended for field work and not for accurate determinations.

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