Determination of Free Chlorine by Methyl Orange

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Abstract
This article discusses the methyl orange test as a satisfactory laboratory and field procedure for determining free and combined chlorine in water samples. All reagents used in the test are stable at room temperature and may be prepared from readily available chemicals. The test may theoretically be used to measure chlorine of any concentration; curves have been prepared for concentrations of up to 5.0 mg/l, although precision deteriorates slightly at the higher concentrations. The only serious interference is from manganese and this can be corrected through the use of an arsenite modification.