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Not less than 95 per cent of the iron content when determined by the following method.

Accurately weigh 0.1 g of sample into a 750 ml conical flask. Add 450 ml 0.2 per cent weight in weight hydrocholoric acid previously warmed to 37°C. Stir continuously for three hours, maintaining the temperature at 37°C. Cool to room temperature and dilute to 500 ml with distilled water. Filter; determine the iron content of the filtrate by a suitable method. Calculate the total iron in solution as a percentage of the metallic iron content of the sample taken.