METHOD OF ASSAY Weigh accurately about 0.2 g of the sample, add 10 ml of 5 N hydrochloric
acid, and heat cautiously to boiling in a 200-ml conical flask until the
sample has dissolved. Allow to cool, add 6 to 7 drops of 30% hydrogen
peroxide solution and again heat cautiously to boiling until all the excess
hydrogen peroxide has decomposed (about 2-3 min). Allow to cool, add
30 ml of water and about 2 g of potassium iodide and allow to stand for 5
min. Add 30 ml of water and titrate with 0.1 N sodium thiosulfate adding
starch TS as the indicator towards the end of the titration. Each ml of 0.1N
sodium thiosulfate is equivalent to 5.585 mg of Fe (III).