Assay
Accurately weigh 0.25 g of sample into a stoppered flask. Add a hot solution of 1.25 g of copper sulphate pentahydrate in 20 ml of water and shake for ten minutes. Filter rapidly and wash the filter with water; acidify the mixed filtrate and washings with sulphuric acid, and titrate with N/10 potassium permanganate. Each ml of N/10 potassium permanganate is equivalent to 0.005585 g of iron.