Iron II sulfate heptahydrate (FeSO4 7H2O). Molar mass 278.02 g/mol. Also known as iron II sulphate, ferrous sulfate, green vitriol, iron vitriol, copperas, melanterite and szomolnokite This salt has uses in horticulture, as a soil improver, and is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. It is used to treat iron deficiency. It also has a range of other industrial applications.