Ferrous Sulfate Heptahydrate, also called copperas, is a blue-green, monoclinic crystals; soluble in water, melts at 64 C. It is commercially generated as a by-product during the manufacture of Titanium Dioxide, or as a by-product of the pickling of steel. It is used as a mordant in dyeing wool, in the manufacture of ink, in water purification as a substitute for aluminum sulfate, as a fertilizer, and as a feed additive. It is used to produce magnetic ferric oxide.