... soluble in water, melts at 64 C. Fertilizer Ferrous Sulfate Heptahydrate Ferrous Sulfate Heptahydrate, also called copperas, is a bluegreen crystals; ... manufacture of ink, in water purification as a substitute for aluminum sulfate, as a fertilizer, and as a feed additive. It ... manufacture of ink, in water purification as a substitute for aluminum sulfate, as a fertilizer, and as a feed additive. It ...