Ferrous sulfate heptahydrate is an inorganic substance with the chemical formula FeSO4 · 7H2O. It appears as a white powder with no odor. This ferrous sulfate specifically refers to the byproduct of titanium dioxide production, ferrous sulfate heptahydrate. Ferrous sulfate is soluble in water and almost insoluble in ethanol. Its aqueous solution oxidizes slowly in the air when cold, and oxidizes quickly when hot. Adding alkali or exposure can accelerate its oxidation. The relative density (d15) is 1.897, which is irritating.