The ferrous sulphate crystals are light green. Ferrous sulphate is also obtained as a by-product in the manufacture of titanium pigment and copper sulphate. The gas given out smells the characteristic odour of burning sulphur. The colour changes from light green to white colour. On further heating white substance turns into dark brown solid.
Ferrous sulphate crystals contain water of crystallisation (FeSO4.7H2O). On heating, ferrous sulphate crystals lose water. So their colour changes from light green to white due to the formation of anhydrous ferrous sulphate (FeSO4). When ferrous sulphate is heated, it gives ferric oxide, sulphur dioxide and sulphur trioxide.