Blue vitriol is also known as blue copperas. The word blue vitriol has a strict and definite meaning. It means sulphate of copper with the chemical formula CuSO4.5H2O. The chemical name for blue vitriol is Copper (II) Sulphate Pentahydrate. This salt occurs in the form of rhomboidal prisms of a deep blue colour, having an exceedingly harsh and styptic taste.
Similarly, “Green Vitriol” refers to Ferrous Sulphate.