It crystallises from air-free H2O to provide the hexahydrate as pale green to bluish-green rhombic prisms. On heating at 49o H2O is lost and the tetrahydrate is formed. On further heating at 83o more H2O is lost and the dihydrate is formed as a light yellow to dark brown hygroscopic powder. The ferrous iron in aqueous solutions of these salts readily oxidises to ferric iron. The salts should be stored over H2SO4 under N2 in tightly closed containers. They have some solubility in EtOH. [Baxter Z Anorg Chem 38 236 1904, Kühln & Ernst Z Anorg Allgmen Chem 317 84 1962, Lux in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II p 1493 1965.]
