From aqueous solutions the orange-pink heptahydrate CoSO4.7H2O crystallizes ; this is isomorphous with FeSO4.7H2O. Crystallization at 30° or by heating the heptahydrate at 41.5° yields the orange-red hexahydrate ; the monohydrate is formed above 70° and the anhydrous sulphate above 250°. This cubic anhydrous salt decomposes at 735° ; it is less deliquescent than the chloride or nitrate and is the salt used for many commercial purposes. Its solubility in water (about 36 g CoSO4 in 100 g H2O at 20°) increases with temperature ; it is insoluble in alcohol. The hydrates are magnetically dilute, having magnetic moments around 4.75 B.M. at room temperature.
Ammonium cobalt(II) sulfate hexahydrate is uses as spectroscopic standard, cobalt plating, catalysis and ceramics. It is also used in pharmaceutical intermediates.
