When copper sulphate is treated with excess of ammonia solution, it gives a deep blue solution due to the formation of tetramine copper (II) sulphate complex. CuSO4+4NH3⟶tetraamine copper (II) sulphate deep blue complex[Cu(NH3)4]SO4
Tetramine copper (II) sulphate is used for making artificial rayon, artificial silk, cupra silk.