To the nitrate salt, add freshly prepared FeSO4 solution and then cone. H2SO4H2SO4 carefully by the sides of test-tube.
A dark brown ring of ferrous nitroso sulphate is formed. NaNO3+H2SO4→NaHSO4+HNO3 2HNO3+6FeSO4+3H2SO4→3Fe2(SO4)3+2no+4H2O FeSO4+NO→ferrous nitrososulphate (brown ring)[FeNO]SO4