The method consists of heating a sample at 360–410°C with concentrated sulfuric acid (H₂SO₄), which decomposes (“digests”) the organic sample by oxidation to liberate the reduced nitrogen as ammonium sulfate. Catalysts like selenium, Hg₂SO₄ or CuSO₄ are often added to hasten the digestion. Na₂SO₄ is also added to increase the boiling point of H₂SO₄. Digestion is complete when the liquor clarifies with the release of fumes.^[3] A distillation system depicted below is built.