... > SECTION VI - PRODUCTS OF THE CHEMICAL OR ALLIED INDUSTRIES > CHAPTER 28 - INORGANIC CHEMICALS; ORGANIC OR INORGANIC COMPOUNDS OF PRECIOUS METALS, OF RARE-EARTH METALS, OF RADIOACTIVE ELEMENTS OR OF ISOTOPES > II. INORGANIC ACIDS AND INORGANIC OXYGEN COMPOUNDS OF NON-METALS > 2811 Other inorganic acids and other inorganic oxygen compounds of non-metals > Other inorganic oxygen compounds of non-metals > Other > Sulphur trioxide (sulphuric anhydride); diarsenic trioxide