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 > V. SALTS AND PEROXYSALTS, OF INORGANIC ACIDS AND METALS > 2830 Sulphides; polysulphides, whether or not chemically defined > Other