WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.32 Sulphites; thiosulphates. 2832.10 - Sodium sulphites 2832.20 - Other sulphites 2832.30 - Thiosulphates Subject to the exclusions mentioned in the introduction to this sub-chapter, this heading covers : (A) Metal sulphites - salts of sulphurous acid (H2S03 (which exists only in aqueous solution and corresponds to the sulphur dioxide of heading 8.11). (B) Metal thiosulphates - salts of thiosulphuric acid (H2S2O3)which does not exist in the pure state. The headin excludes concentrated sulphite lye (heading 38.04 , and the industrial products known as " hydms$phites " stabilised by organic substances (headlag 28. 1). (A) SULPHITES This heading covers both neutral and acid sulpbites. (I) Sodium sul hites. These include sodium hydro en sul hite (NaHS03), disodium disulphite Q&so~.so~ or Na2S205)or and sodium su&hite & 2 ~ ~ 3 .) . results from processes. (b) Disodium disulphite (sodium lan ages, incorrectly referred hy ogen sulphite; oxidises the same purposes as the C (c) Sodium sulphite (neutral sodium sulphite), prepared by neutralising a solution of the hydro en sulphite by means of sodum carbonate. Anh drous (in powder) or crysta lised (with 7 H20) colourless, soluble in water. sed in photography, in breweries, for treating rosin, as an antiseptic or bleaching agent, in the manufacture of other sulphites or thiosulphates and of organic dyes, etc. d f (2) Ammonium sulphite ((W2S03.H20). Results from the action of sulphur dioxide on ammonia. Colourless crysta s, soluble in water, oxidising in the air. Used in organic synthesis. ? (3) Potassium sulphites. Appear in the same forms as sodium sulphites. (a) Potassium hydrogen sulphite, crystalline, used in dyeing and in oenology. (b) Dipotassium disulphite (potassium metabisul hite), a white powder or in scales, used in photography, for the carroting of hair in the elt hat industry or as an antiseptic. F (c) Neutral sulphite, crystallised (with 2 H20) used in textile printing. (4) Calcium sulphites, which include : for bleaching (e-g., sponges), P b (b) Neutral calcium sul hite CaS03), a white crystalline powder or hydrated needles (with 2 H20),sparing y solu le in water, efflorescing in the air. Used in medicine or in oenology. (5) Other sulphites. These include magnesium sulphites (same uses as calcium sulphites), zinc sulphite (antiseptic and mordant), or chromium hydrogen sulphite (mordant). (B) THIOSULPHATES P"4 )2S203).Prepared fiom sodium thiosulphate. Colourless (1) Ammonium thiosulphate ( crystals, deliquescent and so uble in water. Used for photographic fixing baths and as an antiseptic. (2) Sodium thiosulphate (NazS203.5H20. Results from the action of sulphur on a solution of sodium sul hite. In the fonn of colour ess crystals, very soluble in water, unaffected by air. Used as a uring agent m photography, as an antichlor in the bleaching of textiles or paper, in chrome t w n g and in organic synthesis. P (3) Calcium thiosulphate (CaS203.H20).Prepared by oxidation of calcium sulphide. White crystalline powder, soluble in water. Used in medicine and in the preparation of other thosulphates. (4) Other thiosulphates. These include : barium thiosulphate (pigment with a pearly sheen); aluminium thiosulphate (used in or anic synthests); lead thiosulphate (used in the preparation of phosphorus-fi-eematche3.
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemical elements and separate chemically defined compounds, whether or not containing impurities; (b) The products mentioned in (a) above dissolved in water; (c) The products mentioned in (a) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (d) The products mentioned in (a), (b) or (c) above with an added stabiliser (including an anti-caking agent) necessary for their preservation or transport; (e) The products mentioned in (a), (b), (c) or (d) above with an added anti-dusting agent or a colouring substance added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use.