WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.31 - Dithionites and sulphoxylates. - Ofsodium 2831.90 - Other 2831.10 Dithionites (h drosulphites) are the salts of which has not een isolated in the fkee state. They are solutions of hydrogen sulphites employed in the chemical, textile or sugar r, The most im ortant is sodium dithionite (NazS2O4),anhydrous white powder, soluble in water, or hydrated fwith 2 H20) in colourless crystals. It is used in organic synthesis, in the dyeing industry and for a er-makin . It deteriorates rather rapid1 , even when c stallised. For certain uses (e.g., as a isc arge in t e textile industry), sodium thionite must erefore be stabilised with formaldehyde, sometimes with the addition of zinc oxide or glycerol. It may also be stabilised with acetone. 8% g x Dithionites of potassium, calcium, magnesium and zinc, which may be stabilised by similar processes, are products similar to sodium dithionite, with similar properties and uses. The heading includes all these stabilised dithionites and also formaldehyde sulphoxylate which is a s~milarproduct. Sulphites and thiosulphates are excluded (heading 28.32). -
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.