WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.28 - Hypochlorites; commercial calcium hypochlorite; chlorites; hypobromites. 2828.10 2828.90 - Commercial calcium hypochlorite and other calcium hypochlorites - Other Subject to the exclusions s ecified in the introduction to this sub-Cha ter, this heading covers hypochlorites, chlorites an hypobromites of metals and commercial ca cium hypochlonte. f' (A) HYPOCHLORITES These are the most important; they are mainly used for bleachin (" bleaching chlorites "). The are unstable salts, which deteriorate in the air; they ve hypoch orous acid on contact even wit i weak acids. HypochIorous acid, readily giving o chlonne, is a very powerful oxidising and bleaching agent. B f (1) Sodium h ochlorite (NaC10.6H20). Put up in aqueous solutions, is nowadays commerciapknown as " eau de Javel ' .It is prepared by electmlysing an aqueous solution of sodium c oride, or by the action of sodium sulphate or sodium carbonate on calcium h ochlorite, or b treating sodium hydroxide (caustic soda) with chlorine. This salt, very so uble in water, c oes r not exist in the anhydrous state; it is rather unstable and sensitive to heat and li ht. Aqueous solutions of sodium hypochlorite are colourless or yellowish, smelling o chlorine. The generally contain as impurities a small quantity of sodium chloride. Used for bleac ing vegetable fibres or wood pulp, disinfecting urifying water or preparing hydrazine. It is also used in photogra h as a rapld eveloper for antihalation plates, and m medicine as an antiseptic (mixed wit oric acid, it is known as Dakin's soIuhon). & ? il KC r=~ses3 (2) Potassium hypochlorite (KC10.6H20). The aqueous solution of this salt was previously known as " eau de Javel "; it is similar m all respects to the sodium compound. r' (3) Other h ochlorites. These include h ochlorites of ammonium (a disinfectant more powerful';gan calcium hypochlorite), of arium, of magnesium or of zinc; all are bleaching agents or disinfectants. (B) COMMERCIAL CALCIUM HYPOCHLORITE Calcium hypochlorite. The roduct, irn roperly h o w n in commerce as " chloride of lime ", consists mainly of impure ca ciurn hypoc lorite and calcium chloride and, sometimes, calcium oxide or hydroxide. It is obtained by saturating calcium hydroxide with chlorine. It is a white, amorphous, powdery substance, h oscopic when containing calcium chloride, soluble in water, and sensitive to the action o ight, heat and carbon dioxtde. It affects animal fibres and or anic matter, and destroys colouring matter. It is used for bleaching vegetable textiles or wood pu p, as a disinfectant or antiseptic (to puri% water by " javellisation "), for s reading over ground contaminated b lethal gases. Pure calcium h ochlorite occurs in crystalbe masses or m solutions smelling o chlorine; it is slightly more staYgle than the impure product. R f ?'p f Calcium chloride (CaC12) is excluded (heading 28.27). (C) CHLORITES This group covers the salts of chlorous acid (HC102) : (1) Sodium chlorite (NaCIOz). Anhydrous or hydrated (with 3 HzO) masses, or aqueous solutions. Stable up to 100 OC. Powerful oxidising agent, very corrosive. Used in dye~ngor bleaching. (2) Aluminium chlorite. Same uses as sodium chlorite. (D) HYPOBROMITES This group covers the salts of hypobromous acid (HBrO) (heading 28.1 1). Potassium hypobromite is used for measuring the nitrogen content of certain organic compounds. -
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.