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28.01 ‑ Fluorine, chlorine, bromine and iodine.
This heading covers the non‑metals known as halogens, with the exception of astatine (heading 28.44).(A) FLUORINE
Fluorine is a faintly greenish‑yellow gas with a pungent odour; it is dangerous to inhale as it irritates the mucous membranes and is corrosive. It is presented under pressure in steel containers; it is a very active element which ignites organic matter ‑ in particular wood, fats and textiles.
Fluorine is used for the preparation of certain fluorides and organo‑fluorine derivatives. (B) CHLORINE
Chlorine is usually obtained by electrolysis of alkali chlorides, especially sodium chloride.
Chlorine is a greenish‑yellow gas, suffocating, corrosive, two and a half times as dense as air, slightly soluble in water and readily liquefied. It is usually transported in steel cylinders, tanks, railway tank wagons or barges.
Chlorine destroys colouring and organic matter. It is used for bleaching vegetable (but not animal) fibres, and in the preparation of wood pulp. Because of its disinfecting and antiseptic properties, it is also used for sterilising (chlorinating) water. It is used in gold, tin and cadmium metallurgy, in the manufacture of hypochlorites, metal chlorides and carbonyl chloride, in organic syntheses (e.g., synthetic dyes, artificial waxes, chlorinated rubber). (C) BROMINE
Bromine can be obtained by the action of chlorine on the alkaline bromides contained in saline mother‑liquors, or by electrolysing bromides.
It is a very dense (3.18 at 0 °C), corrosive, reddish or dark brown liquid which, even when cold, gives off suffocating red fumes irritating to the eyes. It inflames the skin, turning it yellow, and ignites organic substances such as sawdust. It is presented in glass or pottery containers. It is slightly soluble in water. The heading excludes solutions of bromine in acetic acid (heading 38.24).
It is used in the manufacture of medicaments (e.g., sedatives), dyes (e.g., eosins, brominated derivatives of indigo), photographic chemicals (silver bromide), lachrymatory products (bromo‑acetone), in metallurgy, etc. (D) IODINE
Iodine is extracted either from the mother‑liquors of natural sodium nitrates by treatment with sulphur dioxide or sodium hydrogen sulphite, or from marine algae by drying, incinerating and chemical treatment of the ash.
It is a very dense solid (specific gravity 4.95 at 0 °C), with an odour reminiscent of both chlorine and bromine; it is dangerous to inhale. It sublimes at room temperature and turns starch‑paste blue. When impure, it occurs in specks or as a coarse powder. When purified by sublimation, it takes the form of brilliant, greyish flakes or crystals with a metallic glint; it is then usually put up in glass.
It is used in medicine, and also in the manufacture of photographic chemicals (sodium iodide), dyes (e.g., erythrosines) and medicaments, as a catalyst in organic synthesis, as a reagent, etc.
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