Solid

28.15 - Sodium hydroxide (caustic soda); potassium hydroxide (caustic potash); peroxides of sodium or potassium. - Sodium hydroxide (caustic soda) : 2815.11 - - Solid 2815.12 - - In aqueous solution (soda lye or liquid soda) 2815.20 - Potassium hydroxide (caustic potash) 28 15.30 - Peroxides of sodium or potassium (A) SODIUM HYDROXIDE (CAUSTIC SODA) Sodium hydroxide (caustic soda) (NaOH) should not be confbsed with commercial soda, which is sodium carbonate (heading 28.36). Sodium hydroxide is obtained, for example, by causticising sodium carbonate with milk of lime or by electrolysing sodium chloride. It may be presented as an aqueous solution or an anh drous solid. Evaporation of the sodium hydroxide aqueous solution produces solid sodium hy oxide in the form of flakes or lumps. The pure product is presented in pellets or cubes in glass jars. Solid sodium hydroxide attacks the skin and destroys the mucous membranes. It is deliquescent and very soluble in water; it must therefore be kept 1n well-sealed steel containers. It is a powerful base with many industrial uses : preparation of certain chemical wood pulps by elimination of the lignin, manufacture of re enerated ceIlulose, mercerising of cotton, tantalum or niobium metallurgy, production of har soa s, manufacture of many chemical products, including phenolic compounds (phenol, resorcinof alizarin, etc.). % The heading excludes residual lyes (soda lyes) obtained as residual products fiom the manufacture of b the alkali or sul hate processes (heading 38.04); from these lyes the tall oil of ~ ~ ~ & C ~ i . Obe~obtained c a . anasodium hydroxide regenerated. The heading also excludes the mixtures of sodium hydroxide and lime known as " soda lime " (heading 38.24). (B) POTASSIUM HYDROXIDE (CAUSTIC POTASH) is very similar to the sodium h droxide described potassium carbonate (heading 28. 6) or commercial in certain countries to any potassium salt, particularly the l It is usual1 obtained by electrolysing solutions of natural potassium chloride (heading 3 1.04), but can so be obtamed from potassium carbonate by causticising with milk of lime ving " lime potash "). Pure potassium hydroxide is obtained by treatment with alcohol, or by ouble decomposition of barium hydroxide and potassium sulphate. P d' Potassium h droxide may be resented as an aqueous solution (potash lye), more or less high1 concentrate (usually arounf 50 %), or as a solid containing (amongst other impurities$ potassium chloride. It is stored in the same way as sodium hydroxide and has similar properties. i! It is used in the manufacture of soft soaps, for pickling of parts to be metallised or repainted, for bleaching, in the manufacture of potassium permanganate, etc. It is also used in medicine as a cauterising agent (in sticks), for this purpose it is sometimes mixed with Iime and is then classified m heading 30.03 or 30.04. (C) SODIUM PEROXIDE Sodium peroxide (disodium dioxide) (Na20z),obtained by combustion of sodium, is a very deliquescent white or yellowish powder, speclfic gravity about 2.8. It is decomposed by water, generatin heat and forming hydrogen peroxide. It is also presented in the form of cakes packed in welde metal containers. d It is used in soap manufacture, for bleaching fabrics, as an oxidisin agent in organic synthesis, or for urifying confined air e.g., in submarines . When mixed wit catalysts (traces of copper or nic el salts, etc.) for rapi production of hy ogen peroxide, it constitutes a preparation of heading 38.24. I: d k (D) POTASSIUM PEROXIDE Potassium peroxide (dipotassium dioxide) (K202) is very similar to sodium peroxide as regards manufacturing processes, properties and uses.