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GENERAL
Metal salts are obtained by replacing the hydrogen element in an acid by a metal or by the ammonium ion (NH4+). In the liquid state or in solution, they are electrolytes giving a metal (or a metal ion) at the cathode.In neutral salts all the hydrogen atoms are replaced by the metal, but acid salts still contain part of the hydrogen replaceable by metal; basic salts contain a greater quantity of basic oxide than is necessary to neutralise the acid (e.g., basic sulphate of cadmium (CdSO4.CdO)).
Sub‑Chapter V covers metal salts of the acids classified in sub‑Chapter II (acids derived from non‑metals) or in sub‑Chapter IV (acid‑function metal hydroxides). Double or complex salts.
Certain double or complex salts are specifically referred to in headings 28.26 to 28.41; for example, fluorosilicates, fluoroborates and other complex fluorine salts (heading 28.26), alums (heading 28.33), complex cyanides (heading 28.37). As regards double or complex salts not so specified, see the Explanatory Note to heading 28.42. This sub‑Chapter excludes, inter alia : (a) Salts of Chapter 25 (e.g., sodium chloride). (b) Salts constituting ores or other products of Chapter 26. (c) Compounds of precious metals (heading 28.43), of radioactive elements (heading 28.44), of rare-earthmetals, of yttrium or of scandium or of mixtures of these metals (heading 28.46), or of mercury (heading 28.52). (d) Phosphides, carbides, hydrides, nitrides, azides, silicides and borides (headings 28.48 to 28.50) and ferrophosphorus (Section XV). (e) Salts of Chapter 31. (f) Pigments, colours, opacifiers, enamels and other preparations included in Chapter 32. This sub‑Chapter covers unmixed metal salts (except luminophores), suitable for direct use as pigments; when mixed either together or with other products to form pigments, such salts fall in Chapter 32. Luminophores, mixed or not, fall in heading 32.06. (g) Disinfectants, insecticides, fungicides, weed killers, etc., of heading 38.08. (h) Fluxes and other auxiliary preparations for soldering, etc. (heading 38.10). (ij) Cultured crystals (other than optical elements) weighing not less than 2.5 g each, of the halides of the alkali or alkaline‑earth metals (heading 38.24); when they are in the form of optical elements they are classified in heading 90.01. (k) Precious or semi‑precious stones, natural or synthetic (headings 71.02 to 71.05).
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