Harmonized System

Sub-Chapter I

CHEMICAL ELEMENTS

GENERAL

Chemical elements can be divided into two classes, non‑metals and metals. In general, this sub‑Chapter includes all non‑metals at least in some of their forms, whereas numerous metals are classified elsewhere : ‑ precious metals (Chapter 71 and heading 28.43), base metals (Chapters 72 to 76 and 78 to 81) and radioactive chemical elements and isotopes (heading 28.44) and stable isotopes (heading 28.45).

An alphabetical list of the various known elements, indicating the appropriate classification, is given below. Some elements, such as antimony, behave both as metals and as non‑metals; attention is drawn to their classification in the Nomenclature.

Sub-Chapter II

INORGANIC ACIDS AND INORGANIC OXYGEN COMPOUNDS OF NON‑METALS

GENERAL

Acids contain hydrogen which can be wholly or partly replaced by metals (or by ions with analogous properties, e.g., the ammonium ion (NH₄⁺)) as a result salts are formed. Acids react with bases to form salts, and with alcohols to form esters. In the liquid state or in solution, they are electrolytes which produce hydrogen at the cathode. When one or more molecules of water are eliminated from those acids containing oxygen, anhydrides are obtained. Most oxides of non‑metals are anhydrides.

This sub‑Chapter covers inorganic oxygen compounds of non‑metals (anhydrides and other), and also inorganic acids, the anode radical of which is a non‑metal.

On the other hand it excludes anhydrides and acids formed, respectively, by metal oxides or hydroxides; these generally fall in sub‑Chapter IV (e.g., metal oxides, hydroxides and peroxides, such as acids or anhydrides of chromium, molybdenum, tungsten and vanadium). In certain cases, however, they fall elsewhere, e.g., in heading 28.43 (compounds of precious metals), heading 28.44 or 28.45 (compounds of radioactive elements and isotopes) or heading 28.46 (compounds of rare‑earth metals, of scandium or yttrium).

Oxygen compounds of hydrogen are also excluded and are classified under heading 22.01 (water), heading 28.45 (heavy water), heading 28.47 (hydrogen peroxide) or heading 28.53 (distilled and conductivity water and water of similar purity, including water treated with ion‑exchange media).

Sub-Chapter III

HALOGEN OR SULPHUR COMPOUNDS OF NON‑METALS

GENERAL

This sub‑Chapter covers products which, although known by names (chlorides, sulphides, etc.) similar to those of the metal salts of hydracids classified in sub‑Chapter V, are actually non‑metal combinations such as :

(1) A halogen with a non‑metal other than oxygen or hydrogen (halogen compounds).

(2) The same compounds as under (1) above, combined with oxygen (halide oxides).

or (3) Sulphur with a non‑metal other than oxygen or hydrogen (sulphur compounds).

Sulphide oxides of non‑metals (sulphur + oxygen + non‑metal) are excluded from this sub‑Chapter; they fall in heading 28.53.

Halides, halide oxides, and sulphides of metals (see the General Explanatory Note to sub‑Chapter I) or of the ammonium ion (NH₄⁺) fall in sub‑Chapter V except in the case of compounds of precious metals (heading 28.43) and the compounds of heading 28.44, 28.45, 28.46 or 28.52.

Sub-Chapter IV

INORGANIC BASES AND OXIDES, HYDROXIDES AND PEROXIDES OF METAL

GENERAL

Bases are compounds characterised by a hydroxyl radical (OH) and which react with acids to form salts. In the liquid state or in solution, they are electrolytes giving a metal or an analogous ion (ammonium (NH₄⁺)) at the cathode.

Metal oxides are compounds of a metal with oxygen. Many can combine with one or more molecules of water to form hydroxides.

Most oxides are basic since their hydroxides act as bases. Certain oxides (anhydride oxides), however, react only with alkaline or other bases to form salts, while another more common class (amphoteric oxides) can behave both as anhydride oxides or as bases. These classes of oxides must be regarded as anhydrides of acids, real or hypothetical, corresponding to their hydroxides.

Certain oxides (saline oxides) may be regarded as resulting from the combination of a basic oxide with an anhydride oxide.

This sub‑Chapter covers :

(1) Oxides, hydroxides and peroxides of metal, whether basic, acidic, amphoteric or saline.

(2) Other inorganic bases containing no oxygen, such as ammonia (heading 28.14), or hydrazine (heading 28.25), and those containing no metal, such as hydroxylamine (heading 28.25).

The sub‑Chapter excludes :

(a) The oxides and hydroxides of Chapter 25, particularly magnesia (magnesium oxide), whether or not pure, and quicklime and slaked lime (crude calcium oxide and hydroxide).

(b) Oxides and hydroxides constituting ores (headings 26.01 to 26.17), scalings, ash, slag, dross, scum or other metalliferous residues (headings 26.18 to 26.20).

(c) Oxides, peroxides and hydroxides of precious metals (heading 28.43), of radioactive elements (heading 28.44), of rare-earth metals, of yttrium or of scandium or of mixtures of these metals (heading 28.46), or of mercury (heading 28.52).

(d) Oxygen compounds of hydrogen of heading 22.01 (water), heading 28.45 (heavy water), heading 28.47 (hydrogen peroxide), or heading 28.53 (distilled and conductivity water and water of similar purity, including water treated with ion‑exchange media).

(e) Colouring matter with a basis of metal oxides (heading 32.06), prepared pigments, prepared opacifiers and prepared colours, vitrifiable enamels and glazes and similar products of the kind used in the ceramic, enamelling or glass industries (heading 32.07), and other preparations of Chapter 32, constituted by oxides, hydroxides or bases mixed with other products.

(f) Opacifying preparations for de‑lustring man‑made fibres (heading 38.09) and pickling preparations for metal surfaces (heading 38.10).

(g) Natural or synthetic precious or semi‑precious stones (headings 71.02 to 71.05).

Sub-Chapter V

SALTS AND PEROXYSALTS, OF INORGANIC ACIDS AND METALS

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-earth metals, 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 28.49, 28.50 and 28.53) 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).

Sub-Chapter VI

MISCELLANEOUS