WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.52 Inorganic or organic compounds of mercury, whether or not chemically defined, excluding amalgams. 2852.10 - Chemically defined 2852.90 - Other This heading covers inorganic or organic compounds of mercury, whether or not chemically defined, other than amalgams. The most common compounds of mercury are listed below : d (1) Mercury oxides. Mercuric oxide (HgO is the most important oxide of mercury. It can exist as a bright-red crystalline pow er (red oxide) or as a denser orange-yellow amorphous powder (yellow oxide). These oxides are toxic and turn black on exposure to light. They are used in the preparation of marine paints or mercury salts, and as catalysts. (2) Mercury chlorides. (a) Mercurous chloride (calomel (Hg2C12).Can exist as amorphous masses, as a powder or in white crystals; insolu le in water. Mercurous chloride is used also in pyrotechnics, in the porcelain industry, etc. b (b) Mercuric chloride (mercury dichloride, corrosive sublimate) (HgC12). C stallises in nsms or long white needles. Soluble in water (especially when hot); a vio ent oison. is used for "bronrin iron, for impregnating wood to render it fire-proof as an intensifier in hotograp y, as a catalyst in organic chemistry and in the manufacture of mercuric oxi e. ! B E" (3) Mercury iodides. (a) Mercurous iodide (HgI or H&12). Powder, usually amorphous but sometimes crystalline; usually yellow but sometimes greenish or reddish; sparingly soluble in water and very toxic. It is used in organic synthesis. (b) Mercuric iodide (mercury di-iodide, red iodide) (Hg12). Crystalline red owder, almost insoluble in water, very toxic. Used in photography (as an intensifierrand in analysis. (4) Mercury sulphides. Artificial mercury sulphide (HgS) is black. When sublimed or heated with alkali polysulphides, black sulphide is transformed into a red powder (red mercury sulphide, artificial vermilion), used as a pi ent for paints or sealin wax. The roduct obtained by the wet process is shinier but oes not resist the action o light so we 1. This salt is toxic. 'r f P Natural mercury sulphide (cinnabar, natural vermilion) is excluded (heading 26.17). (5) Mercury sulphates. (a) Mercurous sulphate (H 2S04).White crystalline powder, decom osed by water into basic sulphate. I3mployecfin the preparation of calomel and of stan d electric cells. 8, (b) Mercuric sulphate (H SO4). White, anhydrous and c stalline masses, turning black in the light, or hydrate crystalline flakes (with 1 ~ 2 0 7Used for preparing mercuric chloride or other mercuric salts, in gold or silver metallurgy, etc. f (c) Trimercury dioxide sulphate (HgS04.2HgO) (basic mercury sulphate). (6) Mercury nitrates. (a) Mercurous nitrate (HgN03.H20).Poisonous. Colourless crystals. Used in gilding; in medicine; by hatters for the can-oting of hair before the felting operation (hatters' aqua fortis); for preparing mercurous acetate, etc. P" (b) Mercuric nitrate (Hg O,),).Hydrated salt (generally with 2 HzO). Colourless c stals, or white or ye1 owish slabs, deli uescent and toxic. Used in hat-making and @(kg. Also used as a nitration aid, an as a catalyst in organic synthesis, in the preparation of mercury fulminate or mercuric oxide, etc. (c) Basic mercury nitrates. (7) Mercury cyanides. (a) Mercuric cyanide (Hg(CN)2). (b) Mercuric cyanide oxide (Hg(CN)2.HgO). (8) Cyanomercurates of inor anic bases. Potassium cyanomercurate. Colourless crystals, soluble in water and toxic. sed for silvering mirrors. (9) Mercury fulminate (presumably Hg(ONC)2).White or yellowish crystals, needle-shaped, soluble in boiling water oisonous. Gives off red fumes when exploding. Presented in non-metallic containers hl ed with water. I' (10) Mercuric thiocyanate (Hg(SCN)2). White crystalline powder, sparingly soluble in water. Poisonous salt used in photography to intensifl negatives. (1 1) Mercury arsenates.,Mercuric orthoarsenate (Hg3(As0&). Pale yellow powder, insoluble in water. Used in antl-fouling paints, (12) Double or complex salts. (a) Chloride of ammonium with mercury (ammonium mercuric chloride or ammonium chloromercurate). White crystalline powder, relatively soluble in hot water; toxic. Used in pyrotechnics. (b) Copper mercury iodide. A dark red powder, insoluble in water and toxic. Used in thennoscopics. (13) Aminomercuric chloride (HgNH2C1). White powder, turnin greyish or yellowish on exposure to light; insoluble in water; poisonous. Used in pyroteh~cs. (14) Mercury lactate, salt of lactic acid. (15) Organo-inor anic mercury compounds. These may contain one or more mercury atoms, in particular t e (-Hg.X) group in which X is an inorganic or organic acid residue. g (a) Diethylmercury. (b) Diphenylmercury. (c) Phenylmercury acetate. (16) Hydromercuridibromofluorescein. (17) Mercury compounds not chemically defined (tannates of mercury, alburninates of mercury, nucleoproteids o f m e r c q , etc.). The heading does not include : (a) Mercury (heading 28.05 or Chapter 30). (b) Amalgams of precious metals, amalgams containing both recious metals and base metals (bcahng 28.43) and amalgams wholly of base metal (heading 1 i 5 3 ) .
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.