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Ammonia is obtained either from impure ammoniacal gas liquors produced in coal gas purification or coke works (see Explanatory Note to heading 38.25, Item (A) (3)), or by synthesis from hydrogen and nitrogen.
This heading includes :(1) Anhydrous ammonia (NH3), a colourless gas. It is less dense than air and easily liquefied by pressure. Presented in metal cylinders. (2) Ammonia in aqueous solution (NH4OH), hydroxide of a hypothetical "element" ammonium (NH4). These solutions (generally containing 20, 27 or 34 % of NH3) are colourless or yellowish liquids presented in tightly‑stoppered containers. Alcoholic solutions of ammonia are excluded (heading 38.24).
Ammonia has many uses, for example, in the manufacture of nitric acid and nitrates, ammonium sulphate, other ammonium salts and nitrogenous fertilisers, sodium carbonate, cyanides, amines (e.g., naphthylamine). It emulsifies fatty matter and resins, and it acts as a detergent for removing stains, preparing polishing compounds, treating latex, removing varnish, etc. Liquefied ammonia is used in refrigerating plant.
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