Containing by weight not less than 99.99% of silicon

28.04 Hydrogen, rare gases and other non-metals. 2804.10 - Hydrogen - Rare gases : 2804.21 - - Argon 2804.29 - - Other - Nitrogen 2804.40 - Oxygen 2804.50 - Boron; tellurium 2804.30 - Silicon : - - Containing by weight not less than 99.99 % of silicon 2804.69 - - Other 2804.6 1 2804.70 - P~OSP~O~US - Arsenic 2804.90 - Selenium 2804.80 (A) HYDROGEN Hydrogen is obtained by electrolysing water, or from water-gas, coke-oven gas or hydrocarbons. It is generally regarded as a non-metal. It is presented under pressure in thick steel cylinders. r It is used for h drogenatin oils @reparation of solid fats), for crackin petroleum products, in the synthesis o ammonia, or cutttng or welding metals (oxy-hydrogen low lamps), etc. f !i The heading excludes deuteriurn.(stable hydrogen isoto e) which falls in heading 28.45, and tritium (radioactive hydrogen isotope) which falls in heading 28.f4. (B) RARE GASES 'p ? The term " rare gases gases) a plies to the elements listed below. They are remarkable for their lack of chemic afXnityand or their electrical properties - particularly that of emitting coloured rays (used, for example, in neon signs) under the action of high voltage discharges. (1) Helium (non-inflammable, used, e.g., for inflating balloons). (2) Neon ( 'ves a rosy orange-yellow light or, combined with mercury vapour, " daylight " lighting? (3) A r r n (a colourless and odourless gas used to provide an inert atmosphere in electric lamp bul s). (4) Krypton (same use as argon, or to give a pale violet light). (5) Xenon (gives a blue light). Rare gases are obtained by fractionating liquid air, or also (in the case of helium) from certain natural gases. They are presented under pressure. Radon is a radioactive inert gas of heading 28.44 formed by the radioactive decay of radium. (C) OTHER NON-METALS The other non-metals covered by this heading are : (1) Nitrogen. Nitrogen is a gas which neither burns nor supports combustion, but extinguishes flames. It is obtained by fractional distillation of liquid air, and is presented under pressure in steel cylinders. Nitrogen is chiefly used for the manufacture of ammonia and calcium cyanamide, but is also used to provide an inert atmosphere in electric lamp bulbs, etc. This is a combustion-supporting gas, chiefly obtained by fractional distillation of liquid air. It is presented under pressure in steel cylinders, or sometimes as a liquid in double-walled contamers. Compressed ox gen is used in oxyhydrogen and oxyacetylene blow lamps for welding ? or cutting metals such as iron. It is also used in iron or steel metallurgy (autogenous weIding) and in medicine (inhalations). This headin also includes ozone, an allotropic form of oxygen obtained by the action of electric s arfs or discharges. It is used for sterilisin water (ozonisation), for the oxidation of drying oi s, for bleaching cotton, as an antiseptic and or therapeutic purposes. t' f (3) Boron. Boron is a chestnut-coloured solid generally in powder form. It is used in metallurgy, and for the manufacture of heat regulators and highly sensitive thermometers. Because of its very high rate of absorption of slow neutrons, boron is also used, pure or alloyed with steel, for the manufacture of mobile control rods for nuclear reactors. (4) Tellurium. A solid (specific gravi 6.2), amorphous or crystalline, It is a relatively good conductor of heat and electricity, and as certain metallic properties. It is used in certain alloys (e.g., tellurium-lead alloys), and also as a vulcanising agent. (5) Silicon. Silicon is obtained almost exclusive1 by carbotherma1 reduction of silicon dioxide using electric arc-furnaces. It is a oor con uctor of heat and electricity, is harder than ass, and is put u as a chestnut-coloure powder or, more often, in shapeless lumps. It crystal ses as grey nee!ld es with a metallic lustre. B ! Silicon is one of the most im ortant materials used in electronics. Very pure silicon, obtained by, for example, c stal p mg, may be in forms unworked as drawn, or in the form of cylinders or rods; w en doped with boron, phosphorus, etc., it is used for the manufacture of, for example, diodes, transistors and other semi-conductor devices and solar cells. X d Silicon is also used in metallur 'cal industries (e.g., ferrous or aluminium alloys), and in chemistry for the preparation of si icon compounds (e.g., silicon tetrachloride). P (6) Phosphorus. Phosphorus is a sofl flexible solid obtained by treating mineral phosphates mixed with sand and carbon in an electric furnace. There are two main varieties of phosphorus : (a) " White '' phosphorus, transparent and yellowish, toxic, clan erous to handle, hi 1 k ghE inflammable. Thrs is put u as moulded rods packed in water- illed containers of b ac glass, stoneware or, more o en, metal; these containers should not be exposed to fiost. tP (b) Red phosphorus, known as " amorphous ", but which can actually be crystalIised. This is an opaque solid, non-toxic, non-phosphorescent, denser and less active than white phosphorus. Red phosphorus is used for the manufacture of match compounds, in pyrotechnics, or as a catalyst (e.g., in the chlorination of acyclic acids). Certain medicaments contain phosphorus (e.g., phosphorised cod liver oil). It is also used as rat poison, or in the preparation of phosphonc acids, phosphinates (hypophosphites), calcium phosphide, etc. (7) Arsenic. Arsenic (regulus of arsenic) is a solid extracted from natural arsenical pyrites. It exists in two main forms : (a) Common, so-called " metallic " arsenic, in brilliant, steelgrey crystals, brittle, insoluble in water. (b) Yellow arsenic, crystalline, rather unstable. Arsenic is used in the manufacture of arsenic disulphide, buck-shot, hard bronzes and various other alloys (of tin, copper, etc.). (8) Selenium. Selenium, which is rather similar to sulphur, exists in several forms : (a) Amorphous selenium, in reddish flakes (flowers of selenium). (b) Vitreous selenium, a poor conductor of heat and electricity. It has a brilliant fracture, brown or reddish. r (c) Crystallised selenium, ey or red crystals. It is a relatively good conductor of heat and , especially w en exposed to light. It is used in the manufacture of hotoelectric elec~ci%' cells an , when doped, of semi-conductor devices, in photography, in pow er form (red selenium), for the manufacture of rubber, of special lenses, etc. The heading excludes selenium in colloidal suspension (used in medicine) (Chapter 30). In the Nomenclature, antimony is classified as a metal (heading 81.10). Some of the non-metals in this group (for example, silicon and selenium) may be doped with elements such as boron, phosphorus, etc., in a proportion generally of the order of one part er million, with a view to their use in electronics. They are classified in this heading provided they are in forms unworked as drawn, or in the form of cylinders or rods. When cut in the form of discs, wafers or similar forms, they are classified in heading 38.18. th -