Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/294

278 IKON IX the short space that can be allotted to the wide subjects of IRON and STEEL, it is impossible to do more than briefly describe the main facts in connexion with the general properties and relationships of iron and steel, and their modes of manufacture. These points will be considered under the following general heads. I. General characters of iron; its relationships to other ele ments. 1 . Properties of iron. 2. Chemical and physical relationships of iron. 3. Relationships between iron and steels of various kinds. II. Natural sources of iron. 4. Meteoric iron. 5. Iron ores. 6. Methods of analysis of iron ores, metallic iron, and steel. III. Extraction of iron from its ores. 7. General history of the manufacture of iron and steel. 8. Classification of methods of manufacture. IV. Manufacture of cast iron ; iron smelting. 9. Preliminary treatment of ores. 10. Fuel. II. Fluxes. 12. Construction of blast furnaces. 13. Subsidiary appliances ; hoists and lifts. 14. ,, ,, blowing engines. 15. , , apparatus for superheating the blast, and for determining its temperature ; tuyeres. 16. Collection of pig iron and cinder, and their composition. 17. Utilization of cinder. 18. Collection of waste gases, and their composition. 19. Chemical changes taking place in the blast furnace. 20. Development and appropriation of heat in blast furnaces. 21. Conditions regulating economy of fuel in blast furnaces. V. Conversion of pig iron into malleable iron and steel by decarbon ization pi ocesscs. 22. Malleable cast iron. 23. Refining, fining, and puddling of pig iron. 24. Machine puddling. 25. Machinery and appliances for working malleable iron. 26. Puddled steel and natural steel. 27. Bessemer s original process (pneumatic process). 28. Heaton s process. VI. Production of malleable iron and steel from the ore at one operation without passing through the stage of cast iron. 29. Catalan forge and analogous appliances. 30. Spongy iron processes. 31. Siemens s precipitation process. VII. Conversion of malleable iron into steel by direct carboniza tion. 32. Cementation process and subsequent operations. 33. Cast steel. 34. Case hardening. 35. Crucible steel ; Wootz ; Mushet and Heath s processes. VIII. Methods of steel production essentially involving combina tions of the preceding processes. 36. The Besserner-Mushet process and its precursors. 37. The "basic" process. 33. The Uchatius process. 39. Siemens-Martin processes ; open-hearth steels. 40. The Pernot and Ponsard furnaces. 41. Manufacture of spiegeleisen and ferro-manganese. IX. Physical qiuditics ofiroi. and steel in their practical relation ships. 42. Hardening, tempering, and annealing. 43. Tenacity and strength of iron and steel. 44. Foundry operations ; casting under pressure. 45. Protection of iron from rust. X. Statistics of the iron trade. I. GENERAL CHARACTERS OF IRON AND ITS RELATIONSHIPS TO OTHER ELEMENTS. 1. Properties of Iron. The peculiar physical characters of iron, more especially when in the form of steel or slightly carbonized iron, have rendered this element one of special importance since the earliest ages for the fabrication of cutting instruments, weapons, and tools of various kinds. In the form of moderately-pure malleable or wrought iron, the metal is a substance possessed of considerable lustre and hardness, and of a bluish-white or bluish-grey colour ; it takes a high polish, and when bright does not readily oxidize in dry air, although moist air, especially in presence of traces of acids, even of carbonic acid, readily effects its tarnishing and the subsequent formation of rust. It has a specific gravity near to 7 75, and requires a very high tem perature to effect its fusion, the melting point being the more elevated the purer the substance ; its most valuable and characteristic property is its power of becoming soft and pasty before undergoing complete fusion, so that two hot masses may be pressed or squeezed together into one by the process of welding, and so that by forging, rolling, hammering, or other analogous operations it can readily be fashioned into shapes which its rigidity and strength when cold enable it to maintain. Its strength and tena city are very high, as also are its powers of being drawn into wire and rolled or hammered into sheets (ductility and malleability); these properties, however, are very largely influenced by the presence of impurities. In magnetic characters it is superior to all other substances, nickel and cobalt coming next to it in these respects, but being much lower in power ; when it is almost pure, the magnetic influ ence produced, owing to induction, by the proximity of a per manent magnet or of an electric current disappears entirely on removal of the magnet or current; if, on the other hand, carbon be present (as is usually the case to some extent even in the softest malleable iron), there remains after removal of the magnet or current a greater or less amount of permanent magnetism according to circumstances, hard steel exhibiting the greatest power of becoming permanently magnetized under given conditions, and substances inter mediate between pure iron and hard steel (soft steels and hard irons) possessing this power to a lesser extent. Other elements besides carbon, e.g., oxygen and sulphur, can com municate to iron the power of becoming permanently mag netized, as in the case of the minerals loadstone (magnetic oxide of iron) and magnetic pyrites. The effect of a magnet on iron at high temperatures is far below that exhibited at ordinary temperatures ; according to Matteucci the action of a given magnet on a molten globule of iron is only O OOIS per cent, of that on the same globule when cold, so that the attractive action is wholly insensible in the case of molten iron except when a powerful electromagnet is employed. In electrical conductivity and power of conducting heat (which are always approximately in the same ratio), iron stands about midway amongst metals ; Matthiessen s experiments give the specific resistance (C. G. S. system) of annealed iron as 9827 at C., that of annealed silver being 1521 and that of mercury 96,190 at the same temperature. As with the other physical properties, the presence of small amounts of impurity largely affects the numerical value of the specific resist ance, which is decreased some 35 per cent, by a rise in temperature from to 100 C. The specific heat of iron at the ordinary temperature is 0-11379 (Eegnault), 0110 (Dulong and Petit). Pouillet gives the melting point when in a state of high purity as between 1500 and 1600 (probably somewhat too low), Scheerer as 2100, Deville as near to that of platinum, which is not far from 1 900-2000. The presence of minute quantities of carbon, sulphur, &c., sensibly lowers the fusing point, whilst 1 per cent, of the former furnishes a steel melt ing at several hundred degrees lower than pure iron (at near 1600), cast iron containing some 3 per cent, of carbon