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803
IRON AND STEEL


the hissing of the stake which Ulysses drove into the eye. of Polyphemus to that of the steel which the smith quenches in water, and closing with a reference to the strengthening effect of-this quenching; and that at the time of Pliny (A.D. 23~79) the relative value of different baths for hardening was known, and oil preferred for hardening small tools. These instances of the very early use of this metal, intrinsically at once so useful and so likely to disappear by rusting away, tell a story like that of the single foot-print of the savage which the waves left for Robinson Crusoe's warning. Homer's familiarity with the art of tempering could come only after centuries of the wide use of iron.

5. Three Periods.-The history of iron may for convenience be divided into three periods: a first in which only the direct extraction of wrought iron from the ore was practised; a second which added to this primitive art the extraction of iron in the form of carburized or cast iron, to be used either as such or for conversion into wrought iron; and a third in which the iron worker used a temperature high enough to melt wrought iron, which he then called molten steel. For brevity we may call these the periods of wrought iron, of cast iron, and of molten steel, recognizing that in the second and third the earlier processes continued in use. The first period began in extremely remote prehistoric times; the second in the 14th century; and the third with the invention of the Bessemer process in 1856. 6. First Period.-We can picture to ourselves how in the first period the savage smith, step by step, bettered his control over his fire, at once his source of heat and his deoxidizing agent. Not content to let it burn by natural draught, he would blow it with his own breath, would expose it to the prevalent wind, would urge it with a fan, and would devise the first crude valveless bellows, perhaps the pigskin already familiar as a water-bottle, of which the psalmist says: “ l am become as a bottle in the smoke.” To drive the air out of this skin by pressing on it, or even by walking on it, would be easy; to fill it again with air by pulling its sides apart with his fingers would be so irksome that he would soon learn to distend it by means of strings. If his bellows had only a single opening, that through which they delivered the blast upon the fire, then in inflating them he would draw back into them the hot air and ashes from the hre. To prevent this he might make a second or suction hole, and thus he would have veritable engine, perhaps one of the very earliest of all. While inflating the bellows he would leave the suction port open and close the discharge port with a pinch of his finger; and while blowing the air against the fire he would leave the discharge port open and pinch together the sides of the suction port.

The next important step seems to have been taken in the 4th century when some forgotten Watt devised valves for the bellows. But in spite of the activity of the iron manufacture in many of the Roman provinces, especially England, France, Spain, Carinthia and near the Rhine, the little forges in which iron was extracted from the ore remained, until the 14th century, very crude and wasteful of labour, fuel, and iron itself: indeed probably not very different from those of a thousand 'ears before. Where iron ore was found, the local smith, the Waldlrchmied, converted it with the charcoal of the surrounding forest into the wrought iron which he worked up. Many farmers had their own little forges or smithies to supply the iron for their tools.

The fuel, wood or charcoal, which served both to heat and to deoxidize the ore, has so strong a carburizing action that it would turn some of the resultant metal into “ natural steel, " which differs from wrought iron only in containing so much carbon that it is relatively hard and brittle in its natural state, and that it becomes intensely hard when quenched from a red heat in water. Moreover, this same carburizing action of the fuel would at times go so far as to turn part of the metal into a true cast iron, so brittle that it could not be worked at all. In time the smith learnt how to convert this unwelcome product into wrought iron by remelting it in the forge, exposing it to the blast in such a way as to burn out most of its carbon.

7. Second Period.-With the second period began, in the 14th century, the gradual displacement of the direct extraction of wrought iron from the ore by the intentional and regular use of this indirect method of first carburizing the metal and thus turning it into cast iron, and then converting it into wrought iron by remelting it in the forge. This displacement has been going on ever since, and it is not quite complete even to-day. It is of the familiar type of the replacing of the simple but wasteful by the complex and economical, and it was begun unintentionally in the attempt ro save fuel and labour, by increasing the size and especially the height of the forge, and by driving the bellows by means of water-power, Indeed it was the use of water-power that gave the smith pressure strong enough to force his blast up through a longer column of ore and fuel, and thus enabled him to increase the height of his forge, enlarge the scale of his operations, and in turn save fuel and labour. And it was the lengthening of the forge, and the length and intimacy of contact between om and fuel to which it led, that carburizedthe metal and turned it into cast iron. This is so fusible that it melted, and, running together into a single molten mass, freed itself mechanically from the “ gangue, " as the foreign minerals with which the ore is mixed are called. Finally, the improvement in the quality of the iron which resulted from thus completely freeing it from the gangue turned out to be a great and unexpected merit of the indirect process, probably the merit which enabled it, in spite of its complexity, to drive out the direct process. Thus we have here one of these cases common in the evolution both of nature and of art, in which a change, made for a specific purpose, has a wholly unforeseen advantage in another direction, so important as to outweigh that for which it was made and to determine the path of future development. With this method of making molten cast iron in the hands of a people already familiar with bronze founding, iron founding, Le. the casting of the molten cast iron into shapes which were useful in spite of its brittleness, naturally followed. Thus ornamental iron castings were made in Sussex in the 14th century, and in the 16th cannons weighing three tons each were cast.

The indirect process once established, the gradual increase in the height and diameter of the high furnace, which has lasted till our own days, naturally went on and developed the gigantic blast furnaces of the resent time, still called “ high furnaces ” in French and German. The impetus which the indirect process and the acceleration of civilization in the 15th and 16th centuries gave to the iron industry was so great that the demands of the iron masters for fuel made serious inroads on the forests, and in 1558 an act of Queen Elizabeth's forbade the cutting of timber in certain parts of the country for iron-making. Another in 1584 forbade the building of any more iron-works in Surrey, Kent, and Sussex. This increasing scarcity of wood was probably one of the chief causes of the attempts which the iron masters then made to replace charcoal with mineral fuel. .In 1611 Simon Sturtevant patented the use of mineral coal for iron-smelting, and in 1619 Dud Dudley made with this coal both cast and wrought iron with technical success, but through the op osition of the charcoal iron-makers all of his many attempts were defeated. In 1625 Stradda's attempts in Hainaut had no better success, and it was not till more than a century later that iron smelting with mineral fuel was at last fully successful. It was then, in 1735, that Abraham Darby showed how to make cast iron with coke in the high furnace, which by this time had become a veritable blast furnace.

The next great improvement in blast-furnace practice came in 1811, when Aubertot in France used for heating steel the furnace gases rich in carbonic oxide which till then had been allowed to burn uselessly at the top of the blast furnace. The next was J. B. Neilson's invention in 1828 of heating the blast, which increased the production and lessened the fuel-consumption of the furnace wonderfully. Very soon after this, in 1832, the work of heating the blast was done by means of the waste gases, at Wasseralhngen in Bavaria. Meanwhile Henry Cort had in 1784 very greatly simplified the conversion of cast iron into wrought iron. In place of the old forge, in which the actual contact between the iron and the fuel, itself an energetic carburizing agent, made decarburization difficult, he devised the reverberatory puddling furnace (see fig. 14 below), in which the iron lies in a chamber apart from the fire-place, and is thus protected from the carburizing action of the fuel, though heated by the flame which that fuel gives out.

The rapid advance in mechanical engineering in the latter part of this second period stimulated the iron industry greatly, giving it in 1728 Payn and Hanbury's rolling mill for rolling sheet iron, in 1760 John Smeaton's cylindrical cast-iron bellows in place of the wooden and leather ones previously used, in 1783 Cort's grooved rolls for rolling bars and rods of iron, and in 1838 James Nasmyth's steam hammer. But even more important than these were the advent of the steam' engine between 1760 and 1770, and of the railroad in 1825, each of which gave the iron industr a great impetus. Both created a great demand for iron, not only for themselves but for the industries which they in turn stimulated; and both directly aided the iron master: the steam engine by giving him powerful and convenient tools, and the railroad by assembling his materials and distributing his products.

About 1740 Benjamin Huntsman introduced the “ crucible process ” of melting steel in small crucibles, and thus freeing it from the slag, or rich iron silicate, with which it, like wrought iron, was mechanically mixed, whether it was made in the old forge or in the puddling furnace. This removal of the cinder very greatly improved the steel; but the process was and is so costly that it is used only for making steel for purposes which need the very best quality. 8. Third Period.-The third period has for its great distinction the invention of the Bessemer and open-hearth processes, which are like Huntsman's crucible process in that their essence is their freein wrought iron and low carbon steel from mechanically entangled cinder, by developing the hitherto unattainable temperature, rising to above 1500° C., needed for melting these relatively in fusible products. These processes are incalculably more important than Huntsman's, both because they are incomparably cheaper, and because their products are far more usefaxl than his. »

Thus the distinctive work of thQ$QQQ1'}d Zi.T1d'tvl1'll'd periods is freeing