Discoveries and Inventions of the Nineteenth Century

North Eastern Railway Company, and were found entirely satisfactory, being as good as those made from the Cumberland hæmatite steel. This de-phosphorized process has been brought into operation wherever phosphoric ores are dealt with, and it has been applied with equal success in the “open hearth” furnaces, of which we have now to speak. All discoveries and all inventions may be traced back to preceding discoveries and inventions in an endless series, and it is only by its precursors that each in its turn has been made possible. If we take one of the greatest marvels brought into existence at nearly the close of our epoch, namely, “wireless telegraphy,” we may follow up links of a chain connecting it with the recorded observations of an ancient Greek (Thales) who flourished seven centuries before our era, and even these may not have been original discoveries of his. And it will have been gathered from what has already been said that steel must have been produced, however unwittingly, at the earliest period at which man began to reduce iron from its ores. So the very latest, and for many purposes the most extensively practised, process of modern steel-making, brought indeed to working perfection mainly by the perseverance and scientific insight of two individuals, is the result of the observation and the accumulated experience of former generations. The observations and experience here alluded to are chiefly those that follow two lines: one concerning the properties of the metal itself, the other relating to the means of commanding very high temperatures on a great scale. On this occasion we are able almost to lay a finger on some proximate links of the chain. Réaumur, the French naturalist, made steel in the early part of the eighteenth century by melting cast iron in a crucible, and in this liquid metal he dissolved wrought iron, the product being, as the reader will now easily understand, the intermediate substance, steel; and this was obtained of course at a temperature which was incapable of fusing wrought iron by itself. He published in 1722 a treatise on “The Art of converting Iron into Steel, and of softening Cast Iron.” For this, and certain other metallurgical discoveries, Réaumur received a life-pension equivalent to about £500 per annum,—a treatment very different from that dealt out by the British to Henry Cort. The action in Réaumur’s crucible is precisely that used on the large scale in Siemens’ open hearth. But this last became possible only when Siemens had worked out his “regenerative stove” or heat accumulator, the development of an idea suggested by a Dundee clergyman in 1817. A general notion of the Siemens’ regenerative stove will have been already gained from the account given before of its application to the modern type of blast furnace. Of the inventor himself, C. William Siemens, it may be observed that he was one of a family of brothers, all 68remarkable for their scientific attainments, and in many of his researches and processes he was aided by his brothers Frederick and Otto. In our article on “Electric Power and Lighting” there will be found some notice of a few of Siemens’ inventions pertaining to those subjects. A still more admirable invention of his is the electric pyrometer, an instrument of the utmost utility for measuring, with an accuracy previously unapproachable, the high temperature of furnaces, etc. Indeed there are few departments of science, pure or applied, which have not been enriched by the researches and contrivances of this distinguished man, whose merits were acknowledged by the bestowal upon him of the highest scientific and academical honours, and also of a title, for he became Sir William Siemens. Fig. 26.—Section of Regenerative Stoves and Open Hearth. Siemens was much engaged from 1846 in conjunction with his brother Frederick in experimental attempts, continued over a period of ten years, at the construction of the regenerative gas furnace. At length, in 1861, he proposed the application of his furnace to an “open hearth,” and during the next few years some partial attempts to carry out his process were made, and he himself had established experimental works at Birmingham in order to mature his processes, while Messrs. Martin of Sireuil, in France, having obtained licences under Siemens’ patents, gave their attention to a modification of his process, by which they succeeded in producing excellent steel. Siemens having in 1868 proved the practicability of his plans by converting at his Birmingham works some old phosphorized iron rails into serviceable steel, a company was formed, and in 1869 the Landore Siemens’ Steel Works were established at Landore in Glamorganshire, and a few years after, these had sixteen Siemens 69open hearth melting furnaces at work, giving a total output of 1,200 tons of steel per week. The number of furnaces was subsequently increased. Extensive works specially designed for carrying out the Siemens and the Siemens-Martin process were shortly afterwards erected at other places, as at Newtown, near Glasgow, Panteg in Wales, etc. In Great Britain the open hearth process gradually gained upon the Bessemer, until in 1893, when the total output of both kinds amounted to nearly 3,000,000 tons, this was almost equally divided between them, and since that period the steel made by the former has greatly surpassed in amount that made by the latter. How the regenerative stove, or heat accumulator, works, and how it is applied in the open hearth process, the reader may learn by aid of the diagram Fig. 26, in which however no representation of the disposition of the parts in any actual furnace is given, nor any details of construction beyond what is necessary to make the principle clear. On the right and on the left of the diagram will be seen a pair of similar chambers which are shown as partly below the level of the ground S S´, such being a usual disposition. The outer walls of these chambers are thick and the interior is entirely lined with the most refractory fire-bricks, of which also is formed the partition in between each pair of compartments, as well as the passages from the top of each opening on the furnace H. Each chamber or compartment is filled with rows of fire-bricks, laid chequerwise so as to leave a multitude of channels between. At the bottom of the chamber on the left let us suppose atmospheric air to be admitted by the channels A, A, A, and a combustible gas which we may take to be a mixture of carbonic oxide with some hydrogen is admitted in the same way to the second compartment on the left through the passages G, G, G. Supposing the apparatus quite cold in the first instance, the gas would ascend into the furnace H as shown by the arrows, because it might be drawn by an up-draught in a chimney connected with the six chambers shown at the bottom of the right, and it would also tend to rise up into the space H by its lighter specific gravity, and there it could be set on fire, when a volume of flame would pass across to the right, a plentiful supply of air rushing in through the air chamber from A, A, A, and the products of the combustion, mainly hot carbonic acid gas and hot nitrogen gas, in passing through the right-hand chambers, would make the bricks in both compartments very hot after a time, for the current would divide itself between the two passages, as indicated by the divided arrow. We have not shown the valves by which the workman is able, by merely pulling a lever, to shut off the air supply from A, A, A, and of gas from G, G, G, and put these channels into direct communication with the up-draught chimney, at the same time supplying gas at G´, G´, G´, and air at A´, A´, A´. These rise up among the now heated bricks each in its own compartment, but mix where they enter the furnace H, now hot enough to set them on fire, and the gaseous products of combustion, hotter now than before, descend among the fire-bricks of the left-hand compartments, heating them in turn. After another period, say half an hour, the valves are again reversed, and again gas and air both heated burn in the space H, and their products supply still more heat to the right-hand compartments. And so the action may be continued with a great temperature each time produced by the combustion of the combining bodies at increasingly higher temperatures. Thus, if cold gas and air by combination give rise to 500° of heat, when the same combine, at say the initial temperature of 70400°, the result would be a temperature of 900°; if burnt at this latter degree, then 900° + 500° would be reached, and so on. It would seem as if there were no limit to the temperatures obtainable in this way. But the nature of the materials of which the furnace is constructed imposes a limit, for even the most refractory matters yield at length, and the working would come to an end by the fusing of the brickwork. The diagram is a section through the length of the hearth (for it is usually oblong in plan), and the low arch above H being exposed to the fiercest heat, is formed of the most refractory “silica bricks,” that is, bricks made of coarsely ground silica held together with a little lime; yet this extremely resisting material is acted upon, and the arch has to be renewed every few months or sometimes weeks. The hearth itself is supported by massive iron plates, shown in the diagram by the thick lines, above which is laid a deep bed L, of quartz sand or ganister, or where required a basic lining, beaten hard down, and forming a kind of basin with sides sloping down in all directions to a point immediately below the centre of the fire-brick door D, where is the aperture for tapping, stopped by a mixture of sand and clay until the metal is ready for drawing off, when it runs outside into an iron spout lined with sand and is received into the ingot moulds. B in the figure represents the “bath,” as it is called, of molten metal, which, in the larger furnaces, where 20 tons of metal is operated on at once, may occupy an area of 150 square ft. It need hardly be mentioned that there has to be a certain adjustment between the volumes of air and of gas that pass into the regenerative stoves, in order that the best effect may be obtained. Besides the limit of temperature occasioned by the nature of the materials, there is a chemical reason why the regenerative stoves cannot increase the temperature indefinitely. It is noticed that when the temperature of the furnace has become very high indeed, the flame over the hearth assumes a peculiar appearance, being interrupted by dark spaces. These are attributable to what is called in chemistry “dissociation,”—in this case the dissociation of carbonic acid gas, which by the heat alone separates into carbonic oxide and oxygen gases. In the same way these gases refuse to combine if brought together heated beyond a certain temperature. This phenomenon of dissociation is a general one, for it is found that for any pair of substances there is a characteristic range of temperature above or below which they refuse to combine. The gas used in these stoves is either unpurified coal gas, or that produced by passing steam over red-hot coal or coke. We have spoken of the Siemens and the Siemens-Martin open hearth processes. In the latter a charge of pig iron, say 1½ tons, is first melted on the hearth, then about 2 tons of wrought iron is added in successive portions, and in like manner nearly as much scrap steel (i.e. turnings, etc.), the final addition being half a ton of spiegeleisen containing 12 per cent. of manganese. A furnace of corresponding dimensions will allow of three charges every twenty-four hours. In the Siemens process it