Discoveries and Inventions of the Nineteenth Century

by Robert Routledge

Fig. 25.—Model of Bessemer Steel Apparatus.

The development of the Bessemer process soon had the effect of so reducing the price of steel that this material came into use for almost every purpose for which iron had previously been employed, such as railway bars, girders, etc., for bridges, boiler plates, etc., for all which “steely iron” containing only 0·12 to 0·40 per cent. carbon proved admirably adapted. The practical success of the Bessemer process had not long been demonstrated commercially by the inventor and his partners at Sheffield before other firms began the manufacture: so that in 1878 there were in Great Britain alone twenty-seven establishments making Bessemer steel and using 111 converters. It may give an idea of the magnitude the Bessemer steel manufacture had attained even at that time if we quote the cost of erecting a complete plant for two 5–ton converters: it was £44,400, as given in a detailed estimate. In all these cases pig iron from ores free from phosphorus and sulphur had to be used, for as we have seen the converter failed to eliminate these vitiating elements. Imported pig ores had in general to be used, or pig from the limited supply of British hæmatite ores in West Cumberland. The Barrow Hæmatite Steel Company engaged in the production of Bessemer steel on a very large scale, having by 1878 erected no fewer than sixteen converters of the capacity of 6 tons each. In the meanwhile many efforts were made to discover some method of eliminating phosphorus, so that the ordinary qualities of British pig iron, and iron derived in any part of the world from the coarse phosphorized ores, might be available for the converter. Many of the methods then devised proved correct in principle and feasible in practice; but as, for sundry reasons, none of them came extensively into use, we need not here allude to them further.

The solution of the problem was announced in 1879. Some years before, G. J. Snelus had come to the conclusion that with a siliceous lining it would be impossible to eliminate phosphorus in the Bessemer converter, and that some refractory substance of a basic character must be sought for in order that the slag produced should be in a condition to absorb the phosphoric acid as fast as it is produced. He patented in 1872 the use of magnesian limestone as a material for the lining; as that substance when intensely heated became very hard and stony, being in that condition quite unaffected by water. Two young chemists, Messrs. Thomas and Gilchrist, apparently without being aware of Mr. Snelus’s conclusions, had also convinced themselves that the chief deficiency in the Bessemer process was due to the excess of silica in the slag, and in 1874 they began to try the effect of basic linings, and also of basic additions, such as lime, etc., to the charge in the converter, so that the lining itself should not be worn out by entering into the slag. Their results proved that phosphorus could be eliminated when the slag contained excess of a strong base. An example of an operation at Bolckow, Vaughan, & Company’s Eston works with the highly phosphorized Cleveland pig iron may be quoted. The basic-lined converter received first 9 cwt. of lime, then 6 tons of metal. When the blast at 25 lbs. pressure was turned on, the silicon began at once to burn; for three minutes the carbon was not affected, but for fourteen minutes longer it regularly diminished, the silicon keeping pace with it. After the blow had been continued for thirteen minutes from the commencement, the converter was turned down to allow of the further introduction of 19½ cwt. of a mixture of two parts of lime with one of oxide of iron. So long as 1·5 per cent. of carbon remained in the metal the phosphorus was untouched, and at the end of the blow, i.e. when the flame dropped, only one-third of it had been eliminated; it still formed 1 per cent. of the metal. The blast continued for another two minutes brought it down to ¼ per cent., and in one more minute only a trace was left. Most of the sulphur was got rid of at the same time. From Cleveland pig, thus de-phosphorized in the Bessemer converter, large quantities of steel rails were rolled for the 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 remarkable 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 open 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 400°, 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.