To make Bessemer’s steel from pig iron into steel rails requires about five cwt. of small coal, in the form of coke, to melt the pig iron in the cupola; two cwt. to heat the converting vessel and ladle; two cwt. for the blast engine, which converts five tons of pig iron into fluid cast steel in twenty minutes; and, lastly, for rolling the ingots into rails, sixteen cwt. of coal, making a total consumption of twenty-five cwt. of coal, in producing one ton of Bessemer’s steel rails from pig iron. Thus, common iron rails take two tons of coal; Sheffield cast steel rails, ten tons eight cwt.; Bessemer’s steel rails, one ton five cwt.
But we must also consider other points in connection with these figures, in order to arrive at a correct estimate of the saving of coals, effected by the introduction of steel, as a substitute for iron.
Although the cost of Sheffield steel entirely shut it out of the market for rails, it must be borne in mind that it was extensively used for wheel tires, slide bars, piston rods, and other parts of locomotive engines; and here a saving of over nine tons of coal per ton of steel has been effected. Further, it must be borne in mind that at stations where rails are rapidly worn, the saving by the use of steel, as a substitute for iron, must not be simply estimated as a saving made on one ton of each material. For instance, at the London and North-Western station, at Crewe, the iron rails are so rapidly worn, that they require to be reversed every four months, each rail being completely worn out in eight months. Bessemer’s steel rails were first used at this station, and after being in constant use for seven years, they were removed in consequence of rebuilding the station; one side only of the rail having been used, and this was not quite worn out. During the seven years, therefore, that those rails were down, one ton five cwt. only of coal had been employed in the production of each ton of rails used at this station; whereas ten sets of iron rails would have been entirely worn out in that period, each set consuming two tons of coals in its manufacture, or equal to twenty tons of coals for iron rails, as against one ton five cwt. of coals for steel rails; and these, when turned, would be equal to another seven years’ wear on the side not used.
The above is, no doubt, an extreme case, but the same sort of thing goes on everywhere where steel is used, though in a lesser degree. It has indeed been admitted by competent persons, that the rapid destruction of iron rails would have caused a complete collapse of the Metropolitan railways by continued interference with the traffic, while removing the worn-out rails, had not steel been employed.
It should further be borne in mind that the extra strength of steel over iron admits of a reduction of one-third of its weight in all structures, previously made in iron. Thus, a further saving is effected in the fuel consumed for a given work.
The rapidity, with which Bessemer’s steel is coming into use, will be appreciated, when it is stated that the report of the jury at the London International Exhibition showed that the entire production of steel in Great Britain, prior to Bessemer’s invention, amounted to 51,000 tons per annum; while the quantity of Bessemer’s steel, made in Great Britain during the twelve months ending June 1873, amounted to 481,000 tons, or nearly ten times the amount of production prior to the invention. Had this quantity of steel been made by the old Sheffield process, it would have consumed, according to the foregoing figures, 4,401,000 tons more coal than was actually employed in its production. Should this enormous increase in the manufacture continue, as it at present promises to do, in another five years, we may have treble the quantity of steel made in this country with a corresponding saving of fuel.
Reduced consumption of coal in steamers.
In steam vessels a remarkable economy of fuel has of late been attained. In his lecture at Bradford, Mr. Siemens said, ‘A striking illustration of what can be accomplished in a short space of time was brought to light by the Institute of Mechanical Engineers, over which I have at present the honour to preside. In holding their annual general meeting in Liverpool in 1863, they instituted a careful inquiry into the consumption of coal by the best engines in the Atlantic steam service, and the result showed that it fell in no case below 4½ lbs. per indicated horse-power per hour. Last year they again assembled with the same object in view in Liverpool, and Mr. Bramwell produced a table showing that the average consumption by 17 good examples of compound expansive engines did not exceed 2¼ lbs. per indicated horse-power per hour. Mr. E. A. Cowper has proved a consumption as low as 1½ lbs. per indicated horse-power per hour in a compound marine engine, constructed by him with an intermediate superheating vessel. Nor are we likely to stop long at this point of comparative perfection, for in the early portion of my address I have endeavoured to prove that theoretical perfection would only be attained if an indicated horse-power were produced with 1/5.5 lb. of pure carbon, or say ¼ lb. of ordinary steam coal per hour.’
Inventions of Mr. Siemens.
The furnace invented by the Messrs. Siemens is another highly successful contrivance. In melting one ton of steel in pots, 2½ tons of coke are ordinarily consumed. In Messrs. Siemens’ furnace, a ton of steel is melted with 12 cwt. of small coal.