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Page:Popular Science Monthly Volume 24.djvu/553

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537
FIFTY YEARS OF MECHANICAL ENGINEERING.

ton; to-day they are worth thirty-eight dollars. It is confidently predicted by those who have made it a study, that the downward tendency can not be checked, and that one cent a pound will be reached as soon as the experimenters have worked out plans now in hand.

Considering the many improvements which are now proposed and tested, we can safely assume that the steel-plant of the future will differ widely from the plant of to-day. All the available heat and all the useful elements in the ore will be used. Briefly this is as follows: The ores, limestone, and fuel will be placed in the furnace, the molten metal will be run to converters, and there the foreign elements will be removed by a blast, the metal then recarbonized and cast into ingots, the ingots will be rolled into blooms, then the bloom into rails, and the rails will then be placed on small cars, and, while at a temperature of about 1,000° Fahr., will be placed in the flues of steam-boilers until they have given up about 700° Fahr., and then passed on as finished. The slag flowing from the blast-furnace will be placed on cars, and, while at a temperature of 3,000° Fahr., be run into the flues of other boilers used to generate steam for operating the blowers, rolls, etc. This, in brief, is one of the proposed steps in steel-making, viz., the utilization of all the heat in the coal, and afterward all the heat given to the iron and slag by the coal; by so placing the iron and slag as to give up their heat again to boilers used to generate steam for the roller-mills and blowing-engines, which in turn aid the smelting of the iron.

A rail-mill of 500 tons a day, at a low estimate, would secure heat to run a 1,000 horse-power battery of boilers from the cooling rails alone, and 4,000 horse-power in heat from the slag. Hence the steel-plant of the future will have no heating-furnaces, no gas-producers, no coal-consuming boilers, no cupolas, no ash-piles, and no fuel to be consumed except that required to melt the iron. The converter-slag can now be used instead of limestone by the new process. This, in brief, will be, it is confidently predicted, the new rail-mill of the immediate future. Everything is done by the aid of air, steam, and water. Muscle will be in little demand, brains at a premium. In 1832 cast-iron bridges existed of short span, but wrought-iron had not been used. To-day we think little of trusses of 500 feet span, and suspension-bridges of 1,000 feet; while it is proposed to build a steel truss-bridge over a mile long, with two spans of 1,700 feet each. In the power-printing press, an invention of the eighteenth century, we find that the last half-century has wrought wonders. In 1832 the best presses could turn out about 1,000 poorly printed sheets of printed matter; to-day, thanks to Hoe's revolving type and the processes of electroplating and stereotyping, we have presses capable of printing 50,000 impressions an hour; and, what is almost as wonderful, it will number, fold, and stick together the whole. Such a machine costs about $100,000.