Page:McClure's Magazine v9 n3 to v10 no2.djvu/457

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EDISON'S REVOLUTION IN IRON MINING.

79

THE STEAM SHOVEL LAYING BARE THE VEIN OF ORE-BEARING ROCK.

After the timber has been felled the ground is surveyed with a magnetic needle. The concealed ore-bearing rock is then staked off. The shovel works around the ledge, cleaning away the underbrush, the dirt, and the clay. Then the rock is blasted into boulders. The shovel picks up these boulders, which sometimes weigh as much as six tons, and loads them into trays, or "skips," resting on flat cars. The cars convey the rock to the crushing-plant. This shovel is the biggest in the world; it weighs 200,000 pounds, and will clear away rock at an average rate often tons a minute.

nets, sorting out the iron ore which these rocks contained. After a while the little building lost the distinction of being the only house so occupied, for other small buildings were erected; and then a steam plant began to make the surrounding hills echo with the puff of its engines and the continual churning sound of rock-crushers. Out of this humble beginning has grown the present great establishment. All the original machinery has now disappeared; and all the first buildings, except one small one now used as an office, have been torn down. The first steam plant and the first crushers have proved inadequate to the work.

Mr. Edison had planned the work upon a comprehensive scale, but he had reckoned upon finding equal to his needs crushing-machinery already devised. At last, however, the conviction forced itself upon him that he must invent a new method of extracting the ore from the mountain-side; construct crushing-machinery larger than had ever been used before; introduce a magnetic separating system of his own; devise some way of cementing the iron dust into lumps, so that it could be used in the blast furnace; and, altogether, to re-create the entire enterprise on a plan even more gigantic than his first conception. Engineers, tried engineers, used to large operations, smiled incredulously. Some of them spoke of the enterprise as Edison's "hobby;" others, less charitable, called it his "folly." Those of a calculating turn of mind showed him on paper that no machine could be constructed powerful enough to crush successfully five, six, and seven ton rocks; or if such a machine could be constructed, that it would never withstand the terrific jar which would result. This particular difficulty, it may be said in passing, Mr. Edison surmounted so completely that less than one hundred horse-power is required to reduce rocks weighing six and seven tons to dust in less than three seconds from the time they are thrown into the crushing-machine. Other difficulties were overcome as com-