Page:McClure's Magazine v9 n3 to v10 no2.djvu/464

86 From the steam shovel the rocks, weighing five and six tons, are conveyed to the crushing-plant. The crushing-plant is a large eccentric building, from the open sides of which extends massive iron framework upon which electric cranes are operated. To the casual observer the building seems to be little more than a large platform, the under part of which is closed in, and the upper part of which seems to contain nothing more than an expectant group of men whose business it is to anxiously watch big boulders as they are swung inward by the cranes and dropped into a large square hole in the floor. As each rock disappears, the strained facial expression of each man is enveloped in a cloud of white dust, and a dull boom! boom! announces that some convincing change has taken place in the material. As a matter of fact, the giant, or largest, rolls of the crushing-plant are made to revolve in the first story of the building, and the rock is dumped into the pit which leads down to them from the second story. This remarkable crushing-apparatus consists primarily of two immense rollers over six feet in diameter and five in width.

The rounded surfaces are studded with great teeth, and the great rolls themselves run within eighteen inches of each other. Looked at from above, these monster crushers, revolving with a surface speed of a mile a minute, and weighing 237,000 pounds, form probably the most awe-compelling abyss in the world. The relentless fangs, constantly traveling inward and downward, impress the mind more strongly

than could any bottomless pit, and the feeling becomes all the more intense when one learns that beneath them is another set of rollers somewhat nearer together, with a serrated surface, more wicked if anything in its action than the teeth above. These giant rolls will receive and grind up five and six ton rocks as fast as they can be unloaded from the skips. A skip-load of rock every forty-five seconds was the rate at which the plant was operated for the purpose of testing the capacity of the rolls, but an average of 300 tons an hour is considered a fair running capacity.

It may surprise the superficial observer to learn that the great Corliss engine which operates the rolls takes no part whatever in the crushing process. There is something of a trick in it, but it is an effective answer to the engineers who declared that no machine could be made strong enough to stand the strain of crushing these great boulders. It is the momentum of the seventy tons of metal contained in the moving parts of the rolls which does the crushing. The engine supplies just power enough to run the rolls at a very high speed. If anything—a rock, for instance—drops in between the rolls so as to in any way impede their progress, a clutch by which the rolls are connected to the engine allows the latter to let go its hold. After that the momentum of the rolls does the work of crushing, the engine, of course, immediately catching hold again the moment the impeding rock has been crushed and passed through to the next set of rollers. One might think for the moment