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EDISON’S Edison’s reason for developing this process was to separate low-grade iron ore from the worthless material found with it. In the 1880s, a general belief was that iron ore was growing scarce. Edison had access to 19,000 acres of land that contained, in his words, “over 200 million tons of low-grade iron ore.” He thought that it would be a simple matter to extract the iron and sell it at a good price. And that’s what he set out to do. It was no small operation. His iron mine and ore-processing plant at Ogdensburg, New Jersey, had miles of conveyors, giant rollers that could crush piano-size rocks, and the largest steam shovel in America. The heart of the whole system was a towering structure that housed the ore separator. In this building, powdered rock was hoisted to the top and allowed to fall past a series of screens and large magnets. The iron was deflected by the mag- nets into receiving bins; the sand dropped straight down to be carried away. We can easily make a model of this separator us- ing sand and iron filings as the ore mixture. But we can demonstrate the identical principle in a less messy and more relevant way with the slug (counterfeit coin) rejector. |