time this adjunct to the plant was required, the best dryer on the market was of a rotary type, which had a capacity of only twenty tons per hour, with the expenditure of considerable power. As Edison had determined upon treating two hundred and fifty tons or more per hour, he decided to devise an entirely new type of great capacity, requiring a minimum of power (for elevating the material), and depending upon the force of gravity for handling it during the drying process. A long series of experiments resulted in the invention of the tower dryer with a capacity of three hundred tons per hour. The rock, broken up into pieces about the size of marbles, having been dried and conveyed to the stock-house, the surplusage was automatically carried out from the other end of the stock-house by conveyors, to pass through the next process, by which it was reduced to a powder. The machinery for accomplishing this result represents another interesting and radical departure of Edison from accepted usage. He had investigated all the crushing-machines on the market, and tried all he could get. He found them all greatly lacking in economy of operation; indeed, the highest results obtainable from the best were 18 per cent. of actual work, involving a loss of 82 per cent. by friction. His nature revolted at such an immense loss of power, especially as he proposed the crushing of vast quantities of ore. Thus, he was obliged to begin again at the foundation, and he devised
