larger ones, were positively
driven, reducing the rock to pieces of about one-half-inch size, or
smaller. The whole crushing operation of reduction from massive boulders
to small pebbly pieces having been done in less time than the telling
has occupied, the product was conveyed to the "Dryer," a tower nine
feet square and fifty feet high, heated from below by great open furnace
fires. All down the inside walls of this tower were placed cast-iron
plates, nine feet long and seven inches wide, arranged alternately in
"fish-ladder" fashion. The crushed rock, being delivered at the top,
would fall down from plate to plate, constantly exposing different
surfaces to the heat, until it landed completely dried in the lower
portion of the tower, where it fell into conveyors which took it up to
the stock-house.

This method of drying was original with Edison. At the 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 a crushing-machine which was subsequently
named the "Three-High Rolls," and which practically reversed the above
f