to which are a number of screens of various sizes, designed
to separate the coal into the different grades in which we
see it in the market. The so called waste coal is that por
tion which passes through the smallest screen used, and is
thrown aside with the slate and other waste material that
comes from the mine. The great heaps of this waste coal
,and slate which soon form about every mine are called "culm
heaps" or "culm banks."
The accumulation of these heaps of fine coal in the
Pennsylvania coal fields, dates from the introduction of the
anthracite coal "breaker." Before this machine began to
be used the coal was taken unbroken to the market, and the
waste heaps therefore received very little coal, but consisted
chiefly of slate and slatey coal, which are the surrounding
rocks of the coal in the mine. When these breakers were first
used, in the early fifties, there was very little demand for
chestnut coal, consequently coal of this size and, of course,
all smaller sizes went to the culm heaps. This made the
percentage of coal wasted very large indeed, and during the
first ten years in which breakers were employed in Pennsyl
vania, for every ton of coal that was sold, 1.3 tons was dis
carded as waste. In the early sixties not only chestnut but
also pea coal began to have a market, and in the following
ten years increased the amount of coal sold to about 65,000,-
4)00 tons more than had been been sold in the previous de
cade, and reduced the amount of waste to an equal with the
amount sold. Still the quantity of wasted coal was alto
gether too large, and this fact excited the ingenuity of those
interested in the industry, with the result that machines
called jigs were invented for the preparation of smaller sizes
of coal. Thus buckwheat coal and rice coal were produced
for the market. These machines greatly checked the in
crease of waste coal, and ever since their invention in the
.early seventies, the amount of waste in proportion to the
coal sold has steadily decreased. The average amount of
coal sold per year from the Pennsylvania mines, since the