elevator with one
or two buckets. Essentially a heavy load lifter, it is intended for
material of too large a bulk to be handled economically by ordinary
elevators, and is employed for lifting in either a vertical or, more
often, an inclined direction.

For elevating materials, such as large coal, iron ore, limestone, &c.,
which are too large to be fed into ordinary elevators, and must
therefore be handled intermittently, the single bucket elevator or hoist
may be used with advantage. But as the essential use of mechanical
appliances for handling material is to save human labour as far as
possible, that hoist will prove the most economical the operation of
which is as automatic as possible. The Americans seem to have been
pioneers in the construction of _furnace hoists_, which form the
principal elevators of this class, but some excellent examples of the
modern furnace hoist are now to be found in Great Britain and elsewhere
in Europe. Generally speaking, a furnace hoist consists of an inclined
iron bridge girder set at an angle to the upright shaft of the furnace.
On this incline are laid rails for the ascent and descent of the bucket,
which in this case is known as a skip and is provided with suitable
wheels, while the hoisting gear manipulating the skips by a steel rope
is erected on or near the ground level. The rails when they approach the
upper terminus are usually bent in a more or less horizontal position so
as automatically to tilt and thereby unload the skip. To attain the same
end, the rails supporting the back wheels of the skips may be bent at
the terminus, or the back wheels may have additional wheels of a larger
diameter on the other side of their flanges, so that during the ascent
and descent the skip runs on its four normal wheels, while at the upper
terminus the outer and larger back wheels engage with short lengths of
extra rails and thus tilt and effect the automatic clearance of the
skip. The dead weight of the skip may be balanced by a counter weight,
or double tracks may be laid, so that the empty skip descends on one
track whilst the loaded skip is being raised on the other. In this case
the distributing hopper at the top of the furnace has an elongated shape
so as to take the charges alternately from buckets on either track.
Again, the two tracks may be laid one above the other, so that one skip
runs on the upper rails and the other on the lower. The two buckets will
pass each other at about the