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 centre of the framing, where there will be plenty of room for clearance.