e
good effect is secured of heating the conveyor from end to end uniformly
and gradually. This applies particularly to gas works conveyors.

For the service of coke ovens the plate or tray conveyor might be
suitable because more gentle. It must be remembered that coke oven
conveyors must be of large capacity, and moreover in this case there is
more scope for cooling the coke in front of the oven before it is
removed to the conveyor, the work being all effected in the open.

_Elevators._--This term is here confined to its proper meaning (in
English engineering treatises) of a device for raising material in a
vertical or slanting direction by means of buckets attached to endless
belts or chains. Lifts for passengers are also sometimes termed
elevators (q.v.), and in America the term is also currently applied to
the granary or warehouse in which grain is stored (see GRANARIES).

In the bucket elevator, an endless belt or chain runs over terminal
pulleys which are fixed at different levels, the distance from centre to
centre of these pulleys beings known as the length of the elevator. The
design and construction of the elevator will be varied to suit its
purpose. Grain elevators are invariably cased in wooden or iron trunks,
and the head and foot are also of wood or iron, iron trunks being
particularly used in so-called fire-proof buildings. The trunk of the
grain elevator (fig. 14) is almost always vertical whilst the band to
which the buckets are attached may consist of leather, cotton, hemp,
webbing or other suitable substances. When an elevator is intended for
lifting heavy materials, such as coal, coke or cement, it is usually set
at a slant (figs. 15 and 16), and the endless belt is replaced by one or
two strands of endless chain which support the buckets and run over the
terminal sprocket wheels. The buckets are attached to the links of the
chains, and to prevent these heavy buckets and chains from sagging in
their inclined position, rollers or more often short skidder bars are
fixed to each bucket, sliding on well-oiled angle bars on each side of
the elevator frame.

[Illustration: FIG. 14.--Grain Elevator.]

Both grain and mineral elevators are usually fitted with tightening
gears to keep the belt or chain taut; these are generally placed at the
lower or well end so as not to interfere with the position of the upper
terminal, which is almost invariably the driven one. The tightening of
the band at the bottom t