a powerful volute spring which is
compressed and released by a crank and connecting rod, in place of
being connected to one-half of the conveyor. Two sections of a Zimmer
conveyor can be made to run in opposite directions by merely reversing
the inclination of the spring legs; in such a case the sections of a
trough would be connected by a flexible coupling. Conveyors of this
type have been used in lengths up to 500 ft., and in widths of over 6
ft. The feed can be received or discharged at any desired point in the
length; for drawing off material at intermediate points it is only
necessary to open a slide in the bottom of the trough. If a great
increase be desired in the capacity of this conveyor the connecting
rod may be attached, not to the trough at all, but to the spring legs
at a point of about a third or half-way from the base, so that the
free ends of the legs can swing the trough backward and forward; by
this means the stroke is amplified and consequently the capacity is
increased, while the driving power required is practically the same.

[Illustration: FIG. 9.]

The power absorbed by the Zimmer conveyor is comparatively small; a
length of 100 ft. conveying a load of 50 tons per hour takes 8.75 h.p.
With a speed of 300-370 revolutions per minute of the conveyor, the
material will traverse 40-70 ft. per minute. The gentle action of this
appliance has caused it to be largely used in dealing with friable
materials, such as coal. The simplicity of the mechanism leaves little
to get out of order, and the entire absence of travelling gear, such
as supporting rollers, is a valuable feature. The capacity of the
conveyor may be sensibly increased by running it on a downward
gradient, while the capacity will be correspondingly diminished by
working in an upward direction. Among many purposes for which this
type of conveyor has been found suitable is that of a drainer in
connexion with coal-washing plants. A perforated plate at the head
will allow the water to escape, while the coal is carried to the other
end. A slight upward slant permits the water left with the coal to run
back and escape. In colliery work this conveyor makes a suitable
picking table. The motion of the trough, while not so fast as to
baffle the pickers, has the advantage of uniformly spreading the lumps
of coal. This apparatus also lends itself to the grading of coal. All
that is