under such conditions little will miss the buckets and
drop into the well.

The reason why grain elevators are set vertically, whereas elevators
intended to carry heavy bodies such as coal and ore are generally
inclined at an angle, is that the former can be run at a much greater
velocity than the latter. Grain, for instance, would be uninjured by a
velocity at the delivery end which would fracture coal and seriously
reduce its value, to say nothing of the dust production and the damage
which would be done to the receiving spouts and shoots. Elevators
carrying a light material can be run at a circumferential velocity of
250 to 350 ft. per minute, and if vertically set, will throw the
grain, &c., clear of the elevator into the shoot for its reception. On
the other hand, elevators handling heavy material must be set at an
angle in order to give a clear delivery at a much lower speed of 50 to
60 ft. per minute; in other words, the elevator is so inclined that
the shoot for the reception of the material can be put underneath the
delivering buckets which slowly disgorge their load. To obtain good
results, without taking up too much space, an elevator carrying heavy
material should be set at 40 deg. to 60 deg. to the horizontal. The
same results can be obtained if the main portion of the elevator is
vertical and only the upper portion inclined, or so curved as to bring
the delivery over the shoot. The speed at which vertical elevators
should be run will depend on the diameter of the terminal pulley, that
is, the pulley over which the buckets and bands pass. The centrifugal
force of pulleys revolving at the same speed is in direct proportion
to their diameters, and this is twice as much in a 2 ft. as in a 1 ft.
pulley. It may be taken that the centrifugal force of a pulley will
increase in proportion to the square of its velocity; hence the
centrifugal force of a pulley 2 ft. in diameter running at 50
revolutions per minute will be four times the centrifugal force of a
pulley of the same diameter making only 25 revolutions per minute. It
must not be forgotten that to effect a clean discharge of the buckets
of a vertical elevator, the centrifugal force must be sufficient to
overcome the gravity of the material, because the material thrown off
the delivery pulley in a horizontal direction will be more rapidly
deflected into a parabolic curve the higher its spec