covered
with perforated steel plates with holes 1-1/4 inches in diameter. All
lumps larger than the holes pass out of the end of the cylinder, and
are carried by a pan conveyor to crushing rolls for further treatment.
Worthless stones carried in the ground are picked out by hand as the
lumps move along on the conveyor.
The
pulverized ground which passes through the screen holes of the
cylinders is fed into shallow circular pans, divided so as to form an
annular space, four feet in diameter, between the outer and the inner
rim (see figures on pages 13—14). Here the ground is swept around by
revolving arms attached to a vertical shaft, and carrying wedge-shaped
teeth (see figure). These teeth are set to form a spiral which forces
the diamonds and other heavy minerals to the outer side of the pan,
while the lighter
