CRANE. | Theory of Ore Concentration. 337 
DOWN STROKE 
i 
i he 
Z65 
ame 
Oo. ee 
Saeeet Se boas i seer SS 
x 
=) 
ix 
B 
a. 
=) 
Fig. 64. Jig plunger provided with valves. 
with soft and pliable, the latter with finely divided, ore, 
slimes, etc. 
The movement of the plunger is effected by an eccentric. 
Figure 56. The eccentrics are so arranged that while some 
are descending others are ascending, so distributing the strain 
upon the driving shaft, and thus neutralizing any vibration 
that might result from all acting in unison. The process of 
jigging is also more regular when the plungers descend in 
order successively, rather than when all rise and fall to- 
gether. The eccentric used is the slide or slotted form, and 
allows an adjustment of the stroke from nothing to two and 
one-half tothree inches. Figure61. Thespeed of the various 
jigs ranges from 175 to 450 revolutions per minute; occasion- 
ally a speed as high as 500 to 600 revolutions per minute is 
employed, but is not advisable except in special cases. The 
length and speed of stroke should be so regulated as to pro- 
duce a current of a velocity determined by the size and spe- 
cific gravity of the particles treated. The larger and heavier 
the particles to be moved the greater the velocity required. 
The velocity of rising water currents is regulated by the length 
of the stroke, time of stroke, and amount of under water. The 
length of the stroke should be between two and four times 
the diameter of the grains to be moved—the former for 
coarse and the latter for fine material. There should be an 
increase of from five to ten strokes for each grade treated. 
