CRANE. | Concentration. 327 
second set of rolls, sized, and returned to the rougher, while 
the free or partially clean mineral passes through the bed of the 
jig and comprises the ‘‘hutch’’ of the rougher, which is com- 
monly known as ‘‘smittem.’’ It is conducted to the foot of 
an elevator (smittem) by which it is delivered to the cleaner 
jig; the combined mineral and chert, called ‘‘chats,’’ which 
comes from the bed of mineral on the screens of the rougher, 
is delivered to another elevator (chats), which elevates it to 
a launder, through which it is conducted to a third set of rolls. 
Here it is further reduced, and discharged into the elevator 
handling the material from the first set of rolls, thence by 
revolving screen to the rougher jig. It is evident, therefore, 
that only the hutch of the rougher reaches the cleaner, the 
chats being reduced until it also enters the hutch of the 
rougher or becomes smittem, when it is prepared to enter the 
cleaner. 
The speed of the counter-shaft of the cleaner jig is about 
300 revolutions per minute. When the shaft is in two sec- 
tions, the speeds are 300 and 350 revolutions per minute, re- 
spectively. The jig has six compartments (30x36 inches), 
which are furnished with wire cloth having a mesh varying 
from four to six to the inch. Clean concentrates are obtained 
both in the bed and hutch of the first four or five cells. Both 
hutch and discharge from the first cell are at least galena, 
while the product of the last two or three cells is usually re- 
treated by returning to the elevator which feeds the cleaner. 
The waste from the cleaner escapes into a launder, which 
bears it to the outside of the mill to the tailings pile, or, in 
the latest practice, to classifiers or hydraulic separators. 
Figure 32 shows the general arrangement of a jig room, with 
the relative size and arrangement of jig, elevators, launders, 
-etc., etc., while the arrows indicate the direction of the flow 
of feeds and discharges. 
When sand jigs are employed, the material from the last 
few cells of the cleaner, or the discharge products from the 
classifiers, are delivered to the same. These jigs have a shaft 
speed of 350 to 450 (even up to 600) revolutions per minute, 
and usually from five to six compartments (24x36 inches, 
and are furnished with twelve to fourteen mesh screens). 
