334 University Geological Survey of Kansas. 
will therefore be seen that if one screen has a mesh of 25 mm., 
any other screen used with it must not have a mesh above 
50 mm. 
KINDS OF SCREENING SuRFACES.—Three kinds of screening 
surfaces are used, namely, wire cloth, punched metal, and 
cast iron. 
Woven wire and perforated metal screens are in more gen- 
eral use, while cast iron is seldom used except in the cells of 
the rougher jig. 
Wire screens have the widest range of usefulness and are 
more durable on account of toughness; they also have the 
special advantage that almost any degree of fineness can be 
obtained. 
Punched or perforated metal screens may also be made of 
any degree of fineness, but the waste of metal is too great 
and capacity too small. Up to three-fourths inch, the ca- 
pacity of punched metal screens is probably largest, as the 
openings are smooth and the metal uniform. They are also 
quite durable on account of their uniformity and thickness. 
Cast iron screens are cheapest for large openings, but the 
plates become too thick for openings less than one-half inch. 
They probably resist the action of acid waters better than 
other forms, unless it is woven wire screens of brass or bronze. 
They are hard to cast without warping, which is one of the 
principal objections to their use. 
The following data have been given for the design of re- 
volving screens: 
Inclination of screen surface, from 3° to 6°. 
Diameter of drum, from 2 to 8 feet. 
Length of each segment, 2 feet. 
Tangential velocity, 24 to 3 feet per second. 
Velocity of under water, 2 feet per second. 
Revolutions per minute, from 18 to 25. 
Capacity (mixed ore), 100 cubic feet per hour. 
Capacity (pea and coarse), 60 cubic feet per hour. 
Capacity (sand), 25 cubic feet per hour. 
The speed of revolving screens should be carefully regu- 
lated, as too high a speed causes the ore grains to be carried ~ 
too high, due to the centrifugal force holding them to the 
sides of the screen, but the higher the grains are carried in the 
Sut G2 NG © Sf 
