354 University Geological Survey of Kansas. 
indestructible, as far as acid waters are concerned, and it is 
claimed that the wood becomes harder and better adapted for 
the purpose the longer it is acted upon by the acid waters. 
WEAR OF SCREENS. 
The life of a screening surface depends on what kind of an 
apparatus it is placed in; if in a jig cell, the wear from the 
mechanical abrasion is comparatively slight, as only the softer 
materials pass through (as arule), while the action of the acid 
waters is a maximum; in shaking and rotary screens the re- 
verse is the case, the mechanical action is the maximum, and 
the chemical action is less, though very nearly as great, as in 
the jig cells. : 
As definite data could not be obtained except by a special 
experiments, and as such were not possible, the following fig- 
ures are at best approximate. The life of iron wire screen in 
jig cells is from two to four a week, while, in the rotary screen, 
two to three weeks, Brass wire screens last from one to two 
months in jigs, but are not used in rotary screens. 
There are about 130 square feet of screen surface in the 
cleaner and rougher jig (twelve cells, 36x42 inches), and in 
the neighborhood of 73 square feet on two rotary screens (6 
feet long; dimensions of large and small ends, 23 and 2 feet). 
These figures are small for some mills and large for others. 
The cost of iron or steel wire screen is, for the size (mesh) 
usually employed, about 60 cents per square foot, while brass 
cloth is $2.50. The cost of equipping a plant requiring the 
amount of screening surface given above will be, for the 
jig, $78, for rotary screen, $43.80, approximately. The total 
for both jigs and rotary screens is then $121.80. The jig 
screens last probably four weeks, the rotary screens about 
three weeks, constant use. The cost for iron jig screens 
would then be $19.50, steel, $20.31; and for iron rotary 
screens, $14.60, brass, $15.20, per week. The cost of iron 
screens would then be $34.10, and for brass, $35.51, per week, 
or $4.80 and $5.07 per day. 
There is little difference in the cost of perforated metal 
and wire screening. An advantage in favor of brass screens 
is, besides being more durable, that the worn-out screens 
can be sold for 7% to 8 cents per pound. 
