300 University Geological Survey of Kansas. 
for the sorted product, is provided in one side of the outer 
pyramid, B, and at a point near the apex, F, while on one 
side of the base, several inches from the edge, is attached a 
discharge launder, C, for the wastes or overflow. The 
material to be treated is mixed with a proper amount of water 
-and fed to the inner box, A. Passing downward through the 
opening, H, the then ascending current encounters the four 
sides of the pyramid, B, and is deflected upward between the 
sides of the pyramids and finally overflows at C. Any ac- 
cumulation of sorted material is drawn off from time to time 
through F. 
Owing to the method of feeding the classifier, also the 
position of the discharge for wastes, the level of the water in 
A is higher than in 6; consequently the pressure due to the 
difference in height of water columns causes a positive down- 
ward flow. The velocity of the water currents are further 
augmented by the gradually converging sides of the inner 
passage, A, but, when once past H, the velocity remains con- 
stant and uniform. An increased velocity at this point could, 
however, be produced by making the angle of A greater than 
that of B, which is occasionally done, when too much material 
tends to remain in the classifier, so choking the discharge, F. 
GRAVITY SPOUTS OR LAUNDERS. 
Gravity spouts or launders are forms of conveying appa- 
ratus used in transferring the material to be concentrated, 
with its transporting medium, water, from one part of the 
mill to another. They consist of closed or open troughs 
made of six-inch boards nailed into a square, seldom a Y form. 
Occasionally the spouts are lined with iron spouting or 
sheathing placed within the wooden trough or spout to pre- 
vent undue wear. 
These launders are built of various sizes as the require- 
ments of the mill demand. They are, however, from four to 
six inches wide, and about the same in depth, and should be 
given a pitch sufficiently great to insure the complete and 
rapid discharge of the material handled. The proper slope 
for a square trough is one or two inches per foot for medium 
sizes, and without an excess of carrying water. 
