264 University Geological Survey of Kansas. 
A departure from the ordinary method of constructing ro- 
tary screens in this district is seen in 7, figure 47. Occasion- 
ally two cylindrical screens are combined, forming what is 
known as a jacketed screen. The one with the larger mesh 
or perforation has a diameter somewhat less than the outer 
or finer-meshed screen. The diameter of the outer is gener- 
ally four feet; that of the inner, three feet. ‘These screens are 
fastened together as shown in the cut. This form of screen 
is very efficient, but is hard to get at when repairs are neces- 
sary. As many jackets may be employed as desired, but sel- 
dom more than two are used in this district. 
ORE BREAKERS OR CRUSHERS. 
The reduction of ore to any desired size is a difficult task, 
especially with certain gangues and country rock. | 
The method of application of the power of the crusher must 
vary somewhat with the character of material crushed. With 
hard rock, as flint, which is very brittle, the breaking force 
must be applied by a sudden pressure, while the softer ma- 
terials may be disintegrated by a more gradual pressure, or 
by grinding and impact. 
THe BLakE CrusHER.—The Blake crusher is the form uni- 
versally used, and is especially applicable in treating the 
flints of this district, as the crushing surface is small and 
easily replaced, thus reducing not only the wear of the parts 
but also the expense in changing. The power is applied to 
the hinged jaw, which is actuated by a combination of an 
eccentric movement and elbow or toggle joint. 
Figure 49 shows a longitudinal section, through the work- 
ing parts, of a Blake type of crusher, and a top view, or plan. 
The shaft, A, is mounted in bearings on the frame, B, at C 
and D. An eccentric, H, is keyed to the shaft, A. It is en- 
closed by an elongated casting, /, which, when # is rotated, 
is given an up and down movement. In the lower end and 
on the two sides (front and back) of F, are toggle seats, G, 
into which the toggles, H, fit. Different views of the toggles 
and toggle seats are shown in J, figure 65. In the back 
part of the crusher frame are two movable pieces, J and J, 
which constitute the tightening appliance. By turning the 
