STATE GEOLOGIST. 259 
of chilled iron. One shaft revolves in fixed, the other in movable boxes. 
The movable ones are held up toward the fixed boxes by means of 
powerful springs, or also by levers and weights. Power is usually 
applied by means of gears and pulleys. The shafts are of mild steel. 
Fig. 34. Diagram illustrating the operation or crushing rolls. 
As has been said, rolls are not typical rough grinders, being used 
only by the Edison Portland Cement Co. These are 5 feet in diameter, 
with 5 feet face, and are provided with striking pieces, pyramidal in 
shape, 4 inches high. Below these large rolls smaller ones for inter- 
mediate grinding are arranged, 3 feet in diameter and 3 feet long. 
The rolls make about 150 revolutions per minute. ‘The journals are, of 
course, extremely heavy. Both rolls are driven by pulleys direct. 
These may run loose on the shaft, but not until they have overcome 
the friction of band brakes, which are held up by springs with great 
tension. These rolls can take a charge of about 5 tons, and the capac- 
ity when running 150 revolutions per minute is approximately 
300 tons per hour. However, on dumping in a charge, the speed 
is decreased and it takes some time to pick up again, requiring about 80 
horsepower to do this. This change of retardation and acceleration takes 
up about one-sixth of the time. The average power consumed is 55 
horsepower. The distance between the striking knobs is 10 inches. 
INTERMEDIATE GRINDING MACHINES. 
Of machines of this kind we have the following types: 
Rolls. 
Disintegrator. 
Kent mill. 
Ball-mill. 
Dry pan. 
mike po 
Rolls.—It cannot be said that rolls are now used in American 
cement works with the exception of one, but their xeneral efficiency 
