24 
BULLETIN 220, U. S. DEPARTMENT OF AGRICULTURE. 
jaw returns it grips the stone and crushes it. The maximum size of 
the product is determined by the distance between the jaw plates at 
the lower edge. 
The essential feature of the gyratory crusher consists of a per- 
pendicular iron shaft which revolves with an eccentric motion. 
Around the top of the shaft, which is conically shaped, is a hollow 
iron receptacle somewhat resembling an inverted bell. By the 
eccentric motion of the shaft the conical portion crushes the rock 
alternately against different sides of the inner surface of the bell. 
Fig. 2.— Model of road grader. 
ROAD GRADERS. 
Figure 2 shows in miniature a road grader which is used in building 
earth roads and in preparing the subgrade for hard-surfaced roads. 
The frame supports an adjustable scraper blade, the front end of 
which may be used to plow a furrow, while the rear end pushes the 
earth along the surface of the blade toward the center of the road or 
distributes it smoothly. The blade may be set at any angle or tilted 
either backward or forward according to the work to be done. 
It is advisable to use the grader when the ground is soft, preferably 
in the early summer, in order to give the loose earth time to settle 
and pack before the fall rains begin. If the work is done in the fall 
not more than 3 or 4 inches of loose earth should be put on at one 
working. 
ADDITIONAL COPIES 
OF THIS PUBLICATION MAT BE PROCURED FROM 
THE SUPERINTENDENT OF DOCUMENTS 
GOVERNMENT PRINTING OFFICE 
WASHINGTON, D. C. 
AT 
15 CENTS PER COPY 
