32 BULLETIN 691, U. S. DEPAETMENT OF AQBICULTUEE. 



250° F. to 300° F. before mixing. The mixture should contain 

 from 7 per cent to 11 per cent bitumen and will vary within these 

 limits with the character of the rock and the exact grading of 

 the aggregate. The hot mixture should be deposited in a uni- 

 form layer over a concrete or a well-compacted broken stone or 

 gravel foundation to such depth that it will yield a uniform layer 

 two inches in thickness after thorough rolling. A seal coat should 

 not be necessary on this type of pavement, which is usually main- 

 tained by patching with the same mixture used in construction. 



