32 BULLETIN 691, U. S. DEPARTMENT OF AGRICULTURE. 
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. 
