2 BULLETIN 691, U. S. DEPARTMENT OF AGRICULTURE. 
was secured, new methods of use devised, and the character of avail- 
able crude materials and their method of refining changed, these 
typical specifications were modified from time to time by the Office. 
Owing to the fact that they are widely distributed among engineers 
not in close touch with the reasons necessitating their modification, 
certain of the older specifications are still in use, although not up to v 
date. In so far as possible these engineers have been notified of 
changes which the Office has seen fit to make, but as, in many cases, 
the originals have been passed on from one engineer to another all 
have not been informed of the changes which have been made. 
Very recently all of the typical specifications for bituminous ma- 
terials prepared by the Office have been revised, and it has been con- 
sidered advisable to publish them in bulletin form for more general 
distribution. The specifications given in the following pages, there- 
fore, are intended to supersede all prior specifications for bituminous 
materials issued by the Office. It is felt that these revised specifica- 
tions have been made as brief and simple as possible without sacri- 
ficing to too great an extent three essential purposes, which are (1) 
to secure a suitable grade of material, (2) to insure reasonable uni- 
formity of supply, and (3) to sufficiently identify the material by 
type. 
Xo specification should be encumbered with unnecessary require- 
ments, and test limits, of course, should be thoroughly practicable 
from a manufacturing standpoint. With this in mind the coopera- 
tion of all manufacturers of bituminous road materials was sought. 
In July, 1917, a set of tentative revised specifications was sent to all 
manufacturers who were thought to be interested, with a request 
that they review the specifications, suggest changes if they so de- 
sired, and state the reasons for such suggested change. In addition 
the manufacturers were requested to furnish to the office samples of 
each of their products which conformed to the specifications, to- 
gether with samples of any products which would meet the specifi- 
cations if changed in accordance with their suggestions. 
Upon receipt of all of the information that could be secured, the 
comments of the manufacturers were tabulated, together with the 
test results which they furnished and the analyses of the samples 
examined in the laboratory of the office. These data were carefully 
studied and when justified, modifications were made in the tentative 
specifications which in their revised form are presented in this 
bulletin. The forms of specification adopted are in general those 
recommended by the first conference of State Highway Testing 
Engineers and Chemists. 1 
1 U. S. Department of Agriculture Bulletin 555. 
