10 BULLETIN. 257, U. S. DEPARTMENT OF AGRICULTURE. 
flowed readily and, after standing a few minutes, entirely pene- 
trated into the rock course. Sand was then applied and swept into 
the voids. The sand dressing, however, while filling the voids, did 
not incorporate with the bitumen, but remained for the most part 
dry and loose. The individual tar-coated rock particles were left 
projecting and unprotected and would have worn. away rapidly 
under traffic. All free sand was therefore swept from the surface, 
and a light coal tar was applied cold at the rate of 0.33 gallon per 
square yard and allowed to stand for about four hours until com- 
pletely absorbed. The surface was then covered with sand and 
thoroughly rolled. The sample of the light tar was lost in shipment, 
and consequently no analysis 1s given. 
EXPERIMENT No. 3 (REFINED CoaL TAR—PENETRATION MurTHop). 
Location: Station 1+-94 to station 34.68.8=174.8 feet. 
Area: 291.5 square yards. 
Material: Refined coal tars, analyses of which are given in Table 5. 
Method.—The general nature of this experiment is the same as that 
of the preceding, except for the omission of a second application of 
bituminous material and the use of dustless screenings instead of sand. 
From station 3+25 to the end of the next experiment heavy rains 
had so bonded the rock surface that it had to be harrowed, regraded, 
and rolled in order to provide for suitable penetration. The smooth- 
ness of the original cross section could not be restored, and the surface 
of this portion of the road remains slightly irregular. The applica- 
tion of bituminous material was made at the rate of 1.20 gallons per 
square yard, and was immediately. covered with dustless screenings, 
filing the voids and thinly covering the surface, which was then 
thoroughly rolled. The screenings crushed somewhat under the 
roller, but seemed to absorb the bituminous material and form a 
firm, rigid surface. 
Tar of lot No. 1 was used from station 1+94 to station 2+ 76. 
From the latter point to the end of the section material from a second 
shipment, designated in Table 5 as lot No. 2, was used. This mate- 
rial did not flow and penetrate as satisfactorily as lot No. 1, even 
when heated to 185° C. 7 
EXPERIMENT No. 4 (Restmuant ASpHALTIC PETROLEUM—PENETRATION METHOD). 
Location: Station 3+68.8 to station 5+84—215.2 feet. 
Area: 358.6 square yards. 
TABLE 6.—Analysis of residual asphaltic petroleum. 
Spe Gui CpoTavaiin 205/200 Ce oe ee. Seber cc. eine eee ee 0. 980 
PAS MOO OL Uae siete ete Ss wire Niece GS ahah etie ones. ober arm eee te ae Re ee PO we 125 
DUPMIMOIDOIN be wee oes ee Se nk eee. Seek aes Sek Oe eee ee eee 1 eae 143 
Viscosity, Engler; 100ic.ic) at 100° C. specific. oa. -).4 2... 2.22 c ost eee 5, 5 
