8 BULLETIN 586, U. S. DEPARTMENT OE AGRICULTURE. 
Experiment No. 4. — Bituminous Macadam: Trap with Refined Coal Tar Binder 
and Oil Asphalt Seal Coat. 
Location, station 54+55 to station 72+55. 
Total length, 1,800 feet. 
Total area, 3,311.1 square yards. 1 
This experiment differs from No. 2 only in the kind of tar used 
for the penetration course. 
Experiment No. 5. — Bituminous Gravel Macadam, Gravel Being Grouted 
with Mixture oe Sand and Refined Water-Gas Tar. 
Location, station 72+55 to station 77+55. 
Total length, 500 feet. 
Total area, 888.8 square yards. 
The gravel used in this experiment was received from Kichmond, 
Va., and had been washed and screened. The mechanical analysis 
is shown in Table 5. The gravel was spread 3 inches thick, loose, 
and was rolled with a 10- ton roller. The fragments cracked slightly, 
and the surface tended to become wavy under the roller. After 
rolling the gravel, a grout of sand and refined water-gas tar was 
applied for the first 91 feet. The grout was mixed in the heating 
kettle in the proportion of about 3 parts of sand by volume to 5 parts 
of tar. The sand was not dry and considerable foaming in the ket- 
tle resulted. In mixing the materials it was found impossible to 
prevent the sand from settling to the bottom of the kettle, regardless 
of the care used hi stirring, so that this method was abandoned. It 
had been expected to apply 1J gallons of this mixture to the square 
yard. The section was covered with pea gravel, rolled, and a seal 
coat applied later, as described below. The remainder of the experi- 
ment was constructed as follows: A penetration coat of refined 
water-gas tar was applied as in experiment No. 1, and sand, as 
shown in the mechanical analysis of Table 5 was applied by shovels 
to the surface until all voids were filled. The surplus sand was 
swept off and areas showing voids were filled carefully. A seal coat 
of refined water-gas tar and pea gravel to the amount of 0.6 gallon 
of tar and about 0.02 cubic yard of pea gravel per square yard then 
was applied to the entire section. A final rolling with the 10-ton 
roller completed the section. 
Experiment No. 6. — Bituminous Gravel (Penetration Method). Oll Asphalt 
for Penetration and Seal Coat. 
Location, station 77+55 to station 82+61. 
Total length, 506 feet. 
Total area, 899.5 square yards. 
Experiment No. 6 was built according to the same method em- 
ployed in experiments Nos. 1 to 4, except that an asphaltic oil was 
1 Includes 111.1 square yards -widening on curve. 
