DUST PREVENTION AND ROAD PRESERVATION, 1915. 15 
an extra depth of about three-fourths of an inch of trap was spread, 
so that the total depth of stone averaged nearly 4 inches loose. The 
"l^-inch" crushed trap used was of physical properties and mechanical 
analysis shown in Tables 4 and 5, respectively. The oil-asphalt 
analysis is given in Table 8. The mechanical analysis of the trap 
screenings or chips is shown in Table 7. 
The experiment was constructed otherwise as previously described 
for the penetration macadam experiments with sandstone and gneiss. 
Experiment No. 14. — Bituminous Macadam (Penetration Method). Trap rock 
with Fluxed Native Asphalt A. 
Location: Station 163+00 to station 173+00. 
Length: 1,000 feet. 
Total area: 1,777.8 square yards. 
This experiment was constructed exactly like experiment No. 13, 
except that fluxed native asphalt was used instead of oil asphalt, and 
that the extra depth of stone for the base was not required. 
Experiment No. 15. — Bituminous Macadam (Mixing Method). Trap Rock with 
Fluxed Native Asphalt A. 
Location: Station 173+00 to station 182+80. 
Total length: 980 feet. 
Total area: 1,742.2 square feet. 
This experiment was constructed on the same kind of base as 
experiments Nos. 13 and 14. Trap rock of physical properties and 
mechanical analysis shown in Tables 4 and 6, respectively, and trap 
chips of mechanical analysis shown in Table 7 were used. Otherwise 
the construction was similar to that of experiments Nos. 3 and 8. 
The mixing plant was located near station 215 + 00. 
Experiment No. 16. — Bituminous Macadam (Mixing Method). Trap Rock with 
Oil-Asphalt X. 
Location: Station 182+80 to station 192+00. 
Length: 920 feet. 
Total area: 1,621.4 square yards. 
This experiment was constructed on the same kind of base as 
experiments Nos. 13, 14, and 15. From station 187 + 00 to station 
190 + 50, 84.5 tons of "lj-inch" trap was added to the foundation in a 
uniform layer and rolled with a 10-ton roller. This spread stone was 
unfortunately traveled over for nearly 30 days and it became some- 
what rounded before the surface was laid. It was necessary to replace 
the old pipe culvert at station 189 + 64, and bad weather during the 
progress of the work caused considerable settlement of the adjacent 
fill before the new culvert was completed. 
The experiment was exactly like experiment No. 15, except that 
oil-asphalt was used instead of fluxed native asphalt. Mixing for 
the area between stations 182 + 80 and 192 + 00 was done at position 
