46 BULLETIN 407, U. S. DEPARTMENT OF AGRICULTURE. 
depression 55 feet from the south end of section 5, reported in Bulletin 
No. 257, was still noticeable, but had not increased in size appreciably. 
A few minor repairs had been made by using a mixture of sand and 
oil and the surface was in very good condition. 
SUPPLEMENTARY REPORT OF EXPERIMENTS AT WEST PALM BEACH, 
FLA., 1914. 
OIL, TAR, OIL-ASPHALT, CORALLINE ROCK. 
These experimental sections were constructed on the Miami-Quebec 
Highway, about 2 miles south of West Palm Beach, in May, 1914. 
The original report giving the details of materials and methods is 
published in U. S. Department of Agriculture Bulletin No. 257. As 
shown in Table 9 in that report, the traffic over this road is heavy 
suburban and the test of the various sections is therefore rather 
severe. 
The work was inspected December 10, 1915, and the condition of 
the sections at that time was as follows: 
Experiment No. 1 . (Residual asphaltic petroleum, 2.3 gallons. Pen- 
etration method.) — This section is in very satisfactory condition. The 
bituminous material is still viscous, but the exudation and flow of 
the excess has ceased and the inequalities in the surface resulting 
from this flow are not sufficient to cause discomfort to traffic. There 
is no evidence of weakness developing at any point. 
Experiment No. 2. {Refined coal tars, 1.3 gallons. Penetration 
method.) — The bituminous material has continued to harden and the 
surface is becoming pitted, owing to the fact that individual rocks 
have been broken and worked out of their setting. These pits are 
small and uniformly distributed and do not cause noticeable vibra- 
tion in passing vehicles. About 25 feet from the south end of the 
section a shallow depression has formed. It is due apparently to 
settling of the pavement and not to wear. 
Experiment No. 3. (Refined coal tars, 1.2 gallons. Penetration 
method.) — The proportion of rock exposed in the surface by the re- 
moval of the binder under traffic has increased visibly in the past 
year. These exposed rocks have worn lower than the surrounding 
areas still coated with tar and the surface is full of small shallow 
pits. The tar has become very hard and brittle. 
Experiment No. 4- (Residual asphaltic petroleum, 1.4 gallons. 
Penetration method.) — The surface is in good condition, but is becom- 
ing slightly rough, due to pits where the rock is exposed. The differ- 
ence in appearance between the part of the section treated with sand 
and that treated with stone chips is becoming more pronounced. 
Experiment No. 5. (Oil-asphalt, 1 .8 gallons. Penetration method.) — 
This section has changed little in appearance or condition and has 
resisted the action of traffic very satisfactorily. 
