DUST PREVENTION AND ROAD PRESERVATION, 1915. 47 
Experiment No. 6. {Oil-asphalt, 1 .5 gallons. Penetration method.) — 
The surface of this section is in perfect condition. While the asphalt 
has gradually hardened it has not lost its recementing power and is 
very efficacious as a binder. 
Experiment No. 7. {Coralline rock-waterbound macadam.) — The sur- 
face of this section has worn down uniformly over the entire cross 
section and is nearly 2 inches below the surface of section No. 6, 
which it adjoins. 
SUPPLEMENTARY REPORT OF EXPERIMENTS AT MIAMI, FLA., 1913. 
OIL-CORALLINE ROCK. 
The original report of these experiments appeared in U. S. Depart- 
ment of Agriculture Bulletin No. 105 and the statement of their 
condition in January, 1915, was published in U. S. Department 
Bulletin No. 257. By that time it had become evident that experi- 
ments Nos. 1 and 2 were not successful and they were dropped from 
the record. The remaining experiments were inspected December 
11, 1915, and their condition at that time was as follows: 
Experiment No. 3. {Penetration method. 0.6 gallon hot heavy oil.) — 
The surface appearance of this section has not changed noticeably 
in the past year, except for the gradual exposure of a few particles 
of coralline rock under traffic. The slight inequalities in the surface 
reported last year remain unchanged. There were no breaks or 
seriously worn or weak spots. 
Experiment No. If.. {Penetration method. 0.7 gallon cold light oil.) — 
This section, which last year had developed only a few worn depres- 
sions, is deteriorating rapidly. The binder has become brittle and 
the tendency of the rock particles to break away and form holes 
has become general over the entire area. Repairs made with rock 
only have failed under traffic, but those in which asphaltic material 
were added have worn satisfactorily. 
Experiment No. 5. {Penetration method. 0.6 gallon hot heavy oil.) — 
The worn depressions and holes reported last year have increased 
greatly in size and number. The bituminous material has lost its 
cohesive power and is crumbling. Repairs have been made with 
coralline rock without bituminous material. It is probable that the 
entire section will be reconstructed during the coming year. 
Experiment No. 6. {Penetration method. 1 .0 gallon hot heavy oil.) — 
This section is in excellent condition and shows no signs of local 
failure or undue wear at any point. It is probable that no repairs 
will be required during the ensuing year. 
