DUST PEEVENTIOlsr AND ROAD PEESERVATIOlSr, 1915. 47 



Experiment No. 6. (Oil-aspTialt, 1 .5 gallons. Penetration metTiod.) — 

 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 rocTc-waterhound 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 traflS.c. The sUght inequalities in the surface 

 reported last year remain unchanged. There were no breaks or 

 seriously worn or weak spots. 



Experiment No. 4- {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 trajQB.c, 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 crumbUng. Repairs have been made with 

 coraUine 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 

 wiU be required during the ensuing year. 



