18 BULLETIN 257, U. S. DEPARTMENT OP AGEICULTTJEE. 



crossing has somewhat increased the surface-repair costs. No re- 

 pairs, however, have been large in size. The experiment is in gener- 

 ally good condition except for the uniform wear, and it is free from 

 holes or weak spots. 



The part of this experiment in Bradley Lane is suffering severely 

 by reason of the very heavy traffic in both directions. The frequent 

 passing compels practically every vehicle to run off the metal at some 

 point, and the continual wear at the edges has reduced the effective 

 width and caused damage that can not be satisfactorily repaired short 

 of reconstruction. This is an obvious case of the traffic being too 

 heavy for a single-line road. 



Experiment No. 2 (Refined Water-Gas Tar — Cold Application). 



In the early summer of 1914 the surface of this experiment began 

 to fail so rapidly through numerous breaks in the mat that it became 

 practically impossible to prevent total failure by means of patrol 

 maintenance. The failure seemed more pronounced over that portion 

 of the experiment where gravel had been used, and this is attributed 

 to the fact that the gravel was coarser than it should have been. 



Therefore, between June 29 and July 3 a second treatment was 

 applied. Refined water-gas tar purchased under the specification for 

 the original treatment was used, and the application was made by 

 means of an automobile pressure distributor. The tar was brought 

 directly from the stills of the manufacturer and applied at a tempera- 

 ture of 150° to 175° F. Clean trap-rock chips and f-inch gravel were 

 used as a covering material, each over the same parts of the experi- 

 ment where it had been originally used. The characteristics of the 

 bituminous material are given in the following table, and the cost data 

 will be found at the end of this supplementary report. 



Table 11. — Analysis of refined water-gas tar. 



Specific gravity 25°/25° C 1.123 



Viscosity, Engler, 50 c. c. at 50° C, specific 27. 



Free carbon per cent. . 0. 80 



Distillation: volume, weight. 



Water per cent. . 0. 0.6 



First light oils to 110° C do 1 .1 .1 



Second light oils (110°-170° C.) do 1 .6 .5 



Heavy oils (170°-270° C.) do 2 26. 5 23. 4 



Heavy oils (270°-315° C.) do 2 13. 8 12. 5 



Pitch residue do 3 59. 63. 4 



Total do 100. 99. 9 



This surface is now fully as good, if not better, than at the time of 

 original construction. There are two sections of surface, near Nor- 

 wood trolley station and south of Edgewood station, where the 



1 Trace solid. 2 One-fourth solid. 3 Fairly hard and glossy. 



