DUST PREVENTION AND ROAD PRESERVATION, 1915. 51 



during the coming summer. The surface has not become so muddy 

 at any time during the winter of 1915-16 as during that of 1914-15. 

 The bumps due to faulty distribution at the time of original treat- 

 ment are still visible and cause considerable trouble. They have 

 been repeatedly cut and trimmed, but owing to the excess of bitu- 

 minous material the spots have required top dressing in the hottest 

 weather, and this builds them up again. There has been considerable 

 repair work necessary over all of the experiment, but no place shows 

 marked weakness. Patches made on this experiment are miusuaUy 

 smooth and serviceable, and so far there appears no tendency for 

 the original sm-face to break or give way aroimd patches. 



Experiment No. 5. — ^Residual Asphaltic Petroleum, Hot Application. 



This experiment, Hke No. 4, shows less tendency to become muddy 

 during thaws, although dampness of subgrade continues to be very 

 noticeable. During the past summer a great deal of patching has 

 been necessary and the breaks have been somewhat more numerous 

 in the bottoms and poorly drained sections than elsewhere, although 

 they have been general. It is now expected that the experiment 

 will require re-treatment during the coming season. 



Experiment No. 6. — ^Water-Gas Tar Preparation, Hot Application. 



This experiment required but little attention during 1914, but 

 early in the spring of 1915 it began to break up rather rapidly. 

 The nature of the failure was very similar to that described for 

 experiment No. 2 in 1914. Breaks in the mat at the sides of the 

 road progressed rapidly toward the center and any raw edge of the 

 mat had a tendency to crumble away rapidly. It was always neces- 

 sary to give immediate attention to patching, and even with care 

 in some instances patches had to be made that extended from the 

 sides nearly to the center of the road and were from 4 to 6 feet long. 

 It finally became necessary to re-treat November 8 to 12. The 

 work was done by contract, using the same type of bituminous 

 material as originally applied and covering with clean, washed 

 gravel passing a f-inch screen. The contract price was $1,170 or 

 11.] cents per square yard. The characteristics of the material 

 used are shown in Table 50 and additional data are given at the end 

 of this report. 



Table No. 50. — Analysis of water-gas tar preparation used on experiment No. 6. 



Spef.ific gravity 25725° C 1. 136 



Float test at 32'" C, time 2' 11'' 



Free carbon (insoluble in CS2), per cent 1. 71 



