DUST PREVENTION AND ROAD PRESERVATION. 27 



pleted when a heavy rain fell and. on the following morning the sand 

 mat was found washed into ridges and to a large extent carried off 

 the road entirely. The portion of the experiment on which the oil 

 had stood the shorter time became rather mushy and uneven, while 

 the remainder of the section was fairly smooth and hard. The section 

 was resanded hut the same condition was evident two weeks later. 



Experiment No. 3. — Penetration method — Hot, heavy oil. 



Location: From station 5+49 to station 74-49. 

 Length: 200 feet. 



Method. — In this experiment, after the old surface had been 

 regraded, a course of new unscreened rock was spread to a loose 

 depth of 2\ inches. This course was brought to the required shape 

 with a very light rolling in an effort to permit penetration by leaving 

 the crust as open as possible. Light rains previous to the application 

 of oil caused the surface to become slightly water-bound. The hot 

 oil was applied at the rate of approximately 0.6 gallon per square 

 yard, but owing to the varying texture of the surface it readily pene- 

 trated on some areas and remained almost entirely on the surface of 

 others. The surface was sanded and rolled as in the previous 

 experiments. 



Experiment No. 4. — Penetration method — Cold, light oil. 



Location: From station 7+49 to station 9+16. 

 Length: 167 feet. 



Method, — This experiment was quite similar to No. 3, in that the 

 application was made on a 2^-inch course of new, unscreened rock. 

 The rock was, however, heavily rolled in an effort to tighten the sur- 

 face sufficiently for brooming the oil. This was partially effected and 

 the penetration seemed to be as good as in the more lightly rolled 

 section. Oil was applied at the rate of 0.7 gallon per square yard and 

 allowed to stand for three hours before sanding, and at the end of 

 this time it was practically all absorbed. 



Experiment No. 5. — Penetration method — Hot, heavy oil. 



Location: From station 9+16 to station 11+55. 

 Length: 239 feet. 



Method. — This experiment was essentially the same as experiment 

 No. 4 except for the reason that the course of new, unscreened rock 

 was reduced to a loose thickness of 1^ inches in an effort to reduce the 

 cost of this type of experiment. From station 9 + 16 to station 10 + 

 87 sand was used for a top dressing. The surface cracked and lifted 

 under rolling, and required patching in several spots a few days later. 

 From station 10 + 87 to station 11+55 new rock screenings were used 

 for the top dressing. 



