DUST PREVENTION AND ROAD PRESERVATION, 1914. 5 



ably reduced. Conditions were generally better than in the other 

 experiments of the series. The bitumen (water-gas tar preparation 

 No. 2) was heated to an average temperature of 90° C, and applied 

 at an average rate of 1.08 gallons per square yard, covered with 

 sand, and rolled. 



Experiment No. 6 (Calcium Chloride). 



In connection with the foregoing series of bituminous experiments, 

 a section of ordinary coralline-rock surface was treated with an 

 application of calcium chloride, which is a hygroscopic salt obtained 

 as a by-product in the manufacture of soda by the Solvay process. 

 No record of the cost of this work was obtained. 



The coralline-rock road is at its best when slightly wet or moist, 

 and its rapid wear occurs when dry. It was hoped, therefore, that 

 the application of a hygroscopic salt in this area bordering on the 

 ocean would have the effect of keeping the surface damp, thus secur- 

 ing a serviceable and lasting condition. 



Seven drums of calcium chloride, each weighing 350 pounds net, 

 were furnished by the manufacturer. Five of these drums were 

 used, the remaining two being reserved for a second application to 

 the center of the roadway when necessary. The section which was 

 treated on January 28, 1914, lies immediately north of experiment 

 No. 1 and is 590 feet long and 18 feet wide, containing an area of 1,175 

 square yards. The rate of application was 1.49 pounds per square 

 yard, heav} r in the center and light on the extreme sides. The mate- 

 rial came from the drums in a lumpy condition and was difficult to 

 spread evenly. After several weeks of wear the surface was damp 

 at all times, but pitted to some extent, showing bare rock in spots. 



SUMMARY OF EXPERIMENTS AT LEMON CITY, FLA. 



When inspected, on January 16, 1915, none of the experiments on 

 which bituminous materials were used showed any decided evidence 

 of failure. No. 1 appeared to be in slightly better condition than No. 

 3, on which the same heated oil had been used. It was fairly smooth, 

 had a good cross section, and the bitumen still possessed life. 



Experiment No. 2, where the light oil was used, was in good con- 

 dition, bul the bitumen had a brownish, dead appearance, and the 

 individual rock particles showed throughout the section. 



Experiment No. 4, which received the double surface treatment, 

 :.-cd :i fine-grained mosaic surf ace with a few incipient potholes. 

 It hud not worn appreciably below the adjacent section. 



L periment No. 5 had a perfccl mosaic surf ace, with slight indenta- 

 tions around the individual particles of stone. The bitumen had 

 become quite bard, and the section should be given a light surf ace 

 treatment at an early date. One depression was noted in this experi- 

 ment, on the west side, at the joint about 55 feel from (lie. south end. 



