THE MACADAM PAVEMENT 119 



the road is again thoroughly cleaned, from | to f of a gallon 

 of oil to the square yard under normal conditions is spread 

 over it, and the road closed for 48 hours and covered with 

 sand or screenings as before. This treatment is continued 

 from year to year. 



" Instead of handling the oil in barrels, we have found it 

 much cheaper to buy it delivered in tank cars, from which 

 it is unloaded into the sprinkling wagons. A pressure- 

 tank wagon was used to advantage for the first application 

 of oil to the road surface, but ordinary sprinkler wagons 

 with an oil-distributing attachment and a squeegee fixed 

 behind the distributor were found more economical and 

 equally efficient in spreading the oil the second year. 

 To insure coating all parts of the road with an oil layer of 

 uniform thickness, men with stiff brooms followed the 

 sprinkler." 



6. Surfacing macadam pavements with asphaltic oils, 

 asphalts, coal-gas tars and water-gas tars by one application 

 to form a surface which endures for at least one year. 



The application of the bituminous material must be 

 preceded by a thorough cleaning of the macadam road 

 which is to be treated. Pavements whose surfaces are of 

 the larger sizes of broken stone offer a good bond for the 

 bituminous application, which may be made by hand or by 

 gravity or pressure distributors. A type of American 

 pressure distributor is shown in Fig. 37, page 121. 



Pressure distributors seem to have an advantage over 

 gravity distributors in that by their use a better bond is 

 secured between the macadam and the surface applica- 

 tion. The explanation seems to be found in the washing 

 away of the dust film coating the macadam surface due to 

 the high velocity of the bituminous material as discharged 

 from the nozzles of the distributor. 



