THE MACADAM PAVEMENT 117 



2. Sprinkling with Salt Water. The results are more 

 durable than fresh-water sprinkling, since the salts in the 

 water are hygroscopic in their properties. Should the 

 pavement become dry, the dust containing salt is thrown 

 into the air and is extremely irritating to the throat and eyes. 



3. Sprinkling with Water and Calcium Chloride. This 

 salt is strongly hygroscopic and roads treated in this manner 

 have proved quite satisfactory in England, where the cli- 

 mate is moist. The mixture to be used is 1 pound to 1 gallon 

 of water, using ^ of a gallon of the solution for each square 

 yard. Ten applications per season are usually sufficient. 



Calcium-chloride treatment has been adopted by the 

 Metropolitan Park Commission of Boston and by the 

 Department of Parks of Hartford, Conn. 



Calcium chloride is also applied as a dry powder, the 

 pavements being first swept by hand. The amount of 

 chloride used varies from J to 2J pounds per square yard. 



4. Sprinkling with an oil emulsion consisting of water, 

 oil and an alkali. Vegetable oils, crude petroleum and 

 coal tar have been used in municipal practice. Potash, 

 soda, ammonia and soap solutions are the mediums em- 

 ployed to render the oil miscible with the water. The 

 mixture is sprinkled from an ordinary watering cart, though 

 a power sprinkler as described on page 119 would give 

 more satisfactory results. The surface may be left un- 

 covered or else treated with a thin coat of sand. 



5. Treating the Surface with Light Oils and Light Tars. 

 The oils and tars are distributed preferably by pressure dis- 

 tributors. Those with hoods have been employed to pro- 

 tect pedestrians. The palliatives employed are vegetable 

 oils, paraffin and asphaltic petroleums, tar oils, water-gas 

 tars, coal-gas tars and various patented compounds. 



This treatment is effective in laying the dust for about 



