Relations to Asj>haltio Pavement. 33 



If sand could be cemented together with carbon, it would 

 only be necessary to grind up anthracite slack and mix it with 

 sand in order to produce a paving material. It is evident that 

 the hydrogen combined with the carbon gives it adhesive 

 properties, and this within certain limits, for the moment a 

 sufficient amount of hydrogen is removed to convert the petro- 

 lene into asphaltene, or whenever the softening material is a 

 petroleum or residuum that will not dissolve asphaltene, the 

 elements of disintegration are present. 



The observation made by Boussingault more than half a 

 century ago, and quoted above, that prolonged heating at high 

 temperatures, converts petrolene into asphaltene, which has no 

 more adhesive properties than anthracite slack, appears to have 

 been overlooked by Messrs. Richardson and Towle, for they 

 do not appear to regard the manner of refining and blowing 

 the asphaltic cement as of any importance. Neither for the 

 same reason do they appear to appreciate the bearing of my 

 own researches or those of Messrs. Cabot and Jenney upon 

 this question, although they have been on record now more 

 than twenty years. While it has been well known for years 

 that bitumens occur in great variety, the selection of a proper 

 material for softening the asphalt to the exclusion of others 

 less desirable or wholly unfit, appears also to have escaped 

 attention. A properly selected material for such a purpose 

 would by entering into solution and chemical union with both 

 the constituent parts of the bitumen of the asphalt, thereby 

 increase its adhesive and binding properties upon the other 

 constituents of the mastic. Added to all these omitted ele- 

 ments of the problem just enumerated, we have another of 

 great importance, and that is the total proportion of bitumen 

 to the total proportion of sand and other non-bituminous in- 

 gredients of the mastic. Experience proves that less than 

 10 per cent-11 per cent to 90 per cent-89 per cent gives too 

 little stability to the mass, while a larger percentage of bitu- 

 men makes the pavement too soft. 



One more element of a good asphaltic pavement is mechan- 

 ical rather than chemical, and that is solidity. The pavemeut 

 must be rolled as solid as asphaltic rock in order to keep out 

 rain water and the action of the oxygen dissolved in it ; for 

 the effect of oxidation is to gradually convert the petrolene of 

 the asphalt into ashpaltene, leaving the small amount of soften- 

 ing material as the only binding constituent of the mixture. 

 When this softening material is not a solvent for asphaltene 

 the pavement inevitably disintegrates. 



I would therefore commend to the consideration of those 

 who act as advisers to Commissioners of Public Works, not a 



Am. Jour. Sci.— Third Series, Vol. XLVII, No. 277.— Jan., 1894. 

 3 



