334 THE POPULAR SCIENCE MONTHLY 



were of the motor car variety. The conditions in both countries are 

 seen to be the same. Lord Montagu, of Beaulieu, has calculated that 

 the amount of gasoline used in motors in England in the year 1910 was 

 sufficient, at 15 miles travel per gallon to represent a mileage of 600,- 

 000,000, and Mr. Maybury says: "What are we engineers doing to 

 meet this revolution in traffic ? " 



The very general answer to Mr. " Maybury's question is that some 

 form of bituminous binder must be used, either in or on the surface of 

 the road to enable it to resist the destructive action of the motor vehicle. 

 This was the conclusion reached at the two International Eoad Con- 

 gresses held in 1908 and 1910. The water-bound broken-stone road is 

 a thing of the past on our main arteries of travel which are carrying the 

 present enormous motor traffic. 



In working out the problem of a new type of road construction in 

 which some form of bitumen is employed as a binding or surfacing 

 material science can, and is, taking an important part. Fortunately 

 for the past twenty-five years or more, the native solid bitumens, the 

 liquid forms and their surrogates, the tars, have been studied very thor- 

 oughly as to their character and in their application to the construction 

 of street pavements. It is not, therefore, difficult, for one who has had 

 an extended experience, to apply the knowledge gained thereby to the 

 construction with the same materials, of country highways of broken 

 stone. The contribution which science has offered to the solution of 

 the road problem in this direction is, therefore, important, while it sup- 

 plies at the same time means of controlling the uniformity of the bind- 

 ing materials in use and determining the fact that any particular 

 bitumen is of suitable character for the purpose to which it is to be 

 applied. For the collection of these data and also, to a great extent, 

 for their interpretation the highway engineer is dependent on the 

 chemist, who is, therefore, becoming a considerable factor in success- 

 ful road building. 



Bitumen is a native material, that is to say, it is found in nature. 

 The by-products of industrial operations, such as tar from the manu- 

 facture of illuminating gas and coke ovens, is not bitumen in the accep- 

 tation of the word as it was originally applied by the Latin writers. 

 Coal tar is a bituminous substance merely from its resemblance to 

 bitumen. 



Bitumen is a mixture of hydrocarbons and their derivatives and may 

 be gaseous, liquid, a very viscous liquid, sometimes called a maltha, or 

 a solid. These hydrocarbons may be representatives of very different 

 series, each having its own peculiar character, both chemical and phys- 

 ical, or a bitumen may be made up of hydrocarbons of different series. 

 The value of any bitumen or combination of bitumens for road con- 

 struction depends on the series of hydrocarbons and their derivatives, 



