Page:Popular Science Monthly Volume 80.djvu/338

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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 Congresses 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 thoroughly 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 supplies at the same time means of controlling the uniformity of the binding 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 successful 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 manufacture of illuminating gas and coke ovens, is not bitumen in the acceptation 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 physical, or a bitumen may be made up of hydrocarbons of different series. The value of any bitumen or combination of bitumens for road construction depends on the series of hydrocarbons and their derivative