6iz THE POPULAR SCIENCE MONTHLY. 



pieces, and melted in caldrons with bitumen at a temperature be- 

 tween 150 and 170 Cent. Then from 60 to 70 per cent, of sand is 

 added, and the mixture is ready for application to the surface to be 

 covered. 



But still a good pavement for roadways was a desideratum. First 

 the experiment was tried of laying down a bed of broken freestone, 

 and pouring over this melted asphalt mastic. This method, however, 

 proved unsuccessful, for, when cold, the mastic was too brittle, and if 

 one of the corners of the stones was struck and broken by carriage- 

 wheels, a hole was made, which gradually widened, and was difficult 

 to mend. In Lyons, a layer of asphalt mastic, two inches in thickness, 

 was spread over four inches of concrete. This was found to be an ex- 

 cellent pavement, but a fatal objection to it was its costliness. 



It was at last observed that the roads and paths leading to the 

 quarries of the Val de Travers were always in good condition, firm, 

 solid, and elastic. Here was an asphalt pavement, formed of the small 

 pieces of the mineral which fell from the carts, and which were pressed 

 down and flattened by the wheels. The first highway asphalted on 

 this principle was that between Bordeaux and Rouen. The road was 

 first macadamized, and then covered to the depth of an inch and a 

 half with asphalt, broken up in small pieces. As the plan appeared to 

 be a complete success at first, several other roads were asphalted in 

 the same way. Soon, however, the crushed granite of the macadam 

 began to cut its way through the asphalt, and broke its continuity, 

 thus allowing it to be permeated with dirt and water. Finally the 

 problem was solved by a Swiss engineer, A. Merian, of Basle, who 

 proposed to lay down powdered asphalt in a warmed state on the 

 street, and, by applying strong pressure, to form at once an imper- 

 meable, elastic surface. The French engineers readily adopted the 

 suggestion, and the first trial of the new method was made in the Hue 

 Bergere. The engineers cried " Eureka ! " and well they might, for 

 experience in Paris shows that 1. The asphalt costs, in the first in- 

 stance, one-third less than stone pavement ; and 2. That the annual 

 cost of maintenance is three-quarters less than that of a macadamized 

 road. 



The process of preparing the asphalt pavement is thus described 

 by M. Leon Malo : The asphalt-stone is brought direct from the quar- 

 ries, and broken up into small pieces, about the size of those used for 

 macadamized roads ; it is then heated over a stove in a drum-shaped 

 iron vessel with feet, till it crumbles into powder. In order that the 

 powder may not lose its heat, the whole apparatus is conveyed on to 

 the street where it is to be applied. Then a foundation of b'eton is 

 laid, about four inches deep, which may, however, be thicker or thin- 

 ner, according to the nature of the soil. On a macadamized road the 

 concrete may be omitted ; but on loose soil it should be laid as thick 

 as six inches. The arch of the roadway should only be just sufficient 



