86 THE POPULAR SCIENCE MONTHLY. 



not sustained by modern scientific tests. Seen in thin layers under 

 the microscope, the bitumen, the color of which is otherwise a deep 

 black, shows a transparent yellowish mass, while coal-pitch is visible 

 as a mass of coherent black points on an orange-colored ground. 

 This investigation of the mastic relied upon suffices to explain in the 

 one case the quality of toughness and binding power, and in the other 

 that of brittleness. 



Efforts are now being made to jn'oduce concrete pavements based 

 on mixtures of silicate of soda with Portland cement. The latter, 

 along with native asphaltum, is undoubtedly the most important mod- 

 ern building-material, but it has its separate province, and lacks just 

 those qualities of the native asphaltum which are so highly appre- 

 ciated for paving-purposes. It will hardly ever be successful in the 

 long-run when encroaching on the sphere of the competing material 

 which it has fairly outrivaled as a cement for brickwork and masonry, 

 for which, in ancient times, asphaltum enjoyed a ju^t celebrity, as 

 attested by the remnants of the walls of Babylon and Nineveh. This 

 class of pavement has been tested carefully in France with the well- 

 known hUon coignet and has failed. While the artificial mixtures 

 soon require expensive surfacing, the native asj^haltum when taken up 

 for piping, or otherwise, after many years' wear, may be used again 

 by simply heating and treating it as at first. In this aspect it bears 

 such a relation to the artificial concretes as a copper roof does to a 

 common tin roof. 



ISTature has unfortunately produced this valuable mineral deposit 

 in but very few cases, and it has not yet been found in America, for 

 the so-called Trinidad asj^haltum consists mainly of bituminous scoriae, 

 cemented together with vitrified sand and earth ; and even the more 

 esteemed Cuban asphalts contain from 27 to 34 per cent, of earthy 

 substances. The deposits from Tyrimont-Seyssel, on the banks of the 

 Rhone, in France, were the first to be used for pavements. But, as 

 they contain only from 6 to 8 per cent, of bitumen, the powdered rock 

 was foimd rather too dry, and thei*efore was superseded by the exten- 

 sive deposits of the Val de Travers, the most important valley de- 

 bouching from the Jurassic mountains of Switzerland into the Lake 

 of Neufchatel. These, with steady march, have conquered the mar- 

 kets of the world. The deposits known as Neufchatel rock contain, 

 with a constancy not found anywhere else, from 11 to 12 per cent, of 

 bitumen a most favorable proportion. Besides, they have absolutely 

 greater toughness as a result of their degree of oxidation. They 

 were foi*merly extensively used as a mastic for sidewalks, and form an 

 excellent material for carriage-ways. They liave been used since 1854 

 in Paris, and since 1868 in the principal thoroughfares of London and 

 other European capitals. 



The success of this bituminous rock pavement is by no means 

 due to the lucky hit of one individual; it is the legitimate result of 



