i 9 2 THE POPULAR SCIENCE MONTHLY. 



pavements, and is much enrployed in Paris. The powdered rock is used 

 without any addition. It is applied hot, on a prepared bed of con- 

 crete, four to seven inches thick, and compressed, with heated rammers 

 and a heated roller, to the thickness of one and a half or two inches. 

 The smooth surface is given by a. heated smoothing-iron. One block 

 of compressed Val de Travers asphalt, two inches thick, laid on a Port- 

 land cement concrete foundation seven inches thick, may be seen on 

 Fifth Avenue, between Twenty-sixth and Twenty-seventh Streets. 



The third form of pavement, which seems to be one of the best 

 for roadways, is the " Trinidad." It is made of prepared bitumen, 

 i. e., Trinidad asphalt and still-bottoms, mixed with about twice its 

 weight of calcareous marl or powdered limestone. None of the im- 

 ported asphalt mastics or rock are used in this pavement. 



Various imitations of both asphalt and mastic have been palmed 

 off on the public, or substituted by dishonest contractors, some of 

 whom will keep a few blocks of real mastic of a well-known brand 

 lying about, as if they were to be used, while inferior materials are 

 thrown into the caldrons. Some imitations are but little inferior to 

 the genuine, while others are nearly worthless, and have done much 

 to bring asphalt into disrepute. Among the latter are those made in 

 whole or in part of the pitch left in the distillation of coal-tar. Al- 

 though useful for a great variety of purposes, it will not answer for 

 asphalt pavements. It is usually possible to distinguish good bitumen 

 by its smell when warmed. When heated with excess of concentrated 

 or fuming sulphuric acid for twenty-four hours, and then diluted and 

 filtered, the pure natural bitumen yields a nearly colorless solution, 

 but if pitch is present the solution will be dark-brown or black. 

 Another distinction between real bitumen and coal-tar is found in the 

 solubility of the latter in alcohol, the former being nearly insoluble. 

 If a grain of material that has been heated to 200 C. is pulverized and 

 mixed with 5 c. c. of strong alcohol, the latter will acquire a yellow 

 color and bluish-green fluorescence if there is more than two per cent 

 of pitch present. 



There are several uses to which asphalt may be applied, the most 

 important being the one already so often referred to, namely, as paving 

 material. In Paris about thirty-three miles of street are covered with 

 asphalt pavement, more than three fourths of it being the so-called 

 " compressed asphalt," while the remainder is made of cast or mastic 

 asphalt. The use of asphalt pavements for roadways began in Paris 

 in 1854, since which time their use has been steadily increasing until 

 the present time. In London there are about nine miles of asphalted 

 streets. Asphalt pavements have but recently begun to find favor in 

 Berlin, and at the close of 1881 there were only six miles of street 

 paved with it. Of asphalt sidewalks, etc., Paris has three million 

 square metres, equivalent to four hundred miles of walks, seventeen 

 feet wide. 



