536 



POPULAR SCIENCE MONTHLY. 



cement is swept over the surface, and it is thorouglily rolled with 

 a steam roller of not less than ten tons, the rolling to be continued 

 as long as the roller makes any impression on the surface. 



The foundation is usually of cement concrete about six inches 

 thick, though asphalt pavements are often laid over old stone pave- 

 ments. Between the foundation and the wearing surface there is 

 generally laid wdiat is called a binder course, one inch thick and 

 formed of small broken stone, to which has been added asphaltic 

 cement, the same as is used in making the wearing surface. Five 

 or six pints of this cement are used to each cubic foot of stone. 



The pavement just described is made from Trinidad asphalt, 

 the material from which nearly all the earlier artificial asphalt 



King's IIic-hwav, Bijooklvn ; Sixtkkn Feet in Centek of Uoad Macadamized. 



pavements in this country were made, and which was used almost 

 exclusively until within the last half dozen years. 



Within that time, however, it has been discovered that there 

 are a number of other deposits of asphalt well adapted to use for 

 street pavements. A very large deposit containing a high per- 

 centage of bitumen and very little mineral matter is located near 

 the coast in the State of Bermudez, in Venezuela. Large deposits 

 have been found in several places in California, and in Utah, Ken- 

 tucky, and Texas, and a number of other })laces. The Kentucky 

 ]iroduct is classed as a luilural rock asphalt, as it is a sandstone im- 

 ])regnated with bitumen. It has been mixed with about an equal 

 ]jortion of German rock as])halt and used with very satisfactory 

 results in Buffal'j. These asphalts are quite different in their com- 



