MODERN CITY ROADWAYS. 



537 



position, and each requires somewhat different treatment. The 

 Bermndez, being richer in bitumen and softer, requires the addi- 

 tion of very little flux. The California deposits furnish their own 

 flux in a liquid asphalt or maltha, which is almost absolutely pure 

 bitumen, and the use of petroleum residuum is thereby avoided 

 altogether. 



It has been recognized since 1836 that the bitumen which forms 

 the greater part of natural asphalts can be separated into two 

 substances, which have been commonly known as petrolene and as- 



AsriiALT I'avkmknt o>- Clinton Avenie, Biiouklyn. 



phaltene, the former of which possesses the cementitious qualities 

 essential to the making of a successful pavement. Instead of the 

 arbitrary names — petrolene and asphaltene — these substances are 

 sometimes more aptly designated as active and inert bitumen. It 

 has been found that of the bitumen extracted from asphalts which 

 have given the most satisfactory results in making street pavements, 

 sixty-nine per cent or more is soluble in petroleum naphtha having 

 a specific gravity of 72° Beaume. 



An asphalt pavement can not be economically kept in good 



TOL. LTI. — 42 



