HIGHWAY CONSTRUCTION 107 



darker color being due to a large percentage of bitumen. At a tem- 

 perature of from 55 to 70 F., the material is hard and sonorous, and 

 breaks easily with an irregular fracture; at temperatures between 70 

 and 140 F. it softens, passing with the rise in temperature through 

 various degrees of plasticity, until, at between 140 and 160 F., it 

 begins to crumble; at 212 it commences to melt; and at 280 F. it is 

 completely disintegrated. Its specific gravity is about 2.235. 



Bituminous limestone is the material employed for paving pur- 

 poses throughout Europe. It is obtained principally from deposits 

 at Val-de-Travers, canton of Neufchatel, Switzerland; at Seysell, in 

 the Department of Ain, France; at Ragusa, Sicily; at Limmer, near 

 Hanover; and at Vorwohle, Germany. 



Bituminous limestone is found in several parts of the United 

 States. Two of these deposits are at present being worked one in 

 Texas, the material from which is called "lithocarbon"; and one on the 

 Wasatch Indian Reservation. These deposits contain from 10 to 30 

 per cent of bitumen. 



The bituminous limestones whkh contain about 10 per cent of 

 bitumen are used for paving in their natural condition, being pimply 

 reduced to powder, heated until thoroughly softened, then spread while 

 hot upon the foundation, and tamped and rammed until compacted. 



Bituminous sandstones are composed of sandstone rock imp^eg- 

 nated with bitumen in amounts varying from a trace to 70 per cent. 

 They are found in both Europe and America. In Europe, they are 

 chiefly used for the production of pure bitumen, which is extracted by 

 boiling or macerating them with water. In the United States, exten- 

 sive deposits are found in the Western States; and since 1880 they have 

 been gradually coming into use as a paving material, so that now up- 

 wards of 150 miles of streets in Western cities are paved with them. 

 They are prepared for use as paving material by crushing to powder, 

 which is heated to about 250 F. or until it becomes plastic, then spread 

 upon the street and compressed by rolling ; sometimes sand or gravel 

 is added, and it is stated that a mixture of about 80 per eent of gravel 

 makes a durable pavement. 



Trinidad Asphaltum. The deposits of asphaltum in the island 

 of Trinidad, W. I., have been the main source of supply for the asphal- 

 tum used in street paving in the United States. Three kinds are found 

 there, which have been named, according to the source, lake-pitch, 



