ASPHALTUM AND BITUMINOUS ROCK 397 



Tlio substances classed as hitiiinens are hy(lr()car))()ri com- 

 pounds, the more important of wiiich, arranged in the order 

 of their specific <z;ravities at 70° F., are divided into six groups: 



1. Natural gas. 



2. Natural naphtha. 



3. Petroleum, or natural oil. 



4. Maltha, or soft, sticky bitumen. 



5. Asphaltum, or stiff, sticky })itumen. 



6. Glance [)itch, or dry, brittle bitumen (often called 

 gilsonite). 



In addition to the substances comprising the above list, 

 there are other bitumens of chemical interest only which pos- 

 sess no commercial value. 



In commerce there are four chief classes into which asphal- 

 tum is divided: (1) The natural liquid form, called liquid asphal- 

 tum or maltha; (2) asphaltum niLxed with more or less veget- 

 able and earthy matter, which 3'ields, by the removal of the 

 mechanically contained impurities, the product called hard, 

 refined, or gum asphaltum; (3) asphaltum contained in sand 

 or sandstone, cidled bitiuninous sandstone; (4) asphaltum 

 contained in limestone, called bituminous limestone. 



In addition to the natural products given in the above 

 list mention sliould be made of by-product asphaltum, which 

 is obtained in the refining of crude petroleum having an asphal- 

 tic base to yield commercial illuminating and lubricating oils. 

 There is no strict line of demarcation between oils classed as 

 petroleum oils and those considered as asphaltum oils. 



The term bituminous rock is apphed to both sandstones 

 and limestones impregnated with asphaltum. Bituminous 

 rock is sold and shipped without previous refining, and is con- 

 sumed chiefly for street pavements, being generally mixed 

 with other ingredients at the place of use. An inconsider- 

 able proportion, however, is treated for its asphaltic content, 

 the product being sold as refined or gum asphaltum. 



Asphaltic or bituminous Hmestone is a natural compound 

 of asphaltum and limestone, at times containing, in addi- 

 tion, other bituminous substances, sand, and sulphur bearing 

 compounds. The quantity of asphaltum present varies in 

 different deposits, and even in different portions of the same 



