CHAPTER VIII. 

 LIQUID FUELS. 



SHALE-OILS. PETROLEUM. 



THE mineral oils comprehend the liquid hydrocarbons 

 extracted from bituminous schist or coal and its congeners by 

 distillation, as well as the oils which exist already formed in 

 the earth, and called by the special name of petroleum. 



While the former are seldom employed in heating, petro- 

 leum has become an important fuel in the countries which 

 produce it. Its special qualities, light weight, and low price 

 per calorie compared with other fuels insure a great future. 

 The knowledge of its heat of combustion has become, then, of 

 considerable interest. 



Its ultimate percentage composition varies within rather 

 close limits, yet it is of a very complex proximate composi- 

 tion. The industry of refining crude petroleum extracts from 

 it some 50 per cent of refined oil for use in lamps, and hav- 

 ing a density of 45 to 47 Beaume, boiling-point 170 C. 

 (328 F.); 10 per cent of naphtha with a lower density and 

 boiling-point ; and 20 per cent of paraffin oil of a higher den- 

 sity and boiling-point. 



Crude petroleum contains a large number of hydrocarbons 

 of the general formula C w H 2M+2 , and running from CH 4 to 

 C 16 H 31 , with many isometric modifications. The industrial 

 treatment modifies it profoundly. Hydrocarbons containing 

 95 per cent of carbon have been found in the products of 

 distillation.* 



*Wurtz, Dictionnaire de Chimie, Supplement. 



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