82 COMBUSTION AND FUELS 



The Babcock & Wilcox Company state that on the average 

 1 Ib. of good bituminous coal may be considered as the equiva- 

 lent of 2 Ib. of dry peat, 2 Ib. of dry wood, 2 to 3 Ib. of dry 

 tan bark or sun-dried bagasse, 3 Ib. of cotton stalks, 3J Ib. of 

 straw, 6 Ib. of wet bagasse, and from 6 to 8 Ib. of wet tan bark. 



LIQUID FUEL 



Nature of Petroleum. The fuel most extensively employed 

 in the generation of steam is coal, the most valuable of the solid 

 fuels. In some parts of the world, however, it has been found 

 convenient and economical to use liquid fuel. This is obtained 

 chiefly from petroleum, which is a natural oil obtained from the 

 earth. In its original state it is usually of a dark-green color 

 when viewed in the sunlight; but when held up to the light, so 

 that the light passes through it, it has a reddish-brown color. 

 The appearance of the oil will vary somewhat, depending on 

 the locality from which it is derived. In some cases it is 

 almost as clear and colorless as water, and in other cases it is 

 black; but American petroleum is commonly brown or red- 

 dish-brown with a green luster. 



Composition of Crude Oil. Petroleum in the form in which 

 it issues from the earth is known as crude oil. It usually con- 

 tains from 83 to 87% of carbon, from 10 to 16% of hydrogen, 

 and small percentages of oxygen, nitrogen, and sulphur. Some 

 crude oils are devoid of sulphur and nitrogen, but all those 

 obtained along the Pacific coast contain oxygen, sulphur, 

 nitrogen, and a small percentage of moisture. The presence of 

 sulphur in an oil is manifested by a very disagreeable odor. 

 The following analyses of crude oils from Beaumont, Texas, 

 and Bakersfield, Cal., will serve to give an idea as to the compo- 

 sition of the oils from these fields. 



