82 



CALORIFIC POWER OF FUELS. 



hard. It has a dead gray-black color and is not susceptible 

 of polish. It is principally used in furnaces requiring a 

 blast, although limited quantities of it have been used in 

 domestic heating, for which purpose it must be broken up 

 much finer than its usual size. Petroleum coke is generally 

 in large irregular lumps, perforated with cavities of greater or 

 less size, the interior of which is usually quite smooth and 

 shining. Its color is blacker than that of gas or oven coke, 

 and its hardness intermediate. It is used principally for mak- 

 ing electric carbons, although considerable quantities are used 

 for fuel. 



With the exception of gas-coke very little use is made of 

 this fuel for steaming, the fire being too intense locally, and 

 hence very apt to burn out the boiler directly over it. In all 

 cases plenty of air is needed to keep up the combustion, which 

 is also a drawback for steaming purposes. For metallurgical 

 furnaces it is different. Here it is almost the ideal fuel, giv- 

 ing an intense reducing heat at just the part of the furnace 

 where most needed. It has been used in iron furnaces for 

 years, and is still the favorite fuel. It is superior to anthracite, 

 as it has no tendency to splinter and crack with the heat, and 

 bears its burden very well. Of course this does not apply to 

 ordinary gas-coke, which crushes easily. 



Coke is essentially carbon, and the mineral portions of the 

 coal from which it is made. It contains small quantities of 

 hydrogen and nitrogen, as may be seen from the tables. The 

 percentage of these, however, is very low, so that the cal- 

 culated and observed heat-units are usually within the limits 

 of error, as is shown in the following table : 



