78 COMBUSTION AND FUELS 



Mixture Elements Products 



in Pounds in Pounds in Pounds 



Hydrogen, 1.0 Hydrogen, 1.0 1 



Air 348=( Xygen ' 8-0/- Water ' 



\Nitrogen, 26.8 Nitrogen, 26.8 



35.8 35.8 35.8 



Incomplete Combustion. There is one other case that may 

 occur; the combustion of carbon may not be complete. If 

 insufficient air or oxygen is supplied to the burning carbon, 

 it is possible for the carbon and oxygen to form another gas, 

 carbon monoxide, CO, instead of carbon dioxide, COz. The com- 

 bustion of 1 Ib. of carbon to form CO, of course, requires only 

 one-half the oxygen that would be necessary to form COz. This 

 is because in CO gas 1 atom of carbon seizes 1 atom of oxygen 

 instead of 2. To burn 1 Ib. of carbon to COz requires 11.6 Ib. of 

 .air. To burn it to CO would, therefore, require but 5.8 Ib. of air. 

 Calorific Value of Fuels. The amount of heat, in B. T. U., 

 developed by the complete combustion of 1 Ib. of a fuel is 

 termed the calorific value of that fuel; it is also sometimes 

 called the heat value or the heat of combustion. It may be 

 determined most accurately by burning a known weight of 

 the fuel with oxygen in an instrument known as a calorimeter. 

 The gases resulting from the combustion are passed through a 

 known weight of water and give up their heat to the water. 

 By noting the rise of temperature of the water, it is possible 

 to calculate the amount of heat absorbed, and thus to determine 

 the heat that would be produced by the combustion of 1 Ib. 

 of the fuel. The calorific values of the elements most commonly 

 found in fuels are as follows: 



B. T. U. per Lb. 



Hydrogen, burned to water, H->O 62,000 



Carbon, burned to COi 14,600 



Carbon, burned to CO 4,400 



Sulphur, burned to SOi 4,000 



If the various percentages, by weight of the elements, com- 

 posing a fuel are known, the approximate calorific value of 

 that fuel may easily be calculated by the formula 



X=14,600C+62,000 \H ) +4,0005, 



H 



