Fire and Heat 143 



may run as high as 15,500 B. T. U. per pound. If the same price 

 is charged for both, or if a higher price is charged for 'a coal 

 with a higher heat value than that charged for a coal with a 

 lower heat value, the fact is worth knowing and computing in 

 the cost of heating. 



When the heat value for a unit measure of a given fuel is 

 known, such computation is simple. Comparisons of one fuel 

 with another are equally easy. There must be included, of 

 course, the advantages which one fuel or source of heat may 

 afford as compared with the advantages or disadvantages of 

 another. Gas, for example, is very convenient, involving much 

 less work than coal, and distributing heat much less widely, 

 an advantage during hot seasons. Electricity may have ad- 

 vantages, such as comfort and convenience, which may more 

 than compensate for its cost in excess of that of gas. 



Heat values of chemical constituents of fuels. In the table 

 of common fuels and some typical coals the heat values given 

 are at best only approximate. Coal from the same mine varies 

 in heat value. The table shows that the heat value of a fuel 

 depends upon the relative quantities of the combustible sub- 

 stances of which it is composed. The chief of these substances 

 are carbon, hydrogen, and sulfur. One pound of carbon com- 

 pletely burned is estimated to give 14,544 B. T. U., hydrogen 

 gives 62,028 B. T. U., and sulfur 4050 B. T. U. Hydrogen, it 

 appears, has a heat value about four and one half times that 

 of carbon. Thus a fuel, such as kerosene or gasoline, which has 

 a large proportion of hydrogen, has a higher heat value than 

 a fuel having a small amount of hydrogen and a larger pro- 

 portion of carbon. 



Calculating a fuel's value in B. T. U. When the chemical 

 composition of a fuel is known, the heating value of the fuel may 

 be computed approximately by this formula: 



Carbon X 14,544 + 62,028 X (Hydrogen - Qxygen ) + 4050 X sulfur 

 gives the heating value in B. T. U. 



