33 



Lord and Haas found that the results of their work did not 

 correspond to the above figures. The theoretical heating- 

 value of coals varies between about 7000 and 16,000 B.T.U., 

 depending on their nature. 



In order to completely burn one pound of carbon, 2.661b. 

 of oxygen are necessary; but as air, the usual source of 

 oxygen, only contains 21 per cent, of that element, it follows 

 that 12.661b. of air must be provided to oxidise lib. of carbon. 



Since a calorimeter burns all the fuel, it gives a better 

 result than is possible in a boiler, for a boiler does not take all 

 the heat out of the gases generated by the fuel : then there is 

 always an excess of air supplied to the fire which carries away 

 quantities of heat up the stack; also all the fuel is never 

 burnt in the fire box of a boiler, therefore some of the heat 

 is not developed. It will thus be seen that the value of a fuel 

 for heat-producing purposes depends largely on the efficiency 

 of the boiler, and a fuel that will do good work in one class of 

 boiler may not come up to expectations in another; if, how- 

 ever, the true heating power of a fuel is given as ascertained 

 by a calorimeter, it serves, other things being equal, as an in- 

 dication of the relative value of different fuels. There are 

 yet other points to be considered, such as the skill of 

 the stoker, and the size of the fuel. In the latter case, lump 

 coal, having the same thickness of bed on the fire bars as that 

 given to slack, will permit more air to pass through it than 

 the slack, and this excess of air lowers the temperature. 

 If, on the other hand 4 an insufficient supply of air is admitted/ 

 then there is a loss of heat by incomplete combustion. Some 

 boilers are so constructed that the proper amount of air cannot 

 be regulated and consequently a superior coal burnt in such 

 an apparatus may give a worse result than that of an inferior 

 coal burnt in a properly constructed boiler. It is not possible 

 to arrive at the value of a fuel by analysis alone. Analysis 

 may show the heating power of a fuel, the moisture, ash, 

 volatile matter and fusibilitv of the ash : but it does not give 

 C 



