GASEOUS FUELS. 95 



COAL GAS. 



The heat of combustion of illuminating gas obtained from 

 the distillation of coal in closed retorts is very variable. It 

 depends not only on the nature of the fuel, but also on the 

 rapidity of the distillation and the heat by which it is accom 

 plished. The heat of combustion varies from 5200 to 6300 

 calories per cubic metre. It cannot be represented by any 

 average number. 



According to Witz, at the same gas-works and with the 

 same fuel, yields may occur from 4719 to 5425 calories. 

 According to Bueb-Dessau, the illuminating gas of the same 

 city during the same day will sometimes vary 20 per cent. 

 Dr. Birchmore reports the same result from his examinations 

 of the gas of Brooklyn, N. Y. 



We are not certain that the composition assigned to coal 

 gas by analysis corresponds always to the gas as obtained by 

 distillation ; in Europe, especially, a portion of the heavy 

 hydrocarbons is taken out for sale separately, and the deficiency 

 supplied by cheaper oils. 



From several experiments which he made, Bueb-Dessau* 

 thought that the heat of combustion of illuminating gas was 

 directly proportional to the candle power; but in addition to 

 this being opposed to the theory of heat, the experiments of 

 Aguitton show the contrary. He concluded from his deter- 

 minations that each illuminating gas of different candle power 

 has a definite heat of combustion which corresponds to the 

 intensity of the light. His experiments were carried on with 

 more than a hundred samples, rich and poor, the former kind 

 from cannel coal, the latter from the end of the run carried to 

 an extreme. He represents by the following formula the 



* Bueb-Dessau cites the following among others: 



Candle-power. Heat-value. 



Gas of Dessau.. 14- 4400 calories 



Gas of Bremen 21.9 5977 



Gas from cannel coal 26.0 6559 



