and the Economy of Fuel. 1 1 5 



quantities of heat which equal weights of the given 

 kinds of fuel are capable of generating, or directly as 

 the quantities of the kind of fuel in question, which are 

 required to produce the same heat, it is 1089 to 600, as 

 66 1 1 Ibs. of wood to 363! Ibs. of coal, supposing the 

 foregoing estimate to be exact. 



Whether it would be possible to cause so large a 

 quantity of water (1681 wine-gallons), at the given tem- 

 perature (65!), to boil, with this small quantity of coal, 

 I leave to those who are conversant in experiments of 

 this kind to determine. 



From the result of my 2Oth Experiment it appeared 

 that 2OiV Ibs. of ice-cold water might be heated 180 

 degrees, or made to boil under the mean pressure of the 

 atmosphere at the level of the surface of the ocean, with 

 the heat generated in the combustion of i Ib. of pine- 

 wood. Computing from the result of this experiment, 

 and from the relative quantities of heat producible from 

 pine-wood and from pit-coal, it appears that the heat 

 generated in the combustion of i Ib. of pit-coal would 

 make 363;% Ibs. of ice-cold water boil. 



Hence it appears that pit-coal should heat 36 times its 

 weight of water, from the freezing point to that of boiling ; 

 and, as it has been found by experiments made with great 

 care by Mr. Watt that nearly 5! times as much heat 

 as is sufficient to heat any given quantity of ice-cold 

 water to the boiling-point is required to reduce that 

 same quantity of water, already boiling-hot, to steam, 

 according to this estimation, the heat generated in the 

 combustion of i Ib. of coal should be sufficient to re- 

 duce very nearly 7 Ibs. of boiling-hot water to steam. 



How far these estimates agree with the experiments 

 that have been made with steam-engines, I know not ; 



