.60 Economy of Fuel. 



The experiments are stated in two modes, so far as respects 

 the temperature of the water with which the boilers were sup- 

 plied ; the first expresses the real temperature at the time of 

 making the experiment; the second exhibits the proportion 

 of coal required to evaporate the water, supposing the latter 

 to have entered the boiler at 212°. These latter columns 

 are given, in order that the results of the several experiments 

 might appear upon equal terms, which would not have been 

 the case, unless the water which entered the boiler in the 

 different experiments, was reduced to an uniform temperature. 

 This temperature I have fixed at 212°, because it is at that 

 degree of heat that water begins to be converted into elastic 

 steam equal to the pressure of the atmosphere. In order to 

 separate the quantity of coal burnt in heating the water to 

 212° from that actually spent in evaporating it. I have 

 assumed Mr. Watt's figures for the latent heat of steam. 



In the eight first columns of the Table, the facts and infer- 

 ences from each experiment are stated. In the three last the 

 results are given as deduced from the theory, that a just com- 

 parison may be made between the several experiments. This 

 comparison appears in the last column. An example (a) is 

 also given of the operation by which I obtain the figures in the 

 three last columns, which are therefore subject to verification, 

 should the method employed be found objectionable. 



Manchester, Feb. 26, 1822. Josiah Parkes. 



