262 Dr Fyfe on (he Evaporative Power of Coal. 



that as our furnaces are never so constructed as to effect com- 

 plete combustion, and that as the combustion varies very 

 much in different furnaces, the results ought not to be relied 

 on. Now this is undoubtedly so far a valid objection ; but if 

 our trials are conducted with what will be allowed to be a 

 furnace constructed on proper principles, and if the trials are 

 made on the different fuels, making such adjustments and 

 alterations as may be requisite for the fuel under use, then 

 the results, though they do not give what ought to take place, 

 yet give the comparative evaporative power in practice, and 

 in this respect become extremely valuable, as pointing out the 

 kind of fuel that is most beneficial for the purposes required. 



From the opportunities I have had of testing different fuels 

 in this way, both on a large and on a small scale, I trust the 

 results will be found of sufficient importance to require no 

 apology for my laying them before the Society. 



In the following statement I shall give the results by actual 

 trial in furnaces, and compare them with those which ought 

 to be got according to the composition of the fuel, and also 

 according to the method proposed by Berthier. 



In conducting the analysis of the fuel, I have not thought 

 it necessary to ascertain minutely the proportion of all the 

 ingredients. I have determined merely the quantity of mois- 

 ture, of gaseous matter evolved by heat, of fixed carbon, and 

 of ashes or incombustible material ; and this was done in the 

 usual way by expelling the moisture by cautious application 

 of heat ; then driving off the volatile matter by exposure 

 to a strong heat, excluded from air; and lastly, heating in con- 

 tact with air, to burn off the fixed carbon, and thus to ascer- 

 tain the proportion of it and of the ashes. The combustion 

 by the process of Berthier was conducted with the usual pre- 

 cautions, so as to secure success. 



With regard to the furnaces in which these trials were made, 

 they were sometimes small, at other times and most frequent- 

 ly large, such as those attached to a four and ten-horse en- 

 gine. In carrying on the experiments with one particular 

 kind of fuel, I mean anthracite, it was necessary to have re- 

 course to a peculiar construction of furnace, so as not only 

 to secure the complete combustion of the coal, but also to try 



