Dr Fyfe on the Evaporative Power of Coal 259 



and Ed. Phil. Mag. for August 1838. From his experiments 

 he has given the composition of the coal, and the quantity of 

 oxygen necessary for the combustion. The following table 

 shews the results, dividing the coals into four classes, as men- 

 tioned by Dr Thomson. 



From this table it appears that there is not much differ- 

 ence in the heat evolved by the perfect combustion of the va- 

 rieties of coal mentioned ; assuming that the heat is in the 

 ratio of the oxygen consumed, thus leaving out the cannel 

 coal, which is not used for steam-engines, and also the Wy- 

 lam, which is not now in the market, the extremes are 

 122.56, and 112.12 ; that is, as 100 to 109.3. Or, taking the 

 average of the two samples of Scotch coal and that of the 

 English,- it is as 100 and 109.6. These numbers may there- 

 fore be considered as representing, the former the Scotch, and 

 the latter the English, caking coal* 



The analysis of organic matter, such as that used for fuel s 

 requires a great deal of nicety in the manipulation ; it has 

 therefore been proposed to adopt a simpler method for arriving 

 at the quantity of oxygen necessary for the combustion, than 

 by ascertaining the proportions of the ingredients. A very 

 ingenious method of doing so has been recommended by Ber- 

 thier, founded on the decomposition of metallic oxides by in- 

 flammable matter. It is well known that when these oxides 

 are heated with carbon, carbonic acid is expelled, and the 



* Higher results than that given above have been obtained by others ; but 

 I wish those stated to be considered as applying merely to the coals used ; 

 though, I believe, they will be found as very nearly the average compara- 

 tive power of Scotch and English coal. 



