Dr Fyfe on the Evaporative Power of Coal. 275 



In this trial 51 lb. of coal were used, and 400 lb. of water 

 evaporated ; hence, for each pound of coal used, 7.84 of water 

 were evaporated. 



Different results were obtained in some of the other expe- 

 riments, some of them giving a lower amount of evaporation. 

 Taking the average of the whole it very nearly agreed with 

 the above ; according to it, 5.88 : 7.84 : : 100 : 133. 



The average of the trials properly conducted gives a result 

 as 1 00 to 131.5. We are not therefore far from the truth if 

 we take it as 100 to 133, that is as 3 to 4. 



The composition of the Scotch and English coal was found 

 to be 



100.0 100.0 



The table given by Mr Richardson already quoted, shews 

 that the evaporative power, calculated according to the quan- 

 tity of oxygen required for combustion, ought to be in the 

 ratio of 100 to 109.6. In the experiments I have made on the 

 coals used in the trials above referred to, I found the evapora- 

 tive power by the litharge test to be as 100 to 105.2, numbers 

 not differing much from those of Richardson. But the evapo- 

 rative power by the furnace trials was as 100 to 133, which is 

 very different from the other. It becomes, therefore, an im- 

 portant question, what is the cause of this difference ? for if 

 we can solve this, it may perhaps lead to the means of mak- 

 ing the available power of the Scotch approximate to that of 

 the English coal. To this I will afterwards refer. 



On viewing the results of the experiments now detailed, 

 one remarkable circumstance at once strikes us, — it is the 

 great practical evaporative power of anthracite over the 

 other kinds of coal, which, though they contain less fixed car- 

 bon, yet have much more volatile matter, the hydrogen of 

 which, I have already said, gives out thrice as much heat as 

 carbon does. In the anthracite which I employed, the fixed 

 carbon amounted to 71.4 per cent., in the caking coal it was 



