84 



Dr Fyfe oti the Comparative Evaporative 



In this trial, which lasted for 11 hours, the coal used 

 amounted to 82 lb. and the water evaporated was 460 lb. ; 

 and Vg'' = 5.61 ; accordingly, for each pound of coal consumed, 

 5.61 of water were evaporated ; but, as the water was at 42, 

 the result would have been only 5.56, provided the tempera- 

 ture of the water were at 32. 



In another trial the result was 5.8, or supposing the water 

 at 32, it was 5.66. 



From the results of the experiments which have now been 

 stated, it is evident that the practical evaporative power of 

 coke is by no means so great as that of the coal from which 

 it is obtained ; for, had it been so, a much greater amount of 

 evaporation OHght to have been procured. It has been stated 

 that 1 lb. of coal evaporated in the furnace and boiler which 

 I used, 5.66 lb. of water from 32. Now, this coal yielded 

 52.5 per cent, of coke ; 1 lb. of the coke got from the same 

 coal evaporated 7.33 ; consequently .525 would have given 

 only 3.84. 



It may be objected to these trials, that as the coal evapo- 

 rated only 5.66 of water, the furnace was not well adapted 

 for the consumption of fuel. It must be allowed that the loss 

 of heat appears to be considerable, yet it was not much more 

 than we frequently find in furnaces of steam-engines, with 

 which it is considered a good result when 1 lb. of coal evapo- 

 rates 6 lb. of water. Besides, the trials were made not with 



