266 Dr Fyfe on the Evaporative Power of Coal. 



a Scotch coal got from a different place, and with another fur- 

 nace, not fitted with the hot-air apparatus. It was one at- 

 tached to a ten-horse high-pressure engine. This trial was 

 conducted in the same way as the former, and nearly at the 

 same pressure, due attention heing paid to the weighing of the 

 fuel, the state of the fire at the commencement and termina- 

 tion, and also to the height of the water in the boiler, which 

 was ascertained also by a float and index. Without giving 

 the particulars, I may merely mention, that the trial lasted 

 from eleven till four o'clock. The total quantity of coal used 

 was 540 lb., and the total amount of evaporation was 3580, 

 thus making the result 6.62 lb. for each pound of coal used. 



In the former trial the water supplied to the boiler was at 

 45°, in the latter the return-water from tbe boiler was thrown 

 into the supply tank, and hence the temperature was higher. 

 It was found on an average to be at 170°, which will so far ac- 

 count for the greater amount of evaporation. 



In the table given by Richardson, already referred to, the 

 quantity of oxygen necessary for the combustion of the spe- 

 cimens of Scotch coal analysed, is 247, which would make the 

 evaporative power 11.3 compared to that of pure carbon as 

 12.3. By the test with litharge as proposed by Berthier, I 

 found that the greatest quantity of oxygen required for the 

 combustion of the fuel with which the first trial above given 

 was made, was 205, which would make its evaporative power 

 9.48. But by the furnace trial only 6.22 were evaporated. 



Now 9.48-6.22=3.26 and 9.48: 3.26 : : 100 : 34.38 ; with- 

 out taking into account the slight difference in temperature 

 between 32° and 45°, there was therefore a loss of 34.38 per 

 cent, of the heat supposed to be evolved, provided the whole 

 of the fuel was consumed ; but in this trial the cinders in 

 the ash-pit amounted to 52 lb., and deducting this from the 

 fuel used, there were only 732 lb. actually consumed, which 

 would make the evaporation amount to 6.66, and 9.48 — 6.66 

 =2.82, and 9.48 : 2.82 : : 100 : 28.97 : thus giving a loss of 

 28.97 per cent, of the heat evolved, supposing 732 lb. of coal 

 had undergone complete combustion. 



I am aware that it may be objected to this trial, that as the 

 loss is so great, the furnace must have been very defective in 



