416 Proceedinga of the Society of Arts, 



naco?, ns now constructed, tho only way of finding the practical evaporative 

 power was by consuming the fuel in properly constructed furnaces, and 

 ascertaining liow much water is boiled off. It was to this method he had 

 recourse in ascertaining the evaporative power of the fuel. The first series 

 of experiments was made with the view of trying the power of common 

 Scotch coal, and of Antliracito. From the numerous trials he had made, 

 he found that the practical evaporative power of Scotch coal was about 6, 

 compared to that of pure carbon as 12 ; or, deducting the cinders not con- 

 sumed, it amounted to 6.6. The evaporative power, as determined by the 



^ quantity of oxygen necessary for its combustion, was 9.5, so that there was 

 a loss of nearly 29 per cent, of the heat evolved, supposing the combustion 

 complete. The composition of numerous specimens of Anthracite was 

 given ; some of them were shewn to contain no less than 94 per cent, of 

 pure carbon. That with which Dr F.'s trials were made had only 71.4 per 

 cent, of fixed carbon, 13 of volatile matter, and 10 of ash'es. It was there- 

 fore not of good quality. Its evaporative power, when tried in the furnace, 

 was very nearly 8, and, deducting the cinders, it amounted to 8.7. The 

 evaporative power, according to the quantity of oxygen necessary for its 

 combustion, Dr F, found to be 10.7, and accordingly the loss of heat 

 amounted to nearly 19 per cent. Dr F., however, shewed that, considering 

 the pressure at which the evaporation was conducted, the loss amounted 

 to only about 12 per cent. 



The next series of experiments were made with the view of ascertaining 

 the comparative power of common Scotch coal, and English caking coal : — 

 from numerous trials, he found it to be in the raiio of 3 to 4, or very nearly 

 so. On reviewing the result of the experiment, Dr F. alluded to the great 

 practical evaporative power of Anthracite over other kinds of coal, which, 

 though they contain much volatile matter, the hydrogen of which gives 

 out much heat during its combustion, yet do not evaporate nearly so much 

 ■water — indeed, he found the evaporative power to be according to the fixed 

 carbon ; that coal which contained most giving out tho most heat, which 

 he accounted for by the volatilization of the gaseous elements, which must 

 absorb heat when expell-od from the coals, and which heat can only be re- 

 placed by their undergoing combustion. From his numerous trials, Dr F. 

 Avas inclined to suppose that the practical evaporative power of a fuel would 

 be found to be as the fixed carbon in each, which evaporates 12.3 times its 

 own weight of water. In his trials, the Scotch coal evaporated G.66, the 

 Anthracite he used, 8.73, — of another Anthracite, it was 10.54. The 

 quantity that ought to have been eva]porated by the fixed carbon in these 

 coals (which was as 50.5, 71-4, and 92.4), was 6.2, 8.7, and 10.3 ; — ^num- 

 bers so nearly approximating to those in the above practical results, as to 

 induce him to believe that he was correct in the opinion he had advanced ; 

 and hence the superiority of Anthracite over other coals, when consumed 

 in furnaces as commonly constructed. 



Thanks voted to Dr Fyfe for this elaborate communication, and it was 



o*' derodto be printed in the Society's Transactions. 



