Dr Fyfe on the Evaporative Power of Coal. 263 



its power in raising steam rapidly, which, it is well known, is 

 necessary when the fuel is to bo used for steam-engine fur- 

 naces ; and it is of the utmost consequence to keep this in view ; 

 for however great the evaporative power even in practice may 

 be, that fuel is of little value if it cannot be burned so as to 

 make it applicable for the purposes for which fuel is generally 

 used, such as the rapid raising of steam, and keeping up a 

 sufficient supply for the engine. 



The experiments, the results of which I am first to detail, 

 were made with the view of ascertaining the comparative 

 practical evaporative power of anthracite and of Scotch coal. 

 They were conducted with a furnace attached to a four-horse 

 high-pressure boiler ; the furnace bars, of which there were 

 from 12 to 14, according to circumstances, were each 3 feet 6 

 inches in length, and in all 2 feet 4 inches in breadth, including 

 the spaces between them, giving 7 feet of fire surface. It 

 Mas at first fitted up with flash-flues, which were afterwards 

 changed to the common flue, 18 inches by 14, passing along 

 the boiler on one side, returning on the other, and then en- 

 tering the chimney. The chimney-stalk was 22 inches by 18, 

 and 33 feet in height, in addition to which an iron tube of a 

 foot in diameter and 12 feet in height was attached, thus 

 making the whole height 45 feet. To this furnace and boiler 

 there was attached an apparatus by which the fuel could, when 

 required, be supplied with warm air. It consisted of a me- 

 tallic box placed immediately be}'ond the end of the bars 

 forming the floor of the furnace, from which there proceeded 

 tubes that passed through the boiler, and so placed in it as to 

 be surrounded by the water. From these, after passing 

 through the front of the boiler, a larger tube was transmitted 

 to the ash-pit. A drain was carried from the side of the fur- 

 nace to the box situate beyond the fire-bars to supply air, 

 and the ash-pit was furnished with a door which fitted tight 

 so as to prevent any current up through it. By this adjust- 

 ment, when the ash-pit door was shut, the air for combustion 

 was supplied through the box, heated to a considerable de- 

 gree, and after passing through the tubes in the boiler, then 

 proceeded to the ash-pit, and rushing up through the fuel 

 kept up the combustion. By apertures left for the purpose 



