TRANSACTIONS OF THE SECTION'S. 



207 



(figs. 1, 2, and 3) 33 feet long, 5 feet 6 inches diameter, with two round flues 19 inches 

 diameter through the centre ; this boiler had 40 feet of heating surface to the nominal 

 horse-power of the engine : the two flues contained 20 feet, and the shell 20 feet per 

 nominal horse-power ; the furnace was below the boiler at the fore-end, had a fire-grate 

 of 26 square feet; the fire passed underneath the boiler to the opposite end from the 

 furnace, and returned along the sides, and then passed back again through the flues 

 to the chimney. The temperature above the centre of the fire was found to be, upon 

 one occasion, 3200°; at the top of the bridge 1730'; the temperature of the gases 



Fie. 1. Pig- 2. 



Fig. 3, 





gradually reduced as they passed back the remaining length of 26 feet under the 

 boiler and along the side flues, till they entered the centre flues at 1 163°, and left 

 tbem at about S00°. Thus the furnace containing a surface of 2 feet per nominal 

 horse-power reduced the heat about 1500°; the shell of the boiler behind the furnace, 

 of about 18 feet per nominal horse-power, reduced the temperature about 600°; and 

 the flues containing a surface of 20 feet per nominal horse-power reduced the tem- 

 perature about 350°. The temperatures of the gases in the flues were found to be 

 about the same in the centre as at the top ; but at the bottom of the flue the tempe- 

 ratures of the gases were at the fore-end rather less than at the top, but towards the 



Fi"r. 4. Fig. 5. 



n 



-A 





back end the temperature of the bottom of the flues reduced gradually below the 

 temperature at the top to the extent of 300°. Upon another occasion the tempe- 

 rature over the centre of the fire was found to be 3610°; at the top of the bridge 

 1739° ; and the different temperatures of the flues were as indicated in fijr. 1, where 

 the average temperatures of the flues at B 1 = S2i)°, B- = 879°, B' = 937°, B' = 959°, 

 and at B 5 = 93 1°. The temperatures at the top of the flues at C J = 982, at C 1 = 1034°, 

 at C J = 1037. The temperatures at the bottom of the flues at A 1 = 571°, A 2 = 603°, 

 A^ = 678°, A 1 = 764°, A 5 = 822°. It would therefore appear that, notwithstanding 

 the large amount of surface in this boiler, the evaporative power is very inferior, as 



