ON THE STRENGTH OF LOCOMOTIVE BOILERS. 59 



equal increments of absolute heat produce equal increments of sensible tem- 

 perature as indicated by the thermometer. 



To determine the time, estimated from a given pressure, at which the 

 boiler would burst, — 



1st. Let the given pressure be that of the atmosphere, and let the boiler 

 be able to sustain 240 lbs. pressure per square inch. 



From an experimental table of pressures and temperatures, we find 240 lbs. 

 pressure to correspond to 403° temperature, and 15 lbs. pressure to 212° 

 temperature ; hence we have by formula (3), 



403—212 .„ . , 



t, — = ^43 minutes, 



' 4-44 



which is the time in which the boiler would burst, estimated from the time 

 at which the water begins to boil. 



2nd. Let the given pressure be 60 lbs- per square inch, and the boiler- 

 pressure 240 lbs. per square inch, then 



405—296 —2^'\ minutes. 

 ' 4-44 



3rd. Let the given pressure be 60 lbs. per square inch, and the boiler- 

 pressure 300 lbs., then 



422—296 _2g ^jnutes, 



' 4-44 



which is nearly the time in which the boiler experimented upon would burst. 



These facts appear to be sufficiently conclusive to enable us to judge of 

 the dangers to which people expose themselves under circumstances where 

 the necessary precautions are not taken for allowing the steam thus gene- 

 rated with the fire under the boiler to escape. The great majority of acci- 

 dents of this kind have arisen during the time the engines are standing, pro- 

 bably with the safety-valve fastened and a brisk fire under the boiler. How 

 very often do we find this to be the case in tracing the causes of these 

 melancholy and unfortunate occurrences I 



The statements contained in the earlier part of this paper regarding the 

 strength of the stays of the fire-box would have been incomplete if we had 

 not put those parts of a locomotive boiler, comprised in the flat surfaces or 

 sides of a fire-box, to the test of experiment. 



This was done with more than ordinary care ; and in order to attain con- 

 elusive results, two thin boxes, each 22 inches square and 3 inches deep, 

 were constructed ; the one corresponding in every respect to the sides of 

 the fire-box, distance of the stays, &c., the same as those which composed the 

 exploded boiler ; and the other formed of the same thickness of plates, but 

 different in the mode of staying, which, in place of being in squares of 5 inches 

 asunder, as those contained in the boiler which burst, were inserted in 

 squares of 4 inches asunder. In fact, they were formed as per annexed 

 sketch (Figs. 4 and 5), the first containing 16 squares of 25 inches area, and 

 representing the exploded boiler, or old construction ; and the other, with 

 25 squares of 16 inches area, representing the new construction. 



