410 Mr. Henwootl on the lirplosion of Steam-Boilers. 



then appears to preponderate in favour of the idea of its ex- 

 plosion originating in the expansive force of the steam, which 

 it would seem was permitted to attain too strong an elasticity. 



" At the Pen-j'-fion engine we see that the fire-door is 

 thrown open, and then the current of air up the flue is stopped 

 by closing the damper: the interior is filled with atmospheric 

 air mixed to a certain extent with coal-gas ; the latter is in- 

 creased by the distillatory action of the fire, until the propor- 

 tion is attained which is explosive ; it takes fire, producing the 

 rush of flame which would be followed by a sudden vacuum in 

 the tube ; while the other side, pressed by the steam, gives 

 way to this sudden impulse, and is destroyed by a force very 

 much smaller than would be required if uniformly exerted." 



What Mr. Taylor says may be very possible, with the ex- 

 ception of the formation of a vacuum. Motion only obtains 

 when the resistance is inferior to the force applied, and ceases 

 (except under particular circumstances) as soon as thetwoforces 

 become equal. This then is the case in the phsenomena be- 

 fore us : the explosion may occasion a rush of air outward 

 through the fire-door, because the elastic force of the fluids 

 within the tube exceeds that of the atmosphere ; but as soon 

 as that within has so expanded as to be reduced in elasticity 

 equal to the pressure of the atmosphere, no further emission 

 of air from within the boiler can possibly ensue. Again, sup- 

 posing the possibility of a diminution in volume of the gaseous 

 matter within the boiler, the fire-door (say 1^ foot wide and 

 2\ feet long) in such boilers would afford an aperture quite 

 sufficient to supply (at the moment of the diminution of vo- 

 lume) the void. Hence then it is evident that no force at all 

 varying from the atmospheric pressure, can under any cir- 

 cumstance be exerted on the part of the boiler exposed to the 

 fire. 



" By some it has been suggested that hydrogen may have 

 been generated by the decomposition of water from leaks in 

 the boiler." 



This is not improbable in many instances : but we can about 

 as easily admit that the gas extricated from the coal, and 

 which is required in order to support combustion in ordinary 

 cases, produces the explosion. We also know that the coal 

 when thrown into the fireplace is never perfectly dry, so that 

 hydrogen is constantly evolved if water be decomposed. If 

 hydrogen produce explosion, such explosions are constantly 

 occurring ; and if the water be not decomposed, of course the 

 hydrogen cannot explode. In either case it is evident it would 

 be alike innocuous. 



But I believe the water is not decomposed when the boiler 



leaks 



