THE 

 LONDON/ EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



— «* — - 



[FOURTH SERIES.] 



NOVEMBER 1863. 



XLVII. On the Numerical Expression of the Destructive Energy 

 in the Explosions of Steam-boilers, and on its comparison with 

 the Destructive Energy of Gunpowder. By George Biddell 

 Airy, Astronomer Royal*. 



1. A LITTLE consideration of the changes in the state of the 

 il water and steam, which occur during the bursting of a 

 steam-boiler, will show that very little of the destructive effect 

 of an explosion is due to the steam which is contained in the 

 steam-chamber at the moment of the explosion. The rupture 

 of the boiler is effected by the expansive power common at the 

 moment to the steam and the water, both at a temperature 

 higher than the boiling-point ; but as soon as steam escapes, 

 and thereby diminishes the compressive force upon the water, a 

 new issue of steam takes place from the water, reducing its tem- 

 perature ; when this escapes, and further diminishes the com- 

 pressive force, another issue of steam of lower elastic force from 

 the water takes place, again reducing its temperature ; and so 

 on; till at length the temperature of the water is reduced to the 

 atmospheric boiling-point, and the pressure of the steam (or 

 rather the excess of steam-pressure over atmospheric pressure) is 

 reduced to 0. It is the enormous quantity of steam, of gradu- 

 ally diminishing power, which is thus produced from water during 

 the course of the explosion, that causes the disastrous effects of 

 the explosion : compared with this quantity, the small volume of 

 gas which may happen to be in the steam-chamber at the time 

 is, in boilers of ordinary construction, wholly insignificant, and 



* Communicated by the Author. An abstract was communicated to the 

 Mechanical Section of the British Association at their late Meeting at 

 Newcastle. 



Phil. Mag. S. 4. Vol. 26. No. 176. Nov. 1863. Z 



