186 ON SUPERHEATED STEAM. 



pansion of steam- water, such as here mentioned, is 

 sufficient to account for any amount of explosions. 

 Let us refer again to the diagram of the boiler ; 

 the pressure we will suppose at 100 lbs. ; the fire 

 to be at its full intensity (''for the consumers of 

 steam are always crying out for more"). Whilst 

 the engine and works are in full operation, the 

 danger of the boiler bursting is not so great, for 

 the whole mass is pretty nearly of equal tempera- 

 ture, and all inside is in boiling agitation. But 

 dinner-time comes ; the engine is stopped ; the 

 water then is in a comparative state of rest, and 

 does not boil or agitate, in obedience to the law 

 of not doing so under pressure if the outlet be 

 stopped ; the water is a slow conductor ; the lower 

 stratum is somewhat hotter, the deposit and 

 bottom of the boiler, perhaps, nearly red-hot as 

 the time approaches to start the engine. Suddenly, 

 the communication is opened, and the pressure is 

 lessened at the top by the steam passing off ; the 

 whole mass opens, and heaves to rush out at the 

 opening, and is then lifted up from the bottom 

 along with a large mass, perhaps, of red-hot earthy 

 deposit ; in a moment, a great mass of water 

 flashes into 1,700 times its volume, for it is a 

 noticeable fact that explosions take place mostly 

 when steam-engines or works are started. When 

 a boiler bursts, it is invariably found to have done 

 so at the side or ends, being weakened there by 

 the water mechanically, as well as chemically, 



