8TBA1* BOILER EXPLOSIONS. 49 



ttitfefent proportion, an explosion will take place. Steam is the 

 form of gas which rises from water when at a temperature of 212 

 As water is composed of two gases, it of course follows, that 

 steam must be composed of the same. If we take this steam and 

 allow it to pass through a red hot iron tube, the gases separate ; 

 tlio uxy^i-n being absorbed by the hot iron, while the hydrogen, 

 if allowed to escape through a jet, and lighted, will burn like 

 ordinary gas. It is thus that hydrogen gas is produced. 



Another fact about steam is, that it cannot be much compress- 

 ed, as may be inferred from observing the lid of a kettle rising 

 by its force j and hence comes the absurdity of trying to obtain 

 and utilise an excessive pressure of steam. 



We think we have now facts enough before us, to consider 

 And explain the cause of explosions. Let us suppose, for the 

 eake of clearness, that the iron boiler is transparent, as a glass 

 bottle, or retort. Let it be half full of water. Put fire under 

 it, and after a time the water begins to boil at the bottom, 

 and change into its gases, which rise through the water and fill 

 the upper chamber. There they remain transparent, till they 

 issue from the boiler into the atmosphere, with which they 

 chemically unite in the form of cloud. 



Suppose we aow shut off steam. The gases cannot be com- 

 pressed, and the water cannot be made to reach a higher tem- 

 perature than 212 F. without changing into steam, although 

 the latter may be raised to a temperature of 600, As the fire 

 is still burning at the bottom of the boiler, the water then must 

 be continuously changing into steam, and as it cannot gain the 

 surface, because the upper part is already completely occupied 

 by the gases, it must remain at the bottom. The water then 

 is gradually being auspended above the bottom of the boiler, 



