STEAM AND VAPORISATION. 



fairly broad and flat, it will collapse with a 

 moderate reduction of pressure on the inside. 

 But a round shape is stronger, and if the flask 

 be well rounded at the bottom, or of thick 

 strong glass, it may be necessary to secure a 

 good difference of pressure by getting a con- 

 siderable vacuum through a more complete 

 condensation of steam. To effect this the 

 flask can be placed in any convenient holder and 

 a quantity of cold water poured over it. 



Many a flask is, of course, strong enough to 

 stand a complete vacuum inside, and then it 

 becomes necessary to break it by a smart blow 

 with a hammer or other hard instrument. 



We still have the loud noise and flying glass 

 and water, while the fact that the steam has 

 been condensed with cold water shows that 

 the result cannot be an explosion. 



3. Water boiled by Cold instead of by Fire or 



Flame. 



The simple apparatus for the last experi- 

 ment will serve to illustrate another striking 

 paradox. But this time we want neither col- 

 lapse nor explosion, so the flask should be one 

 that is rounded all over except at the neck, and 

 of rather stronger make, and the water should 

 half fill it, instead of being only about half an 

 inch deep. 



Boil the water, and, as before, close the 



K I 45 



