CH. xxviii. CONDENSATION OF STEAM. 249 



ice, E. Now as long as the tap, c, is kept open, the steam 

 which is constantly rising from the water in b will rush along 

 the tube into the empty flask, a, and will there be turned into 

 drops of water by the cold of the ice underneath, and this 

 will go on as long as there is any water left in b, because 

 there will always be an empty space or vacuum in a to re- 

 ceive the steam as it rises. When the tap, c, is shut, the 

 steam in b will become very dense, and when it is opened 



Fig. 42. 



Steam condensed in a separate VesseL 



A, Flask empty of air. B, Flask half-full of water and empty of air. c, Tap con- 

 necting the two bottles. D, Spirit lamp keeping the water m B boiling, e. Basin 

 of ice cooling down the steam which passes into A. 



again the greater part of the steam will rush out and be 

 cooled down in A, while b remains hot as before. 



Watt's Engine. — This was exactly the plan Watt adopted 

 in his steam-engine ; b answers to his cylinder (Fig. 43), 

 which could be kept always hot, and a to his condenser, in 

 which his steam was turned back into water. We cannot 

 follow out all the different steps of his invention, and must 

 content ourselves with a rough description of his engine 

 after he had completed it, as shown in Fig. 43. 



In the first place you must notice that cold water is kept 

 flowing down from the tank a into b, and out through the pipe 

 C, so that the condenser standing inside b is kept quite cold : 



