STEAM. 95 



remainder of the distance, by its own expansive force. 

 By this arrangement, instead of using a cylinder full 

 of steam at each movement of the piston, only one- 

 fourth, or even less, according to its density, suf- 

 fices. Steam employed in this manner is said to be 

 used expansively. The term is applied especially to 

 this case, although it is a fact that steam always acts 

 expansively. 



228. CONVERSION OF VAPORS INTO LI- 

 pors convened QUIDS. If a vapor, in any way, loses its 

 into liquids? latent heat, it at once becomes liquid. If, 



for example, steam be led into a cool pipe, 

 the metal abstracts the latent heat, and the steam be- 

 comes water. At the same time, the heated pipe im- 

 parts warmth to the air around it. 



229. HEATING HOUSES BY STEAM. 



How are 



houses heated Houses are thus heated, by steam pipes 

 passing through the various apartments. 

 The pipes abstract the heat, and give it out again to the 

 air of the house. The steam thus converted into wa- 

 ter, runs back into the boiler to be reheated, and to start 

 again on its journey. And as long as heat is supplied, 

 the water continues its service as a carrier of heat. 



230. WATER HEATED BY STEAM. When 



How is water 



heated by steam is led into water, the effect is the 

 same as on leading it into a cold pipe. 

 The water abstracts its latent heat, and becomes hot, 

 while the steam itself becomes additional hot water. 

 Water in different parts of a room, or even of a large 

 manufacturing establishment, may thus be made to 



