134 



THE PRODUCTION AND USE OF HEAT 



Steam heating is especially adapted to the heating of large 

 buildings and rooms which are considerably removed from 

 the boiler (Fig. 97). In many cities large, central steam 

 heating plants are constructed. Steam pipes extend from 

 the plant throughout large portions of the city. These pipes 

 are supported within brick conduits beneath the surface of the 

 street. Smaller SUPPLY PIPES lead from the MAINS to the 

 business blocks and the residences * on either side of the street. 

 Steam heat is then sold to customers just as gas (Art. 77) and 

 water (Art. 564) are sold. 



TEMPERATURE OP STEAM VARIES WITH PRESSURE 



164. "Boiling Point" of Water. We saw in Art. 21 that 

 what is known as the " boiling point 7 ' of water is really the 

 temperature of the steam arising from water 

 when the pressure upon the steam, and, 

 therefore, upon the water, is equal to the 

 average pressure of the atmosphere at sea 

 level. We shall now see that water will 

 boil at much lower temperatures if the 

 pressure be decreased below that point, and 

 at much higher temperatures if the pressure 

 be increased above that point. 



Exercise 40. Boiling Water at Low Temperatures 



Arrange a round bottom flask using a two-hole 

 stopper and connect it with an air pump as in 

 Fig. 98. The stopper in the flask carries a 

 chemical thermometer in one hole and an L-tube 

 in the other. The L-tube and the rubber tubing 

 connect the flask and the air pump. All joints 

 must be air-tight. First, without applying heat 

 to the flask remove all air possible from the flask 

 by means of the pump. Does the water boil? 

 If your pump is in good condition, the water will boil. If your 

 pump is not in good condition, you may find it necessary to heat 

 the water somewhat. Note and record the lowest temperature at 

 which you are able to make the water boil. 



FIG. 98. Boiling 

 water at low temper- 

 atures. 



