io8 



GENERAL SCIENCE 



in the early fall, when not much heat is needed in the 

 rooms, to cause the water to flow from the boiler to the 

 radiators. The water thus flowing through the radiators 

 is not very hot and will not give to the rooms an excess 

 of heat like steam radiators. For example, the water 

 in the radiator may be at a temperature 

 of only 140 F., and therefore not much 

 heat will pass into the room, while in 

 the steam system the radiator with steam 

 in it has a temperature of 212 F., and 

 hence will give off to the air in the room 

 much more heat than is usually wanted. 

 The expansion tank in the upper part 

 of the house is usually kept about half 

 full of water. As the boiler and all the 

 water pipes and radiators must be kept 

 completely full of water, the water will 

 have to have some open vessel into 

 which the extra volume due to expansion 

 by heating can flow, or else the radiators 

 or pipes or boiler would burst when the 

 water is heated. The expansion tank 

 is usually connected with the outside 

 of the house by an open pipe leading to 

 a sink or to the roof. Through this pipe 

 the water can flow if the expansion tank 

 is too small to hold the extra volume of 

 WATER SYSTEM or water j ue to expansion by heating. 



HEATING . . 



During extremely cold weather the 



boiler and the water pipes in the hot water system must 

 be drained if no fire is kept in the boiler, in order to pre- 

 vent the bursting of the pipes by freezing. 



76. Fireless Cooker. A fireless cooker may be made 



APPARATUS ILLUS- 

 TRATING THE HOT 



