26 INTRODUCTION TO GENERAL SCIENCE 



over the flame and to one side of it so that the flame will heat 

 one side of the water only. Tell what you see, and explain. 

 Why is sawdust added to the water ? 



19. VENTILATION AND HEATING OF BUILDINGS 



Nearly every application of knowedge which we make use 

 of in business or for our comfort is founded upon some of the 

 various phenomena of nature. In the last experiments we 

 saw how easy it is to produce currents of air and water by 

 means of heat, while at the same time the heat was distributed. 

 We make use of these facts in the ventilation and heating of 

 buildings. 



The Hot-air System. Coal or wood is burned in a fire pot 

 which is surrounded by an air space. This space has one 

 inlet for cold and fresh outdoor air, and several outlets, each 

 of which leads to some room of the house. The air around 

 the fire pot becomes hot, and therefore expands, and is lighter 

 per given volume. This is pushed out of the heating space by 

 the outside cold and heavier air coming in. Thus the rooms 

 of the house are supplied with a continuous stream of warm, 

 fresh air. This system ventilates as well as warms the whole 

 building. Its great disadvantage is that the windy side of 

 the building does not receive its share of the heat. In order to 

 overcome this fault, power-driven fans are placed near the 

 furnace, and the warm air is forced to go where it is required. 



The Hot-water System. In this system the fire box is partly 

 made of coils of iron pipes which contain water. The ambi- 

 tion of the builder is to have all of the heat of the fire given to 

 the water. The water, when warm, expands, is lighter than 

 the colder water, and circulates around the pipe system of 

 the whole house. The rooms are supplied with coils of pipes, 



