2. Raise the chimney by supporting it on two small pieces of wood. Note the result.
3. Cover the raised chimney with a piece of cardboard. Note the result.
Experiments to show the necessity for oxygen
Conclusions.—1. A fresh supply of oxygen is constantly required.
2. Two openings are required to ensure a constant supply of oxygen, one below the fuel and one above it.
3. Oxygen is obtained from the surrounding air.
4. The passage of air through these openings creates a draught.
It will be necessary next to lead the class to see that the supply of oxygen can be controlled:
1. By the relation of the openings: