In introducing a lesson on the kitchen fire, ask the pupils to imagine that they have built a new house, which the workmen have just vacated. Before they can move in it must be cleaned. What kind of water is best for cleaning? Hot water. What is necessary to provide hot water? A fire.
Find out from the pupils and then write on the black-board what is necessary for a fire. What is the first requisite? Something to burn. What do we call such a substance? Fuel. Where shall we put the fuel? In a stove. Why is a stove necessary? To confine the fire.
Using a candle as fuel and a lamp chimney as a stove, light the candle and place it in the chimney. It burns only a short time and then dies out. Why? Because the oxygen of the air in the chimney is all exhausted. Then what is another requisite for a fire? Oxygen.
Imagine the room to be a stove and the chairs, books, tables, etc., to be fuel. The air in the room also contains much oxygen, so that in this room we have three requisites for a fire. It is very fortunate for us that something else is needed. We shall try to find out what it is.
Watch while I hold these strips of paper over this lighted gas stove high enough to be out of reach of the flame. What happened to them? They burst into a flame. What did the paper that I held receive that it did not get when it was lying on the table? Heat. We shall try a match in the same way, also some thin shavings. They also burn when they receive heat from the fire. Then what is another requisite for a fire? Heat. Name all of the requisites for a kitchen fire. Fuel, stove, oxygen, and heat.
Note.—Just here it is a good thing to impress the care that is necessary in regard to gasolene, coal-oil, benzine, etc., or any substance that burns at a low temperature. Bring out the fact very clearly that it is the heat that makes fuel burn, that a flame is not necessary.
HEAT
Experiments to show on what the amount of heat required depends:
1. Heat together two strips of paper of the same size but of different thicknesses and observe which burns first.
2. Heat together a strip of very thin paper and a match which is much thicker than the paper, and observe which burns first.