difficulty of making hard coal burn, it becomes evident that some
substances require only a small amount of heat before they will burn,
while others require much heat. Different materials, then, require
different degrees of heat to burn. The phosphorus and other substances on
the tip of a match ignite readily. The heat that is developed by rubbing
the tip over some surface is sufficient to make the phosphorus burn. The
burning phosphorus and other substances heat the match stick to the
temperature at which it begins to burn; the burning match stick applied to
paper heats the latter to the temperature at which it burns. The
temperature to which a substance must be heated in order to burn and
continue to burn is called the _kindling temperature_ of that
substance.

DRAFT; OXYGEN.--

EXPERIMENT 3: LACK OF DRAFT.--(_a_) Place a short candle on a pan.
Light the candle and put a tall slender lamp chimney over it. Does the
candle continue to burn? Why?

(_b_) Again light the candle and replace the chimney, but this time
support it on two sticks of wood or on the handles of a knife and fork so
that it will not rest directly on the pan. Place a saucer or a piece of
cardboard over the top of the chimney. Does the candle continue to burn?
Why?

EXPERIMENT 4: PRESENCE OF DRAFT.--Remove the cover from the top of the
chimney, and again light the candle. Does it continue to burn? What
substance necessary for combustion is present in the chimney? Explain why
the candle soon went out in Experiment 3, but continued to burn in this
experiment.