BURNING OR OXIDATION


35. Why Things Burn. The heat of our bodies comes from the food we
eat; the heat for cooking and for warming our houses comes from coal.
The production of heat through the burning of coal, or oil, or gas, or
wood, is called combustion. Combustion cannot occur without the
presence of a substance called oxygen, which exists rather abundantly
in the air; that is, one fifth of our atmosphere consists of this
substance which we call oxygen. We throw open our windows to allow
fresh air to enter, and we take walks in order to breathe the pure air
into our lungs. What we need for the energy and warmth of our bodies
is the oxygen in the air. Whether we burn gas or wood or coal, the
heat which is produced comes from the power which these various
substances possess to combine with oxygen. We open the draft of a
stove that it may "draw well": that it may secure oxygen for burning.
We throw a blanket over burning material to smother the fire: to keep
oxygen away from it. Burning, or oxidation, is combining with oxygen,
and the more oxygen you add to a fire, the hotter the fire will burn,
and the faster. The effect of oxygen on combustion may be clearly seen
by thrusting a smoldering splinter into a jar containing oxygen; the
smoldering splinter will instantly flare and blaze, while if it is
removed from the jar, it loses its flame and again burns quietly.
Oxygen for this experiment can be produced in the following way.

[Illustration: FIG. 22.--Preparing oxygen from potassium chlorate and
manganese dioxide.]

36. How to Prepare Oxygen. Mix a small quantity of potassium