27. Why does the fire burn more brightly when blown by a bellows?
Because it receives, with every current of air, a fresh supply of oxygen, which unites with the carbon and hydrogen of the coals, causing more rapid combustion and increased heat.
28. Why does not the oxygen of the air sometimes take fire?
Because oxygen, by itself, is incombustible. The wick of a candle, which retains the slightest spark, being immersed in oxygen, will instantly burst into a brilliant flame; and even a piece of iron wire made red-hot, and dipped in oxygen, will burn rapidly and brilliantly. Oxygen, though non-combustible of itself, is the most powerful supporter of combustion.
29. Why do we know that oxygen will not burn of itself?
Because when we immerse a burning substance into a jar of oxygen, it immediately burns with intense brilliancy; but directly it is withdrawn from the oxygen, the intensity of the flame diminishes, and the oxygen which remains is unaffected.
30. Why do we know that oxygen is necessary to our existence?
Because animals placed in any kind of gas, or in any combination of gases, where oxygen does not exist, die in a very short time.
It is found in the air, mixed with nitrogen; in water combined with hydrogen; in the tissues of vegetables and animals; in our blood; and in various compounds called, from the presence of oxygen, oxides.