Q. Where does the oxygen of the air come from, which is blown to the lighted tinder?
A. The air itself is composed of two gases (nitrogen and oxygen) mixed together.
(Every 5 lbs. of common air contain 4 lbs. of nitrogen, and 1 lb. of oxygen.)
Q. What is the good of blowing oxygen gas to lighted tinder?
A. Oxygen gas supports combustion; and lighted tinder is quickened by the breath, in the same way as a dull fire is revived by a pair of bellows.
Q. Why do horses sometimes strike fire with their feet?
A. When iron horse-shoes strike against the flint-stones of the road, very small fragments (either of the shoe or stones) are knocked off red-hot, and look like sparks.
Q. What makes these fragments red-hot?
A. The percussion condenses the part struck, and squeezes out its latent heat.