Part 22 (1/2)
Q. _Why does STRIKING a FLINT against a piece of STEEL produce a SPARK?_
A. The blow _condenses_ those parts of the flint and steel which strike _together_, and squeezes out their latent heat.
Q. _How does this development of HEAT produce a SPARK?_
A. A very small fragment (either of the steel or flint) _is knocked off red-hot_, and sets fire to the tinder on which it falls.
Q. _Why is it needful to keep BLOWING the TINDER with the breath?_
A. Because _blowing_ the tinder, drives the _oxygen of the air_ towards it.
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_.
CHAPTER VIII.
2.--FRICTION.
3.--CONDENSATION.
Q. _What is meant by FRICTION?_
A. The act of _rubbing two things together_; as the Indians rub two pieces of _wood_ together to produce fire.