Part 21 (2/2)
CHAPTER VII.
MECHANICAL ACTION.
1.--PERCUSSION.
Q. _How is heat produced by MECHANICAL ACTION?_
A. 1.--By Percussion. 2.--By Friction. 3.--By Condensation.
Q. _What is meant by PERCUSSION?_
A. _The act of striking_; as when a blacksmith strikes a piece of iron on his anvil with his hammer.
Q. _Why does BEATING IRON make it RED-HOT?_
A. _Beating_ the iron _condenses the particles_ of the metal; and squeezes out its latent heat, as water from a sponge.
Q. _Does COLD iron contain HEAT?_
A. Yes; _every thing_ contains heat; but when a thing _feels cold_, its heat is LATENT.
Q. _What is meant by LATENT HEAT?_
A. Heat _not perceptible to our feeling_. When anything contains _heat_ without _feeling_ the hotter for it, that heat is called ”_latent_.”
(See p. 31.)
Q. _Does COLD iron contain latent HEAT?_
A. Yes; and when a blacksmith _compresses the particles_ of the iron by his hammer, he _squeezes out_ this latent heat, and makes the iron red-hot.
Q. _How did blacksmiths use to LIGHT THEIR MATCHES before the general use of lucifers?_
A. They used to place a soft iron nail upon their anvil; strike it two or three times with a hammer; and the point became _sufficiently hot to light a brimstone match_.
Q. _How can a NAIL (beaten by a hammer) IGNITE a brimstone MATCH?_
A. As the particles of the nail are _compressed by the hammer_, it cannot contain _so much heat as it did before_; so some of it _flies out_ (as water flows from a sponge when it is squeezed).
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