A blacksmith can make the following very serviceable apparatus: A scrap of iron about eleven inches long, one inch wide, and one-eighth inch thick, has one inch bent up at each end. A rod one-eighth inch in diameter is made just long enough to pass between the upturned ends of the first piece when both are cold. The rod is heated and the experiment conducted as in the case of the ball. Two additional facts are learned: (1) Iron expands as well as brass; (2) solids expand in length as well as in volume. The pupils may now be told that other solids have been tried and expansion has invariably followed heating. The conclusion may then be made general.
PRACTICAL APPLICATIONS
1. When your ink-bottle was placed on the stove, which end became warmer? Which expanded the more. Why then did it crack?
2. What other examples like this have you noticed? (Lamp chimneys, fruit jars, stove plates)
3. The earth was once very hot and is now cooling. How is the size of the earth changing? Does it ever crack? What causes earthquakes?
4. Find out by observation how a blacksmith sets tires.
5. Invent a way to loosen a glass stopper stuck in the neck of a bottle.
6. What does your mother do if the metal rim refuses to come off the fruit jar?
7. Next time you cross a railway, notice whether the ends of the rails touch. Explain.
8. What allowance is made for contraction in a wire fence? A railway bridge? Why?