"Somehow it seems to get more than full when it boils," said Donald.
"See, it is boiling over."

Just then Jane took a pan of apples out of the oven. Each one looked
like a small volcano.

"What happens to the apples when they bake?" asked Uncle Robert.

"They just swell up so big their jackets won't hold them," said Donald,
laughing.

"It is heat that makes the bread rise, isn't it?" asked Frank.

"Of course," said Susie. "Don't you know sometimes if the bread doesn't
rise, mother says it is because it is too cold?"

"There is something besides heat that makes the bread rise," said Uncle
Robert.

"Yes," replied Susie, "the yeast; but it must be warm--I know it must."

"It seems as though everything is bigger when it is hot than when it is
cold," said Frank. "And now I believe I understand something that
happened not long ago."

"What was it?" asked Uncle Robert.

"Peter and I were driving to town," began Frank, "and the tire of one of
the wagon wheels slipped right off. We managed to get to the
blacksmith's shop, and he put the tire in the fire until it was hot. Then