"Be careful; you'll break the bottle!"
"What will make it break?" asked Uncle Robert, pausing.
"Why, the hot water," said Susie.
"It always breaks glass if you put it in too quickly," said Donald.
[Illustration]
"Well, we'll warm it a little first," holding the bottle close to the water. "I think I can try it now."
As he spoke he lowered the bottle into the water, and the rubber tied over the neck began to bulge out.
"See!" cried Susie. "What makes it do that?"
"Try the cold now," said Uncle Robert. "Here, Donald, hold the bottle in this pail of cold water."
"The rubber is going down," said Donald in a moment. "It is going right into the bottle."