"What is the name of it?" asked Rollo.
"Why, the people in the mines call it choke damp; but I believe it has got another name besides."
"What do they call it choke damp for?" said Rollo.
"Because," said Jonas, "if the miners get into it and breathe it, it kills them. It is not any better to breathe than it is to make fires burn."
"I wish I could see some choke damp," said Rollo.
"O, you can't see it at all," said Jonas, "if it was right before you, any more than you can see common air. If a well or a mine is full of it, they cannot find it out by looking down."
"How do they find it out?" said Rollo.
"Why, they let a candle down," replied Jonas.
"And will the candle go out?" asked Rollo.
"Yes," said Jonas, "if there is choke damp in the well. Sometimes they make a little of it in a tumbler or a jar upon the table, and so let a little flame down into it, and it goes out immediately."