"The gas first filled the bottle, and then passed away down the tube into some gas jars, one by one, standing on the table.""Then, I suppose," said Norah, "this is a gas that you can see?""No, it is an invisible gas," said Fred, "and we had to take teacher"s word for it at first that he had filled the jars with the gas. It was no use to smell it even, for this gas is odorless.""It seemed very funny to me," said Willie, "when teacher simply dipped the end of the tube in the jar, and presently said the jar was full of gas.""You see," said Fred, "this gas is heavier than air. If we had poured water into the jar, the water would have sunk to the bottom, and pushed the air out as it rose. This carbonic acid gas does just the same.""But how did you know there was carbonic acid gas at all in those jars, Fred?" asked Norah.
"I"ll tell you," said Fred. "Teacher took one of the jars, and poured into it some clear lime-water.""Oh yes, I know," said Norah. "The
