“That is a queer answer, Frank. The candle burned for a time in the bottle before it went out.” “Because it used up that part of the air which makes things burn,” said Frank. “That is _very_ good,” said Uncle George. Uncle George then poured some water into the large dish. He fixed the candle on a big cork, lighted it and set it floating on the water. Then he placed the glass bell-jar over it. But first of all he marked the level of the water on the outside of the bell-jar. Very soon the flame of the candle became small, and at last went out. Just then the water inside the bell-jar rose far up above Uncle George’s mark. He marked this new level, and asked the boys if they could tell him why the water rose in the jar. Both Frank and Tom shook their heads sadly. [Illustration: Candle in Stoppered Jar—burning.] “Then I must explain,” said Uncle George. “Some of the air has gone,” said Tom. “Yes,” said Uncle George. “How much of the air has gone?” Frank pointed to the space between the two marks. “That is right,” said Uncle George. “The water has risen up in the bell-jar to take the place of the air that has been used up by the burning of the candle. Where has this used-up air gone?” “It must have gone into the water,” said Tom. “Why did it not go into the water before the candle burned?” “Perhaps the burning of the candle has _changed_ this part of the air,” said Frank. “Very good, Frank. You are right again. The burning of the candle has changed a certain part of the air. It has, indeed, so changed it that it can dissolve in water just as if it were sugar or salt.” Uncle George now poured water into the outer dish until it was level with the water inside the bell-jar. Then he took out the stopper and pushed a lighted taper into the bell-jar. The taper at once went out. [Illustration: Candle in Stoppered Jar—gone out.] “This shows us,” he said, “that a part of the air causes things to burn. The other part of the air does not. It puts burning things out. If we blow the fire with a bellows or fan, it burns more brightly and quickly. Why? Just because we are forcing a stream of air upon it, and a part of that stream of air is changed by the burning.” Uncle George next put some bright iron tacks in a small dish. He poured some water out of the large dish, and placed the bell-jar in the dish. After that he added water until it was just up to his first mark on the bell-jar. Then he floated the dish with the tacks on the water. Next he wetted the tacks with water, and then placed the bell-jar over them and put in the stopper. “Now,” he said, “we will leave this just as it is for a few days.” The boys watched the bell-jar every day, and this is what they saw. The water rose slowly in the bell-jar. As it rose the bright tacks turned red with rust. The water rose higher and the tacks turned redder every day. At length it rose to Uncle George’s second mark. It rose no farther, although left for a whole week.