  It was a cold wet day—so cold and wet that neither Dolly nor her brothers could venture out. They had grown tired of reading books and drawing pictures, and were indeed feeling very dull. They sat looking at the bright fire. Uncle George laid down his paper and said: “Come, let us have a lesson. What shall it be? The rain? The cat? Or shall it be the cosy fireside?” “The fire,” said Frank. “Tell us why the fire burns, Uncle George!” “I will,” said cheery Uncle George. “Just wait until I get some things from the kitchen. Come along, boys.” When Uncle George and the boys came back to the room, they brought a lot of curious articles with them. These were an empty pickle-bottle, a small saucer, a glass bell-jar, a large dish, a piece of candle, some tacks, and a taper. A Baby Cloud THE BALLOON “Now,” said Uncle George, “we are ready to begin.” He first lighted the piece of candle and lowered it into the bottle. It burned for a short time, then it went out. “Can you tell me why it goes out?” he asked. “Want of air,” said Tom and Frank at the same time. “But there is air in the bottle,” said Uncle George. “Yes, but not the kind of air the candle wants,” said Frank. Candle burning in Open Jar. “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 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. 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. 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 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. Then Uncle George called the boys and “The tacks have rusted, and some of the air in the jar has been used up,” said Frank. “How much air has been used up?” Uncle George asked. “Just exactly the same as was used up when we burned the candle,” said Tom, pointing to the top mark. “Let us see, then,” said Uncle George, “what part of the air has gone.” He poured water into the large dish until it was level with the water inside the bell-jar. Then he put a lighted taper into the bell-jar as before. It went out at once. “It is the same part of the air as the burning candle used up,” said Frank. “Then we have found out,” said Uncle George, “that when a thing burns it uses up a certain part of the air; and that when iron rusts, exactly the same part of the air is used up. “In the first case, the burning of the candle changed part of the air into a gas which dissolved in the water. In this case, that same part of the air has joined up to part of Questions and Exercises.
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