1. How is rust formed? 2. Explain why things which are made of iron should be painted. 3. A grate full of coals burns away and only a small quantity of ash is left in the grate. What has become of the coals?
VIII.—THE FIRE-BALLOON.
One day Uncle George made the children a fire-balloon. He took twelve strips of tissue-paper shaped as you see in the picture. These he pasted neatly together at the edges so as to form a kind of bag with a round opening at the bottom. A ring of wire was then fixed at the bottom to keep it firm, and across the ring was stretched another piece of wire. This was to hold a dry sponge by and by.
Uncle George swung the balloon till it was filled with air. He told Frank to hold it by the ring while he heated the air inside the balloon.
This was done by holding the mouth of the balloon over a piece of rag which had been dipped in spirits and set on fire.
Strip for Balloon.
Soon Frank felt the balloon rising. He lifted it up away from the flame, while Uncle George moved the little sponge along the wire to the middle of the ring. Then he soaked the sponge with spirits and set fire to it.
“Let go!” said Uncle George; and away went the balloon, soaring up towards the sky. Higher and higher it rose, moving with the wind. The children watched it until at last it seemed a mere dot in the sky, and then it went quite out of sight.
“What makes the balloon rise up?” Dolly asked, as they returned to the house.