Q. When bottled ale and porter is set before a fire, why is the cork forced out sometimes?
A. If the bottle be not quite full, there will be air between the liquor and the cork; this air (expanded by the heat of the fire) forces out the cork.
Q. Why does ale or porter froth more, after it has been set before the fire?
A. The froth of ale or porter depends upon the pressure to which it is subjected; and as the air (between the liquor and the cork) is expanded by the heat, it presses against the liquor, and increases the quantity of froth.
Q. Why is the froth of ale and porter increased by pressure?
A. Because the liquor absorbs carbonic acid so long as it is under pressure; and the moment that the pressure is removed, the carbonic acid escapes in foam or froth.
Q. When a boy makes a balloon, and sets fire to the cotton or sponge (which has been steeped in spirits of wine), why is the balloon inflated, or blown out?
A. The air inside the balloon is expanded by the flame, till the whole balloon is blown out without a crumple.
Q. Why does the balloon rise, after it has been inflated by the expanded air?