Read "How Balloons are Made" by Leo Tolstoy online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
If you take a blown-up bladder under water and let go of it, it will fly up to the surface of the water and will swim on it. Just so, when water is boiled in a pot, it becomes light at the bottom, over the fire, -- it is turned into a gas; and when a little of that water-gas is collected it goes up as a bubble. First comes up one bubble, then another, and when the whole water is heated, the bubbles come up without stopping. Then the water boils.
Just as the bubbles leap to the surface, full of vapoury water, because they are lighter than water, just so will a bladder which is filled with hydrogen, or with hot air, rise, because hot air is lighter than cold air, and hydrogen is lighter than any other gases.