Common Science

by Carleton Washburne

Fig. 51. In a minute the cork will fly out.

Experiment 37. Pour about half an inch of water into the bottom of a flask. Bring it to a vigorous boil over the burner and let it boil half a minute. Now take the flask off the flame and quickly slip the mouth of a toy balloon over the mouth of the flask. Watch what happens. If things go too slowly, you can speed them up by stroking the outside of the flask with a cold, wet cloth.

When the balloon has been drawn into the flask as far as it will go, you can put the flask back on the burner and heat the water till it boils. When the balloon has been forced out of the flask again and begins to grow large, take the flask off the burner. Do this before the balloon explodes.

The reason the balloon was drawn into the flask was that the steam in the flask turned back to water as it cooled, and took very much less space. This left a vacuum or empty space in the flask. What pushed the balloon into the empty space?

Fig. 52. A toy balloon has been slipped over the mouth of a flask that is filled with steam.

Fig. 53. As the steam condenses and leaves a vacuum, the air pressure forces the balloon into the flask.

How steam makes an engine go. The force of steam is entirely due to the fact that steam takes so much more room than the water from which it is made. A locomotive pulls trains across continents by using this force, and by the same force a ship carries thousands of tons of freight across the ocean. The engines of the locomotive and the ship are worked by the push of steam. A fire is built under a boiler. The water is boiled; the steam is shut in; the only way the steam can get out is by pushing the piston ahead of it; the piston is attached to machinery that makes the locomotive or ship move.

One theory about the cause of volcanoes. The water that sinks deep down into some of the hot parts of the earth turns to steam, takes up more room, and forces the water above it out as a geyser. It is thought by some scientists that volcanoes may be started by the water in the ocean seeping down through cracks to hot interior parts of the world where even the stone is melted; then the water, turning to steam, pushes its way up to the surface, forcing dust and stone ahead of it, and making a passage up for the melted stone, or lava. The persons who hold this view call attention to the fact that volcanoes are always in or near the sea. If this is the true explanation of volcanoes, then we should have no volcanoes if steam did not take more room than does the water from which it comes.