SOLAR-POWERED RAINMAKER
Did you ever wonder where rain comes from? Most of it comes from the sea. About 208 cubic
miles of water evaporates from the world's oceans every day, to fall down as rain. But the sea
is salty and rainwater is fresh. Why is that? You can build a solar still to purify saltwater, and
see for yourself. (Just to be safe, and not too messy, have an adult around while you do this.)
The Materials:
a clean jar (either glass or plastic is OK), with a wide opening and a lid a
container that will hold water and is small enough to fit upright inside the jar
salt, water, and a spoon
The Setup:
1.
2.
3.
4.
5.
Fill the small container about three-quarters full of water.
Stir in a couple of teaspoons of salt (taste it).
Place the lid upside-down on the table or counter.
Stand the container of saltwater inside the upside-down lid.
Turn the big jar over and carefully screw it onto the lid, over the water
container.
6. Put your new solar still in a sunny window for a few hours.
Note: If you don't have a jar, you can use a large bowl and cover the top with
plastic wrap. You can use tape or a rubber band to seal it tightly.
What Has Happened:
After your solar still is in the sun for a while, you should notice droplets forming
on the inside of the jar. The heat from the sun caused water to evaporate (turn
from liquid to gas) from the saltwater solution, leaving the salt where it was. As
some of the fast-moving water vapor molecules came in contact with the sides
of the jar, which were exposed to cooler air outside, they slowed down. When
the molecules slowed enough, they condensed, changing from gas back to
liquid form. (If you put the jar in the refrigerator for a while, it would speed up
the condensation.)
Test the Water Yourself:
Carefully open the jar and use your finger to taste any water droplets that
collected in the lid or on the insides of the jar. Are they fresh or salty? Taste the
saltwater again for comparison. Would this experiment work if you mixed dirt in
with the saltwater? Try it and see.
Copyright ©2003 by World Almanac Education Group, Inc.