in shallow open tanks and let the water evaporate. The salt is
left behind.

EXPERIMENT 35. Dissolve some salt in warm water until no more
will dissolve. Pour the clear liquid off into an evaporating
dish, being careful not to let any solid particles of the
salt go over. Either set the dish aside uncovered, for several
days, or heat it almost to boiling and let it evaporate to
dryness. What is left in the dish?

_APPLICATION 28._ Some girls were heating water for tea, and
were in a hurry. They had only an open stew pan to heat the
water in.

"Cover the pan with something; you'll let all the heat out!"
Helen said.

"No, you want as much heat to go through the water as
possible. Leave the lid off so that the heat can flow through
easily," said Rose.

"The water will evaporate too fast if the lid is off, and all
the heat will be used up in making it evaporate; it will take
it much longer to get hot without the lid," Louise argued.

"That's not right," Rose answered. "Boiling water evaporates
fastest of all. We want this to boil, so let it evaporate;
leave the lid off."

What should they have done?

_APPLICATION 29._ Two men were about to cross a desert. They
had their supply of water in canvas water bags that leaked
just enough to keep the outside of the bags wet. Naturally
they wanted to keep the water as cold as possible.

"I'm going to wrap my rubber poncho around my water bag and
keep the hot desert air away from the water," said one.

"I'm not. I'm going to leave mine open to the air," the other
said.

Which man was right? Why?

INFERENCE EXERCISE

Explain the following:

151. When you go up high in an elevator, you feel the pressure
of the air in your ears.

152. Water is always flowing into Great Salt Lake; it has no
outlet; yet it is getting more nearly empty all the time.

153. A nail sinks while a cork floats in water.

154. Steep hillsides are paved with cobblestones instead of
asphalt.

155. If you place one wet glass tumbler inside another you can
pull them apart only with difficulty, and frequently you break
the outer one in the attempt.

156. Sausages often break their skins when they are being
cooked.

157. A drop of water splashed against a hot lamp chimney
cracks it.

158. When you shoot an