e are a couple of experiments that will help to make clear
what happens when anything dissolves to make a _solution_.

EXPERIMENT 80. Fill a test tube one fourth full of cold water.
Slowly stir in salt until no more will dissolve. Add half a
teaspoonful more of salt than will dissolve. Dry the outside
of the test tube and heat the salty water over the Bunsen
burner. Will hot water dissolve things more readily or less
readily than cold? Why do you wash dishes in hot water?

EXPERIMENT 81. Fill a test tube one fourth full of any kind
of oil, and one fourth full of water. Hold your thumb over the
top of the test tube and shake it hard for a minute or two.
Now look at it. Pour it out, and shake some prepared cleanser
into the test tube, adding a little more water. Shake the test
tube thoroughly and rinse. Put it away clean.

When you shake the oil with the water, the oil breaks up into tiny
droplets. These droplets are so small that they reflect the light that
strikes them and so look white, or pale yellow. This milky mixture is
called an _emulsion_. Milk is an emulsion; there are tiny droplets of
butter fat and other substances scattered all through the milk. The
butter fat is _not_ dissolved in the rest of the milk, and the oil is
_not_ dissolved in the water. But the droplets may be so small that an
emulsion acts almost exactly like a solution.

[Illustration: FIG. 146. Will heating the water make more salt
dissolve?]

But when you shake or stir salt or sugar in water, the particles
divide up into smaller and smaller pieces, until probably each piece
is just a single molecule of the salt or sugar. And these molecules
get into the spaces between the water molecules and bounce around
among them. They therefore act like the water and let the light
through. This is a solution. The salt or sugar is _dissolved_ in the
water. Any liquid mixture which remains clear is a solution, no matter
what the color. Most red ink, most blueing, clear coffee, tea, and
ocean water are solutions. If a liquid is _clear_, no matter what
the color, you can be sure that whatever things may be in it are
dissolved.

[Illustration: FIG. 147. Will the volume be doubled when the alcohol
and water are poured together?]

EXPERIMENT 82. Pour alcohol into a test tube (square-bottomed
test tubes are best for this experiment), standing the tube
up beside a ruler. When the alcohol is just 1