inch high in the
tube, stop pouring. Put exactly the same amount of water
in another test tube of the same size. When you pour them
together, how many inches high do you think the mixture will
be? Pour the water into the alcohol, shake the mixture a
little, and measure to see how high it comes in the test tube.
Did you notice the warmth when you shook the tube?

If you use denatured alcohol, you are likely to have an
emulsion as a result of the mixing. The _alcohol_ part of the
denatured alcohol dissolves in the water well enough, but the
_denaturing_ substance _in_ the alcohol will not dissolve
in water; so it forms tiny droplets that make the mixture of
alcohol and water cloudy.

The purpose of this experiment is to show that the molecules of water
get into the spaces between the molecules of alcohol. It is as if you
were to add a pail of pebbles to a pail of apples. The pebbles would
fill in between the apples, and the mixture would not nearly fill two
pails.

The most important difference between a solution and an emulsion is
that the particles in an emulsion are very much larger than those in
a solution; but for practical purposes that often does not make
much difference. You dissolve a grease spot from your clothes with
gasoline; you make an emulsion when you take it off with soap and
water; but by either method you remove the spot. You dissolve part of
the coffee or tea in boiling water; you make an emulsion with cocoa;
but in both cases the flavor is distributed through the liquid. Milk
is an emulsion, vinegar is a solution; but in both, the particles
are so thoroughly mixed with the water that the flavor is the same
throughout. Therefore in working out inferences that are explained in
terms of solutions and emulsions, it is not especially important for
you to decide whether you have a solution or an emulsion if you know
that it is one or the other.

HOW PRECIOUS STONES ARE FORMED. Colored glass is made by dissolving
coloring matter in the glass while it is molten. Rubies, sapphires,
emeralds, topazes, and amethysts were colored in the same way, but by
nature. When the part of the earth where they are found was hot enough
to melt stone, the liquid ruby or sapphire or emerald, or whatever
the stone was to be, happened to be near some coloring matter that
dissolved in it and gave it color. Several of these stones are made
of exactly the same kind of material, b