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 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.