Plants are as badly off. The life-giving sap turns to water with specks of the one-time nourishment floating uselessly through it. Most plant cells, like the cells in the man, turn to water, with fibers and dust flecks making it cloudy. Within a few seconds there is not a living thing left in the world, and the saltless waves dash up on a barren shore.
Probably we had better let the Solution switch alone, after all. Instead, here 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?
Fig. 146. Will heating the water make more salt dissolve?
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.
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.
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.
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, but different kinds of coloring matter dissolved in them when they were melted.