HOW ROCK CANDY IS MADE. Rock candy is made by hanging a string in a strong sugar solution or syrup
and letting the water evaporate slowly until there is not enough water to hold all the sugar in solution. Then
the sugar crystals gather slowly around the string, forming the large, clear pieces of rock candy.
The sugar around the mouth of a syrup jug is formed in the same way.
You always get crystallization when you make a liquid too cool to hold the solid thing in solution, or when
you evaporate so much of the liquid that there is not enough left to keep the solid thing dissolved.
When you make fudge, the sugar forms small crystals as the liquid cools. When a boat has been on the ocean,
salt crystals form on the sails when the spray that has wet them evaporates.
But crystals may form also in the air. There is always some moisture in the air, and when it becomes very
cold, some of this moisture forms crystals of ice. If they form up in the clouds, they fall as snow. If they form
around blades of grass or on the sidewalk, as the alum crystals formed on the string, we have frost.
Still another place that crystals occur is in the earth. When the rocks in the earth were hot enough to be melted
and then began to cool, certain substances in the rocks crystallized. Some of these crystals that are especially
hard and clear constitute precious and semi-precious stones.