What makes gelatin jell?

   A strange thing happens when you pour hot water onto gelatin powder to make dessert. The powder disappears. You can't see it any more, but it is there. The hot water breaks the powder up into tiny bits, like small strings, so small that you can't see them floating in the water. They are little but strong. As each tiny string gets cool, it acts as if it were a magnet. You have seen a magnet pick up a tack. The invisible strings of gelatin can't pick up tacks, but they can pick up water. A bit of water sticks to each string.
   If you keep the gelatin cool, it holds the water very tight. But as soon as you heat gelatin, water escapes. When you put the mixture back in the refrigerator, the tiny strings pick up their water drops again.