Fill a clear plastic liter bottle 3/4 full with water. Add blue food coloring then add cooking oil. Leave about 1 inch at the top of the bottle. Show preschool children how the oil and water do not mix. Tilting the bottle back and forth causes a wave effect.
The Pepper Likes to Move it, Move It.
Sprinkle pepper over the top of a cup of water. Put a dab of soap on your finger and touch the center of the pepper. Show children that the soap breaks the surface tension of the water and the tension on the rest of the water pulls the floating pepper away from the soap.
Secret Agent Invisible Ink
Using a cotton swap or paint brush, let children write messages or paint designs on white typing paper with lemon juice. Let dry. The adult is to hold the paper close to a light bulb until the writing becomes visible by turning brown.
Place an empty mason jar on a tray. Surround the jar with clay or play dough. Form the dough to look like a mountain. Put a drop of red food coloring and a tablespoon of baking soda in the jar. Then add some vinegar to it to make it erupt.
Mix food coloring and vinegar. Place different colors in different bowls. Cover a 9×13 pan with a layer of baking soda. Using an eye dropper or another small container or even a spoon, drop colored vinegar onto the baking soda. Watch the mini color explosions.
Ice, Ice, Baby
Fill a glass with water and add one ice cube. Let a child lay a piece of string across the ice and try to pick up the ice with the string. Sprinkle a little salt over the ice cube, count to 10 and have child try again. Show child how the salt melted the ice just enough to bond around the string.