What do you need?

• Old ExLax™ Pills - most other laxatives will not work - including new formula Exlax
• Rubbing Alcohol
• Paper Toweling - higher quality ones work better
• Windex™ - with ammonia D

What do you do?

1. Crush an exlax tablet with a spoon (we used a mortar and pedestal, but that isn't needed).
2. Use the rubbing alcohol to dissolve the crushed tablet. You'll need a few teaspoons per tablet to accomplish this.
3. Use a paintbrush to paint your message on the paper towel.
4. After it dries you can see nothing until you spray the Windex on the area. Then the words you painted will appear as pink letters.

Why does it work?

The active ingredient in ExLax™ is a chemical called phenolphthalein. This chemical was first synthesized in 1880 and has long been known to change color depending on whether it is in acidic or basic conditions. It is colorless under acidic (or neutral) conditions and pink/red in basic solutions. The Windex™ contains a chemical, ammonia, that turns the conditions basic. By spraying the ammonia on the paper, the phenolphthalein turns pink and you can see the letters that were painted in advance.

Links for web pages about acids and bases.

ChemTutor - a page with a high school chemistry level description of acids and bases

pH - Lab - explore how scientists determine if a solution is an acid or a base using pH

Chem 4 Kids - the acids/bases section of this nice page for kids.