Warning: Adult supervision required.


Here’s a great little experiment you can do at home that will demonstrate an important scientific principle: Charles’s Law. This law says that as a gas gets hotter, it takes up more space. Now, Ivory soap is a great way to show Charles’s Law, because the manufacturers have whipped air into the bar of soap. The air also makes a bar of Ivory soap float in water, while most brands of soap sink. When you microwave the soap, those tiny bubbles of air expand rapidly, and the whole thing turns into a billowy, pillowy puff of soap!


What You Need

  • Bar of Ivory soap (don’t try this with any other brand of soap)
  • Microwave–safe dish
  • Microwave oven


What You Do

  1. Unwrap the bar of Ivory soap and place it in the dish.
  1. With an adult’s help, microwave the soap for about 2 minutes.
  2. Watch as the soap expands and billows!
  3. With an adult’s help, remove the dish carefully and allow the fluffy soap foam to cool.
  4. Play around with the soap foam—poke it, slice it or break off a bit and wash your hands with it. Yep, it’s still soap!


Good to Know

The same process that causes Ivory soap to expand so much in the microwave works on popcorn kernels and marshmallows, too. There are tiny pockets of air in each kernel and each marshmallow that expand rapidly when heated.


Photos by Sherida Mock


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