Halloween is my favorite holiday. The ghosts, the goblins, the candy — and all the special effects you can dream up! Every Halloween, our family creates realistic spooky cauldron effects using dry ice. Now that my daughter is a little older, we’ve even upped our game to add a little extra science fun by taking our cauldron idea and making glowing “crystal balls.” I see a lot of fun in your future as you try this experiment, too!
- 5 pounds dry ice (available at most grocery stores)
- Tongs and/or heavy gloves
- Safety glasses
- Liquid dish soap
- Warm water
- Large bowl (10-12 inches in diameter), preferably glass, with a smooth lip
- Small bowl
- Dish towel
- Shoelaces or 20-inch fabric strips
- Glow sticks (optional)
Note: Always use dry ice with adult supervision. Dry ice will cause severe burns if it comes in contact with bare or unprotected skin, so it must be handled while using heavy gloves or tongs. Also: Wear safety goggles when handling dry ice, especially when breaking it into smaller pieces. Never put dry ice in your mouth, and never store dry ice in an airtight container.
- Fill the large bowl about half full of water.
- Use your fingers to wipe a layer of dish soap along the rim of the large bowl. Try not to get any soap in the water.
- Fill the small bowl about half full of water. Add a big squirt of dish soap and mix.
- Wrap the dry ice in the dish towel and use the hammer to break it into smaller pieces. (The towel will prevent pieces from flying).
- Using gloves and tongs, add a few pieces of the dry ice to the water in the large bowl. This will make it look like an eerie bubbling cauldron! For added effect, add an activated glow stick to the water (I prefer green, but any color looks great!).
- Dip the strips of fabric in the soapy water in the small bowl and squeeze out a little so it’s not dripping.
Hold the cloth tight and drag across the rim of the large bowl, spanning the diameter to create a soap film.
Watch as your spooky, smoke-filled “crystal ball” bubble appears!
Dry ice is not frozen water — it’s actually solid (frozen) carbon dioxide, which freezes at about -109°F. As the dry ice warms in the water, it actually skips the liquid state and converts directly into a gas. This process is called sublimation.
You can see these gas bubbles forming in the water, and the fog oozing out of the bowl is a mixture of cold carbon dioxide gas and water vapor condensing into droplets from the air around it.
When you create a soap film over the top of the bowl, this gas fog gets trapped underneath. As the gas builds, it pushes the film in all directions, forming a large, fog-filled, crystal ball-like bubble. How big does your bubble get before it breaks? Try adjusting your bubble solution to get the biggest bubble possible. If you’re done making big bubbles, what happens if you add the bubble solution to the big bowl?
For more Halloween family fun, join the Arizona Science Center for Weird Science Halloween. Throughout October you’ll enjoy spooky science experiments, demonstrations and much more.