Dry ice is not only cool, it’s dangerously cold. Dry ice is a solid, frozen form of carbon dioxide that sublimates—that is, it turns directly from a solid into a gas at room temperature. Understanding the science behind dry ice doesn’t make it any less fascinating, and Halloween is the perfect excuse for a bit of dry ice science fun. (Be aware that dry ice can cause a severe frostbite, so handle with care and insulated gloves.)
We buy dry ice from a local ice cream shop, but it may also be available at grocery stores. Just a couple of pounds will provide plenty of science fun and typically costs less than $5.
Note that even if your ice comes tightly wrapped in newsprint, and even if you keep it in a freezer, it will continue to slowly sublimate. So, for example, if a child-related event prevents you from using the dry ice the day you originally planned, and then you forget about it for a few days, and then you remember and you get your kid all excited to do dry ice experiments, you will have a very disappointed child. This might have happened to me. Twice. Of course, if your child is young enough, you can write it off as a Halloween mystery.
Witch’s Brew
The foggy effect generated by dry ice creates a spooky atmosphere, but when you add water, the sublimation process speeds up. The escaping carbon dioxide gas creates delightful-sounding bubbles that leave behind a puff of vapor when they pop. You can turn everyday punch into a roiling witch’s brew that will be safe to drink—just make sure partygoers don’t get any dry ice in their party drinks. A frostbitten tongue will definitely put a damper on your festivities. If you want to play it safe, use the boiling cauldron as an eye-catching centerpiece.
If you go the centerpiece route, take your display up a notch by adding a few drops of dish soap to the water before adding dry ice.
To make it even more dramatic, place it in a clear container and add a few drops of food coloring or the contents of an activated glowstick. This will surely elicit “oohs” and “ahhs” from a crowd of kids. Although your bubbles won’t glow (ours didn’t, at least), it’s still fun to watch the colorful mixture brewing.
Ghost Hunting
We know that flames are fueled by oxygen, right? Because dry ice gives off carbon dioxide, if you place a bit of it in a jar or fishbowl with a lit candle, the flame will essentially suffocate and die out. You can simply demonstrate this or tell a spine-tingling ghost tale by candlelight and watch as your flame is suddenly and mysteriously extinguished.
You can find more simple and engaging Halloween science ideas from the Liz Heinecke, the Kitchen Pantry Scientist.