Fire Bubbles

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Combustion, Heat

Alternative titles: Hold Fire in Your Hand, Methane Bubbles

Summary

Soap bubbles filled with flammable gas from an aerosol spray are ignited while resting on a water-soaked hand. The bubbles burn away quickly, but the water absorbs the heat, protecting the hand from burns.

Procedure

Fill a large bowl with water and add a small amount of dish soap, mixing to create soapy water.
Thoroughly soak one arm in a bucket of water, making sure it is wet up to the elbow.
Place a tube from a gas tap to the bowl to form bubbles.
Scoop up a handful of bubbles (not foam) with the soaked arm, keeping your palm flat and facing upward.
Hold your hand at arm’s length, away from your face, and above head height.
Ensure there is enough clearance from the ceiling and nearby objects.
Use a lighter or candle flame to ignite the bubbles, holding still until the fire burns out.

Links

Fire Bubbles - Methane Madness - SpanglerScienceTV:

Fire bubbles - The Experiment Archive:

📄 Fire bubbles - Experiment Archive: https://www.experimentarchive.com/experiments/fire-bubbles/

Variations

Instead of holding the bubbles, place them on a fireproof surface such as a ceramic plate before lighting.

Safety Precautions

Safety goggles required.
Keep a fire extinguisher, a bucket of water, and a fire blanket nearby.
Perform only under adult supervision by someone experienced with fire.
Do not perform outdoors, as wind can blow flames toward the face.
Soak arm fully in water before holding bubbles.
Hold hand away from face and above head height.
Maintain at least 1.5 meters (5 feet) clearance from the ceiling or flammable objects.
Practice emergency procedures in case of fire or burns.

Questions to Consider

Why doesn’t your hand burn even though the bubbles are on fire? (Because water has a high heat capacity and absorbs much of the released heat.)
What gases are inside the bubbles that make them flammable? (Propane and butane from the aerosol spray.)
What type of reaction occurs when the bubbles are lit? (An exothermic combustion reaction producing carbon dioxide, water, heat, and light.)
Why must your hand be soaked in water before holding the bubbles? (The water layer provides protection by absorbing heat from the flame.)
What state of matter might exist in parts of the flame besides gas? (Possibly plasma, if the temperature is high enough to ionize gas molecules.)