Magic Trick: Smoking Fingers

Although the smoke magic trick looks awesome if you use your hands, you may wish to wear disposable plastic gloves to avoid absorbing phosphorus through your skin.
Although the smoke magic trick looks awesome if you use your hands, you may wish to wear disposable plastic gloves to avoid absorbing phosphorus through your skin. Sam Bloomberg-Rissman / Getty Images

Here's a simple magic trick. It's easy to make your fingers smoke and glow in the dark when you rub them together. All you need is a matchbox and a way to burn its striker portion.

Difficulty: Easy

Time Required: About a minute

Materials

Here are the materials for this project:

  • Matchbox of safety matches with a striker strip
  • Cold water faucet or a chilled pan
  • Scissors
  • Lighter (or matches from the matchbox)

Preparation

Here's how to set up and perform the trick:

  1. Cut out the striker strip from a matchbox of safety matches. Trim off any paper around the striker.
  2. Fold the striker in half lengthwise, striker sides facing each other.
  3. Chill the metal. One easy way to get cold metal is to run cold water through a faucet until the faucet gets cold. If the water from your tap isn't cold enough, refrigerate a metal pan or set it on a dish of ice.
  4. Set the folded striker strip on top of the chilled metal.
  5. Set fire to the striker strip. Ignite both ends. Then run the lighter or match along the length of the folded striker. It won't burn to ash, which is fine.
  6. Discard the burned striker.
  7. You will see a brown residue along the top of the faucet or on the metal pan. Run your fingertip along the residue to pick it up.
  8. Slowly rub your finger and thumb together. Smoke will appear. If you do this in the dark, your fingers will have a greenish glow. It's very, very cool.

Tips for Success

Here are some ways to make sure the trick works safely:

  1. If you don't have scissors, tear off the striker portion of the matchbox with your fingers. It's easier, though, to use scissors.
  2. Use either matches from the matchbox or a lighter to light the strip on fire.
  3. Avoid breathing in the smoke, and wash your hands after you've finished. The trick probably involves white phosphorus, which can be absorbed through your skin and is toxic.

How the Trick Works

It's commonly believed the smoke is vaporized white phosphorus. Here's how it works:

Phosphorus is a chemical element that can take several forms, called allotropes. The type of phosphorus in the striker on matchboxes is red phosphorus. When you burn the striker, the phosphorus is vaporized and condenses into a solid on the cool metal surface. This is white phosphorus. The element has not changed identify, just the structural arrangement of the atoms. Rubbing your fingers together produces enough heat from friction to vaporize the phosphorus into what appears to be smoke.

The "smoke" glows green in the dark. While you might assume this is phosphorescence (you're using phosphorus, after all), it's actually an example of chemiluminescence. Phosphorus reacts with oxygen from air to release energy in the form of light. The reason scientists know the red phosphorus from the striker vaporizes into white phosphorus is because of the green glow. Only white phosphorus glows in the dark.

White phosphorus readily reacts with oxygen in air to form a flammable compound. Because of this, one of the earliest uses of the purified element was to make matches. Early friction matches have been around since Robert Boyle made them back in 1680, although they did not become popular until 1830. The early phosphorus-based matches were dangerous, containing enough phosphorus to poison a person. Modern matches are called "safety" matches because they don't use highly toxic chemicals.

Safety

The smoking fingers trick used to be a popular school science demonstration. It is not performed much anymore because of concerns about the risk from the phosphorus, but if you do the trick infrequently, the dose of phosphorus is small. While red phosphorus is the form of the element that is essential for human life, white phosphorus can cause chemical burns and have a negative effect on bones. You can lessen the exposure by wearing thin, disposable gloves and taking care not to breathe the vapor.

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