Try this: All meshed up

What’s happening?

Step 2Although the sieve is full of holes, the flame from a candle won’t pass through them. The fire is actually the candle’s wax evaporating from the wick. When you light a candle with a match, you are actually heating the wax near the wick so it turns into a gas, then the heat from the match causes the gas to react with oxygen in the surrounding air, creating carbon dioxide, water vapour and solid carbon (soot). This process releases even more energy as heat and light so the wax-burning continues after you take the match away.
The paper burns because the glowing gas is hot enough to cause the chemicals in the paper to also react with oxygen – this is called combustion. While the gassy wax is able to pass through the sieve, the mesh absorbs most of its heat, spreading it over a wider area and conducting it away from the paper before the temperature gets high enough for combustion to occur. This effectively cools the gas. The paper stays safe as long as the candle’s gas isn’t hot enough to make it burn.

Applications

Coal mining has been a particularly dangerous profession throughout history. Even if you ignore the threat of collapsing tunnels and rockslides, pockets of methane can form throughout a coal seam. In the days when work was conducted under the quivering glow of an oil lantern’s flame, explosions were all too common.
In 1815, the British chemist Sir Humphrey Davy created a simple device that would reduce the risk that a lantern’s flame would ignite flammable gases. The Davy Safety Lamp, as it would come to be called, was a fine wire grill that surrounded the flame. In the event the miner walked into a cavern full of methane, the gas could burn inside the lantern, however the resulting flame wouldn’t escape to create an explosion. A similar device was being marketed by the engineer George Stephenson at the same time, however Sir Humphrey’s lamp was preferred for its simplicity and robustness.
Ironically, the device actually led to more accidents. Feeling safer, workers would enter mines that were once deemed too dangerous, suffocating in the methane instead.

Warning: This activity involves fire. Younger scientists should get help from an adult. Ensure you use proper safety equipment and work in a suitable environment.

You will need

  • Metal mesh sieve
  • Candle
  • Matches
  • 2 x small pieces of paper
  • Wooden clothes peg
  • Fire blanket or other appropriate fire safety materials

What to do

  1. Find a quiet place outside, away from any breeze.
  2. Light the candle.
  3. Clip a piece of paper into a clothes peg and hold it about 1 cm above the candle, in the flame.
  4. How quickly does it catch alight and burn?
  5. Place the second piece of paper in the sieve.
  6. Hold the bottom of the sieve about 1 cm (the same distance as with the first piece of paper) above the candle, in the flame.
  7. How quickly does it catch alight and burn?
    Step 1
    Find a candle, a metal sieve, a peg and some paper.
    Step 2
    Hold the first piece of paper about 1 cm above the flame.
    Step 3
    Can the candle burn through the mesh?