HONOLULU (HawaiiNewsNow)- Kids always make sure you have parent supervision for this experiment. This week Dr. V uses a simple mess grill to control the flame of a small candle.
Dr. V Show: Looking into a Flame
Things you need:
- metal mesh or sieve
Please perform this and all experiments under the supervision and with the assistance of an adult. What does it look like inside a candle flame? Light your candle and let it burn for a while. It might also help to pour some of the wax out of the candle too. Then carefully hold the metal mesh over the candle flame until it's about halfway into the flame. Look in through the top of the mesh. What do you see? You are looking into the flame. Try moving the mesh carefully and slowly up and down the length of the flame. Watch what happens to the smoke coming out of the flame.
How does it work?
When you have the mesh halfway through the candle, the flame looks hollow! A candle is usually a cylinder of wax (usually a hydrocarbon) with a wick in the center. The wax is the fuel for the flame, which melts and is drawn up the wick by surface tension. Then it evaporates and mixes with the oxygen in the air and burns. This reaction produces heat, carbon dioxide and water. However, this reaction can only occur where the air and the wax vapor mix. This only happens around the outside of the flame, the interior of the flame is all wax vapor and no oxygen.
Why doesn't the flame come through the mesh? The metal mesh conducts the head away from the flame, which cools the wax and the air below the temperature at which they burn. This means that the combustion, or burning, is stopped and whatever was in the flame passes through the mesh and floats upwards. What you see coming from the mesh as you raise and lower the mesh in the candle are unburnt wax vapor which condenses to form tiny white droplets that look like white smoke, and partially burnt wax. When wax burns, the hydrogen from the hydrocarbon, or wax, reacts, leaving tiny particles of carbon. These look like sooty black smoke. Inside the flame, the carbon is heated to yellow hot, which makes the flame give out light. When the mesh is near the bottom of the flame, there is lots of unburnt wax vapor, but there is little time for the soot to be created, so the smoke looks white. Near the top of the flame, there is no unburnt wax left and a lot of carbon, so the smoke looks black, or sooty.
Do different sizes of mesh make a difference in this experiment?
What happens when you use a wider or taller candle?