Relight my Fire

In this experiment, we’ll learn how to use the smoke coming from an extinguished candle to relight the candle. The experiment requires adult supervision!

Equipment

·   Two candles

·   Long matches or a long-neck lighter

The experiment

Watch the video to see how we conduct this experiment.

Explanation

Candles are made of wax with a wick at the center. The wax is the candle’s main “flammable material” (the wick is also flammable but its part is relatively small compared to the wax) – it is what burns and makes the fire. But if you tried to light a candle without a wick, just the wax, you would find it really difficult, if not impossible – the wax simply wouldn’t burn.

We’ve conducted other experiments with flammable materials which don’t burn in some situations: A steel screw, for example, is inflammable – but if you turn it into thin threads, i.e., steel wool, it becomes flammable. Corn flour and cornstarch will not burn when piled into a heap – but if you blow on them and create a cloud, it can burst into flame.

The same happens with wax. It doesn’t burn when it’s in a solid lump – but using a burning wick that melts it (turning it into liquid – look at the wax under the flame) and then vaporizes it (by turning it into a gas around the wax-soaked wick) – will cause it to burn.

The reason this happens has to do with access to oxygen. For fire to burn, three elements are required all at once, AKA the “fire triangle”: Fuel, oxygen, and heat. If we have all three – we’ll have fire, but if even one is missing, then no fire.

There is plenty of oxygen in the air, but when you have a solid block of wax, the oxygen doesn’t mix with the wax and won’t react with it. There is only a small amount of oxygen near the surface of the wax that could possibly start the combustion, but it simply isn’t enough.

The same is true for flour and steel. Only when you blow the flour to form a cloud, or turn steel into thin strands of wool, or burn wax into gas, then enough oxygen can react with them and fuel a fire. That is because the oxygen, no longer restricted to the outer layer of material, has access to almost every grain of flour, strand of steel wool, or particle of vaporized wax. When materials are properly distributed in the air, all you need is some heat (from an external source) to get a fire going that can maintain itself – as it supplies itself more and more heat to continue burning.

In this experiment, we put out the candle and saw that in the first few seconds, after it was extinguished, white smoke was rising from the candle. That’s because in those first few seconds, the wick and the wax are still quite warm, so there is a trail of hot wax vapor rising up from the wick. As it rises, the vapors cool, thicken, and solidify, thus forming a “cloud” of small, white wax particles that float in the air; particles that were created from the gaseous wax as it cooled.

In this state, the flammable material (wax) is mixed well with oxygen – a cloud of tiny particles surrounded by oxygen, just like the “flour cloud”. The moment we bring heat close to this cloud, with another candle or a lighter, it lights up and burns through its entire “length,” until reaching the wick and relighting it.

This isn’t the easiest experiment to carry out, because the wax vapors are only produced in the few seconds after the candle is extinguished. The experiment also has to be conducted away from wind, so that the cloud isn’t dispersed: You will need an unbroken trail of white smoke reaching up to the wick. And of course, as with any experiment that involves fire – you must be very careful and perform it only under adult supervision.