How do trick birthday candles work?

Candles are simple yet ingenious light-producing devices, and it only takes one extra ingredient to turn them into trick candles. Find out how regular and trick candles work in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstuff front house storks dot com where smart happens.
Hi am Marshall Brain with today's question, how do trick
birthday candles work? You know the kind that relight themselves
after you blow them out. You have to imagine a

(00:22):
birthday party with the poor guy turning forty years old.
Here's his cake and it's beautiful. It comes complete with
forty candles and they're all burning brightly, and now it's
time for him to blow the candles out. He makes
his first attempt, and then he realizes the agony of
what he faces because their trick candles. He can't blow

(00:43):
them out because they relight themselves automatically. This brings up
a good question, how do those trick candles work? And
what about normal candles? Candles are actually pretty amazing devices.
A candle has only two pieces. It has a solid
fuel made of paraffin wax or bees wax, and a wick.

(01:03):
But talk about something being greater than the sum of
its parts. A block of wax by itself is pretty useless,
and a wick by itself will burn in just a
few seconds. But when you put them together, you have
something that will provide a source of steady light and
heat for many hours. The wick of a candle actually
has two jobs. It's a pump and it's a fuel vaporizer.

(01:28):
When the wax melts, capillary action in the fibers of
the wick pumps the liquid wax upward. There, the heat
of the flame vaporizes the wax so it can burn. Meanwhile,
the top of the candle forms a small cup that
holds the liquid wax so it can enter the pump.
This brings up an obvious question, what is paraffin wax?

(01:50):
It's actually a hydrocarbon, just like gasoline or kerosene. In fact,
paraffin wax comes from crude oil, just like gasoline and
kerosene do. The reason why paraffin wax is a solid
while gasoline is a liquid has to do with the
length of the carbon chains in the fuel. In gasoline,
the carbon chains are eight carbons long. In kerosene, which

(02:14):
is a little thicker and oilier, there are twelve carbons long.
Paraffin wax has carbon chains thirty carbons long, long enough
to solidify it room temperature. The paraffin wax liquefies due
to the heat of the flame. The wick pumps the
wax upwards into the flame. The wax then turns to
a vapor that is quite flammable. To see how flammable

(02:37):
it is, try this experiment. Light a candle and after
it has been burning for a minute or two, blow
it out. You will see a stream of white smoke
rising from the wick. There is a tiny glowing ember
in the wick, and it's hot enough to keep vaporizing
the wax until the ember goes out. That white smoke

(02:57):
is actually paraffin wax vapor. If you touch a lit
match to the vapor right after you blow out the candle,
the flame will shoot down the stream of vapor like
a fuse and relight the wick. You can light the
stream as much as twelve inches away from the wick,
and the flame will travel down and light the candle.
It's a fun trick to show your friends. Now you

(03:19):
can see all the working parts in a normal candle.
There's the cup of liquid wax at the base of
the wick, the wick acting as a pump and vaporizer,
and the wax vapor that's actually burning in the flame.
The flame provides the heat to do the vaporizing, as
well as the heat to create the liquid in the cup.
It's genius. So how does a trick candle work? You

(03:42):
need to add one more thing to the wick. We
need something that the glowing ember can ignite so that
its ignition can relight the stream of vapor. That's something
is normally magnesium powder. The ember can light the specks
of magnesium. If you care only watch the wick of
a trick candle, you can see the specs bursting into

(04:05):
minuscule explosions of flame every few seconds. Those little explosions
of flame are enough to light the vapor, which relights
the wick, and the candle keeps burning. The addition of
that magnesium dust to the wick is all you need
to create a trick candle. It's simple but quite effective.
Try one of these trick candles at your next birthday party,

(04:27):
but not forty they'll ruin the case. For more on
this and thousands of other topics, is it how staff
works dot com