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Observe, a candle. That little cotton wick, it is burning. And then after producing heat and light for a number of hours, nothing is left. The candle is gone. And that can be pretty confusing. But like we all get that something is going on here. No one would expect to light a ten inch long cotton string on fire and have it still be burning in an hour.

So where did the candle wax go? Here's the short answer: you burned it. Now, here's the long version. Wax is a fuel, like the gas in your car's gas tank. But it is an extremely convenient fuel. This is hard to believe if you're, like used to light bulbs, but at one point candles were a tremendous innovation. Specifically, they were an innovation over oil lamps. 

The oil used in lamps was usually plant oil, often olive oil or seed oils, possibly even animal fat. The oldest oil lamp we've ever found was at Lasco Cave in France, which has proved hard to date, but the paintings in the cave are from around 17 thousand years ago.

And to make an oil lamp work, a wick would need to be laid in a shallow dish, and that dish was then filled with oil. Now oil by itself doesn't always burn easily, that's what the wick is for. The wick draws the oil up and increases its surface area enough that in the presence of a flame, a lot of it will vaporize into a gas. Then it can freely mix with oxygen, and all the energy added by the flame allows it to combust. 

Combustion is a chemical reaction in which a carbon-containing molecule and oxygen from the air are converted into carbon dioxide and water, and sometimes other products. In the oils, those carbon-containing molecules are fatty acids. In the case of modern candles, it's waxes, which is a different class of compounds, though they are structurally similar. 

And the process of combustion is exothermic, meaning it releases energy. And that's super useful when you don't have lightbulbs or if you wanna set the mood in a fancy restaurant. The heat of the reaction keeps the oil vaporizing and mixing with oxygen, keeping the reaction going for as long as there is oil.

So the wick is not what's burning. What's burning is the oil that's being drawn up into the wick. Lamps, however, have their problems, especially lamps that are just dishes of flammable oil with some cotton laid into them. Accidentally bump into it, and you have a big problem for your skin, which might now be on fire. And potentially for your whole neighborhood.

The reason candles were such an innovation is that they turned the fuel itself into it's own lamp. By putting the wick into a solid fuel, and building both the wick and the candle carefully, most of the fuel in your basic taper candle remains solid until it gets close to the flame.

But wax near the flame melts and then is drawn up into the wick where it heats up further, vaporizes into waxous gas molecules and then combusts. The wax molecules react with oxygen to form carbon dioxide and water.

And that is where the wax goes. It becomes CO2, which is a gas at room temperature, and water which is a gas at the temperature in a candle flame.

You can actually see this happening. If you put something cold over a candle flame, you can actually see the water vapor condense out of the air. Likewise, if you put a cup over a candle flame, it quickly stops burning because the concentration of oxygen drops while with concentration of CO2 increases. 

And that smoke you see coming off of a blown out candle, well that smoke actually represents unburned fuel. The wick is still hot so wax is still evaporating. That hot wax rises in the air because it is hot. But as it rises, it does not burn so it cools down and then condenses back into tiny solid wax droplets. 

So unburned wax it what you see and what you smell after you blow out a candle. This is also why you can hold a match to that steam of wax and the flame will trace the trail of vaporized and condensed fuel back down to the wick. Good party trick.

There are times, knowing what I know that I am somewhat surprised that people don't get that a candle disappearing is functionally the same thing as your gas tank being empty after you drive a few hundred miles, except instead of going somewhere, you got a little bit of light in the bathroom, full of better smells than it would otherwise contain.

But there are other times when I look at a candle, I think actually it's very weird that when a candle burns it becomes air. It's wierd,  and it's cool, and now when people ask you "Where does the candle wax go?", you can tell them. Or you can just send them here, I know that's what I'll be doing.

So candles become air, and the water in the air becomes clouds, and it's all kinda weird and amorphous. But the online cloud has clear boundaries to protect your data, especially when you use linode cloud computing.

This scishow video is supported by linode, a company that's been a wonderful supporter of scishow, and a company that helps keep your cloud use safe and secure. And if you aren't a expert in those areas, you can still follow linode's step-by-step guides and videos to help keep your cloud infrastructure up to date and secure.

A lot of people leave their computers vulnerable just because updating them is such a hassle, so linode's guide shows you how to automate that process and rest easy knowing your computer's security systems are up to date. Try it yourself, click the link in the description or head to linode.com/scishow. That link gives you a 100 dollar 60 day credit on a new linode account.

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