It's Okay To Be Smart

Slow Burn

Isn’t watching a match burn in slow motion a hypnotic sight? Want to know what you’re looking at?

For something as ubiquitous as matches, it strikes me that very few people know what goes into creating fire on the end of a stick. Let’s open the book and illuminate the science behind this burning question.

I’ll stop the puns now.

Having a source of fire on demand was not always such a trivial pursuit that we were willing to give things like matches away for free at the Olive Garden hostess stand. As far back as the 6th century A.D. the Chinese were using sulfur-coated sticks to spread fire from camp to camp, because without fire, you died or ate raw food.

Most of what’s in a match today is a chemical called potassium chlorate, which is really just a good source of the oxygen atoms that every flame needs in order to burn. There’s also a good bit of sulfur, which is what’s doing most of the burning and what gives matches their characteristic smell (and why some people keep them in the bathroom), glue, and inert stuff. The “strike” part of the match was added later, when inventors in the 1800’s added a chemical called “white phosphorous”.

White phosphorous is a common explosive that burns super-vigorously when it comes in contact with oxygen under the right conditions, like when a little heat is added. Unfortunately it works a little too well, and it’s also enormously toxic. It was eventually replaced with a less volatile, less toxic form called “red phosphorous” after factory workers began dying left and right.

So what happens when you strike a match?

If you try striking a common match on regular sandpaper, nothing will happen except that you end up with a handfull of toothpicks. The special red sandpaper has a tiny bit of red phosphorous embedded in it, and when you drag the match across it creates heat. If you make enough heat, a wee bit of red phosphorous gets turned into white phosphorous and starts microscopic explosions. Remember the sulfur in the match head? At regular atmospheric oxygen concentrations the sulfur isn’t very flammable. But add some pure oxygen and heat and sulfur goes ballistic. The tiny sparks from the red-to-white phosphorous release oxygen from the potassium chlorate so that the sulfur is able to burn in a high oxygen environment.

Eventually, the wood catches, and you try to say the alphabet or something before it burns out.

So it’s more than just a cool slow-motion video, it’s a close-up on chemistry!