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Speaker 1: Welcome to brain Stuff, a production of iHeart Radio. Hey

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Speaker 1: brain Stuff, Lauren Vogelbam Here. When the weather is so

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Speaker 1: cold that even your best gloves and socks can't keep

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Speaker 1: your digits toasty, those little packets of magic that we

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Speaker 1: call disposable handwarmers can bring big relief. Handwarmers are good

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Speaker 1: to have an emergency's and they're perfect to tuck inside

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Speaker 1: your bittens during winter activities like skiing, ice skating, or

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Speaker 1: just on your daily commute. But how exactly do these

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Speaker 1: little packets work. They are not filled with tiny demons

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Speaker 1: who warm your hands with hell fire, nor is it

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Speaker 1: some gamma radiating goo that will turn your paws into

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Speaker 1: hulk smash style superhands. The science behind those handwarmers is

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Speaker 1: actually pretty simple. It turns out they use the same

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Speaker 1: process that transforms iron into rest, just a lot faster.

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Speaker 1: There are five main ingredients inside a disposable handwarmer iron powder, water, salt,

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Speaker 1: activated charcoal, and some kind of water absorbent material. But

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Speaker 1: of course they don't get hot until you open the

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Speaker 1: air tight plastic wrappers that the packets come in. That's

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Speaker 1: because the final ingredient that makes them work is oxygen

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Speaker 1: to become hot. Oxygen from the air flows into the

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Speaker 1: packet and reacts with the iron powder, water and salt

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Speaker 1: that's already there, which oxidizes the particles of iron, that is,

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Speaker 1: it turns them into iron oxides, also known as rust.

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Speaker 1: Oxidation is sometimes used as another term for rust, because

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Speaker 1: rust is perhaps the most well known version of oxidation,

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Speaker 1: but lots of different substances can oxidize anyway. What's happening

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Speaker 1: in the packet is that the iron powder is giving

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Speaker 1: away electrons to the oxygen that comes in. Water has

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Speaker 1: to be present in order to break up molecules of

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Speaker 1: oxygen so that the reaction can happen. The water absorbent

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Speaker 1: material in the packet hangs onto the water molecules for

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Speaker 1: safe keeping until you open the packet. Meanwhile, the salt

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Speaker 1: helps the oxidation along because it accelerates the flow of electrons.

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Speaker 1: You've probably observed this if you've noticed that exposed metal

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Speaker 1: on a car will rest more quickly if the car

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Speaker 1: is driven on salt treated roads in the winter, or

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Speaker 1: if you've noticed a lot of rust on chains or

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Speaker 1: fences that are in or near seawater the versus ones

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Speaker 1: that aren't. But okay, the process of rusting is exothermic,

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Speaker 1: meaning it gives off heat, But when your car's fender rusts,

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Speaker 1: it doesn't feel hot, and that's because that process happens

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Speaker 1: very slowly, even when it is accelerated by salt. The

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Speaker 1: reaction is greatly sped up in disposable handwarmers, and that's

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Speaker 1: where the construction of the packet and the other ingredients

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Speaker 1: come in. It may be simple science driving this reaction,

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Speaker 1: but control holling it for the precise effect of creating

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Speaker 1: a certain amount of warm for a certain period of

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Speaker 1: time is complicated. The material of the packet has to

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Speaker 1: let in just the right amount of oxygen. They're made

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Speaker 1: with microporous materials, meaning they have tiny holes to let

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Speaker 1: oxygen in at the gaseous equivalent of a slow drip.

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Speaker 1: Warmers for hands have very tiny holes, whereas the warmers

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Speaker 1: designed for feet have slightly larger ones. That's because there's

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Speaker 1: less air inside your boots and shoes, so those warmers

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Speaker 1: need more access to oxygen in order to activate. Then

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Speaker 1: you've got that activated charcoal, which serves to distribute the

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Speaker 1: heat that's created evenly throughout the packet so that you

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Speaker 1: don't wind up with any extra hot clumps. Manufacturers can

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Speaker 1: tweak how fast the reaction happens and how long it

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Speaker 1: continues producing heat by changing the size of the iron

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Speaker 1: powder particles. Smaller particles with more surface area will heat

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Speaker 1: up faster, and by increasing the amount of iron in

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Speaker 1: the PA could Overall, they're designed to last anywhere from

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Speaker 1: a few hours up to a full day. So it's

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Speaker 1: not demons and it's not scary chemicals. It's not even magic.

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Speaker 1: But the heat in that handwarmer is toasty. Those little

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Speaker 1: packets can produce temperatures between a hundred and a hundred

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Speaker 1: and eighty degrees fahrenheit. That's eighty two degrees celsius, which

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Speaker 1: should keep your digits nice and cozy. And it's totally

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Speaker 1: safe throw used disposable handwarmers in the garbage. No has

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Speaker 1: Matt team required. Today's episode is based on the article

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Speaker 1: how do disposable handwarmers work? On how stuffworks dot com

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Speaker 1: written by Kristen Hall Geisler. Brain Stuff is production of

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Speaker 1: i Heeart Radio in partnership with how stuffworks dot com,

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Speaker 1: and it's produced by Tyler Klang. Four more podcasts my

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Speaker 1: Heart Radio, visit the heart Radio app, Apple podcasts or

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Speaker 1: wherever you listen to your favorite shows,