- A viewer called Killian
Heanue sent me this question. If you boil alcohol in an electric kettle will it ever turn itself off? It's an interesting question, isn't it? Because electric kettles
turn off automatically when water reaches boiling
point, but alcohol, specifically the chemical ethanol has a lower boiling point than water. So my prediction is that
a kettle full of ethanol will not turn off automatically. It will boil dry because that mechanism that turns the kettle off
automatically would never kick in because it's based on temperature. We could just assume that
that's what will happen, but let's go through the
motions of proving me right. We'll start off with vodka, and you'll notice I'm doing this outside. That's because ethanol
vapor can be dangerous. I don't recommend trying
this at home, but if you do, do it outside. Vodka is about 40% ethanol, 60% water. So what's the boiling
point of that mixture? Well, water's boiling point is a 100C, which you might know as 212F and the boiling point of ethanol is 78C. So you might think that when
the solution reaches 78C, the ethanol will start to
boil leaving the water behind, but that's actually
not quite what happens. Instead, the mixture has a boiling point that's somewhere between a 100C and 78C. In this case, it's about 83C. And it does look as if the kettle is just going to continue boiling. Oh, well, that does seem to prove me wrong or does it? Crucially when a 40, 60 mix
of ethanol and water boils, the vapor it produces is
not in that same ratio. Instead it's in a ratio of
about 80% ethanol to 20% water. In other words, as it boils, the concentration of ethanol
in the liquid that remains is going down. The liquid that remains is
getting closer to pure water. And so the boiling point
is getting closer to 100C and it must be then that the
concentration reaches a point that actually turns the kettle off. Let's do a taste test and see. Well, it is weird cause it's warm. It's definitely alcoholic, but it's definitely not
as strong as neat vodka. So I'd say a lot of the alcohol
has disappeared from there. So I haven't been proven wrong yet. Let's try pure alcohol or 99% ethanol, that's the best that I could do. Let's see what happens. Wow, that is surprising. Damn. That's surprising, that turned
off quicker than the vodka. That's really surprising. So clearly my prediction was wrong. And at this point you might
be formulating an explanation for why that goes like this. The boiling point of ethanol is 78C. So eventually it reaches that temperature and starts to boil, but
the kettle stays on. So the temperature of the
liquid continues to increase until it reaches a 100C and that's when the kettle turns off, but that's actually not how boiling works. Interestingly, when you boil a liquid, you then can't physically
get it any hotter than that. Like you put a pot of
water on the stove to boil and it reaches a 100C and you think, well, I'll turn up the stove
to get it even hotter than 100C, but it doesn't work. What happens is once
the liquid is boiling, all the energy that
you put into the liquid goes into turning that liquid into a gas. It goes into the phase transition and none of the energy goes
into increasing the temperature. In other words, if you turn
up the burner on your stove, you don't increase the temperature, you just make it boil quicker. As a side note, that's way a good way to melt chocolate is to put it in a bowl over boiling water, because then, you know, it's never gonna get
above a 100 degrees C, you're not gonna damage the chocolate. So what's going on with this kettle? I decided to dig into the
workings of it a bit more. There's a switch here and
this switch will stay closed so long as the kettle is in its base, which I'm faking here by
pressing this piece of metal into the contact point where
there's a little button, but watch what happens. When I heat up this metal disc here, the disc buckles, which
forces the switch back open, which I assume was being
held in place by a magnet. So this disc must be a by metallic strip, two different metals fused together that expand at different rates
as the temperature changes that causes the disc to buckle. But the disc is down in
the base of the kettle where it's dry and relatively cool. So how does it work? Well, look, at the top, you can see there's this
tube and the tube runs down into the base and under here. And look, it exits out
across that metal disc, just to prove that look, if I pour water into the hole at the top, it comes out the bottom
there, which by the way, explained something I
found really confusing in this footage. What is this liquid doing down here? Where does it come from? Well, you can see the bubbling liquid very easily reaches the
opening of that tube. And a lot of it must be
pouring down and coming out. So what's the purpose of this design? Well, it's actually really clever because it detects the
presence of boiling in general, not a specific temperature. Like you could have a liquid in there, that's at 100 degrees,
but if it's not boiling, then it's not producing vapor. And there's no pressure to
force that vapor down the tube to the bio metallic strip. The crucial thing is that
at whatever temperature, if the liquid in the kettle is boiling, it will produce a vapor that
will increase the pressure inside the kettle, forcing that vapor over
the bio metallic strip. And the manufacturers of this kettle have clearly chosen a trigger temperature for that bio metallic strip
that is significantly lower than the boiling point of water. And actually that makes sense because well, we say that
water boils at a 100C, but that's only true at
atmospheric pressure at sea level. Like if I took a kettle that worked according to my hypothesis and went up a mountain with
it, it would never turn off. It would boil dry because
at higher altitudes where the pressure is lower, the boiling point of water is also lower. So here we have a kettle
that works at many altitudes. So it's a really clever design
then I thought, hold on, maybe there's a way to
rescue my prediction because I've got another kettle that doesn't have that tube thing in it. So how does that work? Well, looking inside,
there's this component here that's touching the base of the kettle. And if you look at there's
actually some thermal paste between the two, so
clearly the manufacturer wants there to be a good thermal
connection between the two. This must be the thermal switch. So surely this will switch at about 100C, meaning this ethanol
should simply boil dry. Let's see what happens. Damn, damn. I'm just wrong, it's weird though because I just don't understand
how this kettle works. It doesn't make sense to me because surely if this little kettle is able to bring water to the boil, this thermal switch can't
shut off before 100C and yet it seems to be. You know, one possibility is that, well, water is a good heat sink because it's a good conductor of heat and it has a high heat capacity. So maybe the water inside the kettle is able to maintain this
piece of metal beneath it at under 100 degrees C, so long as the water
is under 100 degrees C. And so the metal will
only reach a 100 degree C when the water reaches 100 degrees C because it's such a good heat sink. Whereas the ethanol, which
isn't such a good heat sink, while the ethanol itself
would never get above 78C, it doesn't have the heat sinking abilities to maintain the metal beneath
it at that temperature. And so the metal base is able to eventually reach 100 degrees C because of the heating elements around it. Yeah. It's a funny one though, isn't it? So I was about to do this bit about how the different
mechanisms in these two kettles caused them to behave differently when they're operated with the lids off. So with the lid off this
kettle, all the vapor escapes, there's no buildup of pressure forcing the vapor down the tube. And so this won't switch
itself off when the lid is off. Whereas this one, because it's thermally
coupled to the metal base, it will turn itself off
even when the lid is open, but then I set it up
and this flipping kettle just kept boiling. It didn't turn off when the lid was open, but it did when the lid was closed. So, I mean, what's going on? I did a bit of investigating. Look, in here, there's a little hole, that there, is that the steam goes through
that hole, through the handle and into the base where
the bio metallic strip is, but that's confusing. Why have they thermally
coupled it to the base? Maybe it's a safety thing, like in case it boils dry
or something, I don't know, but it's definitely how it
works because I covered it up, the hole with some like
water resistant tape and it just kept boiling
even with the lid closed. So there you go, this has
been an interesting video. It's been an exercise in
me being wrong about stuff, which is fun because, you know, I like trying new things and, well, I've never been wrong
about anything before. I don't get as much time
to watch documentaries as I would like to, which is why I appreciate
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Which I believe is also how most rice cookers work. The temp inside is hot enough to boil the water and if the temp rises over that then it means all the water is boiled out as steam or absorbed into the rice and thus the cooker shuts off.
Nice try Russell Hobbs and Smirnoff marketing
The temp sensor he found on the second kettle is most likely a thermal fuse design to cut power if the kettle over heats.
Answer?
is this the same result that Technology Connections found when dissecting his rice cooker?
Before I actually watch:
It depends on the kettle and pot you use. Some kettles will turn off once it detects a higher temperature than the necessary temp. to boil water, others will be on a timer, others will measure the overall temperature of the device itself.
Most rice cookers do the first, and most tea kettles will do the do the last. The method in the middle should be avoided as there is no reason to have those types of kettles as it's neither cheaper, more convenient, and it's certainly less efficient for getting the right result for whatever you wanna cook/boil.
As for the experiment itself: This is a chemistry experiment! Most alcohols are not JUST alcohol. It's a percentage of alcohol and water which is why we indicate the % ratio via "proof". So, if you boil ANY % proof of alcohol that's not 100% (or over) it will turn off as what will remain is the water which WILL get to boiling point.
I'm just making assumptions as I'm pretty interest in tea, so I use kettles a lot.
Also, if you don't have a rice cooker - get one. They're fantastic. Wash your rice and use jasmine thai rice for that "asian" texture before you cook it in a rice cooker.
Unless you wanna make a risotto in which you don't want to wash the rice (and you shouldn't use thai rice in the first place) as you want the starchiness that washing rice is supposed to remove.