May 16, 2013 • 23 mins
In the 87 years since they were invented aerosol cans have protected soldiers, temporarily fixed flat tires, killed a boy who used too much deodorant and had their contents banned by most countries for wrecking the ozone layer. Tune in to learn more.
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Episode Transcript
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Speaker 1 (00:01):
Welcome to Stuff you Should Know from House Stuff Works
dot com. Hey, and welcome to the podcast. I'm Josh Clark.
There's Charles W Chuck Bryant, and this is Stuff you
Should Know podcast. Yeah, what are you excited about this one?
(00:23):
I'm going to try to be excited for everybody enough
for everybody, because I imagine, like there's a you know,
there's a lot of people out there who don't listen
to every single episode. I just I find it biting
in weird because I do that with my podcast. So
if I'm like, if I'm listening to like if I
look at Mark Marrin', so I listen to that one.
If it's a guest that I'm not super into, I
(00:44):
want right, that's other podcasts. I'm talking about Stuff you
Should Know. Man, you must be confused. Yes, I feel
like every single one of them is worth listening to.
I agreed. I suspect though, that people are going to
skip over this one. Well, I am going to take
the rap because I picked this out. I like it,
but as I looked into it, I was like, you
know what, I don't know how an aerosol can work,
(01:05):
and I would like to and it's not super complicated.
It's not. In a matter of fact, now that you
read this and researched it, you understand how an aerosol
can works. You can go to the hardware store on
a Saturday when your board is just stand around and
explain it to people and get like applause. I could
do that. Every anyone who listens to this episode will
be able to do the same thing. That would be
(01:26):
like ACE Hardware, and there'll be some seventy five year
old guy with the red vest next to me. Like
all piste off, they always have old timer's working there. Well.
They are big on keeping the economy going on the
backs of aged baby boomers and that there's a slogan, Yeah,
I think it's ACE is the place. Well, you have
(01:47):
to read between the line, Um, chuck. Have you ever
seen a movie called Style Wars. It's a documentary from
Uh no, I haven't. It's pretty cool man. It's it
basically arnicles the the rise of graffiti, hip hop, clothing
and stuff, and break dancing, just that whole culture. And
(02:09):
it's amazing the stuff that people were doing, like even
back then as far as graffiti goes, and breakdancing and
hip hop and all that, sure, but it's just like
the seminal documentary that you just kind of have to see.
It's just so cool. It's like it kind of makes
you feel cool watching it, you know what I mean? Well,
I need that in my life. But the what the
reason I raised style Wars is because the graffiti that
(02:32):
was being carried out would not have ever been able
to be done had it not been for a Norwegian
engineer named Eric Rothheim who in put in the first
patent for an aerosol can in Norway and then five
years later the first one in the US. Yeah, and
they had the little photo of some of his initial drawings,
(02:52):
and the author of this article points out that although
it has evolved somewhat, it's he's He was pretty right
on with that first, is right, you know, almost out
of the gate, because as we said, it's kind of simple.
The Yeah, one of them was simple to me. One
of them I didn't quite understand. Well, okay, so um
so Rothheim he comes up with this, this patent files,
(03:13):
it kicks back and waits for the money to come
rolling in, but it doesn't. It took many many years
or so maybe a little less before anyone fully understood
the value of an aerosol can, and it was um insecticides,
bug bombs, cans of um insects spray that was being
(03:34):
used by soldiers in the Pacific and World War Two.
When people finally said, oh, that is a good idea. Yeah,
I wonder if I mean they had atomizers and things
at the time. I wonder if that was his initial
inspiration was to take that concept and jam it into
a can basically, because that's what's going on. Yeah, you're
(03:56):
atomizing product. Yeah, and there's a lot of um advantages
to atomizing. Number one, if you spray something in a
fine mist, it doesn't hit the ground. Is a bunch
of liquid that seeks into the groundwater usually sticks to
whatever you're spraying it to. Sure, and it's delightful if
you wear perfume or have you ever like had the
rose water sprayed on your face, like the face sprays. Oh,
(04:18):
I thought you meant like an aerosol can of perfect
no atomizing in general? Yeah, sure, sure, I'm fresh. I've
I've had an avian sprits sprayed on my face. You
mean I have before? It's very nice. Yeah, I've had
like the rosewater. Emily will spraying me occasionally. It's very nice.
It just feels good. Does she like hide behind around
a corner and yeah, no, that's the mace. Oh she
(04:40):
mazes me occasionally for kicks. Um. So yeah, there's advantages
to atomizing things. There's reasons. It's at the very least
it's lovely. It is um and the whole premise behind
this though, the delivery method of an aerosol can Like
we said, it's very basic, it's very old, and all
(05:01):
you have to do is understand a little bit about
fluid dynamics to to get what's going on. So let's
let's do let's give a brief prime around fluid dynamic
shall yeah, and fluid period Like you know, fluid isn't
necessarily liquid like you might think it's an actual thing.
Fluid is any kind of substance that has free flowing
(05:22):
particles that it's made up of that and it could
be something liquid, could be something gas that those are
both fluids. It just can't be a solid basically pretty much. Yeah, yeah,
as long as you got those free flowing particles. Um,
these particles, uh, if it's a liquid, they're loosely bound,
but they're still bound. So it means it's gonna have
a fixed volume if it's a liquid. Yeah, which is why,
(05:42):
like when you put water into a glass, it doesn't
just keep going and going and going. That'd be terrifying. No,
it would make it. It would have a gaseous um characteristic.
Then that's right, because gas does expand to fill the
volume that you put it in. That's right, and well,
spoiler or that's what happens with gas. It expands. Uh,
(06:03):
if you heat liquid um applying energy to it, basically
it's gonna vibrate and it's gonna break those forces and
they're not gonna be bound together anymore. Then you're gonna
have a gas. And that's called boiling. Yeah. And I
mean we think of boiling is like applying enough heat
that you will burn your skin. But boiling points vary
for different types of fluids. Um. So any volatile fluid
(06:27):
is a fluid that um boils or turns from a
liquid state to a gasy state. That's boiling um at
room temperature, right, Yeah, Which that that's the part I
had a hard time getting my head around because I
associate boiling with like heat and hot. Yeah. Because you
think of boiling, you think of water, Yeah, exactly. And
it takes a certain amount of temperature, of heat of
(06:48):
heat energy to break those intermolecular bonds to turn water
from a liquid into a gas, that's right. But it
takes less for alcohol or for propane or whatever you
want to use. Right. And so lastly there's another fluid
dynamic trait that we have to have down and then
we'll have all of the stuff in place to understand
an aerosol can expansion of gas. Yeah, So so we
(07:12):
said that when you put gas into something and expands
to fill the volume, Yeah, and gas will decrease in
pressure as it expands, which is why like a tiny
little CEO two cartridge, it's like got tons of pressure
in there, and that's why it can shoot your awesome
industrial arts model car down the track. Because did you
(07:32):
ever do that? Really? I had a Pinewood Derby racer once.
What's that like the car you sit in? No, that's
the cub scout car. Okay, it didn't have any CEO
two though you'd be immediately disqualified. Yeah. In high school,
we we made the little cars that have the CEO
two cartridge in the battle. I know what you're talking about.
And we raced each other and my brother one county
(07:53):
of course, and then and then flashed this winning smile,
and three years later, it's so funny. I forgot all
about this. I tried to be his car design when
I took the class, and mine was not nearly as like,
it just wasn't quite right, and I didn't win county.
I didn't even win my classroom. Somehow, the the compressed
(08:14):
air decompressing into the atmosphere made like a sad trombo
and sad is it so cool? And that really kind
of just sums it all up with my brother and I.
He was always really great at stuff, and I always
tried to do that and was not nearly as good
at it. You're good at other things. Well, I'm yeah,
I can run my mouth, if that's how you want
to put it. Anyway, So that's compressed gas. And when
(08:37):
gas is compressed, it can you know, do some great
things like shoot the car or in this case, spray
paint or something. Right, right, exactly, Okay, So you have
compressed gas, you have all these fluid dynamics, and you've
had everyone now right, Okay, So all an aerosol can
is is all of these principles kind of put into
a very simply mechanically functioning state. Right. Yeah. So you
(09:02):
have a can and you have to to things in there.
You have the propellant, which is the stuff you use
to force the other thing, the product out. Yeah. And
it could be hair spray, bug spray, could be painting oil,
could be that foamy stuff you ever use that, the
(09:23):
stuff to like seal like insulation or sure or like
fix the flat. All that, all that has myriad myriad uses. Okay, right, So, um,
you've got the product in liquid state. Yes, uh say,
it's just kind of floating in the bottom of the can.
You put it in the can, seal it so it's
there's there's no air going it's air tight. Yeah, this
(09:45):
is part one. There's two two ways to do this.
This is the first, right, This is the simple way.
And then you add some sort of compressed air to it,
call it air compressed air. Okay, okay. So you have
this um the propellant in there, and it's it's basically
filling up as much of it as it can until
it's reaching the top of the can, the side of
(10:06):
the can, in the top of the water, and it
pushes all that product down to the bottom, which is
one reason you gotta shake it chack it up exactly.
So you have a tube going down from the nozzle
at the top of the can valve system all the
way down to the bottom of the can where the
liquid is right and that look, that valve has a
seal that's being pushed up by a spring. So the
(10:29):
head the nozzle when it's when it's not being pushed,
it's stealed tight. But when you push it down a
channel opens. It goes below the seal and you now
have the outside atmosphere, which is at a much lower
pressure than inside the can um opened up to the
inside of the can at that much higher pressure, and
(10:50):
it drives it up the tube out the little tiny,
tiny hole which atomizes it. And that's basically the simpler
method of the aerosol can. Yeah. The air pushes the
liquid down and then up the tube. Yeah, because it's
like I want to get out too exactly. It expands. Done.
I mean that's pretty easy. Yeah. So the second way
(11:10):
that this can happen, and I didn't know this is
the more common way, but it is. Uh they use
liquified gas, so uh, that is the propellant. You've still
got the same product. And the product is is sitting
there at room temperature just fine as a liquid. So
they just pour that in. Then they steal it up,
and then the same way with the other way. They
pump in this liquefied gas and it mixes though this time,
(11:35):
right or does it press it down? This is where
I got a little confused. So a liquefied guess you said,
is um, it's a gas that goes into a liquid
state under a certain amount of pressure, right, yeah, okay,
so under high pressure. Yeah, so it does mix because
it's all liquid in there. Once it gets in there,
the whole thing turns liquid, and you keep that pressure
up so it doesn't have any room to expand, so
(11:55):
it's just in their mix together. And then when you
press the nozzle down own and you break the seal
as it were, um, the you form a channel with
the outside air and the inside air. That change in
pressure converts some of that propellant into gas, and it
does the same thing is that standard can. The gas
presses down forces the liquid up, but some of that
(12:18):
propellant is still in liquid form mixed with the product,
and as it goes out, it evaporates, it turns into gas,
and it also kind of um, it turns that liquid
product into a finer miss. Yeah. But what I don't
get is is that it actually boils in the liquid
gas system. It's like, once you relieve that pressure, it
(12:39):
starts to boil, and that's what does it. That's what
I was a little confused about. Yeah, I have a
feeling that this is a different part of fluid dynamics,
that it's not necessarily the boiling point, although it could be,
because I don't think any average gas turns into a
liquid under under all under pressure. There's just certain kinds
that do. I think. Okay, so I think, what's your question, Well,
(13:04):
it's actually boiling in the second in the in the
liquid gas type of aerosoli, at the very least, it's
converting into a gassy estate because of the release of pressure, right,
all right? And why did they can sometimes get cold?
Did you figure that out? Okay? Boy, there's some guts.
There's some people in chemistry lab right now that are
just like, oh my god, you guys, I thought we
(13:25):
had this one, man. I think we had we do
I had it, and I could have done a tap
dance doing this earlier, and now it's like, but wait,
let me complicate it a little more. Now, I think
it's I think the message got through. Um. If in
the case of paint, sometimes you need a little help
mixing these things together. So that's why a paint can,
spray paint can will have the little metal ball bearing
(13:45):
on the inside, right, because you actually do want to
mix the propellant and the product together in a liquefied can,
liquefied gas can, right, because it helps atomize it. As
you said, that's very pleasant, exact. Um, what about the
rounded bottom of this very can you know why that's
that way? If it was flat, it's so pressurized, it
(14:08):
could be a bad scene. It could actually go the
other way. And everyone knows if you studied architecture, that
a dome is more structurally sound than just a flat surface.
So that's basically the same concept at play. So that's
one reason, Um, it's to protect the integrity of the can.
And the second one is is so you can help
(14:29):
get all of the product out, because if it was flat,
it's like when you're down at the bottom of your
of your soda cup with your straw and you're making
that terrible little noise and you're tilting the cup and
trying to stick the straw on the little corner where
it meets the edge. This does it for you. If
it's a rounded bottom, it just puts all the product
there at the edge and that's where the little tube is,
(14:49):
and so you're all set. Yeah, And did you know
there's about nineteen billion steel and aluminum cans that include
aerosols and other products that are recycled every year and
that's equal to enough to build twenty golden gate bridges. Wow,
isn't that amazing? So we mentioned there's a variety of
different products that you can have that you're trying to
(15:11):
get out of your can, from foam to like whipped
cream to a bug spray, stuff like that hair spray,
although does anyone still use aerosol hair spray? I think
some people do, is it? Remember? Do you remember the
Bizarre Ways to Die episode? The deodorant boy asol deodorant
that he died totally man, that was a long time ago. Um.
(15:33):
So the way they accomplished this though with a different product,
um is you can have a variety of consistencies. And
what they do is they just play with, UM, the
ratio propellant to product. Maybe maybe the chemical makeup of
the propellant the product have to be just right. Maybe
the pressure of the propellant has to be a little
different depending on what kind of product you're working with.
And then um, the size and shape of the valve system.
(15:57):
Like in the case of a fix, the flat that
you put in your higher it's not the same as
you know, a spray can. It's not atomizing. It's got
like the tube hooked up and it's Uh. If you've
ever sprayed that stuff in your house, like the Philip Crack,
like a whole can of it, It's amazing how much
stuff is packed in there. Like when it gets out,
you're just like wow, it's like the clown car of
the industrial engineering scene. Um, do you want to know
(16:22):
a little bit about CFC's chlorofluora carbons. Yeah, I didn't
get a chance to look into this, but I'm glad
you did so. Prior to the late twenties, there was
people were using ammonia and refrigerators and dying from ammonia leaks,
and it was just a bad scene. And so everybody said, well,
we've got to figure out some sort of toxic, non
toxic chemical that we can use as a refrigerant, and
(16:45):
a general motors engineer of all people came up with
what du Pont later turned into free on, a chlorofluora
carbon which supposedly was non toxic. It was. It basically
changed everything. Um it was much less harm harmful compared
to like ammonia. UM. It allowed us to make cheap refrigerators,
(17:06):
car A C, A C window units, like all those
things came from the advent of chlorofluora carbons, right, And
it was also very ubiquitous as a propellant in aerosol
can sprays. Well. I think that's why everyone, you know
quit using aquinette, right, because everybody was going in the
spraying these things, and they were going up in the atmosphere,
(17:28):
and everyone was like, look at them. Go it's cool.
They're like, you know, innert, non toxic chemicals going up
in the atmosphere, but we're all getting cancer. The problem
is when a CFC enters the atmosphere and gets high
enough and it's exposed to UV radiation, it breaks down
and into its constituting components, one of which is chlorine,
(17:48):
chlorine reeks, havoc on the ozone layer. One atom of
chlorine can destroy about a hundred thousand ozone molecules, and
we need those molecules. The ozone layer protects us from
UVB ray from the sun, which are they kind of
give you skin cancer and destroyed crops. So in nineteen
seventy four some scientists realized that CFCs were doing this
in the ozone layer and is gonna be big trouble.
(18:11):
And then in the eighties we figured out that there's
a hole in the ozone layer over the Arctic. So, uh,
a bunch of countries I think seventies signed on to
basically outlaw CFC production. Yeah, and then later on another
like hundred and twenty I think signed another treaty. So
it's very very difficult to find CFC's these days. But
(18:34):
they're still around, are they. Yeah? They still use them
in some um nasal sprays UM and they're also used
in halan, which is a fire extinguisher for airplanes. Did
they not still use free on? No? I don't believe. So, Okay, Yeah,
it's basically like we did away with those. It's gonna
take a while to repair. But they found that the
(18:55):
ozone layers no longer growing the hole in the ozon
layers growing, it's just holding steady and hopefully patching itself
back up. They just forced people to go out and
be innovative and find different ways to do these things exactly.
And if you compare your airsol can propellant today to
one that had CFCs before, you're not going to notice
the least bit different. So that's canna aquinit that looks
(19:17):
exactly the same as it did in nineteen seven is
no longer dangerous, not to the ozone layer. It is
the spiders though, if you have a lighter. Yeah, don't
ever do that. Kids. Ah, that's it for airsol cans
unless you have like another ten minutes on it. Uh No,
that's all I got. I mean, what else is there?
(19:37):
I genuinely looked in There is nothing else. Ye, go
out and do some graffiti, That's what I say. Um
artful graffiti though, don't tagg and stuff. You should probably
practice at home first. I hate that. Just stupid. Yeah, Like,
educate yourself on different types of nozzles, like practice, don't
do don't be a punk, agreed, be an artiste. Uh.
(19:59):
If you we want to learn more about aerosols, or
at the very least, want to see the article where
we told you everything there is to know about aerosolis.
You can type that word A E R O S
O L S into the search bar how stuffworks dot
com and that will bring it up. And I said
the search bar, which means it's time for message break
(20:23):
and now it's time for listener mail. I thought you
might say it, okay, Josh, listener mail time. UM, I'm
gonna call this uh police sketch eye witnessed stuff. It's
from Terry Bennett. Um, Hey, guys, uh listen to the
police Sketch episode, and wanted to share my story. I
was robbed when I was a teller of a bank
(20:43):
in n and at that time, bank robbery was a
federal crime, probably still is. I was immediately taken into
the back room of the vault and the FBI was
called in. When they arrived, a sketch artist brought a
large binder, not full of women, but full of pictures.
They aces and eyes and noses and mouths, et cetera.
(21:04):
Transparencies of face shapes were the base, and the rest
of the face was built on the base, one eye
and nose at a time. UM I was not allowed
to talk to anyone, including the staff of my bank,
until I talked to the FBI. I was instructed to
write everything I could remember about the robber and the
robbery before talking to anybody else. In those days, of course,
we did not have digital cameras in the film had
(21:25):
to be sent out for processing. Um, all of it
in those days. I mean, it's the same like seven
years ago. Um. Actually when did digital come around? The
early two thousands? Seems like it became. I guess it's
more than seven three years on. So uh. The pictures
(21:45):
took a couple of days to get back, and my
composite drawing was posted in the paper, and my robber
was actually caught a couple of days afterward at a
methodon clinic in town. When the film was developed, the
side by side pictures were incredibly closed. So she did
for good job. Sounds like, by the way he was
caught using my composite and not the true picture. We're
(22:07):
pretty cool. Yeah, it's very cool. We were trained to
observe all these details and also to watch for the
six ft mark as the robber left the building. And
you talked about the call it stores. Yeah, Um, I
guess I visit banks. Luckily, even though I was only
twenty years old, the training had taken a hold gave
me great resources to catch this guy. And to this day,
I always observed shady or odd things in everyday life,
(22:29):
including license plates like you talked about. By the way,
my robber had robbed eight other banks up and down
the coast in California. And I got to be a
hero for a minute. And that is Terry Bennett. And
that's a cool story. Yeah, that's very cool, Terry. Um,
thanks for Sharon. I bet she just eyeballs everybody, right, Yeah,
she said that like a weird lady. Now she takes
out methodon clinics. Yeah, what are you doing? Just getting
(22:52):
the methodone. If you want to give us a story,
we love our stories. Um, you can tweet very very
very short story to us at s y s K podcast.
That's our Twitter handle. You can post one on Facebook
dot com slash Stuff you Should Know. You can send
in an email to Stuff Podcast at Discovery dot com
and you can't really tell us a story, but you
(23:13):
can hang out with us at our home on the web.
Stuff you should Know dot com for more on this
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dot com. This episode of Stuff You Should Know is
(23:35):
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Welcome to Stuff you Should Know from House Stuff Works
dot com. Hey, and welcome to the podcast. I'm Josh Clark.
There's Charles W Chuck Bryant, and this is Stuff you
Should Know podcast. Yeah, what are you excited about this one?
(00:23):
I'm going to try to be excited for everybody enough
for everybody, because I imagine, like there's a you know,
there's a lot of people out there who don't listen
to every single episode. I just I find it biting
in weird because I do that with my podcast. So
if I'm like, if I'm listening to like if I
look at Mark Marrin', so I listen to that one.
If it's a guest that I'm not super into, I
(00:44):
want right, that's other podcasts. I'm talking about Stuff you
Should Know. Man, you must be confused. Yes, I feel
like every single one of them is worth listening to.
I agreed. I suspect though, that people are going to
skip over this one. Well, I am going to take
the rap because I picked this out. I like it,
but as I looked into it, I was like, you
know what, I don't know how an aerosol can work,
(01:05):
and I would like to and it's not super complicated.
It's not. In a matter of fact, now that you
read this and researched it, you understand how an aerosol
can works. You can go to the hardware store on
a Saturday when your board is just stand around and
explain it to people and get like applause. I could
do that. Every anyone who listens to this episode will
be able to do the same thing. That would be
(01:26):
like ACE Hardware, and there'll be some seventy five year
old guy with the red vest next to me. Like
all piste off, they always have old timer's working there. Well.
They are big on keeping the economy going on the
backs of aged baby boomers and that there's a slogan, Yeah,
I think it's ACE is the place. Well, you have
(01:47):
to read between the line, Um, chuck. Have you ever
seen a movie called Style Wars. It's a documentary from
Uh no, I haven't. It's pretty cool man. It's it
basically arnicles the the rise of graffiti, hip hop, clothing
and stuff, and break dancing, just that whole culture. And
(02:09):
it's amazing the stuff that people were doing, like even
back then as far as graffiti goes, and breakdancing and
hip hop and all that, sure, but it's just like
the seminal documentary that you just kind of have to see.
It's just so cool. It's like it kind of makes
you feel cool watching it, you know what I mean? Well,
I need that in my life. But the what the
reason I raised style Wars is because the graffiti that
(02:32):
was being carried out would not have ever been able
to be done had it not been for a Norwegian
engineer named Eric Rothheim who in put in the first
patent for an aerosol can in Norway and then five
years later the first one in the US. Yeah, and
they had the little photo of some of his initial drawings,
(02:52):
and the author of this article points out that although
it has evolved somewhat, it's he's He was pretty right
on with that first, is right, you know, almost out
of the gate, because as we said, it's kind of simple.
The Yeah, one of them was simple to me. One
of them I didn't quite understand. Well, okay, so um
so Rothheim he comes up with this, this patent files,
(03:13):
it kicks back and waits for the money to come
rolling in, but it doesn't. It took many many years
or so maybe a little less before anyone fully understood
the value of an aerosol can, and it was um insecticides,
bug bombs, cans of um insects spray that was being
(03:34):
used by soldiers in the Pacific and World War Two.
When people finally said, oh, that is a good idea. Yeah,
I wonder if I mean they had atomizers and things
at the time. I wonder if that was his initial
inspiration was to take that concept and jam it into
a can basically, because that's what's going on. Yeah, you're
(03:56):
atomizing product. Yeah, and there's a lot of um advantages
to atomizing. Number one, if you spray something in a
fine mist, it doesn't hit the ground. Is a bunch
of liquid that seeks into the groundwater usually sticks to
whatever you're spraying it to. Sure, and it's delightful if
you wear perfume or have you ever like had the
rose water sprayed on your face, like the face sprays. Oh,
(04:18):
I thought you meant like an aerosol can of perfect
no atomizing in general? Yeah, sure, sure, I'm fresh. I've
I've had an avian sprits sprayed on my face. You
mean I have before? It's very nice. Yeah, I've had
like the rosewater. Emily will spraying me occasionally. It's very nice.
It just feels good. Does she like hide behind around
a corner and yeah, no, that's the mace. Oh she
(04:40):
mazes me occasionally for kicks. Um. So yeah, there's advantages
to atomizing things. There's reasons. It's at the very least
it's lovely. It is um and the whole premise behind
this though, the delivery method of an aerosol can Like
we said, it's very basic, it's very old, and all
(05:01):
you have to do is understand a little bit about
fluid dynamics to to get what's going on. So let's
let's do let's give a brief prime around fluid dynamic
shall yeah, and fluid period Like you know, fluid isn't
necessarily liquid like you might think it's an actual thing.
Fluid is any kind of substance that has free flowing
(05:22):
particles that it's made up of that and it could
be something liquid, could be something gas that those are
both fluids. It just can't be a solid basically pretty much. Yeah, yeah,
as long as you got those free flowing particles. Um,
these particles, uh, if it's a liquid, they're loosely bound,
but they're still bound. So it means it's gonna have
a fixed volume if it's a liquid. Yeah, which is why,
(05:42):
like when you put water into a glass, it doesn't
just keep going and going and going. That'd be terrifying. No,
it would make it. It would have a gaseous um characteristic.
Then that's right, because gas does expand to fill the
volume that you put it in. That's right, and well,
spoiler or that's what happens with gas. It expands. Uh,
(06:03):
if you heat liquid um applying energy to it, basically
it's gonna vibrate and it's gonna break those forces and
they're not gonna be bound together anymore. Then you're gonna
have a gas. And that's called boiling. Yeah. And I
mean we think of boiling is like applying enough heat
that you will burn your skin. But boiling points vary
for different types of fluids. Um. So any volatile fluid
(06:27):
is a fluid that um boils or turns from a
liquid state to a gasy state. That's boiling um at
room temperature, right, Yeah, Which that that's the part I
had a hard time getting my head around because I
associate boiling with like heat and hot. Yeah. Because you
think of boiling, you think of water, Yeah, exactly. And
it takes a certain amount of temperature, of heat of
(06:48):
heat energy to break those intermolecular bonds to turn water
from a liquid into a gas, that's right. But it
takes less for alcohol or for propane or whatever you
want to use. Right. And so lastly there's another fluid
dynamic trait that we have to have down and then
we'll have all of the stuff in place to understand
an aerosol can expansion of gas. Yeah, So so we
(07:12):
said that when you put gas into something and expands
to fill the volume, Yeah, and gas will decrease in
pressure as it expands, which is why like a tiny
little CEO two cartridge, it's like got tons of pressure
in there, and that's why it can shoot your awesome
industrial arts model car down the track. Because did you
(07:32):
ever do that? Really? I had a Pinewood Derby racer once.
What's that like the car you sit in? No, that's
the cub scout car. Okay, it didn't have any CEO
two though you'd be immediately disqualified. Yeah. In high school,
we we made the little cars that have the CEO
two cartridge in the battle. I know what you're talking about.
And we raced each other and my brother one county
(07:53):
of course, and then and then flashed this winning smile,
and three years later, it's so funny. I forgot all
about this. I tried to be his car design when
I took the class, and mine was not nearly as like,
it just wasn't quite right, and I didn't win county.
I didn't even win my classroom. Somehow, the the compressed
(08:14):
air decompressing into the atmosphere made like a sad trombo
and sad is it so cool? And that really kind
of just sums it all up with my brother and I.
He was always really great at stuff, and I always
tried to do that and was not nearly as good
at it. You're good at other things. Well, I'm yeah,
I can run my mouth, if that's how you want
to put it. Anyway, So that's compressed gas. And when
(08:37):
gas is compressed, it can you know, do some great
things like shoot the car or in this case, spray
paint or something. Right, right, exactly, Okay, So you have
compressed gas, you have all these fluid dynamics, and you've
had everyone now right, Okay, So all an aerosol can
is is all of these principles kind of put into
a very simply mechanically functioning state. Right. Yeah. So you
(09:02):
have a can and you have to to things in there.
You have the propellant, which is the stuff you use
to force the other thing, the product out. Yeah. And
it could be hair spray, bug spray, could be painting oil,
could be that foamy stuff you ever use that, the
(09:23):
stuff to like seal like insulation or sure or like
fix the flat. All that, all that has myriad myriad uses. Okay, right, So, um,
you've got the product in liquid state. Yes, uh say,
it's just kind of floating in the bottom of the can.
You put it in the can, seal it so it's
there's there's no air going it's air tight. Yeah, this
(09:45):
is part one. There's two two ways to do this.
This is the first, right, This is the simple way.
And then you add some sort of compressed air to it,
call it air compressed air. Okay, okay. So you have
this um the propellant in there, and it's it's basically
filling up as much of it as it can until
it's reaching the top of the can, the side of
(10:06):
the can, in the top of the water, and it
pushes all that product down to the bottom, which is
one reason you gotta shake it chack it up exactly.
So you have a tube going down from the nozzle
at the top of the can valve system all the
way down to the bottom of the can where the
liquid is right and that look, that valve has a
seal that's being pushed up by a spring. So the
(10:29):
head the nozzle when it's when it's not being pushed,
it's stealed tight. But when you push it down a
channel opens. It goes below the seal and you now
have the outside atmosphere, which is at a much lower
pressure than inside the can um opened up to the
inside of the can at that much higher pressure, and
(10:50):
it drives it up the tube out the little tiny,
tiny hole which atomizes it. And that's basically the simpler
method of the aerosol can. Yeah. The air pushes the
liquid down and then up the tube. Yeah, because it's
like I want to get out too exactly. It expands. Done.
I mean that's pretty easy. Yeah. So the second way
(11:10):
that this can happen, and I didn't know this is
the more common way, but it is. Uh they use
liquified gas, so uh, that is the propellant. You've still
got the same product. And the product is is sitting
there at room temperature just fine as a liquid. So
they just pour that in. Then they steal it up,
and then the same way with the other way. They
pump in this liquefied gas and it mixes though this time,
(11:35):
right or does it press it down? This is where
I got a little confused. So a liquefied guess you said,
is um, it's a gas that goes into a liquid
state under a certain amount of pressure, right, yeah, okay,
so under high pressure. Yeah, so it does mix because
it's all liquid in there. Once it gets in there,
the whole thing turns liquid, and you keep that pressure
up so it doesn't have any room to expand, so
(11:55):
it's just in their mix together. And then when you
press the nozzle down own and you break the seal
as it were, um, the you form a channel with
the outside air and the inside air. That change in
pressure converts some of that propellant into gas, and it
does the same thing is that standard can. The gas
presses down forces the liquid up, but some of that
(12:18):
propellant is still in liquid form mixed with the product,
and as it goes out, it evaporates, it turns into gas,
and it also kind of um, it turns that liquid
product into a finer miss. Yeah. But what I don't
get is is that it actually boils in the liquid
gas system. It's like, once you relieve that pressure, it
(12:39):
starts to boil, and that's what does it. That's what
I was a little confused about. Yeah, I have a
feeling that this is a different part of fluid dynamics,
that it's not necessarily the boiling point, although it could be,
because I don't think any average gas turns into a
liquid under under all under pressure. There's just certain kinds
that do. I think. Okay, so I think, what's your question, Well,
(13:04):
it's actually boiling in the second in the in the
liquid gas type of aerosoli, at the very least, it's
converting into a gassy estate because of the release of pressure, right,
all right? And why did they can sometimes get cold?
Did you figure that out? Okay? Boy, there's some guts.
There's some people in chemistry lab right now that are
just like, oh my god, you guys, I thought we
(13:25):
had this one, man. I think we had we do
I had it, and I could have done a tap
dance doing this earlier, and now it's like, but wait,
let me complicate it a little more. Now, I think
it's I think the message got through. Um. If in
the case of paint, sometimes you need a little help
mixing these things together. So that's why a paint can,
spray paint can will have the little metal ball bearing
(13:45):
on the inside, right, because you actually do want to
mix the propellant and the product together in a liquefied can,
liquefied gas can, right, because it helps atomize it. As
you said, that's very pleasant, exact. Um, what about the
rounded bottom of this very can you know why that's
that way? If it was flat, it's so pressurized, it
(14:08):
could be a bad scene. It could actually go the
other way. And everyone knows if you studied architecture, that
a dome is more structurally sound than just a flat surface.
So that's basically the same concept at play. So that's
one reason, Um, it's to protect the integrity of the can.
And the second one is is so you can help
(14:29):
get all of the product out, because if it was flat,
it's like when you're down at the bottom of your
of your soda cup with your straw and you're making
that terrible little noise and you're tilting the cup and
trying to stick the straw on the little corner where
it meets the edge. This does it for you. If
it's a rounded bottom, it just puts all the product
there at the edge and that's where the little tube is,
(14:49):
and so you're all set. Yeah, And did you know
there's about nineteen billion steel and aluminum cans that include
aerosols and other products that are recycled every year and
that's equal to enough to build twenty golden gate bridges. Wow,
isn't that amazing? So we mentioned there's a variety of
different products that you can have that you're trying to
(15:11):
get out of your can, from foam to like whipped
cream to a bug spray, stuff like that hair spray,
although does anyone still use aerosol hair spray? I think
some people do, is it? Remember? Do you remember the
Bizarre Ways to Die episode? The deodorant boy asol deodorant
that he died totally man, that was a long time ago. Um.
(15:33):
So the way they accomplished this though with a different product,
um is you can have a variety of consistencies. And
what they do is they just play with, UM, the
ratio propellant to product. Maybe maybe the chemical makeup of
the propellant the product have to be just right. Maybe
the pressure of the propellant has to be a little
different depending on what kind of product you're working with.
And then um, the size and shape of the valve system.
(15:57):
Like in the case of a fix, the flat that
you put in your higher it's not the same as
you know, a spray can. It's not atomizing. It's got
like the tube hooked up and it's Uh. If you've
ever sprayed that stuff in your house, like the Philip Crack,
like a whole can of it, It's amazing how much
stuff is packed in there. Like when it gets out,
you're just like wow, it's like the clown car of
the industrial engineering scene. Um, do you want to know
(16:22):
a little bit about CFC's chlorofluora carbons. Yeah, I didn't
get a chance to look into this, but I'm glad
you did so. Prior to the late twenties, there was
people were using ammonia and refrigerators and dying from ammonia leaks,
and it was just a bad scene. And so everybody said, well,
we've got to figure out some sort of toxic, non
toxic chemical that we can use as a refrigerant, and
(16:45):
a general motors engineer of all people came up with
what du Pont later turned into free on, a chlorofluora
carbon which supposedly was non toxic. It was. It basically
changed everything. Um it was much less harm harmful compared
to like ammonia. UM. It allowed us to make cheap refrigerators,
(17:06):
car A C, A C window units, like all those
things came from the advent of chlorofluora carbons, right, And
it was also very ubiquitous as a propellant in aerosol
can sprays. Well. I think that's why everyone, you know
quit using aquinette, right, because everybody was going in the
spraying these things, and they were going up in the atmosphere,
(17:28):
and everyone was like, look at them. Go it's cool.
They're like, you know, innert, non toxic chemicals going up
in the atmosphere, but we're all getting cancer. The problem
is when a CFC enters the atmosphere and gets high
enough and it's exposed to UV radiation, it breaks down
and into its constituting components, one of which is chlorine,
(17:48):
chlorine reeks, havoc on the ozone layer. One atom of
chlorine can destroy about a hundred thousand ozone molecules, and
we need those molecules. The ozone layer protects us from
UVB ray from the sun, which are they kind of
give you skin cancer and destroyed crops. So in nineteen
seventy four some scientists realized that CFCs were doing this
in the ozone layer and is gonna be big trouble.
(18:11):
And then in the eighties we figured out that there's
a hole in the ozone layer over the Arctic. So, uh,
a bunch of countries I think seventies signed on to
basically outlaw CFC production. Yeah, and then later on another
like hundred and twenty I think signed another treaty. So
it's very very difficult to find CFC's these days. But
(18:34):
they're still around, are they. Yeah? They still use them
in some um nasal sprays UM and they're also used
in halan, which is a fire extinguisher for airplanes. Did
they not still use free on? No? I don't believe. So, Okay, Yeah,
it's basically like we did away with those. It's gonna
take a while to repair. But they found that the
(18:55):
ozone layers no longer growing the hole in the ozon
layers growing, it's just holding steady and hopefully patching itself
back up. They just forced people to go out and
be innovative and find different ways to do these things exactly.
And if you compare your airsol can propellant today to
one that had CFCs before, you're not going to notice
the least bit different. So that's canna aquinit that looks
(19:17):
exactly the same as it did in nineteen seven is
no longer dangerous, not to the ozone layer. It is
the spiders though, if you have a lighter. Yeah, don't
ever do that. Kids. Ah, that's it for airsol cans
unless you have like another ten minutes on it. Uh No,
that's all I got. I mean, what else is there?
(19:37):
I genuinely looked in There is nothing else. Ye, go
out and do some graffiti, That's what I say. Um
artful graffiti though, don't tagg and stuff. You should probably
practice at home first. I hate that. Just stupid. Yeah, Like,
educate yourself on different types of nozzles, like practice, don't
do don't be a punk, agreed, be an artiste. Uh.
(19:59):
If you we want to learn more about aerosols, or
at the very least, want to see the article where
we told you everything there is to know about aerosolis.
You can type that word A E R O S
O L S into the search bar how stuffworks dot
com and that will bring it up. And I said
the search bar, which means it's time for message break
(20:23):
and now it's time for listener mail. I thought you
might say it, okay, Josh, listener mail time. UM, I'm
gonna call this uh police sketch eye witnessed stuff. It's
from Terry Bennett. Um, Hey, guys, uh listen to the
police Sketch episode, and wanted to share my story. I
was robbed when I was a teller of a bank
(20:43):
in n and at that time, bank robbery was a
federal crime, probably still is. I was immediately taken into
the back room of the vault and the FBI was
called in. When they arrived, a sketch artist brought a
large binder, not full of women, but full of pictures.
They aces and eyes and noses and mouths, et cetera.
(21:04):
Transparencies of face shapes were the base, and the rest
of the face was built on the base, one eye
and nose at a time. UM I was not allowed
to talk to anyone, including the staff of my bank,
until I talked to the FBI. I was instructed to
write everything I could remember about the robber and the
robbery before talking to anybody else. In those days, of course,
we did not have digital cameras in the film had
(21:25):
to be sent out for processing. Um, all of it
in those days. I mean, it's the same like seven
years ago. Um. Actually when did digital come around? The
early two thousands? Seems like it became. I guess it's
more than seven three years on. So uh. The pictures
(21:45):
took a couple of days to get back, and my
composite drawing was posted in the paper, and my robber
was actually caught a couple of days afterward at a
methodon clinic in town. When the film was developed, the
side by side pictures were incredibly closed. So she did
for good job. Sounds like, by the way he was
caught using my composite and not the true picture. We're
(22:07):
pretty cool. Yeah, it's very cool. We were trained to
observe all these details and also to watch for the
six ft mark as the robber left the building. And
you talked about the call it stores. Yeah, Um, I
guess I visit banks. Luckily, even though I was only
twenty years old, the training had taken a hold gave
me great resources to catch this guy. And to this day,
I always observed shady or odd things in everyday life,
(22:29):
including license plates like you talked about. By the way,
my robber had robbed eight other banks up and down
the coast in California. And I got to be a
hero for a minute. And that is Terry Bennett. And
that's a cool story. Yeah, that's very cool, Terry. Um,
thanks for Sharon. I bet she just eyeballs everybody, right, Yeah,
she said that like a weird lady. Now she takes
out methodon clinics. Yeah, what are you doing? Just getting
(22:52):
the methodone. If you want to give us a story,
we love our stories. Um, you can tweet very very
very short story to us at s y s K podcast.
That's our Twitter handle. You can post one on Facebook
dot com slash Stuff you Should Know. You can send
in an email to Stuff Podcast at Discovery dot com
and you can't really tell us a story, but you
(23:13):
can hang out with us at our home on the web.
Stuff you should Know dot com for more on this
and thousands of other topics. Is it how stuff works
dot com. This episode of Stuff You Should Know is
(23:35):
brought to you by audible dot com.
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