Hi everyone! Welcome back to Cody's Lab.
so James Dewar - when he was making liquid hydrogen
he used a bath of liquid oxygen as a
coolant. Now this seems kind of strange
because liquid hydrogen and liquid
oxygen combine to make rocket fuel.
Why would you put something so explosive
together when you could use liquid
nitrogen which boils at even lower
temperature than oxygen, and perhaps get
the hydrogen to go better?
well there is one very important reason
for this, which I hope to demonstrate today.
So I have some liquid oxygen being produced.
I'm just making it from the air today. Got an
aquarium pump hooked up here and a Dewar
flask full of liquid nitrogen. And of
course over here I have some more liquid
nitrogen. I'm gonna be putting that both
of those into a vacuum chamber here in
each of these little dishes. One will
have oxygen the other will have nitrogen.
You see there's a couple little magnets
in there hold it together. And if we have
oxygen then the oxygen should be
magnetic. Okay, so first let's add liquid
nitrogen. That will help cool things off.
Okay. There's our nitrogen and now i'm
going to add the liquid oxygen.
The oxygen has a bit of contamination which
includes co2 and water that came from
the air. See, if i bring another magnet over
here you should be able to see that
indeed the oxygen is magnetic.
looks like I've buried the other magnet.
That's alright so we put the lid on the
vacuum chamber now. And now i'm going to
turn on the vacuum. It may be kind of
loud so headphone users might want to
turn down the volume.
Okay that wasn't too bad.
So now as i suck out the air the
pressure will decrease and that makes
the liquids boil at a lower and lower
temperature. Eventually they'll be
boiling at such a low temperature that
they'll actually reach the triple point
and freeze. looks like the oxygen's boiling quite
profusely here. The nitrogen seems to
have stopped.
And the nitrogen has frozen and then it
thawed out again all of a sudden. *chuckle*
tends to do that doesn't it. let's get a little bit
better look over this. Looks like the pressure's
down to negative 20 inches of mercury.
I think 24 inches of mercury is the current
barometric pressure. So there's the
nitrogen freezing and turning into snow That means the temperature that I've
reached is now about 63 degrees Kelvin.
And you notice the oxygen is still
liquid. In fact it's actually climbing
onto the magnet a little bit more.
Yes, very nice.
Now I doubt that the oxygen will
actually freeze until all of the
nitrogen is frozen solid. Because as you
may have guessed already oxygen has a
lower freezing point the nitrogen does.
It also has a higher boiling point so
oxygen has a wider liquid range. There's
a metal pan next to the vacuum pump so
that is making so much noise. I can see
the nitrogen is actually sublimating a
little bit. See how it's like pulling
away from the sides of the container,
because there is still quite a lot of
heat sources nearby.
Yeah I think the last of the oxygen just
boiled away.
Tell you what let's actually do one of
these rounds, but instead of having
nitrogen next to it let's just do pure
oxygen. That way I don't have to wait for
the nitrogen to boil off that took over
10 minutes and my vacuum pump is now
overheated so i need to let it cool off
before I try again.
so while i was waiting for the pump to
cool and the oxygen to generate I did a
little bit of research online and I
looked at some phase diagrams. And it
looks like nitrogen this triple point
was about a hundred Torr or roughly 0.12
ish atmospheres whereas oxygen's triple
point is one Torr, or about 1% of what
nitrogen is. So of course as long as I
had nitrogen in the chamber,
I wouldn't have any solid oxygen that
actually means if you had liquid
nitrogen on the surface of Mars, it would
freeze solid where oxygen would remain
liquid. So I'm actually going to try to
filter the oxygen this time so that I
get some of that ice crystals out. See
how this works.
You know I think that was mostly
success. That let's put this under vacuum
and see if we can bring it down to one
Torr. We will not have any nitrogen to bother this.
There we go, now the pressure should drop
even lower than last time because
there's no nitrogen to sublimate away
and build up the pressure. At least that's the
idea. We are negative 23 inches of mercury
and dropping so i wouldn't expect the
oxygen to freeze yet. Oh no my
vacuum pump just shut off. Too hot.
So now that my vacuum pump has had a little bit of
time to cool off i'm going to do a
couple of things different. This time I'm
actually going to put the oxygen cup
down inside of the Dewar flask with it
already chilled to a very low
temperature.
Let's actually take this oxygen, may as well
pour in here now. There we go.
Now we're gonna take this and pour off the nitrogen,
and hopefully get this in there
And then put the oxygen down inside of it.
Okay that'll keep it colder. Let's put this
over into the chamber. So the pressure is
definitely lower than it was last time.
We're very close to negative 24 inches.
so that's practically zero atmosphere but
obviously since the oxygen still liquid
we're still above one Torr.
Something's happening in there.
The oxygen seems to be kind of slushy at
the moment. I can see it's still kind of
moves around but it's definitely more
viscous than it was before. You know what, I think
I've got solid oxygen in there. let me adjust
this light a little bit. See when I move it
the oxygen doesn't slosh around. Its
frozen! And the pressure is
basically zero. This is awesome!
There we go that's a little better. So you can
actually see that the oxygen is
definitely crystallized. It seems the
surface of it refuses to completely
freeze that is probably because of the heat
that's coming in from the top.
Look at that we've got solid oxygen in
there. That's 54 Kelvin. I think that's the
coldest I've ever gotten.
let's turn the vacuum pump off and see
if it melts again.
Okay now i'm going to let in the
atmosphere.
It's definitely liquefied it. haha So how
about that I actually made solid oxygen. It's
liquefied again. In order to get the
hydrogen as cold as possible,
he didn't have his cooling gases inside
of an open container at one atmosphere.
Instead, he put it under vacuum and pulled
it down to the point where the gas is
nearly froze. If you want to use nitrogen
he would have had to lowered the hydrogen's
temperature by expanding it by another
40 kelvin or get to the 20 Kelvin needed
to liquefy the hydrogen. By using oxygen
he only needed to lower by about 30
Kelvin, which meant that he had to
pressurize his hydrogen much less. Which,
I suppose made it worth the risk of
putting the hydrogen so close to the
oxygen.
I'm sure he still have explosions and
stuff but he was able to liquefy the
hydrogen in the end. At some point I hope
to recreate this and liquify hydrogen on my
own
of course I've got a little bit better
materials to use than
Dewar did. Hope you guys enjoyed i'll see
you next time.