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.
