Fun with liquid nitrogen

[Cuddles]

So you like your ice cream partially melted and then refrozen? That's like saying that you prefer hamburgers to be burnt.

Weird.

Of course not, that's not even close to what I said. The whole point of using LN2 to make ice cream is that the ice crystals are smaller because it freezes faster. You don't need to melt and re-freeze icecream to have larger crystals, you just need to freeze it slower, which is exactly what is normally done. Having the crystals too large, which tends to be the case in really cheap ice-cream, isn't particularly nice, but neither is having them too small.

Edit: To stick with the hamburger analogy, you want a burger to be made up of ground beef. You don't want the pieces to be too large, which would just be a chopped steak, but you don't want beef puree either. Chopping the meat into smaller pieces is not necessarily going to make it better. Same with ice-cream.

 

[arthwollipot]

Of course not, that's not even close to what I said. The whole point of using LN2 to make ice cream is that the ice crystals are smaller because it freezes faster. You don't need to melt and re-freeze icecream to have larger crystals, you just need to freeze it slower, which is exactly what is normally done. Having the crystals too large, which tends to be the case in really cheap ice-cream, isn't particularly nice, but neither is having them too small.

Edit: To stick with the hamburger analogy, you want a burger to be made up of ground beef. You don't want the pieces to be too large, which would just be a chopped steak, but you don't want beef puree either. Chopping the meat into smaller pieces is not necessarily going to make it better. Same with ice-cream.

OK, gotcha. I'd still love to try LN2 ice cream.

 

[EHocking]

...We also had a lab manager that was always leaving his pass lying around (you know the ones with a chain or ribbon to hang around your neck). We got the biggest container we could find, filled it with water, dangled his pass in then froze it with LN2. We also had a very cold freezer (-50°C or something) and put the block of ice in there for the rest of the day. At the end of the day we left the block out and scarpered. Lab manager was last seen walking across the car park swinging this massive block of ice with a very disgruntled look upon his face! That'll teach him to leave his pass lying around.

Being a curmudgeonly urban legends fan, there was probably an embellishment to that story that you should have left out, and that's the detail, "seen walking across the car park swinging this massive block of ice..".

Since the chain/ribbon for hangin ID badges around a person's neck have weak links to prevent strangulation, I doubt that he left the lab swinging 1kg plus of ice from such a necklace.

Oh, and CaveDave's family are just weird, "My dad was a dermatologist and used LN2 to burn off warts and skin cancer/moles. He sometimes brought leftovers home to let me play with."

 

[ImaginalDisc]

Being a curmudgeonly urban legends fan, there was probably an embellishment to that story that you should have left out, and that's the detail, "seen walking across the car park swinging this massive block of ice..".

Since the chain/ribbon for hangin ID badges around a person's neck have weak links to prevent strangulation, I doubt that he left the lab swinging 1kg plus of ice from such a necklace.

Not at all impossible. The landyards commonly used for ID tags and passes are often fairly study nylon or polyester and the cheaper ones don't have any safety catch. Those that do tend to have them low, near where the badge would be, to keep from having the catch release all the time.

 

[pannarrans]

oh the memories!

Throwing it on the floor had this very nice effect, yes. I remember having to tap it from the big container outside using those very thick mittens. Tapping it was especially fun on hot days (if I remember correctly) when the difference between the LN and the outside temp was large enough to create a big fog-cloud around me.

Leftover were also used to blow up plastic gloves and freeze leftovers from lunch (when you break open a deep-frozen kiwi it looks remarkably like a geode).

I also remember making a very fast frozen pie using the -80 Degrees C freezer, the thing was impossible to cut though.

The most fun however we had with dry-ice, especially combined with those little 1.5 ml eppendorf tubes. Delayed minibombs, not much oomph but enough bang to startle a colleague or, with the combined effort of several colleagues, a whole class of veterinarian students getting an open air lecture precisely under our lab's balcony. Fun times!!

 

[pgwenthold]

What happened to the good old days when a chemist could tell you what something tasted like?

I'm a chemist and can say..."not much, really"

Of course, that's because you don't let it hit your tongue and don't swallow, of course.

But it's fun to blow LN2 smoke.

 

[EHocking]

Of course, that's because you don't let it hit your tongue and don't swallow, of course.

... and remembering which finger you used to sample...

 

[CaveDave]

<SNIP>
Oh, and CaveDave's family are just weird,

True, but not in the way you seem to imply.

"My dad was a dermatologist and used LN2 to burn off warts and skin cancer/moles. He sometimes brought leftovers home to let me play with."

I think it was stated clearly enough that the "leftovers" were of the LN2, but you seem to have had fun thinking of the possible ways to misinterpret my statement.

Had I meant it as you suggest, I would have called them "pathology specimens".
He did bring some of those home, too, in the form of microscope slides, stained and under cemented cover slips.

Cheers,

Dave

 

[EHocking]

True, but not in the way you seem to imply.

Yeah, but I just couldn't resist it...

 

[sanguine]

What happened to the good old days when a chemist could tell you what something tasted like?

One of the faculty I knew back in my undergrad days could identify molecular biology buffer solutions by taste.

"Hm....TAE."

The one that caught me rather more off guard was watching an older faculty member mouth-pipette some Salmonella. When I asked her if that was a good idea, she called me a wuss.

 

[CaveDave]

Yeah, but I just couldn't resist it...

I understand, hence the grin.

Just friendly banter...

Dave

 

[ElMondoHummus]

Hmmm... Leidenfrost effect... I guess you can do the old standby and blow "smoke" out your mouth with it.

Or hold it in your mouth and see if vapor comes out your ears . But, how much damage if the vapor layer collapses? Or if, heaven forbid, you swallow?

ETA: Ahhh... "answer" (yes, humor quotes) found.
http://www.darwinawards.com/personal/personal2000-25.html?

 

[MattusMaximus]

The one that caught me rather more off guard was watching an older faculty member mouth-pipette some Salmonella. When I asked her if that was a good idea, she called me a wuss.

That's hardcore - I always had such great respect for my "old school" science colleagues, just for reasons such as this

 

[MattusMaximus]

Hmmm... Leidenfrost effect... I guess you can do the old standby and blow "smoke" out your mouth with it.

Or hold it in your mouth and see if vapor comes out your ears . But, how much damage if the vapor layer collapses? Or if, heaven forbid, you swallow?

ETA: Ahhh... "answer" (yes, humor quotes) found.
http://www.darwinawards.com/personal/personal2000-25.html?

I like to do a demo where I take "goldfish" and dump them into a vat of LN2. Then I let the kids scoop some out and eat them...

... it's okay though. The "goldfish" are crackers, and though they get very cold they don't soak up enough LN2 for it to be dangerous for students. The crackers get a nice flavor to them and one can blow lots of nitrogen gas as the crackers warm up!

 

[CORed]

My A level physics teacher managed to lay his hands on some liquid nitrogen and he gave us all the usual demos; shattering roses and bits of rubber tubing, that sort of thing. At the end, he had some left over, so for want of something better to do, he poured it over the table. Guess who was the poor unfortunate standing at the opposite end, who took a direct hit at hip height? No injuries, but I did get severely laughed at, standing there as I was with the front of my trousers smoking.

The best LN2 trick I've ever heard about (although never seen deployed) is to pour it down a sink, put the plug in and block up the overflow pipe. This causes a pressure build-up somewhere in the plumbing system, which will cause the water to shoot out of the u-bends in some other random sinks in the building.

I don't think the sink trick would actually work, because a properly constructed waste system is vented through the roof. The purpose of the traps (u bends) is to make sure that sewer gas goes out the vent, not out the drains. Sewer gas stinks, and, as it contains methane, can be a fire hazard as well.

 

[CORed]

I've heard that it's incredible. The ice cream freezes so quickly that there's no time for ice crystals to form. Or that they do form but they can't grow large, so the ice cream is smooooth.

I'd love to try it someday.

I've never tried it, but it's got to be a lot easier than the old ice, rock salt, and turn the crank for half an hour routine.

 

[Spud1k]

I don't think the sink trick would actually work, because a properly constructed waste system is vented through the roof. The purpose of the traps (u bends) is to make sure that sewer gas goes out the vent, not out the drains. Sewer gas stinks, and, as it contains methane, can be a fire hazard as well.

I can't personally vouch for his story, but it's entirely possible the trick only worked in the specific building that he was talking about. I can certainly attest to the general hokeyness of the plumbing in some of Britain's older university buildings; to quote but one example from a couple of months back, we arrived one morning to find one of our offices ankle-deep in water thanks to a valve being opened to a pipe that went nowhere. Fortunately though, the office only housed PhD students...

 

[luchog]

it's okay though. The "goldfish" are crackers, and though they get very cold they don't soak up enough LN2 for it to be dangerous for students. The crackers get a nice flavor to them and one can blow lots of nitrogen gas as the crackers warm up!

When I was in school, they did the same demonstration with graham crackers.

 

[arthwollipot]

Who's Graham Crackers?

 

[Almo]

Well, there's a mail on the ice cream guy's site allegedly from someone who worked at a Dippin Dots factory. He said they make them with N2.