Crushed Dry Ice would be just as effective and alot cheaper, you`ll maybe find that you can get small amounts of it for free, ask some of the guys that drive Ice Cream vans for a bit, most will say yes after asking what you want it for.

keeping it in a thermos is the traditional way, they do often have a small pressure release opening as a safe guard against excess pressure build up. these backpack weed sprayers I wouldn`t trust, maybe as an experiment you could put the plastic hose in the freezer and try bend it after half an hour, LN would make it considerably colder!, as for the valve actuator (usualy a spring) the cold would shatter that also. I expect you`de need significant modifications before the idea becomes viable in the way you sugested, lots of lagging and tinfoil etc...

If you can find a place that`ll sell you LN, let me know, I`ve never used it myself only ever dry ice. there`s a few supper conductor experiments I`de like to have a go at, Good Luck

Sayonara³ said in post # :

You'll need an awful lot of expensive equipment to turn nitrogen into a liquid form, and keep it that way. It would be dangerous and horribly impractical.

 

It's not all that expensive in the grand scheme of things to make liquid nitrogen. To keep it you use something called a joyst (sp?). I've seen a few, you can keep about 20-30 litres (or more) of liquid nitrogen liquid for about a month or so. They're about £300 and they're essentially big thermos flasks.

you can pour LN on your hand, its just boils off, but never submerge your hand in LD it will fall off.

dave said in post # :

It's not all that expensive in the grand scheme of things to make liquid nitrogen. To keep it you use something called a joyst (sp?). I've seen a few, you can keep about 20-30 litres (or more) of liquid nitrogen liquid for about a month or so. They're about £300 and they're essentially big thermos flasks.

For what he wants to do, it's going to cost more than that.

i can buy some liquid nitrogen over here for less then 90c a liter and the dewar for holdin it costs a bit though but my main question was not the price or the implecations but could you spray it out of a back pack type thing

Yes. Yes you can.

 

But I wouldn't.

"shattering chewing gum from pavements" this was my idea exacly its a pproblem alot of big cities have and they only thing to combat it is to power wash it but liquid nitrogen would do it ten times better maybe farfetch but mu 14 year old mind is quite imaginative i reckon it could make ya a bit of money too

ohh crap imaginitive maybe but i better get these spelling right lol

I would actually think as you were spraying the LN out, it would evaporate before it even reached the plant/weed.

wolfson said in post # :

I would actually think as you were spraying the LN out, it would evaporate before it even reached the plant/weed.

And the finer the spray is, the worse that problem will get.

smokey-nitro said in post # :

"shattering chewing gum from pavements" this was my idea exacly its a pproblem alot of big cities have and they only thing to combat it is to power wash it but liquid nitrogen would do it ten times better maybe farfetch but mu 14 year old mind is quite imaginative i reckon it could make ya a bit of money too

 

Don't think that'd work unless you could make sure that the concrete/surface underneath wasn't affected, otherwise you'd have large holes in the pavement afterwards. Much better to use high powered water pressure I would imagine.

I've been reading this thread for a couple of days and I think some of you guys have got the wrong idea about making things very cold.

 

When you reduce the temperature of something it becomes more brittle - liquid nitrogen will make things very cold and very brittle but it won't make a slab of concrete as delicate as a sheet of glass.

 

You'd still have to hit the paving slap with something like a sledgehammer to break it because it is still inherently strong - it's just more brittle and less able to absorb an impact.

 

The demonstrations using delicate roses are all well and good but rose petals aren't particularly strong as well as being very thin so easy to snap if made rigid.

 

The liquid NO2 would not need to be sprayed either - it could quite effectively be administered by allowing it to slowly flow out of a nozzle using gravity alone.

Even so, safety issues and costs seem to outway the time saved.

What happens if someone steps on it?

What happens if they accedently spay it on a dog or something? He's a dogcicle. I'd imagine it would be the same with a cat, but I've never tryed a cat.

The sole of their shoe might feel cold for a moment.

 

I'm not supporting the idea because I don't think it's sensible for safety and cost etc. I just want to point out that making the pavement cold will not result in holes everywhere.

If it was sprayed on a dog or cat it would probably burn the localised area but it wouldn't make a dogcicle unless the dog was fully immersed for quite some time.

 

Liquid NO2 isn't THAT cold and time is need for the transfer of energy when freezing any object.

Well then, try liquid helium II (or is it hydrogen? no, helium) THAT is cold.

I'm not allowed to talk about the frozen dog science fair experiement gone wrong, it's part of the goveronment agrrement.

Ooooh! If the government is involved, you must have also frozen a missile silo!

When I say it's not THAT cold I don't mean relative to other liquid gasses I mean not so cold as to instantly freeze a large, warm object.

Like a dog?

Indeed - a large, warm, waggy object called Rover.

The missle silo "Dog".

It was fun.

I'm sorry, my mind wonders.

PS: where's Gandalf?

Is "waggy" even a word?

Gandalf is probably buying some LN right now.