[billnotgatez]

I thought most of the stuff welding suppliers have is compressed gasses. Welding supply houses as a source for liquid nitrogen is news to me. I will have to check this out for curiosity sake. By the way, since liquid nitrogen can be very dangerous, I bet it is still hard to convince them to sell it to you.

[Borek]

When you need compressed gases they can be sold in a bottle that you have to return, perhaps it works the same way for Dewar flask. Sure, you have to convince seller that you have a legitimate reason to buy liquid nitrogen. In my experience as long as it is not something otherwise forbidden your chances of convincing seller are directly proportional to your age

[jdurg]

I thought most of the stuff welding suppliers have is compressed gasses. Welding supply houses as a source for liquid nitrogen is news to me. I will have to check this out for curiosity sake. By the way, since liquid nitrogen can be very dangerous, I bet it is still hard to convince them to sell it to you.

It's actually cheaper and easier for the gas companies to supply liquid nitrogen than compressed nitrogen.  When welding, you often need to have completely oxygen free atmospheres to avoid instant corrosion of the metal.  By using liquid nitrogen, you can create a heavy blanket of nitrogen gas over your metal surface and prevent any oxidation from occuring as you weld.  N2 is by far much cheaper than argon is, or any other "blanket gas".  In addition, it's easier to keep nitrogen in a liquid form than it is to compress it safely into gas cylinders.  The welding supply companies can keep a large tank of liquid nitrogen around and provide a lot more gas to the customers than they can if they just bought hundreds of compressed cylinders of it.

As for convincing them to sell it to you, you really don't have to.  You can't make a bomb out of liquid nitrogen, it's not going to oxidize everything and start a fire, you can't really use it to make drugs, so the only real use for it is to freeze things.  The only thing the gas companies have to be assured of is that the container you're bringing it home in won't rupture and break due to poor design causing you to be suffocated by the N2(l).  This is why they will ONLY sell it to you if you have a legitmate transport dewar.

[billnotgatez]

One wonders if they are not concerned that you might spill it on your hand, which would probably cause loss of that limb. Since everyone is being sued now days, it seems that most places would be cautious. Selling it to someone over 18 is one thing, but persons under that age would be a liability.

[jdurg]

One wonders if they are not concerned that you might spill it on your hand, which would probably cause loss of that limb. Since everyone is being sued now days, it seems that most places would be cautious. Selling it to someone over 18 is one thing, but persons under that age would be a liability.

Spilling it on your hand won't do anything.  You'd have to be pretty damned stupid and ignorant of pain in order to damage yourself by spilling liquid nitrogen.  I've poured liquid nitrogen over my bare hands and it did nothing.  The heat of my body instantly boils away the liquid that is in direct contact and I let the liquid N2 flow right off.  Sure it stung a little bit, but I didn't go and shove my hand in the flask and let it freeze. 

As long as the contact isn't a submersive type, you're not going to hurt yourself.  It's a similar risk to giving someone a pair of skis and letting them go skiing.  Unless you're a complete idiot, you're not going to have to worry about frostbite.   

[The Tao]

Yeah, it's not really considered dangerous except to your eyes.