SpudFiles

http://en.wikipedia.org/wiki/Liquid_air

now if someone could find a way to easily produce this as a hobbyist then you could build one of the most powerful pneumatic cannons ever or a combustion cannon with liquid fuel and oxidiser!!

you do realise that the air has to be stored at -194 degrees c you cant exactly make that in your freezer

it has been used before, on a mini airplane engine



http://www.powerlabs.org/engines.htm

you get flasks called dewar flasks to hold the stuff!!
pretty much just a very efficient vacuum flask

you can stand the liquid air in open air to enrich it with oxygen(the nitrogen evaporates and condenses oxygen out of the air) and then this could be used as an oxidiser in combustion cannons!!!
maybe if we could make liquid hydrogen too you could then make a liquid fuel cannon!!! very powerful probably supersonic!!

That engine ran ON liquid air not made it. And you couldn't call the tools used by powerlabs to amature. Even if you could create those temperatures and maintain them, they could cause the materials used for the chamber to become brittle to the point that the act of firing the cannon will almost certainly cause the cannon to fail.

Edit:

Due to its cryogenic nature, LOX can cause the materials it touches to become extremely brittle. Liquid oxygen is also a very powerful oxidising agent: organic materials will burn rapidly and energetically in liquid oxygen. Further; if soaked in LOX some can detonate unpredictably on subsequent contact.

A good reason NOT to use cryogenic oxidisers

i was just stating the fact that it can be used to propel/make something move.

Some people have suggested using liquid fuels in real-steel firearms, often LOX/LH2, for the higher speed of sound in the propellant gasses.

However, the high pressures that this produces are not suitable for anything we would recognize as a 'potato gun', and thus liquid-liquid propellants are impractical for the spudder.

(besides, liquid-liquid mixtures violate the spirit of the "no solid fuels" rule)

However, using liquid air to provide gaseous air is a viable possibility. In fact, it's really nice, because the air formed is COLD, and cold air increases performance in combustion cannons.