you know those can duster things? the ones that are just aerosol spray cans full of nothing, pull the trigger and they squirt "air"?

what they're actually full of is liquid butane. Butane is a gas at room temperature and atmospheric pressure, but when compressed in a bottle like that it's liquid, except for a gaseous layer on top. If you open the valve (pull the trigger) the gaseous butane on top will rush out the nozzle, while the liquid part of the butane rapidly boils to keep the pressure constant

this has two immediate consequences: one, you should absolutely never use one of these near a source of heat or flame, because butane is very flammable; and two, if you turn the can upside down like it tells you not to do, you can get liquid butane out (because with it upside down, the liquid part is what's next to the nozzle)

A neat thing about physics is that when a liquid boils, it absorbs heat energy from all around it. Quite a lot of heat, in fact. Liquid butane, of course, will rapidly boil when not pressurized, and this boiling will quickly cool anything around it to the boiling point of butane at atmospheric pressure, which is approximately 0 °C/32 °F.

This is a very convenient way to rapidly cool something down if you ever need to do that.

As a warning: some spray dusters will use propane instead, which has a boiling point of around -42 °C/-44 °F, which will very quickly cause cold burns or frostbite if sprayed on skin. Do not do this on skin.

Other spray dusters use things like R-134a or other refrigerants, which have a variety of boiling points and generally should not be put on your body anyway
-F