How to make liquid oxygen: an unusual experiment
At first glance, the easiest way to get a little liquid oxygen for experiments is to open an oxygen cylinder cooled to the desired temperature. Having sweated a lot, the “King of Random” found out that this strategy is no good, because, despite the high cost, there is very little oxygen in the cylinders. The most productive was the method with the simple extraction of oxygen from the air using liquid nitrogen, which can also be made at home.
"Popular mechanics" warns that liquid oxygen is flammable, and therefore experiments with it should be carried out in compliance with safety precautions.