The fact that gases can be liquefied provides a neat way
of separating oxygen and nitrogen
from air.
Here’s how it works:
First, air is compressed in a pressurized chamber.
As the pressure increases, the molecules in the air get
squashed closer together.
Eventually, the molecules get close enough for the gas
to become a liquid.
In the process of cooling the air,
components such as water and carbon dioxide freeze and is removed.
Gaseous air becomes liquid air and during the process,
the temperature drops to around
-212 C.
Next, the cold, liquefied air is allowed to warm up
slowly.