What do you think of this fact?
Oxygen is the most boring-looking thing you’ll ever depend on: no color, no smell, just air. But cool it to minus 183 degrees Celsius, where it turns liquid, and it suddenly shows two hidden talents.
It’s blue
In a glass flask, liquid oxygen is pale blue. Liquid nitrogen, which boils at minus 196 degrees, stays colorless right next to it.
The reason is unusually weird. According to Purdue’s chemistry demo notes, liquid oxygen absorbs red light at a wavelength of 630 nanometers. And it does it as a team: a single photon excites two oxygen molecules at the same time. That’s what removes some red from the light and leaves you with blue.
In the gas around you, this trick almost never happens, because two molecules rarely sit close enough together when a photon arrives. Liquid oxygen packs the same amount into a much smaller space, about 800 times less volume than the gas. Suddenly the molecules are close enough to pull it off.
It sticks to magnets
The second talent is even stranger. Pour liquid nitrogen between the poles of a strong magnet and it just runs through. Pour liquid oxygen there and it collects in the gap and hangs on. In Harvard’s lecture demonstration, a slosh of liquid oxygen can stay suspended in the magnetic field for 30 or 40 seconds while it boils away.
This is called paramagnetism. Both oxygen’s color and its love of magnets come from the same source: two unpaired electrons in the molecule’s outer orbital. Nitrogen has none of that, so nothing happens.
Bonus fact: Oxygen isn’t the only gas with this combo. According to Imperial College London, liquefied nitric oxide is a deep blue liquid and is paramagnetic as well.
So the oxygen in your lungs is secretly a blue liquid that magnets can grab. It just needs a lot of cold to show it.