> While oxygen in the form of gas is colorless, what color is liquid oxygen?And the answer: blue.Slightly denser than ice, liquid oxygen has a pale blue color. As a cryogenicliquid, it's extremely cold and will start boiling at any temperature above -147degrees Celsius.Photo credit: public domain.While oxygen in its gaseous form comprises most allof the life around us in one way or another, liquid oxygen serves uniquepurposes for scientists and experimentation. Interestingly, though, the two areless separate than you may think: oxygen is often liquified so that it can bemore effectively transported and stored in large volumes. The oxygen used byhospitals or other medical practices is frequently stored in a liquid statebefore being converted back to a gas. Ultimately, liquid storage is less bulkyand less costly than the equivalent capacity of high-pressure gaseous storage,and so much of the oxygen stored in medical facilities is in a liquid form. Liquid oxygen serves several primary purposes. Most significantly, it is used asan oxidant for liquid fuels in the propellant systems of missiles and rockets.Otherwise, it is widely applied in the metal industries in conjunction withother fuel gases for metal cutting, welding, hardening, cleaning, and melting.In medical practices, patients can even receive liquid oxygen therapy fordiseases of the lung or other pulmonary systems. The additional oxygen intakecan help patients' lungs cope and make up for the loss of breathable O2. See it in action below.