Supercritical processing

In 1822 the French physicist Baron Charles Cagniard de la Tour was looking for an answer to the question: 'What happens when you boil a liquid in a sealed environment?'. He placed liquid ethanol and a ball bearing inside a sealed gun barrel and heated. Above a certain temperature he could no longer hear the liquid sloshing inside the tube when the barrel was moved. He had discovered the 'critical point' of the substance - the temperature above which it was neither liquid nor gas, but a single phase, a 'supercritical fluid'.²