This is a demonstration used to show the principle of heat of compression. This is the physical process that makes Diesel engines possible. To work the demonstration, a small sample of cotton is placed in the chamber. The plunger is then forced down and held in place with considerable force. The air in the chamber is forced into a very small volume, thus heating the air above the flash temperature of the Cotton. The same process take place in a Diesel engine, but the fuel is oil. The Diesel engine is much more efficient that a gasoline engine.