The Hyman Fire Piston demonstrates the rise in temperature when a fixed mass of gas is compressed. A portion of tinder supported inside a
transparent cylinder is ignited when the contained air is compressed by a hand operated piston. Repeated compressions without removing the cylinder will show reduced effect as the oxygen is used up. Subsequent decompression of the air inside the cylinder will create a cloud:
the reduction in pressure lowers the temperature and immediately condenses the water vapour inside the cylinder.