Soda acid fire extinguisher, c 1950s.
© Science Museum / Science & Society Picture Library
This sectioned soda acid extinguisher, made by Antifire Ltd, uses a chemical reaction to shoot out water. Its steel shell contains a bottle of sulphuric acid and a cylinder of sodium bicarbonate. When the extinguisher is used, the two substances mix to produce carbon dioxide gas. This gas then forces the water through the nozzle.