Chemical fire engine, 1902.

UNITED KINGDOM - JULY 03: Model (scale 1:6). These engines were designed to provide an instant response to a fire. They were introduced so that firefighters could immediately tackle a fire during the time that other fire engines were being connected to a hydrant. This model represents the chemical engine used in Bristol from 1902 to 1914, made by Merryweather and Sons. The copper cylinder contained a solution of water and sodium bicarbonate. The top fitting contained a lead bottle of sulphuric acid, which was punctured by turning the handle at the rear. The acid reacted with the bicarbonate solution, generating carbon dioxide gas which expelled the liquid at high pressure. (Photo by SSPL/Getty Images)