1) Locomotive part 
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam. The fire-tube boiler developed as the third of the four major h...
A boiler where the primary heating surface is tubes with hot gas flowing inside and water outside. . See also water-tube boiler
(from the article `boiler`) ...is necessary on all boilers, because continued addition of heat to water in a closed vessel without means of steam escape results in a rise in ...
any boiler for generating steam by passing hot gases and other combustible products through tubesimmersed in water to a chimney or uptake. Cf. water-tube boiler.