What is "fire tube"

Tube \Tube\, n. [L. tubus; akin to tuba a trumpet: cf F. tube.]

1. A hollow cylinder, of any material, used for the conveyance of fluids, and for various other purposes; a pipe.

2. A telescope. ``Glazed optic tube.''
   --Milton.

3. A vessel in animal bodies or plants, which conveys a fluid or other substance.

4. (Bot.) The narrow, hollow part of a gamopetalous corolla.

5. (Gun.) A priming tube, or friction primer. See under Priming, and Friction.

6. (Steam Boilers) A small pipe forming part of the boiler, containing water and surrounded by flame or hot gases, or else surrounded by water and forming a flue for the gases to pass through.

7. (Zo["o]l.)

   1. A more or less cylindrical, and often spiral, case secreted or constructed by many annelids, crustaceans, insects, and other animals, for protection or concealment. See Illust. of Tubeworm.

   2. One of the siphons of a bivalve mollusk.

8. (Elec. Railways) A tunnel for a tube railway; also (Colloq.), a tube railway; a subway. [Chiefly Eng.]

   Note: In the New York area, the subways running under the Hudson River are sometimes referred to as the tube.

   Capillary tube, a tube of very fine bore. See Capillary.

   Fire tube (Steam Boilers), a tube which forms a flue.

   Tube coral. (Zo["o]l.) Same as Tubipore.

   Tube foot (Zo["o]l.), one of the ambulacral suckers of an echinoderm.

   Tube plate, or Tube sheet (Steam Boilers), a flue plate. See under Flue.

   Tube pouch (Mil.), a pouch containing priming tubes.

   Tube spinner (Zo["o]l.), any one of various species of spiders that construct tubelike webs. They belong to Tegenaria, Agelena, and allied genera.

   Water tube (Steam Boilers), a tube containing water and surrounded by flame or hot gases.