The Collaborative International Dictionary of English v.0.48:

Gasogen \Gas"o*gen\, n. [Gas + -gen.]
   1. An apparatus for the generation of gases, or for
      impregnating a liquid with a gas, or a gas with a volatile
      liquid.
      [1913 Webster]

   2. A volatile hydrocarbon, used as an illuminant, or for
      charging illuminating gas.
      [1913 Webster]