c4h10

from The Collaborative International Dictionary of English v.0.48

Butane \Bu"tane\ (b[=u]"t[=a]n), n. [L. butyrum butter. See
   {Butter}.] (Chem.)
   An inflammable gaseous saturated hydrocarbon, {C4H10}, of the
   marsh gas, or paraffin, series.
   [1913 Webster]