Source : Webster's Revised Unabridged Dictionary (1913)

Ethylsulphuric \Eth`yl*sul*phu"ric\a. (Chem.)
   Pertaining to, or containing, ethyl and sulphuric acid.

   {Ethylsulphuric acid} (Chem.), an acid sulphate of ethyl,
      {H.C2H5.SO4}, produced as a thick liquid by the action of
      sulphiric acid on alcohol. It appears to be the active
      catalytic agent in the process of etherification.