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.