EthylsulphuricEth`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.