Midgley, Thomas (1889–1944)

US industrial chemist and engineer whose two main discoveries, universally adopted, were later criticized as damaging to the environment. He found in 1921 that tetraethyl lead is an efficient antiknock additive to petrol (preventing pre-ignition in car engines), and in 1930 introduced Freons (a group of chlorofluorocarbons) as the working gases in refrigerators, freezers, and air-conditioning units.

Midgley was born in Beaver Falls, Pennsylvania, and studied mechanical engineering at Cornell. From 1916 he worked for the Dayton Engineering Laboratories Company, Ohio, later taken over by General Motors. He became a vice-president of the Ethyl Corporation 1923 and ten years later a director of the Ethyl-Dow Chemical Company.

Midgley discovered empirically that ethyl iodide (iodo-ethane) prevents pre-ignition in car engines using low-octane fuel. He spent several years teaching himself the relevant chemistry and looking for a less expensive additive, and came up with tetraethyl lead 1921. It became a standard additive, but because of the hazardous effects of airborne lead compounds emitted in exhaust fumes, from the 1980s unleaded petrol became increasingly common.

In 1930 Midgley introduced Freon (CF2Cl2) as a nonflammable, nontoxic refrigerant. Freon compounds also became extensively used as propellants in aerosol containers. Because chlorofluorocarbons contribute to the destruction of the Earth's ozone layer, their use was phased out from the 1970s as propellants, and in the 1990s practical substitutes were found for use in refrigeration.