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Midgley, Thomas

lead freon compound table

(1889–1944) US engineer and inventor: introduced tetra-ethyl lead (TEL) anti-knock and Freon refrigerant.

Midgley was the son of one inventor and the nephew of another. He studied engineering at Cornell, finishing with a PhD in 1911. Working with C Kettering for Delco in the First World War, he led a team working on the problem of ‘knocking’ in petrol engines. (‘Knocking’ or ‘pinking’ is the metallic noise caused by pre-ignition.) After finding some anti-knock additives as a result of random trials, Midgley realized that their effectiveness could be related to the position of the heaviest atom in the compound, within the periodic table. On this basis, working at General Motors in 1921, he tried tetra-ethyl lead, Pb(C2H5 )4 , and found it to be very effective, used with some 1,2-dibromo-ethane to reduce lead oxide deposits in the engine. The mixture was widely used, but rising concern from 1980 that lead in vehicle exhausts was a health hazard for children caused it to be phased out in the 1990s. Midgley also devised the octane number method of rating petrol quality.

In 1930 Midgley introduced Freon-12 (CF2Cl2 ) as a non-toxic non-flammable agent for domestic refrigerators; again, he used the periodic table as a guide to select a suitable compound with the required properties. From the 1980s there was concern that chlorofluorocarbons (CFCs) such as Freon cause destruction of the ozone layer of the upper atmosphere, with potentially damaging climatic and other effects as a result of the increased passage of ultraviolet radiation following ozone loss. Political will to deal with this has been sluggish, and the ‘ozone hole’ over the south polar region, and its effects, are worsening.

For one man to invent two major environmental hazards is curious; and so was his death. A polio victim, he had devised a harness to help him rise in the morning. Becoming in some way entangled in it, he strangled himself.

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