In 1941, the Priestley Medal was awarded to Thomas Midgley by the American Chemical Society “to recognize distinguished services to chemistry,” the Society’s most prestigious award.

Midgley’s career is defined by four major accomplishments. He eliminated the problem of “engine knock” by identifying the gasoline additive tetraethyl lead. He also developed a method to extract large quantities of bromine from seawater when he learned that bromine was needed to prevent tetraethyl lead from corroding engine valves and spark plugs.

In addition, Midgley discovered that dichlorodifluoromethane, also known as Freon, could be used as a nontoxic and nonflammable refrigerant. Finally, his research on natural and synthetic rubber contributed enormously to the scientific literature on these topics.