Dec 9, 1921: GM engineers discover that leaded gas reduces "knock" in auto engines

On this day, a young engineer at General Motors named Thomas Midgeley Jr. discovers that when he adds a compound called tetraethyl lead (TEL) to gasoline, he eliminates the unpleasant noises (known as "knock" or "pinging") that internal-combustion engines make when they run. Midgeley could scarcely have imagined the consequences of his discovery: For more than five decades, oil companies would saturate the gasoline they sold with lead--a deadly poison. In 1911, a scientist named Charles Kettering, Midgeley's boss at GM, invented an electric ignition system for internal-combustion cars that made their old-fashioned hand-cranked starters obsolete. Now, driving a gas-fueled auto was no trouble at all. Unfortunately, as more and more people bought GM cars, more and more people noticed a problem: When they heated up, their engines made an alarming racket, banging and clattering as though their metal parts were loose under the hood. The problem, Kettering and Midgeley eventually figured out, was that ordinary gasoline was much too explosive for spark-ignited car engines: that is, what we now call its octane (a measure of its resistance to detonation) was too low. To raise the fuel's octane level and make it less prone to detonation and knocking, Midgeley wrote later, he mixed it with almost anything he could think of, from "melted butter and camphor to ethyl acetate and aluminum chloride...[but] most of these had no more effect than spitting in the Great Lakes." He found a couple of additives that did work, however, and lead was just one of them. Iodine worked, but producing it was much too complicated. Ethyl alcohol also worked, and it was cheap--however, anyone with an ordinary still could make it, which meant that GM could not patent it or profit from it. Thus, from a corporate point of view, lead was the best anti-knock additive there was. In February 1923, a Dayton filling station sold the first tankful of leaded gasoline. A few GM engineers witnessed this big moment, but Midgeley did not, because he was in bed with severe lead poisoning. He recovered; however, in April 1924, lead poisoning killed two of his unluckier colleagues, and in October, five workers at a Standard Oil lead plant died too, after what one reporter called "wrenching fits of violent insanity." (Almost 40 of the plant's workers suffered severe neurological symptoms like hallucinations and seizures.) Still, for decades auto and oil companies denied that lead posed any health risks. Finally, in the 1970s, the Environmental Protection Agency required that carmakers phase out lead-compatible engines in the cars they sold in the United States. Today, leaded gasoline is still in use in some parts of Eastern Europe, South America and the Middle East.(History.com 2014) (http://www.history.com/this-day-in-history/gm-engineers-discover-that-leaded-gas-reduces-knock-in-auto-engines)