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The New York Times Magazine
March 15, 2023

Midgley walked into Kettering’s office one day and asked, “What do you want me to do next, Boss?” Kettering wrote after Midgley’s death. “That simple question and the answer to it turned out to be the beginning of a great adventure in the life of a most versatile man.”

The technical riddle Kettering tasked Midgley with solving was one of the few remaining impasses keeping the automobile from mass adoption: engine knock.

As the name implies, for the automobile passenger, engine knock was not just a sound but a bodily sensation. “Driving up a hill made valves rattle, cylinder heads knock, the gearbox vibrate and the engine suddenly lose power,” Sharon Bertsch McGrayne writes in her excellent history of modern chemistry, “Prometheans in the Lab.” The problem was made all the more mysterious by the fact that no one had any idea what was causing it. (“We don’t even know what makes an automobile run,” Kettering admitted at one point.) In a sense, the question that Kettering and Midgley set out to solve was figuring out whether knock was an inevitable secondary effect of a gas-powered engine, or whether it could be engineered out of the system.

To investigate the phenomenon, Midgley devised a miniature camera, optimized for high-speed images. The footage he eventually shot revealed that fuel inside the cylinders was igniting too abruptly, creating a surge of pressure. The unpleasant vibrations passengers were feeling reflected the fundamental fact that energy was being wasted: rattling the bones of the car’s occupants instead of driving the pistons.

The footage at least gave the problem some specificity: How do you make the fuel combust more efficiently? In the early days, Midgley was groping in the dark; his training was as a mechanical engineer, after all, not as a chemist. One of his first lines of inquiry came from a bizarre suggestion from Kettering — that perhaps the color red could somehow improve the fuel’s combustion. Kettering had long been impressed by the way that leaves of the trailing arbutus plant could turn red even when covered by a layer of snow, somehow capturing the energy of the sun’s rays more effectively than other plants. Perhaps adding a red dye to the fuel would solve the problem of knock, Kettering suggested. So Midgley used iodine to dye the fuel red, and it did seem to have some mild antiknock properties. Ultimately he realized that it was the iodine itself, not its color, that was the active agent in subduing the knock. It wasn’t a solution per se, but it suggested something important nonetheless: that the ultimate solution would come from chemistry, not from engineering.

The search for that solution would ultimately last five years. Kettering later said that Midgley and his team tested 33,000 different compounds. For most of that period, they meandered in a random walk through the periodic table, adding elements to the fuel to see if they did anything to mitigate engine knock. “Most of them had no more effect than spitting in the Great Lakes,” Midgley recalled years later.

The first material advance came via a newspaper article that Kettering stumbled across, reporting the discovery of a new “universal solvent” in the form of the compound selenium oxychloride. When added to the fuel, the compound produced mixed results: Knock was reduced considerably, but the new fuel eroded spark plugs almost on contact. Midgley kept searching, systematically plowing through a new version of the periodic table that had recently been introduced, identifying promising clusters of elements, effectively teaching himself industrial chemistry on the fly. He soon discovered that the further you moved toward the heavy metals clustered together on the table, the more the engine knock dissipated. Soon the random walk through the elements became a beeline to what was, at the time, the heaviest metal of them all: lead.

In December 1921, Midgley’s team in Dayton concocted enough of the compound tetraethyl lead to do a test run with a kerosene-powered engine suffering from a serious case of engine knock. A single teaspoon of tetraethyl lead silenced the knock completely. Further tests revealed that you could subdue engine knock with a shockingly small supplement of lead; they ultimately settled on a lead-to-gasoline ratio of 1-to-1,300. The effects on engine performance were profound.

Automobiles running on leaded gasoline could take on steep inclines without hesitation; drivers could accelerate to overtake a slower vehicle on a two-lane road without worrying about their engine being seized with knock while in the wrong lane.

Kettering branded the new fuel Ethyl, and in February 1923 it was first offered for sale at a gas station in downtown Dayton. By 1924, General Motors, the DuPont Corporation and Standard Oil had started a joint venture called the Ethyl Corporation to produce the gasoline at scale, with Kettering and Midgley appointed as executives.

Henry Ford’s assembly-line production of the original Model T in 1908 is usually credited as the point of origin for the American love affair with the automobile, but the introduction of high-octane Ethyl gasoline was instrumental as well. Over the course of the 1920s, the number of registered vehicles in the United States tripled. By the end of the decade, Americans owned close to 80 percent of all the automobiles in the world, increasingly powered by the miraculous new fuel that Thomas Midgley concocted in his lab.
Article continues at link with "famous" 2nd invention.

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My first job as a mechanical engineer was with Ethyl Corp in Ferndale, Mich. That was June '72. Did engine dynamometer work. Great people there. The writing was on the wall, though. Lead was going to be phased out of gasoline. Research on a manganese compound was being evaluated to suppress "knock" and replace tetraethyl lead, but it plugged the new catalytic converters, and an effective dispersant to prevent the manganese buildup was proving to be too elusive. After two years there, I left to go to grad school at Univ of Mich while working for the EPA's Mobile Source Pollution facility. Alas, the Ferndale facility on a beautiful piece of land with all of its many individual buildings meant to provide safety in the event of a big fire (they had underground gasoline piping all over the place to do research on fuel additives, etc) was sold.
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