Thomas Midgley, Jr, died 66 years ago today. His dual inventive legacy - leaded petrol and CFCs - is now reviled, but they were created with the good of all mankind in mind
Which chemist's work has touched the most lives? Marie Curie? Louis Pasteur? Joseph Lister? Our minds are drawn to the heroic inventors of medicines and the pioneers of bacterial understanding.
I’d like to put forward another, lesser-known candidate: Thomas Midgley, Jr (1889-1944). His chemistry legacy extends to perhaps more than all the others put together, but sadly his noble ambitions and lifetime of hard work will be overlooked owing to the unforeseen consequences of his two chemical discoveries.
Engine knock and TEL
An engineering graduate from Cornell University in the US, Midgley worked for Dayton Research Laboratories (of General Motors) for 10 years under Charles Kettering, inventor of the electric starter motor, working on ways of combating the phenomenon of engine knock.
When engines burn petrol correctly they ignite an air-petrol mixture. The combustion produces heat, and the expanding gas drives the cylinders, which provide the drive in, say, a car. The timing involved in igniting the gas is very precise to ensure maximum engine efficiency.
If the gas isn’t completely ignited, however, some might ignite at the wrong time because of the change in pressure (ignition by pressure is called detonation). The shockwave caused by detonation disrupts the flow of gas in the cycle, making a knocking or pinging sound, and makes the engine far less efficient – or in the worst cases make it explode.
Midgley discovered that a little iodine added to fuel would reduce the effect. He was a pragmatic chap and, after a trial-and-error run through hundreds of compounds of 20 elements, he found the best possible candidate that completely eliminated knocking in 1921: tetraethyl lead (TEL) or simply 'ethyl'. Leaded petrol was born.
Why lead? Combustion is a chain reaction, involving very reactive chemicals called radicals, formed when the fuel is ignited. The lead in TEL reacts with these radicals, stopping from combustion continuing at the wrong point in the engine cycle. The TEL is mixed with “scavengers” like bromides and chlorides, which stop the lead building up in the engine. Unfortunately the only way out was through the exhaust and into the atmosphere…
The dangers of lead poisoning were little understood at first. Although there was a dramatic reduction in car accidents, ten people died in the first two years' operation of the two TEL plants, and the public image of the chemical was severely shaken. Midgley, in a hands-on effort to convince the public of its safety, held a press conference where he poured TEL over his hands, and inhaled deeply of it for a full minute.
The immediate danger of working with ethyl was apparent, but its most potent exposure to the public, in exhaust fumes, was unknown for many years. It was only in the late 1970s that TEL’s phasing out was required in the US, and completed in 1986. In 2000 the EU banned the sale of leaded petrol in all but a few circumstances.
Lead accumulates in the body and so the effects get worse the longer one is exposed to it, and causes brain damage with symptoms such as low IQ and violent tendencies. Children are particularly at risk from lead poisoning.
The removal of TEL from use in the western world had another catalyst, so to speak: it has a damaging effect on catalytic converters, a requirement for cars in much of Europe and the Americas in the 1970s owing to new emissions regulations.
But back to the 1920s. Health scandals and development issues didn’t derail TEL, and its use as an additive continued for half a century. Despite his reputation and health suffering throughout, General Motors weren’t yet finished with Thomas Midgley.
Freon and refrigeration
After a few embarrassingly ineffective years as vice president of the newly formed General Motors Chemical Company, Midgley was relieved due to his inexperience in organisational matters. He was instead charged with discovering a safe refrigerant for household use – the commonly-used refrigerants were ammonia, methyl chloride or sulfur dioxide, all corrosive and toxic, or butane, which is highly flammable.
Midgley rolled up his sleeves and, in his systematic way, examined many candidate oxides, sulfides, nitrides and the like, assessing each for toxicity, flammability and corrosiveness. Fluorine- and chlorine-based short-chain alkanes gave excellent results, and thus, just three days after being given the task, Midgley proudly presented to his superiors dichlorodifluoromethane: the first ever chlorofluorocarbon or CFC.
Dichlorodifluoromethane was announced to the world at the annual meeting of the American Chemical Society in 1930. In another crowd-pleasing public demonstration Midgley inhaled a large amount of the gas, and then blew out a candle flame, showing it to be non-toxic and non-flammable. GM and the DuPont Company promptly agreed to manufacture together the new wonder-gas, branding it Freon, and in the process saving GM's failing refrigerant partner Frigidaire from financial disaster.
Midgley was again hailed as a hero, having made safe the wonderful new home appliance that would epitomise the luxury of convenience in the American 1950s. As propellants CFCs were also remarkable: unreactive, non-flammable and safe to human health. He was awarded the prestigious Priestley Medal in 1941 and appointed president of the American Chemical Society.
Sadly we know the end to this story too. Many years later it was discovered the CFCs released from aerosols and refrigeration units around the world had collected in the atmosphere, destroying the ozone layer and exposing the Earth to the Sun’s more harmful UV radiation. They have since been banned in most commercial applications.
Midgley spent the last few years of his life crippled with polio. He was released from his role as vice president of Kinetic Chemicals – GM and DuPont's Freon-producing company – when his research became unprofitable. Wishing to remain active, he devised a system of ropes and pulleys to allow him to get in and out of bed: his last invention. On the 2nd of November, 1944, he became entangled in the ropes and was strangled to death, aged 55.
So passed the inventor Thomas Midgley, Jr, hero of the automotive and refrigerant industries for many years. Although his legacy, from a modern point of view, is stained with being by far the largest personal contributor to health and environmental damage, his intentions were always to improve human life. We should remember Midgley for being a chemical pioneer with his heart in the right place.
A shorter version of this article appeared in Chemistry World in 2008 (£).
blog comments powered by