The Right Chemistry: A journey through the history of neon

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It begins in 1785 with Henry Cavendish discovering that a tiny amount of gas remained when nitrogen and oxygen were removed from a sample of atmospheric air.

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Ask a Montrealer to name the city’s iconic landmarks and you will likely hear about St. Joseph’s Oratory, Schwartz’s deli, Olympic Stadium and the Five Roses neon sign. That sign has been part of the city’s skyline for about 70 years and actually used to read “Farine Five Roses Flour” until 1977, when the word “flour” was removed, believe it or not, because it was English. But that sign, with its 15-foot-high letters, still glows bright red every night and prompts a journey through the history of neon.

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That journey begins in 1785 with “natural philosopher” Henry Cavendish, as scientists were called at the time, discovering that a tiny amount of gas remained when “phlogisticated air” (nitrogen) and “dephlogisticated air” (oxygen) were removed from a sample of atmospheric air. Cavendish was unable to identify the gas and it remained a mystery for another 100 years until William Ramsey and Lord Rayleigh became interested in the problem. They passed air over red-hot copper to remove oxygen as copper oxide, and then over hot magnesium to remove nitrogen as magnesium nitride. A tiny amount of gas, roughly one per cent of the original, still remained and it had a curious property. It would not engage in any chemical reactions! They named this residue “argon” from the Greek for “inactive” or “lazy.”

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Ramsey, with colleague Morris Travers, managed to liquify this residue by cooling it, and discovered that when it was slowly heated, tiny amounts of other gases boiled off. These turned out to be a series of new elements that they named neon, krypton and xenon from the Greek for “the new one,” “the hidden one,” and “the stranger.” They came to be known as the “noble gases,” because like nobility, they had no tendency to associate with commoners.

Some 40 years before Ramsey identified the noble gases, German glassblower Heinrich Geissler had managed to use a vacuum pump to partially evacuate a glass tube. When he applied a high voltage to the electrodes that had been fitted to the ends of the tube, the inside of the tube began to glow. At the time there was no explanation for this phenomenon, which is actually a consequence of trace amounts of gases present in the tube. A rationale is to be found in modern quantum theory, which describes how electrons in an atom can exist in different energy states. When they absorb electrical energy they become excited, and on returning to the ground state they release the absorbed energy as visible light. If a trace of nitrogen is present in the tube, the emitted light is pink, if there is carbon dioxide, the light is white, and traces of mercury vapour result in blue-green light. In the early 20th century, Daniel Moore, a former Edison employee, made use of this observation and commercialized the “Moore fluorescent lamp.”

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The noble gases were invisible, but Ramsey found that when sealed in a Geissler tube and energized, neon produced a bright orange-red light that he excitedly described in his acceptance speech for the 1904 Nobel Prize, awarded for the for the discovery of the noble gases. Commercial application, however, would have to wait until neon could be produced on a large scale. This is when Georges Claude, dubbed the “French Edison,” enters the picture. His goal was to liquify air so that it could then be fractionally distilled to yield oxygen, which was needed for the manufacture of steel. Claude managed to do this on an industrial scale, which also meant that the byproduct noble gases, especially neon, could now be produced in significant amounts. Inspired by Moore’s fluorescent tubes, Claude was able to produce neon tubes. He first exhibited these at the Paris Motor Show in 1910, and in 1912 installed the first-ever commercial neon sign in a Paris barber shop, opening the way for a blitzkrieg of neon signs in cities around the world. Times Square in New York became a neon extravaganza with signs that gave the illusion of movement by cleverly turning variously shaped neon tubes on and off. Most of these signs have now been replaced by giant television screens and more efficient, eco-friendly LED lighting.

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William Ramsay went on to identify another noble gas, radon. At the time, the danger of working with radioactive substances was not clear, and there is little doubt the nasal cancer that ended his life was caused by emissions from radon. While Georges Claude deserves credit for his work with neon, another aspect of his life was less than glowing. He publicly supported French collaboration with the Nazis, for which he was tried after the war and sentenced to life imprisonment.

With the dawning of the computer age, neon donned another mantle. Tiny neon tubes found application as binary switches in digital circuits, and the first electronic desktop calculators had large neon-lit readouts. These now are historic relics, with neon switches and readouts being replaced by semiconductor chips and LED displays. But that does not mean neon has been dismissed. Quite the opposite. The gas is a critical component of lasers that are used in the manufacture of computer chips. Such an “excimer” laser depends on the reaction of argon with fluorine to produce a transient molecule of argon fluoride, which then relaxes back to argon and fluorine with the emission of ultraviolet light that is bounced back and forth between mirrors to produce a laser beam. The physics here is very complicated, but neon is needed to enhance collisions between argon and fluorine, the key to the workings of the laser.

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About half of all the semiconductor-grade neon used in the world has been produced by two Ukrainian companies. This stems from Ukraine being a prime producer of wheat and steel. Wheat needs ammonia-based fertilizer that requires nitrogen for its production, and steel-making needs oxygen. Both of these are produced from liquid air, with neon being a byproduct. Due to the current war, the two companies have stopped production, sending the semiconductor chip industry into a frenzy.

Perhaps now you can look at the Five Roses sign with greater insight and admiration.

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Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

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