34. Selenium: A Fit Of Heat And Light

Throughout history, copying information has been arduous, messy, and even dangerous — until one bored, depressed man figured out the secrets of selenium.

Featured above: The first “xerographic” photocopy in history, which Chester Carlson made by hand.

Show Notes

Connections: So many connections in this episode as to get tied in knots. For instance: One of Trithemius’ most notable students was the man himself, Paracelsus. Even more remarkable, Alexander Graham Bell won the Volta Prize for his efforts with the telephone — named after Alessandro Volta, whom we mentioned in episode 30. With that prize money, he founded Bell Labs — the same where the transistor would later be invented. And, funnily enough, Chester Carlson also worked at Bell Labs for a time, but was unfortunately canned before making his breakthrough.

Kids Today With Their Photocopiers: Like literally every single new technology, the photocopier inspired plenty of hand-wringing upon its debut. Even from a Xerox executive named Linowitz, who was quoted in Life magazine as saying, “Have we really made a contribution by making it easier to reproduce junk and nonsense?

Verbatim: The below is an absolutely incredible little video from a New York Times series called Verbatim. I think they only produced two episodes, but the idea is they take court transcripts and reenact them. This one, beyond being true and absurd, is perfectly cast, in my estimation. I hope you enjoy as much as I did.

Episode Script

Alexander Graham Bell is most famous for inventing the telephone — something of a controversy, due to competing claims by a contemporary inventor named Elisha Gray.

But there is no question that Bell was an inventor. He held less disputed patents for machines as diverse as a water desalinator, aerial vehicles, and a device that could supposedly locate icebergs from afar.1

One that stands out among the rest is for an invention he called the photophone. It works similarly to the telephone, but rather than converting sonic vibrations into an electrical signal that could be transmitted over a wire, a mirror placed over an audio speaker converted sound into a vibrating wave of light. A photoreceptive sensor several meters away changed the fluctuating light signal back into an electrical signal, which was then pumped to a speaker, replicating the original sound.2

Selenium is a semiconductor that’s sensitive to light, and it made the perfect material for the sensor that the entire device is dependent upon.

Clearly, the photophone didn’t bring Bell as much acclaim as the telephone had, but only because it was way ahead of its time. The year was 1880, and Bell had invented the first machine capable of wirelessly transmitting speech — fifteen years before the radio.3

It also had a few drawbacks — like the fact that it didn’t work very well over long distances, or on a rainy day, and fidelity was quite low. But Bell knew he had created something valuable. He was more proud of it than anything else he invented, including the telephone, calling the photophone “the greatest invention I have ever made, greater than the telephone.”4

Bell was so enthusiastic that he wanted to name his second daughter Photophone, but his wife insisted they name her Marian instead.5

Even if no one else appreciated it as much at the time, the photophone was a remarkable invention — and a direct precursor to the fiberoptic communications networks that cover the globe today.6 Perhaps Alexander Graham Bell should be more renowned for the photophone.

And for more reasons than this, selenium deserves a place in the Communications Hall of Fame.

You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.

Today, we’re circulating information about selenium.

Jons Jakob Berzelius is one of early chemistry’s most prominent and creative figures. Among his many achievements, he transformed chemical notation from an arcane script known only to alchemists into something simple and logical, as we discussed in our episode on sodium. He coined words that are essential to chemistry today, like “allotrope,” “catalysis,” and “polymer.” He was also the first scientist to isolate chemical elements silicon, cerium, thorium, and today’s topic, selenium.

Clearly Berzelius was a man with a knack for naming things, and element 34’s name is fittingly clever. While he was first working with it, Berzelius noted the element’s similarity to tellurium — the element directly below on the periodic table. Since tellurium is named after the Latin word for the Earth, he named this new element selenium, after the Greek word for the moon.

He didn’t know it at the time, but that makes an appropriate name for another reason, too: Much like the moon, selenium stands out the most when it’s reflecting the light of the sun.

That’s because selenium is both photoconductive and photovoltaic. That is, it not only becomes more conductive when it’s exposed to light, but it also naturally generates a small electrical charge, too.

These uncommon behaviors have allowed for the creation of fantastic new machines that would’ve been impossible before selenium’s discovery. Not just the photophone, but also light meters and solar panels. But frankly, the most popular device to take advantage of selenium’s properties is one that has occasionally driven office workers to bouts of violence.

One of the founding inventions of human civilization, right up there with fire and agriculture, is written language. And from the day we first learned how to put pen to paper — or papyrus, or clay tablet, or whatever — we’ve searched for ways to duplicate those records efficiently.

For most of human history, the only way to do so was to write things down twice. Legions of scribes spent their entire lives copying papers and books by hand. If you wanted copies made faster, you hired more scribes.

If a gradeschool teacher ever made you write lines, you understand what an unpleasant job this could be. And medieval scribes made sure future readers would know their complaints by writing them in the margins of their manuscripts. Sometimes these missives could be surprisingly poetic, like one that reads, “As the harbor is welcome to the sailor, so is the last line to the scribe.” Often these notes, also called “marginalia,” were more humorous in nature: “Oh, my hand!” or, “Thank God, it will soon be dark.”7 8

With the invention of the printing press, first in 9th-century China and a few centuries later in Europe, most of those scribes got their wish… and lost their jobs. Funnily enough, they changed their tune pretty quick. One abbot, named Johannes Trithemius, was so moved as to write a treatise, many chapters long, called “In Praise Of Scribes.” A short excerpt reads:

However well we behave, however fruitfully we teach, all that would be lost to oblivion if the work of the scribe did not record them in letters. It is therefore scribes who lend strength to words, memory to things, vigor to time. If they were taken from the Church, faith would weaken, charity would freeze, hope would die, law would perish, Scripture fall into oblivion. … The printed book is a thing of paper and in a short time will decay entirely. But the scribe commending letters to parchment extends his own and the letters’ lifespan for ages.9

Of course, Trithemius wanted to ensure his pamphlet would reach as wide an audience as possible, so he had it published by a local printing press.

But it’s another clergyman who really became famous for his association with the printing press. In 1517, Martin Luther wrote Disputation on the Power of Indulgences, a protest against the Catholic Church’s practice of lessening punishments for sin in exchange for cold, hard cash.

Part of Martin Luther’s legend is that he nailed his 95 theses to the door of the local church, but that doesn’t appear to be true. If he did, it’s not something he ever wrote about. In fact, he only intended to bring the document by the church for a colleague to review. As he later wrote,

My purpose was not to publish them, but first to consult a few of my neighbors about them, that thus I might either destroy them if condemned or edit them with the approbation of others. But now they are printed and circulated far beyond my expectation, I feel anxious about what they may bring forth.”10

He had good reason to be anxious. What his document brought forth was nothing short of a religious revolution, ending the hegemony of the Catholic Church.

The printing press had other effects, too. With printed books made much more affordable, commoners had both good reason and a way to learn how to read. Universities sprang into existence. During the English Civil War in the 17th century, all sides mass produced propaganda to convert people to their cause.

No doubt, these were all incredible advances in humanity’s ability to communicate. But sometimes, you only need one or two copies of a document, not ten thousand. The printing press was wildly impractical for that purpose, and a satisfying solution remained out of reach for centuries.

Not that people didn’t try. Thomas Jefferson used a device called a pantograph, which replicated the strokes of his pen so he could write two copies of a document at once.

Incremental improvements followed. By the turn of the 20th century, there were several methods of copying documents, from carbon paper to mimeographs to the Ditto machine. Many of these were wet systems, meaning they used liquid chemicals to achieve the desired effect. The process used to duplicate architectural drawings employed a solution of potassium ferricyanide, developing a copy rendered in rich Prussian blue. It was called “cyanotype,” or, more casually, a blueprint.

But none of these was a perfect solution. All those systems could be messy, and dangerous, and prone to failure. There were a lot of problems.

Chester Carlson also had a lot of problems. In the 1930s, he was trapped in a boring job at the patent office. His marriage was an unhappy one, and he lived with his in-laws. He would spend hours hiding away in the New York Public Library’s science reading room, where the problems of document duplication seemed simple in comparison.11 12

Research gave way to experimentation. This may have put additional stress on his marriage, as the only laboratory he had access to was the kitchen in his cramped Jackson Heights apartment. Only a few small fires broke out, and in 1938, he came up with a new way to copy documents. It worked like this:

Carlson started by rubbing a photoconductive plate to give it a static electric charge. Black letters are then placed atop the plate, and a bright light is shined upon it.

The parts of the plate that get exposed to the bright light lose their static charge. But the parts that were covered up by the dark lettering do not. A sprinkling of fine, black dust would be electrostatically attracted only to the parts of the plate that retained their charge. By applying a little heat, the dust could then be baked onto a sheet of paper, and ta-da! An instant duplicate.13

The world’s first photocopied document commemorated the time and place where it occurred: October 22, 1938. Astoria.

Carlson conducted this process by hand, and his photoconductive plates were made of sulfur. But it didn’t take long to figure out that sulfur’s downstairs neighbor on the periodic table, selenium, was even better suited to the task.

It took a few years, but Carlson eventually sold the idea to the Haloid Company. He also divorced his first wife, and later married a woman who actually got along with him.

Haloid bought the idea because they were a photography business that was desperate to succeed in any arena that wasn’t dominated by Eastman Kodak. They thought this could be their ticket — and they were right.

Haloid called it a “xerographic” process, from the Greek xeros, meaning “dry.” And the machine that conducted that process was called the  Xerox 914.

The simple push of a button, ordinary paper, a fast process, and no wet chemicals. We might take such luxuries for granted in 2019, but when the Xerox 914 debuted 60 years ago, these features were truly revolutionary.

The machine was such a runaway success that Haloid changed its name to Xerox in 1961.14

The photocopier changed the way information was disseminated. A memo no longer needed to snake its way around the office, person to person, from top to bottom. Everyone could get their own copy simultaneously.

The photocopier had societal effects, too. In the time before the internet, access to such a machine was powerful. The Soviet Union put tight restrictions on access to copy machines, and activists around the world depended on xerography to get the word out when they needed to organize. Often, the people conducting those efforts were advancing grassroots movements focused on feminism, the AIDS crisis, et cetera.15

Daniel Ellsberg was not one of those people, though. He worked for the RAND Corporation, a sort of public/private hybrid think tank that’s advised the US military since 1948. He had access to a photocopier in those offices, and he used it to duplicate classified documents that detailed the many ways the U.S. government lied to the public and to Congress about its involvement in Vietnam. Briefcase by briefcase, Ellsberg smuggled these copies out of the office late at night, occasionally enlisting the help of his 13-year-old son. (I guess the machine really was easy to use.)

Those became known as the Pentagon Papers, and their publication in 1971 was a defining moment in the relationship and trust — or lack thereof — between the American government and its constituents. It’s difficult to imagine how that could have come to pass without the ability to copy individual documents reliably, quickly, and discretely.16

Of course, walking past a copy room probably doesn’t stir feelings of courage and justice deep within you. Photocopiers are part of our daily lives — in our workplaces, office supply stores, libraries, and the DMV. And they’re incredibly intricate machines. On a weekly basis, we send thousands of razor-thin sheets of paper through their innards, where, in a fit of heat and light, dry powder is slung onto that paper by the power of electricity, in such a precise manner as to make it nigh-impossible to tell which is the original and which is the duplicate.

But that’s not what we see. We only notice the copy machine when it breaks down. The hardworking photocopier is the eternal pariah of office culture, subject to great vengeance and furious anger from those who butt up against it when it malfunctions.

So true is this that the seminal 1999 film Office Space dedicates ninety seconds of screen time to showing three main characters destroy such a machine in slow motion. Future electronic intelligences will surely describe this scene as “gratuitous violence,” but audiences at the time felt it was highly cathartic.

If someone you know is disposing of a copy machine, you might want to ask if you can rummage around inside it first. Depending on when it was made, the drum might be a good source of selenium. But it’s rather big, and newer machines tend to use plastics that are even better photoconductors than selenium. So where to turn instead?

Outside of the workplace, you can also find element 34 in your local drugstore. Some dandruff shampoos use SELenium SUlfide as their active ingredient. That’s where Selsun Blue gets its name.

Whether you’re plagued by dandruff or not, you’ll want to make sure some of that selenium is getting inside your body, too. It’s one of those essential elements in trace amounts. The Royal Society of Chemistry estimates that every cell in our bodies contains about one million atoms of selenium.17 If that’s considered a trace amount, it gives you a good idea of how incomprehensibly tiny an atom is.

Selenium deficiency is more of a problem in modern life than it used to be, largely because we don’t eat as many organ meats as we used to — kidneys and liver and the like.

If that idea doesn’t whet your appetite, perhaps because you eat a vegan diet, there’s good news. A single Brazil nut contains almost exactly the recommended daily allowance for an adult human.

However, and surely you saw this coming, you don’t want to down Brazil nuts by the fistful on a daily basis, because, all together now? The dose makes the poison.

A toxic dose of selenium can have ghastly effects, including sloughing of nails, neurological damage, cirrhosis, and death. But you’ll get ample warning well before that point, because at considerably lower doses, selenium will make you reek of garlic, upset your stomach, and make you quite irritable.

Perhaps the easiest way to add element 34 to your collection would be to purchase a small, cheap solar cell. It’s easy to display, and it makes an elegant little statement, too: This element, named after the moon, can gather light from the sun to provide clean power to the inhabitants of Earth.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To see an incredible reenactment of a court case that posed the qeustion, “What is a photocopier,” visit episodic table dot com slash S e.

Next time, we’ll get in the hot tub with bromine. For the next two weeks, I’ll be traveling with limited access to the internet, so that episode won’t air until Monday, April 22.

Until then, this is T. R. Appleton, reminding you that, as Chester Carlson knew, public libraries are a crucial component of vibrant, healthy communities.


  1. The Canadian Encyclopedia, Alexander Graham Bell, Aviation Pioneer. Terrance Macdonald, August 29, 2017.
  2. The Vintage News, Back To The Future: In 1880 Alexander Graham Bell Invented The Photophone,The World’s First Device For Wireless Communications. Tjana Radeska, September 18, 2016.
  3. ThoughtCo., Alexander Graham Bell’s Photophone Was An Invention Ahead Of Its Time. Mary Bellis, March 7, 2019.
  4. Alexander Graham Bell: Making Connections, p.84. Naomi Pasachoff, 1999.
  5. Alexander Graham Bell For Kids: His Life And Inventions, With 21 Activities. Mary Kay Carson.
  6. My San Antonio, Fiber-Optic Communication Began 130 Years Ago. Arturo Gallardo, June 21, 2010. ed: This is a pedantic note, but no it didn’t. There was no fiber involved whatsoever with the photophone. It was wireless, remember?
  7. io9, Medieval Monks Complained About Their Jobs In The Margins Of Ancient Manuscripts. Annalee Newitz, March 23, 2012.
  8. Atlast Obscura, The Strange And Grotesque Doodles In The Margins Of Medieval Books. Anika Burgess, May 9, 2017.
  9. In Praise Of Scribes. Johannes Trithemius, 1492.
  10. The Life And Letters Of Martin Luther.
  11. nypl.org, NYPL, Mother Of Invention. Michael Wenyon, January 30, 2009.
  12. Xerox, The Story Of Xerography.
  13. Business Insider, This Is The First Xerox Copy Ever Made. Kelly Dickerson, October 22, 2013.
  14. Slightly messy here, as they changed their name to “Haloid Xerox” first, in 1958.
  15. Smithsonian Magazine, How The Photocopier Changed The Way We Worked — And Played. Clive Thompson, March 2015.
  16. The New York Times, At Age 13, Creating The Pentagon Papers, Photocopies, At Least. James Barron, January 28, 2010.
  17. Royal Society Of Chemistry, Selenium.

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