56. Barium: Glow-Getter

When you really want to suck all the air out of a room, barium will help you out.

Featured above: To fix the earliest computers, you had to walk inside them.

Show Notes

Today’s episode is on the short side, and rather straightforward. These show notes are correspondingly brief!

As Promised: That stream of electrons, flying away from the cathode, is fittingly called a “cathode ray.” That’s the CR of “CRT Television” — “cathode ray tube.” Those TVs work by firing a stream of electrons toward the screen, exciting phosphors to create an image. (Incidentally, another use of the vacuum tube!) Nowadays, though, televisions operate on very different technology.

Episode Script

You might not be surprised to learn that barium was discovered by our old pal, Humphry Davy.

Davy performed pioneering research with boron, sodium, potassium, magnesium, calcium, strontium, fluorine, chlorine, iodine, and more. At this point, it would probably be more surprising if he didn’t pop up every few episodes.

That’s why I wanted to let you down gently. After this episode, we won’t be seeing nearly as much of Professor Davy. Most of the elements in periods 6 and 7 weren’t discovered until well after Davy’s death in 1829.

Now, we certainly haven’t been shy about jumping around in time, and elements like gold and mercury will ensure we don’t forget the past completely. But you can consider this another trend of the periodic table: From here on out, our cast of recurring characters will usually be sporting lab coats rather than cravats.

So let’s take a brief moment to raise a flask. Here’s to Humphry Davy, the wizard of wires with a love for laughing gas, whose experiments earned him a medal and lost him an eye, who lived the kind of life that guaranteed this program plenty of material.

Thank you, Mr. Davy, and dare we say, adieu.

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 processing information about barium.

Element 56 is a very blunt sort. No games or tricks with this one, even when it comes down to its name: “Barium” comes from the Greek for “heavy metal,” and that is precisely what it is.1 2

Specifically, it’s the fifth of the six alkaline earth metals that make up group two on the periodic table, and it acts a lot like its fellows. Like the other alkaline earth metals, barium is soft, silvery, shiny, and quite reactive.

It will easily combine with oxygen or moisture in the air, even if there isn’t very much around. That’s what makes it so useful as a “getter.”

A vacuum is a very difficult thing to create. (You may have heard that nature abhors them.) Even if you have a pump strong enough to suck all the atmosphere out of a glass bulb, it won’t remain a vacuum for long. Very slowly, molecules of air from the outside will pass right through the glass walls of the bulb.

But a small amount of metallic barium coating the inside of the glass can counteract that effect. Not long after the air enters the bulb, it will bump into the barium and chemically combine with it in solid form. Barium oxide, for example. The barium “gets” any stray particles that find their way in, so it’s a “getter.”3

There are plenty of reasons why a glass bulb completely devoid of any atmosphere might come in handy. The most obvious case is an incandescent light bulb, which works by heating a metal filament so hot that it glows. The problem is, at such high temperatures, the metal is more readily reacts with the surrounding air, causing the filament to quickly crumble to dust. No air, no problem.

Aside from producing heat and light, Thomas Edison noticed that something interesting was happening here: An electrical current could bridge the gap between the heated filament and a positively charged plate inside the bulb.

The vacuum was important here: That current was created by electrons being shed by the heated filament, or cathode, and flying through empty space toward the positively charged plate, the anode. If that space were filled with atmosphere, the electrons would bounce off molecules of nitrogen and oxygen, scattering every which way and cutting off the flow of electricity.4 5

Incidentally, that is the only bit of original science Thomas Edison ever performed, and he couldn’t think of any useful applications for this phenomenon.6

Two decades later, in 1904, John Fleming discovered a pretty good use: Such a tube permitted electrical current to flow in only one direction, turning an alternating current, AC, into a direct current, DC. The component was called a valve, or diode.7 8 9

Lee de Forest improved the technology further in 1906 by adding a mesh grid in between the filament and the plate. By applying a positive electrical charge to this grid, it accelerates the electrons as they fly toward the anode. This amplifies the electrical signal — and an amplifier is a very useful piece of tech.10

Some of the most iconic inventions of the twentieth century relied on vacuum tube amplifiers: The radio, the microwave, hearing aids, radar, continent-spanning telephone networks, and, naturally, the amplifier for electric guitars11

But that’s only half the picture — what the vacuum tube does when the mesh grid carries a positive charge. By applying a negative charge to the grid, electrons are repelled, and can’t make their way to the anode. The circuit breaks.

That might not sound very useful. The whole reason the tube is evacuated in the first place is so the circuit doesn’t break.

The difference is that the mesh grid’s charge can change. In an instant, we can apply a positive charge, then a negative charge, then a positive charge again. The circuit breaks, then closes, then breaks again.

In other words, it’s a switch. Off, then on, then off again. And that is a way to convey information. One bit of information, to be precise. Either a one if it’s turned on, or a zero if it’s turned off. String several of these together and you can convey a lot of information. Bytes, kilobytes, megabytes. And by programming the electrical inputs, this information can be processed.13

The first digital computers like ENIAC were a natural evolution of the intricate mechanical devices we discussed in our last episode, and eventually, they would be supplanted by the solid-state transistor, which we discussed in episode 32, Germanium.

During their time at the top of the technological heap, vacuum tubes were ubiquitous. They illuminated the glow of the television screen and the glow of the mushroom cloud.

Barium can bring a special glow to your element collection, too, if you follow in the footsteps of the Italian shoemaker and amateur alchemist Vincenzo Cascariolo. In 1603, he found some milky white stones on the slopes of Mount Paderno, near Bologna. He didn’t know it, but those stones were barium sulfate, doped with a small amount of copper.

Cascariolo baked his stones in a furnace, transforming them into barium sulfide, and imbuing them with a strange property: After absorbing light from the sun, they could glow in the dark for several days. He couldn’t quite figure out what to do at that point, though. It was impressive, but it was no Philosopher’s Stone. Pebbles of the stuff became known instead as Bologna Stones.14 15 16

You would be in good company if you stocked your element shelf with this curiosity. Over the next few centuries, it caught the attention of Galileo, Robert Boyle, and even John Evelyn — the pamphleteer who composed the ode to air pollution we read all the way back in episode 6.

Wherever you source your barium from, you’ll want to be careful with it. It is poisonous in pretty much every incarnation, and it’s been the implement of at least one modern murder.17

There is an exception, though. There may come a point in your life when a doctor asks you to drink a slurry of barium sulfate. In this and every other case, you should consider the doctor more trustworthy than “that podcast you heard that one time.”

The prescribed liquid, called “barium meal,”  is non-toxic and blocks x-rays. When swallowed, an x-ray will show the structure of a patient’s stomach and intestines in great detail. Doctors can then see the locations of any hernias, obstructions, constrictions, and inflammation.18

There’s only one caveat: the patient can’t have any other food in their system if the procedure will be effective. A combination of temporary fasting and laxatives will do the trick.

So it’s kind of the opposite of John Fleming’s diode: In that case, a vacuum is created in the tube by including a little bit of barium. For the medical procedure, the patient makes room for barium by evacuating their tubes.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn another name for a flowing stream of electrons, visit episodic table dot com slash B a.

Next time, we’ll take a detour with lanthanum.

Until then, this is T. R. Appleton, reminding you that when choosing a laxative, you’ll always want to choose magnesium over antimony.


  1. Elementymology & Elements Multidict, Barium. Peter van der Krogt.
  2. LiveScience, Facts About Barium. Carol Stoll, November 7, 2017.
  3. PeriodicTable.com, Barium. Theodore Gray.
  4. Nuts And Volts, Vacuum Tubes. H. Ward Silver, 2018.
  5. Engineering.com, Vacuum Tubes: The World Before Transistors. Michael Alba, January 19. 2018.
  6. Transistorized! The Vacuum Tube. PBS, 1999.
  7. Wired, November 16, 1904: Vacuum Tube Heralds Birth Of Modern Electronics. Tony Long, November 16, 2009.
  8. Popular Mechanics, Scientists Are Bringing Back Vacuum Tubes For Computers Of The Future. Avery Thompson, November 8, 2016.
  9. Encyclopedia Britannica, Sir John Ambrose Fleming. Last updated April 14, 2019.
  10. Encyclopeia Britannica, Lee de Forest. Raymond E. Fielding, last updated August 22, 2019.
  11. Tedium.co, Totally Tubular. Andrew Egan, November 13, 2018.
  12. You might call such a machine an Electronic Numerical Integrator And Computer — or ENIAC, for short.

    That’s what the US Army’s Ballistic Research Laboratory called it when, in 1945, they unveiled the world’s first general-purpose programmable electronic computer.

    The Army found all sorts of uses for this machine: Ballistics calculations for artillery units, designing wind tunnels, even predicting the weather. But the first problem assigned to the world’s first all-purpose computer was “the Los Alamos problem.” After spending six weeks chewing through half a million punch cards of data, ENIAC provided the answer to its first question: Yes, it would be feasible to construct, deploy, and detonate a hydrogen bomb.12Dark Sun: The Making Of The Hydrogen Bomb, p. 251-252. Richard Rhodes, 2012.

  13. Chemistry World, A Lode Of Bologna. Philip Ball, November 22, 2016.
  14. Encyclopedia Britannica, Bologna Stone. Last updated June 16, 2016.
  15. io9, The Bologna Stone Was A Glowing Mystery For 400 Years. Esther Inglis-Arkell, August 17, 2015.
  16. Texas Monthly, Poisoning Daddy. Skip Hollandsworth, 1996. I sincerely recommend that you do not read this story. It’s heartbreaking. There’s a reason I didn’t include it as part of the episode.
  17. News Medical Life Sciences, Principles Of Barium Meal. Dr. Ananya Mandal, June 28, 2019.

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