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20 years ago I visited the Energetica museum in Amsterdam. One of the exhibits was a large cart/trailer that was used to charge submarines from the WWI era (!). It had two HUGE hand-blown glass mercury rectifiers in the front of it; you could fit a small person inside each, and there was a couple inches of mercury sitting at the bottom.

I was shocked when a docent walked over and turned it on. The rectifiers lit the whole room up with a beautiful purple glow. Beautiful.

Doing a quick web search it looks like the museum is no longer. Too bad - even though I couldn't read the plaques, it was still one of the most fascinating museum experiences I've ever had.

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The early days of radio are just as fascinating with plenty of big electronics for transmitters. Droitwich the BBC's main LW transmitter is 500kW and still uses some of the old, water cooled valves. Thanks to the last round of govt budget cuts the transmitter won't last beyond the last stock of those valves.

See here for some background of their early days and photos : http://www.bbceng.info/Operations/transmitter_ops/Reminiscen...

No glow from the mercury rectifiers though - they're steel cased thanks to being 600kW

If you want to see that sort of thing in the SF Bay Area, visit the Marine Radio Historical Society in Marin.[1] They have a big ship-to-shore station, built on Federal land a century ago and turned over to the Park Service when it shut down.

They operate many of the transmitters each weekend. They applied to the FCC for a commercial coast station license, probably the last one, and got it. So they can send at quite high power. They talk to museum ships around the world.

[1] http://www.radiomarine.org/

The Isle of Man Electric Railway had a huge mercury vapor rectifier in active use until 2010.[1] I saw it in operation once. It would glow brightly when the trams were drawing high power.

[1] https://www.flickr.com/photos/trained_4_life/10978575914

Word of the day: docent.

I rarely see this in common expression. Nice choice.

Old tech has great appeal. Scale is our size, and features forces, artifacts we can see, hear and feel easily. I can imagine that glow. Damn cool.

what other word is used for the volunteers who interact with patrons at a museum?

> The title "docent" is not widely used outside the United States, with the terms "guide", "facilitator", or "educator" preferred.

https://en.wikipedia.org/wiki/Museum_docent

Nailed it.

It is not all that widely used in the US either, in my experience anyway.

Interestingly, the same word is used at some european universities to mean roughly "associate professor".

docent is common in Czech and Slovak.

There is also a particle "do" which means "into" and also "up/until". In Czech, the opposite of this sense is "přes", meaning "over/beyond".

So this is the basis of an old joke that "docent" means someone weighing up to 100 kg; above that they become a "přescent":

https://cestina20.cz/slovnik/prescent/

Thank you. That was fun to learn.

> The rectifiers lit the whole room up with a beautiful purple glow. Beautiful.

I wonder what other EM ranges it emits. Glowing purple makes me think of UV but maybe also some X-Rays?

Tons of UV, that's how legacy fluorescent lamps work, a nice intense UV flux excites the phosphors inside the tube. The UV can't escape the glass but the white light from the phosphors certainly can. Germicidal lamps use UV-transparent quartz.

As for x-rays the typical voltage drop across a long tube is like 100 volts, the whole point of a ballast is matching the normal hundred or so volt drop to whatever your local line voltage is using at a constant controlled current. Anyway the penetrating power of an xray is linked to the voltage drop, so it would be difficult even theoretically to generate xrays stronger than a hundred volts or so. So given that it takes 50 KV to 100 KV for a dental xray source to beam completely thru a head, you're looking at like a thousandth the penetrating power. Very hand wavy estimate that 100 volt xray source will likely not penetrate the glass and almost certainly not penetrate clothing or the surface layer of dead skin and skin oils.

The risk assessment for being nearby a heavy cloud of vaporized hot mercury would seem to imply the main risks would be biochemical in nature not physics in nature. Actually the most realistic risk is an economic death penalty if that leaks and requires hazmat cleanup.

AFAIK, x-rays are the result of electrons slamming into metal at high speed from a high voltage accelerating potential (>20kV). The glow inside Mercury rectifiers comes from ionization of Mercury vapor. Various other voltage regulator tubes glow from the ionization of low pressure gases inside the tube.

Common beam power tubes and power pentodes sometimes glow blue from residual gas in the tube even with plate potentials ~500V.

Probably not mercury rectifiers or thyratrons, but hydrogen and deuterium thyratrons do (edit - emit X-rays, that is). They're much higher voltage devices. Example at [1]

[1] https://www.e2v.com/shared/content/resources/File/documents/...

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