The Noble Rack


I bid on a set of five glass flasks on eBay, and won the auction for $13.50. They were described as dirty and "probably empty", but they were labled with the names of the first five noble gases, and I thought I might be able to get them filled and use them to hold samples.

Well, they were dirty, but they are definitely not empty. At the point where the tube meets the sphere on each one there is an internal breakaway seal that is clearly intact on each of them.

I made the rack to hold them between 10PM and midnight on the evening I got the samples, because I was just so excited to find out they were still filled. It's made out of the same Carlson Maple that the noble gas tiles are, with legs of walnut. It's shown here on the table, but normally it's kept on a nearby bookcase:

After many unworkable suggestions for proving whether the gasses were still in there, several people came up with the idea of using a high voltage transformer, such as one finds in those now inexpensive plasma ball novelty lights, to try to set up an arc inside the flask, and identify the gas from the color of the discharge. Whether this is possible is sensitive to the pressure of the gas, which is not known.

Fortunately, it worked beautifully on three out of the five, and proved beyond a reasonable doubt that those three at least contain the gas claimed. The others almost certainly failed because the type and pressure of gas in them does not support an arc, not because they are empty. In fact, if they were empty, I would have gotten an arc, because the arc works through up to about half an inch of ordinary air.

You can see the arcs from each of the five flasks on the right. To make these pictures I took a plasma-ball novelty light (mine was a lava-lamp shaped model for $30, but just about any one one would have worked) and disconnected the ball from the transformer (cutting the single wire connecting them). Then I set the transformer on the floor under my desk (because it's dark there) with the bare end of the wire sticking up. I set my camera on a mini-tripod on the floor about 4 inches from the wire, then held the gas flasks up to the wire. With the exception of neon (which makes a bright arc if you even so much as sneeze in its direction), I had to put my finger within a fraction of an inch of the wire to get an arc going. The arc starts when the end of the wire comes within striking distance of something with enough capacitance to allow the very, very high frequency voltage source to push and pull electrons out of it, creating a continuous arc. A finger works well, though it's best not to let the arc touch your finger directly. That causes little pin-hole burns, of which I now have three.

A note on color: Don't believe any of these pictures. It is basically impossible to photograph the color of these arcs, because their colors consist of several sharp spectral lines that do not correspond to the red, green, and blue colors that cameras are sensative to. It's hard enough to deal with color in normal objects whose color is made out of broad swaths of spectrum, but impossible with spectra like this. So take the colors only as a very general indication of what the real thing is like.

A couple of months after I got the flasks, I finally got a set of noble gas discharge tubes (like mini-neon signs):

I have installed them in the appropriate slots in the table and wired them from below:

You can see pictures of all those arcs on the right side of this page.

When I first hooked them up a few displayed a curious string-of-pearls effect due to the high frequency transformer, but it went away and hasn't come back:

Helium Flask

Neon Flask

Argon Flask

Krypton Flask

Xenon Flask

Helium Tube

Neon Tube

Argon Tube

Krypton Tube

Xenon Tube