| | |   Argon signal lamps. I'm guessing that these antique bulbs are filled with nearly pure argon, but I don't really know.  Connected to a hundred or so volts they produce a characteristic purple-blue glow over the surface of the electrodes.  Not enough to create usable light, but perfect as a signal light, the kind of thing that today would be done with an LED or neon indicator light.
 Source: eBay seller ramblingguy
 Contributor: Theodore Gray
 Acquired: 28 February, 2009
 Text Updated: 12 March, 2009
 Price: $10
 Size: 3"
 Purity: 90%
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