Thyratron. 
The source of this military surplus tube reports it contains over 1/2 gram of gold (a few dollars worth).  Please no jokes about gold-plated military hardware.  The gold here is sintered, not plated.  Solid state electronics are fantastic, but the artistry of vacuum tubes is of a more human scale, and it will be missed when, in a few more decades, tubes like this will be purely museum curiosities. 
Source: eBay seller heruur 
Contributor: eBay seller heruur 
Acquired: 24 December, 2003 
Price: Donated 
Size: 5" 
Purity: >99%
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