Natural sample, 78% Pure. 
I collected this sample of naturally occurring air (78% pure nitrogen) from about 20 feet away from the table in May, 2002.  The sound for this sample is a beautiful 78% nitrogen, 21% oxygen wind sound borrowed from ftp://ftp.zib.de/ pub/ UserHome/ Luegger/ Urania/Sound/ FX-03.WAV . 
 
I've got a story and video of making ice cream by pouring liquid nitrogen directly into a mixture of cream and chocolate syrup. 
 
Source: Air 
Contributor: Theodore Gray 
Acquired: 18 May, 2002 
Price: $0/Free like the air we breathe 
Size: 2.5" 
Purity: 78%
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