CrimpJiggler
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Purging your reaction flask of air
In college we purged a 3-neck reaction flask of air by feeding nitrogen into the flask via this glass contraption which had oil at the outlet which
served as an airlock. We had a reflux condenser in one of the necks so this piece of glassware somehow allowed nitrogen to pass through but did not
allow solvent vapours to escape. This was a few months ago, I can't really remember the apparatus, anyone know the name of this piece of glassware I'm
talking about?
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smaerd
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A Gas Bubbler?
http://en.wikipedia.org/wiki/Gas_bubbler
I have one from laboy, I bet dr. bob or one of the other people with large lots of lab glass-ware has one of these laying around  .
Of course you need gas in-lets/out-lets as well.
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AirCowPeaCock
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Because the nitrogen didn't condense in the condenser. 
BOLD
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Dr.Bob
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There is also a device called a "Firestone valve" which has a one way design to avoid sucknig oil into the flask, which is really good. They are
pretty pricy, but work well. I have been using one for years, work best when pulling a vacuum on a flask, then allowing nitrogen in. They are
really useful when doing a hydrogenation or other reaction where any oxygen left in the flask is very bad. (H2 + O2 + Pd = BOOM!)
I do have some of them, but currently all are lacking some piece like the stopcock, and they are a special one that I have to dig through a box of
parts to find one. But I will eventually probably find the missing parts for one or two of them. See below for details. Ace and a few others also
sell a similar design.
But for most cases a simple oil bubbler works to show the gas flow as well as reduce suckback potential. I just sold one, and have one left for
sure, and I think more in another box. They are only $5.
http://www.sigmaaldrich.com/catalog/ProductDetail.do?D7=0&am...
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Arsole
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You do not lie those are pricey. 
Thoughts, like fleas, jump from man to man, but they don't bite everybody.
-Stanisław Jerzy Lec
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BromicAcid
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These are the ones we use at work:
http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en...
Basically there is a T at the top, gasses from your reaction come in one side of the T and nitrogen goes into the other side. The bottom of the T
terminates in an oil reservoir. In the area above the oil there is another barb for the exit gasses. You always keep nitrogen on the bubbler so if
there is suckback in the reaction it sucks back nitrogen.
Still I prefer the valve that Dr. Bob provided the link to, they're pretty awesome for repeated purge cycles.
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leu
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Argon works a lot better as far as purging air from an enclosed system 
Chemistry is our Covalent Bond
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