[DeJarnett (OP)]

Since argon is heavier than air, could something very light float on it if it was poured into an open top air-tight container?  Would an argon/air mixture (one breath) lower your voice the way helium raises it?

I realize that exhaling all oxegen from the lungs and then breathing pure argon could cause problems, at least causing you to pass out due to inert gas replacing oxegen, so I'm not suggesting that.

[Cut Chemist]

Density (at STP):

Helium: 0.1786 g/L
Air:    1.2 g/L 
Argon:  1.784 g/L

It may be possible to float an air filled ballon on top of a bed of argon.  But the balloon would have to be made out of an extremely light material. 

The difference in density between helium and air is much, much larger than the difference in density between argon and air.

[DrDick]

There's also the issue of mixing.  Gases diffuse very quickly, so they would mix very quickly.  That hypothetical "bed of argon" wouldn't last very long.

The argon (or better yet krypton or xenon) should have a deepening effect on your voice, however.

Dick

[Bored chemist]

Just a thought; experiments with argon are unlikely to be chemistry.