Back purging with Argon

[NDAV8R]

Hi gang:
I was approached with a TIG welding project of welding a bottom drain plug on a New Aluminum Gas tank on a Hot Rod project. It has a bottom plug already welded on it already, but he wants another. It is a round cylinder type tank with a vented gas cap on top.
I would like to purge the tank with 100% argon before I tig the bottom 3/8" drain plug coupler.
My question is this: Is argon heavier than air? Do I remove the top or bottom port while purging?
Anyone who has any similar situations??? I plan on using my 200Dx with 2% Thoriated and 4043 filler. Any input?

Thanks
Ndav8r

[GTA/SPEC]

Here is a link to the Periodic Table. It provide alot of information regarding chemical and physical properties of elements.

http://www.dynacore.de/images/periodic.jpg

In regards to mass, the table is laid out so that the lightest elements are on top and they get progressively heavier as you go down the list.

[Old Sporty]

Remove the top plug. Argon is heavier than air.

[YvesVT]

Yep, it's heavier than air

Like GTA-SPEC said,

You'll see, if using the periodic table, that Argon is heavier than air,

Air is more or less composed of 78% Nitrogen, 20% oxygen, 0-4% water vapour, 0.9% Argon, and tiny fractions of other elements....(by volume)

To see how you can tell, check out that periodic table and look up the atomic "weight" which, in practical terms represents the mass of one mole of that element...(a "mole" = a term similar to a "dozen" but it represents ((6,022×10 to the power of 23)) atoms of the particular element you are measuring)..

for example 1 mole of hydrogen "weighs" 1.008 grams.
So... one mole of Argon, weighs 39.9 grams

while one mol of atmospheric (2 atoms together) Nitrogen
= N2 =28.0 grams of N2/mol x 78% = 21.84 grams
+ 1 mole of oxygen
x 2 because it's 02 in air =32.0 grams 02/mol x 20% = 6.4 grams

without getting into molar volumes of gases..., you see that for the same number of atoms of Argon and for the same number of molecules of atmospheric Nitrogen, Argon has almost twice the mass of Nitrogen.

So, in theory, air should rise to the top as Argon sinks beneath.....like oil always finds its way on top of water.

I would think you should remove the top plug to let air rise to the top and out.

pardon the lengthy explanation!
Cheers