How do I know if my tank is filled with CO2 and not something else?

Got a tank off of craigslist. Looks to me in good condition and it's full. Guy said it was CO2, but I don't see any marks. How do I know its not Argon or something else?

had the same delima, but i got mine from friend!
used for awhile but it gave us gas!
without a label u cannot tell whats inside!
so i took to a welding supply and exchanged for a good known unit w/co2~ cost aprox $12 bucks!!

The brown paint finish of the bottle indicates that it is a nitrogen tank. Could still be filled with co2 as the pressure requirements are lower for co2 than nitrogen. But for the cost of a trade in, why take the chance? Take it to a gas supply house and trade it in for a full one, as long as it is within hydro test date. (Pressure vessels are required to undergo hydrostatic pressure testing every 5 years, there should be a date stamped into the tank, that is the expiration date for it's last test.)

Looks like a CGA 320 CO2 fitting. It's been a while since I've been in the business of compressed gasses but I believe inert gases (N2, He, Ar, etc.) come with a CGA 350 fitting that looks completely different (It threads on the inside). I can't believe any shop would fill a CO2 tank with Nitrogen if for no other reason it would be easier to swap someone a tank than try to adapt their CGA 350 supply to a CGA 320 tank since you aren't really paying for the gas, you are paying for the guys time to actually fill the tank.

In the end, gas is cheap. Just swap the cylinder if you have any doubt.

Yep, that's a CGA 320 filter. NO ONE would fill that with any other gas than CO2. CGA fittings are a safety protocal and while I'm not sure if it would be illegal to manipulate the system, I know it would open them up to any number of liability lawsuits.

Anyway, bottom line is that it's CO2.

put the gas in a balloon... if it floats away then you know its not co2

One definite test, which wastes a fair amount of gas, tie a cloth bag over the outlet then open the valve. If dry ice forms in the bag, it's CO2. Very few gases have a solid state at atmospheric pressure.

Note: this is a good way to case permanent bodily damage.

david_42 said:

One definite test, which wastes a fair amount of gas, tie a cloth bag over the outlet then open the valve. If dry ice forms in the bag, it's CO2. Very few gases have a solid state at atmospheric pressure.

Note: this is a good way to case permanent bodily damage.

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Now I wish I had a video feed for all of us home brew dorks who are now heading out to the keg fridge to try this with a tank.

ER's be on alert, we are armed with enough internet knowledge to be dangerous to ourselves!

david_42 said:

Note: this is a good way to case permanent bodily damage.

Click to expand...

It's also a good way to make dry ice. ;-)

chefmike said:

Now I wish I had a video feed for all of us home brew dorks who are now heading out to the keg fridge to try this with a tank.

ER's be on alert, we are armed with enough internet knowledge to be dangerous to ourselves!

Click to expand...

A slightly safer way to do is to shoot it out of a tight nozzle to make dry snow.

chefmike said:

Now I wish I had a video feed for all of us home brew dorks who are now heading out to the keg fridge to try this with a tank.

ER's be on alert, we are armed with enough internet knowledge to be dangerous to ourselves!

Click to expand...

Meh, I used to go out back of where I worked and tie a burlap sack on the valve of a CO2 tank the size of a semi tanker and let it rip to make dry ice to shrink fit things.

The only thing you really had to watch out for was the static charge. It would light you up. Needless to say, it was wasteful, but I wasn't paying for it and had to have it.