Help! (Can I switch a tank from nitrogen to CO2?)

[FearItself]

I bought a used 5-lb. tank locally via Craigslist for the kegerator I'm building (I'm currently using a borrowed CO2 tank). When I looked it over after I got home, I saw that the sticker on it said "Nitrogen, Compressed." (I didn't notice the label when I picked up the bottle this afternoon; I was too busy looking for the inspection date to check out the label.) The bottle is heavy enough that I think there's still some gas in there.

This is my first time serving from a keg rather than bottling, so I have a few noob-ish questions:
1) is there any reason I won't be able to use this tank to hold CO2 once it is purged of nitrogen?
2) Can I make any use of the nitrogen that's left in this tank if I'm serving a "regular" (non-stout/porter) beer? Right now, I have an amber ale in my keg that I plan to serve at a party next weekend. It is already carbonated, and if I can use the nitrogen to serve it without ill effect, I would rather do that than waste the gas. But I don't want to spoil the beer.

The person I bought this from had another tank, too; that might be a CO2 tank. I could call and ask, and if so, trade it back with them. I will definitely do that if I can't use this for CO2 in the future. But if it's just a matter of one tank of gas, I'll keep the tank and either flush it out or just use it for serving in the short term, depending on the answer to question #2.

So I'd welcome any wisdom you can drop on me here. Thanks!

 

[day_trippr]

CO2 regulators are typically stemmed for CGA320 cylinder valves.
Nitro or Nitro/CO2 typically comes in mixed gas cylinders sporting CGA580 valves.
Regulators for each usually come with the mating stem, so you might have issues.
I'd do the exchange thing with the seller if that option is available...

Cheers!

 

[FearItself]

CO2 regulators are typically stemmed for CGA320 cylinder valves.
Nitro or Nitro/CO2 typically comes in mixed gas cylinders sporting CGA580 valves.
Regulators for each usually come with the mating stem, so you might have issues.
I'd do the exchange thing with the seller if that option is available...

Cheers!

Ah, yes. I checked out the connection, and the Nitro bottle has female threads where the threads on the CO2 bottle are male. So even if I got the right gas, my regulator obviously wouldn't fit without another piece. Plus, getting refills of the right gas would become a hassle.

Thanks for the information! I'll work on getting an exchange/refund from the seller.