Trouble in Gasland

Took my Nitrogen bottle to AirGas on Clairemont Blvd this morning. Friends have used them to get their CO2 refilled and I called and they said they could fill the N/CO2 mix.

I get there and the look at my valve and say, "that's all wrong". Kept referring to it as Guiness Gas, which is correct, but it made me wonder if they just meant it wouldn't fit on a Guinesses setup or something. But that wasn't it. They said I needed a CO2 valve (320) and a syphon tube. Basically convert my Nitrogen bottle into a CO2 bottle.

So I went back to BeverageFactory and asked them what the deal was. They said the setup I had was fine and he had just filled up a bottle for that purpose at WestAir. I headed over there and, sure thing, not a question, they took the bottle and will call me when it's ready.

It does raise the question... If CO2 normally needs a syphon tube that means, the gas is basically heavy. And the Nitrogen bottle doesn't have one so it's lighter. Then what happens to the mix? If it stays mixed, i guess, no problem, since with 75% Nitrogen it'll still be a lighter gas. Hrm...