[Kirk Keyes]

It is but we have an excess, that's the nature of Metabisulphite it's seems more than the Molecular weight, and it acts that way in use.

I think the whole Bisulphite/Metabisuphite properties are poorly defined and explained, there is lot of free SO2 when you buy fresh Metabisulphite, not included in the MW.

There's more than it "seems" as the metabisulfite uses some of the water it's dissolved in to make the SO3--.

But there's not going to be more than there actually is...