Washaid: effective differnce between bisulfite and metabisulfite

[Ulophot]

I happen to have sodium metabisulfite on hand. I can't remember why; it must be for something I needed to mix up a good while ago, unless someone gave it to me with some other things.

Meanwhile, back at the sink, having finished my Permawash, I am switching to the washaid published by Doremus and others here: one Tblsp of sodium sulfite plus one pinch of sodium bisulfite per liter. You can see where this is going: I have no bisufite, only the metabisufite, and am wondering if I can substitute the latter.

According to one source, "The key difference between sodium bisulfite and sodium metabisulfite is that the sodium bisulfite has only one sulfur atom and three oxygens, and the bisulfite anion is monovalent whereas, the sodium metabisulfite has two sulfur atoms, five oxygens, and the anion is divalent." Well, I know the words sulfur, oxygen, and atom....

I'll certainly spring for the bisulfite if I need to. Whoever knows whether it will make a difference to my print washing, please speak up.

Thank you.

[Michael R]

You can use metabisulfite.

It’s worth noting the only reason bisulfite or metabisulfite are added is to reduce the pH of the solution to approximately neutral, and the only reason that is done is to lessen the chance of metal compounds (mostly calcium) precipitating from hard water. If you’re worried about that use distilled/deionized water and skip the bisulfite/metabisulfite. A 2% sodium sulfite solution is all that is needed.

[Ulophot]

Thanks, Michael, enjoy your Fourth!

[j.e.simmons]

One of the chemists over on APUG (Gerald Koch?) told me years ago that for photographic purposes there’s no difference.

[Michael R]

I miss Gerald Koch. He was a nice guy and always a really helpful presence on APUG.

One of the chemists over on APUG (Gerald Koch?) told me years ago that for photographic purposes there’s no difference.

[Ulophot]

Excellent. Thanks to you also, j.e.

[Alan9940]

The word I got from ArtCraft Chemicals years ago is that Sodium Bisulfite becomes Sodium Metabisulfite when it hits water. He doesn't carry Sodium Bisulfite because in terms of water-based chemistry it's the same.