Life of weak (~1%) Potassium Ferricyanide solution?

Steve Goldstein · Dec 12, 2012

I believe the dry chemical in brown bottles keeps about forever with proper storage, but what about solutions? I'd like to keep some on hand to save mixing every time, but as I can't get into the darkroom frequently I'm concerned if it's likely to go bad over time. While it's not that expensive, I don't want to waste it.

Thanks.

Gerald C Koch · Dec 12, 2012

Not a problem IF the solution is protected from light and kept in a brown glass bottle.

jochen · Dec 13, 2012

Hello Steve,
i'd recommend not to store the solution for more than about a week. Always make only the amount you need in a forseeable time. The hexacyanoferrate(II) is light-sensitive and can be oxidized to iron (III) compounds, so a brown bottle is the least you can do.

Steve Goldstein · Dec 13, 2012

I do have appropriate small brown glass bottles for storage. Mainly I want to avoid the need to weigh out very tiny quantities like 0.25gm, which requires resolution better than my small electronic scale can provide.

How about a stronger ferri solution, like maybe 10%? Is there any storage advantage to that, again in a brown bottle? I have some small syringe bodies so measuring out 1-2 ml is not difficult.

Steve Goldstein · Dec 13, 2012

Problem solved. I didn't realize how cheap a scale with 0.01g could be. $10 including shipping on you-know-where.

David Lyga · Dec 13, 2012

Is 'you know where' Amazon or EBay? - David Lyga

Steve Goldstein · Dec 13, 2012

eBay in this case, I looked there first.

Rudeofus · Dec 14, 2012

jochen said:
I'd recommend not to store the solution for more than about a week. Always make only the amount you need in a forseeable time. The hexacyanoferrate(II) is light-sensitive and can be oxidized to iron (III) compounds, so a brown bottle is the least you can do.

Please note that Ferricyanide is the Fe-III complex (K3Fe(CN)6), so it won't be oxidized by O2.

Doremus Scudder · Dec 14, 2012

I don't know about a weak solution, but I have a PET bottle of ferricyanide/bromide bleach that I use for bleach-redevelopment that is well over two years old and still works fine. It's about 2% if I remember correctly.

Best,

Doremus

www.DoremusScudder.com

RalphLambrecht · Dec 14, 2012

from experience, i'd guess >1 year.

Kirk Keyes · Dec 16, 2012

Ferricyanide solution at 1000 ug/ml as CN only lasts about a week before it starts to form a precipitate. But that's only important when testing for CN...
For use as bleach, it's good for much longer. I'd say over a year, easy. But store in the dark, like in a cupboard.

Life of weak (~1%) Potassium Ferricyanide solution?

Privacy & Transparency

Privacy & Transparency