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FX15 - sodium metabisulphite or sodium bisulphite?

Kevin Caulfield

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I'm going to mix up a new batch of FX-15. I haven't used it for years but I do love it.

Checking the Film Developing Cookbook, i noticed that I used to use sodium bisulphite, as listed by them, but I double-checked Crawley's original recipe in BJP and it uses sodium metabisulphite. I do actually have a Ph.D. in chemistry but as far as I remember, metabisulphite and bisulphite are two different beasts.

I assume they both work just as effectively as each other for the purposes of FX-15?

Please let me know if you can help.

Thanks,
Kevin
 
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Metabisulphite is puré, normal commercial Bisulphite is a mixture of Metabisulphite and the less stable Bisulphite, the ratio can vary but there's more Metabisulphite usually 70-80%. Analytical grade Bisulphite is quite unstable.

JT Baker sell both, Metabisulphite is used where it's greater ant-oxidant power is require, in solution there's greater free SO2. It's used in Part A of some two part powder developers even though it doesn't appear in the published formulae. Kodak Ltd did publish a substitution table at one time.

Ian
 
As I thought, in my 'cookbook' on page 191 and 193, it is stated that the two maybe interchanged weight for weight. That is if you have made a mis-spell, as both chemicals are with a 'f' meaning sodium bisulfite and 'sodium metabisulfite'.

Terry S
 
In FX-15 it will make little difference the amount is so small. I wouldn't use Bisulphite in Pyrocat HD Part A as it will have a shorter shelf life compared to using Metabisulphite.

Ian
 
Thanks for your replies. I think this time I'll go with Crawley rather than the FDC. I'm sure as discussed above that the sodium metabisulphite will be fine.
 
tezzasmall said:
As I thought, in my 'cookbook' on page 191 and 193, it is stated that the two maybe interchanged weight for weight. That is if you have made a mis-spell, as both chemicals are with a 'f' meaning sodium bisulfite and 'sodium metabisulfite'.

Terry S
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Sorry, Terry. It's not completely a mis-spell. It's a force of habit. "Sulphite" wasn't changed officially to "sulfite" by IUPAC until after I did my chemistry degree.
 
Terry it was changed by IUPAC in 1990, between my B. Sc. (Hons) and my Ph. D.
http://bit.ly/ADqbi
 
They say "And so when IUPAC decided that element 16 should be spelled as 'sulfur' — either in 1971 (ref. 1) or 1990 (ref. 2) depending on the source — " but it's definitely 1990 not 1971. I know because I was right in the midst of my chemistry studies.
 
Kevin Caulfield said:
Sorry, Terry. It's not completely a mis-spell. It's a force of habit. "Sulphite" wasn't changed officially to "sulfite" by IUPAC until after I did my chemistry degree.
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Interesting! And I will agree with anything you say on this matter, as you are much more knowledgeable than me on this subject.

Terry S
 
tezzasmall said:
Interesting! And I will agree with anything you say on this matter, as you are much more knowledgeable than me on this subject.

Terry S
Click to expand...
Thanks, Terry. Officially I am now incorrect as IUPAC make the rules, but it's more a force of habit than anything.
 
Ian Grant said:
In FX-15 it will make little difference the amount is so small. I wouldn't use Bisulphite in Pyrocat HD Part A as it will have a shorter shelf life compared to using Metabisulphite.

Ian
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And I remember a post from you, Ian, which stated that the metabisulphite should be fresh for use in Pyrocat-HD, which was news to me.
 
john_s said:
And I remember a post from you, Ian, which stated that the Metabisulphite should be fresh for use in Pyrocat-HD, which was news to me.
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Maybe not stale would be another comment, Metabisulphite keeps quite well so as long as it's reasonably fresh Pyrocat HD keeps for over 3 years made up in water even in a part full (diminishing) bottle.

Ian
 
Ian Grant said:
Maybe not stale would be another comment, Metabisulphite keeps quite well so as long as it's reasonably fresh Pyrocat HD keeps for over 3 years made up in water even in a part full (diminishing) bottle.

Ian
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I never really got around to working out why I had reliability problems with Pyrocat-HD in a Jobo. Suspect it was down to oxidation of the developer during processing.

Tom
 
Tom Kershaw said:
I never really got around to working out why I had reliability problems with Pyrocat-HD in a Jobo. Suspect it was down to oxidation of the developer during processing.

Tom
Click to expand...

In use the Metabisulpite in Part A protects the Pyrocatechin from Oxidation, however it also breaks down to Sulphite in the presence of the Carbonate in Part B, however it's not an instant reaction.

The level of Metabisulphite in Part A is very low it's only 10g/l in Part A before dilution, so in 1+1 to 100 that's 0.1g/l in the working solution. Increasing the Metabisulphite in Part A to 15 or 20g in Part A will help with oxidation and have little to no effect on staining etc - I know because I've tried it It also will help with shelf life.

I use Ilford IT-8 toner sometimes, this uses a plain Pyrocatechin Carbonate re-developer with an extremely short tray life, so these days I use Pyrocat HD as the re-developer asit oxidises more slowly.

Ian
 
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