[pure-silver] Chemical subsitution
- From: Eric Nelson <emanmb@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 26 Apr 2007 18:25:43 -0700 (PDT)
I have discovered that I am out of sodium bisulfite
and need to make some HCA tonight for prints I just
finished.
I have tons of sodium metabisulfite and have looked
through the archives to see if this compound is
specifically addressed as an AKA or substitute
compound for sodium bisulfite.
I've included some quotes below of Richard's that seem
to answer this question, so I'm wondering if there is
a definitive answer out there as to whether I can use
metabisulfite in place of bisulfite gram for gram in
the HCA formula or at what ratio it would need to be
at.
I'm a cook not a chef so molar aspects of these
compounds and the Avogadro's number will go over my
head. ;-)
And what the heck is bisulfite lye? Found that
mentioned in one of my search results.
Eric
"Long ago there was a discussion of what exactly was
meant
by sodium bisulfite in Kodak and other formulas. It
appears
that the compound is actually metabisulfite, or mostly
so.
Sodium metabisulfite is much less expensive than real
sodium
sulfite and is certainly suitable for this formula."
."various MSDS list either Sodium Bisulfite or
> Sodium Metabisulfite.
> > Kodak
> > Sodium Bisulfite appears to be mostly the
> metabisulfite. Evidently it
> > does
> > not matter which is used.
> > Because the formula is not published the amount of
> EDTA and Citrate are
> > not
> > firmly established. The MSDS for the concentrate
> (powder) lists the
> > amount
> > of either as 1 to 5% by weight. It disappears from
> the working solution.
> > It's possible the amount in the stock should be
> only 1 gram of each but I
> > think from Haist or somewhere I got the idea that
> it should be more.
> > Perhaps a compromise of 2 grams each should be
> used.
> > I think 15 grams of the bisulfite/metabisulfite is
> correct. In any case
> > the
> > target pH is 7.0"
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