Re: Sodium Bisulfite

From: Katharine Thayer ^lt;[email protected]>
Date: 08/24/04-05:08:59 PM Z
Message-id: <>

Christina Z. Anderson wrote:
  The reason
> why potassium metabisulfite is recommended the most is it is very water
> soluble and thus requires shorter wash times afterwards for archival
> purposes--10 minutes as opposed to 20-30 or more.

Do you have a reference for this? I've never heard anyone say this
before; the arguments for using potassium metabisulfite I've seen or
heard have always been based on it being less apt to soften the gum.

This argument doesn't even make sense to me on the face of it, but I'm
willing to be enlightened. To me the water soak isn't about something
going into solution in the water; after all the xsulfite is in solution
when the paper goes into it, and the paper is still soaking wet when it
goes from the clearing bath into the water bath. So it's a matter of the
solution that's in the paper diffusing out into the water, rather than
something actually going into solution, no? What you're doing is just
make an already existing solution more dilute, rather than putting
something that wasn't in solution into solution. So if you've got a
solution in the paper that's 5% sulfite, or in other words 95% water,
oozing out into 100% water, why would the sulfite move into the water
more slowly than say a 5% solution of metabisulfite? I can sort of make
myself imagine that theoretically the solubility of the material in
solution might possibly make a slight difference in the speed with which
the 95% water diffuses into the 100% water, but I'd need to be shown
empirically that that's the case, and how it could account for the "less
soluble" bisulfite solution taking 2 or 3 times longer to leach out of
the paper than the "more soluble" metabisulfite solution does.

At the same time, in my own experience I haven't seen a whole heck of a
lot of difference, at least between sodium bisulfite and sodium
metabisulfite, in the inherent solubility of the two.

I did look for the paper Richard mentioned on Ryuji's website that talks
about the difference between sodium bisulfite and sodium metabisulfite,
but didn't see it there. And clicking on "photographic chemistry" or
"notes on chemicals" gave me a "not found" error. (As a matter of
fact, clicking on anything on the site gives me a "not found" error).

Unfortunately I took solution chemistry as a summer course, five days a
week-- lecture all morning, lab all afternoon, homework all night. As
anyone who knows anything about the psychology of learning can tell
you, this is a surefire way to learn nothing, as time is needed between
sessions to absorb the information. I can vaguely remember equations
with equilibrium constants and other gizmos, but I'm afraid I didn't get
a whole lot out of it. So if someone knows enough about this to explain
to me why this argument makes sense, I'd appreciate it. Thanks,
Katharine Thayer
Received on Wed Aug 25 00:05:08 2004

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