Re: Help with what I believe is a hardening issue

From: "T. E. Andersen" <postlister@microscopica.com>
Subject: Re: Help with what I believe is a hardening issue
Date: Wed, 10 Nov 2004 15:33:15 +0100

> The oxidation should be very minimal due to the methanol added to
> commercial formalin. As much as 15% is added to prevent/ reduce the
> oxidative formation of the formic acid and/or disproportionation
> (not sure that's the correct english term.

I don't use formaldehyde or glyoxal as a photographic hardener, but we
prepare formaldehyde solution by dissolving paraformaldehyde, because
people use it for electron microscopy as well. I know methanol
somewhat prolongs shelf life and suppress polymerization as well, but
I am not sure if that's all that effective, especially when metal
impurity level is unknown. I you can say "by the principle of Le
Chaterier" for that. The term appears in first year college chemistry
textbooks. (it was on a highschool textbook in Japan but that was
years ago.)

> Btw. formaldehyde
> should be kept at room temperature, as keeping it in the fridge
> accelerates the polymerization into paraformaldehyde.

I think formaldehyde sans methanol is better kept
refrigerated... though it would last only for a couple of weeks
anyway.

> The paraformaldehyde may be redissolved by adding sodium hydroxide and
> heating to 70*C. This is, however DEFINITELY NOT RECCOMMENDED, unless
> you have a fume hood, and are skilled in laboratory practices.

Agreed.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)