Re: Help with what I believe is a hardening issue

I've had, since the late 1960's, a gallon of Formalin (37%
formaldehyde) which is the primary form used in photography. It comes
from a local Bay Area laboratory. There are a few small flakes of a
white substance on the bottom of the heavy duty plastic jug and other
than that there seems to be zero deterioration.
Jack Fulton

On Nov 9, 2004, at 10:53 PM, Ryuji Suzuki wrote:

Just to set the facts straight(er)...

From: Judy Seigel <jseigel@panix.com>
Subject: Re: Help with what I believe is a hardening issue
Date: Wed, 10 Nov 2004 01:28:59 -0500 (EST)

> Formaldehyde is a preservative; it does not go bad.

This is actually not the case. Formaldehyde goes bad in two major
ways. One is oxidation to make formic acid and other is polymerization
to make paraformaldehyde, which is the white stuff that precipitates
out. The latter can be redissolved and gain hardening action again,
but the former is ineffective as a hardener. This oxidation is
catalyzed by metal impurities like iron, like many other oxidation
process.

Also,

> I've kept the same bottle for 10 years, or longer, in fact until the
> contents dried into a white powder at the bottom of the bottle.

formaldehyde does not dry to make solid form. It is the polymerized
paraformaldehyde that does.

--
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)