Re: Help with what I believe is a hardening issue

Possibly even straighter...:

Ryuji Suzuki wrote:

>Just to set the facts straight(er)...
>
>
>>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.
>
>
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. It means that while some molecules
turn into acid, an equal number of molecules are turned into the
alcohol. By adding the alcohol, the formation of the acid is prevented).
If there is only a little bit in a bottle (or a very long storage time,
with axxess to oxygen), oxidation may still be a factor, but I would be
surpriced if it has any major practical influence. The formation of
paraformaledhyde is a very real problem, though, and I've had bottles
starting to precipitate in just a couple of years. Btw. formaldehyde
should be kept at room temperature, as keeping it in the fridge
accelerates the polymerization into paraformaldehyde.

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.

Best regards,

Tom Einar
Received on Wed Nov 10 08:33:47 2004