Re: Help with what I believe is a hardening issue

Christina Z. Anderson wrote:

> Candace,
> I feel for you...
> Formaldehyde is 37% solution of paraformaldehyde powder. You can
> get it from Tri Ess Sciences in Burbank CA (800-274-6910) and mix your
> own solution.

This is not the case!

Formaldehyde is a gas. Formalin is an aqueous solution of about 37%
formaldehyde, with the addition of up to 15% methanol, and sometimes
other additives as well.

A pure solution of paraformaldehyde is very unstable. It will suffer
quickly from oxidation (see Ryujis and my posting on that). After a
fairly short time it will also start to polymerize, due to the lowered
pH following the formation of formic acid.
 
I use it for histology, and it is made fresh for each use. Depending on
the application, it will keep from a day or two, up to a week. It is NOT
RECOMMENDED to make the solution at home. It requires heating to 70*C,
while adding sodium hydroxide. I can testify that the fumes from hot
formaldehyde solution are vicious! Unless you have the proper equipment
and skills, DON'T DO IT!

Best regards,

Tom Einar
Received on Wed Nov 10 08:43:44 2004