Two things could have happened to unopened
formalin in 12 years:
1. Polymerization (to paraformaldehyde). This is
   evident as a white precipitate. It slightly
   reduces the concentration in the liquid,
   but that does not matter for fixation.
   Polymerization is accelerated by low room
   temperature, and it is claimed that the
   process can be reversed by autoclaving(paper
   in Stain Technol about 40 years ago).
2. Cannizzaro's reaction, in which 2 molecules
   of formaldehyde react together, producing
   one molecule each of methanol and formic
   acid. This happens in all formaldehyde solutions
   and causes lowering of the pH. This doesn't matter 
   if you make a neutral buffered fixative solution. 
   Small amounts of methanol and formate ions are not 
   going to change the fixative properties.
Bottom line: OK to use, but be sure to check the
pH of the working fixative solution and adjust if
necessary.
-- 
-------------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan[AT]uwo.ca
   http://publish.uwo.ca/~jkiernan/
   http://instruct.uwo.ca/anatomy/530/index.htm
_______________________________
Andrea Grantham wrote:
> 
> One of the labs here is closing and they have a case of formaldehyde,
> 37.5%, that they are trying to give away. They have had it in their lab
> since 1993. The bottles have not been opened. Is it still good to use?
> Andi
> .....................................................................
> : Andrea Grantham, HT(ASCP)     Dept. of Cell Biology & Anatomy     :
> : Sr. Research Specialist       University of Arizona               :
> : (office:  AHSC 4212)          P.O. Box 245044                     :
> : (voice:  520-626-4415)        Tucson, AZ  85724-5044    USA       :
> : (FAX:  520-626-2097)          (email:  algranth@u.arizona.edu)       :
> :...................................................................:
>            http://www.cba.arizona.edu/histology-lab.html
> 
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