Yes, formaldehyde is a gas. Maybe back in the "old" days it was termed that 
way for the pupose of distinguishing between the two. I was taught that way 
in school and the pathologists always used those terms to specify 
differnences between formalin (10%) and formaldehyde (37-40%).

At 12:54 PM 5/13/05, Jackie M O'Connor wrote:

>Formaldehyde is a gas.  Full strength formalin is 37-40% formaldehyde gas 
>in water.    10% Formalin is in effect 3.7 - 4% formaldehyde.
>10% Neutral Buffered Formalin is just that - 10% formalin buffered to a 
>neutral pH, usually with sodium phosphates.
>
>Jacqueline M. O'Connor HT(ASCP)
>Assistant Scientist
>GPRD Cancer Research
>Abbott Laboratories, Abbott Park, IL
>Jackie.OConnor@abbott.com
>
>
>LuAnn Anderson 
>Sent by: histonet-bounces@lists.utsouthwestern.edu
>
>05/13/2005 12:43 PM
>
>         To:        histonet@lists.utsouthwestern.edu
>         cc:
>         Subject:        RE: [Histonet] quick question about formaldehyde
>
>
>At 12:43 PM 5/13/05, LuAnn Anderson wrote:
> >Hi Joyce,
> >That is exactly what we were taught. formaldhyde=37% and formalin=10%
> >LuAnn
> >
> >
> >
> >>For all my years I have believed that formaldehyde was the 37%
> >>concentrate without buffers, and that formalin was 10% buffered... learn
> >>something new every day! Thanks John! -----Original Message----- From:
> >>John A. Kiernan [mailto:jkiernan@uwo.ca] Sent: Friday, May 13, 2005 11:31
> >>AM To: Weems, Joyce Cc: histonet@lists.utsouthwestern.edu Subject: Re:
> >>[Histonet] quick question about formaldehyde Dear Joyce, Formalin = 37%
> >>formaldehyde; so no, it doesn't make a difference. Formalin is not
> >>buffered; it does contain about 10% methanol, which is put in to retard
> >>polymerization. When diluted to make a 4% formaldehyde fixative, the
> >>methanol concentration is 1%. Buffering of the dilute solution offsets pH
> >>changes due to the Cannizzaro reaction. It also inhibits the formation of
> >>blood-derived "formalin pigment" which forms after fixation in an acidic
> >>formaldehyde solution. Tim Morken is correct in saying we don't know the
> >>extent of chemical change in 12 year-old formalin. The fact that there's
> >>no expiry date sugggests that it's not much. For what it's worth, I've
> >>used formalin that's more than 5 years old and fixation has been
> >>OK.                       John Kiernan                       london,
> >>Canada ---------------------------------------------- "Weems, Joyce"
> >>wrote: > > Also, John said "formalin" - was the solution formalin or 37%
> >>formaldehyde  - without buffers? Would that make a difference? > >
> >>Joyce > > -----Original Message----- > From:
> >>histonet-bounces@lists.utsouthwestern.edu >
> >>[mailto:histonet-bounces@lists.utsouthwestern.edu]On Behalf Of Morken, >
> >>Tim - Labvision > Sent: Thursday, May 12, 2005 2:08 PM > To: 'John
> >>Kiernan'; Andrea Grantham > Cc: histonet@lists.utsouthwestern.edu >
> >>Subject: RE: [Histonet] quick question about formaldehyde > > John,  you
> >>said "   Small amounts of methanol and formate ions are not going > to
> >>change the fixative properties." > > But after 12 years  will it really
> >>be a "small amount?" How do we know what > percentage of the solution
> >>will have been converted? > > Tim Morken > > -----Original Message----- >
> >>From: histonet-bounces@lists.utsouthwestern.edu >
> >>[mailto:histonet-bounces@lists.utsouthwestern.edu] On Behalf Of John
> >>Kiernan > Sent: Thursday, May 12, 2005 10:48 AM > To: Andrea Grantham >
> >>Cc: histonet@lists.utsouthwestern.edu > Subject: Re: [Histonet] quick
> >>question about formaldehyde > > 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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