[Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde (lengthy)

[Bryan Hewlett]

Tim,

"Formal" is quite different, it is another name for Methylal
(dimethoxymethane) a flammable colourless, volatile liquid used as a
solvent.

Bryan

----- Original Message -----
From: "Morken, Tim - Labvision" <tpmorken <@t> labvision.com>
To: <histonet <@t> lists.utsouthwestern.edu>
Sent: Friday, February 04, 2005 2:33 PM
Subject: RE: [Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde
(lengthy)


> I think "Formalin" and "Formal" were trade names from a company and just
> went into common usage.
>
>
> Tim Morken
>
> -----Original Message-----
> From: histonet-bounces <@t> lists.utsouthwestern.edu
> [mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Bryan
> Hewlett
> Sent: Friday, February 04, 2005 11:24 AM
> To: histonet <@t> lists.utsouthwestern.edu
> Subject: [Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde
> (lengthy)
>
>
> I was hoping that John Kiernan would jump in reply to this issue with his
> usual eloquence! However, here goes.
>
> Confusion in terminology has been common since Blum introduced this agent
as
> a fixative in 1893! It never ceases to amaze me that this should be so,
the
> issue has been repeatedly addressed in all major Histotechnology texts
since
> before the early fifties ( my student days in the UK).
>
> The following information is from the 10th Edition(1981) of the Condensed
> Chemical Dictionary and the10th Edition(1983) of the Merck Index (the only
> ones at hand).
>
> Formaldehyde is a gas.
> It is readily soluble in water up to 55% and is commercially available to
us
> as 37%, 44% and 50% aqueous solutions which may contain up to 15%
methanol.
> These commercial grades are called Formalin.
>
> Formaldehyde solution (Merck Index)
> The USP grade is about 37% (37-40%)  w/v formaldehyde gas in water,
usually
> with 10-15% methanol added to prevent polymerization. This solution is
> considered to be full strength and is also known as Formalin 100% or
> Formalin 40 which signifies that it contains 40 grams of formaldehyde
within
> 100mL of the solution. It is this solution that produces most of the
> confusion since it is referred to and thought of as 100% Formalin.
>
> Paraformaldehyde (Merck Index)
> A white crystalline powder of polymerized formaldehyde, obtained by
> concentrating formaldehyde solution. Upon solution in water
depolymerization
> and evolution of formaldehyde occurs. Thus an aqueous solution containing
4
> grams of paraformaldehyde is essentially the same as a solution of 4%
> formaldehyde. There is NO such thing as a solution of paraformaldehyde.
> Right John?
>
> The concentration of formaldehyde used for fixation has been the subject
of
> much confusion (see above). The concentration of formaldehyde in compound
> fixatives varies widely - ranging from 0.5 to 15% w/v. The majority of
> fixatives, using formaldehyde as the sole fixative agent, have a
> concentration of formaldehyde between 2.5 and 4% w/v. The concentration of
> formaldehyde in a fixative should be stated as the percentage by weight of
> the gas, rather than as a percentage of the
> formalin(sic) or paraformaldehyde(sic) used to prepare it.
>
> Thus:
> "4% formaldehyde" - not 10% formalin.
> "4% formaldehyde, from paraformaldehyde" -  not 4% paraformaldehyde. "NBF
> means Neutral buffered formaldehyde" - (not formalin) and is 4% w/v
> formaldehyde in phosphate buffer pH 7.0- 7.2.
>
> Bryan Hewlett
>
> Consultant Technologist
> QMP-LS
>
>
>
>
>
>
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