[NHCOLL-L:4202] Re: De-polymerization of Fish

[John E Simmons]

Chris,
In most cases, when formaldehyde-based preservatives become cloudy due to
polymerization of the formaldehyde or a preservative becomes cloudy due to
the congealing of lipids caused by low temperatures, the fluid will clear
when you warm it back up to room temperature (above 18).

I have done some informal experiments on this with jars of specimens by
placing a test group in the refrigerator and leaving a control group at room
temperature.  After a couple of days I was able to induce cloudiness in
several jars (having no budget, I did not test the cloudy fluid to determine
whether it was paraformaldehyde formation or lipids, but I did use both
formaldehyde-based and alcohol-based preservatives).  When the jars were
allowed to return to room temperature, in all cases the cloudiness cleared
up.

Cathy Hawks has cautioned that if you cool down a jar of a
formaldehyde-based preservative so that paraformaldehyde begins to form (the
cloudiness), then open the jar as it warms up, you run a risk of getting
more formaldehyde gas coming out of the fluid than you might get just from
opening a jar containing formaldehyde at room temperature.  Thus I would
recommend that you not open jars of cold cloudy fluid until they have
reached room temperature.

The reason that the amount of methanol in commercial formaldehyde varies
with the season is that more is added to formaldehyde manufactured in cold
weather to prevent the formation of paraformaldehyde.

I have not seen this happen, but I suspect that if you cooled a jar of
formaldehyde-based preservative sufficiently, a paraformaldehyde solid would
form in the solution that would not dissolve unless the formaldehyde was
heated very hot.  I have seen the paraformaldehyde solid form in jars of
commercial formaldehyde that were exposed to very cold temperatures or were
left on the shelf a very long time, but I have not seen it happen (yet!!) in
a jar of specimens.

You can purchase parafomaldehyde as a dry solid (powder, flakes, or pellets)
and mix formaldehyde solutions in the field, but this is rarely done due to
the difficulty inj dissolving the paraformaldehyde.  You can use a
synergizer such as sodium hydroxide as you boil the paraformaldehyde in
water, or mix sodium hydroxide and sodium carbonate if you don't want to
boil it.  In either case, you get a formaldehyde solution with a pH of
11-12, which then has to be adjusted to about 7 to use as a preservative
(the alkaline pH will cause tissues to clear).

Please let me know if you have any other questions about this.

--John

John E. Simmons
Museologica
128 E. Burnside Street
Bellefonte, Pennsylvania 16823-2010
simmons.johne at gmail.com
303-681-5708
www.museologica.com
and
Adjunct Curator of Collections
Earth and Mineral Science Museum & Art Gallery
Penn State University
19 Deike Building
University Park, Pennsylvania 16802-2709
jes67 at psu.edu

On Tue, Feb 17, 2009 at 10:21 AM, Del Re, Christine <delre at mpm.edu> wrote:

>  I have a question about the following information that I have been using
> to guide our off-site storage of fish collections.
>
>
>
> "The ideal temperature for specimens that were formalin-fixed and are
> stored in 70% (v/v) ethanol is 18C (about 65F) because this is cool enough
> to slow chemical reactions, yet above the range where formaldehyde may
> polymerize and lipids would congeal in the preservative fluids." *Simmons
> pg. 173-"Storage of Fluid-Preserved Collections" in Storage of Natural
> History Collections: A Preventive Conservation Approach.*
>
>
>
> What I do not know is if polymerization has occurred – do the fish
> de-polymerize at higher temperatures? I haven't found any info on this
> question, but I may not know where to look.
>
>
>
> With thanks, Chris Del Re
>
>
>
> Christine Del Re                      Voice:  (414) 278-2780
> Senior Conservator                 Fax:    (414) 278-6100
> Milwaukee Public Museum    e-mail:* delre at mpm.edu*
> 800 W. Wells St.
> Milwaukee, WI  53233-1478
>
>
>



--
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.yale.edu/mailman/private/nhcoll-l/attachments/20090217/37b9f937/attachment.html