[Nhcoll-l] Bouin's formula

Thu Nov 17 06:01:28 EST 2022

Hi Tonya,
I’ve moved alot of material, both invertebrate and vertebrate, out of Bouin’s over the years through an alcohol series with no issues. You may not remove all traces of the original fluid in that a yellow tint will appear in the new solution over time, but any residual ‘Bouin’s’ is going to be highly diluted by this stage. Dried picric acid in jar threads etc is a potential hazard but as already mention a soak in water will sort this. Similarly this may be an issue with dried out material and this presents a good case for attempting rehydration of such material if it is to be retained.
All the best
Jules
From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> On Behalf Of Dirk Neumann
Sent: 17 November 2022 07:33
To: nhcoll-l at mailman.yale.edu
Subject: Re: [Nhcoll-l] Bouin's formula

Hi Tonya,

Simon's and Paul's  recommendation are straight forward, and we have to assume that specimens in Bouin's are present in many collections. They are usually very easy to spot because of the intense and bright light yellow colour of the fluid, which also stains the alcohol after the transfer of the specimens.

Often these specimens entered collections as research specimens after taking histological samples from those vouchers, therefore, they often are not stored in qualitatively high and especially tight closing jars we normally would use for storage of specimens. Thus transferring them to better jars is an option to stabilise them, but if you know that you have Bouin-preserved specimens in your collection, it is useful to know where these jars are and to have a closer monitoring for those jars in the collection. Often, the volume of the jars is less then 50 ml and thus these jars have a higher risk to dry up unnoticed.

Bouin's is a water-based acidic fixative, often leading to considerable shrinkage of tissues and of course loss of calcium carbonate from bones. If they are no longer needed or wanted for histology and should be transferred into alcohol, you would like to avoid rinsing them in water and exposing them for too long in low concentrated alcohol. In Fact - at least for larger and specimens with a more stable tissue matrix - it might be better not to step but to transfer them into 50% EtOH or even higher. A key factor here is the question how stable the tissues and tissue membranes are to withstand this sudden osmotic shock (as this more or less direct transfer extracts water from the cells, of course), or, vice versa, how damaged tissues and membranes are after prolonged exposure in an highly acidic storage fluid.

Usually, after the transfer into alcohol, more picric acid escapes from the specimens, which you can easily notice because of the vivid yellow staining of the alcohol. As we have to assume that this has an effect on the pH equilibrium (without wanting to dive into the details of "measuring pH in alcohols" here), it is worth considering to exchange the alcohol after some time has lapsed again. Time intervals depend on common factors as 'number of specimens', 'volume of the container', 'osmotic pressure', etc. My rule of thumb was if I could notice a considerable yellow stain after transfer, I would exchange the alcohol again.

Again and as often, not a clear cut answer, but hopefully somewhat useful.

With best wishes
Dirk

Am 17.11.2022 um 01:58 schrieb Simon Moore:

Hi Tonya,

I used to deal with Bouin’s fluid back in my histology days.  The only slight risk is if the picric acid content has dried to yellow crystals and you have screw top jars.  The picric acid is a tri-nitrate so yes, it’s unstable and might spark a bit in this situation.  If this is so, then immerse the jars in cold water so that the picric acid goes back into solution and is then quite safe.  I have had dry picric acid situations like this before and this method has always worked well and no fireworks!

With all good wishes, Simon

Simon Moore MIScT, RSci, FLS, ACR

Conservator of Natural Sciences and Cutlery Historian,

www.natural-history-conservation.com<http://www.natural-history-conservation.com>

On 16 Nov 2022, at 23:31, Haff, Tonya (NCMI, Crace) <Tonya.Haff at csiro.au><mailto:Tonya.Haff at csiro.au> wrote:

Hello all,

We have quite a few specimens (mostly macropod pouch young, turtle embryos and turtle organs) that have been preserved in Bouin’s formula, which contains picric acid. I know that picric acid is explosive on impact, and so we are wary of the potential risk that the jars of those specimens may pose. However, I don’t have any real understanding of what the actual risk of explosion might be… should these specimens and their jars be disposed of because opening them poses too much of a risk, or are the levels of picric acid so insignificant as to not pose a risk? Or is there some halfway point, but a way of safely opening the jars without calling the bomb squad? If any of you have thoughts or experience with this I would really appreciate it!

Cheers,

Tonya

-------------------------------------------------

Dr. Tonya M. Haff

Collection Manager

Australian National Wildlife Collection

CSIRO

+61(0)419569109

https://www.csiro.au/en/about/facilities-collections/collections/anwc

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Stiftung Leibniz-Institut zur Analyse des Biodiversitätswandels
Postanschrift: Adenauerallee 127, 53113 Bonn, Germany

Stiftung des öffentlichen Rechts;
Generaldirektion: Prof. Dr. Bernhard Misof (Generaldirektor), Adrian Grüter (Kaufm. Geschäftsführer)
Sitz der Stiftung: Adenauerallee 160 in Bonn
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