[Nhcoll-l] Mixing EtOH

[John E Simmons]

Another reason to let the alcohol and water mixture sit for 24 hr before
using it (in addition to Rob's explanation of mixing vs dissolving) is to
allow it to cool off to room temperature. You have probably noticed that
when the alcohol and water are mixed the container becomes slightly warmer,
commonly called "heat of mixing," but more properly called enthalpy (
https://en.wikipedia.org/wiki/Enthalpy_of_mixing).

Several people over the years have questioned the use of compressed air to
mix the alcohol, as Andy described, assuming either that this would cause
more bubbles to form on specimens or that it would tend to acidify the
alcohol from the reaction with oxygen. In the years I was at Kansas we did
not experience either phenomenon with the alcohol. Bubbles rarely formed on
specimens, the alcohol is a steady 70% coming out of the spigot on the
container, and none of the problems common to acidic alcohol mixtures ever
were apparent.

The binary azeotrope is what causes alcohol to evaporate from the mixture
faster than the water, hence the phenomenon of "the angels share" that
evaporates from whisky barrels in storage. In an azeotrope, each substance
retains its own properties, so the alcohol evaporates faster than the
water. For this reason, I recommend that containers of ETOH never be left
open while specimens are being examined (always replace the lid) and that
alcohol that is poured into a tray be checked for concentration before
being returned to a container. It does not take long for the alcohol
concentration to drop significantly. The higher the alcohol concentration,
the faster the drop.

Paul and I have discussed concentrations before and we disagree on this
point. I prefer 70% for most uses because at that concentration alcohol is
an excellent biocide. Higher concentrations dehydrate specimens more, and
can interfere with the passage of alcohol through the tissues by
dehydrating the outer layers rapidly. Preservation in alcohol is always a
trade-off between good preservation and dehydration of the specimen. In my
experience, for most purposes, higher concentrations of ETOH (above 70%)
are not appropriate.

Our local micro-distillery, which is an excellent venue (
https://www.bigspringspirits.com/), sells a t-shirt that says "Alcohol is
not a problem, it's a solution" which of course is incorrect It should say
"Alcohol is not a problem, it is a mixture..."

--John

John E. Simmons
Writer and Museum Consultant
Museologica
*and*
Associate Curator of Collections
Earth and Mineral Science Museum & Art Gallery
Penn State University
*and*
Investigador Asociado, Departamento de Ornitologia
Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima


On Wed, Sep 7, 2022 at 10:32 AM Robert Waller <rw at protectheritage.com>
wrote:

> Hi Tonya,
>
> Good for you in doing those tests to discover that!
>
> The key is to remember that “mixing” and “dissolving” are two distinct
> processes that occur at different rates.
>
>    1. The mixing creates a mixture of 95% ethanol and 0% ethanol (water).
>    This is evidenced by a lack of optical clarity (waviness) in the mixture.
>    2. Those two separate components of the mixture gradually dissolve
>    into each other creating a homogenous solution that will not separate.
>    3. Before a true and inseparable solution is formed, ethanol poor
>    parts of the mixture can sink below ethanol rich parts and ethanol poor
>    solution can sink below ethanol rich solution.
>
>
>
> Therefore, the key is to continue mechanical mixing until the mixture has
> formed a homogenous solution throughout. As you have discovered,
> dissolution may take more on the scale of hours while mixing requires just
> minutes. Sorting this out will require some repeated testing of layers, as
> you have done, each time allowing some time after mechanical mixing for any
> possible separation (I suspect a few hours), until you are confident your
> mixture has become a homogenous solution.
>
> I suspect many people on this list will be interested in your results so
> please do share. Could also make for an interesting poster at our next
> SPNHC meeting and an entry in STASHC.
>
> Best,
>
> Rob
>
>
>
> *From:* Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> *On Behalf Of *Haff,
> Tonya (NCMI, Crace)
> *Sent:* September 6, 2022 9:40 PM
> *To:* nhcoll-l at mailman.yale.edu
> *Subject:* [Nhcoll-l] Mixing EtOH
>
>
>
> Hello all,
>
>
>
> I have a question about mixing storage strength (70%) undenatured EtOH.
> Typically we add the correct proportions of 95% EtOH and water to a
> container and paddle or invert the container repeatedly to mix the liquids,
> and allow it to sit for ~24+ hrs. The containers we like best to use for
> dispensing 70% EtOH are 20L plastic water containers with a tap at the
> bottom. Recently we used our digital alcohol meter to test the alcohol
> concentration from the top and bottom (tap) of one of these containers and
> found the alcohol concentrations wildly different  - ~80% at the top and
> ~60% at the bottom – despite having been mixed more than 24 hours earlier.
> This makes me really concerned that we could be regularly using
> concentrations that are much above 70% with specimens. I wonder if any of
> you have had a similar problem, or if anyone can suggest a solution? Is
> there a better way of mixing or of ensuring the solution is properly
> combined? Any thoughts appreciated.
>
>
>
>
>
> Thank you!
>
>
>
> 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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