<div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">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 (<a href="https://en.wikipedia.org/wiki/Enthalpy_of_mixing">https://en.wikipedia.org/wiki/Enthalpy_of_mixing</a>).</div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">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.<br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">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. <br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">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. <br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">Our local micro-distillery, which is an excellent venue (<a href="https://www.bigspringspirits.com/">https://www.bigspringspirits.com/</a>), 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..."</div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000">--John<br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;font-size:small;color:#000000"><br clear="all"></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><font size="2"><span style="font-family:tahoma,sans-serif">John E. Simmons<br>Writer and Museum Consultant</span></font></div><div dir="ltr"><font size="2"><span style="font-family:tahoma,sans-serif">Museologica<br><i>and</i><br>Associate Curator of Collections<br>Earth and Mineral Science Museum & Art Gallery<br>Penn State University<br><i>and</i><br>Investigador Asociado, Departamento de Ornitologia<br>Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima</span></font><br></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Sep 7, 2022 at 10:32 AM Robert Waller <<a href="mailto:rw@protectheritage.com">rw@protectheritage.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg6985215113941126053">
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<p class="MsoNormal">Hi Tonya,<u></u><u></u></p>
<p class="MsoNormal">Good for you in doing those tests to discover that!<u></u><u></u></p>
<p class="MsoNormal">The key is to remember that “mixing” and “dissolving” are two distinct processes that occur at different rates.<u></u><u></u></p>
<ol style="margin-top:0cm" type="1" start="1">
<li class="m_6985215113941126053MsoListParagraph" style="margin-left:0cm">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.<u></u><u></u></li><li class="m_6985215113941126053MsoListParagraph" style="margin-left:0cm">Those two separate components of the mixture gradually dissolve into each other creating a homogenous solution that will not separate.<u></u><u></u></li><li class="m_6985215113941126053MsoListParagraph" style="margin-left:0cm">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.<u></u><u></u></li></ol>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">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.<u></u><u></u></p>
<p class="MsoNormal">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.<u></u><u></u></p>
<p class="MsoNormal">Best,<u></u><u></u></p>
<p class="MsoNormal">Rob<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Nhcoll-l <<a href="mailto:nhcoll-l-bounces@mailman.yale.edu" target="_blank">nhcoll-l-bounces@mailman.yale.edu</a>>
<b>On Behalf Of </b>Haff, Tonya (NCMI, Crace)<br>
<b>Sent:</b> September 6, 2022 9:40 PM<br>
<b>To:</b> <a href="mailto:nhcoll-l@mailman.yale.edu" target="_blank">nhcoll-l@mailman.yale.edu</a><br>
<b>Subject:</b> [Nhcoll-l] Mixing EtOH<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-AU">Hello all,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Thank you!<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Cheers,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Tonya<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">-------------------------------------------------<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Dr. Tonya M. Haff<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Collection Manager<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">Australian National Wildlife Collection<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">CSIRO<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU">+61(0)419569109<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><a href="https://www.csiro.au/en/about/facilities-collections/collections/anwc" target="_blank">https://www.csiro.au/en/about/facilities-collections/collections/anwc</a><u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-AU"><u></u> <u></u></span></p>
</div>
</div>
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