[Nhcoll-l] Mixing EtOH

[Simon Moore]

Hi Tonya,

This is because water and ethanol form a binary azeotrope when mixed. Someone may take the time to explain this phenomenon in more detail but have a look on the I’net. Even when thoroughly mixed, two miscible fluids of differing specific gravity will start to separate out once again if mixed in large quantities. I mix mine in 2.5 litre bottles but I’m only a ’small producer’ and I tend to upend the bottles gently before decanting, to ensure that the mix is accurate.
I am not sure whether introducing the paddle again after 24 hours will help to reverse this situation or whether it will keep on recurring.
A useful point to consider and hopefully John Simmons, Rob Waller et al., will be able to shed further light.

With all good wishes, Simon

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian,

www.natural-history-conservation.com




> On 7 Sep 2022, at 02:39, Haff, Tonya (NCMI, Crace) <Tonya.Haff at csiro.au> wrote:
> 
> 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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