[Nhcoll-l] Antw: Re: FW: use of air to bubble through ethanol to mix solutions.

Tue Jun 22 05:24:05 EDT 2021

As Dirk already said - we make great efforts to get bubbles out of the
ethanol. I would nothing undertake to get additional bubbles in the
mixture.

All the best
Joachim

--  
Joachim Haendel

Center of Natural SciencesCollections
of the Martin-Luther-University
- Entomological Collection -

Domplatz 4
D-06099 Halle (Saale)
Germany

Phone:  +49 345 - 55 26 447
Fax:  +49 345 - 55 27 248
Email: joachim.haendel at zns.uni-halle.de

>>> Simon Moore <couteaufin at btinternet.com> 22.06.21 10.01 Uhr >>>
I have not heard of using gas to mix ethanol and water before and it
seems a rather elaborate / unnecessary process. Like Dirk, I have always
mixed my solutions together using a magnetic stirrer or just using a
glass stirring rod. For larger amounts, using a stick or larger rod
would seem to be fine. Letting the mixture rest is important as the
mixture will evolve dissolved air for at least a few hours.
I’ve only noted precipitation of white salts when diluting with a
non-purified water.

With all good wishes, Simon

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

www.natural-history-conservation.com

> On 22 Jun 2021, at 08:11, Dirk Neumann <neumann at snsb.de> wrote:
> 
> Good afternoon Tonya,
> interesting question - do you use pure ethanol, or denatured ethanol,
and if the latter, which denaturant is added?
> 
> If you use the bubbler to aerate the ethanol to fix it, my first
thought would not be the oxygen (assuming that you do not use pure,
bottled oxygen for mixing), but the carbon dioxide, which surely leads
to an acidification of the remaining water fraction, even more so, if
distilled or bi-distilled water is used to dilute the ethanol, because
distilled water has a very high affinity for carbon dioxide. Even though
a bicarbonate-puffer system establishes, the pH is rather at the low end
and usually around pH 4-5 in distilled water, so rather acidic. This
surely is different in tap-water (assuming it is of certified quality
without any additives such as chlorine), especially if it is calcareous.
But still, when mixing both fluids, you shift the dissolving
equilibrium, and what you can spot is a lot of fine air bubbles that
escape from the mixture (carrying capacity for the physically dissolved
gases shifted), and (usually) a fine white precipitation (calcium
carbonate).
> 
> Thus the carbon dioxide likely has more effect than the oxygen on the
acidity of the aqueous fraction of the mixture. 
> 
> Next step: secondary reactions like oxidation. 
> 
> While ethanol is a rather stable molecule, less stable molecules would
be attacked and oxidised first, because their unsaturated polar bindings
have the higher affinity to attract electrons. For example, residual
formaldehyde escaping from specimens might be oxidised to formic acid.
Same applies to highly polar denaturants like ketones, which are more
susceptible to be oxidised. The more such molecules are present and
oxidised, the less the ethanol will.
> 
> And you less likely can prevent this by mixing the ethanol with N2,
because stirring the mixture will also allow other gases to dissolve
(unless this is done in a hermetically closed atmosphere). And even if,
upon initial filling or topping, the fluid will have a lot of contact
with the surrounding air and will be stirred up, and carbon dioxide and
other gases will dissolve etc. ...
> 
> We you use a big stick to stir the fluids when mixing the ethanol in a
drum, we usually mix 60 litres and let it rest for two days until we use
it. We have two of these drums, which is sufficiently enough for our
daily work, and we are careful when filling jars to avoid any air
bubbles, i.e. we fill in the ethanol slowly.
> 
> Hope this helps,
> Dirk
> 
> 
> 
> Am 22.06.2021 um 05:12 schrieb Haff, Tonya (NCMI, Crace):
>> Hello all,
>>  
>> We typically use a fish bubbler to mix ETOH and water together when
we mix up 70% ETOH. We are iI recently got the below feedback about doing this – the dangerous goods
consultant says that this has the risk of acidifying the solution, and
that using N2 to mix the solution might be a better idea. Do any of you
have thoughts on this? If so, I would really appreciate hearing them!
>>  
>> Cheers,
>>  
>> Tonya
>>  
>>  
>> Email:
>>  
>>  
>> As per our conversation last week, you mentioned that CSIRO plan on
using air to bubble through their ethanol solutions to help mix the
solution. Can you please confirm if this is correct with CSIRO?
>>  
>> Normally when you mix/bubble air through ethanol solutions, you may
run the risk of oxidation of the ethanol, although this reaction is very
slow, you may generate some acetylaldehyde and eventually ethanoic acid.
>>  
>> Can you confirm with CSIRO if using nitrogen is better? This would
still help mix the solutions and would have the added benefit of
degassing the ethanol by removing dissolved oxygen from the solution.
This long term, would help minimise the risk of oxidation of the ethanol
and generation of acetylaldehyde and eventually ethanoic acid.
>>  
>>  
>> Regards
>> Paulo Da Silva
>>  
>> <image001.png>
>> Dr Paulo Da Silva
>> PhD, BSc(Hons), M.RACI, M.AIDGC,
>> NABERS Accredited Assessor
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> 
> 
> -- 
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> 
> 
> Dirk Neumann
> 
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> Fax: 089 / 8107-300
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> ---------
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> 
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