[Nhcoll-l] Acidity in alcohol
Dirk Neumann
dirk.neumann at zsm.mwn.de
Tue Oct 18 17:10:05 EDT 2016
... maybe just to add: depending on which sort of specimens are under
storage in your wet collection, they could either release larger amounts
of fatty acids (e.g. in insect collections with fats leaching out of
specimens) or acids such as formic acid which might dissolve directly
out of specimens which could result in even lower pH values. You
mentioned that you aim to restore on old collection: be careful with old
specimen jars or insects which are sorted to small glass tubes inside
jars. Low pH-values create a highly reactive surface layer on the glass
which not only corrodes the jar surface (you might know this effect from
dishwashers) but also specimens.
If crustaceans et al. are on storage, the pH might shift to values
around 8 or 9 due to the shells, which producing an likewise unhealthy
environment inside your specimen jar ....
Best would be to keep the condition stable, i.e. change the fluid only
if there is a real conservation issue that needs to be dealt with.
Hope this helps
Dirk
Am 18.10.2016 um 22:54 schrieb rw at protectheritage.com:
>
> Hi Nicolas,
>
> Your calculation of pH is good. I get 4.22 for 12mg/L and 4.27 for
> 9.6mg/L so all are in the same ball park.
>
> Roughly, a mg of acetic acid will dissolve about a mg of calcium
> carbonate (shell material) or a mg of hydroxyapatite (bone mineral) so
> that gives you a sense of how much reaction you can anticipate: one
> litre of solution will dissolve about 10mg of each of those materials.
> Depending on the composition of specimens and the fluid to specimen
> ratio that may or may not be significant.
>
> I think Dirk’s suggestion is very sensible. Can you find out whether
> or not your water is chlorinated?
>
> Best,
>
> Rob
>
> Robert Waller, PhD, CAPC, FIIC
> President and Senior Risk Analyst
> Protect Heritage Corp.
> 622 Simoneau Way
> Ottawa ON K4A 1P4
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>
> *From:*nhcoll-l-bounces at mailman.yale.edu
> [mailto:nhcoll-l-bounces at mailman.yale.edu] *On Behalf Of *Dirk Neumann
> *Sent:* October 18, 2016 10:32 AM
> *To:* nhcoll-l at mailman.yale.edu; Margraf Nicolas <Nicolas.Margraf at ne.ch>
> *Subject:* Re: [Nhcoll-l] Acidity in alcohol
>
> Dear Nicolas,
>
>
> it might be worth to compare the attached paper; my colleague did some
> tests which are summarized therein. Normal pH-paper tests will not
> work, you need to dilute the alcohol to get reliable measurements (see
> attached paper).
>
> If your tap water is not chlorinated and pure but calciferous, you
> might dilute your 96% EthOH with tap water to 80%; the dilution needs
> to rest for at least one day, as calcium carbonate starts to
> precipitate; the residual carbonate in solution gives you some sort of
> buffer capacity.
>
> Hope this helps
> Dirk
>
>
> Am 18.10.2016 um 16:00 schrieb Margraf Nicolas:
>
> Dear all,
>
> The MHNC is a small natural history museum located in the hearth
> of the Jura Mountains in La Chaux-de-Fonds, Switzerland. The MHNC
> team is currently re-conditioning the alcohol collection, changing
> containers and alcohol using an 80% Ethanol solution. The team was
> told to check the acidity of the alcoholic solution as acidity is
> not good for the specimens but had trouble doing so.
>
> Is a 9.6 mg/l acidity expressed as acetic acid too acidic? (12
> mg/l in 96% Et-OH diluted to 4/5)
>
> Additional questions:
>
> The alcohol dealer was asked about the acidity of the 96% Ethanol
> he provides us with. The value he gave us is 12 mg/l of acidity
> expressed as acetic acid. We tried to calculate the pH based on
> that value and obtain a value of 4.23. Does that sound right?
>
> We tried measuring the pH of the solution with both pH-paper and a
> pH-meter and found conflicting values. Is the pH-paper reading
> valid for an alcoholic solution? Or is the pH-meter value valid
> for an alcoholic solution?
>
> A pH of 4.23 seems too acidic to preserve specimens so we tried to
> calculate the amount of Na2CO3 necessary to neutralize the 12 mg/l
> of CH3COOH and obtain 10.6 mg/l. Is it correct (and sufficient) to
> add this amount of Na2CO3 to every liter of our 96% Et-OH solution?
>
> Any advice or help would be greatly appreciated.
>
> Thanks,
>
> Sincerely,
>
> N
>
> *****************************************
>
> Nicolas Margraf
>
> Collaborateur scientifique
>
> Musée d'histoire naturelle de La Chaux-de-Fonds
>
> Av. Léopold-Robert 63 - CH 2300 LA CHAUX-DE-FONDS
>
> T +41 (0)32 967 60 71 - mhnc at ne.ch <mailto:mhnc at ne.ch>
>
> www.mhnc.ch
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>
>
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Dirk Neumann
Tel: 089 / 8107-111
Fax: 089 / 8107-300
email: Dirk.Neumann(a)zsm.mwn.de
Postanschrift:
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---------
Dirk Neumann
Tel: +49-89-8107-111
Fax: +49-89-8107-300
email: Dirk.Neumann(a)zsm.mwn.de
postal address:
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