[Nhcoll-l] Acidity in alcohol

Tue Oct 18 10:52:01 EDT 2016

Dirk’s solution (in both senses!) is probably the easiest option.  
Purified waters have their own acidity levels ‘built-in’ by the purification process, especially glass distilled waters (down to 4!)  pH levels are fine at 6 and OK-ish down to 5 but below that and decalcification and other denaturing processes are initiated.

With all good wishes, Simon.

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian,
www.natural-history-conservation.com 

On 18 Oct 2016, at 15:31, Dirk Neumann <dirk.neumann at zsm.mwn.de> wrote:

> 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
>> www.mhnc.ch
>>  
>>  
>> 
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