[Nhcoll-l] Preservation of invertebrate collections in AGW [Alcohol + Glycerin + Water]

[Robert Waller]

Hi Nate,
The glycerin will not appreciably effect ethanol concentration measurements based on density.
See: N. Boase and Robert Waller, The effect of propylene glycol on ethanol concentrations determined by density measurement. Collection Forum 10(2), 41-49, 1994.
The part of the solution being lost (expecting glycerin to have minor effect on ethanol and water partial pressure ratios) will be 90%v/v ethanol
See: Robert Waller and Tom Strang, Physical-chemical properties of preservative solutions I: Ethanol-water solutions. Collection Forum 12(2), 70-85, 1996.
You may want to simply top up jars with,  more than say half, fluid remaining with 90%v/v ethanol.
Rob

From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> On Behalf Of Shoobs, Nate
Sent: Thursday, August 26, 2021 1:12 PM
To: nhcoll-l at mailman.yale.edu
Subject: [Nhcoll-l] Preservation of invertebrate collections in AGW [Alcohol + Glycerin + Water]

Hi all,
I'm looking for advice on best practices for maintaining my collection's  fluid preserved mollusk specimens. It has come to my attention, that the preservative fluid used in the majority of the wet collection (approximately 50,000 gallons by volume) is not ethanol, but an apparently proprietary solution called 'AGW' which is a mixture of ethyl alcohol, glycerin, and water, sometimes with phenopthalein and methyl red pH indicators added (end result is purportedly 80% ethanol, 5% glycerin, 15% water, with <.1% of the pH indicator dyes.)

According to interviews with former curatorial staff, AGW was developed by the first curator of the collection in the 1960s as an alternative to normal 70% ethanol for invertebrate collections, as it supposedly had a greater resistance to evaporation, improved tissue flexibility for morphological study (this part seems true based on my observations of the collection), and coated specimens with glycerin to keep them moist in cases of jar lid failure. The phenopthalein and methyl red were apparently only added to provide color to distinguish the solution from ETOH.

Does anyone else have any experience managing alcohol-glycerin solutions like this?

Is it safe to rehouse specimens in new jars with 80% ETOH? This is my current plan for lots in jars that need topping off.

Given the heterogeneity of the solution, does anyone know of a possible method to measure the concentration of ethanol present in jars?


It seems to me that glycerin would interfere with both traditional hydrometers (different buoyancy in glycerin than water) and electronic concentration meters such as those made by Anton-parr. But please correct me if I'm wrong.

Thanks!
Nate
-
Nathaniel F. Shoobs, B.A., M.Sc.
Curator of Mollusks
Dept. of Evolution, Ecology and Organismal Biology
The Ohio State University Museum of Biological Diversity, Columbus, OH
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