[NHCOLL-L:2904] More on my closure test.

[Thomas Labedz]

NHCOLL-L subscribers,
	First, thank you all for the great suggestions and I hope someone with 
space and time can look further at the question of closures.
	Second, I didn’t try to design any kind of true experiment.  It was 
just an opportunity that got out of hand on the calendar and I thought 
would be interesting.
	Third, here are some more notes and numbers.  I’ve copied my original 
note to the bottom of this message for reference.
	The 3 mm decline in meniscus elevation corresponded to a 7.5 ml loss 
in volume.  I carefully opened the jar on my shelf and used a syringe 
to raise the meniscus to the ink mark made in 1995, measuring the fluid 
I added.  The total volume at the ink mark corresponded to 105 ml.  I 
carefully emptied the jar into a graduated cylinder to obtain that 
figure.  If the jar had been filled full to the collar it would contain 
approximately 136 ml fluid.  The percent volume lost over ten years was 
7.5 ml / 105 ml X 100, or 7.14%.  Had the same loss occurred on a full 
jar it would have been a 5.51% loss in volume.  Incidentally, the 
alcohol tested at 61% using a hydrometer (I have no way to know the 
exact alcohol concentration from 10 years other than it was around 60%, 
obviously it was higher).
	Fourth, to answer to questions from others.  My office has very stable 
temperature and moderately stable humidity controls, and no exposure to 
sunlight and UV filtered lighting. My office, where the jar sat for ten 
years, is 70 F and about 40-50% RH.
The collection room containing our fluid-preserved specimens has 
similar stability but about 5 F cooler.
	I too have about 15,000 jars of fluid-preserved specimens to monitor.  
Virtually all of our closures are the screw down type, and we have a 
wide variety of those including two-part canning lids, bakelite, 
plastic, enameled metal with paper liners, and these newer 
polypropylene lids with foamed polyethylene liners.  I replace closures 
with new ones at every opportunity, but the task is daunting and 
budgets are low.  My current monitoring scheme is that every five years 
every jar is lifted and examined for loss of fluid.  If fluid loss is 
noted the jar is pulled, alcohol concentrations tested, the jar and 
closure examined for defects, the alcohol brought to an acceptable 
concentration (70%), closed and replaced to the shelf.  We do not get 
the use of larger or better-known collections so purposeful, periodic 
monitoring is necessary.  My hope is that these new closures will 
expand that period from 5 to 10 years.
	The repeated use, opening and closing, of closures really does need to 
be examined to help estimate a product’s useful longevity.  Many of the 
closures in use in collections are probably designed for single use 
sealing of commercial products and not intended for such long-term 
operations.
	I would also like to see a comparison of the seal on wider (up to 110 
mm) polypropylene lids versus the smaller lids like the 48 mm one used 
in my experiment.  My gut feeling is that the seal is less effective on 
the larger diameter closures.
	Again, thank you all for your interest and support.  Now I've got to 
dust my shelf where that jar was sitting.
	Thomas E. Labedz, Collections Manager
Division of Zoology and Division of Botany
University of Nebraska State Museum
W-436 Nebraska Hall
Lincoln, NE  68588-0514
402.472.8366	fax 402.472.8949
tlabedz1 at unl.edu   www.museum.unl.edu

> Wanting to know more about potential alcohol evaporation rates from a 
> new jar closure for our fluid-preserved specimens I ran what I thought 
> was going to be a little, short-term experiment.  On December 1, 1995 
> I sealed a 4 ounce, tall-form, flint glass jar with a polypropylene 
> lid with a foamed polyethylene (F-217) liner.  The jar had been filled 
> with 60% ethyl alcohol (un-denatured alcohol diluted with distilled 
> water) to within 20 mm of the jar’s collar.  I then put a piece of 
> clear tape on the outside of the jar, set it on a shelf in my office, 
> and marked the bottom of the fluid’s meniscus with an ink line.  Then 
> I waited.  In ten years the level of fluid within the jar has dropped 
> 3 mm.  I had only intended for the experiment to run a year or two but 
> things kept getting busier and busier and I never got back to it.  I 
> hope this helps someone decide what type of closure to use in their 
> museum’s fluid-preserved collections.
>


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