If you are doing PMMA work, a dessicator under vacuum in the refrigerator
basically doesn't work.  It is best to vacuum before putting into the
refrig for 4 hours or so,  then release vacuum, tightly cap the jar and put
that into the refrigerator.  

Having been through this, I tried vacuuming, going into refrig, and it was
a bust. Besides that, the grease you use seizes up and you can't get the
lids off after letting them sit for a day or so! I do not know what the
physical explanation is, but I am not sure that the vacuum draws very well
under cold temperatures, and you would need to put the vacuum pump in a
HOOD! to avoid methacrylate fumes.    

As for dessicators, you can buy any kind from Fisher, VWR, etc.  make sure
they are glass, MMA monomer fumes will eat plastic dessicators.  You can
also buy O ring dessictors, Wheaton, to avoid using grease. The O ring
expands in presence of fumes, you need extra O-rings which can be hung
inside a hood to go back to normal size.  These dessicators will not hold a
vacuum after a time due to O-ring expansion, but are wonderful for a days
work under vacuum at RT, no more messy vacuum grease. The same goes for the
stopcock area, these are ground glass surfaces, and need to be kept clean
in order to turn.  

Ground glass dessicators must be cleaned of grease more often than we
wanted to deal with - acetone and xylene will do that job, but if grease
sets up like hard, concrete like glue on the ground glass area, you will
have a mess trying to get it open. Been there, done that, had to shut the
door from bad language!  

YOu also need to have a dessicator cage or plastic guard in case the glass
desiccator explodes, rather implodes.  Dessicator sits in this cage while
drawing vacuum and under vacuum. 




 and At 06:48 PM 8/11/02 -0500, you wrote:
>I need a purchase source for a good vacuum dessicator that has a control
>stop cock to allow pressure in and shuts it off to maintain pressure.  This
>dessicator will then be place in a 4 deg C fridge for a number of days.  I
>hope to maintain the same vacuum pressure all through out while in the
>refrigerator.  Any ideas? (a source will be nice).
>
>Boring a hole in the fridge to maintain pressure is not an option.  I will
>be using a plastic/monomer organic solvent(Methyl Methacrylate) in the
>dessicator.  It needs to be under vacuum pressure.
>
>Thanks histonetters(especially in plastic)
>
>
>
Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
19th and Lincoln St
Bozeman MT 59717-3610

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