> ...The gas law formula is PV=nRT  so V (volume) = n (avogadro's
 > number, 6.02 x 10 to the 23) x R (molecular weight, or weight of one 
 > mole ...

Exactly.  I was hoping someone had those figures at hand and would find 
the problem trivial.  It isn't for me, nor does it appear important 
enough to spend much time on it.  More below.

 > But the temperature to use for the calculation is problematic.  I
 > would suggest that you use the melting point of oxalic acid...

This is the question. To my mind, if the acid and the water sublimate,
at some moment, the volume would be at the temperature of vapourization
give or take,  In current practice, though, I doubt the entire volume of 
gas ever endures.

My interest in that volume, for the OA PLUS the water of hydration is 
merely that I assume that, at some moment in time, the OA and water 
expand into gas and wondering about accommodating that volume at 
vaporization temperature or slightly above, say in a balloon which would 
subsequently be deflated into an air stream.  How big would the balloon 
have to be to hold 2g of OA dihydrate vapour?  (Idle dreaming...)

 From casual observation using current devices, since the vapour is 
immediately intermixed with air at the ambient temperature, I assume 
that the gaseous phase must not last more than an instant.  The first OA 
to sublimate is apparently condensed and solidified again before the 
last OA in the vessel has been sublimated.

In the process of reaching sublimation temperature for the OA, the OA 
and the water of hydration part their ways, or do they?  Has anyone 
really analyzed what happens?  Do they recombine immediately on 
re-solidification or before?

The suggestions I have read are that the purpose of sublimating the acid 
is to create a mist of fine particles which coat the hive interior.  How 
these fine OA particles disable the varroa is not well described, but 
suggestions are that it affects their feet.  Other suggestions are that 
the varroa have more moist exteriors than bees and are therefore more 
vulnerable to OA than bees which are dry on the exterior.  We have 
observed bees running around acting normal when entirely coated with OA 
dust.  (We do not know their eventual fate).  OA is pretty much harmless 
to human skin unless moistened, at which point it becomes very corrosive.

I figure that understanding what is happening in a practical process 
that obviously works could help isolate the factors which make it work 
and potentially allow us to eliminate the unnecessary aspects.

It is entirely possible in my mind that distributing a fine OA powder 
though out a hive is the actual actor and that the sublimation and all 
that heavy gear associated with the heating and blowing could be 
unnecessary.

If a fine, fine dust could be created otherwise, distribution into hives 
could be as simple as using a pulse of compressed air or propane from a 
bottle, and all the clunky, expensive gear now used could be scrapped.

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