> James I have read that heating OA too quickly makes 
> a difference in the vapors produced; that it will sublime into formic
acid. 
> Do you (or anyone) have any insight to whether or not that is true?

We know it is true, but we do NOT know if it actually happens with the sort
of vaporizers beekeepers use.

My source for this information was the "CRC Handbook", a carefully curated
book that is now in its 96th edition.
To call it "authoritative" is a bit of an understatement. 

The CRC handbook say that to heat Oxalic Acid to the sublimation point, you
want something in the range of 314 F to 370 F.
If you overheat oxalic acid you get carbon dioxide and formic acid.
At even higher temps, you get carbon dioxide, carbon monoxide, and water
vapor.

The temperatures that these evaporators can quickly become hot enough to
light a smoker, which would be above Ray Bradbury's "Fahrenheit 451" metric,
(the temperature of burning books).

There have been some attempts to address this point in beekeeper magazines
and in online forums, and these attempts have produced "more heat than
light".  :)

But the results from the IBRA (Francis Ratnieks, et al) paper prompts me to
want to ask Jerry to use some of his new thermal imaging gear to look the
actual surface temps of Oxalic Crystals in a vaporizer as it heats up.  My
comparatively primitive non-contact thermometer is only a single "pixel"
with a single temp reading, Jerry's toys are much more gooder, with lots of
resolution.

> What would be the definition of too quickly?

Before this new IBRA paper hit my desk, I would have said that without a
large thermal mass  or an actual temperature control to slow the temperature
rise, the electric coil would quickly heat up to well above 400 F, and you
would not be sublimating much Oxalic at all.  From what little I've seen
others do, and what I've done myself, this does not take long.  But the
Ratnieks paper specifically mentioned that they did not even let the
vaporizer cool off between hives, and look at the results they got.

There's several possibilities here, given Prof Ratnieks' team's results:

a) The first-stage degradation is to formic acid.  Formic acid vapors are an
effective varroacide in their own right.  Could we be so lucky as to have
the bulk of the Oxalic Acid either sublimate or decompose to the formic
acid, and only a negligible amount being heated to the point where even the
formic breaks down too?  This would explain how even apparently negligent
practices still give good control over varroa. 

b)  Maybe all we are really doing here is "vaporizing formic acid".   (To
only slightly misquote Marguerite de Navarre: "Dieu aide a quatre sortes de
personnes, aux fous, aux enfants, aux ivrognes, et les apiculteurs." [The
Lord helps four kinds of people: fools, children, drunkards, and
beekeepers.])

c)  It could be that the "dose" required is far less than everyone thought,
If absolutely everyone has been actually sublimating only a small fraction
of the Oxalic, and the rest has been decomposing every time anyone has tried
it, you would get a smaller dose - whatever fraction actually sublimated.
This scenario might explain why some vaporization attempts have been said to
result in significant collateral damage.  No one seems to have really logged
temperatures of the evaporator, and I seem to have been the only person to
ever build a thermally stable unit with a thermocouple and a pulsed power
feed, and I barely used it before scrapping it and going to the "dribble
method" solely for reasons of employee safety. 

d)  Oxalic Crystals MIGHT have much better thermal conductivity than I would
give them credit for having, so the entire dose MIGHT have time to melt and
sublimate before even a completely unregulated heating coil can get the
crystals from the minimum sublimation temp to the minimum degradation temp.
The surface temp of the evaporator is going to be hotter than the surface
temp of the crystals themselves, we want to look at both temps, and see what
the lag is between the two (Jerry, I'll do the scut work, if you shoot the
pix.)  

The above are listed in what I view as "order of plausibility".  The fact
that no one has apparently even looked at the engineering end of how to
sublimate the Oxalic over the past decade of use says much about how
beekeepers and "bee science" approach problems that involve engineering.
The word I am grasping for is "asymptotically".  :)




		

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