Hello all !
 
On May 1993 Kerry Clark asked ...
 
> Does formic acid also have such a fixed process of evaporation. Specifically,
> are there "threshold" concentrations of liquid formic acid that will produce
> different vapour concentrations?
>       This is of interest because liquid formic acid may be used in beehives
> to kill Varroa or tracheal mites. The usual 85 % concentration has been
> associated with increased queen rejection, while 65 % is apparently much less
> likely to result in such problem. Is there a way of predicting what
> concentrations intermediate between these two, would result in vapour
> concentration similar to that resulting from one or the other?
 
> Do you have the equivalent values for the concentration of formic
> acid/water that will evaporate from a 65 % formic acid liquid (and
> does temperature affect the ratio as well as the rate of evaporation?)
> from a 85 % formic liquid?
 
I answered to him (May 1993) ...
 
1/ The problem of formic acid is whole different as that of acetic
acid !  With formic acid, the azeotropic point give a boiling point of
107.1DC superior to the boiling point of the pure elements (water
[100DC] and formic acid [100.7 DC]).  May be because formic acid
increases the hydrogen bonds of the water in the solution !  The
concentration of the azeotropic mixture is 77% formic acid, 23% water.
 
With these properties, the two different solutions you can use (65%
and 85%) run quite different way when evaporating (remember azeotropic
schema) :
 
- when you evaporate a 85% solution (over the azeotropic point 77%),
the vapour is more concentrate (I don't know the number but perhaps
90-95% formic acid) than the initial solution (85%).
 
- when it is the 65% solution (before the azeotropic point 77%), the
vapour is less concentrate (perhaps 30-40% - I don't have the real
values but it is possible).  You can imagine the difference of
toxicity : for the bees and for the beekeeper of course ! ?
 
2/ It is may be an anthropomorphic view but I don't like at all the
use of formic acid to kill varroa or acarapis.  Actually we have some
others drugs, not harmless but effective and smoother than formic acid
which is, at the concentration used, a too dangerous product (see :
causes severe burns, keep out of reach of children, don't inhale gas
and vapour, in case of contact with eyes, rinse immediately with
plenty of water and seek medical advice).  It's very agressive
material - try : inhale very carefully -> I don't wish that to my
bees.  You never use a such treatment to another pet of you !?
Furthermore, it attacks (as acetic acid, but harder) all the metallic
hardware (iron !).  I think it isn't to be used by common beekeeper.
 
Hoping I have add a 2 cents at the discussion
Regards                                         Jean-Marie
 
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 Jean-Marie Van Dyck                    Fax +32 81 72 42 72
 B.P. 102                               email : [log in to unmask]
 B-5000     NAMUR(Belgium)              Medical school - Biochemistry dept
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