I looked at the reference and notice that they mention variability in the
concentration of formic purchased.

"... we used a lowcost hydrometer ($5 at www.williamsbrewing.com) to obtain
exactly 50% FA (sp. grav. = 1.110). The hydrometer was needed because we
found considerable variation in strength of formic acid in containers that we
purchased; some were off as much as 30%. This may be one reason that
published reports gave variable results for the use of formic acid."
 
That is most interesting and makes me wonder where they were getting
it.  We purchased by the 210 litre drum from Univar and never doubted that
the product was exactly as described.

I suppose that an hydrometer would be useful to verify the concentration
purchased if there is any doubt, but once the starting concentration is
known, the math is simple and no hydrometer should be required.

I also wonder about the insistence on being precise in the concentration.  
For research purposes, this is admirable, but in practice the environmental
variability is such that minor differences in acid concentration should be
of no consequence.

"Beekeepers must also be aware that formic acid obtained from some
commercial sources may contain heavy metal contaminants; these may be
harmful to the bees, to humans and to the environment. "

I wonder about that, too.  What I investigated formic acid, I learned that
the acid from reputable major suppliers differs little from so-called "food-grade".

Has anyone encountered formic with more than tiny traces of metals?  I'm
guessing that there is more lead going into beehives from the air than we
could ever introduce with a formic treatment using any acid I have seen.

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