Let me add several other things to my previous comments:

When we used formic, it was evaporated from pads, which were discarded.

1. I do not know if the minuscule amounts of impurities
    documented evaporate with the formic or stay in the pad.

2. Apparently the formic dissipates from the hive fairly rapidly,
   leaving no measurable residue after a time.  I do not know if
   the impurities leave with the formic, but if they are so bound
   with the formic that they have not been left behind to that
   point I wonder.

Any such question is a good question.  Assumptions should be tested, and
sometimes in the process, we are surprised by what we learn.  Also, with the
rapid expansion of knowledge underway these days, what was assumed correct
ten years ago may be subject to reconsideration today.

allen
A Beekeeper's Diary: http://www.honeybeeworld.com/diary/

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