Van & Little John,
The other cool thing about Oxalic Acid (vaporizing) is that it's most effective when used correctly. Having been on a farm the most of my life one thing I know first hand is just how quick you can loose an animal, a crop, or something else, plus everything has a window. You must operate within that time frame. That's why I read and read about what folks did with their bees to keep them alive. I started on this forum board and read backwards for a year's worth of time. I got to reading how the beeks in Europe have been successfully applying the OAV method for 30 years or so. I didn't see any other choice. At that point chemicals or no chemicals I was planning to keep my bees alive. The only foreign thing I have introduced to my hives has been OAV. Like you said, it crystalizes and the bees clean it up. I went from one, to three, ect and now my problem is trying to get BELOW the number of hives I desire to have. 30+ swarms in a year's time is a norm for me. This year I hived at least 25 swarms, and said goodbye to at least 10 that I couldn't get. I later sold 20 of them as nucs.
OAV - You can't argue with success!