> 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". :) *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html