[psm1212]

I learned something interesting a few weeks ago listening to Dr. Cameron Jack discuss oxalic acid applications. There has long been great confusion among beekeepers about whether we were actually vaporizing or sublimating oxalic into our hives.

Vaporization being taking a solid, converting it to liquid and then to gas. Sublimation being taking the solid and converting it straight to gas without ever liquefying it.

According to Jack, oxalic acid dihydrate, which is the approved compound in the US for treating varroa, is vaporized and not sublimated.

Only pure oxalic acid can be sublimated directly from solid to gas.

Virtually all of us (at least in the US) use oxalic acid dihydrate, therefore, we are vaporizing and not sublimating.

Many of you probably knew all of this, but that was not my previous understanding of the reaction. Thought I would share.

 

[johno]

Maybe we are just playing with words hers as there might be a difference in the reaction between heating up anhydrous Oxalic acid and oxalic acid dihydrate. But I think the importance here is that the water of crystallization provides the pressure which forces the vapor into the closed hive, but I am sure you would not get those tiny crystals if the OA did not sublimate. I think that the liquid we see from the heated OA is the water being released as the OA starts to become a gas.

 

[psm1212]

I honestly don't know johno. Before listening to Dr. Jack, I was under the impression that we were sublimating the oxalic acid dihydrate.

Here is the link to the podcast with Dr. Jack. I think it is a little over 20 minutes in.

https://podcasts.google.com/feed/aH...1NDBiZGQtMDc0OS00NmJlLWJkYzgtMzNmMTBiZDk5NGI4

 

[msl]

the device is a heat vaporizer... weather it goes liquid to gass (like the water in OAD) or from sold to gas doesn't mater, the tool still turns things to vapor.

Anhydrous sublimates after as the water is cooked out of it. while is may be a "liquid" supersaturated soulstion for a bit (the "splatter" you some times get), the OA is in a dissolved state and a sold not a liquid

How does oxalic vaporization work? In the CRC Handbook of Chemistry and Physics we find that upon heating oxalic acid, the water of hydration boils off first, then at 315°F the oxalic acid starts to sublime (go directly from solid to vapor), and finally at 372°F any oxalic acid which has not yet sublimed decomposes to initially to formic acid and carbon dioxide, and then to CO2, carbon monoxide, and water). One of the problems with some vaporizers is that they get too hot too quickly and decompose, rather than evaporate the acid.

http://scientificbeekeeping.com/oxalic-acid-heat-vaporization-and-other-methods-part-2-of-2-parts/

 

[psm1212]

msl:

Jack's point is that we are not using oxalic acid. We are using oxalic acid dihydrate. Pure oxalic acid would sublimate. Oxalic acid dihydrate does not. It must pass through the liquid stage. I posted a link to the podcast above where Jack explains it. Like I said, it was news to me.

 

[msl]

I will dig a bit deeper later
But on face value OAD melts at 101c, the water boils out of it and it becomes sold OAA, at 189-191c OAA melts, at 190c the OAA boils in to vapor, or sublimes depending on the melt point.. but +-1c doesn't mater in the practical sense like tossing a 1g ice chip on a white hot steel plate vs a 1g water drop the end is the same.

 

[msl]

Indeed that's what happens

Set the band heater vap to 115c, once to temp I loaded a charge
ended up with a pool of slightly bubbling liquid (very tiny bubbles).. a little bit of Vape comeing off.
Changed the setting to 150c.. by the time it hit 125c it was bubbling rapidity(very large bubbles), by 150c it was a dry sold, little bit of vape coming off
turned the heat back up to 230c and the sold started subliming hevey at 185 or so and was gone by 200

my observation is right in line with the CRC Handbook of Chemistry and Physics refrance and my sujested range in post 6


So it appears we do melt OAD , boil out the water to turn it to sold OAA then sublime the OAA
if we were vaporizing OAD as Dr jack suggests the vapor should have all boiled out of the liquid, not changed to a sold state