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but the decomposition point is definitely to be avoided.
Decomposition also is not critical. All chemicals of decomposition are known and in quantities of 1 gram are not an issue. And if temperature of heat source is to hight OA will sprinkle. The whole thing can bi reduced to: if sublimation is not very rapid and finishes in 2 minutes the temperature of heater is fine.
 

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Decomposition also is not critical. All chemicals of decomposition are known and in quantities of 1 gram are not an issue.
I am glad you brought this up. I am no chemist, but it makes sense to me that there is an appreciable difference in decomposition between heating large quantities vs. small quantities.
 

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In the case of the crack pipe comparison, the amount that crystallizes in the snout short changes the dose actually administered and if the next usage inputs a bit more heat the previous leftover gets added to the current one, which then gives a greater dose. Really oxalic vapor is quite flexible in its safety margins but guessing is not the best approach.
Thanks for addressing my question. I tend to agree with your take on crystallization. If I were to use the crack pipe method I suspect I would first try to avoid cristallization, by heating the entire pipe and I would clean the pipe after every use. Most importantly, I would try to avoid overheating.
 

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Decomposition also is not critical. All chemicals of decomposition are known and in quantities of 1 gram are not an issue. And if temperature of heat source is to hight OA will sprinkle. The whole thing can bi reduced to: if sublimation is not very rapid and finishes in 2 minutes the temperature of heater is fine.
Two minutes after the OA powder liquifies until the sublimation is finished would be about right. If you are familiar with the particular units habits you can cut power before completion and let it coast for the last part.

Two grams is the dose for a double deep.
 

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Two minutes after the OA powder liquifies until the sublimation is finished would be about right. If you are familiar with the particular units habits you can cut power before completion and let it coast for the last part.

Two grams is the dose for a double deep.
How exactly do you have a liquid phase if it sublimated?

Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water.

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Sublimation is an endothermic phase transition that occurs at temperatures and pressures below a substance's triple point in its phase diagram.

Notice the above includes "Pressure" in order to achieve sublimation. So what is it? does OA sublimate which is what would be required to convert to Formic Acid or does it Vaporize in which case it remains Oxalic Acid? What you are describing would be vaporization.

Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor There are two types of vaporization: evaporation and boiling.

Vaporization is what is desired while avoiding sublimation. I have yet to see anyone demonstrate that OA can be sublimated with these devices. I have yet to see anyone sublimate OA with any device.
 

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There are some people with actual educations that think that sublimation and evaporation are synonyms. Good explanation but lets just let them keep using the term sublimation since it's been used in articles and documents that describe the OAV process.
Arguing semantics with beekeepers gets old really fast.
 

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Valid point! Most here only care about killing mites. If adding heat to OA causes the OA to sublimate or evaporate and this kills mites then great. If the OA process is deficient in killing mites, then by all means let's discuss the semantics.
 

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How exactly do you have a liquid phase if it sublimated?
We are not actually using OA but OA dihydrate.
From Wikipedia: "Typically, oxalic acid occurs as the dihydrate with the formula C2H2O4·2H2O"
Dihydrate liquefies and water evaporates, then pure OA is changing phase from solid to gaseous (sublimation). Soon after OA is again in solid phase (crystalline form).
 

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Dihydrate liquefies and water evaporates, then pure OA is changing phase from solid to gaseous (sublimation). Soon after OA is again in solid phase (crystalline form).

A very concise and correct description of the process we do when treating for mites with Oxalic Acid.
Some people are confusing themselves and others while trying to get their heads around it.
 

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Just watched my OAV do it's thing and it's not sublimating.

From the Varrox instructions:

2. MODE OF ACTION
" Oxalic acid is added to the pan, then the appliance ... As a result of the heating action of the pan, the oxalic acid liquifies and vaporises. Oxalic acid vapour fills the hive..."

Apparently the English instructions are written in Great Britain English.

Now would be a good time to re-visit the concept of "latent heat". That explains why the solid does not completely turn to liquid before it vaporizes. Oh it liquifies just not all at once.
 

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aunt betty; I thought you said beekeepers were not interested in things like "latent heat" and all those semantic things;) Maybe when it thinks no one is watching your OAV sublimates!
 

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I searched this thread figuring someone would have already asked this but not so far??
Anyway how can one treat with OAV if a top entrance is used? Is the vapor lighter or heavier than air?
Thanks
 

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I searched this thread figuring someone would have already asked this but not so far??
Anyway how can one treat with OAV if a top entrance is used? Is the vapor lighter or heavier than air?
Thanks
Make a 2" shim/rim the same size as the hive body. Cut a slot in the shim for the Vap. Place the Vap on a 1/4" piece of plywood (4"x4") right on top of the frames. (The plywood is to keep the frames from scorching. Cover all with the inverted top cover. Connect the vap.
As to the vapors. They will spread throughout the hive as a mist from a waterfall. The bees will fan it as well.
Not hard at all.
 

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Hello
It is true that between 100ºC and 160ºC oxalic boils because it loses water of hydration. But between 160ºC and 200ºC (more or less) I have always seen that oxalic also continues to boiling in a certain way, and gradually disappears. I can not clarify to what extent sublimation or evaporation. Apparently, it seems evaporation. Maybe that happens because the temperature is not uniform in the pan, and the process is not simultaneous in all areas.
 

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Hello
It is true that between 100ºC and 160ºC oxalic boils because it loses water of hydration. But between 160ºC and 200ºC (more or less) I have always seen that oxalic also continues to boiling in a certain way, and gradually disappears. I can not clarify to what extent sublimation or evaporation. Apparently, it seems evaporation. Maybe that happens because the temperature is not uniform in the pan, and the process is not simultaneous in all areas.
I added bold to the above quote. My comment. Exactly, a simultaneous process would be called an explosion. You don't see that with most materials.
 

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I will agree with the idea that what is boiling "Could" be other substances such as water boiling off. I have considered that and looked for informatin in regard to OA specifically. Does pure OA melt and boil or not. and have not come up with anything yet. Other than OA vaporizes at 315 degree but will sublimate at the higher temperature. so it is capable of doing both but requires a higher temperature for sublimation. sublimation is also what would convert it to Formic Acid. Coming full circle it would require the OA being at a higher pressure to even reach that higher temperature required for sublimation. And that is the best I have been able to gather information and that information is not of the highest calibur of reliability. Basically piecing together fragments here and fragments there. So both claims are true. vaporization of OA will produce crystals of OA while sublimation will produce Formic Acid. the question is is are we capable of sublimating OA and OA hot plate in a hive and I say no way unless you place that hive in a pressure chamber.

The idea that the OA vapor will get hotter simply becasue it is in a hot enough environment is nto true. OA cannot and will not take on any more heat unless it is placed under more pressure. all that other heat will do a lot of other things but it will not get the OA hotter. The OA cannot take on more heat. So OA starts out at room temperature. is exposed to a hot plate. IT increases in temperature to a certain temperature. at that point it can no longer take on more heat so it does something else with that energy. It melts. melting requires energy becasue it is work. After it melts it has to find something else to do so it vaporizes. Vaporization is converting to gas and this conversion also requires energy. So as the OA increases in temperature how it uses the energy of the heat changes. From warming to melting to vaoprizing. next it will combust.

Now if you put the oa in a pressure chamber you could get it hotter than that 315 degrees that normally it would have melted becasue Under pressure it can withstand more heat. get it hot enough by apply enough pressure and once again it will reach a temperature that it has taken all it can. it will then break down into other chemicals Formic Acid being one of those. a completely different use of he energy it has to do something with. Think of it as so much energy to expend it actually requires the molecules of OA being torn down and recombined. Btu you have to have leaped frogged over that melting temperature to get to energy level that high. and that would require higher pressure.

Keep in mind I am making a distinction between how hot OA while solid or OA as a liquid or OA as a gas can get. Since Sublimation is conversion directly from a solid to a gas. then of course we are discussion how you can get solidified OA past its melting temperature to it's sublimation temperature.
 

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sublination is going directly from a solid to vapor state, evaporation is going from a liquid to a vapor. to "evaporate" a solid, usualy the solid melts and evaporates. a liquid quickly evaporating we call boiling. slow sublination is called "freeze drying",,, unless your hobby is combining vocabulary and thermo-dynamics we are trying to split hairs here. i do not know what difference this makes??
 

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Is it fact or fiction that oxalic acid breaks down to formic acid, carbon monoxide and water when it undergoes sublimation? If it is false we can forget about that whole idea!

According to the above post sublimation will only occur at a higher temperature than vaporization. Not talking about adding more heat energy; heat and temperature are not even close to being synonymous!

OA has been used as a catch all term but as viesnest pointed out the two forms of it monohydrate and dihydrate have very different properties. Some of the arguments here seem to take for granted they are identical. In the form beekeeps will see the OA Dihydrate first has to be converted to the monohydrate which is a solid from whence the sublimation occurs. We see this as melting into a liquid as the water boils off. If you apply energy too quickly it will boil over or splatter. As the water boils off the percentage of solids will increase and some vaporization or sublimation will start to occur. As has been mentioned these processes will overlap and occur together.

I think everyone is familiar with how a drop of water will dance around on a hot stove top supported by the layer of steam escaping from it.

Now if you use drops of muddy water or containing dissolved solids you will see colored trails where the water droplet danced around. The water drop itself would not be above 212F, (its boiling point), but the temperature of the steam layer between it and the stove will be above this temperature otherwise no heat would be transferring into the droplet but we know it is getting smaller so have to assume a temperature differential. Note, the deposited mud or dissolved solids underneath the water ball or in its trail are quite free to rise to the temperature of the stove top.

The oxalic acid monohydrate that is left behind as the water of hydration is driven off would be in contact with the pan of the vaporizer in a similar situation as the dissolved solid in the dancing water ball is it evaporates.

What is the decomposition temperature? I think it is a fair bit higher than the vaporization or sublimation temperature and unless the pan is greatly over driven I doubt there would be more than a rather small percentage of the charge that experienced it. Somebody must have deemed it to be of some importance though as it used to be quite a precautionary advisory. Unless we ensure proper sizing of heat input by design or luck, we should not assume that portions of the pan are not at some higher temperatures than some of the contents and we also cannot assume that some solids cannot in that scenario, be overheating.

Incidentally many substances will sublimate from the solid to the vapor without going through the liquid stage and often at a much lower temperature than the melting point. Water is one such substance.
 
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