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Diffusion Confusion. When discussing how odor spreads, surface area matters more than amount.


When discussing how odor spreads, surface area matters more than amount.

For example, 55 gallon drum of odor filled 3/4 of the way up, with a soda can sized hole in the lid, effusion describes how that odor would leave the container. Graham's law would explain this then.

Diffusion would be taking the lid of the 55 gallon drum and dumping an inch thick amount of odor on it and setting it out. That evenly distributed odor then would leave the source and try and balance out and "Fill" the space it is in like a room.

So the basic laws of odor: 1. Odor Drops with gravity, 2. Temperature impacts odor movement ( depending on molecular weight heat makes it rise, cold makes it drop), 3. Odor follows the path of least resistance, and 4. Odor, doesn't mix with liquids.

This all means that more odor escapes from an inch thick spread of odor on the lid, than 3/4 filled drum with a soda can sized hole.


This matters when we think about the vessels we use and the "weight" of the odors. When we choose to use a Straw or a Tin we need to know that the "odor picture" the dog sees matters. Also, there are more applications of these concepts than Sport Scent detection like Explosive and Narcotic detection to name a couple. My M.S. Ed. and B.S. In education make me want to understand it on behalf of all my students. The vapor pressure of the odor fills the vessel and looks to escape. When we choose the vessel we need to understand that.


Now I understand and common sense says more holes, more odor. The average straw opening is 0.3" in diameter, so when we place a Q-Tip with essential oil on it in the straw, then the side with the "tip" on it releases more odor than the stem of the tip. So the side of the straw with tip on it, at 0.3" of space to release odor, means that less odor is available to the dog. Choosing to understand vapor pressure and how odor diffuses or effuses is, in my opinion, a core skill and competency for training dogs to find liquid essential oils. No we don't need to teach our students the science, and the dogs don't need it explained to them, but as teachers/instructors/practitioners we need to know how to apply the science. Then there's the discussion of AKC buried hides and understanding how to train our teams to find them.



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