I store essence oils - lemon grass and eucalyptus to be precise - in dropper bottles.
For many months everything was fine, until recently I noticed a strong sweet smell of lemon grass in the bathroom. I though the bottle had fallen on the floor and broken. Nope - it’s still sealed tight but the oil has been drawn up into the glass dropper tube and seems to be seeping out through the rubber membrane bulb at top (where you squeeze to draw liquid into/out of the tube).
I squeezed the bulb to expell all the oil from the tube and screwed the cap back on, but the next day it had happened again. This is not happening with the eucalyptus oil, only the lemon grass.
Here’s a picture of the two bottles. I just squeezed it back to “normal” a few hours ago and it looks like the oil is already starting to be drawn up into the tube again. You can see the bulb at top is mis-shapen probably due to being constantly filled with volatile essence oil of lemon grass.
What’s going on and why isn’t it happening to both bottles?
My first thought is capillary action , though I’m not sure of the properties of lemon grass compared to eucalyptus, so I can’t say for sure if that makes sense.
It sounds like something is causing gas volume to increase inside the bottle and the pressure is forcing the liquid up the pipette- perhaps thermal expansion (is the bottle kept somewhere warm or sunny) or perhaps there’s something fermenting or growing (bacteria, yeast or something) in there .
If the bulb material is permiable to lemon grass oil/solvent, but not air, you may have Drinking bird type setup going. Evaporation of the oil from the bulb surface would provide the cooling needed to drive the system.
To stop the cycling, get a bulb made out of something that isn’t permiable.
Bingo. Usually this means you have buggers inside your bottle and it’s time to toss it. It’s awfully uncommon in essential oils, though, as they’re all antimicrobial to one degree or another. Is it in a carrier oil? I had a beautiful batch of rose hip seed oil once (rather expensive!) that got ruined this way. I’ve also had essential oils dissolve the rubber tops and they fall clean off even with the ring! (This only happens when the bottle falls on its side and the e.o. has prolonged contact with the rubber.)
What happens if you don’t screw the cap on tightly?
Microbes do fit the bill as long as the rubber bulb is semi-permeable. I don’t think I can go with the drinking bird scenario, because the gas in the bulb has to be going somewhere in order to draw the liquid all the way into the bulb. I’m assuming here that the bulb is not huge compared to the dropper. Otherwise PV=nRT would require one hell of a temperature differential for an ideal gas.
On second thought, non-microbial decomposition would also fit the bill
If gas is being generated inside the bottle, wouldn’t the bulb have expanded instead of being pinched down? Seems like something happened to cause a reduction of pressure inside the bottle.
