Ok I tried a run with a mason jar, the top is screwed on but not too tightly. Its been going half a day and I am not seeing any noticeable evaporation. Thanks for your advice, I will be able to achieve higher temperatures now without worrying that the solvent will be all dried up in the morning. The hot plate was set at 80c, and the temperature of the solution, checked at 2 hour intervals, was 40-42c. FYI, I used direct heat from the hotplate, no water bath. Do you think there would be any difference in the results when using water bath/direct heat?You definitely have to seal the container otherwise the heated ethanol will "rapidly" evaporate off, I use canning jars because they're ideally suited for the heat and pressures involved. The trick is to seal the container tight enough to prevent evaporation but loose enough to allow excess pressure to vent past the lid seal, exactly the same as when canning foods. Low temp extractions (<150F) don't produce significant pressure but those that approach Ethanol's boiling point (>170F) can and the pressure -must- be allowed to vent otherwise the jar could break spilling its contents into the water bath. The way I seal canning jars is I place a lid on the jar and then install the lid ring tightening it until it just contacts the lid and begins pushing it down against the mouth of the jar, that's tight enough. While air-tight at normal pressure excess pressure inside the jar can vent past this seal, exactly what canning jars were designed to do.
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