Have you tried filling the extra space with fireplace insulation and then inserting the probe like in the picture below? That’s a 1000ml in a 2000ml OSS heating mantle. Have used it to vac distill smaller quantities. Temperature control is slowed down but it works for me. Might be worth trying.
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even if it’s a small stir bar it’ll make a noticeable difference. easiest way to see that would be to start your process, get to a stable vac level without the stir bar, note that number, then turn on the stir bar and watch your vacuum level weaken–meaning, the stir bar is increasing the rate of evaporation and adding more gas to weaken your vacuum (temporarily, if your pumps are up to the job you will likely re-stabilize somewhere near the level you were at before you turned the stir bar on). you’ll see a concurrent increase in what you’re condensing too.
difference between ‘no stir bar’ and ‘smol stir bar’ is far greater than ‘smol stir bar’ vs ‘bigger stir bar’. imo it’s silly to do this without some kind of agitation
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