Thanks to you both. It's very strange because :
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The Acetone is "99.5% Ultra Pure Acetone" from a very reputable Chemical Supplies company.
I hadn't evap tested it because of its kosher source...but perhaps I ought to now.
It had been in the freezer for 4-5 hours, and was too cold to keep your finger in.
I didn't time the pulls, but I was aiming for them to be one minute...they may have got up to 2 minutes maybe.
Definitely did a 24 hour "settle" though (I'm very anal about my settling / separating! :? )
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Anyway, thanks again for your comments...I have a new batch of Acetone just arrived today from a different source - so I will try a 30mg extraction with that to compare.
Actually, now I think of it...the whole evaporation went very quickly until the very last bit, which took ages to evaporate...like almost all of it was Acetone, but the last bit was like evapping water. Given that this is supposedly 99.5% pure, is that a bit odd?