ahill
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distillation - seperating fractions under vacuum
Hi - I'm a pretty raw beginner teaching myself lab techniques at home - I've done a few distillations with moderate degrees of success, and have been
recently playing around with using vacuum.
I just found this piece of glassware which is something I haven't encountered before - and am wondering if it is the answer to some of the challenges I am
experiencing.
When performing a distillation, discarding the different fractions (heads and tails in brewing lingo) is fairly obviously often important. However the
actual mechanics of how to do that when performing operation under a vacuum is something that has eluded me. Undoing clamps, releasing vacuum,
separating glass joints, swapping a receiver out, and then reassembling and reapplying vacuum every time I get the feeling some boundary or other has
been passed is not super practical.
What is the proper way to deal with separating fractions under vacuum - is the thingy above (a distillation receiver) part of the solution ? I have a
mental image of mounting the thing at an angle, and rotating it to send the distillate to the next flask.
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Mailinmypocket
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It is called a cow receiver. Look it up on google or lab manuals. Basically you affix a flask to each neck and rotate the receiver when you are
wanting to switch the receiving flask.
Note to self: Tare the damned flask.
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Metacelsus
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I've also seen a piece of glassware that allows disconnecting of a flask from the rest of the apparatus, while maintaining vacuum, and replacing the
flask with another. It uses two stopcocks as sort of an "airlock". (This was at a university chemistry lab, and I haven't seen any such pieces
anywhere else. It might have been custom-made.)
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Boffis
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@Cheddite Cheese the "airlock" thing you are referring to is called a Perkin's Triangles and it is basically what you describe. It has a small
reservoir separated from the receiver flask by a stopcock. The rest of the piping and stopcocks simply changes the flow of gas/vacuum so that you can
isolate the receiver and change it without letting down the vacuum in the rest of the equipment. The are standard glass ware but expensive. Second
hand ones come up on ebay from time to time at reasonable prices. They are much more elegant when working with large numbers of fraction.
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ahill
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Ah yes - a cow receiver. Just the business. And what a great name - I've been chuckling since I searched on it and found this image - very uddery !
Keeping to the stockyard theme I see there are pig receivers / adapters too - I think they are exactly what I am after. Thanks !
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