Galiffus (Stranger)
08-08-02 19:22
No 343059
      Bumping prevented by glass wool in flask?  Bookmark   

From Vogel's Textbook of Practical Organic Chemistry 3rd edition, page 105, in the section on vacuum distillation:

'Bumping is said to be entirely prevented by packing enough glass wool into the flask to rise about 5mm above the surface of the liquid.'

Has anyone tried this, or does anyone have any specualtions about its likely success or drawbacks? It almost seems too simple to be true...

I'll most likely try it and report back, just wanted to hear any opinions.
(Hive Bee)
08-08-02 21:15
No 343097
      sounds like it would work  Bookmark   

also the pumice stones (Dr sholl's) that you use to remove corns from your feet would work too.
(Hive Bee)
08-08-02 22:33
No 343140
      RE: seems to simple to be true  Bookmark   

Preventing bumping is simple! I haven't tried this specifically with glass wool, but it certainly seems that it would provide enough nucleating points to prevent bumping.

The above post is purely fictional. Any resemblance to "real-life" is purely coincidental.
(Old P2P Cook)
08-09-02 05:02
No 343339
      Stirring is best.  Bookmark   

I imagine that the glass wool will work especially since Vogel says so. I used to routinely use teflon boiling chips to prevent bumping but I don't think that anything is as effective as vigorous stirring with a teflon covered magnetic stir bar.
(Chief Bee)
08-09-02 14:46
No 343461
      Speaking of teflon stir bars, does anyone else ...  Bookmark   

Speaking of teflon stir bars, does anyone else have a problem with getting their teflon stir-bars all brown after using them 2-3 times for distillations at 150-200C of mixtures containing a lot of tar? They can simply not be cleaned, the brown has penetrated into the plastic itself.
(Official Hive Approximator)
08-09-02 15:23
No 343469
      no comment  Bookmark   

couch terrorist
(Chief Bee)
08-09-02 15:35
No 343473
      Hey! Have you been papparazzing my stir bar ...  Bookmark   

Hey! Have you been papparazzing my stir bar collection? wink
(Stoni's sexual toy)
08-09-02 15:35
No 343474
      I've seen lots of brown and black stir bars, but ...  Bookmark   

I've seen lots of brown and black stir bars, but I have yet to blacken one myself. They are all still white.
What do you guys do with them? Distilling using the highest setting on your heating mantles? I don't think this is caused by tar penetrating the teflon, must be some overheating issue.

I'm not fat just horizontally disproportionate.
(Official Hive Approximator)
08-09-02 15:40
No 343477
      heh :)  Bookmark   

i believe the lower one went black after an high temperature rP/I reduction in phosphoric acid.

couch terrorist
(Synaptic Self-Mutilator)
08-09-02 17:47
No 343507
      I won't even post pics  Bookmark   

After distillations of MDP2P at 280C with a teflon stir bar, I think y'all'd be scared what my stir bars look like now. I think what happens is the teflon softens at lower temps, and other chemicals mix in with it and bond. I don't think it's until you get above 200C that the teflon really starts to break down.
(PVC-Analog Taste-Tester)
08-10-02 09:09
No 343962
      I've refluxed/isomerized many essential oils, and ...  Bookmark   

  I've refluxed/isomerized many essential oils, and have avoided bumping/splashes with a few chips of clean glass

Love my country, fear my government.
08-10-02 19:40
No 344067
      N.b. the quote was about *vacuum* distillation  Bookmark   

Judging by some of the replies, I may not have stressed enough that the passage I quoted was from the section on vacuum distillation. In my experience boiling chips and other strategies for providing nucleating points are useless under strong vacuum. Hence I was suprised that Vogel suggests that simply packing glass wool in the flask will totally prevent bumping under vacuum. Makes me wonder why anyone ever bothered with glass capillary air inlet tubes (maybe concerns about slight contamination from glass wool?). Terbium, I hear you regarding vigorous stirring being the best method. However, I don't have a stirbar suitable for distillation in a small pear-shaped flask, which I am currently contemplating. I will probably simply invest in such a stirbar, though I'll give the glass wool thing a go too.

Re teflon stirbars slowly going uncleanably brown, I can confirm that mine are no exception. Don't think they've ever been subjected to more than 180oC, either...
08-11-02 04:56
No 344240
      glass wool  Bookmark   

Interests me 2,
Vogels says pack the wool a cm or so above the liquid,.
Anybody tried this???

IQ is the rate of logic, as Wisdom increases logic, fear & compromise decrease to reveal objectivity
(Chief Bee)
08-11-02 17:20
No 344386
      I used it in o-chem lab when distilling ...  Bookmark   

I used it in o-chem lab when distilling salicylaldehyde once, and I can't remember having any trouble with bumping then... I remember that the soggy wool stunk (sp?) to high heaven when disassembling the setup afterwards though.
(Hive Bee)
08-11-02 20:43
No 344414
      An alternative  Bookmark   

When distilling under vacuum, you know when you get those really big bumps, a friend of mine used to pack fiberglass wool in the Y adapter to prevent overflow into the receiving flask.  There's an idea anyway.

"Holy shit, would you look at that?"  - Flip (8/4/2002)
08-13-02 04:47
No 344929
      fibreglass wool  Bookmark   

So simple, fibreglass wool, where have i been,
To ask a simple question, fibreglass wool is 100% glass right,
It's not just a resin polymer sold under the name "fiber glass", having used it so many times in the auto industry,
you just don't stop to question these fundamental things,.
Now that question would be a lot harder to answer in the"who wants  to be millionaire hot seat" right?-smilewink

IQ is the rate of logic, as Wisdom increases logic, fear & compromise decrease to reveal objectivity