From sci.chem Tue Nov 12 18:29:27 1996
From: keith@eve.cchem.berkeley.edu (Keith Rickert)
Newsgroups: sci.chem
Subject: Re: Lab Accidents.......
Date: 10 Nov 1996 01:07:40 GMT
Organization: University of California, Berkeley

>2.  Another time, I was making trimethylarsine with methyl magnesium iodide 
>and arsenic trichloride, in an n-butyl ether solvent.  The TMA boils at 50C 
>and is distilled off from the higher boiling nBu ether.  Except it didn't 
>boil.  It just got hotter and hotter.  Well, everyone in the lab was nervous, 
>and I was the most nervous.  I realized that the magnesium iodide precipitate 
>in the flask was not going to act as a boiling nucleation, so I cleverly 
>dropped a boiling stone in through the condenser.  In about three seconds, the 
>flask was empty, all over the inside of the hood.  There was a stampede out of 
>the lab.  I stayed for a minute to close the windows so that the discharge 
>from the hood wouldn't blow back in, and my coworkers thought I had been 
>killed until I came out still holding the breath I had taken when the flask 
>blew.

This reminds me of something similar.In one lab I worked in,
as a summer job, we once got a large batch of tech grade
acetone which was contaminated with some sort of heavy oil.
The stockroom told us that 'The whole batch was like that'
and there wasnt much we could do about it till the next batch.
Ok, so we decided to redistill some of this, use a big still,
no problem.  Threw in a few boiling stones, let it warm up,
then wondered why there was no bubbling near the stones as
the flask warmed up.  Dropped in a new chip and the contents
bumped, fortunately not even over into the receiver, it hadnt
gotten a chance to get too overheated.
Looking at the flask afterwards, it became clear that if
you added the boiling stones while the solvent was cold,
they got coated with the heavy oil and failed to nucleate
much of anything.  Unfortunately, this meant that every batch
of this we redistilled, had to be accompanied by the same
dropping the boiling stone in while it was hot and
hoping for the best.  We were very relieved when we got
through this stuff and acceptably clean tech acetone was available again.

Keith
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