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5 tube balancing argument

Bill Burnett bbur at wpo.nerc.ac.uk
Fri Oct 11 10:11:23 EST 1996

jpcd0 at mole.bio.cam.ac.uk (John Dixon) wrote:

>At the risk of starting a bandwidth hungry inconsequential argument

Sounds like a perfect activity for a Friday afternoon...

>Some one here was doing 5 minipreps (equal volume) and was loading a 12
>hole microcentrifuge, when he found that the balance tubes had been
>cleared away. He was about to fill another sixth tube to balance 3
>opposite 3, when I said that you can balance five anyway. This started a
>massive debate, which has now come down to three positions. 
>I reckoned that if you put three tubes in, in a triangle ie in holes 1,5,9
>these are balanced. Then you can balance the two others opposite each
>other in holes 2 and 8.

>One guy maintains that this is not balanced at all, on the grounds that
>you can split the fuge into two halves where one half has two tubes and
>the other has three, therefore it must be unbalanced. I am not convinced. 

You're right and he's wrong... It's clearly possible to split a rotor 
with 3 tubes in it into 2 halves one of which has 2 tubes and one of 
which has one, but you can still balance a rotor with 3 tubes... 
complicating things by adding additional pairs of balanced tubes makes no 
difference.  The proof of the pudding's in the eating and my 'fuge has no 
problems with this, but spits the dummy at the slightest hint of 

>Then another guy said that he balances five by putting them in as near a
>pentagonal position as he can ie 1, 3, 5, 8, 10. I dont think this is OK
>because you cannot remove a balanced pair to leave a balanced three,
>although I doubt it does much harm.

It's not okay because it's simply not balanced to start with...  

>Are there any centrifuge balancing experts out there?

Well, I can manage six on a good day, does that count?

>Apologies for innapropriate use of the newsgroup, but maybe some of us are
>trashing our fuges and more importantly several pints are resting on this!

Never balance a pint on a centrifuge
1) It contravenes safe lab practice.
2) It'll probably fall off.


Bill Burnett: bbur at dml.ac.uk            
Scottish Association for Marine Science
P.O. Box 3, Oban, Argyll, PA34 4AD.

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