water floats on oil?

Nicola Collie alocin at sanger.otago.ac.nz
Tue Mar 1 18:13:43 EST 1994

Roger Mitchell (rogerM at qimr.edu.au) wrote:
> This is just an observation I have noticed recently when doing some PCR 
reactions. After setting up the reactions I place the tubes opened into the PCR 
>  machine (Perkin Elmer 480) and add two drops of mineral oil (Sigma) by a
>  sterile pasteur pipette, close the lids, then immediately begin the relevant
>  file for the reactions. Later I have checked the machine to ensure all is
>  going well,(you never can tell when FATE strikes you down) and noticed 
condensation inside the lid of some of the tubes, though not all. 
>  and WHY the water can escape from under the oil layer to be deposited by
>  evaporation onto the lid of the tube? ( by the way the PCR reaction does
>  work, despite this transgression of the laws of PHYSICS)
Perhaps your oil has a small amount of water suspended in it ie an
emulsion.  This could evaporate out of the oil when the tube is heated.
BTW, I have seen this myself - there is usually a fine mist on the side
of the tube just above the oil.

Nicola Collie
alocin%sanger at otago.ac.nz

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