Re: Xylene BeadsX

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From:"J. A. Kiernan" <>
To:"Colbert, Laurie" <>
Content-Type:TEXT/PLAIN; charset=US-ASCII

On Tue, 23 May 2000, Colbert, Laurie wrote:


  You can buy granular material that absorbs water. It's called
  _molecular sieves_ and your chemical catalogue should have
  explanations about which type to use for various solvents. A
  layer of molecular sieves in the bottom of a bottle of alcohol
  or acetone can ensure that it's truly 100% anhydrous solvent.

  BUT water and xylene don't mix. The water sinks to the bottom
  as droplets. The only way you can get water invisibly in xylene
  is if there's also quite a lot of alcohol present. Removing
  water from an alcohol-xylene mixture would not leave you with
  a liquid suitable for immersing slides in before coverslipping,
  because alcohol does not mix with the usual resinous mounting

  Xylene collects two contaminants: alcohol during dehydration,
  and dissolved wax during de-waxing of mounted paraffin sections.
  Water isn't part of the picture. The story about removing water
  with clay beads has to be something from a snake-oil salesman.
  If there are molecular sieves that extract wax or alcohol from
  xylene, these might be useful if they were extremely cheap. They
  could never prolong the life of the solvent "indefinitely" because
  molecular sieves cannot sequester immense volumes of the liquids
  they preferentially absorb. It would almost certainly be more
  economical to replace used xylene regularly, baeed on experience.
  If you get through a lot, consider buying a still and recycling
  it in the lab. Several HistoNet messages in the last 2 years have
  encouraged redistilling xylene in big & busy labs.  

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

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