"Derek Andrews" wrote in message
...
George wrote:
Yep, alcohol is used to _dehydrate_ cells for histological examination,
too. Note, this is not drying.

As I understand it, dehydration is a chemical process, drying is a
physical one. Does it matter to the wood how the water is removed?


No, dehydration by alcohol is pretty much a mechanical process. Alcohol and
water will mix in any proportion, so soaking wet wood in alcohol long enough
to get complete mixing would result in a dilute solution of (pick one)
alcohol or water. The solution is discarded, replaced with undiluted
alcohol, and the process repeated. Picture two partial buckets of sand, one
white, one black. Dump equal white into the black, mix thoroughly, take
away half. There's only half as much black as there used to be. Add white,
discard half of that, and so forth until the proportions are where you want
them.

Been a while since lab, but seems there were three or four dilutions on
fixed specimens back when. Of course those were some pretty thin samples,
so fifteen-minute soak cycle was pretty meaningful. What was removed was
the equivalent of "unbound" water in wood.

The water that needs removing from wood is the "bound" water. That's
chemically bonded to the sugars that make up the hemi/cellulose - hydrogen
bonds. You have to get enough energy into the process to break up the
association - low relative humidity or other methods of increasing molecular
energy levels, like warming, or both, are the traditional. Dilute with air
rather than alcohol, as it were. Easier to discard the air, too.

Chemical processes to disrupt the H bonds would involve something more
ionic. Probably something more unpleasant, like sulphuric acid.