Just a few notes about silica gel drying. I'm a chemist, and I used silica=
gel (about 10 kg at a time) to dry a 3000 L anaerobic glove box used to gro=
w
bacteria. What we found was that silica gel can absorb vast quantities of
water without appearing to change much and that drying the silica gel was a=
n
art and when done wrong needed to be replaced rather often.
The art is in the rate of drying. The slower the better. Sometimes we neede=
d
a quick turnaround and dried the grains in a hot oven. This resulted in
browning of the gel and (more significantly) powdering. When dried too fast=
the outer layers of the grains dry much faster than the underlying bulk, an=
d
the change in volume causes the outer layer to flake away in the form of a=
powder. Initially this increase in surface area seemed like a good thing,
but because air does not circulate inside a powder, and the powder sat at
the bottom of the container, it effectively removed that gel from service.
So we started a two-day drying routine, at 105 centigrade. We used mostly
non-indicating gel, but put a small amount of indicating gel (containing
cobalt(II) chloride: blue=3Ddry, red=3Dwet) in to monitor the state of the =
gel;
first sign of loss of blue meant it was time to regenerate; it doesn't turn=
red until it's past the bulk of water absorption and into the saturation
range. My problem with the packets is that they don't let you see the gel.
Bulk gel is obtainable through VWR or Fisher scientific, and I have no
suggestions for a container other than a flat glass pan, which is what we
used.
Bruce Wilson KF7K
http://science.uvsc.edu/wilson
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