26 Oct
2004
26 Oct
'04
1:26 p.m.
On Oct 26 2004, 12:55, John Foust wrote:
That's the CaCl in it, and there's usually not much. Calcium chloride
is not merely hygroscopic but deliquescent. It's "use once" -- you
can't really dry it off again, effectively.
If you don't mind a liquid, concentrated sulphuric acid is a more
active dessicant than either silca gel or calcium chloride ;-)
Phosphorus pentoxide is good too, and doesn't get wet and sticky.
Pricey, though!
At 12:12 PM 10/26/2004, Paul Koning wrote:
>If it's calcium chloride you want, try snow melting "salt" --
that's
>often CaCl.
>Right. Silicagel is one of those. I don't think calcium chloride
is,
though -- but
I'm not positive.
Yes, but a mixture of NaCl and CaCl will happily suck up water
from the air until turns into a rich, gooey, metal-eating mess. A silicate solution would be less reactive, I think,
and if
it dried, it's almost a protectant. "Water glass" was once a
common way to extend the shelf life of eggs, as it prevented
evaporation through the shell.
For a different reason, though. There's a slow double-decomposition
reaction between the calcium carbonate in the shell and the sodium
silicate (water glass) which leaves a layer of relatively impermeable
calcium silicate on the eggshell. Sodium silicate isn't a drying
agent.
The drying action of silica gel (silicon dioxide) is due to adsorbtion,
a purely physical (and easily reversible) process. Water molecules
stick to the surface of the silica. The granules are extremely porous
on a microscopic scale so they can have quite a lot of water adhering
to them.
--
Pete Peter Turnbull
Network Manager
University of York