Here are a couple of answers:
Refrigerated air-conditioning lowers room humidity. If you have controls, then 
use recirculate (recycling more dehumidified air) and low fan speed (less 
efficient cooling but more efficient moisture collection) settings for better 
dehumidification.

Moisture condenses on the coldest surface, which is of course, your cryostat. 
If you have ready access to liquid nitrogen or dry ice, place some on / in a 
suitable uninsulated container within the cryostat. A sizeable metal container 
would be most efficient in collecting moisture, but don't burn yourself on the 
cold metal.
Cheers
Jim Darley
ProSciTech                 Microscopy PLUS
PO Box 111, Thuringowa  QLD  4817  Australia
Ph +61 7 4774 0370  Fax:+61 7 4789 2313  service@proscitech.com
Great microscopy catalogue, 500 Links, MSDS, User Notes
ABN: 99 724 136 560                      www.proscitech.com

On Sunday, July 02, 2000 2:51 AM, Valleygal@aol.com [SMTP:Valleygal@aol.com] 
wrote:
> Fellow Histonetters,
> This question is directed mostly to those techs who live in humid areas and
> do lots of frozens in old labs which are not "climate controlled".
> Usually Tucson has a very dry climate but during the summer monsoons it gets
> a little swampy. We are in the monsoon season now and the rain is great for
> most things but not for my cryostat.
> My cryostat, a Leica 2800N, has been frosting up something awful because it
> is so humid in our room. I put a tray of drierite in the chamber and it
> turned pink almost immediately. Of course it doesn't help to be cutting
> sections and having the window open for long stretches of time. Does anybody
> have any tips on preventing the frost build up in a normally frost free
> cryostat?
> Thanks!
> Andi Grantham
> University of Arizona
>
> **********************************************************************
>   =^..^=