I have used molecular sieve encased in dialysis tubing, which seems to have prevented any obvious dust problems. But unless the sieves themselves are scrupulously dry, they can acutally ADD water to your solvent. For freeze substitution work, I have had nice results with adding 1% acidified dimethoxypropane to substitution solvents (ethanol or acetone). This compound reacts chemically with water to produce acetone and methanol. Of course, I don't know if the benefits in freeze substitution come from simply having more strictly anhydrous reagents, or if the dmp actually speeds up substitution of the tissue. I should also mention, that most of my work is at the light micrscope level, so I also can't comment about ultrastructure. But I like the concept of removing water chemically, with dmp, as opposed to physically with a sieve.
Hope this helps, Tobias Baskin
baskin@biosci.mbp.missouri.edu

............................................................................................................
We use commercial absolute ethanol and acetone. We keep both dry with dehydrated copper sulphate, which is made by baking cuso4.5h20 in a crucible over a bunsen flame until the salt becomes a white powder. When its cool, we put it in a "sausage skin" of dialysis tubing (say 10 mm diam.), opened out and with a knot tied at one end. We tie off the other end and put the cus04 sausage in the solvent. Unless you actually put water into the bottle, it seems never to need changing. It is self indicating in that the cuso4 goes blue again in the presence of water.

Mel dickson
m.dickson@unsw.edu.au ....................................................................................................................

We place the molecular sieve inside a bag of dialysis tubing in order to avoid the dust problem and add a bit of indicator silica gel to determine when the useful life of the desiccant is over. This doesn't work for acetone since the indicator dye is soluble .

Greg Erdos (gwe@biotech.ufl.edu)