Desiccant Silica Gel

It isn't.

Silica 'gel' isn't a gel, it's a solid crystal.

Mary

Until it gets saturated with water, at which point I expect it's quite gel-like.

I've never heard of silica gel being added to compost, and I can't think what good it would do.

The stuff in compost is either vermiculite (white, porous, dusty) or a polymer (softer, maybe clear, no dust). Neither works as an effective dessicant for the air.

Not the indicator gel type at any rate (the sort that goes pink when wet)

- stays crystalline

Nope, not even when it's wet as a really wet thing.

This is just silica gel with added indicator.

No, it's still solid when it can't absorb any more water. That's why sometimes it has a colour indicator added to let you know when it's saturated.

It's easy to refresh in an oven. But it's never a gel and I wondered why it was called that when I first used it fifty years ago in the lab.

Wondeful stuff - but never, ever lick it!

Mary

Silica gel is lickable, although I'd hardly recommend it.

However _never_ lick the "crystal" cat litter (an acrylic polymer absorber). Good stuff though, if you have an older cat that's gone particularly pungent.

DAMHIKT ....

Thanks Tricia

so it's ok to lick the non crystal cat litter ;o)

Bad news: it absorbs spit so dramatically that it can stick to your tongue - as I found out to my cost :-(

Good news: it's not poisonous :-)

Assuming that you have experience I promise not to do it.

Why on earth would you want to?

? That's one I don't think I've seen before and can't work it out. Well, can't be bothered ...

Mary

A good question indeed.

I feel an urge to go find some and try it right now :-)

It is silicon dioxide. It's called a 'gel' because it has a very porous structure (which is why it's a good dessicant).

Don't ask me how I know that.

poh.

S'obvious, really ... thanks :-)

Thinks - I wonder how he knows it ...

Mary

I didn't know I had a child called Morley ...

Mary

Mary

To discover whether it was a super-absorbent polymer or not. It is.

Or rather "If ith" 8-)

Don't ask me how I know that.

They're the polymer sort (so not really "crystals")

Silica gel is "fluffy glass". It has an adsorbent surface, so will adsorb (with a "d") moisture from the air and hold it on the surface of the beads. Because this just happens at the surface, it's a limited volume.

Vermiculite is similar, except that it is porous throughout and so can hold a useful amount of water for a plant's needs. It also has a less active surface than silical, so it won't adsorb water vapour from the air. Fuller's earth (if we're talking cat litter) works similarly.

The polymers absorb (with a "b") moisture, the difference being that it's a volume effect, not a surface effect. They aren't strong enough attractors to work as a dessicant, but they will absorb a _lot_ of moisture, hence their use for plants.

If you just need a small quantity of the polymer, cut some disposable super-dry nappies open.