Hi, I have a lot of packs of silica gel which have lost their moisture absorbing properties. Can they be regenerated by heating ? any suggestions as to how ...temperature / time etc. ? I guess it wouldn't be sensible to put them in our gas oven.
Chris
Yes, about 100C for a few hours will do it.
It used to be recommended to put them in a warm oven after it had been turned off, so your gas oven should be ok.
Dave
About 90-100 deg.C for a few hours. Note that some pack materials melt at much above this. You should see a very noticeable colour change, typically from white/pink to deep blue
Only if it has a water content indicator - pure silica gel is clear/white, and most packets used in packaging have no indicator - it'll be white regardless of moisture content.
Unless your gas oven uses Zyklon B then it will work fine.
much above this.
From "Howstuffworks" :- Silica gel can adsorb about 40 percent of its weight in moisture and can take the relative humidity in a closed container down to about 40 percent. Once saturated, you can drive the moisture off and reuse silica gel by heating it above 300 degrees F (150 C).
The 150degC figure is what I recall from when I handled it professionally.
above this.
They dont supply white/pink to blue anymore its carcinogenic the new colouring is dark yellow to light yellow/white. But it still regenterates the same.
Paul
I recently baked a load of gel from a variety of sources and it all turned blue
The good denizens of this newsgroup would no more _buy_ new silica gel than we'd buy new Dexion !
Some Californians are whining, you mean. If cobalt is so terribly nasty, then are we all going to start using lead driers in oil paint again ?
Or "beige to beige" as it's generally known. Like the new 3 phase colour coding, this was a really stupid decision.
All my big silica gel bags (a few cubic feet, because I fill the tool cabinets over winter) have cobalt chloride indicator strips sewn to them. If they didn't when I got them, I made them and sewed them on.
About 110-120 does the trick. Silica gel does not melt before steel, so don't be too worried, your oven cannot really go over the top. The new colouring is typical knee-jerk legislation. Cobalt is an essential nutrient, somewhere about 10 mg per day is required. It also a component in vitamin B-12. Even if your digestive system could abtract all of the cobalt in silica gel (it cannot even get close), you would have to consume a quite fantastic amount to cause damage. Table salt, on the other hand, needs less than a kilogram to cause death. BAN SALT TODAY!
John Schmitt
Hell, table salt contains cyanide!
(Fbqvhz sreevplnavqr. V'ir orra gelvat gb trg n Hfrarg ehzbhe fgnegrq gung gurer'f plnavqr va fnyg sbe lrnef. Hafhpprffshyl, fb sne.)
I was only trying to be helpful I didnt say I agreed with the new ruling. It has been enforced on us at work.
Sorry for being helpful - my comment has to be better than the continued insults thrown around.
Paul
I think that should be mcg.
-- LSR
sreebplnavqr.
Wbua Fpuzvgg
B*gger. And ta. I CBA to go and look and 'A' level chemistry was a *long* time ago. And iron has too many oxidation states. I'd still like to get the rumour started, though. Like the guy with "crystal homeopathy".
Interesting. The first pages I found were for cattle feed, which I interpolated. Further research indicates this is about the limit where toxicological problems become acute. It appears that the sulphate is used a a foam stabiliser in some beers. Be afraid, be very afraid.
John Schmitt
As it happens they put quite a variety of anticaking agents in salt. I believe that there are still some laboratories (mostly organic - cyanide is useful for sticking an extra carbon onto other basic structures) which have a pair of solutions, which are mixed to give ferrous citrate, which complexes with cyanide accidentally (or deliberately) swallowed. The consensus seems to be that this is more or less futile. Cyanide is not a particularly strong poison somewhere like .5g is the lethal dose, ricin being about 5000 times more potent and botulinum toxin more than 10 million times stronger. Cyanide is, however, fast.
John Schmitt
Talking about rumours.
I live very near to Preston, Lancs. I was doing some shoping at Sainsburies (South Rings, just South of Bamber Bridge, opposite our local B&Q shed) and was just packing it into my boot when a middle aged couple drove up behind me and asked for directions to Ikea.
After finding that they had driven from Manchester, up the M61, I pointed out that the only Ikea I knew of was at Warrington.
'Yes, that's the one we want' they said. I pointed them to the M6 and told them to take exit 22 and ask again.
As you all know Buy and Spew are going through a bad patch and I thought it amusing to drop the idea that the super store was going to close and that Ikea were going to open one of their stores. From what I have been told, the site was originally destined to become an Ikea.
My question is...
How do I feed the rumour to the shed? I might add, that I am well known there.
Dave
IKEA are looking for a site in Manchester and have recently been disappointed at Stockport (again). Preston is probably the nearest suitable site. ;-)
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