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Re: Cleaning glass

On Mon, 3 Apr 2000, Eric Tulskey wrote:
> As has been said: silicon dioxide is *not* soluble in water, to even the
> parts per billion level.

Quartz (common form of crystalline SiO2) has a temperature-dependent
solubility that gives about 20 ppm SiO2 in ground water from sand and
sandstone aquifers.  We see those concentrations very frequently.  
Breakdown of unstable silicate minerals and natural glass produces higher
silica concentrations in water.  My tap water, for instance contains 60
mg/l of SiO2.  High concentrations are possible because precipitation of
solid SiO2 at low temps is kinetically slow.

The solubility of amorphous hydrous silicates (hyalite and opal) is higher
than the solubility of quartz, but I'm not sure exactly what it is.

Man-made glass is another thing entirely.

I once had an exchange with Charley Bay (this was back in FishRoom) on a
related topic. As I recall, I claimed that silica in the water of a glass
aquarium was unavoidable because of the solubility of glass.  He checked
with a friend who was more conversant with glass chemistry (this is a
specialty with a large literature) and reported that some common glass
formulations were essentially insoluble in water.  I *think* some
formulations probably are more soluble than others.

Charley, are you still reading?  Do you recall the details here?  Or how
about this... Is there anyone reading that actually has credentials in
glass chemistry and would like to comment?

Anyway, this might lead to the possibility that Paul's covers were made
from an unusually soluble glass formulation and that the problem might be
avoided by using a different kind of glass.

Roger Miller