url: http://escribe.com/health/thesilverlist/m62773.html
CS>Half gallon brew
From: Dan Nave
Date: Thu, 25 Sep 2003 13:02:15
Hi Dan,
I guess you are using fairly low current density, otherwise you
wouldn't see the gray sludge. You would be getting black silver
oxide instead.
The gray sludge is formed at the cathode where silver ions have
picked up an electron to become atoms. These tend to surround
hydrogen bubbles that also form at the cathode. It makes a gray
sludge that can hang down from the cathode in small whiskers.
I use the formation of these whiskers as an indication the brew is
finished. If you let it go much longer, the voltage across the cell
starts to flatten, which indicates the silver ions are forming gray
sludge, and also forming silver oxide in the Nernst diffusion layer
at both electrodes.
The silver oxide, Ag2O, will combine to form larger particles that
give the cs a yellow tint.
If you get a yellow tint to the solution, you can add a bit of H2O2
to the cs and see an interesting reaction. Whack the electrodes
first to break the gray whiskers so they fall to the bottom of the
jar.
Soon after you add the H2O2, the yellow tint disappears. This shows
the H2O2 acts as a catalyst to convert the silver oxide to ions:
2Ag2O + H2O2 --> 4Ag(+) + O2(g) + H2O2
You may start to notice bits of gray sludge rising to the surface,
then falling back down to the bottom. This is caused by the H2O2
reacting with the pure silver to form ions and oxygen. The oxygen
bubbles make the gray bits rise to the surface, where the bubble
breaks and the bit falls back down.
This reaction is quite different from the prevous one:
2Ag + 2H2O2 --> 2Ag(+) + O2(g) + 2H2O
The H2O2 is consumed to form oxygen and water, plus silver ions.
This reaction is very slow, and it takes a lot of H2O2 to convert
even a tiny amount of pure silver to ions.
I don't worry about the gray sludge. I just give the electrodes a
good whack before removing them from the solution so they fall to
the bottom of the jar. I leave them in the jar while transferring
the cs to another container, then dump them in the sink.
The gray sludge is harmless if you happen to drink it. It is pure
silver and will simply pass through the body without interacting.
Best Regards,
Mike Monett
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