Thanks you. You have provided some excellent information below. I was
not aware that an abundance of citrate ions would enhance the solubility
of Silver citrate, although I do know that is the case with Silver
chloride and chlorine ions.
Marshall
Norton, Steve wrote:
I first sent this as Rich Text but it did not appear to post, so here
it is as HTML.
Marshall,
You are right that the amount of citric acid is high but I think it is
not as high as you indicate. As you noted before, you can only achieve
about a 285 ppm concentration of silver citrate in water. To get
higher concentrations, you need to have the silver citrate dissolved
in a citric acid solution and that is the reason for the additional
citric acid. In my first attempt at silver citrate, I used a 10
percent solution because the following patent performed testing with
solutions of 1, 5, and 10 percent:
http://www.freepatentsonline.com/6197814.html. According to the
patent, 400 ppm SC made with 5 and 20 percent solutions of citric acid
are stable during storage but with 1 percent it was not. I had plenty
of citric acid powder so I went with 10 percent for the first try.
Next, I used a 5% solution, by volume, of citric acid dissolved in
distilled water for concentrations of up to 600 ppm. Measurement of
the citric acid was not critical since I used more citric acid than is
necessary.
Currently, I am using 1/8 cup for 2 liters water, which I think is in
the 2 – 3% range. I do it to keep the tart taste of the SC at an
acceptable level while easing the effort to make the SC. The solution
is stable over time too. I use a manual setup with no stirring. When I
make the SC, I just cut the top off a gallon distilled water plastic
bottle to where I will have 2 liters water in the container and a
little additional height to prevent spillage. The separation if the
electrodes is determined by the container’s width..Given, the
conductivity of the solution, I could use a wider container but there
is no need to.
My earlier attempts with higher citric acid concentrations showed a
little formation of silver oxide on the negative electrode near the
end if the generation. With the current concentration I see oxide
formation starting just around the 200 ppm concentration. So I
continue to use the 1/8 cup of citric acid to minimize the need to
clean the electrode. Also, the higher citric acid concentrations
showed little or no current drop off during the generation. At the
present concentration, I do see some drop off of electrode current.
The current plus the silver oxide formation indicate to me that I
might be getting around the max ppm for the concentration. Remember
that the patent indicated that 400 ppm at a 1% solution is not stable
and that some of the citric acid is consumed in the making of the
silver citrate.
Just FYI:
If you use enough citric acid you can generate silver citrate
solutions to over 23,000 ppm. See Figure 4 in:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2590638/:
"Silver citrate is a white substance with a very limited solubility in
water. Under the normal physicochemical conditions, 1 part of silver
citrate is soluble in 3500 parts of water, which corresponds to 285
ppm of Ag(I) ion in the solution [11]."
"Formation of silver citrate/citric acid complexed solutions was
investigated. Although, silver citrate is minimally soluble in water,
it can successfully be dissolved in citric acid solutions. The maximum
concentration of Ag(I) in solution is estimated at 23 to 25 g/L if the
concentration of citric acid is at least 4 mol/L or higher."
In the report above, the graph in Figure 4 shows how much citric acid
you need vs the ppm of the silver citrate. Please note that the graph
does not include the citric acid needed to create the silver citrate
in the first place so one will need to use more than is shown.
Regards,
Steve N
-----Original Message-----
From: Marshall Dudley [mailto:[email protected]]
Sent: Monday, November 30, 2009 10:27 AM
To: [email protected]
Subject: Re: CS>Use of high ppm CS
That seems excessive for the citric acid. That would produce over 2000
ppm silver citrate if you ran it to completion.
Marshall
Norton, Steve wrote:
>
> You need to use powdered citric acid. I use 1/8 cup for 2 liters
> water. The citric acid increases the conductivity of the solution so
> you cannot use an automated CS generator. Also if the generator uses
> current limiting it will take a long time to get to a high ppm. A
> manual setup without current limiting is best. Also, a battery powered
> setup may not have enough current capability.
> - Steve N
>
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