Correction: formula for estimating PPM silver should have been shown as:
PPM silver = current (mA) X run time (seconds) X 0.00112 / volume (litres).
Working too late at night!
Original Message:
"Hello Reid,
The following relates to LVDC production of CS. It has
been well discussed that higher quality CS requires the current density, in
particular at the anode, to be below a certain level - the going figure
seems to be around 1.2 mA/ sq in. One problem with brewing CS using only
distilled water (DW) or demineralized water is the huge changes in
conductivity that occur during a run - beginning with the very high values
for DW and subsequently dropping at a steepening rate as conductive Ag+ and
OH- ions are introduced electrolytically more and more rapidly. The simplest
arrangement of a constant voltage supply (eg, 3 nine-volt batteries in
series) then means current and thus electrode current densities increasing
from much less than to eventually much more than the recommended limit of ~
1.2mA/sq in, unless there is some user intervention or automatic voltage
adjustment - ie a constant current circuit). A crude method of user
intervention suggested on this list has been to start with closely spaced
electrodes and occasionally increase the spacing, which effects a partial
but time consuming means of countering the increasing conductivity during
the run. Whether by a regulating circuit or manually juggling electrode
spacing, the total brew time to achieve a desired final PPM silver will be
quite sensitive to the initial conductivity, owing to the highly nonlinear
current vs time relation inherent in this process. High-end CS makers will,
for big bucks, automatically monitor PPM and shut off at the desired value.
By use of a PWT meter or similar conductivity measuring equipment, and an
accompanying chart (or rule-of-thumb), a reasonable estimate of brew time
can be made, but still necessitating a fair dollar outlay and increased
labour. Many list members will no doubt be quite happy to stick with one
such or similar arrangement. Things could be simplified and I think
considerably improved.
Adding an appropriate quantity of citric acid at the outset effects a
dramatic increase in initial conductivity that is much larger than that
contributed by the ionic silver introduced during the run. This provides a
number of potential benefits. A simple constant voltage source gives
essentially constant-current FROM THE OUTSET without any solid state
electronics being involved. Initially one would use a multimeter to
establish the relation between current draw and applied voltage for a given
quantity of added citric acid. Once established, at most the addition of a
single resistor in series is all that is required to gaurantee a desired
current draw (within a few %) throughout the run. Assuming plate-out is
negligible (which wrapping the cathode with cotton cloth pretty well
achieves), one can work from the approximate relation:
current (mA) X run time (seconds) = 0.00112 X PPM silver / volume (litres).
Reduced resistivity also means power consumption and the supply voltage can
be much lower than otherwise - possibly a single 1.5V battery. Obviously
that frees from needing a mains power source, and any attendent dangers of
electrocution. Stirring is still desireable, and the water should be low in
dissolved chlorine or chlorides to avoid producing AgCl. I have found the
product to be clear, very stable, and quite effective. Hopefully a report
from Bob Berger on achieved PPM, particle size, etc is not far off. Details
of my own setup are included in another recent posting.
regards, Kevin Nolan
----- Original Message -----
From: "Reid Harvey" <ceram...@bol-online.com>
To: "silver list" <silver-list@eskimo.com>
Sent: Monday, April 01, 2002 1:30 PM
Subject: CS>brewing with citric acid
> Hi Kevin,
> Will you kindly explain to me some of what you've written here, since I
> don't understand. For example, why would there be no need to space the
> electrodes? Are you saying that citric acid somehow counters the effect
> of the conductivity? And why no need for any constant-current
> electronics? Does this mean that purity of the water isn't so much an
> issue?
> Thanks.
> Reid
>
> Kevin Nolan said:
> One real advantage of brewing CS with citric acid is the absence of any
> sensitivity to DW initial conductivity. No need for any PWT meters or
> the like. No need to be adjusting electrode spacing during a run, or
> carefully monitoring current draw. No need for any constant-current
> electronics. The one thing I have found that does need attention is to
> not make the mistake of using chlorinated tap water. As related above,
> the presence of citric acid will not then prevent a cloud of AgCl
> forming.
>
>
>
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"
