In view of the ongoing debate about the suitability of conductivity meters (and TDS meters) in measuring the concentration of silver, I offer this graph of a run I made recently. It is admittedly a bit rough and ready (interruptions, running out of buffer solution etc.) but the trends are clear,... the computer drew the lines.
The test system configuration I chose was the 9V AC wall adaptor type as this is to hand, and as I have posted this configuration to the list , some people out there may be using it. Other configurations to follow, hopefully the data will be a little more 'clean'. The conductivity probe I used has a range 1 - 199 uS + or - 1uS and was calibrated using a known concentration of silver nitrate. Conversion factor; 1uS = 1.08ppm as silver. PPM reading was supplied by a silver Ion Selective Electrode. Water was Purified Water BP and read 1uS before electrolysis. You will notice that the ppm and conductivity readings show pretty good correlation. I also added a resistance trace as found by dividing the generating voltage by the current which also shows good (negative) correlation, implying that this could also be used as a concentration indicator. I think that the conclusion may be drawn that, at least during generation of clear silver sols, the conductivity meter can give a good indication of concentration. Also, after the power was withdrawn half of the solution was poured into a clean glass beaker and later through a bleached coffee filter. This was a big mistake, the concentration immediately dropped 10ppm and the conductivity reading rose by 4uS. Contamination by something. The lid (holding the electrodes) was replaced on the generating container holding the remaining solution and left to stand. The conductivity and concentration continued to rise (with no power supplied) and continues to rise even now. The conductivity reading and concentration within 1ppm of each other. 24hrs - 20uS - 20ppm 30hrs - 21uS - 21ppm 54hrs - 25uS - 26ppm 58hrs - 26uS - 27ppm The solution remains clear. There is more work to be done to establish the relationship between conductivity and concentration, large particles affect conductivity differently to small particles and this relationship is still to be established. Regards Ivan Anderson.
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