----- Original Message ----- From: Marshall Dudley <mdud...@execonn.com> To: <silver-list@eskimo.com> Sent: Friday, 5 November 1999 08:11 Subject: Re: CS>Graph Only(Ivans)
> I have noted a few things about the graph that don't seem quite right. Let me restate my introduction that accompanied the original post: "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,... " And in a later post: "I had a bit of trouble with the ISE measurement. I had run out of KNO3 buffer and so the readings were drifting a bit and I couldn't afford the time to let the measurements settle. Must invest in a magnetic stirrer, as long as that doesn't upset the ions, then I will be able to measure without a buffer. Anyway the all important last measurement put the curve into perspective, and it is not drawn freehand, but by the graph program." > > Although the actual graph of ppm starts at 0, the data points > extrapolate to about 1 ppm. The fit of the ppm to the data points is > extremely poor. The last data point is way off the extrapolation of the > other points and appears to be a flyer. I did not draw this graph freehand. The graphing program made the curve, the only point I stipulated was the zero point. I had some problems reading the ppm as I did not use a buffer solution to stabilise the reading and I had to make the readings quickly or the time points would be meaningless. My stirring technique was not consistent This is why the data points are up and down. The final ppm reading is one that I know is correct, because I had time to let the reading settle. > Looking at the data points, instead of the graph of ppm, it seems that > we start off with ppm being less than uS, and at about 130 minutes the > slope is equal to the uS and after that time the slope is much higher > than the uS slope. You might draw that conclusion, without further information. In fact the ppm curve is about right. The conductivity meter was calibrated using known concentrations of AgNO3 but the conversion factor was not correct, also the conversion factor for Ag+ was not correct, as the posts on conductivity of Ag I posted a week or so ago, testify. > The implication of this is that small particles are formed initially and > larger ones later, which we already know. But even more important is > that we cannot use a simple linear relationship between the uS and the > ppm, as the ppm goes up, the uS goes up less fast since the particles > get bigger. Given what I have just written you cannot draw these implications at all. The reason that I posted this graph in the first place was to show that there is a relationship between the readings of a conductivity meter, concentration, and resistance as measured at the electrodes. The next set of graphs should be less ambiguous. > Marshall Ivan -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: silver-list@eskimo.com List maintainer: Mike Devour <mdev...@id.net>
