Trem Williams wrote: > Hi Mike, > > Here's something else to throw us off. I just had several samples measured > for PPM by a lab using the atomic absorption process. I asked them if they > digested the CS before running the test. Answer was "yes". I asked them to > run the test on each sample two times; once with and once without digestion. > I did this because another lab had done the same tests for me without using > digestion. I was interested in seeing what differences would be uncovered. > Well, the results were strikingly different. With digestion (and by that I > mean boiling in aqua regia) the PPM in 16 ounces of water using constant > current production was about 3.5 PPM per hour. The highest reading sample > was 35 PPM after running the generator for 10 hours and the reading for 5 > hours was 18 PPM. Pretty straightforward I thought but then the undigested > samples threw me off. They were 19 PPM for the 10 hour run and 11 PPM for > the 5 hour run. These readings were still proportionate to time but only > about 54-58% of the digested readings. The chemist told me that you cannot > get accurate readings without complete digestion. I wonder how many of > those using spectrophotometers, such as "Ole Bob" digest their samples. He > told me once that he bleached the samples but didn't mention digestion. >
We always digest our samples. > Since I really don't know that much about the process, I can't speak with > much authority but I suspect that those using spectrophotometers would also > get much different readings between digesting and not digesting their > samples. I'd be interested in hearing reports from those who have them if > they could run the tests both ways. > > As a side note, I tried a Hanna instrument silver colorimeter and was > disappointed. One used 4 different chemicals to react with the sample and > the blank and then measured the color difference. When I ran the unit to > test undigested CS, the reading was always zero PPM. In order to see if the > unit was operable, I dissolved 1 mg silver in nitric acid by boiling and > then added it to enough distilled water to get a 1 PPM standard solution. > When I tested this sample, the unit did give a reading but it was very low > (about 30% of the actual PPM). I sent the unit back because it was not > working accurately enough with my home made standard and didn't work at all > with the undigested CS. > Yes, I bought a Hanna first also, and got results of about 20% to 30% of the true ppm. It is sitting on a shelf here somewhere, never to be used again. > Afterward, I was told by the lab that did my last tests that digestion in > nitric is not good enough. One should use aqua regia for complete > digestion. So the upshot of all this to me was that you have to digest > completely to get an accurate reading of the total amount of silver in the > dispersion. It is possible I could have gotten better results from the > Hanna unit if I had used aqua regia but I didn't know it at the time. Nitric should be good enough if you boil it dry, then add nitric a second time and heat to boiling. That is what I do. Marshall -- 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: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
