### Ah, that clears up a lot of questions and makes sense. There was a fellow from a water softener company that came by here to test my well water. He used a process similar to what you describe and compared the results to a set of color charts. [I guess I don't need mineral supplements :-)] KD'C
At 12:51 PM 4/6/00 -0600, you wrote: >Re: Measuring the color and absorbency of sols. >"If the particle size is so small as to not transmit a color, how would a >colorimeter possibly be used to accurately determine concentration? There >is a direct contradiction here." >You react the Ag with substance(s) which create another compound in direct >proportion to the available silver, and then measure with a photodetector >how much light gets through. It is usually expressed in "absorbance", or >how much light did not get through the sample. >One is the inverse of the other, but there is a math consideration which >makes absorbance easier to work with. >The color solution---in my case, a clear magenta/purple---can be eyeballed > after some experience within a few PPM-mg/l after the color forms as the >silver is added to the prepared reagents. >In the pre-electronic age it was done by visually comparing the strength of >the color sample of the unknown with a stable prepared set of solutions in >sealed tubes representing various concentrations. >The instrument is zeroed to 100% transmission using a bleached [sodium >thiosulfate, same a photo bleach] sample of the reacted silver which is a >clear medium yellow, and the readout is set to Zero. Then a test tube or >cuvette of the colored sample replaces the "blank" and the amount of light >absorbed is read. >The measurement is made with light of a specific frequency [expressed in nM >of wavelength; i.e. color] so that you are only measuring that light >absorbed by the reaction product. >I know that I am calibrated correctly for Silver Nitrate [strongly ionized >monatomic Ag] because I can take a sample of ACS grade silver nitrate >which has been diluted precisely with class A volumetric flasks and >precision pipettes to 4.0 mg/l and the Spec reads 4.0. That is how I >created the slope on the graph with Absorbance up the X and concentration >on the Y axis, by measuring the absorbance of 6 different precise >dilutions . This forms a "curve" which is really a straight line [the >process I am using is basically linear]. I used Excell [any spreadsheet, >graphing program will probably have the same function available] to do a >linear regression on the string of points to make a best-fit straight line >for the graph. >Bob Berger gave me a great tip. Lacking a program to construct the line, > view the dots representing the individual measurements at a very low >angle, [as in placing your head very near the surface on which the paper is >laying. Your eye will 'see' the line through to dots well enough to do a >satisfactory linear regression by eyeball and brain. You then draw it in. >At issue is the reactivity of the metal particles with the color-forming >reagents. >I do not know the precision available compared with AA spectroscopy, but it >is certainly good enough with wet chemistry to determine the Ag sol >concentration to at least a tenth of a mg/L. With more sophisticated >instruments you can move the precision over to the right, but I am not sure >how far; I don't need it and could not afford it if I did. >The present issue for me is: Will the reagents I am using react fully with >the metallic particles, or, as some say, it must be reduced to ionized, >i.e. individual "dissolved" atoms of silver. Some say firmly one and others >firmly the other. >Other devices measure the amount of and wavelength of light refracted, >reflected, and absorbed with sensors at various angles to the incident >beam. They then use a complex software algorithm to calculate particle >size. >Any input based on experience or a reference regarding digestion v no >digestion will be welcome. >James Osbourne Holmes >[email protected] > -- 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] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
