Marshall, You wrote, >>snip>> Either ppm is lower than > thought, something is different to allow this to happen from what we have > tested, or the subjective viewing of the colloid to determine what is > "clear" and what is "colored" is different. I do know that what I call > gold, appears totally clear when put into an 8 oz glass, but it will appear > gold when in a gallon glass jug.
Yes , subjective views will be always be a problem. Lets look at this another way. By your reasoning, a 20 ppm solution cannot be clear, ok, but if a 20 ppm sol can be yellow - green, yellow, gold, orange etc. that means it can exist in a range of particle sizes and hence a range of particle numbers. Also, If I can make a 20 ppm sol to look clear to my eyes and then evaporate the water untill it reads 50 ppm with no visible change in appearence other than less volume, that would also suggest that particle size does not depend on concentration. This is all a bit academic, all I am trying to do is to point out to the list that 5 ppm is not necessarily the optimum concentration, at least not for the reason you proposed. There are other reasons to support this also, one list member reported that in his studies, it was the total silver content not the concentration that determined its effectiveness. One other researcher postulated that a range of particle size is probably advantageous in combatting a range of different pathigens. I tend to agree that the smaller the particle size the better, if only for reasons of stability, and lets face it, we are talking about the difference between 5 and 15 nanometers, that is smaller than any bacteria and probably all viruses also, and is way smaller than a human cell. > > Higher zeta potential should allow one to go to higher ppm with the same > particle size. I wish I had a way to measure zeta potential, but all the > instruments I have looked at are way our of my price range. Do you have a > method of measuring zeta? I believe there is a way, involving a u shaped glass tube. The tube is half filled with the test sample, and electrodes (inert) are placed one in each end and a direct current applied. The height that the water rises up one side of the tube is measured and is supposedly proportional to the Zeta Potential. > I am intrigued by this device. Do you know where on the web I can find more > information on it? We may want to acquire one to improve our testing > ability. I have done some searching on the net for "silver ISE", but have > not found any references. You will find many references under Ion Selective or Ion Specific Electrode, they are quite common. > Maybe you can explain more how it works. I had assumed that something that > measures the ionic concentration would give a low ppm measurement for a > colloid. Would this not be true? It seems that it would either measure > each multi-atomic particle as one atom, or as how many atoms were > represented by the charge on the particle. Both of these should give a ppm > that is less than actual. If it is giving actual ppm, accurately, on > colloids, then I don't understand the mechanism by which it works. The ISE is a potentiometric device that compares a known potential via a reference electrode, with an unknown potential generated by the solution under investigation. The potential is generated across a membrane by the number of ions that contact it at any one time. If a siver colloid is made with care, then all the particles will be formed from monoatomic ions, the sum of the charge of the colloid being the equal to the number of atomic ions it is composed of. This is confirmed by the correlation between the ISE results and the AA (atomic absorption) results being within 1 or 2 ppm of each other. Regards - 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: [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]>
