On 26 Mar 98 at 13:34, Donna wrote: > >Gee, I don't know, Donna! My distilled water reads zero! <g>
> How do you calibrate the machine then? I guess what I should > ask is what do I have to do before I use it to read the ppm of the > CS. I think that is where I am confused. Gee! I try to make a smart remark and Donna goes and gives me a serious answer. What's a guy gotta do to get a yuk around here! <g> This is being well discussed in another thread, but here's the story: To answer your earlier question, yes, once you're calibrated, then subtracting the beginning measurement of your distilled water from the final measurement of your CS is probably the right thing to do. Although I hope you don't see *too* much of anything in your distilled water to begin with! In terms of calibration, you need to be sure of two very different things: 1) The meter reads something that reflects the real world, and 2) The meter *stays* calibrated to the real world. To do the latter, you need a standard solution that will be stable for a really long time and/or can be accurately replaced when needed. Salt recommends itself since it is available, easy to measure, cheap, and stable. We can't use our CS as a calibration standard, since it is known or expected to have a shelf life of only days/weeks/months, and its measurable concentration would be a moving target. The other part of calibration, then, is to relate the standard solution to the CS you're trying to measure. Probably the easiest thing to do is make a standard salt solution that reads in the general neighborhood of the CS, maybe 50 ppm? Then you need to figure out what the *calibration factor* is between salt and *your* CS. You need to be able to say something like "My CS reads XX% more (or less) than salt." Finding out what "XX" is requires another way of measuring a sample of your CS. This is where a testing lab comes in. You'll have to send a sample or two to be tested, and measure the same batch with your TDS meter before and after the lab test to average out any changes in the CS strength over that time. Say Donna makes a batch of CS using her standard recipe and puts some of it aside for testing. She checks the ppm meter against her salt solution, and it still reads the right number. Then she checks some of the CS, and it reads, say, 12 ppm on the meter. She bottles up 2 samples from this same batch and sends them to the testing lab. A week or two later the results come back. The two samples checked out at 18 and 16 ppm. That gives us a clue how precise the lab measurement is. She measures the CS she kept from the same batch again, first checking that the meter is working right using the salt standard. Now the CS reads 11 ppm. This means that a little deterioration took place, but not much, in the two weeks the CS sat there. Now we know, *FOR DONNA'S CS ONLY,* that a meter reading of 11.5 (averaging the 11 and 12 ppm readings before and after) is equivalent to about 17ppm of silver as tested by the lab. Her calibration factor would be 17/11.5 or about 1.5. Now Donna makes her next batch of CS, but this time she "cooks" it a little longer by mistake. She re-checks that her meter still reads the salt standard correctly, then measures her CS. It reads 15. Because she knows the calibration factor between salt and her CS, she calculates that her second batch is 15 x 1.5 = 22.5 ppm, and adjusts her doseage accordingly. Or she might dilute this slightly stronger CS until it reads the same as the last batch and use the same dose. **** There is another variation on calibration technique. You could, if you choose, re-adjust the meter calibration screw to read the same as the results from the lab. Then re-measure the salt standard and mark down what *it* reads once the meter has been re-calibrated. Then to make future measurements, simply test the salt standard as before and make sure it still reads the *corrected* value before reading the CS directly. Now your meter doesn't read salt accurately, but will be calibrated for *your* CS. Using the example above, Donna got back the results for her two samples, 16 and 18 ppm. Before re-calibrating the meter, the CS measures 11. She calculates the calibration factor of 1.5, just as we talked about above. Then she adjusts the meter to read 11 * 1.5 = 16.5 ppm. Now all that is left is for Donna to measure the salt standard again, and mark down the new reading for future reference. In this case, her 50 ppm standard solution now reads 75 ppm (hopefully!). In the future she tests her meter, making sure it reads 75 ppm on the salt standard. Then she can measure her CS directly, as long as she hasn't changed things too much. **** And that's how it ought to work. I like the first method above, because it *constantly* reminds you that your measurement depends on that calibration factor, which could change. Until we have a *lot* more experience, we won't know what the calibration factor will be or what things will change it. If you make changes to your recipe -- like switching to no-salt from salt, cooking twice as long, raising the temperature, using another voltage or a different generator setup -- you'll want to re-test and verify the new calibration factor. Once we get enough experience with this meter among the members of the silver list, we may find out the calibration factor is pretty much the same for certain general types of CS recipe. This would save others from having to do the calibration for themselves. Oh, yes. A little remark about precision. Don't bother to try to calculate or measure ppm to 2 or 3 decimal places. You can't measure *anything* in this process that closely. Just round things to the nearest whole number and be happy! Saying that you have 22.3 ppm is lame. You only know you have *about* 22 ppm. <g> I hope this helps some. Be well, Mike D. [Mike Devour, Citizen, Patriot, Libertarian] [[email protected] ] [Speaking only for myself... ] -- 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]>
