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I just bought a radio shack cat. No. 276-124A silicon solar cell 2x4 cm. Cost $4.99. I soldered on two leads. Not that easy a task they didn't want to stick. I recommend finding a solar cell with leads already soldered on. I already had a Laser pointer that I bought from harbor freight tools for about $12.00. I used a digital voltmeter that I bought in the past at harbor freight for $39.00. But they also sell some for $10.00 that would work just as well. I tested the current on some previous samples I have saved from the past. These were in 1/2" diameter round glass vials.

The solar cell current was highest when nothing was between the laser and the solar cell with a reading of 1.36 MA, to 1.28 MA for a Dec 94 low PPM sample, to .58 MA on a Jan 95 high PPM sample. I held the solar cell right up against one side of the vial and the laser pointer against the other side. Turned down the lights and clicked on the laser and took the readings. Bit crude but proved the concept of workability.

Did notice some things: The current output spread looks great enough to be easily measurable with the proper length of laser beam travel in solution. The rounded glass vial deflected the beam such that it came out the other side of the vial much broader in width. Nearly as wide as the solar cell. The beam coming out the other side had about the same height. The 4"-6" of travel I talked about earlier may not be needed, especially at higher PPM. I think our first tests can be done with a simple test tube. I do think a box or rectangle shape with parallel sides would be more ideal. This is so as to not distort the beam. If we use a test tube or round object we will need to position it as much as we can in the same spot each time. This so as to not get variations due to light dispersion of the rounded glass.

I have been doing some more thinking about the calibration process and the use of commercial lab tests and how to minimize this cost by use of one basic test sample only. If one produces the highest PPM sample that one can of colloidal silver. Then let it stabilize for say 2 months. Send for a official lab test of it's PPM. Using an appropriate amount of the high PPM solution prepare 5 standards at different lower PPM by thinning down each sample with water. For example say you start out at 400 PPM. If you thin it 50-50 with water you get 200 PPM. Now prepare your graph with 5 points on it as detailed in the earlier post. This may make it more affordable and encourage construction without waiting for some one to sell it.