Since the circuit seems to be causing trouble, let's work around it.
Disconnect the photoresistor from the circuit. The circuit in the project has a voltage output, which is standard for most detectors, but resistance will work just fine for this project.
Attach the photoresistor to the multimeter probes. Use alligator clips if needed. Polarity does not matter.
Set the multimeter to read Resistance.
Check the resistance in various levels of light. Point the photoresistor toward or away from light, cover it with your hand, etc. You should see dramatic changes in the resistance in various levels of light. The resistance goes down in brighter light.
Once the photoresitor and multimeter are working, use the photoresistor as the detector.
Try clear water and a turbid solution. If there is any scattering you should see a signal (decreased resistance). You will need to protect the photoresistor from surrounding light.
If you have a signal from the turbid solution, make a standard curve, and proceed with the rest of the steps.
The signal will decrease with increasing light scatter (opposite of voltage output) but the data can still be graphed and used as a standard curve.
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