Quote Originally Posted by kb3lms View Post
Thanks, Kirk. So add some glass tubing or similar to the shopping list. Coax with BNCs or other connectors I already have. In fact, I have a few broken oscilloscope probes here at work with a thinner coax that may be ideal.
Old oscilloscope probe leads would be great. The foam insulation on the Radio Shack coax is still pretty thick, and it does make for a rather stiff lead.

Quote Originally Posted by kb3lms View Post
Another question for you. If I have this correct, the reference elctrode sits in a beaker of solution and the salt bridge "connects" that beaker to the emulsion beaker and the silver ISE to complete the circuit. From what I can find, the bridge is made with a thickened electrolyte of KNO3 (potassium nitrate) and PE covers how to make that in his book. What sort of solution is in the beaker with the reference elctrode? I don't think I've seen that anywhere. .
Yes, you have it right. One beaker has the emulsion, the vAg electrode, and one end of a salt bridge in it. The salt bridge connects to a second beaker with some solution and the reference electrode. As I pointed out, the referece electrode mentioned above has a gel in it that helps act as a bridge by isolating the KCl solution in the reference electrode from the outside world. You do not want to use a solution with a halide in it for either the salt bridge to the emulsion or in the beaker with the reference electrode. A salt that will not affect the emulsion is needed. A saturated solution of potassium nitrate (KN03) would be a good choice here as you'll have both potassium and nitrate ions in the emulsion solution too. Get ACS or at least reagent grade so you know you have low halides - don't be temped with hydroponic KNO3!

Quote Originally Posted by kb3lms View Post
And is a pH meter better to use or more useful then a VOM/multimeter? I have use of several very good (Fluke) bench multimeters but do not have a pH meter to which I can connect an external probe. Have looked at used ones on the auction site but they almost never come with probes and new probes are quite expensive. The meters themselves are not too costly. However, I have thought about getting a better pH meter than what I have now.
For vAg, there is nothing wrong with using your bench VOM. It will work just fine - so you may not even want to use BNC connectors on your vAg electrode - use the same type as your VOM. I was going for BNC as I have a couple pH meters that I bought off ebay. Depending on the age of commercial reference electrodes (for pH meters), they typically have a "pin-tip" or a "barrel" type connection to the meter, not a BNC.

I'm partial to Orion, Thermo, Mettler, or Beckman meters, as that's what I've used working in a chem lab and had good results with those brands. I found my meters by waiting along for ones that were tested and shown to at least turn on with the display working...

The advantage with pH meters over VOMs is when you actually put a pH electrode on it - one with a built in reference electrode and even a temp sensor. The pH meter is set up so these will all just plug right in and it will read directly off the readout and it can even correct for temperature that way. When doing vAg, you merely need to measure volts (although temp has a effect too, be we've been ignoring it...)

If you want to look for a commercial reference electrode - look for ones that are called "double junction" as they essentially have the second bridge built right into them, so I think it can reduce the need for the reference electrode being separated from the emulsion by the salt bridge. It's called an Ag/AgCl Double Junction Half-Cell if you want to get specific. These are usually pretty indestructable - a good cleaning and soaking in fresh filling solutions is often enough to revive "dead" ones!