Three gold sensing electrodes were made from 3 mm gold rod. The rod was cut with a diamond wafering saw into 3 mm lengths, soldered to insulated copper wire, placed inside 9 cm lengths of 1 cm (outside diameter) Plexiglas tubing, and cast inside the tubing with epoxy. After the epoxy was set, the gold was polished with 600 grit emery paper. The exposed surface area of gold in the finished electrodes was 0.0707 cm².
A gel-filled, epoxy-body Ag/AgCl electrode was used as a reference electrode. The accuracy of this electrode was checked in Zobell standard redox solution using a freshly polished gold electrode. Unless otherwise indicated, all potentials are reported with respect to the Ag/AgCl reference potential.
ORP Probe Cleaning Procedures
Stability of the readings provided by the gold electrodes was measured in a molybdenite flotation slurry. Molybdenite flotation concentrate was slurried in deionized water at 10% by weight MoS2 pulp density in a Wemco two-liter glass flotation cell. The slurry was agitated by the flotation machine for approximately 8 h each day for the duration of the test. The slurry was open to the air during testing, but air was