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32 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 FEATURE ARTICLE FIGURE 15. An electrolysis surveyor uses a McCollum Earth Current Meter to measure current flow on a buried cast iron pipeline adjacent to a rail line. FIGURE 16. The McCollum Earth Current Meter. FIGURE 18. A cantilevered electrode used with the McCollum Earth Current Meter. FIGURE 19. Shepard Earth Resistivity Meter. FIGURE 17. A trench contacting electrode used with the McCollum Earth Current Meter. survey for the entire East Bay Cities area. At every soil excavation, each of the commit- tee's member utilities used the Leeds & Northrop Potentiometer (Figure 20), an instrument used with EBMUD-designed soil electrodes to measure soil resistivity. Each member agency filled out a test card for each excavation (Figure 21), and com- prehensive soil corrosivity maps were then generated from the data. Areas where soil resistivity measurements were <2,500 Ω-cm were marked as corrosive with colored pen- cils. These maps can be seen in the back- ground of Figures 1, 7, and 11. Soil resistivity continued to be a pri- mary parameter in determining the corro- sivity of soil. By 1950, ground resistance meters had evolved into what the sales lit- erature referred to as the "smooth and mod- ern appearance" of the "jet black" Megger Ground Resistance Meter Model CVM (Figure 22). This 1950 instrument features a Bakelite case and a hand-cranked AC generator. It was manufactured in England by the James G. Biddle Co. and the original cost was $135. Antique instruments used by the Dis- trict for applications other than corrosion control were also found in the collection. The Westinghouse Polyphase Wattmeter (Figure 23) is an exquisite example of early instrumentation used to measure electric power. First patented in 1902, this device surely measured some of the very first watts ever generated. The 500-W General Electric Field Rheostat (Figure 24), with a dial-in steel case and multiple knife switches, is a piece of test equipment that controlled the electrical resistance of a circuit without interrupting the current flow. Two poten- tial transformers housed in walnut cases (Figure 25), manufactured by Weston Elec- trical Instrument Corp. and calibrated in 1930, converted high voltages to low volt- ages so they could be measured with meters, and were most likely used alongside the wattmeter. Most of these instruments, stored in boxes intended for vehicle transportation, were designed to be used in the field by electrolysis professionals, and the tools required to conduct field surveys could eas- ily fill a station wagon (Figure 26). Over the years, testing and remote monitoring tech- niques have advanced significantly; and these antique meters have been replaced