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31 NACE INTERNATIONAL: VOL. 56, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2017 Historic Corrosion Tools Tell the Story of Early Corrosion Control FIGURE 7. Westinghouse Electric 600-V AC Voltmeter. FIGURE 9. A 50-A shunt on an oak base. FIGURE 11. A 10-A shunt with a Bakelite base. FIGURE 13. A 600-A shunt shown on a trolley map. FIGURE 8. A nineteenth-century 150-A DC shunt. FIGURE 10. A 150-A shunt on a wood base. FIGURE 12. A 10-A shunt with an oak base and oak-covered resistance wire. FIGURE 14. A centralized bank of smoked- chart recorders allowed the Electrolysis Department to remotely monitor each bond. (Figure 14). This system, which used the recording voltmeters to remotely monitor the voltage drop across shunts installed at a variety of locations around the railway net- work, is probably the earliest example of remote monitoring of corrosion control equipment. Chart recorders are still used today, but data loggers, supervisory control and data acquisition (SCADA) systems, and satellite monitoring have taken their place for many applications. Early investigators measured DC cur- rent flow in the soil by exposing buried pipe and measuring the flow of current onto a pipe using instruments such as the McCol- lum Earth Current Meter (Figure 15). This rare, unusual instrument, developed by the U.S. Bureau of Standards' physicist Burton McCollum, required an equal amount of current to be supplied in order to accu- rately measure current in the soil. The set featured a built-in galvanometer with a hand-cranked commutating vibrator in a walnut enclosure (Figure 16), a trench con- tacting electrode (Figure 17), or a cantile- vered electrode (Figure 18). The complete set originally sold for $790. The instrument is now obsolete, most likely because its use required the environment around the pipe to be disturbed, which could affect the accuracy of the data being collected. During the early twentieth century it became increasingly clear that soil itself could cause corrosion of underground utili- ties, even in the absence of DC railways. The conductivity of a given soil was discov- ered to be directly related to its corrosivity. The recognition that soil characteristics could influence the rate of corrosion of bur- ied utilities led to widespread soil studies. With these studies came a variety of inno- vative test instruments. The Shepard Earth Resistivity Meter (Figure 19), first described in 1930s litera- ture as an instrument for conducting soil corrosivity testing, measured the resistance of soil between two steel probes. The meter set, which originally cost $95, featured steel rods sheathed in Bakelite and a cast alumi- num handle that contained two dry-cell batteries. One particularly ambitious study autho- rized in 1931 by the Electrolysis Commit- tee—part of the Joint Committee for the Protection of Underground Structures in the East Bay Cities—conducted a soil