The paper describes the results of laboratory tests with gradient lead cathodes in environments of high pH level. By observation of the corrosion limit and corresponding potential it was possible to define the cathodic protection requirements for permanence of metallic lead as a function of the pH of the environment. The increment of cathodic potential required for interface protection of partially immersed lead cathodes was also defined for laboratory test cells. The effects of overprotection and of a soil barrier to diffusion are shown in the paper to increase the susceptibility of the lead system to corrosion loss during periods of minimum current supply.
The instability of a lead electrode was evident in attempts to measure static potentials except under precisely controlled conditions not obtainable in the field. It was recommended, therefore, that potentials in the field be obtained with other standards than the lead electrode. 5.2.4
