Volta potentials of various metals approximately parallel the emf series. Metals abraded wet are more noble than when abraded dry, the transition metals changing an average of 0.28 volt compared with 0.07 volt for the nontransition metals. This owes possibly to the greater tendency of the transition metals to chemisorb oxygen, especially in the presence of moisture. All metals change in the noble direction upon aging in air, the average value being 0.3 volt after six days.Potentials for copper‐nickel alloys, plotted with composition, fall on a sigmoid curve, whereas potentials for composite electrodes made up of separate nickel and copper areas are linear with percent area of nickel exposed. Commercial nickel‐copper alloys above 50 percent nickel age more rapidly than laboratory alloys. The cause may lie in deoxidizers like magnesium or aluminum, present in commercial alloys, but absent in the laboratory alloys. This suggests a nondestructive method for detecting impurities of this kind in metals.