Whenever you have two different metals in contact in the presence of moisture you set up a battery, with one metal serving as the anode, which loses atoms, and the other becomes the cathode, which gains atoms. We tested pairs of metals to see how strong a current forms and its direction. With that information in hand, we discussed situations where understanding these relationships have big consequences in daily life. For example, what metals should, or should not, be used to fasten aluminum siding, or should you use copper joints on iron water pipes.