The use of gold coating on contacts is usually satisfactory from a corrosion point of view, at least when the porosity of the gold coat is minimal. If the atmosphere contains chlorine, however, the gold itself is attacked, producing tetrachloroauric acid which forms solid hydrates below ten-Percent relative humidity (RH) at 25°C. When NO2and Cl2were added simultaneously (0.05 ppm, 0.5 ppm, respectively) at 80percent RH the corrosion of pure gold foil was 60 percent faster than if NO2were absent. An atmosphere which contained NO2at ppm concentrations but no CI2, did not attack gold. The contact samples were electroplated, the thickness of the gold coating being 0.3, 1.0, and 2.0 µm, respectively. The base material was brass containing 73 percent Cu, 23 percent Zn, 3.4 percent Al, and 0.4 percent Co. Atmospheres containing chlorine caused severe pore corrosion On gold-plated contact material and hygroscopic corrosion products containing chloride soon covered most of the surface. Plug-type dezincification of the underlaying brass resulted at the pore-attack sites. Atmospheres containing NO2but no Cl2caused slower corrosion on pore-containing go1d-plated brass. Nitrate was detected in the corrosion products formed in this environ- ment.