Acidic vapors above saturated salt solutions commonly used for control of humidity

The gaseous transfer of chlorine but not sodium from a saturated NaCl solution to copper coupons has been demonstrated in a bell jar that was sealed for nine years. Thermodynamic calculations indicate that the active agent, HCl (g), is in equilibrium with H/sup +/ (aq) and Cl/sup -/ (aq) in the saturated salt solution. Auger electron spectroscopy was used to analyze the surface of the copper coupons, and several equivalent monolayers of chlorine were found on the surface. However, the amounts of chlorine found were significantly less than might be expected to be deposited from air in equilibrium with the saturated salt solution. These results are compared with other reported work. Because laboratory experiments that are designed to accelerate corrosion rates frequently utilize a saturated salt solution to maintain constant relative humidity, the partial pressures of gas phase species in equilibrium with various saturated salt solutions were calculated.>