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

The gaseous transfer from a saturated NaCl solution, of chlorine but not sodium, to Cu coupons has been demonstrated in a bell jar 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 Cu coupons, and several equivalent monolayers of Cl were found on the surface. However, the amounts of Cl found were significantly less than might be expected to be deposited from the saturated salt solutions. 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 have been calculated.