Saturated salt solutions

Description

In a closed environment, saturated salt solutions can maintain an equilibrium with the moisture in the air. At low humidity, fully hydrated (liquid) salts can volatilize water. The solid salts can absorb moisture when the humidity is high. Saturated salt solutions are a low maintenance method to provide a constant humidity level within a display case (Eggert 2022). Unlike silica gel, which requires reconditioning, the saturated salt solutions only need supplemental distilled water added once a year.

Percent relative humidity produced at 20 C (Greenspan 1977):

• Lithium chloride = 12.4
• Potassium acetate = 23.3
• Magnesium chloride = 33.6 (33.1 from Eggert 2022)
• Potassium carbonate = 44 (43.2 from Eggert 2022)
• potassium nitrite = 49
• Magnesium nitrate = 54.9 (54.4 from Eggert 2022)
• Sodium nitrite = 65.3
• Sodium chloride = 75.5
• Ammonium sulfate = 80.6
• Potassium nitrate = 93.2
• Potassium sulfate = 97.2

Synonyms and Related Terms

salt solutions

Resources and Citations

• G. Eggert, "Saturated salt solutions in showcases: humidity control and pollutant absorption", Herit Sci 10, 54 (2022). https://doi.org/10.1186/s40494-022-00689-3
• AIC Conservation Wiki: Exhibit Technical Notes: Environmental Control
• Exhibit Guidelines Technical Note: Conditioning Silica Gel with a Saturated Salt Solution
• L. Greenspan "Humidity Fixed Points of Binary Saturated Aqueous Solutions" J. Research of the NBS, Vol 81A, No. 1 1977.
• Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
• Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002