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.

Relative Humidity % at Selected Temperatures

Saturated Salt Solution	Chemical Formula	68°F	77°F	86°F
Lithium chloride	LiCl H2O	12. 4%	12. 0%	11.8%
Potassium acetate	CH3CO2K	23. 3%	22. 7%	22.0%
Magnesium chloride	MgCl2 6H2O	33. 6%	33. 2%	32.8%
Potassium carbonate	K2CO3 2H2O	44. 0%	43. 8%	43.5%
Potassium nitrate	KNO3	49. 0%	48. 1%	47.2%
Magnesium nitrate	Mg(NO3)2 6H20	54. 9%	53. 4%	52.0%
Sodium nitrate	NaNO3	65. 3%	64. 3%	63.3%
Sodium chloride	NaCl	75. 5%	75. 8%	75.6%
Ammonium sulfate	(NH4)2SO4	80. 6%	80. 3%	80.0%
Potassium nitrate	KNO3	93. 2%	92. 0%	90.7%
Potassium sulfate	K2SO4	97. 2%	96. 9%	96.6%

Table obtained from Technical Bulletin No. 5, Creating and Maintaining Humidities by Salt Solutions. Hygrodynamics, Inc.

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