Equilibrium Relative Humidities Over Saturated Salt Solutions, Technical Information Paper TIP 0808-03 (2002)
The air space immediately surrounding a saturated salt solution will, after several hours, achieve an equilibrium relative humidity that is different for different salts. Hence, saturated salt solutions are useful for controlling relative humidity in small chambers, and for checking the accuracy of electronic humidity sensors.
The salts listed in Table 1 have been selected because of their relative insensitivity to temperature changes. Values for other salts can be found in most chemistry handbooks.