STANDARD SALT SOLUTIONS FOR HUMIDITY CALIBRATION Saturated aqueous solutions of inorganic salts are convenient secondary standards for calibration of instruments for measurement of relative humidity. The International Union of Pure and Applied Chemistry has recommended salt solutions for calibrations in the range of 10% to 90% relative humidity, and the American Society for Testing and Materials has published similar standards. The data in this table are taken from the IUPAC recommendations, except for K2CO3 and K2SO4, which are ASTM recommendations. Details on the preparation and use of these standards may be found in References 1 and 2. Data for other salts are given in Reference 3.
t/Β°C
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
LiCl
11.31 Β± 0.31 11.30 Β± 0.27 11.28 Β± 0.24 11.25 Β± 0.22 11.21 Β± 0.21 11.16 Β± 0.21 11.10 Β± 0.22 11.03 Β± 0.23 10.95 Β± 0.26 10.86 Β± 0.29 10.75 Β± 0.33 10.64 Β± 0.38 10.51 Β± 0.44
MgCl2 33.66 Β± 0.33 33.60 Β± 0.28 33.47 Β± 0.24 33.30 Β± 0.21 33.07 Β± 0.18 32.78 Β± 0.16 32.44 Β± 0.14 32.05 Β± 0.13 31.60 Β± 0.13 31.10 Β± 0.13 30.54 Β± 0.14 29.93 Β± 0.16 29.26 Β± 0.18 28.54 Β± 0.21 27.77 Β± 0.25 26.94 Β± 0.29 26.05 Β± 0.34
References 1. Marsh, K. N., Editor, Recommended Reference Materials for the Realization of Physicochemical Properties, Blackwell Scientific Publications, Oxford, 1987, pp.157-162. 2. Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions, ASTM Standard E 104-85, Reapproved 1991. 3. Greenspan, L., J. Res. Nat. Bur. Stand., 81A, 89, 1977.
Relative Humidity in % K2CO3 Mg(NO3)2 43.1 Β± 0.7 60.35 Β± 0.55 43.1 Β± 0.5 58.86 Β± 0.43 43.1 Β± 0.4 57.36 Β± 0.33 43.2 Β± 0.3 55.87 Β± 0.27 43.2 Β± 0.3 54.38 Β± 0.23 43.2 Β± 0.4 52.89 Β± 0.22 43.2 Β± 0.5 51.40 Β± 0.24 49.91 Β± 0.29 48.42 Β± 0.37 46.93 Β± 0.47 45.44 Β± 0.60
NaCl 75.51 Β± 0.34 75.65 Β± 0.27 75.67 Β± 0.22 75.61 Β± 0.18 75.47 Β± 0.14 75.29 Β± 0.12 75.09 Β± 0.11 74.87 Β± 0.12
KCl 88.61 Β± 0.53 87.67 Β± 0.45 86.77 Β± 0.39 85.92 Β± 0.33 85.11 Β± 0.29 84.34 Β± 0.26 83.62 Β± 0.25 82.95 Β± 0.25 82.32 Β± 0.25 81.74 Β± 0.28 81.20 Β± 0.31 80.70 Β± 0.35 80.25 Β± 0.41 79.85 Β± 0.48 79.49 Β± 0.57 79.17 Β± 0.66 78.90 Β± 0.77
K2SO4 98.8 Β± 2.1 98.5 Β± 0.9 98.2 Β± 0.8 97.9 Β± 0.6 97.6 Β± 0.5 97.3 Β± 0.5 97.0 Β± 0.4 96.7 Β± 0.4 96.4 Β± 0.4 96.1 Β± 0.4 95.8 Β± 0.5
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