SPH-1
Moisture Sorption Analysis in a Semi Automated System using Hygrostates
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A standard method to achieve constant relative humidities is the use of saturated salt solutions. The dry salt is heaped in a cone on the bottom of the Hygrostate. Just enough Water is added to moisten the salt. The cone of salt ideally should show above liquid level. The atmosphere within the hygrostate above the solution will settle to a humidity level determined by the kind of salt and temperature
Table: Relative humidity above saturated salt solutions at various temperatures
| Salt/Temperature | 5.0 | 10.0 | 15.0 | 20.0 | 25.0 |
| Lithium chloride, LiCl | 11.3 | 11.3 | 11.3 | 11.3 | 11.3 |
| Magnesium chloride, MgCl2 x 6H2O | 33.6 | 33.5 | 33.3 | 33.1 | 32.8 |
| Calcium chloride, CaCl2 x 6H2O | 39.8 |
38.0 |
32.3 |
31.0 |
|
| Potassium carbonate, K2CO3 x 2 H2O | 43.1 | 43.1 | 43.1 | 43.2 | 43.2 |
| Magnesium nitrate, Mg(NO3)2 x 6 H2O | ~57 | ~56 | 55.9 | 54.4 | 52.9 |
| Sodium chloride, NaCl | 75.7 | 75.7 | 75.6 | 75.7 | 75.3 |
| Potassium chloride, KCl | 87.7 | 86.8 | 85.9 | 85.1 | 84.3 |
| Potassium sulphate, K2SO4 | 98.5 | 98.2 | 97.9 | 97.6 | 97.3 |
Lewis Greenspan, 'Humidity fixed points of binary saturated aqueous solutions' J. of Research, National Bureau of Standards, 81A (1977) pp 89-96
© PMT Analytical GmbH & Co. KG 2012
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