Desiccants, Drying agents
Laboratory Practice of Organic Chemistry, G. Ross Robertson, 3rd ed. (1954), p. 147-152:
| Water vapor pressure of hydrates of Magnesium Sulfate | |
| MgSO4 . 7H2O | 12 mm |
| MgSO4 . 6H2O | 10 mm |
| MgSO4 . 5H2O | 9 mm |
| MgSO4 . 4H2O | 5 mm |
| MgSO4 . 3H2O | 5 mm |
| MgSO4 . 2H2O | 2mm |
| MgSO4 . 1H2O | 1mm |
Magnesium Sulfate. The best neutral drying agent of good capacity obtainable; compatible with most compounds, being a compound of a strong base and strong acid. Low cost, but not in common use; often difficult to obtain commercially, probably because it is more difficult to preserve than calcium chloride. Readily prepared, however, from ordinary clean technical crystalline Epsom salt ("bath salt") of good grade by preliminary heating at 150o to 175o in an oven, then to low red heat for complete desiccation. [temperatures are in Celsius]
Dessicant Next hydrate Mg. per liter Phosphorous pentoxide (HPO3) ? Not detectable Sulfuric acid (uncertain) Less than 0.001 mg. Magnesium perchlorate Mg(ClO4)2· 3H2O 0.002 mg. Calcium sulfate 2CaSO4 · H2O 0.005 Potassium hydroxide, fused KOH · H2O 0.014 Calcium chloride CaCl2 · H2O 0.036 Sodium hydroxide, sufed NaOH · H2O 0.80 Zinc chloride ZnCl2· H2O 0.98 Magnesium sulfate MgSO4 · H2O 1 Cupric sulfate CuSO4 · H2O 2.8 Sodium sulfate 12
Calcium Sulfate (Drierite, patented product). Excellent from standpoint of intensity, but very low capacity; only 6.6% of water absorbed at equilibrium. Used often to dry organic compounds of the "water class" (with high hydroxyl content) which have already been partially dried by other methods. ( http://en.wikipedia.org/wiki/Drierite , http://en.wikipedia.org/wiki/Calcium_sulfate#Dehydration_reactions )