Moisture Monitor Testing and Calibration

ABS>Electrolytic moisture monitors which continuously analyze the moisture content of gases are commercially available. After a period of operation, these instruments may give erroneous readings, frequently because of damage to the electrolytic cell. A gas with a known and reproducible moisture content within the operating range would be useful for making operational response tests on these monltors and for checking their calibration. A paired- hydrate system of a chemical compound exhibits a water vapor pressure that is constant at a constant temperature. ff an unreactive gas is allowed to equilibrate with a paired-hydrate system, the moisture content of the gas is determined by the vapor pressure of the hydrate pair, the total pressure, and the temperature. Hydrated magnesium perchlorate was prepared which contained between four and six moles of water per mole of perchlorate. This material was pulverized lightly then packed into a stainless steel column and 100 cc/minute of air at atmospheric pressure was passed through the bed. The exit air from the column was analyzed with a moisture monitor. A gas residence time of two minutes in the column was found to be sufficient for establishing moisture equilibrium in the exit flow. The moisture content of the exit air was found to vary from 34 to 70 ppm by volume as the temperature of the paired-hydrate system varied from 20 to 28 un. Concent 85% C. Other paired-hydrate systems can extend this range to higher moisture levels. (auth