On the Hysteresis Phenomena of the Hair Hygrometer

Abstract

Calibration of hair hygrometers of polymeter type was made through a complete cycle of relative humidity changed from 100 per cent. to 5 per cent., at temperatures of 20°, 5°, -5° and -10°C. In the wide range of humidity such as from 30 to 100 per cent., these calibrations showed an evidence of remarkable hysteresis effect, in other word, greater indication for the same humidity in the case of increasing humidity than in that of decreasing. The maximum deviation of these indications was about 10 per cent, in relative humidity scale. The same hysteresis curve could be reproduced in every calibration of the same hair hygrometer and was not influenced by temperature. Other hair hygrometers, however, showed quite different forms of hysteresis curve. In the final stage of a cyclic process of calibration, that is, in the saturated atmosphere after the course of increasing humidity, the pointer of hygrometer indicated at first the scale over 100 per cent. and in the case of room temperature, it restored to 100 per cent in a few minutes. The time of its restoration was longer at lower temperature; for example, about 24 hours at -5°C. Such a hysteresis phenomena would prabably be due to the lag of formation of meniscus in the empty cells, in the course of capillary condensation of moisture in numerous cells contained in the hair. The time lag of indication, which means the lag of hair in getting to moisture equilibrium to the surrounding atmosphere after a rapid change of humidity, is greater at lower temperature. This lag, however, seems to have no relations to the above mentioned hysteresis phenomena.