Abstract
This article presents an extensive examination of a variant of the dynamic method for determining hygroscopic points of pure soluble substances (relative air humidity over the substance’s saturated solution), in which equal amounts of the investigated substance and the reference substance are held in identical sample cups in a sealed chamber for the time that is long enough to change the samples’ mass by 0.05–0.15 g. Examples of the experiment procedures aimed at determining the water vapor absorption/desorption rate coefficient and hygroscopic points values are provided. The effects of the driving force behind the hygroscopic process, relative humidity, cup’s shape, fill level of cups, and chamber volume on the kinetics of samples’ mass changes in the chamber are considered. The experiment technique is organized in such a way that the influence of ambient air is offset in calculations. The method does not require any special laboratory equipment, has a simple implementation technique, and yields the determination results with the reasonable uncertainty that is sufficient for practical purposes.
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