The choice of desiccant is crucial for the effectiveness of the drying process. Desiccant are hygroscopic, so they absorb humidity from the atmosphere around. Furthermore, saturated salt solutions are used to obtain atmospheres of stable humidity, e. g. . Stable hydrates can be formed which bind water, but the hydrates can be still hygroscopic. Therefore, hygroscopic solids can show deliquescence when the surrounding atmosphere is humid.