Abstract: A process for drying hygroscopic materials in which the atmospheric condition for removing the humidity from the hygroscopic materials by a suitable drying means is automatically adjusted to maintain a predetermined temperature difference between the dry and wet temperatures in response to a variation of one of these temperatures. When the drying means is not sufficiently humid to effectively remove the humidity from the drying material, any action tending to reduce the humidity from the drying means is interrupted until it again reaches a predetermined value.