Rock salt is hygroscopic and it deliquesces under conditions of increased relative air humidity.
Human beings have no sense of humidity in the true meaning of the word and so we have no way of being aware of the differences in the pressure of water vapour between our skin and the layer of air contiguous to it. That pressure is the measure of the extent of evaporation from the surface of the body. Humans feel changes in the water vapour content of the ambient air via their sense of temperature.
The impact that the water vapour contained in the air around us has on the equilibrium of human heat management, which is another thing bound up with our sense of wellbeing, is very complex. However, regardless of this complexity, the fact that high ambient air humidity always exercises an adverse effect is something that has been explained beyond question. This applies both to moderate temperature values and in those cases where increased heat is generated as a result of the activities being carried out.
When evaluating conditions in respect of a sense of well-being, or comfort, relative air humidity is of practically no significance as long as its value remains within the limits of 30 to 70%.
Salt has a powerful ability to absorb humidity from the air. It then passes from a solid form to a solution. We can observe this happening when drops of saline water or brine trickle down the surface of a block of salt. This hygroscopy means that salt must be stored under specific environmental conditions.
A dry salt aerosol halogenerator requires the relative ambient air humidity to be maintained at a maximum level of 60%.
If salt chips are used in construction, then it is essential to ensure that the humidity in the room does not exceed 65%.
Maintaining the humidity within the requisite parameters is the task of air-conditioning and dehumidifying devices.