These hygroscopic salt crystals will hold moisture from a humid atmosphere and cause rusting.
A hygroscopic material will tend to become damp and cakey when exposed to moist air (such as the salt inside salt shakers during humid weather).
It is a colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste, hygroscopic and miscible with water, acetone, and chloroform.
When exposed to the atmosphere it is hygroscopic, becomes gluey, and changes colour, becoming darker.
That is nothing at all to do with hygroscopic qualities or tension or anything else: it is to do with how far the quantity goes —and that is right.
And the quantity is completely unaffected by the evaporation or the hygroscopic qualities.
As regards the practical difficulties, these articles are extremely hygroscopic.
In short, containers that are good for preserving cold drinks or potato crisps for a few months have been mistakenly judged adequate to preserve highly hygroscopic dry seeds for decades.
