Etymology: < Latin dēliquēscĕre to melt away, dissolve, disappear, < de- prefix 1c + liquēscĕre to become liquid, melt, inceptive of liquēre to be liquid, clear, etc.intr.
1.a. Chem. To melt or become liquid by absorbing moisture from the air, as certain salts.
b. Biol. To liquefy or melt away, as some parts of fungi or other plants of low organization, in the process of growth or of decay.
2. gen. To melt away (lit. and fig.). (Mostly humorous or affected.) (OED)
"The truest thing I can say about the Amish is that within a week, or even less, they will disappear from the media and from the nation’s consciousness. They will deliquesce — until the next newsworthy incident — into the background of contemporary America."
- Joe Mackall , "Our Amish, Ourselves", 20 October 2011 New York Times
I'd observed this phenomenon in a number of the jars of "dry" chemicals I threw out the other day, and while I suppose if I had thought about it I would have figured that there was a technical term, now I know what it is.