Full Idea
Intuitively, what qualifies a thing as soluble though it never gets into water is that it is of the same kind as the things that actually did or will dissolve; it is similar to them.
Gist of Idea
We judge things to be soluble if they are the same kind as, or similar to, things that do dissolve
Source
Willard Quine (Natural Kinds [1969], p.130)
Book Reference
Quine,Willard: 'Ontological Relativity and Other Essays' [Columbia 1969], p.130
A Reaction
If you can judge that the similar things 'will' dissolve, you can cut to the chase and judge that this thing will dissolve.