The Collaborative International Dictionary of English v.0.48:

Saltness \Salt"ness\ (s[add]lt"n[e^]s), n.
   The quality or state of being salt, or impregnated with salt;
   salt taste; as, the saltness of sea water. In the sense of
   having salt content, saltiness is more commonly used.

   Syn: saltiness.
        [1913 Webster + PJC] Saltpeter