Iron vs ferric

Iron

adj
  • Of or pertaining to the Iron people. 

name
  • The 57th sura (chapter) of the Qur'an. 

  • A group of Ossetians of the northern Caucasus who speak the Iron Ossetian dialect. 

ferric

adj
  • Of compounds of iron in which it has a valence or oxidation number of 3 

  • Pertaining to, derived from, or containing iron. 

How often have the words Iron and ferric occurred in a corpus of books? (source: Google Ngram Viewer )