smelting vs unification

smelting

noun
  • The process of melting or fusion, especially to extract a metal from its ore. 

unification

noun
  • Given two terms, their join with respect to a specialisation order. 

  • The act of unifying. 

  • The state of being unified. 

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